Cork Institute of Technology
Bachelor of Engineering (Honours) in Structural Engineering - Award
(Bachelor of Engineering in Structural Engineering – Award)
(NFQ – Level 8)
Autumn 2005
GEOTECHNICAL AND FOUNDATION ENGINEERING
(Time: 3 Hours)
Answer five questions Examiners: Mr T Corcoran
Dr Prof P O’Donoghue
Mr J P Murphy
1. (a) An embankment has the profile shown in Fig Q1. The unit weight of the soil
γ
= 19.2
kN/m3, its apparent cohesion c
′
is 6.75 kN/m2 and its angle of shearing resistance
φ′
is 17°.
Assuming tension cracks do not develop, determine the factor of safety with respect to
shear strength against failure along the slip circle with centre O. (Use four strips as shown).
(12 marks)
(b) There is the possibility of a seepage pressure developing in the soil mass of the
embankment. Assuming that the values of
γ
, c
′
and
φ′
remain unchanged and that u=0.2
γ
h,
where h is the mid-height of the strip being considered, determine the percentage reduction,
due to pore water pressure, in the factor of safety associated with the same slip circle.
(8 marks)
Fig Q1
2. (a) Determine the total active thrust on the back of a smooth vertical wall, 6 m high which is
supporting granular backfill with
γ
= 19 kN/m3 and
φ
= 33°. The soil surface is horizontal
and there is a surcharge of 12.5 kN/m2 and the water table is well below the base of the
wall.
(6 marks)
(b) If the water table in part (a) rises to 1.8 m below the top surface, what is the total active
thrust? Assume
γ
sat = 20 kN/m3.
(7 marks)
