Soil Nail Thesis Presentation

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 ?