THE UNIVERSITY OF HONG KONG
M.SC.(ENG.) EXAMINATION
DEPARTMENT OF CIVIL ENGINEERING
FOUNDATION ENGINEERING CIVL 6027
May 6, 2019 (Monday) TIME: 6:30 PM - 8:30 PM (2 hours)
Answer ALL questions in both Sections.
Use a separate answer book for each section.
Use of Electronic Calculators:
Only approved calculators as announced by the Examinations Secretary can be used in this
examination. It is candidates' responsibility to ensue that their calculator operates
satisfactorily 型 and candidates must record the name and type of the calculator used on the front
page of the examination script.
Page 1 of 4
SECTION A (Total 50 marks)
Question 1 (25 marks)
Answer the following questions.
(a) Comment on the major sources of uncertainties in foundation design and the ways to
account for these uncertainties. (5 marks)
(b) Vesic (1963 ; 1973) investigated the failure pa位em of shallow foundations in sand by
conducting model tests. The results, shown in Figure 1, indicate that while shallow
foundations can fail in 組y of the 伽ee modes, deep foundations (Dr/B greater than
about 4.5 ）位e always governed by punching shear failure. Explain this observation
based on soil mechanics theories. (5 marks)
(c) Discuss the ways to reduce settlements of shallow foundations. (5 marks)
(d) Discuss the set國up and relaxation effects associated with pile driving and comment on
the importance of consideration of these effects in pile load testing. (5 marks)
(e) Examine the sketch in Figure 2 and identify whether the use of pile foundation is
appropriate or not. State your reasons and design considerations. (5 marks)
Relative density, Dr
0.2 0.4 0.6 0.8 1.0
。
l mun ’nea...v
um 治
hh
σb
F、
d
--
曲、。
2
///\V//\\
∞法 滋滋滋夠
Fill
3
Sand
4
Results from Vesic (1963 ; 1973)
Soft clay
5
Figure 1 Figure 2
Question 2 (25 marks)
Consider a bored pile of 1 m in diameter and 15 m long, installed in stiff clay. The shaft
capacity of the pile is determined to be 1000 kN and the base capacity is determined to be 500
股..J. Assume that the shaft capacity is fully mobilized at a displacement of 0.5% of the pile
diameter while the base capacity is mobilized at a displacement of 5% of the pile diameter and
that the load settlement curves for both shaft and base resistance 位e linear up to failure.
Page 2 of 4
(a) Estimate and draw the complete load settlement response of the pile. (8 marks)
(b) For a working load of 600 kN, estimate how much of the load is carried by pile shaft
and how much is carried by pile base, and estimate the pile settlement at this working
load. (10 marks)
(c) For a working load of 1100 kN, estimate how much of the load is carried by pile base
and estimate the pile settlement. (7 marks)
SECTION B (Total 50 marks)
Question 3 (25 marks)
3(a) Figure below shows a cantilever wall of a retaining height of Hand an embedded
depth of 1.2d. The wall ’s factor of safety against overturning is F The wall is located
in a site of cohesionless soil with no groundwater. The active pressure coefficient of
the soil is Ka and the passive pressure coefficient of the soil is Kp. No wall friction is
assumed. Use the simplified method to derive a formula showing the relationship
between FoS, Ka, K~H and d. (15 marks)
3(b) You 位e required to assess the factor of safety against overturning failure of the single
level propped embedded retaining wall shown below. (10 marks)
Page 3 of 4
Wall:
Frictionless wall back assumed; retaining height = 10 m ; embedded length = 15 m
Soil parameters:
Ka =0.3; Kp = 3 ; unit weight = 20 kN/m3
Groundwater:
On the retained side, the groundwater table is on the ground level.
Within the excavation, the groundwater table is on the excavation level.
Seepage is assumed.
Question 4 (25 marks)
4(a) Please discuss and comp訂e the following types of embedded retaining walls with
respect to their stiffness, suitability in different ground conditions, water tightness,
working space requirement, and construction time, etc. (20 marks)
(i) Sheet pile wall
(ii) Soldier pile / pipe pile wall
(iii) Bored pile wall
(iv) Diaphragm wall
4(b) The following chart is typically used in the assessment of hydraulic stability of an
excavation. Please explain, based on engineering principles, why the factor of safety
against hydraulic failure (5 marks)
’,1/
、
．唔，A
increases with the wall penetration depth; and
‘’，
／． ，1
’,/ ..
、、
﹒ 旬，
F
increases with the width of excavation.
A
1 /
2.0
E ︱
有叫月斗汗
”,
、
El
－
、。
－ －
l！
..
、、
、、
、、
’
87
.
、
一－
、、
、
主主、℃
斗小，︱︱ 一－
..
、
℃、h也
、、
JUM 叫－
、
Ef
骨 、
1.5
、、
片斗川 L
、、
－－－
、
、
v」D
O心工
－－
』『
J
－U
﹒
d帆 2
4
心江 COZO
UZOV的。」h
～－ι
』扭曲chva
－－～～一一
℃Z 缸。
一－－－－－ 1.s---
2.0
z
。5
Leg@nd .
- - -- Lo 。sesand Factor or s且fety against ，，刻，
ht!qving 10 loost! S口 nd or /
一一－ Dense sond
-1. I
0 1.0 2.0 3.0 4.0
Notes: Assumptions in your answers should be stated clearly on your answer books.
- END OF PAPER-
Page 4 of 4
