university of bolton rak academic centre beng …rak academic centre beng(hons) civil engineering...
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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
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 continued …
Table Q1a: Minimum factors of safety for shallow foundation
Table Q1b: Shape Factors
Question 1 continued over the page…
Page 4 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 continued …
Table Q1c: Bearing capacity factors
Page 5 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
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
University of Bolton RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module No. CIE6003
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
University of Bolton RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module No. CIE6003
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
Question 3 continued over the page…
Page 8 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 3 continued...
Figure Q3-1
Page 9 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 3 continued over the page…
Question 3 continued...
Figure Q3-2
Please turn the page
Page 10 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 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
University of Bolton RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module No. CIE6003
Figure Q4-1
Question 4 continued over the page…
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)
Please turn the page
Page 12 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 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
University of Bolton RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module No. CIE6003
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
University of Bolton RAK Academic Centre BEng(Hons) Civil Engineering Semester 2 Examination 2017/2018 Geotechnical Engineering and Ground Improvement Module No. CIE6003
ccwtt
cu
yzdW
RCF
...5.0.
)180
.(..
2
2
END OF PAPER