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UNIVERSITY OF GLAMORGANPrifysgol Morgannwg

Examinations: MAIN ASSESSMENT SESSION 2010/11

Exam paper version number:

Module Code:CE2S24

Module Title:Geotechnics & Engineering Geology

Academic Registry Use:

Date and time

Duration: (multiples of 30 mins only)

3 hours

The following items are provided to Candidates:

Examination Books (inc 2 sheets of graph paper)2 sheets of tracing paper

Figures Q1A, Q1B, Q1C, Q2, Q3, Q5A and Q5BEquation sheets 8pages

Instructions to Candidates:YES NO

Calculators are permitted

English Dictionaries are permitted

English

Foreign Language Dictionaries are permittedThis examination paper is an OPEN book examination

If YES, please specify literature permitted: ___________________________________

Answer any FOUR questions

All questions carry equal marksThe mark allocation includes, where appropriate, an allowance for style,organization and clarity.Start on a new page for the solution of each question and any late additionalsolution to a question.

This paper contains a total of examination questions. over no. of pages

FOR EXAMINATIONS OFFICE USE ONLY

Module Leader Admin Check

Print Name: Dr Rod Robinson Melanie Gapper

Signature: Rod Robinson Mel GapperContact Number:

Continued

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QUESTION 1

a. Discuss the engineering requirements that would be considered necessary to enable

a shallow foundation to perform satisfactorily over its design life. 6 marks

b. A series of square pad foundations are required to carry individual column loads of

350kN as illustrated in Figure Q1A. The load on the foundation will be rapidly

applied.

Stating appropriate assumptions, use Figures Q1B and Q1C to:-,

i. establish the over-design factor for the foundation using the EC7 design

approach 1combination 2 (A2+M2+R1) and comment on its value and

ii. determine the new over-design factor if the load had an eccentricity of

0.15m along the breadth of the foundation and comment on the effect this

may have on the original design

13 marks

6 marks

Total marks for Question 1 25 marks

See Equation Sheet

please turn over

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QUESTION 2

a. Prove a relationship between the active coefficient if earth pressure, ka and theeffective angle of internal friction, ', for a granular soil. 8 marks

b. A cantilever sheet pile retaining wall is illustrated in Figure Q2. It is required as

part of the temporary works for the construction of deep foundations for a bridge

pier. The soil properties and a cross section of the wall are given in Figure Q2. The

uppermost surface is level with the top of the wall and will carry a surcharge of

10kN/m2. The water table is well below the base of the wall.

Stating appropriate assumptions determine the required length of the sheet pilewall.

12 marks

c. During the excavation the ground water was found to be 2m below the original

ground level. Discuss how this would affect the retaining wall design.

5 marks


See Equation Sheets

Please turn over

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QUESTION 3

a. Explain the effect the development of a tension crack would have on the slope

stability analysis on a trial slip surface. 4 marks

b. The slope profile and relevant soil properties for a total stress analysis on a trial

circular slip are given in Figure Q3 and Table Q3.

Stating appropriate assumptions determine the factor of safety using the (Swedish)

method of slices for the trial slip surface,:-

i assuming that a tension crack does not form,

ii if a tension crack 1.25m in depth forms near the crest of the slope and

iii comment on the stability of the slope, if necessary suggest suitable

remedial measures.

12 marks

5 marks

4 marks

Note: Return Figure Q3 with your answer book


See Equation Sheet

Soil Data:

= 20kN/m3

cu = 20kN/m2

u = 25

Table Q3

Please turn over

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QUESTION 4

An embankment consisting of 10m of fill is to be placed on 2m of gravel which

is underlain by 4m of clay resting on well jointed sandstone. The water table is at

the surface of the gravel.

Considering only the settlement of the clay layer determine:

a the ultimate oedometer settlement beneath the centre of the embankment. 6 marks

b the time from the start of construction to 90% of the ultimate oedometer

settlement of the clay if the construction period is 6 months.

6 marks

c the extra height on the embankment needed to create a surcharge in order to

halve the time taken to reach 90% of the settlement in part (a).

13 marks

Soil Data

fill (above and below the water table) = 18kN/m3

mv = 2.710-4m2/kN

cv = 0.7m2/year

Total Marks for Question 4 25 marks

See Equation Sheet

please turn over

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QUESTION 5

A sandstone quarry near Pontypridd is to be developed for road aggregate in a small

valley which runs east to west. The quarry can be developed on the side of thevalley that proves to be most suitable. The results of a site investigation revealed:

that overlying the rock is a 0.5m thick layer of glacial till.

the top 2m of the rock are of weathering Grade 2 and the remainder of

Grades 1 and 0 as shown in Eurocode 7.

the rock mass data indicated in Table Q5.

a Indicate the essential points of the Eurocode 7 rock weathering classification and

briefly explain why the weathering profile found in the site investigation is typical

of South Wales. 7 marks

b Using Figures Q5A and Q5B as appropriate, and the tracing paper provided, plot a

stereo net analysis of the data in Table Q5 and suggest a suitable plan for the quarry

with particular regard to the stability of the faces. Justify the decisions you have

made by reference to the structural analysis.

Return the tracing paper with your answer script.

18 marks

Dip (degrees) Bearing (degrees) (degrees)

Bedding planes 60 80 40Joint set 50 162 40

Table Q5


Return the tracing paper with your answer script

please turn over

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QUESTION 6

a. Explain, with sketches, why effective stress paths for soils tested in consolidated

undrained triaxial tests with pore pressure measurement curve to the left for

normally consolidated soils and to the right for over consolidated soils. 6 marks

b. A series of consolidated undrained triaxial tests with pore water pressure

measurements were carried out on four identical samples of normally consolidated

clay. All four samples were first consolidated at a confining pressure of 240kN/m2

and were then tested at the confining pressures shown in Table Q6.

i. Plot the modified total and effective stress failure envelopes and determine

the effective shear stress parameters.

ii. Sketch on the graph the total and effective stress paths for the four tests and

comment on them.

13 marks

6 marks

Confining pressure kN/m 40 60 120 240

Deviator stress at failure kN/m 88 100 130 188

Pore water pressure at failure kN/m -14 0 42 120

Results at failure for Consolidated Undrained Triaxial Tests

Table Q6


See Equation Sheet

End of Paper

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CE2S24 - Geotechnics & Engineering Geology

8

Soil Properties Foundation Properties

b = 18kN/m3.

sat = 20kN/m3.

c'= 0kN/m2

.'= 30.cu= 80kN/m

2.u= 0.

concrete = 24kN/m3.

UNIVERSITY OF GLAMORGANFaculty of Advanced Technology

Civil Engineering Scheme

Geotechnics & Engineering GeologyCE2S24

Figure Q1A

Scale: Not Required

0.5m

0.5m

B=1.25m

C

Axial LoadPermanent Load = 350kN

Pad FoundationWater Table

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Meyerhof Meyerhof Br Hansen Vesic EC7

Nc Nq N N N0 5.14 1.00 0.00 0.00 0.00

1 5.38 1.09 0.00 0.07 0.002 5.63 1.20 0.01 0.15 0.01

3 5.90 1.31 0.02 0.24 0.03

4 6.19 1.43 0.05 0.34 0.065 6.49 1.57 0.07 0.45 0.10

6 6.81 1.72 0.11 0.57 0.15

7 7.16 1.88 0.16 0.71 0.22

8 7.53 2.06 0.22 0.86 0.30

9 7.92 2.25 0.30 1.03 0.4010 8.34 2.47 0.39 1.22 0.52

11 8.80 2.71 0.50 1.44 0.66

12 9.28 2.97 0.63 1.69 0.84

13 9.81 3.26 0.78 1.97 1.05

14 10.37 3.59 0.97 2.29 1.29

15 10.98 3.94 1.18 2.65 1.58

16 11.63 4.34 1.43 3.06 1.9117 12.34 4.77 1.73 3.53 2.31

18 13.10 5.26 2.08 4.07 2.77

19 13.93 5.80 2.48 4.68 3.3020 14.83 6.40 2.95 5.39 3.93

21 15.81 7.07 3.50 6.20 4.66

22 16.88 7.82 4.13 7.13 5.51

23 18.05 8.66 4.88 8.20 6.50

24 19.32 9.60 5.75 9.44 7.66

25 20.72 10.66 6.76 10.88 9.01

26 22.25 11.85 7.94 12.54 10.59

27 23.94 13.20 9.32 14.47 12.43

28 25.80 14.72 10.94 16.72 14.59

29 27.86 16.44 12.84 19.34 17.12

30 30.14 18.40 15.07 22.40 20.09

31 32.67 20.63 17.69 25.99 23.59

32 35.49 23.18 20.79 30.21 27.72

33 38.64 26.09 24.44 35.19 32.59

34 42.16 29.44 28.77 41.06 38.37

35 46.12 33.30 33.92 48.03 45.23

36 50.59 37.75 40.05 56.31 53.40

37 55.63 42.92 47.38 66.19 63.18

38 61.35 48.93 56.17 78.02 74.90

39 67.87 55.96 66.76 92.25 89.01

40 75.31 64.20 79.54 109.41 106.05

41 83.86 73.90 95.05 130.21 126.74

42 93.71 85.37 113.96 155.54 151.94

43 105.11 99.01 137.10 186.53 182.80

44 118.37 115.31 165.58 224.63 220.7745 133.87 134.87 200.81 271.75 267.75

46 152.10 158.50 244.65 330.34 326.20

47 173.64 187.21 299.52 403.65 399.3648 199.26 222.30 368.67 496.00 491.56

49 229.92 265.50 456.40 613.14 608.5450 266.88 319.06 568.57 762.86 758.09

Bearing Capacity Factors for Strip Foundations




Figure Q1B

Scale: Not Required

Date: May 2011

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B=1.25m

C

Pad Foundation

UNIVERSITY OF GLAMORGAN

Faculty of Advanced TechnologyCivil Engineering Scheme

Geotechnics & Engineering Geology

CE2S24

Figure Q1C

Scale:

Not Required

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2.0




Figure Q2 Date:

Drawing not to scale

4.0m

dSoil 2C = 0

= 35

sat = b = 20kN/m3.

Originalground level

Soil 2C = 0

= 35

sat = b = 21kN/m3

Soil 1C = 0

= 30

sat = b = 20kN/m3.

New excavatedground level

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Equatorial equal-area stereonet marked in 2 intervals


Faculty of Advanced Technology

Geotechnics andEngineering Geology

CE2S242010-2011

FIGURE Q5A

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Polar equal-area stereonet marked in 2 intervals


Faculty of Advanced Technology

Geotechnics andEngineering Geology

CE2S242010-2011

FIGURE Q5B

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EQUATION SHEET

Lateral Earth Pressures

a

ok

cz

2

Consolidation

i

iic

i

ioed C

e

H10log

1

r

si

S

mGe

oed v im H d = (Hi +Hf)/4

'

1

21 11

1 H

HH

e

eem

i

fi

v ii H

H

e

e

1

When Uv 60% : Tv =

4 100

2Uv %

When Uv 60% : Tv = 1.781 - 0.933 log10 (100 - Uv%)

Tv =C t

d

v

2Cv = k/(mv w)

Tv50 = 0.197 & Tv90 = 0.848

Continued.

sin1

sin1aK

aaaba qKKczKp 2

h

pv

R

PRslidingFOS

tan

MomentsDisturbing

MomentsResistinggoverturninFOS

B

e

B

Rp v

b

61

if

fi

c

eeC

1010 loglog

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EQUATION SHEET (CONTINUED)Slope Stability

360

2 rLa

sin

costan

W

WLcF

uau

Bearing Capacity

idsqiqdqsqcicdcscf FFFBNFFFDNFFFcNq 5.0

Depth & inclination factors

Assume all depth and inclination factors = 1 for shallow foundations.

Shape factors

Shape of base Fcs Fqs F sLong strip 1.0 1.0 1.0

Rectangle 1 + 0.2B/L 1 + 0.2B/L 1 - 0.4B/L

Square 1.3 1.2 0.8

Circle (diameter B) 1.3 1.2 0.6

Skempton's Nc values Meyerhofs correction for eccentric loading

Nc = 5(1 + B/5L)(1 + D/5B) B = B 2e

Piles

In claybucsuf AcNAcQ

In sand

)1(tan qbsf NAAKQ

FoSQ E n

WLgroup NSF n

ui f

Continued.

We

RcF

r

u

2

yPeW

rLcF

w

au

BLNccLBDQ cbu 2

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EQUATION SHEET (CONTINUED)

Eurocode 7 Bearing Capacity Equations

N = 2 (Nq 1) tan ' (for a rough base, such as a typical foundation)s

q= 1+ (B' / L') sin ' (for a rectangular foundation)

sq = 1 + sin ' (for a square or circular foundation)s = 1 0.3 (B' /L') (for a rectangular foundation)s = 0.7 (for a square or circular foundation)

1

1

q

qq

cN

Nss (rectangular, square and circle foundation)

m

m

q

m

q

c

q

qc iicAV

Hi

N

iii

1

;cot

1;tan

1

WhereV = vertical load acting on foundationH = horizontal load (or component of inclined load) acting on foundationA' design effective area of foundation

L

B

L

B

mmB

1

2

when H acts in the direction of B';

B

L

B

L

mmL

1

2

when H acts in the direction of L'.

Stress Paths

Skemptons Equation 313 ABu

22

hvhv tands

= - u

103 K

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past paper 20102011

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