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DEC 302 – Geotechnical Engineering

DIPLOMA IN CIVIL ENGINEERING
GEOTECHNICAL ENGINEERING
(DEC 302)

ASSIGNMENT NO. 1

NAME

ID NO

LECTURER: NOORBAYA BINTI MOHD SALLEH
DATE OF SUBMISSION:

SEPT 2012

Page 1 of 4

DEC 302 – Geotechnical Engineering

QUESTION 1 [TOTAL = 50 MARKS]
a)

Indicate THREE (3) differences of short term stability and long term stability for slope failure analysis.
[CLO1-PLO2:C1] (6 marks)

b)

Discuss briefly THREE (3) methods of changing geometry of the slope for the purpose of slope stabilization.
[CLO1-PLO2:C2] (6 marks)

c)

Explain and illustrate briefly FOUR (4) types of slope failure. [CLO1-PLO2:C3] (8 marks)

d)

For the slope shown in Figure Q1 (d), find the factor of safety against sliding for the trial surface AC.

Figure Q1 (d)
[CLO1-PLO6:C4] (15 marks)

SEPT 2012

Page 2 of 4

DEC 302 – Geotechnical Engineering

e)

Figure Q1 (e) shows a slip circle. By using the method of slices for total stress analysis, calculate the factor of safety against slipping along failure surface AB for the following conditions:
i.
ii.

Allowing for the tension crack empty of water
Allowing for the tension crack when full of water

4m

γ = 21kN/m3
c = 10 kN/m2
ϕ = 12˚

PLO2:C3] (8 marks)
Figure Q1 (e)
[CLO1-PLO6:C4] (15 marks)

SEPT 2012

Page 3 of 4

DEC 302 – Geotechnical Engineering

QUESTION 2 [TOTAL = 50 MARKS]
a)

Discuss briefly the principle of Rankine’s active and passive state. [CLO2-PLO2:C2] (5 marks)

b)

A retaining wall with a smooth vertical back of height 9m retains soil having an unsurcharged horizontal surface. The position of water table is 5m from the bottom. The soil properties are:
c’ = 0

ϕ’ = 32˚

γsat = 20.5 kN/m3

and above WT, γ =18kN/m3

Determine the distribution of horizontal stresses on the wall and also the magnitude and position of the resultant horizontal thrust when the groundwater level is standing (without seepage flow) at 4.0m below the surface. [CLO2-PLO6:C4] (15 marks)

c)

The smooth vertical wall shown in Figure Q2 (c) supports a surcharge pressure of 30 kN/m2 placed on the ground surface. Neglecting the passive resistance in front of the wall, determine:
i)
ii)
iii)

The total active thrust on the wall and the position where it acts. The factor of safety against overturning and sliding.
Determine the distribution of ground bearing pressure under the base of the wall.

Figure Q2 (c)
SEPT 2012

Page 4 of 4

DEC 302 – Geotechnical Engineering

[CLO2-PLO6:C4] (15 marks)
d)

Figure Q2 (d) shows a cross-section of a reinforced concrete wall supporting a granular backfill with a uniform surcharge of 10 kN/m2 on top of it. i)

Check the stability of the wall against overturning about the toe (Ignore the passive resistance and the factor of safety required against overturning. FoS ≥ 2.0).

ii)

Check the stability of the wall against sliding along the base. (use base friction, δ = 25˚ and the reduction factor for the passive resistance, α = 0.5. the factor of safety required aganst slding, FoS ≥ 1.5).

iii)

Determine the distribution of ground bearing pressure under the base of the wall. Is the wall safe against bearing capacity failure if the allowable bearing pressure of the foundation soil is 150 kPa.

Figure Q2 (d)
[CLO2-PLO6:C4] (15 marks)

SEPT 2012

Page 5 of 4

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