soil nail thesis presentation
DESCRIPTION
Thesis presentationTRANSCRIPT
University of Technology, Sydney
Faculty of Engineering & Information Technology
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 landslideSlide type landslideSlides are usually caused by mass movements that present a well-
defined failure wedge and surface
Hong Kong , 1995
Type of landslideFlow type landslideFlow 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 , 1990
Hong Kong , 2008
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 methodsSurface 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 methodsLandslide prevention
Soil nail Slope reinforced by the inserting steel reinforcing bars
Soil re-compactionExcavate loose soil and backfill re-compaction
Soil replacementUse other material replacing loose soil (No-fine concrete replacement)
Hong Kong
Hong Kong
Slope stabilisation methodsLandslide prevention
Bio- EngineeringUse tree root or plant root to prevent shallow slope failure
Sub-surface DrainageReduction of pore water pressure of slope
Stone ColumnsIncrease average shear resistance of soil along potential slip surface by using compacted stone
Hong Kong
Soil NailWhat is SOIL NAIL ?
Steel bar
Centraliser
Grout columnSoil nail head
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
- Adaptability to different soil types
- Flexibility
- Reinforcement Redundancy
Hong Kong
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
2. Bleeding test & Flow Cone test (for Liquid grout )
3. Compressive strength test(for harden grout)
4. Pull out & proofing Tests
Bleeding Test
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
-
- Other methods
Morgenstern-price’s Method
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
1. Next to the sport centre , high risk (Consequence-to-life)
2. According to bore hole log record, cohesion=5kPa , Friction angle = 38o
3. 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 SandSilty Sand
Bedrock
Case Study ( Hong Kong )
Use Morgenstern-Price’s Method Minimum FOS = 0.986
FOS (0.986) < 1.4 (HK requirement)
Case Study ( Hong Kong )
Slip No FOS
1 1.112
20.986
(minimum)
3 1.157
4 1.367
5 1.572
Estimate potential slip surface
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 )
Row Nail Length (m)
Bond Length (m)
Inclination Angle
(degree)Nail
Spacing (m)Design
resisting force KN
A 12 3.3 15 2 55
B 12 3.8 15 2 50
C 8 4.3 15 2 20
D 8 4.2 15 2 15
E 8 5.7 15 2 8
Use Trial and error method to determine the preliminary soil nail parameter
Case Study ( Hong Kong )
Row No.Level
(mPD)
Bar Length
(m)L
Bar Size (d)
(mm)D
Horizontal
Spacing (m)
S
Force per m
Width F (kN)
F
Force Required=F x S
Max. Allowable Tensile
Force
Ta > Tr
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.
Maximum allowable tensile force of steel bar ( Final Checking )
Case Study ( Hong Kong )
Maximum allowable force between steel & grout ( Final Checking )
Row No.
Level (mPD)
Bar Length
(m)
Bar Size (d)
(mm)
Horizontal
Spacing (m)
Free length
La (m)
Bond length Le
(m)
Force per m Width
F (kN)
Force Require
d
Max. Allowable
ForceTmax > Tr
Tr (kN) Tmax (kN)
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 )
Row No.
Effective Vertical Stress
Force Mobilised
Total Force Mobilised
Force Require
dF.O.S.
F.O.S. > 2
sv (kPa)
Tf (kN)= ( 1.571 +
0.140 s’v ) x Le
CDG CDG Tf (kN) Tr (kN) Tf / Tr
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.
Case Study ( Hong Kong )
Final Soil nail design summary
Row No.Level
(mPD)
Bar Length
(m)
Bar Size (d)
(mm)
Horizontal
Spacing (m)
Free length
La (m)
Bond length Le
(m)
Force per m
Width F (kN)
Force Require
d
Tr (kN)
Row E 58.80 8.0 25 2 4.70 3.30 8.00 16.00Row D 56.80 8.0 25 2 4.20 3.80 15.00 30.00Row C 54.80 8.0 25 2 3.70 4.30 20.00 40.00Row B 52.80 12.0 32 2 3.80 8.20 50.00 100.00Row A 50.80 12.0 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
31.529
(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 youThank you
Any Questions ?Any Questions ?