MAJ1053: SOFTWARE APPLICATION IN GEOTECHNICAL ENGINEERING

PROF. MADYA IR. AZMAN KASSIM

ASSIGNMENT NO. 1

NAME: EDA SUHAILI SHARUDIN

IC NUMBER: 841212-06-5444

ID NUMBER: MA131055

SOIL SLOPE STABILITY ANALYSIS

1.0 Introduction

Slope stability analysis is performed to assess the safe design of a human-made or natural slopes and

the equilibrium conditions. The term slope stability may be defined as the resistance of inclined surface

to failure by sliding or collapsing. The main objectives of slope stability analysis are finding endangered

areas, investigation of potential failure mechanisms, determination of the slope sensitivity to different

triggering mechanisms, designing of optimal slopes with regard to safety, reliability and economics,

designing possible remedial measures, e.g. barriers and stabilization.

Successful design of the slope requires geological information and site characteristics, e.g. properties

of soil/rock mass, slope geometry, ground water conditions, alternation of materials

by faulting, joint or discontinuity systems, movements and tension in joints, earthquake activity etc.

Choice of correct analysis technique depends on both site conditions and the potential mode of failure,

with careful consideration being given to the varying strengths, weaknesses and limitations inherent in

each methodology.

2.0 Geotechnical Parameters and Dam Embankment Geometry

The soil profile with three main stratums is as shown in Figure 2.1.

4 m

4 m

4 m

3 m

3 m

1

1

Silty Sand

Clayey Sand

Bedrock

Groundwater Table

3 m

1 m

3.5 m

5 m

6 m

2 m

Figure 2.1: Slope Geometry

The geotechnical parameters of the slope materials are as Table 2.1 below.

Material Property

Silty Sand

Clayey Sand

Unit Weight, (kN/m3)

sat

21.4 20.4

22.6 24.4

Adopted Shear Strength

= 27o, c = 2 kN/m2

= 10o, c = 5 kN/m2

Permeability (m/s)

5 x 10-5

2.67 x 10-7

Table 2.1: Geotechnical Parameters of the Slopes Materials

3.0 Method of Slope Stability and Deformation Analysis

The dam embankment stability and deformation analyses have been executed using Slope W version

2007. Features of the programme include:

Limit equilibrium methods include Morgenstern-Price, GLE, Spencer, Bishop, Ordinary and Janbu, and more.

Soil strength models include Mohr-Coulomb, Bilinear, Undrained (Phi=0), anisotrophic strength, shear/normal function, and many types of strength functions.

Specify many types of interslice shear-normal force functions.

Pore-water pressure options include Ru coefficients, piezometric lines, pressure contours, a kriged grid of values, or finite-element computed heads or pressures.

Define potential slip surfaces by a grid of centers and radius lines, blocks of slip surface points, or fully specified shapes.

Use probabilistic soil properties, line loads and piezometric lines.

4.0 Computation result 4.1 SEEP/W A flux boundary of 1.49 x 10-6 m/s applied on along the surface of the slope. By using SEEP/W to

model the slope profile (Figure 2.2), the seepage pattern of water flow in the earth dam is as

shown in Figure 2.3. The procedure of analyzing the slope profile using SEEP/W is attached in

Appendix A.

Figure 2.2: Model of the Slope Profile using SEEP-W

Figure 2.3: Water Seepage Pattern

4.2 SLOPE/W

The results from SEEP-W are then integrated to SLOPE/W. A surface water table is found at the

toe of the slope during wet season. In addition, 11/2 storey building with total height of 6 m and

width = 5 m apply the total weight per meter square of 120 kN/m2 at the crest of the slope.

Tension crack is found to be at 1.5 m depth from crest of the slope (water in tension crack). The

factor of safety of the soil slope is determined by using Bishop, Ordinary, Janbu and GLE (half-

sine function) methods. The soil profile has been analyzed in Grid and Radius Slip Surface Option

and Entry Exit Slip Surface Option. The procedure analyzing the slope profile using SLOPE /W is

attached in Appendix B.

The inputs for geological parameter are as described in Figure 2.4.

Figure 2.4: Geological Parameter Input

4.2.1 Grid and Radius Slip Surface Option (Bishop, Ordinary, Janbu Method)

The factor of safety derived from the analysis for Bishop, Ordinary, Janbu Method by

using Grid and Radius Slip Surface Option is 0.860 (Figure 2.5).

Figure 2.5: Factor of Safety from Grid and Radius Slip Surface Option for Bishop, Ordinary, Janbu Method

4.2.2 Grid and Radius Slip Surface Option (GLE Method)

The factor of safety derived from the analysis for GLE Method by using Grid and Radius

Slip Surface Option is 0.849 (Figure 2.6).

Figure 2.6: Factor of Safety from Grid and Radius Slip Surface Option for GLE Method

4.2.3 Entry and Exit Slip Surface Option (Bishop, Ordinary, Janbu Method)

The factor of safety derived from the analysis for Bishop, Ordinary, Janbu Method by

using Entry and Exit Slip Surface Option is 0.802 (Figure 2.7).

Figure 2.7: Factor of Safety from Entry and Exit Slip Surface Option for Bishop, Ordinary, Janbu Method

4.2.4 Entry and Exit Slip Surface Option (GLE Method)

The factor of safety derived from the analysis for GLE Method by using Entry and Exit

Slip Surface Option is 0.790 (Figure 2.8).

Figure 2.8: Factor of Safety from Entry and Exit Slip Surface Option for GLE Method

5.0 Conclusion

The minimum factor of safety for slope is 1.3. Hence, the slope profile analyzed is not safe since the

factors of safety gained from the analysis are less than 1.3.

Some recommendation can be made to stabilize the slope as tabulated below:

Category Group

Control Measures Earthworks: Cutting and Filling.

Bio-Engineering: Various methods of vegetation

and small scale engineering work in the slope and

its vicinity.

Water Management: Surface and subsurface

drainage.

Restraint Measures Slope Work: Stone pitching, frame work.

Anchoring: Rock Bolt, Nailing and Ground Anchor,

Walls and Resisting Structure: Gabion, Stone

Masonry, Frame Wall etc.

Protection work: Rock Fall Wire-net, Check Dam.

Piling Work: Steel pipe, Pile Shaft work

APPENDIX A

Question 3

1. Define

a. Set Page = 266.7mm x 203.2mm

b. Set Scale

i. Horizontal 1 = 230

ii. Vertical 1 = 230

c. Grid Spacing

i. X = 0.5

ii. Y = 0.5

d. Axis

e. Save as Seep-Q3

f. Key in the material and hydraulic conductivity function for both of the soil type.

i. Silty Sand, Ksat = 5x10-5 m/s

ii. Clayey Sand, Ksat = 2.67x10-7m/s

g. Key in the boundary conditions for Head = 7m, Head = 5m, Head = 4m and

Flux = 1.49x10-6 m/s.

2. By using polyline option sketch the model of earth dam following the given coordinates.

3. Draw regions

4. Assign the given material at every regions.

5. Assign the boundary condition for Head = 7m, Head = 5m, Head = 5m, Head = 5m and Flux =

1.49x10-6m/s.

6. Draw the mesh properties.

7. Run the analysis

8. Analysis Output

APPENDIX B

Question 4

1. Intergrate result from SEEP/W file to SLOPE/W. Use Name as Slope-BOJ.

2. Specify the analysis method

a. Grid and Radius Slip Surface and Bishop, Ordinary and Janbu method.

b. Checked the Tension Crack Line box

3. Save as SLOPE-Q4-gr.

4. Key in the material properties for both type of soils.

a. Silty Sand

i. = 20.4 kN/m3

ii. sat = 21.4 kN/m3

iii. = 27o

iv. c = 2 kN/m2

b. Clayey Sand

i. = 22.6 kN/m3

ii. sat = 24.4 kN/m3

iii. = 10o

iv. c = 5 kN/m2

c. Bedrock

5. Assign material slope model.

6. Assign surcharge load to the model.

a. Surcharge Load No. 1 = 9.81kN/m3.

b. Surcharge Load No. 2 = 120kN/m3.

7. Draw the tension crack line at 1.5m depth from crest of the slope.

8. Draw the radius and grid for slip surface option.

9. Run the analysis.

10. Analysis Output.

11. By using the same model, clone the model to SLOPE/W and change the Name to SLOPE-GLE.

12. Run the analysis.

13. Analysis Output.

14. For Entry and Exit Slip Surface Options, the procedures to model the slope are just the same

with Grid and Radius Slip Surface Options. Earlier we selected the entry and exit method to

control the location of the trial slip surfaces. Choose Slip Surfaces from the DRAW menu. Use

the curser to define zones where the slip surface will enter and then exit the ground surface

line.

15. Analysis Output.