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 ?

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