UNIVERSITY OF BOLTON RAK ACADEMIC CENTRE BEng …RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module

OCD041

UNIVERSITY OF BOLTON

RAK ACADEMIC CENTRE

BEng (HONS) CIVIL ENGINEERING

SEMESTER TWO EXAMINATION 2017/2018

GEOTECHNICAL ENGINEERING AND GROUND IMPROVEMENT

MODULE NO: CIE6003

Date: Tuesday 29 May 2018 Time: 10.00am -1.00pm INSTRUCTIONS TO CANDIDATES: There are FIVE questions on this

paper. Answer any FOUR questions. All questions carry equal marks. Marks for parts of questions are

shown in brackets. This examination paper carries a

total of 100 marks. Formula sheet/supplementary

information is provided at the end question paper.

All working must be shown. A

numerical solution to a question obtained by programming an electronic calculator will not be accepted.

Page 2 of 14

University of Bolton RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module No. CIE6003

Question 1 (a) A thorough site investigation was conducted in a barren clayey area to build a

warehouse. Rectangular foundations of 3m wide and 4m long were designed,

which is to be laid at 2.1m below ground level in a thick deposit of firm saturated

clay. From a subsurface exploration conducted, the water table was found to be

steady at a depth of 1.8m. The soil at the site has the following properties.

γ sat=20kN/m3, u= 00 , = 300 , cu =23kN/m2 and c’ =2.5kN/m2

i) Determine the ultimate bearing capacity and the net safe bearing capacity of

soil immediately after construction

(8 marks)

ii) Determine the ultimate bearing capacity and the net safe bearing capacity

of soil 25 years after construction

(7 marks)

iii) Comment on the critical situation for soil’s bearing capacity

(2 marks)

NOTE: Clearly state any assumptions made in your calculations to determine the

safe bearing capacity. Refer the Tables Q1a, Q1b and Q1c on Pages 3 and 4.

(b) The bearing capacity of soil is the maximum average contact pressure between

the foundation and the soil which governs the design of foundation. Bearing

capacity is affected by various factors like change in level of water table,

eccentric loads, inclined loads, dimensions of the footings, etc. Explain with the

help of sketches how the position of ground water has a significant effect on the

net safe bearing capacity of soil.

(8 marks)

Total 25 marks

Question 1 continued over the page…

Page 3 of 14


Question 1 continued …

Table Q1a: Minimum factors of safety for shallow foundation

Table Q1b: Shape Factors


Page 4 of 14


Question 1 continued …

Table Q1c: Bearing capacity factors

Page 5 of 14


Please turn the page

Question 2

The details of the subsoil conditions at a site are shown in Figure Q2a on

page 6 together with the details of the soil properties. The ground surface is

subjected to a uniform loading of 60kPa and the groundwater level is 1.8m

below the ground level. It can be assumed that the gravelly sand has a degree

of saturation of 50% and that the clay layer is fully saturated.

(a) Determine the distribution of Effective stress, Pore Water Pressure and Total

Stress at each soil strata. Hence plot the diagram to illustrate the variation of

total stress and the effective stress with depth from ground surface to a depth

of 7.8m below ground level.

(10 marks)

(b) The following results were obtained from an oedometer test on a specimen of

saturated clay from the clayey layer above:

Table Q2

Applied stress σ

(kN/m²) 0 50 100 200 400 600 800

Void ratio (e) 1.5 1.3 0.98 0.86 0.75 0.67 0.59

Plot the e / σv’ curve using the values provided in Table Q2 on the graph

paper provided.

(5 marks)

(c) Determine the coefficient of compressibility, mv for the effective stress range

at 200kN/m² with respect to the soil conditions before the loading of 60kPa on

the ground as mentioned in Question 2

(7 marks)

Page 6 of 14


Question 2 continued over the page… Question 2 continued …

(d) Calculate the consolidation settlement for the layer of clay having a layer

thickness of 6m as shown in the Figure Q2a. (3 marks)

Total 25 marks

FIGURE Q2a

Please Turn the Page

Page 7 of 14


Question 3

a) A concrete pile of 450 mm diameter is driven to a depth of 16 m through a

layered system of sandy soil (c = 0). Water table is close to the ground

surface.

The following data are available:

Top layer 1: Thickness = 8 m, = 10.36 kN/m3 and = 33°

Layer 2: Thickness = 6 m, = 10.57 kN/m3 and = 35°

Layer 3: Extends to a great depth, = 10.05 kN/m3 and = 37°

Determine the safe working load of this pile by adopting factors of safety of

1.5 and 2.5 for the shaft and end bearing resistance respectively .Use

Figures Q3-1, Q3-2 provided on page 8 and 9 respectively.

(18 marks)

b) In the above scenario if the pile is constructed as a bored and cast-in-situ pile,

how will that affect the pile capacity? Estimate the pile load capacity and

illustrate your answer with the help of equations if all the other data remain the

same.

(7 marks)

Total 25 marks


Page 8 of 14


Question 3 continued...

Figure Q3-1

Page 9 of 14



Question 3 continued...

Figure Q3-2


Page 10 of 14


Question 4

a)

A deep cut of 400 slope is excavated to a depth of 8m in a layer of saturated clay

for the construction of a road. On inspection, the slope is found to have tension

crack behind the crest of the slope as shown in Figure Q4-1.

The clay is having strength parameters as follows:

Undrained cohesion cu = 60 kN/m2

Saturated unit weightsat= 19 kN/m3.

Using rotational analysis of the trial slip circle, compare the factor of safety

against the short term failure for the two situations outlined below.

i. If a dry tension crack is present

(5 marks)

ii. If a water filled tension crack is present (7 marks)

iii. Explain how inspection of the proposed development area can reveal the

presence of past or current mass movements.

(6 marks)

2 m

Page 11 of 14


Figure Q4-1


Question 4 continued…

b)

An earthen reservoir with side slope has water levels at A throughout the year

as shown in Figure Q4-2. Discuss the consequences, if a sudden drawdown

of the water surface causes the water level to drop from level A to B. Use

suitable equations and sketches to support your findings.

Figure Q4-2

(7 marks)


Page 12 of 14


Question 5

a) A retaining wall of 6 m height having 2m width at its top and 3m width at its base retains a backfill made up of two strata as shown in Figure Q5a . Assume the backfill above the water table remains dry. State any assumption you have made. Relevant Parameters:

Ground water level: 2.0 m below retained surface

i. Construct the active earth pressure diagram and find the magnitude and

point of application of the resultant thrust.

(13 marks)

ii. Determine the Factor of Safety against overturning (ignore water pressures

on the base of the foundation). Comment on the value obtained.

(5 marks)

Figure Q5a.

b) Discuss how the introduction of ‘Key’ in retaining walls is affecting the factor

of safety of retaining wall. Explain using suitable diagrams and equations.

(7 marks)

Total 25 marks

END OF QUESTIONS

Page 13 of 14


Please turn the Page for Supplementary Geotechnical Information

Supplementary Geotechnical Information

Earth Pressure:

sin1

sin1

ak

Consolidation: ∆H = mv ∆σ’ Ho

Shallow Foundations:

Terzaghi’s equation: SBNSDNSCNq qqccu 5.0

When water table at depth <D

DF

Dqq u

safenet

capacitybearingaffectingistablewaterwhenwsatsub ,

Pile Foundations,

D

AKQANQsoilssscohesionleFor

ACQANCQsoilsCohesiveFor

QQQ

v

bvssbvqb

susbcub

bsu

.

..tan.,'..,

.,,

Slope Stability,

Page 14 of 14


ccwtt

cu

yzdW

RCF

...5.0.

)180

.(..

2

2

END OF PAPER

Documents

UNIVERSITY OF BOLTON RAK ACADEMIC CENTRE BEng …RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module