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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2011
Module Title: Geotechnical Engineering
Module Code: CIVL
School: Civil, Structural and Environmental Engineering
Programme Title: Bachelor of Engineering in Civil Engineering – Year 3
Programme Code: CCIVL_7_Y
External Examiner(s): Mr J. Murphy, Ms. M. Kyne
Internal Examiner(s): Ms. Norma Hurley
Instructions: Answer FOUR Questions. Please state the units of each numerical answer
Duration: 2 hours
Sitting: Semester 2 2011
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
Q1 The cross-section of a proposed concrete retaining wall is shown below in Fig. Q1. The unit weight of the concrete is 24 kN/m^3. Determine the factor of safety against overturning , the factor of safety against sliding (ignoring passive resistance) and the vertical bearing stress imposed on the soil for the following conditions:
(a) supporting cohesionless soil, fully drained c’ = 0 kN/m^2 , φ = 35o, γ = 22 kN/m^3 (10 marks)
(b) supporting a cohesive soil, assuming that cracks will develop in the tension zone. cu = 21 kN/m^2 , γ = 18 kN/m^3 (10 marks)
(c) Comment on the differing results for the two soil types. (5 marks)
Useful formulae:
FOSsliding =
PA
V tan
FOSoverturning = o
s
M
M
V x = Ms - Mo
qmax = 2
B
Ve
B
V
(trapezoidal distribution) z =
2 c u
qmax =
x
V
(triangular distribution) FOSsliding = A
u
P
cB
Fig Q all dimensions in metres
Useful formulae
T
c L c L N N
F A A B B A B
( ' ' ) (tan' ' tan ' ')
W ( 1 h 1 2 h 2 ) b
T W sin
All dimensions in metres
Q5 (a) What factors should be considered in the design of a slope? (10 marks)
(b) Adopting a factor of safety of 1.5, determine the maximum permissible angle for a slope in the following sandy soil, γ=20 kN/m 3 ; c′= 0; φ′=36° (15 marks)
i) When dry
ii) When just waterlogged, with steady seepage parallel to the surface
iii) Calculate the factor of safety of the waterlogged slope against failure along a slip plane parallel to the surface at a depth of 4 m if at this depth there is a thin layer of cohesive soil with the following properties. γ=18 kN/m^3 ; c ′= 12 kN/m^2 ; φ′=24°
Useful Formulae:
tan
'tan '
F
sin cos
' ( )cos^2 tan '
z
c z h
F w
