The development of slope stability program considering ... - ISSMGE
The development of slope stability program considering rainfall and presence of transmission tower Titre en français. Le développement du programme de stabilité de la pente compte tenu des précipitations et de la présence de la tour de transmission Jung-Tae Kim, Ah-Ram Kim, Gye-Chun Cho Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Republic of Korea, [email protected]
Dae-Hong Kim KEPRI, KEPCO, Republic of Korea ABSTRACT: Over 70% of Korea’s power transmission towers are located in mountainous terrain due to the limitations of space for development. Slope failures, which are caused by heavy rainfalls, have frequently been reported and cause both serious economic losses and human casualties. The number of slope disasters in Korea are concentrated during the monsoon period from July to September. Various analysis programs have been developed to assess slope stability. However, commercial programs such as Geostudio and Talen cannot adequately consider the effects of rainfall and the presence of power transmission towers. In this study, a slope stability program based on the LEM (Limit equilibrium method) was developed using FORTRAN95 to analyze slope stability Parametric studies on rainfall, pile spacing and its position were performed and the optimal transmission tower position was suggested for a testbed site in Gyeonggi province. The developed program can be used to prevent slope failures and reduce human and economic losses. Moreover, the developed program can suggest the optimal position of transmission towers on mountainous terrain prior to construction. RÉSUMÉ : Plus de 70% des tours de transmission de puissance de la Corée sont situées dans un terrain montagneux en raison des limites d'espace pour le développement. Les défaillances des pentes, qui sont causées par de fortes pluies, ont été fréquemment signalées et causent à la fois de graves pertes économiques et des pertes humaines. Le nombre de catastrophes en pente en Corée est concentré pendant la période de la mousson de juillet à septembre. Différents programmes d'analyse ont été mis au point pour évaluer la stabilité de la pente. Cependant, les programmes commerciaux tels que Geo-studio et Talen ne peuvent pas considérer correctement les effets des précipitations et la présence de tours de transmission de puissance. Dans cette étude, un programme de stabilité de la pente basé sur le LEM (méthode d'équilibre limite) a été développé à l'aide de FORTRAN95 pour analyser la stabilité des pentes. Des études paramétriques sur la pluviométrie, l'espacement des pieux et sa position ont été effectuées. Province de Gyeonggi. Le programme développé peut être utilisé pour prévenir les défaillances des pentes et réduire les pertes humaines et économiques. En outre, le programme développé peut suggérer la position optimale des tours de transmission sur un terrain montagneux avant la construction. KEYWORDS: unsaturated slope stability program, rainfall infiltration, power transmission tower 1 INTRODUCTION Most transmission towers in Korea are installed at intervals of 300 to 500 meters to prevent deflection of power cables and are often located in mountainous areas due to the limitations of space for development. Frequent slope failures near transmission powers caused by heavy rainfall have been reported (Song, 2013). Slope stability analysis considering rainfall and the presence of power transmission towers is needed to assess slope failure susceptibility in such regions. There are many methods to analyze slope stability such as the limit equilibrium method (LEM), finite differential method (FDM), and finite element method (FEM). LEM is the most commonly used method for slope stability analysis due its accuracy and speed. In the past, the soil was assumed to be either fully saturated or dry for convenient analysis. However, most slopes in Korea consist of weathered granitic soil under the unsaturated condition andthe matric suction in unsaturated soils increases its shear strength (Lee et al., 2003, Lee et al., 2006). Hence, previous analyses that assume the soil is either fully saturated or dry cannot estimate the real behavior of soil and induces over-estimated design. Unsaturated slope stability analysis considering matric suction has been studied extensively
by geotechnical researchers since 1970s (Fredlund and Raharjdo, 1995). Previous studies have noticed that shallow surface failures caused by rainfall infiltration, rather than the increase in groundwater level, is the main factor that causes stability issues in slopes containing power transmission towers (Kim et al., 2004, Lu and Godt, 2008). Thus, it is necessary to conduct slope stability analysis that considers the change in wetting depth with the rainfall. For slopes containing power transmission towers, the horizontal resisting force is generated in front of foundation of the tower and it serves as a resisting moment against the failure direction, resulting in increased slope stability. In this study, the slope stability program considering the presence of power transmission towers and rainfall intensity was developed using FORTRAN 95. The developed program was verified by comparing the analysis results with the results obtained from commercial analysis programs such as SLOPE/W or FLAC2D. Parametric studies on rainfall, pile spacing and its position were performed and the optimal transmission tower position was suggested for a testbed site in Gyeonggi province
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Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017
moment arm and inserted in to Bishop’s stability equation as a resisting moment. The final slope stability equation is given below.
2 THEORETICAL BACKGROUND 2 .1
Limit equilibrium method
Various slope stability analysis methods based on the limit equilibrium method exist (Fellenius,1927; Bishop, 1955; Janbu, 1973; Spencer, 1967) and provide similar results with differences within 5%, except for the Fellenius model (Byeon, 2001). The developed program applies the unsaturated soilshear strength equation (Eq.1) considering matric suction, suggested by Fredlund and Raharjdo (1995), to Bishop’s model shown in Eq. 2.
Sm [c ' ( n ua )tan ' (ua uw)tanb ] / Fs
Fm
M r Rallow L Md
(5)
where, M r is resisting moment, M d is driving moment, Rallow is the allowable resisting force [ ton ], and L is the distance of moment arm [ m ].
(1) Ɵ
where, Sm is shear strength [ t / m 2 ], ( n ua ) is effective vertical stress [ t / m 2 ], ( ua uw ) is matric suction [ t / m 2 ], b is apparent friction angle [ ], and ' is effective friction angle [ ]. The governing equation adjusting revised shear strength equation is given below.
←
←
W
Ru
z
3D
D
α
M Fm r Md sin
c 'l cos (W u l F tan ') u l tan M ( ) W sin w
b
Figure 1. Schematic diagram of resisting force (Maeda, 1983)
w
(2)
where, l is the width of slices [ m ], is the tangential angle of slices [ ], M ( ) cos sin tan '/ F , and W is the weight of soil [ ton ]. 2 .2 Theory for rainfall infiltration It is noted that rainfall infiltration is the major cause of shallow surface failure (within 3 m from the slope surface) in mountainous terrain (Fredlund et al., 1995; Kim et al., 2004; Lu and Godt, 2008). The reduction in shear strength induced by infiltration has be considered in the slope stability analysis. The Mein and Larson model (1973) was used to estimate the wetting depth. Zw
K s i i Ks
3 DEVELOPMENT OF PROGRAM 3 .1 Algorithm for program The algorithm for developed slope stability analysis program is presented as Fig 2. The initial input parameters such as density ( t ), cohesion ( c ), friction angle ( ' ), apparent friction angle ( b ), and geometry of slope are entered at first stage. The properties of the transmission tower foundation are entered according to the presence of transmission tower on the slope. The third stage is related to the rainfall infiltration. Finally, the slope stability is estimated considering the presence of power transmission towers and rainfall infiltration. Start
(3)
where, K s is the saturated permeability [ cm / hr ], i is the matric suction at wetting depth [ cm ], and i is the rainfall intensity [ cm / hr ].
Input Initial values
2 .3 Theory for foundation
NO
The horizontal force induced by the soil in front of the power transmission tower foundation served as the resisting force when calculating the factor of safety. To estimate the resisting force, the Maeda model (1983) was used in this study. The governing equation is given below. Ru 0
W (cos sin tan ') c A sin cos tan '
Foundation
YES
Input foundation properties Location of foundations Pile foundation properties -Diameter -Length
NO
(4)
where, 0 0.6 (Experimental parameter), A is the sliding area [ m 2 ], ' is the friction angle [ ], c is the cohesion [ t / m 2 ], 45 '/ 2 / 2 , is the slope angle [ ], and W is the weight of soil [ m 2 ]. The allowable resisting force was estimated by dividing the calculated resisting force by the allowable safety factor of the foundation, F 1.5 . The allowable stress is multiplied by the
Geometry of slope Soil properties -Unit weight -Cohesion -Friction angle -Apparent friction angle
Rainfall
YES
Input rainfall condition Rainfall intensity Rainfall duration
Stability analysis
End
Figure 2. Algorithm for program
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Technical Committee 103 / Comité technique 103
3 .2 Verification of program 3.2.1 Slope analysis considering unsaturated soil The analysis results obtained from the developed program were compared to the results obtained from SLOPE/W under the same given unsaturated conditions for verification. SLOPE/W was selected as it is one of the most commonly available program for slope stability analysis. The analysis parameters are shown in Table 1. Both programs provided similar results with differences within 0.4%. The results obtained from both programs are shown in Fig. 3.
difference in factor of safety between results obtained from FDM-based and LEM-based slope stability analyses are approximately 10%. Hence, the developed program displays highly accurate analysis results. The results are shown in Fig. 4.
Table 1. The parameters for unsaturated slope analysis Geotechnical properties Cohesion, c ' [ t / m 2 ]
1.00
Density, t [ t / m3 ]
1.80
Effective friction angle, ' [ ] Apparent friction angle,
b
FoS = 1.79
30.0
[]
21.0
Initial matric suction, i [ kPa ]
-19.6
Saturated volumetric water content, s [-]
0.43
Initial volumetric water content, i [-]
0.18
Saturated permeability, K s [ cm / hr ]
2.07 FoS = 1.85
Figure 4. Verification of presence of transmission tower
4 TESTBED ANALYSIS 4 .1 Testbed site parameters
(a)
A numerical analysis was conducted to evaluate the slope stability of a testbed site in Gyeonggi province. The properties used in the analysis are shown in Table 2. The geometry of the slope and the position of transmission tower is shown in Fig. 5. The diameter and height of the transmission tower are 4.0 m and 16.5 m respectively.
Result of developed program ( Fs 1.668 ) 1.674
Figure 5. The geometry of slope and position of transmission tower
(b) Result of SLOPE/W ( Fs 1.674 ) Figure 3. Verification of unsaturated slope analysis
Table 2. The parameters for testbed Geotechnical properties
3.2.2 Presence of power transmission towers Analysis considering the presence of power transmission towers on the slope were compared and verified with the results obtained from FLAC2D, an FDM based program. Both results display similar failure curves and the difference in the factor of safety was 3.2%. Mansouur and Kalantry (2011) noted that the
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2
Cohesion, c ' [ t / m ]
0.80
Density, t [ t / m3 ]
1.69
Effective friction angle, ' [ ]
31.71
Apparent friction angle,
17.74
b
[]
Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017
Initial matric suction, i [ kPa ]
-18.38
Saturated volumetric water content, s [-]
0.25
Initial volumetric water content, i [-]
0.11
Saturated permeability, K s [ cm / hr ]
1.08
4 .2 Results and analysis The rainfall intensity was assumed to be 2.0 cm/hr for the testbed analysis. The factor of safety decreased gradually with increased rainfall duration and displayed a significant decrease after 20.0 hours. The factor of safety was below the standard factor of safety, Fs 1.3 (wet condition), and slope failure occurred at after 27.0 hours of rainfall. The results indicate that the presence of the power transmission tower had no effects on the slope stability of the testbed site. This implies that the testbed slope can be more stabilized by moving the tower transmission tower. The developed program is expected to provide the optimal position of power transmission towers from the analysis results during the design stage before construction.
FACTOR OF SAFETY
1.7 1.6 1.5 1.4 1.3
und Kohäsion (Adhäsion) und Unter Annahme Kreiszylindrisher Gleitflächen, W. Ernst. Fredlund, D. G., and H. Rahardjo (1993), Soil mechanics for unsaturated soils, John Wiley & Sons. Janbu, N. (1975), Slope stability computations: In Embankment-da m Engineering. Textbook. Eds. RC Hirschfeld and SJ Poulos. JOH N WILEY AND SONS INC., PUB., NY, 1973, 40P, paper pres ented at International Journal of Rock Mechanics and Mining S ciences & Geomechanics Abstracts, Pergamon. Kim, J., S. Jeong, S. Park, and J. Sharma (2004), Influence of rai nfallinduced wetting on the stability of slopes in weathered soils, E ngineering Geology, 75(3), 251-262. Lu, N., and J. Godt (2008), Infinite slope stability under steady unsaturated seepage conditions, Water Resources Research, 44 (11). Maeda, H. (1983), Horizontal Behaviour Of Pier Foundation On A Soft Rock Slope, paper presented at 5th ISRM Congress, Internation al Society for Rock Mechanics. Mansour, Z. S., and B. Kalantari (2011), Traditional Methods vers us Finite Difference Method for Computing Safety Factors of Slop e Stability, Electronic Journal of Geotechnical Engineering, 16. Mein, R. G., and C. L. Larson (1973), Modeling infiltration durin g a steady rain, Water resources research, 9(2), 384-394. Spencer, E. (1967), A method of analysis of the stability of embankments assuming parallel inter-slice forces, Geotechnique, 17(1), 11-26. 변위용 (2001), 불포화 지반 특성 및 최적화 기법을 적용한 사
1.2
면안정해석 프로그램 개발, 한국과학기술원, 석사 학위 논문.
1.1
송영갑 (2013), 강우침투 특성을 고려한 불포화 급경사지 붕괴 예측, 명지대학교, 박사 학위 논문
1 0
5
10
15
20
25
30
35
RAINFALL DURATION (hr) Figure 6. The factor of safety with rainfall duration
이승래, 김윤기, 최정찬, and 오진규 (2006), 강우 침투에 따른
5 CONCLUSION
이인모, 조우성, 김영욱, and 성상규 (2003), 풍화토 사면에서 강
도로성토사면의 불포화 특성 변화 계측 , 대한토목학회 정 기학술발표눈문집, 대한토목학회.
In this study, a slope stability program which can consider the rainfall infiltration and presence of power transmission towers was developed using FORTRAN 95 and verified with commercial programs such as SLOPE/W and FLAC2D. The factor of safety decreases with rainfall duration and increases with the presence of power transmission towers. Analysis of a testbed site indicatesthat the presence of a power transmission tower had no major effect on the slope stability. This indicates that the stability of the testbed can be improved by moving the position of the transmission tower. It is expected that the developed program can be used to prevent slope failures induced by heavy rainfall.
6 ACKNOWLEDGEMENT This research was supported by a grant from the Korea Electric Power Corporation (KEPCO). The first author is supported by the “U-City Master and Doctor Course Grant (Education) Program” under the Korea Ministry of Land, Infrastructure and Transport (MOLIT). 7 REFERENCES (TNR 8) Bishop, A. W. (1955), The use of the slip circle in the stability analysis of slopes, Geotechnique, 5(1), 7-17. Fellenius, W. K. A. (1948), Erdstatische Berechnungen: Mit Reibu ng
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우로 인한 간극수압 변화에 대한 실험연구, 한국지반공학회
논문 집, 19(1), 41-49.
Dae-Hong Kim KEPRI, KEPCO, Republic of Korea ABSTRACT: Over 70% of Korea’s power transmission towers are located in mountainous terrain due to the limitations of space for development. Slope failures, which are caused by heavy rainfalls, have frequently been reported and cause both serious economic losses and human casualties. The number of slope disasters in Korea are concentrated during the monsoon period from July to September. Various analysis programs have been developed to assess slope stability. However, commercial programs such as Geostudio and Talen cannot adequately consider the effects of rainfall and the presence of power transmission towers. In this study, a slope stability program based on the LEM (Limit equilibrium method) was developed using FORTRAN95 to analyze slope stability Parametric studies on rainfall, pile spacing and its position were performed and the optimal transmission tower position was suggested for a testbed site in Gyeonggi province. The developed program can be used to prevent slope failures and reduce human and economic losses. Moreover, the developed program can suggest the optimal position of transmission towers on mountainous terrain prior to construction. RÉSUMÉ : Plus de 70% des tours de transmission de puissance de la Corée sont situées dans un terrain montagneux en raison des limites d'espace pour le développement. Les défaillances des pentes, qui sont causées par de fortes pluies, ont été fréquemment signalées et causent à la fois de graves pertes économiques et des pertes humaines. Le nombre de catastrophes en pente en Corée est concentré pendant la période de la mousson de juillet à septembre. Différents programmes d'analyse ont été mis au point pour évaluer la stabilité de la pente. Cependant, les programmes commerciaux tels que Geo-studio et Talen ne peuvent pas considérer correctement les effets des précipitations et la présence de tours de transmission de puissance. Dans cette étude, un programme de stabilité de la pente basé sur le LEM (méthode d'équilibre limite) a été développé à l'aide de FORTRAN95 pour analyser la stabilité des pentes. Des études paramétriques sur la pluviométrie, l'espacement des pieux et sa position ont été effectuées. Province de Gyeonggi. Le programme développé peut être utilisé pour prévenir les défaillances des pentes et réduire les pertes humaines et économiques. En outre, le programme développé peut suggérer la position optimale des tours de transmission sur un terrain montagneux avant la construction. KEYWORDS: unsaturated slope stability program, rainfall infiltration, power transmission tower 1 INTRODUCTION Most transmission towers in Korea are installed at intervals of 300 to 500 meters to prevent deflection of power cables and are often located in mountainous areas due to the limitations of space for development. Frequent slope failures near transmission powers caused by heavy rainfall have been reported (Song, 2013). Slope stability analysis considering rainfall and the presence of power transmission towers is needed to assess slope failure susceptibility in such regions. There are many methods to analyze slope stability such as the limit equilibrium method (LEM), finite differential method (FDM), and finite element method (FEM). LEM is the most commonly used method for slope stability analysis due its accuracy and speed. In the past, the soil was assumed to be either fully saturated or dry for convenient analysis. However, most slopes in Korea consist of weathered granitic soil under the unsaturated condition andthe matric suction in unsaturated soils increases its shear strength (Lee et al., 2003, Lee et al., 2006). Hence, previous analyses that assume the soil is either fully saturated or dry cannot estimate the real behavior of soil and induces over-estimated design. Unsaturated slope stability analysis considering matric suction has been studied extensively
by geotechnical researchers since 1970s (Fredlund and Raharjdo, 1995). Previous studies have noticed that shallow surface failures caused by rainfall infiltration, rather than the increase in groundwater level, is the main factor that causes stability issues in slopes containing power transmission towers (Kim et al., 2004, Lu and Godt, 2008). Thus, it is necessary to conduct slope stability analysis that considers the change in wetting depth with the rainfall. For slopes containing power transmission towers, the horizontal resisting force is generated in front of foundation of the tower and it serves as a resisting moment against the failure direction, resulting in increased slope stability. In this study, the slope stability program considering the presence of power transmission towers and rainfall intensity was developed using FORTRAN 95. The developed program was verified by comparing the analysis results with the results obtained from commercial analysis programs such as SLOPE/W or FLAC2D. Parametric studies on rainfall, pile spacing and its position were performed and the optimal transmission tower position was suggested for a testbed site in Gyeonggi province
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Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017
moment arm and inserted in to Bishop’s stability equation as a resisting moment. The final slope stability equation is given below.
2 THEORETICAL BACKGROUND 2 .1
Limit equilibrium method
Various slope stability analysis methods based on the limit equilibrium method exist (Fellenius,1927; Bishop, 1955; Janbu, 1973; Spencer, 1967) and provide similar results with differences within 5%, except for the Fellenius model (Byeon, 2001). The developed program applies the unsaturated soilshear strength equation (Eq.1) considering matric suction, suggested by Fredlund and Raharjdo (1995), to Bishop’s model shown in Eq. 2.
Sm [c ' ( n ua )tan ' (ua uw)tanb ] / Fs
Fm
M r Rallow L Md
(5)
where, M r is resisting moment, M d is driving moment, Rallow is the allowable resisting force [ ton ], and L is the distance of moment arm [ m ].
(1) Ɵ
where, Sm is shear strength [ t / m 2 ], ( n ua ) is effective vertical stress [ t / m 2 ], ( ua uw ) is matric suction [ t / m 2 ], b is apparent friction angle [ ], and ' is effective friction angle [ ]. The governing equation adjusting revised shear strength equation is given below.
←
←
W
Ru
z
3D
D
α
M Fm r Md sin
c 'l cos (W u l F tan ') u l tan M ( ) W sin w
b
Figure 1. Schematic diagram of resisting force (Maeda, 1983)
w
(2)
where, l is the width of slices [ m ], is the tangential angle of slices [ ], M ( ) cos sin tan '/ F , and W is the weight of soil [ ton ]. 2 .2 Theory for rainfall infiltration It is noted that rainfall infiltration is the major cause of shallow surface failure (within 3 m from the slope surface) in mountainous terrain (Fredlund et al., 1995; Kim et al., 2004; Lu and Godt, 2008). The reduction in shear strength induced by infiltration has be considered in the slope stability analysis. The Mein and Larson model (1973) was used to estimate the wetting depth. Zw
K s i i Ks
3 DEVELOPMENT OF PROGRAM 3 .1 Algorithm for program The algorithm for developed slope stability analysis program is presented as Fig 2. The initial input parameters such as density ( t ), cohesion ( c ), friction angle ( ' ), apparent friction angle ( b ), and geometry of slope are entered at first stage. The properties of the transmission tower foundation are entered according to the presence of transmission tower on the slope. The third stage is related to the rainfall infiltration. Finally, the slope stability is estimated considering the presence of power transmission towers and rainfall infiltration. Start
(3)
where, K s is the saturated permeability [ cm / hr ], i is the matric suction at wetting depth [ cm ], and i is the rainfall intensity [ cm / hr ].
Input Initial values
2 .3 Theory for foundation
NO
The horizontal force induced by the soil in front of the power transmission tower foundation served as the resisting force when calculating the factor of safety. To estimate the resisting force, the Maeda model (1983) was used in this study. The governing equation is given below. Ru 0
W (cos sin tan ') c A sin cos tan '
Foundation
YES
Input foundation properties Location of foundations Pile foundation properties -Diameter -Length
NO
(4)
where, 0 0.6 (Experimental parameter), A is the sliding area [ m 2 ], ' is the friction angle [ ], c is the cohesion [ t / m 2 ], 45 '/ 2 / 2 , is the slope angle [ ], and W is the weight of soil [ m 2 ]. The allowable resisting force was estimated by dividing the calculated resisting force by the allowable safety factor of the foundation, F 1.5 . The allowable stress is multiplied by the
Geometry of slope Soil properties -Unit weight -Cohesion -Friction angle -Apparent friction angle
Rainfall
YES
Input rainfall condition Rainfall intensity Rainfall duration
Stability analysis
End
Figure 2. Algorithm for program
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Technical Committee 103 / Comité technique 103
3 .2 Verification of program 3.2.1 Slope analysis considering unsaturated soil The analysis results obtained from the developed program were compared to the results obtained from SLOPE/W under the same given unsaturated conditions for verification. SLOPE/W was selected as it is one of the most commonly available program for slope stability analysis. The analysis parameters are shown in Table 1. Both programs provided similar results with differences within 0.4%. The results obtained from both programs are shown in Fig. 3.
difference in factor of safety between results obtained from FDM-based and LEM-based slope stability analyses are approximately 10%. Hence, the developed program displays highly accurate analysis results. The results are shown in Fig. 4.
Table 1. The parameters for unsaturated slope analysis Geotechnical properties Cohesion, c ' [ t / m 2 ]
1.00
Density, t [ t / m3 ]
1.80
Effective friction angle, ' [ ] Apparent friction angle,
b
FoS = 1.79
30.0
[]
21.0
Initial matric suction, i [ kPa ]
-19.6
Saturated volumetric water content, s [-]
0.43
Initial volumetric water content, i [-]
0.18
Saturated permeability, K s [ cm / hr ]
2.07 FoS = 1.85
Figure 4. Verification of presence of transmission tower
4 TESTBED ANALYSIS 4 .1 Testbed site parameters
(a)
A numerical analysis was conducted to evaluate the slope stability of a testbed site in Gyeonggi province. The properties used in the analysis are shown in Table 2. The geometry of the slope and the position of transmission tower is shown in Fig. 5. The diameter and height of the transmission tower are 4.0 m and 16.5 m respectively.
Result of developed program ( Fs 1.668 ) 1.674
Figure 5. The geometry of slope and position of transmission tower
(b) Result of SLOPE/W ( Fs 1.674 ) Figure 3. Verification of unsaturated slope analysis
Table 2. The parameters for testbed Geotechnical properties
3.2.2 Presence of power transmission towers Analysis considering the presence of power transmission towers on the slope were compared and verified with the results obtained from FLAC2D, an FDM based program. Both results display similar failure curves and the difference in the factor of safety was 3.2%. Mansouur and Kalantry (2011) noted that the
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2
Cohesion, c ' [ t / m ]
0.80
Density, t [ t / m3 ]
1.69
Effective friction angle, ' [ ]
31.71
Apparent friction angle,
17.74
b
[]
Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017
Initial matric suction, i [ kPa ]
-18.38
Saturated volumetric water content, s [-]
0.25
Initial volumetric water content, i [-]
0.11
Saturated permeability, K s [ cm / hr ]
1.08
4 .2 Results and analysis The rainfall intensity was assumed to be 2.0 cm/hr for the testbed analysis. The factor of safety decreased gradually with increased rainfall duration and displayed a significant decrease after 20.0 hours. The factor of safety was below the standard factor of safety, Fs 1.3 (wet condition), and slope failure occurred at after 27.0 hours of rainfall. The results indicate that the presence of the power transmission tower had no effects on the slope stability of the testbed site. This implies that the testbed slope can be more stabilized by moving the tower transmission tower. The developed program is expected to provide the optimal position of power transmission towers from the analysis results during the design stage before construction.
FACTOR OF SAFETY
1.7 1.6 1.5 1.4 1.3
und Kohäsion (Adhäsion) und Unter Annahme Kreiszylindrisher Gleitflächen, W. Ernst. Fredlund, D. G., and H. Rahardjo (1993), Soil mechanics for unsaturated soils, John Wiley & Sons. Janbu, N. (1975), Slope stability computations: In Embankment-da m Engineering. Textbook. Eds. RC Hirschfeld and SJ Poulos. JOH N WILEY AND SONS INC., PUB., NY, 1973, 40P, paper pres ented at International Journal of Rock Mechanics and Mining S ciences & Geomechanics Abstracts, Pergamon. Kim, J., S. Jeong, S. Park, and J. Sharma (2004), Influence of rai nfallinduced wetting on the stability of slopes in weathered soils, E ngineering Geology, 75(3), 251-262. Lu, N., and J. Godt (2008), Infinite slope stability under steady unsaturated seepage conditions, Water Resources Research, 44 (11). Maeda, H. (1983), Horizontal Behaviour Of Pier Foundation On A Soft Rock Slope, paper presented at 5th ISRM Congress, Internation al Society for Rock Mechanics. Mansour, Z. S., and B. Kalantari (2011), Traditional Methods vers us Finite Difference Method for Computing Safety Factors of Slop e Stability, Electronic Journal of Geotechnical Engineering, 16. Mein, R. G., and C. L. Larson (1973), Modeling infiltration durin g a steady rain, Water resources research, 9(2), 384-394. Spencer, E. (1967), A method of analysis of the stability of embankments assuming parallel inter-slice forces, Geotechnique, 17(1), 11-26. 변위용 (2001), 불포화 지반 특성 및 최적화 기법을 적용한 사
1.2
면안정해석 프로그램 개발, 한국과학기술원, 석사 학위 논문.
1.1
송영갑 (2013), 강우침투 특성을 고려한 불포화 급경사지 붕괴 예측, 명지대학교, 박사 학위 논문
1 0
5
10
15
20
25
30
35
RAINFALL DURATION (hr) Figure 6. The factor of safety with rainfall duration
이승래, 김윤기, 최정찬, and 오진규 (2006), 강우 침투에 따른
5 CONCLUSION
이인모, 조우성, 김영욱, and 성상규 (2003), 풍화토 사면에서 강
도로성토사면의 불포화 특성 변화 계측 , 대한토목학회 정 기학술발표눈문집, 대한토목학회.
In this study, a slope stability program which can consider the rainfall infiltration and presence of power transmission towers was developed using FORTRAN 95 and verified with commercial programs such as SLOPE/W and FLAC2D. The factor of safety decreases with rainfall duration and increases with the presence of power transmission towers. Analysis of a testbed site indicatesthat the presence of a power transmission tower had no major effect on the slope stability. This indicates that the stability of the testbed can be improved by moving the position of the transmission tower. It is expected that the developed program can be used to prevent slope failures induced by heavy rainfall.
6 ACKNOWLEDGEMENT This research was supported by a grant from the Korea Electric Power Corporation (KEPCO). The first author is supported by the “U-City Master and Doctor Course Grant (Education) Program” under the Korea Ministry of Land, Infrastructure and Transport (MOLIT). 7 REFERENCES (TNR 8) Bishop, A. W. (1955), The use of the slip circle in the stability analysis of slopes, Geotechnique, 5(1), 7-17. Fellenius, W. K. A. (1948), Erdstatische Berechnungen: Mit Reibu ng
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우로 인한 간극수압 변화에 대한 실험연구, 한국지반공학회
논문 집, 19(1), 41-49.
