Moreland Altobelli Associates, Inc
Moreland Altobelli Associates, Inc. SUBSURFACE INVESTIGATION OF
796 SERENITY RIDGE LANE HIAWASSEE, GA 30546
Prepared For:
3077 Highway 64 East, Suite B Sapphire Valley, NC 28774
MAAI Project No.: 11815 October 14, 2011
796 Serenity Ridge Lane Hiawassee, Towns County
1.0
October 17, 2011 MAAI Project Number 11815
INTRODUCTIONS
1.1 Project Information Based on the information provided to us and the observations during the site visit, we understand that a one‐story residential house with basement and a detached 4‐car garage are proposed at this site. The proposed finished floor elevations of the house are 2762.5 for the first floor and 2750.5 for the basement, and the proposed finished floor elevation of the garage is 2754. It is also understood that the basement floor slab will be on residual soils at cut, while the garage floor will be a structure slab supported with grade beams. 1.2 Scope of Work This report presents the results of the geotechnical investigation performed for this site. The purpose of this study was to explore the general subsurface conditions of the subject site and to provide recommendations for the design and construction of the project. Services rendered by MAAI during the course of this investigation can be summarized as follows: • Review the provided project information and requirements; understand the scopes for both construction and geotechnical services. • Review available in‐house data such as similar investigations in the vicinity of reference project site and published geologic, seismic and soil engineering maps pertinent to the project. • Perform a site reconnaissance, stake proposed boring locations and evaluate the site accessibility. • Supervise a drilling subcontractor to conduct Standard Penetration Test (SPT) borings at designated locations and record field logs. • Review and analyze field testing data and evaluate the subsurface conditions with respect to the proposed structures and related construction. • Prepare a report and other graphics presenting the findings, conclusions, and recommendations. 2.0 SUBSURFACE CONDITIONS 2.1 Field Exploration The field investigation consisted of performing a total of three (3) Standard Penetration Test (SPT) borings at the locations indicated on the attached Boring Location Map. Ground surface elevations at the boring locations were interpreted from the provided topo map and rounded to the nearest foot, both boring locations and ground surface elevations should be considered approximate. The drilling and testing were conducted in general accordance to ASTM D‐1586: Standard Test Method for Standard Penetration Test (SPT) and Split‐Barrel Sampling of Soils. In
796 Serenity Ridge Lane Hiawassee, Towns County
2.2
October 17, 2011 MAAI Project Number 11815
general, the boreholes are made with a hollow‐stem auger (3.25” I.D.) mechanically twisted into the ground. At regular intervals, soil samples are obtained through the hollow auger with a standard 1.4‐inch I.D. 2.0‐inch O.D. split barrel sampler. The sampler is typically seated six inches to penetrate any loose cuttings, then it is driven an additional foot with blows from a 140‐pound hammer falling 30 inches. The number of blows required to drive the sampler the final foot is recorded and designated the “Standard Penetration Resistance” or “N‐value” on the boring logs. The penetration resistance is used as an index to derive soil strength, density and foundation bearing capacity from various empirical correlations. An experienced soil technician supervises the drilling operation, and classifies soil samples in general accordance to ASTM D‐2488: Standard Practice for Description and Identification of Soils (Visual‐Manual Procedure). Representative portions of each soil sample are then sealed in labeled glass jars and transported to our AASHTO accredited soil laboratory. All samples are examined again by a registered professional engineer and check the field descriptions. For the presentation of subsurface soil conditions, field logs are entered into a computer program that incorporates sample intervals, penetration resistances, soil descriptions, and groundwater level into a boring log (see Boring Logs in Appendix). Subsurface Soil/Rock/Groundwater Conditions Boring B‐2 was drilled at the proposed house location, the auger was refused at 43 feet where the bedrock was encountered. Soil within top 15 feet is light gray medium dense silty sand with rock fragments/boulders etc., or colluvium soils in a geological term, laying over tan/brown medium dense micaceous silty sand at a depth up to 30 feet where very dense partially weathered rock is present. Boring B‐3 was drilled at the slope below the house, the purpose of this boring was to define the profile of the bedrock. Auger was refused at 5 feet including two offset borings. Refer to the boring logs in the Appendix, the auger refusal elevations were very close at both B‐2 and B‐3, which indicates that the top surface of bedrock at site is relatively flat. Boring B‐1 was drilled for the garage foundation, very similar soil conditions as boring B‐2 were encountered throughout the depth. Ground water wasn’t encountered in any of these borings, shall not cause problems during the construction. (See attached boring logs in the appendix for detail information).
3.0
DESIGN AND CONSTRUCTION RECOMMENDATIONS The following design recommendations have been developed based on the previously described project site conditions and subsurface conditions and our experience with similar
796 Serenity Ridge Lane Hiawassee, Towns County
October 17, 2011 MAAI Project Number 11815
site and subsurface conditions. Should the site plan or structural characteristics differ from the assumed conditions, MAAI should be notified so that we may revise our recommendations in light of such changes. Site Grading and Preparation
3.1
Due to the slope terrain of the site, it is recommended that the house be laid out in such as way so as to have a minimum of 10 feet from the outside edge of the footing to the slope face. It is apparently that foundation soils contain big rock fragments and/or boulders, once excavated to the foundation level, if larger than 6‐inch rocks prevail the site and can not be broken into smaller pieces, the upper 2 feet of the foundation soils shall be dug out and be re‐compacted after removal of large rock fragments. Alternatively, a layer of compacted crusher run or sand may be applied prior to the construction of footings and slabs. The surrounding of the house and garage foundation shall be graded so that the surface water does not infiltrate into foundation areas. Sufficient drainage systems shall be installed to carry storm water down to the bottom of slope. 3.2
3.3
Structure Fill Placement We do not anticipate significant fill be required for this site, however, following information is provided where it applies. The on‐site soils are suitable for structural backfill provided rock fragments larger than 6 inches in diameter can be removed prior to use. Fill material should be placed in thin lifts not to exceed 8 inches loose thickness, unless otherwise directed, and compacted to at least 95% of the maximum dry density as defined by the Standard Proctor test. The upper 12 inches subgrade directly beneath floor slabs should be compacted to at least 98 percent of the maximum dry density. Behind the retaining walls, lift thickness of 4 to 6 inches are recommended, and the compaction may be achieved by hand operated compactors such as “Wacker Packer”. Where fill is placed over a sloping ground surface (steeper than 3H:1V), the ground surface must be “benched” to avoid creating a plane of weakness at the fill/natural ground interface. Benches should extend minimum 8 ft into these slopes and should be cut at a maximum vertical increment of 2 ft. Building Foundation Design Based on subsurface soil conditions and assumed structure foundations, it is our opinion that the proposed building may be adequately supported with a conventional shallow foundation system. It is recommended that maximum allowable soil bearing pressure of 2500 pounds per square foot (psf) bearing on undisturbed residual soils being use for the footing design of the house, and 3000 psf being used for the garage. Due to the slope terrain, we also recommend that all the footings should have a minimum embedment of 2 feet, as measured from the top of the footing to the lowest adjacent
796 Serenity Ridge Lane Hiawassee, Towns County
3.4
October 17, 2011 MAAI Project Number 11815
outside grade. Floor Slab on Grade The basement slab on grade for the building may be adequately supported by residual soil. Expansion and contraction joints should be used to isolate the slab from load bearing walls and/or isolated columns if any. This will allow for possible differential movement and minimize the potential of cracking the floor slabs. In addition, as recommended in ACI’s Concrete Slabs on Grade, moisture barriers should be provided under slab that are likely to receive an impermeable floor finish or used for any purpose where the passage of water vapor through the floor is undesirable. It has been our experience that between completion of grading and slab construction, floor slab subgrade are often disturbed by weather, footing excavations, utility line installations, and other construction activities. The subgrade should be evaluated by a geotechnical engineer or experienced soil technician immediately prior to constructing the slabs. Areas judged by the geotechnical engineer to be unacceptable should be undercut and replaced with compacted crushed stone or structure fill placed and compacted as recommended in section 3.2.
3.5
3.6
3.7
Foundation Excavation Soil exposed at the base of all approved foundation excavations shall be protected against any detrimental changes in condition such as from disturbance during construction, rain and freezing. Surface runoff water should be drained away from the excavation and not allowed to pond. If possible, concrete should be placed as soon as practical after the footing excavation is evaluated and accepted. If a footing excavation has to remain open overnight and rain or snow is forecasted, a layer of 2 to 3 inch lean concrete may be placed at the bottom of the footing to protect the bearing soils. Any flooded footing excavations shall be re‐evaluated, saturated soil should be removed before additional soil replacement may continue. Slope stability Global stability was analyzed for a typical cross section of the slope with the proposed house in place. The minimum factor of safety against failure is approximately 1.92, which indicates the overall site is stable. Additionally, the most critical surface is above the rock elevation, so the possibility of sliding failure along the bedrock is minimal. See attached results in appendix. Foundation Walls Below grade foundation walls will be subject to lateral earth pressures. Walls that are fixed at the top and bottom may be subject to “at‐rest” lateral earth pressure and walls that are not restrained and allowed certain amount movement may be subject to “active” lateral
796 Serenity Ridge Lane Hiawassee, Towns County
October 17, 2011 MAAI Project Number 11815
earth pressure. It is recommended that “at‐rest” and “active” lateral earth pressure be calculated as the equivalent pressure exerted by a fluid density of 60 pcf and 40 pcf respectively. These values are designed for walls above the groundwater table. Therefore, the presence of any groundwater due to surface water intrusion should be handled with drainage layer behind the walls with a collection pipe discharging accumulated water away from the walls. In addition, weep holes may be beneficial in dissipating hydrostatic pressure for walls not associated with buildings. Following soil parameters are recommended for use in the design of the foundation walls: • Angle of internal friction, φ’ = 30o • Cohesion, C = 0 psf • Soil unit weight, γ = 120 pcf • Active earth pressure coefficient, Ka = 0.33 • At‐rest earth pressure coefficient, Ko = 0.50 • Passive earth pressure coefficient, Kp = 3.0 • Coefficient of sliding friction, µ = 0.35 4.0
LIMITATIONS The conclusions and recommendations presented in this report are based on said subsurface exploration and geological and hydro geological reference data. The interpretations from subsurface exploration locations (boreholes, test pits, etc.) are based on geological and hydro geological reasoning, but may not reflect actual conditions. Should significant variations of subsurface conditions become evident due to additional exploration or site excavation, we should be notified so that we may possibly revise our recommendation to reflect the actual conditions encountered. The conclusions and recommendations are intended only for the previously described project. This report should not be used for any purpose other than that indicated. Any application and/or use of the information and recommendations presented herein for any purpose other than that indicated, or for any purpose of any entity other than the original client, shall constitute an agreement to defend and indemnify MAAI, from and against any and all liability in connection with the performance of these services and the information contained herein. MAAI is not responsible for the conclusion or opinions made by others based on finding(s) of this report. This report has been prepared in accordance with generally accepted geotechnical, geological and hydro geological methods. No other warranty is expressed or implied.
796 Serenity Ridge Lane Hiawassee, Towns County
October 17, 2011 MAAI Project Number 11815
APPENDICES
CORRELATION OF SPT N-VALUE WITH SOIL CONSISTENCY
Gravel and Sand SPT Blows / Foot
Relative Density
0-4
Very Loose
5 - 10
Loose
11 - 30
Medium Dense
31 - 50
Dense
> 50
Very Dense
Silt and Clay SPT Blows / Foot
Soil Consistency
0–1
Very Soft
2–4
Soft
5–8
Firm
9 – 15
Stiff
16 – 30
Very Stiff
31 – 50
Hard
> 50
Very Hard
Boring: B-1 at Garage (Page 1 of 1) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
0
2758
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
3-4-10
14
SS
13-12-8
20
SS
8-12-18
30
SS
10-8-8
16
SS
6-8-8
16
SS
5-3-6
9
SS
N Value Graph 0
50
100
Brown silty sand with some clay, slightly moist, medium dense SM
2
2756
Light gray silty sand with rock fragments, dry, medium dense 4
2754
6
2752
8
SM
2750
10
2748
12
2746
14
2744
Gray micaceous silty sand, dry, medium dense
10-17-2011 Q:\Towns County\Charlie Headrick\B-1.bor
SM 16
2742
18
2740
20
2738
22
2736
24
Boring terminated at 20 ft below ground surface
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2758
USCS
Depth in Feet
Sample Condition
: 2758'+/: 20 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Boring: B-2 at House (Page 1 of 2) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
0
2760
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
2-5-5
10
SS
8-14-11
25
SS
9-15-17
32
SS
8-4-5
9
SS
9-9-5
14
SS
4-4-5
9
SS
6-6-8
14
SS
N Value Graph 0
50
100
Multi-color silty sand with rock fragments, dry, loose SM
2
2758
Light gray silty sand with rock fragments, dry, medium dense 4
2756
6
2754
8
2752
10-17-2011 Q:\Towns County\Charlie Headrick\B-2.bor
SM 10
2750
12
2748
14
2746
16
2744
18
2742
20
2740
22
2738
24
Tan/brown micaceous silty sand, dry, medium dense
SM
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2760
USCS
Depth in Feet
Sample Condition
: 2760'+/: 43 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Boring: B-2 at House (Page 2 of 2) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
25
2735
27
2733
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
10-10-10
20
SS
50/5"
50/5"
SS
23-27-50/3"
50/3"
SS
N Value Graph 0
50
100
SM
29
2731
31
2729
33
2727
35
2725
37
2723
39
2721
41
2719
43
2717
45
2715
47
2713
Grey silty sand, very dense, partially weathered rock
10-17-2011 Q:\Towns County\Charlie Headrick\B-2.bor
SM
49
Auger refused at 43 ft below ground surface
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2760
USCS
Depth in Feet
Sample Condition
: 2760'+/: 43 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Boring: B-3, B-3a, B-3b (Page 1 of 1) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
0
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
3-3-3
6
SS
18-50/1"
50/1"
SS
N Value Graph 0
50
100
Brown micaceous silty sand with rock fragments, loose
2724
2 SM 2722
4 2720
6 2718
8 2716
10 2714
12 2712
14 2710
16
10-17-2011 Q:\Towns County\Charlie Headrick\B-3.bor
2708
18 2706
20 2704
22 2702
24
Auger refused at 5 ft below ground surface. Two offsets with 5 feet apart were drilled.
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2725
USCS
Depth in Feet
Sample Condition
: 2725'+/: 5 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Gamma pcf 114 115 120 130
Building Silty Sand PWR Rock
C psf 0 0 0 1000
Phi deg 0 30 36 36
Piezo Surf. 0 0 0 0
Tensar Earth Technologies - Atlanta MAAI # 11815 796 Serenity Ridge Lane October 17, 2011
F = 1.923
2740
2740
2730
2730
2720
2720
2710
2710
2700
2700
2690
2690
0
50
10/17/2011 2:46:20 PM Q:\10WXNW\GSBLDG.GSL Tensar Earth Technologies - Atlanta
100
F = 1.923
150
200
796 SERENITY RIDGE LANE HIAWASSEE, GA 30546
Prepared For:
3077 Highway 64 East, Suite B Sapphire Valley, NC 28774
MAAI Project No.: 11815 October 14, 2011
796 Serenity Ridge Lane Hiawassee, Towns County
1.0
October 17, 2011 MAAI Project Number 11815
INTRODUCTIONS
1.1 Project Information Based on the information provided to us and the observations during the site visit, we understand that a one‐story residential house with basement and a detached 4‐car garage are proposed at this site. The proposed finished floor elevations of the house are 2762.5 for the first floor and 2750.5 for the basement, and the proposed finished floor elevation of the garage is 2754. It is also understood that the basement floor slab will be on residual soils at cut, while the garage floor will be a structure slab supported with grade beams. 1.2 Scope of Work This report presents the results of the geotechnical investigation performed for this site. The purpose of this study was to explore the general subsurface conditions of the subject site and to provide recommendations for the design and construction of the project. Services rendered by MAAI during the course of this investigation can be summarized as follows: • Review the provided project information and requirements; understand the scopes for both construction and geotechnical services. • Review available in‐house data such as similar investigations in the vicinity of reference project site and published geologic, seismic and soil engineering maps pertinent to the project. • Perform a site reconnaissance, stake proposed boring locations and evaluate the site accessibility. • Supervise a drilling subcontractor to conduct Standard Penetration Test (SPT) borings at designated locations and record field logs. • Review and analyze field testing data and evaluate the subsurface conditions with respect to the proposed structures and related construction. • Prepare a report and other graphics presenting the findings, conclusions, and recommendations. 2.0 SUBSURFACE CONDITIONS 2.1 Field Exploration The field investigation consisted of performing a total of three (3) Standard Penetration Test (SPT) borings at the locations indicated on the attached Boring Location Map. Ground surface elevations at the boring locations were interpreted from the provided topo map and rounded to the nearest foot, both boring locations and ground surface elevations should be considered approximate. The drilling and testing were conducted in general accordance to ASTM D‐1586: Standard Test Method for Standard Penetration Test (SPT) and Split‐Barrel Sampling of Soils. In
796 Serenity Ridge Lane Hiawassee, Towns County
2.2
October 17, 2011 MAAI Project Number 11815
general, the boreholes are made with a hollow‐stem auger (3.25” I.D.) mechanically twisted into the ground. At regular intervals, soil samples are obtained through the hollow auger with a standard 1.4‐inch I.D. 2.0‐inch O.D. split barrel sampler. The sampler is typically seated six inches to penetrate any loose cuttings, then it is driven an additional foot with blows from a 140‐pound hammer falling 30 inches. The number of blows required to drive the sampler the final foot is recorded and designated the “Standard Penetration Resistance” or “N‐value” on the boring logs. The penetration resistance is used as an index to derive soil strength, density and foundation bearing capacity from various empirical correlations. An experienced soil technician supervises the drilling operation, and classifies soil samples in general accordance to ASTM D‐2488: Standard Practice for Description and Identification of Soils (Visual‐Manual Procedure). Representative portions of each soil sample are then sealed in labeled glass jars and transported to our AASHTO accredited soil laboratory. All samples are examined again by a registered professional engineer and check the field descriptions. For the presentation of subsurface soil conditions, field logs are entered into a computer program that incorporates sample intervals, penetration resistances, soil descriptions, and groundwater level into a boring log (see Boring Logs in Appendix). Subsurface Soil/Rock/Groundwater Conditions Boring B‐2 was drilled at the proposed house location, the auger was refused at 43 feet where the bedrock was encountered. Soil within top 15 feet is light gray medium dense silty sand with rock fragments/boulders etc., or colluvium soils in a geological term, laying over tan/brown medium dense micaceous silty sand at a depth up to 30 feet where very dense partially weathered rock is present. Boring B‐3 was drilled at the slope below the house, the purpose of this boring was to define the profile of the bedrock. Auger was refused at 5 feet including two offset borings. Refer to the boring logs in the Appendix, the auger refusal elevations were very close at both B‐2 and B‐3, which indicates that the top surface of bedrock at site is relatively flat. Boring B‐1 was drilled for the garage foundation, very similar soil conditions as boring B‐2 were encountered throughout the depth. Ground water wasn’t encountered in any of these borings, shall not cause problems during the construction. (See attached boring logs in the appendix for detail information).
3.0
DESIGN AND CONSTRUCTION RECOMMENDATIONS The following design recommendations have been developed based on the previously described project site conditions and subsurface conditions and our experience with similar
796 Serenity Ridge Lane Hiawassee, Towns County
October 17, 2011 MAAI Project Number 11815
site and subsurface conditions. Should the site plan or structural characteristics differ from the assumed conditions, MAAI should be notified so that we may revise our recommendations in light of such changes. Site Grading and Preparation
3.1
Due to the slope terrain of the site, it is recommended that the house be laid out in such as way so as to have a minimum of 10 feet from the outside edge of the footing to the slope face. It is apparently that foundation soils contain big rock fragments and/or boulders, once excavated to the foundation level, if larger than 6‐inch rocks prevail the site and can not be broken into smaller pieces, the upper 2 feet of the foundation soils shall be dug out and be re‐compacted after removal of large rock fragments. Alternatively, a layer of compacted crusher run or sand may be applied prior to the construction of footings and slabs. The surrounding of the house and garage foundation shall be graded so that the surface water does not infiltrate into foundation areas. Sufficient drainage systems shall be installed to carry storm water down to the bottom of slope. 3.2
3.3
Structure Fill Placement We do not anticipate significant fill be required for this site, however, following information is provided where it applies. The on‐site soils are suitable for structural backfill provided rock fragments larger than 6 inches in diameter can be removed prior to use. Fill material should be placed in thin lifts not to exceed 8 inches loose thickness, unless otherwise directed, and compacted to at least 95% of the maximum dry density as defined by the Standard Proctor test. The upper 12 inches subgrade directly beneath floor slabs should be compacted to at least 98 percent of the maximum dry density. Behind the retaining walls, lift thickness of 4 to 6 inches are recommended, and the compaction may be achieved by hand operated compactors such as “Wacker Packer”. Where fill is placed over a sloping ground surface (steeper than 3H:1V), the ground surface must be “benched” to avoid creating a plane of weakness at the fill/natural ground interface. Benches should extend minimum 8 ft into these slopes and should be cut at a maximum vertical increment of 2 ft. Building Foundation Design Based on subsurface soil conditions and assumed structure foundations, it is our opinion that the proposed building may be adequately supported with a conventional shallow foundation system. It is recommended that maximum allowable soil bearing pressure of 2500 pounds per square foot (psf) bearing on undisturbed residual soils being use for the footing design of the house, and 3000 psf being used for the garage. Due to the slope terrain, we also recommend that all the footings should have a minimum embedment of 2 feet, as measured from the top of the footing to the lowest adjacent
796 Serenity Ridge Lane Hiawassee, Towns County
3.4
October 17, 2011 MAAI Project Number 11815
outside grade. Floor Slab on Grade The basement slab on grade for the building may be adequately supported by residual soil. Expansion and contraction joints should be used to isolate the slab from load bearing walls and/or isolated columns if any. This will allow for possible differential movement and minimize the potential of cracking the floor slabs. In addition, as recommended in ACI’s Concrete Slabs on Grade, moisture barriers should be provided under slab that are likely to receive an impermeable floor finish or used for any purpose where the passage of water vapor through the floor is undesirable. It has been our experience that between completion of grading and slab construction, floor slab subgrade are often disturbed by weather, footing excavations, utility line installations, and other construction activities. The subgrade should be evaluated by a geotechnical engineer or experienced soil technician immediately prior to constructing the slabs. Areas judged by the geotechnical engineer to be unacceptable should be undercut and replaced with compacted crushed stone or structure fill placed and compacted as recommended in section 3.2.
3.5
3.6
3.7
Foundation Excavation Soil exposed at the base of all approved foundation excavations shall be protected against any detrimental changes in condition such as from disturbance during construction, rain and freezing. Surface runoff water should be drained away from the excavation and not allowed to pond. If possible, concrete should be placed as soon as practical after the footing excavation is evaluated and accepted. If a footing excavation has to remain open overnight and rain or snow is forecasted, a layer of 2 to 3 inch lean concrete may be placed at the bottom of the footing to protect the bearing soils. Any flooded footing excavations shall be re‐evaluated, saturated soil should be removed before additional soil replacement may continue. Slope stability Global stability was analyzed for a typical cross section of the slope with the proposed house in place. The minimum factor of safety against failure is approximately 1.92, which indicates the overall site is stable. Additionally, the most critical surface is above the rock elevation, so the possibility of sliding failure along the bedrock is minimal. See attached results in appendix. Foundation Walls Below grade foundation walls will be subject to lateral earth pressures. Walls that are fixed at the top and bottom may be subject to “at‐rest” lateral earth pressure and walls that are not restrained and allowed certain amount movement may be subject to “active” lateral
796 Serenity Ridge Lane Hiawassee, Towns County
October 17, 2011 MAAI Project Number 11815
earth pressure. It is recommended that “at‐rest” and “active” lateral earth pressure be calculated as the equivalent pressure exerted by a fluid density of 60 pcf and 40 pcf respectively. These values are designed for walls above the groundwater table. Therefore, the presence of any groundwater due to surface water intrusion should be handled with drainage layer behind the walls with a collection pipe discharging accumulated water away from the walls. In addition, weep holes may be beneficial in dissipating hydrostatic pressure for walls not associated with buildings. Following soil parameters are recommended for use in the design of the foundation walls: • Angle of internal friction, φ’ = 30o • Cohesion, C = 0 psf • Soil unit weight, γ = 120 pcf • Active earth pressure coefficient, Ka = 0.33 • At‐rest earth pressure coefficient, Ko = 0.50 • Passive earth pressure coefficient, Kp = 3.0 • Coefficient of sliding friction, µ = 0.35 4.0
LIMITATIONS The conclusions and recommendations presented in this report are based on said subsurface exploration and geological and hydro geological reference data. The interpretations from subsurface exploration locations (boreholes, test pits, etc.) are based on geological and hydro geological reasoning, but may not reflect actual conditions. Should significant variations of subsurface conditions become evident due to additional exploration or site excavation, we should be notified so that we may possibly revise our recommendation to reflect the actual conditions encountered. The conclusions and recommendations are intended only for the previously described project. This report should not be used for any purpose other than that indicated. Any application and/or use of the information and recommendations presented herein for any purpose other than that indicated, or for any purpose of any entity other than the original client, shall constitute an agreement to defend and indemnify MAAI, from and against any and all liability in connection with the performance of these services and the information contained herein. MAAI is not responsible for the conclusion or opinions made by others based on finding(s) of this report. This report has been prepared in accordance with generally accepted geotechnical, geological and hydro geological methods. No other warranty is expressed or implied.
796 Serenity Ridge Lane Hiawassee, Towns County
October 17, 2011 MAAI Project Number 11815
APPENDICES
CORRELATION OF SPT N-VALUE WITH SOIL CONSISTENCY
Gravel and Sand SPT Blows / Foot
Relative Density
0-4
Very Loose
5 - 10
Loose
11 - 30
Medium Dense
31 - 50
Dense
> 50
Very Dense
Silt and Clay SPT Blows / Foot
Soil Consistency
0–1
Very Soft
2–4
Soft
5–8
Firm
9 – 15
Stiff
16 – 30
Very Stiff
31 – 50
Hard
> 50
Very Hard
Boring: B-1 at Garage (Page 1 of 1) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
0
2758
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
3-4-10
14
SS
13-12-8
20
SS
8-12-18
30
SS
10-8-8
16
SS
6-8-8
16
SS
5-3-6
9
SS
N Value Graph 0
50
100
Brown silty sand with some clay, slightly moist, medium dense SM
2
2756
Light gray silty sand with rock fragments, dry, medium dense 4
2754
6
2752
8
SM
2750
10
2748
12
2746
14
2744
Gray micaceous silty sand, dry, medium dense
10-17-2011 Q:\Towns County\Charlie Headrick\B-1.bor
SM 16
2742
18
2740
20
2738
22
2736
24
Boring terminated at 20 ft below ground surface
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2758
USCS
Depth in Feet
Sample Condition
: 2758'+/: 20 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Boring: B-2 at House (Page 1 of 2) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
0
2760
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
2-5-5
10
SS
8-14-11
25
SS
9-15-17
32
SS
8-4-5
9
SS
9-9-5
14
SS
4-4-5
9
SS
6-6-8
14
SS
N Value Graph 0
50
100
Multi-color silty sand with rock fragments, dry, loose SM
2
2758
Light gray silty sand with rock fragments, dry, medium dense 4
2756
6
2754
8
2752
10-17-2011 Q:\Towns County\Charlie Headrick\B-2.bor
SM 10
2750
12
2748
14
2746
16
2744
18
2742
20
2740
22
2738
24
Tan/brown micaceous silty sand, dry, medium dense
SM
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2760
USCS
Depth in Feet
Sample Condition
: 2760'+/: 43 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Boring: B-2 at House (Page 2 of 2) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
25
2735
27
2733
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
10-10-10
20
SS
50/5"
50/5"
SS
23-27-50/3"
50/3"
SS
N Value Graph 0
50
100
SM
29
2731
31
2729
33
2727
35
2725
37
2723
39
2721
41
2719
43
2717
45
2715
47
2713
Grey silty sand, very dense, partially weathered rock
10-17-2011 Q:\Towns County\Charlie Headrick\B-2.bor
SM
49
Auger refused at 43 ft below ground surface
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2760
USCS
Depth in Feet
Sample Condition
: 2760'+/: 43 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Boring: B-3, B-3a, B-3b (Page 1 of 1) DATE COMPLETED HOLE DIAMETER DRILLING METHOD DRILLER LOGGED BY
0
PS Piston Sampler
Rock Core
DC Diamond Core Bar.
DESCRIPTION
3-3-3
6
SS
18-50/1"
50/1"
SS
N Value Graph 0
50
100
Brown micaceous silty sand with rock fragments, loose
2724
2 SM 2722
4 2720
6 2718
8 2716
10 2714
12 2712
14 2710
16
10-17-2011 Q:\Towns County\Charlie Headrick\B-3.bor
2708
18 2706
20 2704
22 2702
24
Auger refused at 5 ft below ground surface. Two offsets with 5 feet apart were drilled.
Water Level
ST Shelby Tube
Lost
Moist, %
SS Split Spoon
Undisturbed
Sample
Sampler Type
Remoulded
Sampler Type
GRAPHIC
Surf. Elev. 2725
USCS
Depth in Feet
Sample Condition
: 2725'+/: 5 ft : Not encoutered
SPT-N Value
MAAI Job No.: 11815
SURFACE ELE. DEPTH OF BORING DEPTH TO WATER
: 10/10/2011 : 5.5 inch : CME 550 2.25" HSA w/ SPT : Excalibur Drilling : J.S.
Blow count
796 Serenity Ridge Lane Hiawassee, GA 30546
Gamma pcf 114 115 120 130
Building Silty Sand PWR Rock
C psf 0 0 0 1000
Phi deg 0 30 36 36
Piezo Surf. 0 0 0 0
Tensar Earth Technologies - Atlanta MAAI # 11815 796 Serenity Ridge Lane October 17, 2011
F = 1.923
2740
2740
2730
2730
2720
2720
2710
2710
2700
2700
2690
2690
0
50
10/17/2011 2:46:20 PM Q:\10WXNW\GSBLDG.GSL Tensar Earth Technologies - Atlanta
100
F = 1.923
150
200
