Earthquake Risk Reduction in Himalaya with
Technical Report-5 Earthquake Risk Reduction in Himalaya with Institutional Cooperation between India and Norway (Theme 2: Ground Stability Assessment)
By
Department of Earthquake Engineering Indian Institute of Technology, Roorkee Roorkee, - 247667, Uttarakhand, India and
NGI Authors: Prof. D. K. Paul, Dr. B. K. Maheshwari, Dr. Amir M. Kaynia, and Dr. Rajinder Bhasin, NGI
July 2008
Table of Contents 1. Summary
2
Technical Issues
2
2. Introduction
2
3. Objectives and Scope
2
4. Activities (ongoing and completed)
2
Administrative and Travel
2
Changes / Deviations from the Program
3
Liquefaction Studies Slope Stability Assessment Studies
3 11
5. Future Plans
19
6. References
19
Appendix – 1
21
Appendix – 2
22
Appendix – 3
26
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
1
1.
Summary Technical Issues
In theme 2, key persons involved are: India: Norway:
Prof. D. K. Paul and Dr. B. K. Maheshwari, IIT Roorkee Dr. Amir M. Kaynia and Dr. Rajinder Bhasin, NGI
This report describes the progress made in these areas during last 14 months (July 2007-July 2008) and in continuation to the report submitted in August 2007.
2.
Introduction
The theme 2 of the project is on ground stability assessment and consists of two tasks: (A) Liquefaction susceptibility of selected sites and (B) Slope stability assessment of critical slopes
3.
Objectives and Scope
Aim of the present study can be broadly categorized in two parts. First, to analyze the liquefaction susceptibility of few selected sites near Haridwar/Dehradun, in northern state of Uttarakhand, India. Second is to evaluate slope stability analysis. The scope of the first part of study consists of in situ tests, laboratory tests and numerical modelling. The slope stability assessment would be carried out based on numerical modelling based on the data collected from the sites.
4.
Activities (ongoing and completed) Administrative and Travel
For liquefaction studies, various activities were performed in last year is described below: 1. An IITR team consisting of Dr. B.K. Maheshwari and Dr. M.L. Sharma visited Norway during Sept. 22-30, 2007; the travel report is enclosed (Annex 1). 2. An NGI team consisting of Dr. Amir M. Kaynia and Rajinder Bhasin visited IIT Roorkee during January 7-9, 2008; the travel report is enclosed (Annex 2). 3. Much effort has been made to recruit a Ph.D. student at IIT Roorkee for the research work on liquefaction by putting advertisements a couple of times. The first time, the position was advertised in June 2007, a candidate (Mr. Govardhan with M. Tech degree) was identified. He joined the project as a JRF (Junior Research Fellow) for three months (during Sept.-Nov. 2007). During this period he got familiar with the scope of his assignments in the project. On successful completion of his M. Tech degree and passing a formal interview he has been offered a position of SRF (Senior Research Fellow) from December 2007 and was encouraged to join the Ph.D. programme beginning January 2008. Unfortunately, in the first week of December, he
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
2
4.
5.
6.
7.
8.
quit the position without joining the SRF position. Thus this exercise of recruitment turned futile. In February 2008, the research position (for a Ph.D. candidate) was advertised afresh. The letters were dispatched to abut 100 engineering colleges for wide publicity. A couple of candidates showed interest through including a female student from NIT Silchar (M. Tech in the final semester student); she moved one step forward and formally applied for Ph.D. through regular application. She was called for a formal interview in June 2008 but did not show up for the interview nor responded to followup e-mails. So unfortunately, this attempt was also not successful. It was envisaged that FLAC3D software will be very useful for carrying out research work on liquefaction, the software has been procured at IIT Roorkee with institute funds and has been operational since February 2008. Identification of sites: A team of faculty members from IIT Roorkee and Scientists from WIHG visited Dehradun – Haridwar – Roorkee area for the selection of sites on February 13, 2008. The report of site selection is enclosed (Annex 3). A team from NORSAR, Norway consisting of Dr. Conrad Lindholm and Dr. Juan Jose Galiana visited the four selected sites and witnessed the seismic refraction tests during March 7-11, 2008. The SPT (Standard Penetration Tests) was planned at four selected sites. The field testing at two sites namely Dhanuari (June 23-24, 2008) and Roshnabad (July 19) is already completed. The laboratory tests on the soil samples collected from Dhanuari and Roshnabad is completed using shake table in Soil Dynamics Laboratory at IIT Roorkee. This is described in detail in section 4.3.
Changes / Deviations from the Program It was envisaged in the report submitted in August 2007 that the available resources do not warrant significant contribution to the theme 2 of the project. However, it shall be noted that despite this projection and all the constraints, the significant progress has been made by IIT Roorkee particularly for liquefaction studies. In this regard it shall be noted: 1. The drilling (SPT) has been planned at selected sites; this has been done at a very competitive price. 2. The lab tests were conducted with the help of a research scholar and lab staff at IITR. 3. The FLAC3D software is procured at IITR with institute funds 4. It has been tried to the extent possible that the non-availability of a research scholar doesn’t hamper the project work Liquefaction Studies Modus Operandi: To accomplish the project objectives, three approaches have been proposed. In situ testing, followed by laboratory testing of soil samples collected, and simulation of results using numerical modelling. The in situ tests have been carried out including Standard Penetration Tests (SPT) at selected sites. Laboratory tests using the liquefaction table available at IIT Roorkee has been performed. Results of in situ and laboratory testing will also be simulated using a numerical methodology in software FLAC3D. The progress made so far is described in detail in following sections.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
3
4.3.1 Introduction Himalayan region is one of the most seismic active zones in India. This region was home to many major earthquakes in the past including 1905 great Kangra earthquake, 1934 NepalBihar earthquake, 1991 Uttarkashi earthquake, 1999 Chamoli earthquake and recent 2005 Kashmir earthquake. Many large cities in the region are located within a recent river alluvium valley with soft to very soft geological conditions, with shallow depths to bedrock and may be prone to liquefaction during a major earthquake. Dehradun is a part of the Doon valley and located in the western part of the state of Uttarakhand in North India. Doon valley is bounded by Himalaya in the North, Siwalik in the South, river Ganga in the East and river Yamuna in the West. The city has a population more than a million. Geologically the whole Doon valley can be divided into three regions namely the Lesser Himalaya, the Siwalik group and the Doon Gravels. Selection of sites can be based on the local geology. Ranjan (2005) carried out geophysical survey at many locations in the city. Shear wave velocity of these sites were determined using SASW tests. However, most of sites in Dehradun are dry (water table is very deep) with gravels, and have a fairly high shear wave velocity; so, they may not be prone to liquefaction. Therefore, the focus was shifted to the nearby cities Haridwar and Roorkee. A number of studies are reported in literature for liquefaction susceptibility e.g., Prakash (1981) and Kramer (1996). In the present work, the liquefaction potentials of two sites in Haridwar, India have been investigated using field and laboratory tests. The field test involves SPT (Standard Penetration Test) while in laboratory testing, the sample collected from the field is submerged and imparted horizontal vibration in a shake table. The liquefaction potential of the sites is predicted based on these tests. 4.3.2 Socio-Economic Aspect of the Study Liquefaction has been a source of much damage in the past earthquakes (e.g. Niigata and Alaska earthquakes of 1964, Kobe earthquake of 1995, Kocaeli-Turkey and Chi-Chi earthquakes of 1999, Bhuj Earthquake 2001). New developments are planned in Haridwar. Since the soil condition at many places in Haridwar is loose saturated sands, they may be susceptible to liquefaction. The results of the study in terms of liquefaction assessment would be valuable for the future development and land use planning. Haridwar is a holy religious city and advancing towards both industrial and tourist development. Therefore, the present study has social and socio-economic values. The city has over a million population and is a district headquarter with administrative offices. The city is in a phase of industrialization for energy and for many consumable products. A number of private industries are setting up their businesses on the outskirts of the Haridwar. Therefore, the functionality of the city during an earthquake is very important for the whole district including other important nearby cities such as Roorkee. 4.3.3 Location of Sites and their Characteristics Both selected sites are situated in the Haridwar district as described below: (i) Dhanuari Site: The site is about 10 km from Roorkee and situated between Roorkee and Haridwar. Play ground of an intercollege school is selected as a test site in this small village Dhanuari. The site lies between two canals and there is a river nearby. It was expected that water table may be at shallow depth. Location of the site is Latitude
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
4
29º 56´ 24.6˝ and Longitude 77º 57´ 25.5˝. (ii) Roshnabad: The site is on the outskirts of Haridwar City (about 5 km south from the city centre). An open ground at a distance of about 500 m from the office of the District Magistrate has been selected as the test site which is on the backside of Vikas Bhawan campus. Location of the site is Latitude 29º 58´ 12.8˝ and Longitude 78º 04´ 23.3˝. The SPT (Standard Penetration Tests) as per IS: 2131-1981 were conducted on both sites up to a depth till refusal was met. The samples collected were further tested in the laboratory for evaluation of grain size distribution, unit weight of soil and Atterberg’s limits. It was observed that the soil at both sites is mainly sandy soil and can be classified as SM and SP. At Dhanuari, the water table was encountered at a depth of 4.75 m from the existing ground surface. In Roshnabad, the water table was not encountered up to the depth of exploration (7.5 m) and it may be very deep. Therefore, liquefaction was ruled out at Roshnabad, however further investigation was carried out assuming water table at the same level as observed in Dhanuari i.e. at a depth of 4.75 m from the ground surface. 4.3.4 Liquefaction Potential Based on Field Tests The data obtained from the in situ tests and laboratory tests were analyzed for determination of liquefaction potential of both sites. The cyclic stress approach of Seed and Idriss (Seed and Lee 1966) was used for determination of liquefaction potential of the sites. Shear stresses τav due to earthquake loading is computed based on following two methods (a) Simplified Method (Seed and Idriss, 1971): Average equivalent uniform shear stress at a particular depth, τav is given by
τ av = 0.65σ v 0
amax rd g
(1)
Where σv0 is total overburden pressure at that depth, amax is peak ground acceleration and rd is reduction factor. According to IS: 1893-2002 (Part 1), both sites are situated in seismic zone IV, therefore they have a PGA value amax = 0.24 g. (b) Ground Response Analysis: This has been performed using the program EERA (Bardet et al. 2000) which is based on one dimensional layered soil model. The shear wave velocity is an important parameter for the program EERA. It was determined from the in situ test, SASW. The shear wave velocity for both sites is shown in Fig. 1 (Mahajan 2008). It can be observed that Roshnabad site has higher shear wave velocities compared to Dhanuari site. Also in Roshnabad a bedrock with shear wave velocity 730 m/s is encountered below 54 m, however, in Dhanuari the maximum shear wave velocity recorded was 320 m/s below 16 m. The soil being in loose condition at Dhanuri, the SASW could indicate a shear wave velocity up to 16 m only. These observations are very much in consistent with N (SPT) values recorded on these sites. That is, for Dhanuri: for a depth 0~16 m, N = 2 ~18 and for Roshnabad: for a depth 0~7.5 m, N = 9 ~ 51. In Roshnabad SPT sampler indicated refusal as shallow as 7.5 m depth where N was recorded as 51.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
5
The transient excitation (acceleration time history) was used as input loading to the program EERA. In the present study the N78ºE component of Bhuj (2001) Earthquake recorded at Ahmedabad (Chandra et al. 2002) was used. The acceleration time history has a PGA equal to 0.106 g as shown in Fig. 2. Duration of the actual time history is about 133 s, however the strong portion of it is only about 60s as shown in Fig. 2. For this loading, the maximum shear stresses at different depths were computed using the program EERA. The equivalent linear soil model (Seed and Idriss 1970) was used in the computation. The average shear stress was taken as 65% of the maximum value (Kramer 1996).
Shear Wave Velocity (m/s) 0
100
200
300
Shear Wave Velocity (m/s) 400
0
0.00
200
400
600
800
0
10 4.00
8.00
Depth (m)
Depth (m)
20
12.00
30
40
50 16.00 60 20.00 70
(a) Soil Profile - Dhanuari Site
(b) Soil Profile - Roshnabad Site
Fig. 1: Shear Wave Velocity Profiles of both Sites (Mahajan, 2008)
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
6
Bhuj EQ Time History 0.15
Acceleration (g)
0.10
0.05
0.00
-0.05
-0.10
-0.15 0
20
40
60
80
100
120
Time (sec)
Fig. 2: N78ºE Component of Bhuj (2001) Earthquake Component Recorded at Ahemedabad The average shear stresses in soil at different depths computed using the Simplified Method (Eq. 1) and from Ground Response Analysis are compared for both sites in Fig. 3. It can be observed that at Dhanuri site, the shear stresses obtained from the simplified method is significantly higher than those obtained using the ground response analysis. However at Roshnabad site this difference is not significant. The larger of these stresses were used to evaluate the liquefaction potential of the site. Shear stresses corresponding to liquefaction resistance of soil were computed using the Cyclic Stress Ratio (CSR) approach (Seed et al. 1985) where N values (penetration resistance) collected from the field is a key parameter. The measured value from field was normalized for an overburden pressure of 1 ton/ft2 (100 kPa) and corrected to an energy ratio of 60%. Thus corrected SPT values (N1)60 was evaluated and used for determination of CSR. The magnitude of earthquake is assumed equal to 7.5 for evaluation of CSR. The selection of this magnitude was based on a site specific seismic study conducted for the region (INPIC report 2006). CSR is defined as: CSR =
τ cyc σ v′0
(2)
Where τcyc is cyclic shear stress and σ'v0 is initial effective overburden pressure. Thus τcyc is found from CSR evaluated. Wherever, τav is greater than τcyc, liquefaction is expected to occur. The ratio τcyc/τav provides a factor of safety against liquefaction.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
7
Using Simplified Method
Using Simplified Method
Ground Response Analysis
Ground Response Analysis
Shear Stress (kN/m2) 0
10
20
30
Shear Stress (kN/m2)
40
0
0
10
20
30
1
2 2
4 3
Depth (m)
Depth (m)
6
8
10
4
5
12 6
14 7
16
18
8
(a) Dhanuari Site
(b) Roshnabad Site
Fig. 3: Comparison of Shear Stresses induced due to Earthquake Loading Using Simplified Method and using Ground Response Analysis at both sites The factor of safety against liquefaction is shown for both sites in Fig. 4. It can be observed that the factor of safety is less than unity at all depths (below water table) for Dhanuari site. Thus analysis indicates that site will liquefy in an earthquake of magnitude 7.5 with PGA=0.24g. The outcome is very much consistent with guideline given in IS: 1893-2002 which suggest that to avoid liquefaction in seismic zone IV the N value shall be in the range of 15~25 (increasing with depth). N obtained from SPT at the site are as low as 2. Contrary to this, no threat of liquefaction is indicated in Roshnabad site even assuming that water table exists at a depth of 4.75 m.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
8
Factor of Safety 0.0
0.5
1.0
Factor of Safety 1.5
1.0
6.0
1.5
2.0
2.5
3.0
0
8.0 2
Depth (m)
Depth (m)
10.0
4
12.0
6
14.0
8
16.0
(a) Dhanuari Site
(b) Roshnabad Site
Fig. 4: Factor of Safety against Liquefaction with depth at both sites 4.3.5 Liquefaction Susceptibility Based on Laboratory Tests The tests were performed on a simple but indigenously fabricated vibration table (Gupta 1977) in the Soil Dynamics Laboratory of the Dept. of Earthquake Engineering, IIT Roorkee, India. The test bin is a tank 1.05 m long, 0.60 m wide and 0.60 m high, in which soil sample is prepared. The test set up is shown in Fig. 5. The table can produce one-dimensional (horizontal) steady state vibrations. The tests were conducted on the soil samples collected from both sites. Since a large sample (about 500 kg) of soil was required to conduct a test on this table it was not feasible to conduct the tests on the samples collected from different depths through SPT. However, a sample which is a good mix of the soil collected from different depths in a borelog was used in the shake table. Thus the test results will reflect the liquefaction susceptibility of the site in general but not depth-wise. The known quantity of soil sample was filled in the table and submerged for a couple of hours so that it is fully saturated. A harmonic motion with constant frequency of 5 Hz and amplitude 0.3 g was applied for 60 seconds. The equivalent number of cycles for an earthquake of magnitude 7.5 is 15 only. However, the number of cycles applied was intentionally high to observe the generation of pore water pressure. The pore water
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
9
pressure with time was measured at different depths in the tank. Initially the pore water pressure rises and then reaches to a maximum value and then dissipation starts.
Fig. 5: Liquefaction Table at Dept. of Earthquake Engineering, IIT Roorkee
Bottom Pick-Up 1.60
Top Pick-Up
ru = 0.49
ru = 0.51
1.20
Uexcess (kN/m2)
Middle Pick-Up
ru = 0.57 0.80
0.40
0.00 0
50
100
150
200
250
300
Time (s)
Fig. 6: Excess pore water pressure (Uexcess) time-history for sample collected from Dhanuri site Fig. 6 shows the time history of excess pore water pressure developed for Dhanuari site (this is shown only for first 300 s, though dissipation continues and Uexcess reaches zero after about 20 minutes). It can be observed that the pore water pressure rises for some more time even
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
10
after the end of shaking (60 s) before dissipation starts. Also dissipation starts first in the top pick-up then proceed to middle and bottom pick-ups, as expected. Using Fig. 6, the maximum excess pressure (umax) was evaluated at the three locations of pore water pressure pickups i.e. Bottom (B), Middle (M) and Top (T). This was normalized with respect to effective overburden pressure (σeffective) to obtain the pore water pressure ratio (i.e. ru = umax/σvo). The results for Dhanuari site are summarized in Table 1. It can be observed that the average value of ru is 0.52. A similar analysis (like shown in Fig. 6 and Table 1) was performed for Roshnabad site. The average value of ru obtained was close to that for Dhanuari site. Table 1: Pore water pressure ratio ru of samples collected from Dhanuari Site Location of Pick-up (m)
σeffective (kN/m2)
Udyn (kN/m2)
ru
Remarks
Acceleration = 0.3 g Duration = 60 s Frequency = 5 Hz Average ru = 0.52
From Base of Tank
From top of Soil Sample
0.040 (B)
0.320
3.04
1.50
0.49
0.125 (M)
0.235
2.24
1.15
0.51
0.200 (T)
0.160
1.52
0.86
0.57
Theoretically, the liquefaction occurs when ru reaches unity; if it is less than unity, only partial loss of shear strength occurs. Although shake table result may suggest no liquefaction as ru < 1.0, this outcome may not be necessarily representing the actual behavior in the field. Firstly, in the vibration table due to shaking, the densification of sample takes place and it may not allow pore water pressure to rise to unity. Secondly, the soil samples used in the tests are disturbed samples. Nonetheless, the tests in the vibration table indicate the extent of shear strength loss due to shaking. 4.3.6 Conclusions Field tests indicated that there is a clear threat of liquefaction in Dhanuri but not in Roshnabad for the earthquake magnitude considered. This outcome has much practical significance as Dhanuri is very near to Roorkee, where a large industrial development is taking place. However, more field tests (at different locations) along with laboratory tests (such as cyclic triaxial tests) need to be conducted to come forward with a concrete conclusion. Slope Stability Assessment Studies – Earthquake Stability Analysis of Surbhee Resort Landslide in Garhwal Himalayas, India Modus Operandi: This study was performed by Ms. Shilpa Pal’s during her stay at NGI in the period June-July 2008. The site visits and most of the data collections were done in India prior to this period, and the numerical modelling were performed at NGI with support from the NGI’s experts.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
11
4.4.1 Introduction Landslides are one of the frequently occurring natural hazards in seismically active NorthWest part of Indian Himalayas. In this study, an endeavour has been made to model Surbhee Landslide (longitudes 78o02’ and 78o04’E and latitudes 30o28’ and 30o31’N) in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India. This landslide is active on the road that is joining main road to the down town. This landslide was triggered because of rainfall in July-August 1998. The landslide is still active and there is a need to do some scientific investigations to mitigate future damage. Therefore, modelling of the slope has been carried out with the Distinct Element Method (UDEC & 3DEC) which has the capability to model rock slope stability problems. Understanding the behaviour of the landslide will be helpful for planning and implementing landslide mitigation measures. 4.4.2 Study Area The crown of the landslide (30o29’N and 78o03’) is located at an elevation of about 1650 m between 6 and 7 stone from the Mussorie, on the Mussorie – Kempty road. Hotel Surbhee Hill Resort is located 50 m uphill in the crown portion of the landslide. Further upstream, Mussoorie International Scholl (MIS) and Polo ground are situated. The slope area contains dolomitic limestone together with subordinates variegated shales belonging to the Krol Formation. These rocks are highly jointed and fractured. The rock joints are striking NE-SW, NNE-SSW, NNW-SSE and ESE-WSW and dip moderate to steep slope ranging from 40o to 60o. The area is described as highly unstable that is about 1700 m high and several km wide located near the famous hill station Mussoorie on the Mussoorie – Kempty road in Garhwal Lesser Himalaya (Gupta et al., 2007). In greater area part of the study area, the hill slopes are covered with thick quaternary deposits representing old landslide in the area. Location map of the area showing the movement observed is shown in Fig 7. The slide movement can be divided into three zones as per Fig 8 as Zone of Detachment (1650m - 1325m above msl), Zone of transportation (1325m - 1100m above msl) and Zone of accumulation (1100m 800m above msl). Cross-section of the slope is displayed in Fig 2 and the photograph of the slope towards the northeast is shown in Fig. 9. According to the profile shown in Fig 2.2, the major sliding plane is in the upper part of the slope where the rock is highly jointed.
Fig 7: Location Map of the Study Area
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
12
Zone of
Fig 8: Cross- Section of the Surbhee Resort Landslide (Gupta et al., 2007)
Fig 9: Surbhee Resort Landslide
4.4.3 Modelling of Slide in UDEC For the analysis of rock slope stability, the analysis is carried out in two parts. First is to analyse the structure to assess the orientation of the discontinuities which are predominant in the area that could result in the instability of the slope under study. Second step is to do numerical modelling of the structure under gravity load. As per the geotechnical investigations carried out in the study area by Gupta et al., (2007), it is clear that the area is highly fractured in the zone of detachment which needs to be looked as per the stability is concerned. Figure 10 shows the jointed slope model used for the numerical analysis. This simplified model was constructed based on cross-section of the rock slope given by Gupta et al., 2007 (Fig. 2.2) and site visit, where in the study of orientation of the joints was carried out.
Fig 10: Numerical Model of the Slope
The intact rock is considered to behave as linearly elastic where as the rock discontinuities are assumed to behave non-linearity following the Mohr-Coulomb model.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
13
4.4.4 Static Analysis Various cases were undertaken to study the stability analysis of the Surbhee Landslide. The in-situ conditions and the gravity load were applied and the slope was monitored under static conditions till equilibrium was reached. After gravity loading, it has been observed that shearing of the joints is taking place in the zone of detachment, whereas in the zone of transportation and accumulation, it is observed that it stable under gravity load. From gravity load analysis, it is clear that vulnerable area is the zone of detachment. Fig 11 shows the shearing in the joints.
Fig 11: Shearing of Joints after Gravity Load in Case
To further study the stability of the slope under saturated and weathering conditions, various studies have been carried out. It is assumed that with time due to ingress of water and climatic changes, there is weathering of joints. With this friction angle is bound to be reduced at the joints. To simulate this effect on joints, analysis has been carried out with reduced friction angle 30o, 28o, 25o and 22o. It was observed that when friction angle reduces to 22o, there is detachment (Fig 3.7) of the blocks in the zone of detachment where the displacement increases to a very high value. Degradation of joint with climatic changes can also be studied with there reduction in the shear stiffness values of the joints. Similar study as done with friction value at joints has been carried out with reduced shear stiffness values. Value has been reduced from 1.33e10 Pa to 1.33e9 Pa, 1.33 e8 Pa and 1.33 e7 Pa. It has been observed that with reduced stiffness value to 1.33e7 Pa, slope is unstable with the block separation in the zone of detachment. 4.4.5 Application of Dynamic Loading – Earthquake Conditions Under dynamic loading, an excitation is applied to the rock slope. It is important to analyse the slope under study in the seismic environment as it lies in zone IV of IS Code 1893 – 2002. To account for this, Seismic analysis of the slope under study has been carried out under a sinusoidal wave of frequency 3 Hz. After the application of 3 sec, it was observed that the shearing got concentrated in the top layer of the slope in the zone of detachments.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
14
Displacement of Joints after Seismic Loading – Sine
Fig 12: Displacement at the end of 3 sec
A time history compatible to the response spectrum of the site near the study area has been generated with frequency range equivalent to the Uttarkashi earthquake record of 20 October 2001 with PGA of 0.31g. The applied record is of 65 sec. Calculated time step Δt = 1.232e05 sec. It is observed that as the wave propagates through the rock mass there is amplification of the record. Shearing in this case is also observed in the zone of detachment. To have a better insight into the seismic analysis of slope, another time history was synthetically generated compatible with the IS Code 1893-2002 response spectrum. The site is located in zone IV. Zone factor for this region is 0.24. Artificial time history generated was having PGA 0.24g in the transverse direction. It can be concluded that under seismic conditions with present rock mass and joint strength conditions, shearing of joints is predominant in the zone of detachment. To analyse the behaviour of the slope with reduced joints strength parameters, in the further cases sinusoidal wave is used as the seismic input. To study the overall behaviour of the slope under seismic conditions, model with reduced joint strength were analyzed. With reduced friction angle to 22o, it is observed that displacement is present in the top layers i.e. in the zone of detachment as well as in the zone of transportation. It is a major threat to the stability of the slope, the total slope is unstable. This concludes that with ingress of water, reducing friction angle can be a major threat to the overall stability of the slope. It was observed the block failure of the top layer which is highly weathered rock takes place. The failure mechanism is given in Fig 13. Seismic analysis has also been carried out for the cases with reduced shear stiffness at the joints. Similar results have been observed that with reduced joint strength the slope is unstable. The numerical results indicate the effect of degradation of joints and discontinuities on the stability of the slope. With degradation of joints, the slope becomes unstable and dynamic
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
15
loading results in the instability of the weathered material on the top of the slide i.e. the top most layer. The slope is stable in the present situation but with the rainfall it is susceptible to become unstable where the movement is concentrated in the upper part of the slide and also in the lower area where shearing of the joints.
Max. Disp. = 19.00 m
Max. Disp. = 12.50 m
9 sec
7 sec Max. Disp. = 26.00 m
Max. Disp. = 34.00 m
11 sec
13 sec
Max. Disp. = 43.00 m
15 sec
Max. Disp. = 53.00 m
17 sec Max. Disp. = 58.50 m
18 sec
Max. Disp. = 63.00 m
19 sec Fig 13: Failure Mechanism in Case 15
4.4.6 UDEC Model – Zone of Detachment After the detailed study of the Surbhee landslide, it is clear that the zone of detachment is the most vulnerable part of the slope which is unstable. To study in detail the zone of detachment was modelled again in UDEC and studied under stability in the present condition. Figure 14 shows the model of zone of detachment in UDEC
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
16
Fig 14: Model of the Zone of Detachment in UDEC First analysis was carried out with initial stresses and gravity load, until equilibrium was reached. It was observed that the slope is stable under gravity load with shearing concentrated in the top layer (Fig 15). After the static analysis, analysis was carried out under dynamic load i.e. with a sinusoidal wave of frequency of 3Hz for 3 sec. It was observed the displacement gets concentrated on the top foliation planes of the slope which is highly weathered material in the real situation in the field (Fig 16).
Fig 15: Displacement and Shearing of Joints
Fig 16: Displacement at the end of Dynamic Loading
From the modelling of the zone of detachment in UDEC it is clear that the zone of detachment which is contributing to the displacement in the Surbhee slide. For studying the 3-Dimensional effect of the slide, it was modelled in 3DEC. Further, in the study three dimensional modelling and analysis will be discussed in detail. 4.4.7 Dec Modelling – Zone of Detachment In three dimensional modelling, only the zone of detachment was considered for study referred as Case A. Figure 17 shows the model in 3-DEC which is a replica of UDEC and Fig 18 shows the jointing pattern. Initial stresses were applied and analysis was carried out gravity load until equilibrium was reached. Figure 19 shows the displacement vectors under
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
17
static conditions and the shearing of the joints which is concentrated at the end of the zone of detachment which is in accordance with what was observed in 2-D.
Fig 17: 3-D Model of Case A
Fig 18: Jointing Pattern
Fig 19: Displacement Vectors under Gravity Load in 3-D After the static analysis, model was subjected to a dynamic load i.e. a sinusoidal wave of frequency 3 Hz for 3 sec. it was observed that the displacement reaches a value of 70 cm (Fig 20) against 89 cm as observed in 2-D and maximum shear displacement of 68 cm is observed which is higher than that observed in 2-D which is due to the 3-Dimensional effect of shearing of joints. The amplification the signal as it passes through the model is approximately three times.
Fig 20: Displacement Vectors under Dynamic Loading in 3-D
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
18
From the above analysis it is clear that the top foliation plane of the slope is only under threat which can fail under low friction angle i.e. with degradation or weathering of joints due to ingress of water. To study the three dimensional effect an attempt was made. To account for this, two cases were taken one with the top of the slope was tilted 10o E with Z-Dimension increased to 300 m and other in which the total profile as well as the joints were tilted by the same amount i.e. 10o E and Z-Dimension increased to 300 m. Analysis was carried out both under gravity and dynamic case. After the equilibrium is achieved under gravity, model was subjected to dynamic loading of a sinusoidal wave of 3 Hz for 3 sec. It was observed that displacement increased to 63 cm with maximum shear displacement of 61 cm. It is indicated from the displacement vectors (Fig 22) at the end of dynamic loading that more displacement is experienced at the right end of the slope face which is highlighted in the figure.
Fig 21: Model with Top of the Slope Tilted
Fig 22: Displacement Vectors after Dynamic Loading
Similar study was carried out for Case C and the results obtained were similar to that observed. It was observed that more shearing takes place at the right corner of the top face of the model. 5.
Future Plans
During next one year, the work on liquefaction studies will continue with more field tests, lab tests and numerical modelling using FLAC3D. In this concern it shall be noted that procurement of a sophisticated Cyclic Triaxial System is in pipeline at IIT Roorkee and once this system is installed, using it the lab tests would be conducted on the soil samples collected from the field. Also a fresh attempt will be made to recruit a research scholar. 6.
References 1. Bardet, J.P., Ichii, K. and Lin, C.H. (2000). EERA, A Computer Program for Equivalent Linear Earthquake Site Response Analysis, Dept. of Civil Eng, University of Southern California, USA.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
19
2. Chandra, B., Thakkar, S.K., Basu, S., Kumar, A., Shrikhande, M., Das, J., Agarwal, P., and Bansal, M.K. (2002). Strong motion records. Chapter 5 in Bhuj, India Earthquake of January 26, 2001 Reconnaissance Report, Earthquake Spectra, Supplement to Vol. 18, 53-66. 3. Gupta, M.K. (1977). Liquefaction of Sands during Earthquakes, Ph.D. Thesis, University of Roorkee, Roorkee, India. 4. INPIC Report (2006). Final Report (2003-2006) of Indo-Norwegian Programme of Institutional Cooperation on Earthquake Engineering, by Dept. of Earthquake Engineering, IIT Roorkee, NORSAR, Norway and NGI, Norway. 5. IS: 1893-2002-Part 1: Criteria for Earthquake Resistant Design of Structures: General Provisions and Buildings. Bureau of Indian Standards, New Delhi. 6. IS 2131: 1981. Indian Standard Code of Practice, Method for Standard Penetration Test for Soils. Bureau of Indian Standards, New Delhi. 7. Kramer, S.L. (1996). Geotechnical Earthquake Engineering, Prentice Hall, Inc., Upper Saddle River, New Jersey. 8. Mahajan, A.K. (2008). Personal Communication, Wadia Institue of Himalayan Geology, Dehradun. 9. Prakash, S. (1981). Soil Dynamics, McGraw-Hill Company, New York. 10. Ranjan, R. (2005). Seismic Response Analysis of Dehradun City, India, MSc thesis, Indian Institute of Remote Sensing, National Remote Sensing Agency, Dehradun Dep. of Space, Govt. of India. 11. Seed, H.B. and Lee, K.L. (1966). Liquefaction of saturated sands during cyclic loading. Journal of the Soil Mechanics and Foundation Division, ASCE, 92:SM6, 105-134. 12. Seed, H.B. and Idriss, I.M. (1970). Soil moduli and damping factors for dynamic response analyses, Report EERC 70-10, Earthquake Engineering Research Center, University of California, Berkeley. 13. Seed, H.B. and Idriss, I.M. (1971). Simplified procedure for evaluating soil liquefaction potential. Journal of the Soil Mechanics and Foundation Division, ASCE, 107:SM9, 1249-1274. 14. Seed, H.B., Tokimatsu, K., Harder, L.F., Chung, R.M. (1985). Influence of SPT procedures in soil liquefaction resistance evaluations. J. of Geotech. Eng, ASCE, 111:12, 1425-1445.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
20
Appendix – 1 Travel Report Visit of IITR team to Norway (Sept. 22-30, 2007) Dr. B.K. Maheshwari and Dr. M.L. Sharma from IITR visited NGI and NORSAR respectively during September 22-30, 2007. The aims of Dr. Maheshwari‘s visit were: 1. To carry forward the collaborative project. 2. It was first visit of Dr. Maheshwari to Norway. He had visited the laboratory facilities of NGI including cyclic triaxial test system, direct simple shear test and resonant column test. 3. Dr. Maheshwari has a number of technical meetings with Dr. Kaynia. As a result, strategy to carry forward the liquefaction study (theme 2) has been chalked out. 4. One of the most important accomplishments of the visit was to get familiar Dr. Maheshwari with software FLAC. Few learning sessions were held with Dr. Kaynia to get hands on this powerful software. 5. Next visit of NGI scientists at IIT Roorkee is planned for January 2008. A detailed task programme for the project (theme 2) was discussed and finalized in several meetings held at NGI. Different milestones for theme 2 of the project is also finalized and attached with this report.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
21
Appendix – 2 Travel Report Visit of NGI team to IIT Roorkee (January 2008) Introduction As part of the Geo-related activities in the institutional cooperation project on earthquake risk in India, the two Norwegian participants of the project from NGI, R. Bhasin and A.M. Kaynia travelled to India in the period Jan. 6-13, 2008. The intention was to follow up the planned activities and make plans for the next period. The following describes the results of the meetings and plans made in collaboration with the Indian counterparts, together with the technical activities undertaken during the visit. The meetings and visits included primarily: Dr. D.K. Paul (DKP) Dr. M.L. Sharma (MLS) Dr. Y. Singh (YS) Dr. B.K. Maheshwari (BKM) Ms. Shilpa Pal (SP) Dr. R. K. Bhasin (RKB) Dr. A.M. Kaynia (AMK)
Details of Activities Day 1 – Jan. 6, 2008 – Departure from Oslo Day 2 – Jan. 7, 2008 – Review and planning meeting Participants: DKP, MLS, YS, BKM, RKB, AMK
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
22
A long meeting was held at IITR to review the progress of the project, status of student hiring for the project, actions taken with regards to the measurement campaign in Haridwar in March 2008, selection of the interdisciplinary site. The following is a summary of the findings, observations and conclusions: 1. There have been some difficulties in hiring new students mainly due to the tough competition by the industry which offers considerably higher salaries. In particular, the student who was recruited by BKM for the liquefaction studies had recently switched to another area (AMK had a meeting with the student a few days later and gave a broader view of the project. It appears fairly unlikely that the student changes his mind because he is looking for a theoretical subject and has already been in dialogue with another professor at IITR). 2. The ordering of the equipment required for the liquefaction testing is in progress. Until the new equipment arrives, the old apparatus will be used. 3. The ordering of the system by OYO for noise measurement and processing is in progress. MLS indicated that there is a very good chance that the system will be ready for the March measurement campaign. 4. Preparation work for numerical modelling of slopes has been progressing well. SP presented some recent work done under DKP’s supervision (the results are included in the 1st report of the Geo-group in Jan. 2008). 5. Discussions were made around possible candidate sites for the numerical analyses of slope stabilities. Two sites were nominated: i) Mansa Devi in Haridwar, ii) Surabhi in Mussouri. It was decided that visits be made to these sites during this period. 6. YS gave an overview of the work on the risk assessment and expressed general satisfaction with the work in view of the promised support by NORSAR.
Day 3 – Jan. 8, 2008 – Visit to Haridwar Participants: DKP, MLS, BKM, SP, RKB, AMK The participants travelled to Haridwar to visit the candidate sites for the noise measurement campaign and one of the candidate sites for the slope stability analyses. The trip was very helpful as it provided the opportunity to get a feeling of the sites. From the geological background and visual observations, it appears that the candidate sites are well suited for both the noise measurements and liquefaction studies. In particular, sites are close to areas that are under development and the above studies can be considered, indirectly, contributing to the development plans of these areas. The group also made a thorough assessment of the Mansa Devi landslide. The access to this landslide which is on the mountain outskirts of Haridwar was only possible on foot. This landslide (see photo) has blocked an important route in the region which is also a pilgrimage route and therefore is of special socio-economic importance to the region. For the time being CBRI (Centre for Building Research Institute) has installed a measurement post in the slide area to monitor its movements. The objective is to install an early warning system for the site once it is opened again for traffic.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
23
View from other side of valley
Road destroyed and out of traffic
Views of Mansa Devi Landslide in Haridwar
Day 4 – Jan. 9, 2008 – Technical discussions and planning Participants: DKP, MLS, BKM, SP, RKB, AMK Meetings were held in the morning to review the progress of the work. Students of BKM and LMS gave presentations of their research. Based on the works presented, it was decided that until a new student is identified for the liquefaction studies, one of the current students of BKM (Rajib) continues on the topic. Also the work of MLS’s student, Naveen Parikh, who works with processing of satellite imagery, appeared to be relevant for the project and the group recommended that SP and Naveen spend a few months at NGI to work with the georelated topics. A long meeting was held in the afternoon to make plans for the next period. The following decisions were made: 1. Five sites were nominated in Haridwar for the March measurement campaign as follows (in order of preference): a) Roshanabad (near industrial development) b) Raiwala c) Doiwala d) Gurukul kangari University e) BHEL (Bharat Heavy Electricals Ltd.) 2. MLS and Dr. Mahaja of WIHG make coordination for selecting one of these sites (MLS made the contact during the meeting and already made plans with Dr. A.K. Mahajan). 3. As soon as the site is selected, BKM should mobilise the site investigation contractor to make a borehole and perform SPT to confirm the suitability of the site w.r.t. liquefaction. 4. DKP will guide SP in numerical modelling of the slope stability of either Mansa Devi or Surabhi (to be decided later after RKB and AMK visit Surabhi on 11 Jan.)
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
24
Day 5 – Jan. 10, 2008 – Visit to WIHG, Dehradun Participants: RKB, AMK RKB and AMK travelled to Dehradun and visited Dr. B.R. Arora and Dr. Mahajan. The meeting was very useful as Dr. Arora also promised cooperation w.r.t. providing the necessary data for the slope stability analyses. One of the WIHG’s staff, Dr. Vikram Gupta (VG), was assigned to support with the data collection and was asked to accompany the Norwegian team to the site of the Surabhi landslide in Mussouri the following day.
Day 6 – Jan. 11, 2008 – Visit to Surabhi landslide Participants: RKB, AMK, MLS, VG Dr. Vikram Gupta (VG) of WIHG led en expedition to the site of Surabhi landslide near Mussouri (see photo). The slide is underneath a resort hotel and has been moving at a rate of 8-10 mm per year. One could see debris of previous slides at this site. It is suspected that discharge of wastewater by the hotel has initiated some slides and opening of the cracks, and now rain and other surface water easily seep into the cracks and make the site more vulnerable to landslide. Even a moderate earthquake in this are is believed to be capable of inducing a major slide at this site.
Resort hotel on top of landslide-prone area
Views of Surabhi Landslide in Mussouri While RKB and VG continued inspecting the site and collecting miscellaneous information, MLS and AMK took a trip to Tehri dam. The trips ended back in IIT Roorkee.
Day 7 – Jan. 12, 2008 – Travel to Delhi – free, rest of the day Day 8 – Jan. 13, 2008 – Return to Oslo
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
25
Appendix – 3
SITE SELECTION FOR THE GEOTECHNICAL INVESTIGATIONS Objective Selection of sites for geotechnical investigations with the aim to calibrate the different techniques for site characterization, to determine the liquefaction potential and recommend seismic hazard Field trip A team consisting of the following members visited the Dehradun – Haridwar – Roorkee area for the selection of site on Feb 13, 2008 1. Dr. M. L. Sharma, IIT Roorkee 2. Dr. B. K. Maheshwari, IIT Roorkee 3. Dr. A. K. Mahajan, WIHG 4. Dr. A. K. Mundipi, WIHG 5. Mr. N.P. Aterkar, Soilex Consultant, Roorkee The following nine sites were tentatively selected for the investigations: No.
Location
Latitude
Longitude
Latitude
Longitude
1.
Doiwala
30
9
14.5
78
9
50.1
30.1540
78.1639
2.
NGA
30
4
3.4
78
12
50.2
30.0676
78.2139
3.
Shanti Kunj
29
59
32.1
78
11
23.4
29.9923
78.1898
4.
DAV School
29
54
14.2
78
7
57.4
29.9039
78.1326
5.
Roshnabad
29
58
12.8
78
4
23.3
29.9702
78.0731
6.
Gurukul
29
55
8.1
78
7
34.7
29.9189
78.1263
7.
Dhanori
29
56
24.6
77
57
25.5
29.9402
77.9571
8.
COER
29
53
35.2
77
57
42.1
29.8931
77.9617
9.
Solani
29
52
46
77
53
52
29.8794
77.8978
Doiwala The site is between Dhradun (DD) and Haridwar (HR). By road, it is 25 km from DD and 28 km from HR. As per tube well logging information, the depth of soil is about 3 to 5 meters below which gravels are expected. The site is near Chidaharwala. NGA The site is in the ground in front of the School by Nirmal Gyandan Asharam (NGA). The site was very near to Nepali Farm. The photograph shows the soil exposed while excavating the ground. This may be a good site for the investigations.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
26
Shantikunj The space may not be available for the array and MASW techniques. This site is highly populated now and not recommended due to local public use. DAV School The site lies on the Hardwar-Laksar road in the play ground of the DAV Centenary Public School, Kankal. Here the investigations have been made by Mr. Aterkar for a depth of about 10 meters for some other project. The top 2m is suggested silty sand, then next 3-12 m is gravelly sand and then may be gravels below. The play ground of the school will be a good site for carrying out all the tests and for the calibrations of the methods. Roshanabad-BHEL The site lies in the back of the Vikas Bhawan. The array method can be applied for about 200 meters area. This is the largest area available in all the sites. Here four locations are available for these investigations: A Roshanabad administrative block in Vikas Bhawan Campus B Air Port Ground C Chinmay College of Science, Sector 6, BHEL D CISF Campus Ground, Ranipur Gurukul The ground is available for the testing at Gurukul Kangri University Dhanori This is in Dhanori Village (about 10 km from Roorkee), it may be a good site for the liquefaction studies since this site is in between two canals and also a river is nearby. The site may have considerable silt. COER The ground of College of Engineering Roorkee (COER) may be a good site since the alluvium thickness is increased and the soil investigations can be carried out for more depths. Solani No location is available at this site. Only a small ground (undulating) could be seen in the side of the government workshop. However the site is very good for liquefaction study as it consist of saturated loose sand. One of the sites may be the land belonging to Mr. Aterkar which is one km away towards Iqbalpur on the Iqbalpur Puhana road. This is near to the Roorkee Engineering College. The process of getting permission from concerned authorities for use of these sites is in pipeline. In the first phase of the testing following four sites are recommended: 1. Dhanori 2. Roshnabad-BHEL 3. NGA
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
27
4. DAV School
30.2 Doiwala
30.1 NGA
Shanti Kunj Dav School Roshnabad
30 Dhanori
Gurukul COER
29.9
Solani
29.8 77.8
77.9
78
78.1
78.2
78.3
Location of Various Sites (Courtesy Google Earth)
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
28
By
Department of Earthquake Engineering Indian Institute of Technology, Roorkee Roorkee, - 247667, Uttarakhand, India and
NGI Authors: Prof. D. K. Paul, Dr. B. K. Maheshwari, Dr. Amir M. Kaynia, and Dr. Rajinder Bhasin, NGI
July 2008
Table of Contents 1. Summary
2
Technical Issues
2
2. Introduction
2
3. Objectives and Scope
2
4. Activities (ongoing and completed)
2
Administrative and Travel
2
Changes / Deviations from the Program
3
Liquefaction Studies Slope Stability Assessment Studies
3 11
5. Future Plans
19
6. References
19
Appendix – 1
21
Appendix – 2
22
Appendix – 3
26
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
1
1.
Summary Technical Issues
In theme 2, key persons involved are: India: Norway:
Prof. D. K. Paul and Dr. B. K. Maheshwari, IIT Roorkee Dr. Amir M. Kaynia and Dr. Rajinder Bhasin, NGI
This report describes the progress made in these areas during last 14 months (July 2007-July 2008) and in continuation to the report submitted in August 2007.
2.
Introduction
The theme 2 of the project is on ground stability assessment and consists of two tasks: (A) Liquefaction susceptibility of selected sites and (B) Slope stability assessment of critical slopes
3.
Objectives and Scope
Aim of the present study can be broadly categorized in two parts. First, to analyze the liquefaction susceptibility of few selected sites near Haridwar/Dehradun, in northern state of Uttarakhand, India. Second is to evaluate slope stability analysis. The scope of the first part of study consists of in situ tests, laboratory tests and numerical modelling. The slope stability assessment would be carried out based on numerical modelling based on the data collected from the sites.
4.
Activities (ongoing and completed) Administrative and Travel
For liquefaction studies, various activities were performed in last year is described below: 1. An IITR team consisting of Dr. B.K. Maheshwari and Dr. M.L. Sharma visited Norway during Sept. 22-30, 2007; the travel report is enclosed (Annex 1). 2. An NGI team consisting of Dr. Amir M. Kaynia and Rajinder Bhasin visited IIT Roorkee during January 7-9, 2008; the travel report is enclosed (Annex 2). 3. Much effort has been made to recruit a Ph.D. student at IIT Roorkee for the research work on liquefaction by putting advertisements a couple of times. The first time, the position was advertised in June 2007, a candidate (Mr. Govardhan with M. Tech degree) was identified. He joined the project as a JRF (Junior Research Fellow) for three months (during Sept.-Nov. 2007). During this period he got familiar with the scope of his assignments in the project. On successful completion of his M. Tech degree and passing a formal interview he has been offered a position of SRF (Senior Research Fellow) from December 2007 and was encouraged to join the Ph.D. programme beginning January 2008. Unfortunately, in the first week of December, he
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
2
4.
5.
6.
7.
8.
quit the position without joining the SRF position. Thus this exercise of recruitment turned futile. In February 2008, the research position (for a Ph.D. candidate) was advertised afresh. The letters were dispatched to abut 100 engineering colleges for wide publicity. A couple of candidates showed interest through including a female student from NIT Silchar (M. Tech in the final semester student); she moved one step forward and formally applied for Ph.D. through regular application. She was called for a formal interview in June 2008 but did not show up for the interview nor responded to followup e-mails. So unfortunately, this attempt was also not successful. It was envisaged that FLAC3D software will be very useful for carrying out research work on liquefaction, the software has been procured at IIT Roorkee with institute funds and has been operational since February 2008. Identification of sites: A team of faculty members from IIT Roorkee and Scientists from WIHG visited Dehradun – Haridwar – Roorkee area for the selection of sites on February 13, 2008. The report of site selection is enclosed (Annex 3). A team from NORSAR, Norway consisting of Dr. Conrad Lindholm and Dr. Juan Jose Galiana visited the four selected sites and witnessed the seismic refraction tests during March 7-11, 2008. The SPT (Standard Penetration Tests) was planned at four selected sites. The field testing at two sites namely Dhanuari (June 23-24, 2008) and Roshnabad (July 19) is already completed. The laboratory tests on the soil samples collected from Dhanuari and Roshnabad is completed using shake table in Soil Dynamics Laboratory at IIT Roorkee. This is described in detail in section 4.3.
Changes / Deviations from the Program It was envisaged in the report submitted in August 2007 that the available resources do not warrant significant contribution to the theme 2 of the project. However, it shall be noted that despite this projection and all the constraints, the significant progress has been made by IIT Roorkee particularly for liquefaction studies. In this regard it shall be noted: 1. The drilling (SPT) has been planned at selected sites; this has been done at a very competitive price. 2. The lab tests were conducted with the help of a research scholar and lab staff at IITR. 3. The FLAC3D software is procured at IITR with institute funds 4. It has been tried to the extent possible that the non-availability of a research scholar doesn’t hamper the project work Liquefaction Studies Modus Operandi: To accomplish the project objectives, three approaches have been proposed. In situ testing, followed by laboratory testing of soil samples collected, and simulation of results using numerical modelling. The in situ tests have been carried out including Standard Penetration Tests (SPT) at selected sites. Laboratory tests using the liquefaction table available at IIT Roorkee has been performed. Results of in situ and laboratory testing will also be simulated using a numerical methodology in software FLAC3D. The progress made so far is described in detail in following sections.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
3
4.3.1 Introduction Himalayan region is one of the most seismic active zones in India. This region was home to many major earthquakes in the past including 1905 great Kangra earthquake, 1934 NepalBihar earthquake, 1991 Uttarkashi earthquake, 1999 Chamoli earthquake and recent 2005 Kashmir earthquake. Many large cities in the region are located within a recent river alluvium valley with soft to very soft geological conditions, with shallow depths to bedrock and may be prone to liquefaction during a major earthquake. Dehradun is a part of the Doon valley and located in the western part of the state of Uttarakhand in North India. Doon valley is bounded by Himalaya in the North, Siwalik in the South, river Ganga in the East and river Yamuna in the West. The city has a population more than a million. Geologically the whole Doon valley can be divided into three regions namely the Lesser Himalaya, the Siwalik group and the Doon Gravels. Selection of sites can be based on the local geology. Ranjan (2005) carried out geophysical survey at many locations in the city. Shear wave velocity of these sites were determined using SASW tests. However, most of sites in Dehradun are dry (water table is very deep) with gravels, and have a fairly high shear wave velocity; so, they may not be prone to liquefaction. Therefore, the focus was shifted to the nearby cities Haridwar and Roorkee. A number of studies are reported in literature for liquefaction susceptibility e.g., Prakash (1981) and Kramer (1996). In the present work, the liquefaction potentials of two sites in Haridwar, India have been investigated using field and laboratory tests. The field test involves SPT (Standard Penetration Test) while in laboratory testing, the sample collected from the field is submerged and imparted horizontal vibration in a shake table. The liquefaction potential of the sites is predicted based on these tests. 4.3.2 Socio-Economic Aspect of the Study Liquefaction has been a source of much damage in the past earthquakes (e.g. Niigata and Alaska earthquakes of 1964, Kobe earthquake of 1995, Kocaeli-Turkey and Chi-Chi earthquakes of 1999, Bhuj Earthquake 2001). New developments are planned in Haridwar. Since the soil condition at many places in Haridwar is loose saturated sands, they may be susceptible to liquefaction. The results of the study in terms of liquefaction assessment would be valuable for the future development and land use planning. Haridwar is a holy religious city and advancing towards both industrial and tourist development. Therefore, the present study has social and socio-economic values. The city has over a million population and is a district headquarter with administrative offices. The city is in a phase of industrialization for energy and for many consumable products. A number of private industries are setting up their businesses on the outskirts of the Haridwar. Therefore, the functionality of the city during an earthquake is very important for the whole district including other important nearby cities such as Roorkee. 4.3.3 Location of Sites and their Characteristics Both selected sites are situated in the Haridwar district as described below: (i) Dhanuari Site: The site is about 10 km from Roorkee and situated between Roorkee and Haridwar. Play ground of an intercollege school is selected as a test site in this small village Dhanuari. The site lies between two canals and there is a river nearby. It was expected that water table may be at shallow depth. Location of the site is Latitude
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
4
29º 56´ 24.6˝ and Longitude 77º 57´ 25.5˝. (ii) Roshnabad: The site is on the outskirts of Haridwar City (about 5 km south from the city centre). An open ground at a distance of about 500 m from the office of the District Magistrate has been selected as the test site which is on the backside of Vikas Bhawan campus. Location of the site is Latitude 29º 58´ 12.8˝ and Longitude 78º 04´ 23.3˝. The SPT (Standard Penetration Tests) as per IS: 2131-1981 were conducted on both sites up to a depth till refusal was met. The samples collected were further tested in the laboratory for evaluation of grain size distribution, unit weight of soil and Atterberg’s limits. It was observed that the soil at both sites is mainly sandy soil and can be classified as SM and SP. At Dhanuari, the water table was encountered at a depth of 4.75 m from the existing ground surface. In Roshnabad, the water table was not encountered up to the depth of exploration (7.5 m) and it may be very deep. Therefore, liquefaction was ruled out at Roshnabad, however further investigation was carried out assuming water table at the same level as observed in Dhanuari i.e. at a depth of 4.75 m from the ground surface. 4.3.4 Liquefaction Potential Based on Field Tests The data obtained from the in situ tests and laboratory tests were analyzed for determination of liquefaction potential of both sites. The cyclic stress approach of Seed and Idriss (Seed and Lee 1966) was used for determination of liquefaction potential of the sites. Shear stresses τav due to earthquake loading is computed based on following two methods (a) Simplified Method (Seed and Idriss, 1971): Average equivalent uniform shear stress at a particular depth, τav is given by
τ av = 0.65σ v 0
amax rd g
(1)
Where σv0 is total overburden pressure at that depth, amax is peak ground acceleration and rd is reduction factor. According to IS: 1893-2002 (Part 1), both sites are situated in seismic zone IV, therefore they have a PGA value amax = 0.24 g. (b) Ground Response Analysis: This has been performed using the program EERA (Bardet et al. 2000) which is based on one dimensional layered soil model. The shear wave velocity is an important parameter for the program EERA. It was determined from the in situ test, SASW. The shear wave velocity for both sites is shown in Fig. 1 (Mahajan 2008). It can be observed that Roshnabad site has higher shear wave velocities compared to Dhanuari site. Also in Roshnabad a bedrock with shear wave velocity 730 m/s is encountered below 54 m, however, in Dhanuari the maximum shear wave velocity recorded was 320 m/s below 16 m. The soil being in loose condition at Dhanuri, the SASW could indicate a shear wave velocity up to 16 m only. These observations are very much in consistent with N (SPT) values recorded on these sites. That is, for Dhanuri: for a depth 0~16 m, N = 2 ~18 and for Roshnabad: for a depth 0~7.5 m, N = 9 ~ 51. In Roshnabad SPT sampler indicated refusal as shallow as 7.5 m depth where N was recorded as 51.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
5
The transient excitation (acceleration time history) was used as input loading to the program EERA. In the present study the N78ºE component of Bhuj (2001) Earthquake recorded at Ahmedabad (Chandra et al. 2002) was used. The acceleration time history has a PGA equal to 0.106 g as shown in Fig. 2. Duration of the actual time history is about 133 s, however the strong portion of it is only about 60s as shown in Fig. 2. For this loading, the maximum shear stresses at different depths were computed using the program EERA. The equivalent linear soil model (Seed and Idriss 1970) was used in the computation. The average shear stress was taken as 65% of the maximum value (Kramer 1996).
Shear Wave Velocity (m/s) 0
100
200
300
Shear Wave Velocity (m/s) 400
0
0.00
200
400
600
800
0
10 4.00
8.00
Depth (m)
Depth (m)
20
12.00
30
40
50 16.00 60 20.00 70
(a) Soil Profile - Dhanuari Site
(b) Soil Profile - Roshnabad Site
Fig. 1: Shear Wave Velocity Profiles of both Sites (Mahajan, 2008)
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
6
Bhuj EQ Time History 0.15
Acceleration (g)
0.10
0.05
0.00
-0.05
-0.10
-0.15 0
20
40
60
80
100
120
Time (sec)
Fig. 2: N78ºE Component of Bhuj (2001) Earthquake Component Recorded at Ahemedabad The average shear stresses in soil at different depths computed using the Simplified Method (Eq. 1) and from Ground Response Analysis are compared for both sites in Fig. 3. It can be observed that at Dhanuri site, the shear stresses obtained from the simplified method is significantly higher than those obtained using the ground response analysis. However at Roshnabad site this difference is not significant. The larger of these stresses were used to evaluate the liquefaction potential of the site. Shear stresses corresponding to liquefaction resistance of soil were computed using the Cyclic Stress Ratio (CSR) approach (Seed et al. 1985) where N values (penetration resistance) collected from the field is a key parameter. The measured value from field was normalized for an overburden pressure of 1 ton/ft2 (100 kPa) and corrected to an energy ratio of 60%. Thus corrected SPT values (N1)60 was evaluated and used for determination of CSR. The magnitude of earthquake is assumed equal to 7.5 for evaluation of CSR. The selection of this magnitude was based on a site specific seismic study conducted for the region (INPIC report 2006). CSR is defined as: CSR =
τ cyc σ v′0
(2)
Where τcyc is cyclic shear stress and σ'v0 is initial effective overburden pressure. Thus τcyc is found from CSR evaluated. Wherever, τav is greater than τcyc, liquefaction is expected to occur. The ratio τcyc/τav provides a factor of safety against liquefaction.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
7
Using Simplified Method
Using Simplified Method
Ground Response Analysis
Ground Response Analysis
Shear Stress (kN/m2) 0
10
20
30
Shear Stress (kN/m2)
40
0
0
10
20
30
1
2 2
4 3
Depth (m)
Depth (m)
6
8
10
4
5
12 6
14 7
16
18
8
(a) Dhanuari Site
(b) Roshnabad Site
Fig. 3: Comparison of Shear Stresses induced due to Earthquake Loading Using Simplified Method and using Ground Response Analysis at both sites The factor of safety against liquefaction is shown for both sites in Fig. 4. It can be observed that the factor of safety is less than unity at all depths (below water table) for Dhanuari site. Thus analysis indicates that site will liquefy in an earthquake of magnitude 7.5 with PGA=0.24g. The outcome is very much consistent with guideline given in IS: 1893-2002 which suggest that to avoid liquefaction in seismic zone IV the N value shall be in the range of 15~25 (increasing with depth). N obtained from SPT at the site are as low as 2. Contrary to this, no threat of liquefaction is indicated in Roshnabad site even assuming that water table exists at a depth of 4.75 m.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
8
Factor of Safety 0.0
0.5
1.0
Factor of Safety 1.5
1.0
6.0
1.5
2.0
2.5
3.0
0
8.0 2
Depth (m)
Depth (m)
10.0
4
12.0
6
14.0
8
16.0
(a) Dhanuari Site
(b) Roshnabad Site
Fig. 4: Factor of Safety against Liquefaction with depth at both sites 4.3.5 Liquefaction Susceptibility Based on Laboratory Tests The tests were performed on a simple but indigenously fabricated vibration table (Gupta 1977) in the Soil Dynamics Laboratory of the Dept. of Earthquake Engineering, IIT Roorkee, India. The test bin is a tank 1.05 m long, 0.60 m wide and 0.60 m high, in which soil sample is prepared. The test set up is shown in Fig. 5. The table can produce one-dimensional (horizontal) steady state vibrations. The tests were conducted on the soil samples collected from both sites. Since a large sample (about 500 kg) of soil was required to conduct a test on this table it was not feasible to conduct the tests on the samples collected from different depths through SPT. However, a sample which is a good mix of the soil collected from different depths in a borelog was used in the shake table. Thus the test results will reflect the liquefaction susceptibility of the site in general but not depth-wise. The known quantity of soil sample was filled in the table and submerged for a couple of hours so that it is fully saturated. A harmonic motion with constant frequency of 5 Hz and amplitude 0.3 g was applied for 60 seconds. The equivalent number of cycles for an earthquake of magnitude 7.5 is 15 only. However, the number of cycles applied was intentionally high to observe the generation of pore water pressure. The pore water
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
9
pressure with time was measured at different depths in the tank. Initially the pore water pressure rises and then reaches to a maximum value and then dissipation starts.
Fig. 5: Liquefaction Table at Dept. of Earthquake Engineering, IIT Roorkee
Bottom Pick-Up 1.60
Top Pick-Up
ru = 0.49
ru = 0.51
1.20
Uexcess (kN/m2)
Middle Pick-Up
ru = 0.57 0.80
0.40
0.00 0
50
100
150
200
250
300
Time (s)
Fig. 6: Excess pore water pressure (Uexcess) time-history for sample collected from Dhanuri site Fig. 6 shows the time history of excess pore water pressure developed for Dhanuari site (this is shown only for first 300 s, though dissipation continues and Uexcess reaches zero after about 20 minutes). It can be observed that the pore water pressure rises for some more time even
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
10
after the end of shaking (60 s) before dissipation starts. Also dissipation starts first in the top pick-up then proceed to middle and bottom pick-ups, as expected. Using Fig. 6, the maximum excess pressure (umax) was evaluated at the three locations of pore water pressure pickups i.e. Bottom (B), Middle (M) and Top (T). This was normalized with respect to effective overburden pressure (σeffective) to obtain the pore water pressure ratio (i.e. ru = umax/σvo). The results for Dhanuari site are summarized in Table 1. It can be observed that the average value of ru is 0.52. A similar analysis (like shown in Fig. 6 and Table 1) was performed for Roshnabad site. The average value of ru obtained was close to that for Dhanuari site. Table 1: Pore water pressure ratio ru of samples collected from Dhanuari Site Location of Pick-up (m)
σeffective (kN/m2)
Udyn (kN/m2)
ru
Remarks
Acceleration = 0.3 g Duration = 60 s Frequency = 5 Hz Average ru = 0.52
From Base of Tank
From top of Soil Sample
0.040 (B)
0.320
3.04
1.50
0.49
0.125 (M)
0.235
2.24
1.15
0.51
0.200 (T)
0.160
1.52
0.86
0.57
Theoretically, the liquefaction occurs when ru reaches unity; if it is less than unity, only partial loss of shear strength occurs. Although shake table result may suggest no liquefaction as ru < 1.0, this outcome may not be necessarily representing the actual behavior in the field. Firstly, in the vibration table due to shaking, the densification of sample takes place and it may not allow pore water pressure to rise to unity. Secondly, the soil samples used in the tests are disturbed samples. Nonetheless, the tests in the vibration table indicate the extent of shear strength loss due to shaking. 4.3.6 Conclusions Field tests indicated that there is a clear threat of liquefaction in Dhanuri but not in Roshnabad for the earthquake magnitude considered. This outcome has much practical significance as Dhanuri is very near to Roorkee, where a large industrial development is taking place. However, more field tests (at different locations) along with laboratory tests (such as cyclic triaxial tests) need to be conducted to come forward with a concrete conclusion. Slope Stability Assessment Studies – Earthquake Stability Analysis of Surbhee Resort Landslide in Garhwal Himalayas, India Modus Operandi: This study was performed by Ms. Shilpa Pal’s during her stay at NGI in the period June-July 2008. The site visits and most of the data collections were done in India prior to this period, and the numerical modelling were performed at NGI with support from the NGI’s experts.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
11
4.4.1 Introduction Landslides are one of the frequently occurring natural hazards in seismically active NorthWest part of Indian Himalayas. In this study, an endeavour has been made to model Surbhee Landslide (longitudes 78o02’ and 78o04’E and latitudes 30o28’ and 30o31’N) in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India. This landslide is active on the road that is joining main road to the down town. This landslide was triggered because of rainfall in July-August 1998. The landslide is still active and there is a need to do some scientific investigations to mitigate future damage. Therefore, modelling of the slope has been carried out with the Distinct Element Method (UDEC & 3DEC) which has the capability to model rock slope stability problems. Understanding the behaviour of the landslide will be helpful for planning and implementing landslide mitigation measures. 4.4.2 Study Area The crown of the landslide (30o29’N and 78o03’) is located at an elevation of about 1650 m between 6 and 7 stone from the Mussorie, on the Mussorie – Kempty road. Hotel Surbhee Hill Resort is located 50 m uphill in the crown portion of the landslide. Further upstream, Mussoorie International Scholl (MIS) and Polo ground are situated. The slope area contains dolomitic limestone together with subordinates variegated shales belonging to the Krol Formation. These rocks are highly jointed and fractured. The rock joints are striking NE-SW, NNE-SSW, NNW-SSE and ESE-WSW and dip moderate to steep slope ranging from 40o to 60o. The area is described as highly unstable that is about 1700 m high and several km wide located near the famous hill station Mussoorie on the Mussoorie – Kempty road in Garhwal Lesser Himalaya (Gupta et al., 2007). In greater area part of the study area, the hill slopes are covered with thick quaternary deposits representing old landslide in the area. Location map of the area showing the movement observed is shown in Fig 7. The slide movement can be divided into three zones as per Fig 8 as Zone of Detachment (1650m - 1325m above msl), Zone of transportation (1325m - 1100m above msl) and Zone of accumulation (1100m 800m above msl). Cross-section of the slope is displayed in Fig 2 and the photograph of the slope towards the northeast is shown in Fig. 9. According to the profile shown in Fig 2.2, the major sliding plane is in the upper part of the slope where the rock is highly jointed.
Fig 7: Location Map of the Study Area
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
12
Zone of
Fig 8: Cross- Section of the Surbhee Resort Landslide (Gupta et al., 2007)
Fig 9: Surbhee Resort Landslide
4.4.3 Modelling of Slide in UDEC For the analysis of rock slope stability, the analysis is carried out in two parts. First is to analyse the structure to assess the orientation of the discontinuities which are predominant in the area that could result in the instability of the slope under study. Second step is to do numerical modelling of the structure under gravity load. As per the geotechnical investigations carried out in the study area by Gupta et al., (2007), it is clear that the area is highly fractured in the zone of detachment which needs to be looked as per the stability is concerned. Figure 10 shows the jointed slope model used for the numerical analysis. This simplified model was constructed based on cross-section of the rock slope given by Gupta et al., 2007 (Fig. 2.2) and site visit, where in the study of orientation of the joints was carried out.
Fig 10: Numerical Model of the Slope
The intact rock is considered to behave as linearly elastic where as the rock discontinuities are assumed to behave non-linearity following the Mohr-Coulomb model.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
13
4.4.4 Static Analysis Various cases were undertaken to study the stability analysis of the Surbhee Landslide. The in-situ conditions and the gravity load were applied and the slope was monitored under static conditions till equilibrium was reached. After gravity loading, it has been observed that shearing of the joints is taking place in the zone of detachment, whereas in the zone of transportation and accumulation, it is observed that it stable under gravity load. From gravity load analysis, it is clear that vulnerable area is the zone of detachment. Fig 11 shows the shearing in the joints.
Fig 11: Shearing of Joints after Gravity Load in Case
To further study the stability of the slope under saturated and weathering conditions, various studies have been carried out. It is assumed that with time due to ingress of water and climatic changes, there is weathering of joints. With this friction angle is bound to be reduced at the joints. To simulate this effect on joints, analysis has been carried out with reduced friction angle 30o, 28o, 25o and 22o. It was observed that when friction angle reduces to 22o, there is detachment (Fig 3.7) of the blocks in the zone of detachment where the displacement increases to a very high value. Degradation of joint with climatic changes can also be studied with there reduction in the shear stiffness values of the joints. Similar study as done with friction value at joints has been carried out with reduced shear stiffness values. Value has been reduced from 1.33e10 Pa to 1.33e9 Pa, 1.33 e8 Pa and 1.33 e7 Pa. It has been observed that with reduced stiffness value to 1.33e7 Pa, slope is unstable with the block separation in the zone of detachment. 4.4.5 Application of Dynamic Loading – Earthquake Conditions Under dynamic loading, an excitation is applied to the rock slope. It is important to analyse the slope under study in the seismic environment as it lies in zone IV of IS Code 1893 – 2002. To account for this, Seismic analysis of the slope under study has been carried out under a sinusoidal wave of frequency 3 Hz. After the application of 3 sec, it was observed that the shearing got concentrated in the top layer of the slope in the zone of detachments.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
14
Displacement of Joints after Seismic Loading – Sine
Fig 12: Displacement at the end of 3 sec
A time history compatible to the response spectrum of the site near the study area has been generated with frequency range equivalent to the Uttarkashi earthquake record of 20 October 2001 with PGA of 0.31g. The applied record is of 65 sec. Calculated time step Δt = 1.232e05 sec. It is observed that as the wave propagates through the rock mass there is amplification of the record. Shearing in this case is also observed in the zone of detachment. To have a better insight into the seismic analysis of slope, another time history was synthetically generated compatible with the IS Code 1893-2002 response spectrum. The site is located in zone IV. Zone factor for this region is 0.24. Artificial time history generated was having PGA 0.24g in the transverse direction. It can be concluded that under seismic conditions with present rock mass and joint strength conditions, shearing of joints is predominant in the zone of detachment. To analyse the behaviour of the slope with reduced joints strength parameters, in the further cases sinusoidal wave is used as the seismic input. To study the overall behaviour of the slope under seismic conditions, model with reduced joint strength were analyzed. With reduced friction angle to 22o, it is observed that displacement is present in the top layers i.e. in the zone of detachment as well as in the zone of transportation. It is a major threat to the stability of the slope, the total slope is unstable. This concludes that with ingress of water, reducing friction angle can be a major threat to the overall stability of the slope. It was observed the block failure of the top layer which is highly weathered rock takes place. The failure mechanism is given in Fig 13. Seismic analysis has also been carried out for the cases with reduced shear stiffness at the joints. Similar results have been observed that with reduced joint strength the slope is unstable. The numerical results indicate the effect of degradation of joints and discontinuities on the stability of the slope. With degradation of joints, the slope becomes unstable and dynamic
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
15
loading results in the instability of the weathered material on the top of the slide i.e. the top most layer. The slope is stable in the present situation but with the rainfall it is susceptible to become unstable where the movement is concentrated in the upper part of the slide and also in the lower area where shearing of the joints.
Max. Disp. = 19.00 m
Max. Disp. = 12.50 m
9 sec
7 sec Max. Disp. = 26.00 m
Max. Disp. = 34.00 m
11 sec
13 sec
Max. Disp. = 43.00 m
15 sec
Max. Disp. = 53.00 m
17 sec Max. Disp. = 58.50 m
18 sec
Max. Disp. = 63.00 m
19 sec Fig 13: Failure Mechanism in Case 15
4.4.6 UDEC Model – Zone of Detachment After the detailed study of the Surbhee landslide, it is clear that the zone of detachment is the most vulnerable part of the slope which is unstable. To study in detail the zone of detachment was modelled again in UDEC and studied under stability in the present condition. Figure 14 shows the model of zone of detachment in UDEC
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
16
Fig 14: Model of the Zone of Detachment in UDEC First analysis was carried out with initial stresses and gravity load, until equilibrium was reached. It was observed that the slope is stable under gravity load with shearing concentrated in the top layer (Fig 15). After the static analysis, analysis was carried out under dynamic load i.e. with a sinusoidal wave of frequency of 3Hz for 3 sec. It was observed the displacement gets concentrated on the top foliation planes of the slope which is highly weathered material in the real situation in the field (Fig 16).
Fig 15: Displacement and Shearing of Joints
Fig 16: Displacement at the end of Dynamic Loading
From the modelling of the zone of detachment in UDEC it is clear that the zone of detachment which is contributing to the displacement in the Surbhee slide. For studying the 3-Dimensional effect of the slide, it was modelled in 3DEC. Further, in the study three dimensional modelling and analysis will be discussed in detail. 4.4.7 Dec Modelling – Zone of Detachment In three dimensional modelling, only the zone of detachment was considered for study referred as Case A. Figure 17 shows the model in 3-DEC which is a replica of UDEC and Fig 18 shows the jointing pattern. Initial stresses were applied and analysis was carried out gravity load until equilibrium was reached. Figure 19 shows the displacement vectors under
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
17
static conditions and the shearing of the joints which is concentrated at the end of the zone of detachment which is in accordance with what was observed in 2-D.
Fig 17: 3-D Model of Case A
Fig 18: Jointing Pattern
Fig 19: Displacement Vectors under Gravity Load in 3-D After the static analysis, model was subjected to a dynamic load i.e. a sinusoidal wave of frequency 3 Hz for 3 sec. it was observed that the displacement reaches a value of 70 cm (Fig 20) against 89 cm as observed in 2-D and maximum shear displacement of 68 cm is observed which is higher than that observed in 2-D which is due to the 3-Dimensional effect of shearing of joints. The amplification the signal as it passes through the model is approximately three times.
Fig 20: Displacement Vectors under Dynamic Loading in 3-D
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
18
From the above analysis it is clear that the top foliation plane of the slope is only under threat which can fail under low friction angle i.e. with degradation or weathering of joints due to ingress of water. To study the three dimensional effect an attempt was made. To account for this, two cases were taken one with the top of the slope was tilted 10o E with Z-Dimension increased to 300 m and other in which the total profile as well as the joints were tilted by the same amount i.e. 10o E and Z-Dimension increased to 300 m. Analysis was carried out both under gravity and dynamic case. After the equilibrium is achieved under gravity, model was subjected to dynamic loading of a sinusoidal wave of 3 Hz for 3 sec. It was observed that displacement increased to 63 cm with maximum shear displacement of 61 cm. It is indicated from the displacement vectors (Fig 22) at the end of dynamic loading that more displacement is experienced at the right end of the slope face which is highlighted in the figure.
Fig 21: Model with Top of the Slope Tilted
Fig 22: Displacement Vectors after Dynamic Loading
Similar study was carried out for Case C and the results obtained were similar to that observed. It was observed that more shearing takes place at the right corner of the top face of the model. 5.
Future Plans
During next one year, the work on liquefaction studies will continue with more field tests, lab tests and numerical modelling using FLAC3D. In this concern it shall be noted that procurement of a sophisticated Cyclic Triaxial System is in pipeline at IIT Roorkee and once this system is installed, using it the lab tests would be conducted on the soil samples collected from the field. Also a fresh attempt will be made to recruit a research scholar. 6.
References 1. Bardet, J.P., Ichii, K. and Lin, C.H. (2000). EERA, A Computer Program for Equivalent Linear Earthquake Site Response Analysis, Dept. of Civil Eng, University of Southern California, USA.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
19
2. Chandra, B., Thakkar, S.K., Basu, S., Kumar, A., Shrikhande, M., Das, J., Agarwal, P., and Bansal, M.K. (2002). Strong motion records. Chapter 5 in Bhuj, India Earthquake of January 26, 2001 Reconnaissance Report, Earthquake Spectra, Supplement to Vol. 18, 53-66. 3. Gupta, M.K. (1977). Liquefaction of Sands during Earthquakes, Ph.D. Thesis, University of Roorkee, Roorkee, India. 4. INPIC Report (2006). Final Report (2003-2006) of Indo-Norwegian Programme of Institutional Cooperation on Earthquake Engineering, by Dept. of Earthquake Engineering, IIT Roorkee, NORSAR, Norway and NGI, Norway. 5. IS: 1893-2002-Part 1: Criteria for Earthquake Resistant Design of Structures: General Provisions and Buildings. Bureau of Indian Standards, New Delhi. 6. IS 2131: 1981. Indian Standard Code of Practice, Method for Standard Penetration Test for Soils. Bureau of Indian Standards, New Delhi. 7. Kramer, S.L. (1996). Geotechnical Earthquake Engineering, Prentice Hall, Inc., Upper Saddle River, New Jersey. 8. Mahajan, A.K. (2008). Personal Communication, Wadia Institue of Himalayan Geology, Dehradun. 9. Prakash, S. (1981). Soil Dynamics, McGraw-Hill Company, New York. 10. Ranjan, R. (2005). Seismic Response Analysis of Dehradun City, India, MSc thesis, Indian Institute of Remote Sensing, National Remote Sensing Agency, Dehradun Dep. of Space, Govt. of India. 11. Seed, H.B. and Lee, K.L. (1966). Liquefaction of saturated sands during cyclic loading. Journal of the Soil Mechanics and Foundation Division, ASCE, 92:SM6, 105-134. 12. Seed, H.B. and Idriss, I.M. (1970). Soil moduli and damping factors for dynamic response analyses, Report EERC 70-10, Earthquake Engineering Research Center, University of California, Berkeley. 13. Seed, H.B. and Idriss, I.M. (1971). Simplified procedure for evaluating soil liquefaction potential. Journal of the Soil Mechanics and Foundation Division, ASCE, 107:SM9, 1249-1274. 14. Seed, H.B., Tokimatsu, K., Harder, L.F., Chung, R.M. (1985). Influence of SPT procedures in soil liquefaction resistance evaluations. J. of Geotech. Eng, ASCE, 111:12, 1425-1445.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
20
Appendix – 1 Travel Report Visit of IITR team to Norway (Sept. 22-30, 2007) Dr. B.K. Maheshwari and Dr. M.L. Sharma from IITR visited NGI and NORSAR respectively during September 22-30, 2007. The aims of Dr. Maheshwari‘s visit were: 1. To carry forward the collaborative project. 2. It was first visit of Dr. Maheshwari to Norway. He had visited the laboratory facilities of NGI including cyclic triaxial test system, direct simple shear test and resonant column test. 3. Dr. Maheshwari has a number of technical meetings with Dr. Kaynia. As a result, strategy to carry forward the liquefaction study (theme 2) has been chalked out. 4. One of the most important accomplishments of the visit was to get familiar Dr. Maheshwari with software FLAC. Few learning sessions were held with Dr. Kaynia to get hands on this powerful software. 5. Next visit of NGI scientists at IIT Roorkee is planned for January 2008. A detailed task programme for the project (theme 2) was discussed and finalized in several meetings held at NGI. Different milestones for theme 2 of the project is also finalized and attached with this report.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
21
Appendix – 2 Travel Report Visit of NGI team to IIT Roorkee (January 2008) Introduction As part of the Geo-related activities in the institutional cooperation project on earthquake risk in India, the two Norwegian participants of the project from NGI, R. Bhasin and A.M. Kaynia travelled to India in the period Jan. 6-13, 2008. The intention was to follow up the planned activities and make plans for the next period. The following describes the results of the meetings and plans made in collaboration with the Indian counterparts, together with the technical activities undertaken during the visit. The meetings and visits included primarily: Dr. D.K. Paul (DKP) Dr. M.L. Sharma (MLS) Dr. Y. Singh (YS) Dr. B.K. Maheshwari (BKM) Ms. Shilpa Pal (SP) Dr. R. K. Bhasin (RKB) Dr. A.M. Kaynia (AMK)
Details of Activities Day 1 – Jan. 6, 2008 – Departure from Oslo Day 2 – Jan. 7, 2008 – Review and planning meeting Participants: DKP, MLS, YS, BKM, RKB, AMK
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
22
A long meeting was held at IITR to review the progress of the project, status of student hiring for the project, actions taken with regards to the measurement campaign in Haridwar in March 2008, selection of the interdisciplinary site. The following is a summary of the findings, observations and conclusions: 1. There have been some difficulties in hiring new students mainly due to the tough competition by the industry which offers considerably higher salaries. In particular, the student who was recruited by BKM for the liquefaction studies had recently switched to another area (AMK had a meeting with the student a few days later and gave a broader view of the project. It appears fairly unlikely that the student changes his mind because he is looking for a theoretical subject and has already been in dialogue with another professor at IITR). 2. The ordering of the equipment required for the liquefaction testing is in progress. Until the new equipment arrives, the old apparatus will be used. 3. The ordering of the system by OYO for noise measurement and processing is in progress. MLS indicated that there is a very good chance that the system will be ready for the March measurement campaign. 4. Preparation work for numerical modelling of slopes has been progressing well. SP presented some recent work done under DKP’s supervision (the results are included in the 1st report of the Geo-group in Jan. 2008). 5. Discussions were made around possible candidate sites for the numerical analyses of slope stabilities. Two sites were nominated: i) Mansa Devi in Haridwar, ii) Surabhi in Mussouri. It was decided that visits be made to these sites during this period. 6. YS gave an overview of the work on the risk assessment and expressed general satisfaction with the work in view of the promised support by NORSAR.
Day 3 – Jan. 8, 2008 – Visit to Haridwar Participants: DKP, MLS, BKM, SP, RKB, AMK The participants travelled to Haridwar to visit the candidate sites for the noise measurement campaign and one of the candidate sites for the slope stability analyses. The trip was very helpful as it provided the opportunity to get a feeling of the sites. From the geological background and visual observations, it appears that the candidate sites are well suited for both the noise measurements and liquefaction studies. In particular, sites are close to areas that are under development and the above studies can be considered, indirectly, contributing to the development plans of these areas. The group also made a thorough assessment of the Mansa Devi landslide. The access to this landslide which is on the mountain outskirts of Haridwar was only possible on foot. This landslide (see photo) has blocked an important route in the region which is also a pilgrimage route and therefore is of special socio-economic importance to the region. For the time being CBRI (Centre for Building Research Institute) has installed a measurement post in the slide area to monitor its movements. The objective is to install an early warning system for the site once it is opened again for traffic.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
23
View from other side of valley
Road destroyed and out of traffic
Views of Mansa Devi Landslide in Haridwar
Day 4 – Jan. 9, 2008 – Technical discussions and planning Participants: DKP, MLS, BKM, SP, RKB, AMK Meetings were held in the morning to review the progress of the work. Students of BKM and LMS gave presentations of their research. Based on the works presented, it was decided that until a new student is identified for the liquefaction studies, one of the current students of BKM (Rajib) continues on the topic. Also the work of MLS’s student, Naveen Parikh, who works with processing of satellite imagery, appeared to be relevant for the project and the group recommended that SP and Naveen spend a few months at NGI to work with the georelated topics. A long meeting was held in the afternoon to make plans for the next period. The following decisions were made: 1. Five sites were nominated in Haridwar for the March measurement campaign as follows (in order of preference): a) Roshanabad (near industrial development) b) Raiwala c) Doiwala d) Gurukul kangari University e) BHEL (Bharat Heavy Electricals Ltd.) 2. MLS and Dr. Mahaja of WIHG make coordination for selecting one of these sites (MLS made the contact during the meeting and already made plans with Dr. A.K. Mahajan). 3. As soon as the site is selected, BKM should mobilise the site investigation contractor to make a borehole and perform SPT to confirm the suitability of the site w.r.t. liquefaction. 4. DKP will guide SP in numerical modelling of the slope stability of either Mansa Devi or Surabhi (to be decided later after RKB and AMK visit Surabhi on 11 Jan.)
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
24
Day 5 – Jan. 10, 2008 – Visit to WIHG, Dehradun Participants: RKB, AMK RKB and AMK travelled to Dehradun and visited Dr. B.R. Arora and Dr. Mahajan. The meeting was very useful as Dr. Arora also promised cooperation w.r.t. providing the necessary data for the slope stability analyses. One of the WIHG’s staff, Dr. Vikram Gupta (VG), was assigned to support with the data collection and was asked to accompany the Norwegian team to the site of the Surabhi landslide in Mussouri the following day.
Day 6 – Jan. 11, 2008 – Visit to Surabhi landslide Participants: RKB, AMK, MLS, VG Dr. Vikram Gupta (VG) of WIHG led en expedition to the site of Surabhi landslide near Mussouri (see photo). The slide is underneath a resort hotel and has been moving at a rate of 8-10 mm per year. One could see debris of previous slides at this site. It is suspected that discharge of wastewater by the hotel has initiated some slides and opening of the cracks, and now rain and other surface water easily seep into the cracks and make the site more vulnerable to landslide. Even a moderate earthquake in this are is believed to be capable of inducing a major slide at this site.
Resort hotel on top of landslide-prone area
Views of Surabhi Landslide in Mussouri While RKB and VG continued inspecting the site and collecting miscellaneous information, MLS and AMK took a trip to Tehri dam. The trips ended back in IIT Roorkee.
Day 7 – Jan. 12, 2008 – Travel to Delhi – free, rest of the day Day 8 – Jan. 13, 2008 – Return to Oslo
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
25
Appendix – 3
SITE SELECTION FOR THE GEOTECHNICAL INVESTIGATIONS Objective Selection of sites for geotechnical investigations with the aim to calibrate the different techniques for site characterization, to determine the liquefaction potential and recommend seismic hazard Field trip A team consisting of the following members visited the Dehradun – Haridwar – Roorkee area for the selection of site on Feb 13, 2008 1. Dr. M. L. Sharma, IIT Roorkee 2. Dr. B. K. Maheshwari, IIT Roorkee 3. Dr. A. K. Mahajan, WIHG 4. Dr. A. K. Mundipi, WIHG 5. Mr. N.P. Aterkar, Soilex Consultant, Roorkee The following nine sites were tentatively selected for the investigations: No.
Location
Latitude
Longitude
Latitude
Longitude
1.
Doiwala
30
9
14.5
78
9
50.1
30.1540
78.1639
2.
NGA
30
4
3.4
78
12
50.2
30.0676
78.2139
3.
Shanti Kunj
29
59
32.1
78
11
23.4
29.9923
78.1898
4.
DAV School
29
54
14.2
78
7
57.4
29.9039
78.1326
5.
Roshnabad
29
58
12.8
78
4
23.3
29.9702
78.0731
6.
Gurukul
29
55
8.1
78
7
34.7
29.9189
78.1263
7.
Dhanori
29
56
24.6
77
57
25.5
29.9402
77.9571
8.
COER
29
53
35.2
77
57
42.1
29.8931
77.9617
9.
Solani
29
52
46
77
53
52
29.8794
77.8978
Doiwala The site is between Dhradun (DD) and Haridwar (HR). By road, it is 25 km from DD and 28 km from HR. As per tube well logging information, the depth of soil is about 3 to 5 meters below which gravels are expected. The site is near Chidaharwala. NGA The site is in the ground in front of the School by Nirmal Gyandan Asharam (NGA). The site was very near to Nepali Farm. The photograph shows the soil exposed while excavating the ground. This may be a good site for the investigations.
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
26
Shantikunj The space may not be available for the array and MASW techniques. This site is highly populated now and not recommended due to local public use. DAV School The site lies on the Hardwar-Laksar road in the play ground of the DAV Centenary Public School, Kankal. Here the investigations have been made by Mr. Aterkar for a depth of about 10 meters for some other project. The top 2m is suggested silty sand, then next 3-12 m is gravelly sand and then may be gravels below. The play ground of the school will be a good site for carrying out all the tests and for the calibrations of the methods. Roshanabad-BHEL The site lies in the back of the Vikas Bhawan. The array method can be applied for about 200 meters area. This is the largest area available in all the sites. Here four locations are available for these investigations: A Roshanabad administrative block in Vikas Bhawan Campus B Air Port Ground C Chinmay College of Science, Sector 6, BHEL D CISF Campus Ground, Ranipur Gurukul The ground is available for the testing at Gurukul Kangri University Dhanori This is in Dhanori Village (about 10 km from Roorkee), it may be a good site for the liquefaction studies since this site is in between two canals and also a river is nearby. The site may have considerable silt. COER The ground of College of Engineering Roorkee (COER) may be a good site since the alluvium thickness is increased and the soil investigations can be carried out for more depths. Solani No location is available at this site. Only a small ground (undulating) could be seen in the side of the government workshop. However the site is very good for liquefaction study as it consist of saturated loose sand. One of the sites may be the land belonging to Mr. Aterkar which is one km away towards Iqbalpur on the Iqbalpur Puhana road. This is near to the Roorkee Engineering College. The process of getting permission from concerned authorities for use of these sites is in pipeline. In the first phase of the testing following four sites are recommended: 1. Dhanori 2. Roshnabad-BHEL 3. NGA
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
27
4. DAV School
30.2 Doiwala
30.1 NGA
Shanti Kunj Dav School Roshnabad
30 Dhanori
Gurukul COER
29.9
Solani
29.8 77.8
77.9
78
78.1
78.2
78.3
Location of Various Sites (Courtesy Google Earth)
z:\projects\himalaya\reports\reports_2008\annual reporting\from_yogendra\tech report 5 report_theme2_iitr-ngi.doc
28
