Soil Nail Thesis Presentation
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Faculty of Engineering & Information Technology University of Technology, Sydney
School of Civil & Environmental Engineering
Student : Victor Yeung Project No : S08 – 097 Student No: 10240810 Bachelor of Engineering ( Civil ) Supervisor: Dr. Behzad Fatahi
Outline of Presentation - What is slope failure ? - Type of landslide - Factors causing landslide - Slope stabilisation methods - What is Soil Nail ? - Construction procedure - Quality control of Soil nailing - SLOPE/W slope analysis software - Case Study ( Hong Kong ) - Conclusion
Hong Kong , 1995
What is slope failure ? - The slope can not support itself - Gravitational and seepage forces cause disturbing force - Soil friction provide resisting force - If disturbing moment > resisting moment Slope will failure ( Landslide )
China
Type of landslide Fall type landslide Usually occurring in rock slopes, rock displacement and rock fall with a very fast movement.
Newcastle , Australia
Type of landslide Slide type landslide Slides are usually caused by mass movements that present a welldefined failure wedge and surface
Hong Kong , 1995
Type of landslide Flow type landslide Flow landslide is a continuous viscous slide involving soil or rock. If material is clay or fine soil material, this flow is called mud flow
Hong Kong , 2008 Hong Kong , 1990
Major landslide in past history (Hong Kong & Australia) Hong Kong 18 June 1972 Mid-level Kotewall Road. Two high-rise residential buildings collapsed due to large landslide and killed 67 people Hong Kong , 1972
Major landslide in past history (Hong Kong & Australia) Australia 30 July 1997 A large section of steep mountainside below the Alpine Way road collapsed in Thredbo , NSW. 18 people died in this disaster.
Australia , 1997
Factors causing landslide - Geometrical changes - Surcharge - Shocks and vibrations ( Earth quake, blasting) - Change in water regime (Rainfall ,pipe leakage ) - Removal of vegetation ( Reduce tree root suction) - Weathering ( Reduction of cohesion, desiccation )
Slope stabilisation methods Surface protection Shotcrete - Concrete sprayed on the slope surface Masonry - Use stone pitching as a rigid surface cover to prevent erosion and surface runoff. Chunam - Cement sand mix material for surface protection
Slope stabilisation methods Landslide prevention
Soil nail Slope reinforced by the inserting steel reinforcing bars
Soil re-compaction
Hong Kong
Excavate loose soil and backfill re-compaction
Soil replacement Use other material replacing loose soil (No-fine concrete replacement) Hong Kong
Slope stabilisation methods Landslide prevention Bio- Engineering Use tree root or plant root to prevent shallow slope failure
Hong Kong
Sub-surface Drainage Reduction of pore water pressure of slope
Stone Columns Increase average shear resistance of soil along potential slip surface by using compacted stone
Soil Nail What is SOIL NAIL ?
Steel bar
Centraliser
Soil nail head
Grout column
Function of Soil Nail Provide a resisting force against slope failure
Differences of Soil nail & Soil Anchor Soil nail - Non-prestressed - Faster construction time - Maintenance on soil nail is not necessary Soil Anchor - Prestressed tendon - Longer construction time -Maintenance is necessary (Avoid loss of prestress in tendons)
Advantages of Soil nail - Economy - Fast construction - Light construction equipment
Hong Kong
- Adaptability to different soil types - Flexibility - Reinforcement Redundancy
Hong Kong
Construction procedure of Soil nail
1. Drilling 2. Steel bar installation 3. Grouting 4. Soil nail head construction
Quality control of Soil nail 1. Soil nail Steel bar testing Bleeding Test
1. Bleeding test & Flow Cone test (for Liquid grout ) 1. Compressive strength test (for harden grout) 4. Pull out & proofing Tests
Flow cone test
Soil nail Design Slope Failure analysis - Limit equilibrium design approach - Factor of Safety ( FOS ) calculation Method of analysis - Ordinary / Swedish Method - Bishop Method - Janbu’s Method - Morgenstern-price’s Method - Other methods
SLOPE/W slope analysis software - Developed by GEO-SLOPE International Ltd. - Assessing the realistic FOS
Soil nail design procedure 1. Use SLOPE/W to analysis slope stability 2. Insert soil nails in the SLOPE/W model 3. Use trial and error method to determine the potential failure resisting force of soil nails 4. Use soil nail capacity calculation to determine bond length , bar size, spacing and inclination angle 5. Re- analysis the slope model use final design parameter
Design Criteria 1. Slope critical section FOS > Design requirement
2. Soil nail capacity checking must be satisfy the design requirement
Case Study ( Hong Kong ) Background •
Next to the sport centre , high risk (Consequence-to-life)
•
According to bore hole log record, cohesion=5kPa , Friction angle = 38o
•
Critical section – Height =12m , slope angle approximate= 60o Location: Hong Kong ( Shek Kip Mei Sport Centre )
Case Study ( Hong Kong ) Use bore hole log records to estimate the soil layering Silty Sand
Bedrock
Silty Sand
Case Study ( Hong Kong )
Use Morgenstern-Price’s Method Minimum FOS = 0.986 FOS (0.986) < 1.4 (HK requirement)
Case Study ( Hong Kong ) Estimate potential slip surface
Slip No
FOS
1
1.112
2
0.986 (minimum)
3
1.157
4
1.367
5
1.572
Case Study ( Hong Kong ) After soil nail installed minimum FOS = 1.52 FOS (1.52) >1.4 (require)
Case Study ( Hong Kong )
Case Study ( Hong Kong ) Use Trial and error method to determine the preliminary soil nail parameter
Row A B C D E
Nail Length Bond (m) Length (m) 12 12 8 8 8
3.3 3.8 4.3 4.2 5.7
Inclination Angle (degree)
Nail Spacing (m)
Design resisting force KN
15 15 15 15 15
2 2 2 2 2
55 50 20 15 8
Case Study ( Hong Kong ) Maximum allowable tensile force of steel bar ( Final Checking )
Level Row No. (mPD)
Max. Horizont Force Force Bar Bar Size al per m Required Allowabl Ta > Tr Length (d) Spacing Width F =F x S e Tensile (m) (mm) Force (m) (kN) L D S F Tr (kN) Ta (kN) Check
Row E
58.80
8.0
25
2.0
8.00
16.00
79.66
O.K.
Row D
56.80
8.0
25
2.0
15.00
30.00
79.66
O.K.
Row C
54.80
8.0
25
2.0
20.00
40.00
79.66
O.K.
Row B
52.80
12.0
32
2.0
50.00
100.00
141.62
O.K.
Row A
50.80
12.0
32
2.0
55.00
110.00
141.62
O.K.
Case Study ( Hong Kong ) Maximum allowable force between steel & grout ( Final Checking ) Force Max. Bar Horizo Free Bond Force Require Allowable Bar d Force Row Level Size (d) ntal length length per m Length Le No. (mPD) Spacing La Width (m) (mm) (m) (m) (m) F (kN) Tr (kN) Tmax (kN)
Tmax > Tr
Row E
58.8
8.0
25
2.0
4.70
3.30
8.00
16.00
205.26
O.K.
Row D
56.8
8.0
25
2.0
4.20
3.80
15.00
30.00
236.36
O.K.
Row C
54.8
8.0
25
2.0
3.70
4.30
20.00
40.00
267.46
O.K.
Row B
52.8
12.0
32
2.0
3.80
8.20
50.00 100.00
680.06
O.K.
Row A
50.8
12.0
32
2.0
2.30
9.70
55.00 110.00
804.46
O.K.
Case Study ( Hong Kong ) Maximum allowable force between soil & grout ( Final Checking ) Effective Vertical Stress
Force Mobilised
sv (kPa)
Tf (kN)= ( 1.571 + 0.140 s’v ) x Le
CDG
CDG
Tf (kN)
Row E
68.00
36.65
36.65
16.00
2.29
O.K.
Row D
106.00
62.45
62.45
30.00
2.08
O.K.
Row C
144.00
93.58
93.58
40.00
2.34
O.K.
Row B
180.27
220.16
220.16
100.00
2.20
O.K.
Row A
158.57
230.92
230.92
110.00
2.10
O.K.
Row No.
Force Total Force F.O.S. Require F.O.S. Mobilised >2 d
Tr (kN) Tf / Tr
Case Study ( Hong Kong ) Final Soil nail design summary
Level Row No. (mPD)
Horizont Free Bar Bar Size al length Length (d) Spacing La (m) (mm) (m) (m) 8.0 25 2 4.70
Row E
58.80
Row D
56.80
8.0
25
2
Row C
54.80
8.0
25
Row B
52.80
12.0
Row A
50.80
12.0
Force Bond Force length per m Require d Le Width F (kN) Tr (kN) (m) 3.30
8.00
16.00
4.20
3.80
15.00
30.00
2
3.70
4.30
20.00
40.00
32
2
3.80
8.20
50.00
100.00
32
2
2.30
9.70
55.00
110.00
Case Study ( Hong Kong ) After soil nail installed , the slope stability FOS value has been increased
Slip No
FOS
1
-
2
1.534
3
1.529 (Minimum)
4
1.671
5
1.835
Conclusion - From the Case Study , the slope stability has been significantly improved by Soil nailing - Limit equilibrium method using Slope/W is an accurate approach to design soil nail walls in practice - Soil nailing method has a simple design method and easy construction method - Soil nail is the most cost-efficient solution for slope stabilisation
Thank you Any Questions ?
School of Civil & Environmental Engineering
Student : Victor Yeung Project No : S08 – 097 Student No: 10240810 Bachelor of Engineering ( Civil ) Supervisor: Dr. Behzad Fatahi
Outline of Presentation - What is slope failure ? - Type of landslide - Factors causing landslide - Slope stabilisation methods - What is Soil Nail ? - Construction procedure - Quality control of Soil nailing - SLOPE/W slope analysis software - Case Study ( Hong Kong ) - Conclusion
Hong Kong , 1995
What is slope failure ? - The slope can not support itself - Gravitational and seepage forces cause disturbing force - Soil friction provide resisting force - If disturbing moment > resisting moment Slope will failure ( Landslide )
China
Type of landslide Fall type landslide Usually occurring in rock slopes, rock displacement and rock fall with a very fast movement.
Newcastle , Australia
Type of landslide Slide type landslide Slides are usually caused by mass movements that present a welldefined failure wedge and surface
Hong Kong , 1995
Type of landslide Flow type landslide Flow landslide is a continuous viscous slide involving soil or rock. If material is clay or fine soil material, this flow is called mud flow
Hong Kong , 2008 Hong Kong , 1990
Major landslide in past history (Hong Kong & Australia) Hong Kong 18 June 1972 Mid-level Kotewall Road. Two high-rise residential buildings collapsed due to large landslide and killed 67 people Hong Kong , 1972
Major landslide in past history (Hong Kong & Australia) Australia 30 July 1997 A large section of steep mountainside below the Alpine Way road collapsed in Thredbo , NSW. 18 people died in this disaster.
Australia , 1997
Factors causing landslide - Geometrical changes - Surcharge - Shocks and vibrations ( Earth quake, blasting) - Change in water regime (Rainfall ,pipe leakage ) - Removal of vegetation ( Reduce tree root suction) - Weathering ( Reduction of cohesion, desiccation )
Slope stabilisation methods Surface protection Shotcrete - Concrete sprayed on the slope surface Masonry - Use stone pitching as a rigid surface cover to prevent erosion and surface runoff. Chunam - Cement sand mix material for surface protection
Slope stabilisation methods Landslide prevention
Soil nail Slope reinforced by the inserting steel reinforcing bars
Soil re-compaction
Hong Kong
Excavate loose soil and backfill re-compaction
Soil replacement Use other material replacing loose soil (No-fine concrete replacement) Hong Kong
Slope stabilisation methods Landslide prevention Bio- Engineering Use tree root or plant root to prevent shallow slope failure
Hong Kong
Sub-surface Drainage Reduction of pore water pressure of slope
Stone Columns Increase average shear resistance of soil along potential slip surface by using compacted stone
Soil Nail What is SOIL NAIL ?
Steel bar
Centraliser
Soil nail head
Grout column
Function of Soil Nail Provide a resisting force against slope failure
Differences of Soil nail & Soil Anchor Soil nail - Non-prestressed - Faster construction time - Maintenance on soil nail is not necessary Soil Anchor - Prestressed tendon - Longer construction time -Maintenance is necessary (Avoid loss of prestress in tendons)
Advantages of Soil nail - Economy - Fast construction - Light construction equipment
Hong Kong
- Adaptability to different soil types - Flexibility - Reinforcement Redundancy
Hong Kong
Construction procedure of Soil nail
1. Drilling 2. Steel bar installation 3. Grouting 4. Soil nail head construction
Quality control of Soil nail 1. Soil nail Steel bar testing Bleeding Test
1. Bleeding test & Flow Cone test (for Liquid grout ) 1. Compressive strength test (for harden grout) 4. Pull out & proofing Tests
Flow cone test
Soil nail Design Slope Failure analysis - Limit equilibrium design approach - Factor of Safety ( FOS ) calculation Method of analysis - Ordinary / Swedish Method - Bishop Method - Janbu’s Method - Morgenstern-price’s Method - Other methods
SLOPE/W slope analysis software - Developed by GEO-SLOPE International Ltd. - Assessing the realistic FOS
Soil nail design procedure 1. Use SLOPE/W to analysis slope stability 2. Insert soil nails in the SLOPE/W model 3. Use trial and error method to determine the potential failure resisting force of soil nails 4. Use soil nail capacity calculation to determine bond length , bar size, spacing and inclination angle 5. Re- analysis the slope model use final design parameter
Design Criteria 1. Slope critical section FOS > Design requirement
2. Soil nail capacity checking must be satisfy the design requirement
Case Study ( Hong Kong ) Background •
Next to the sport centre , high risk (Consequence-to-life)
•
According to bore hole log record, cohesion=5kPa , Friction angle = 38o
•
Critical section – Height =12m , slope angle approximate= 60o Location: Hong Kong ( Shek Kip Mei Sport Centre )
Case Study ( Hong Kong ) Use bore hole log records to estimate the soil layering Silty Sand
Bedrock
Silty Sand
Case Study ( Hong Kong )
Use Morgenstern-Price’s Method Minimum FOS = 0.986 FOS (0.986) < 1.4 (HK requirement)
Case Study ( Hong Kong ) Estimate potential slip surface
Slip No
FOS
1
1.112
2
0.986 (minimum)
3
1.157
4
1.367
5
1.572
Case Study ( Hong Kong ) After soil nail installed minimum FOS = 1.52 FOS (1.52) >1.4 (require)
Case Study ( Hong Kong )
Case Study ( Hong Kong ) Use Trial and error method to determine the preliminary soil nail parameter
Row A B C D E
Nail Length Bond (m) Length (m) 12 12 8 8 8
3.3 3.8 4.3 4.2 5.7
Inclination Angle (degree)
Nail Spacing (m)
Design resisting force KN
15 15 15 15 15
2 2 2 2 2
55 50 20 15 8
Case Study ( Hong Kong ) Maximum allowable tensile force of steel bar ( Final Checking )
Level Row No. (mPD)
Max. Horizont Force Force Bar Bar Size al per m Required Allowabl Ta > Tr Length (d) Spacing Width F =F x S e Tensile (m) (mm) Force (m) (kN) L D S F Tr (kN) Ta (kN) Check
Row E
58.80
8.0
25
2.0
8.00
16.00
79.66
O.K.
Row D
56.80
8.0
25
2.0
15.00
30.00
79.66
O.K.
Row C
54.80
8.0
25
2.0
20.00
40.00
79.66
O.K.
Row B
52.80
12.0
32
2.0
50.00
100.00
141.62
O.K.
Row A
50.80
12.0
32
2.0
55.00
110.00
141.62
O.K.
Case Study ( Hong Kong ) Maximum allowable force between steel & grout ( Final Checking ) Force Max. Bar Horizo Free Bond Force Require Allowable Bar d Force Row Level Size (d) ntal length length per m Length Le No. (mPD) Spacing La Width (m) (mm) (m) (m) (m) F (kN) Tr (kN) Tmax (kN)
Tmax > Tr
Row E
58.8
8.0
25
2.0
4.70
3.30
8.00
16.00
205.26
O.K.
Row D
56.8
8.0
25
2.0
4.20
3.80
15.00
30.00
236.36
O.K.
Row C
54.8
8.0
25
2.0
3.70
4.30
20.00
40.00
267.46
O.K.
Row B
52.8
12.0
32
2.0
3.80
8.20
50.00 100.00
680.06
O.K.
Row A
50.8
12.0
32
2.0
2.30
9.70
55.00 110.00
804.46
O.K.
Case Study ( Hong Kong ) Maximum allowable force between soil & grout ( Final Checking ) Effective Vertical Stress
Force Mobilised
sv (kPa)
Tf (kN)= ( 1.571 + 0.140 s’v ) x Le
CDG
CDG
Tf (kN)
Row E
68.00
36.65
36.65
16.00
2.29
O.K.
Row D
106.00
62.45
62.45
30.00
2.08
O.K.
Row C
144.00
93.58
93.58
40.00
2.34
O.K.
Row B
180.27
220.16
220.16
100.00
2.20
O.K.
Row A
158.57
230.92
230.92
110.00
2.10
O.K.
Row No.
Force Total Force F.O.S. Require F.O.S. Mobilised >2 d
Tr (kN) Tf / Tr
Case Study ( Hong Kong ) Final Soil nail design summary
Level Row No. (mPD)
Horizont Free Bar Bar Size al length Length (d) Spacing La (m) (mm) (m) (m) 8.0 25 2 4.70
Row E
58.80
Row D
56.80
8.0
25
2
Row C
54.80
8.0
25
Row B
52.80
12.0
Row A
50.80
12.0
Force Bond Force length per m Require d Le Width F (kN) Tr (kN) (m) 3.30
8.00
16.00
4.20
3.80
15.00
30.00
2
3.70
4.30
20.00
40.00
32
2
3.80
8.20
50.00
100.00
32
2
2.30
9.70
55.00
110.00
Case Study ( Hong Kong ) After soil nail installed , the slope stability FOS value has been increased
Slip No
FOS
1
-
2
1.534
3
1.529 (Minimum)
4
1.671
5
1.835
Conclusion - From the Case Study , the slope stability has been significantly improved by Soil nailing - Limit equilibrium method using Slope/W is an accurate approach to design soil nail walls in practice - Soil nailing method has a simple design method and easy construction method - Soil nail is the most cost-efficient solution for slope stabilisation
Thank you Any Questions ?
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