2014_geot2005_geotechnicalengineering1_december 2014.pdf

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December 2014 Final Examinations GEOT 2005

THE UNIVERSITY OF TRINIDAD & TOBAGO

FINAL ASSESSMENT/EXAMINATIONS DECEMBER 2014

Course Code and Title: GEOT 2005 GEOTECHNICAL ENGINEERING 1

Programme: BASc. IN CIVIL ENGINEERING

Date and Time:

Duration: 3 HOURS

PLEASE READ ALL INSTRUCTIONS CAREFULLY BEFORE YOU BEGIN THIS

EXAMINATION

Instructions to Candidates

1. This paper has 13 pages and 8 questions.

2. Candidates are required to answer any 5 questions.

3. All questions carry equal marks. Marks shown in brackets serve as a guide in allocating time

that should be spent on each part of the question.

4. Candidates must pass this paper since a failure will lead to the failure of the course.

5. Calculations are to be presented clearly and tidily and NOT in pencil.

6. All sketches should be neat and well labeled.

7. A non-programmable calculator is allowed.

8. Candidates MUST return the Question Paper along with your Answer Booklet to the

Invigilator at the end of the examination.

Key Examination Protocol

1. Students please note that academic dishonesty (or cheating) includes but is not limited to

plagiarism, collusion, falsification, replication, taking unauthorised notes or devices into an

examination, obtaining an unauthorised copy of the examination paper, communicating or

trying to communicate with another candidate during the examination, and being a party to

impersonation in relation to an examination.

2. The above mentioned and any other actions which compromise the integrity of the academic

evaluation process will be fully investigated and addressed in accordance with UTT’s

academic regulations.

3. Please be reminded that speaking without the Invigilator’s permission is NOT allowed.



Question 1

In order to determine the unit weight of a clay soil an undisturbed sample was taken in a

sampling tube of volume 0.001664 m3.

The following data were obtained:

Mass of tube only = 1.864 kg

Mass of tube and clay sample = 5.018 kg

Mass of tube and clay sample after drying = 4.323 kg

The specific gravity of the solids was determined to be 2.69.

Determine the following:

(a) Bulk Unit Weight (1 mark)

(b) Dry Unit Weight (1 mark)

(c) Moisture Content (1 mark)

(d) Air Voids Content (2 marks)

(e) Void Ratio (2 marks)

(f) Porosity (1 mark)

(g) Degree of Saturation (2 marks)

(h) Discuss the importance of soil testing to the Structural Design Engineer. Include a local

example to illustrate this importance. (5 marks)

(i) Discuss the importance of soil testing to the Construction Site Engineer. Include a local

example to illustrate this importance. (5 marks)

Question 2

The soil ground conditions at a building site in Sand Fernando are given below.

0-1 m Top Soil Bulk Unit Weight 15 kN/m3

1-4 m Fine Sand Bulk Unit Weight 16 kN/m3

Saturated Unit Weight 17 kN/m3

4-8 m Clay Saturated Unit Weight 22 kN/m3

Below 8m Medium Sand

The water table is 3m below the ground surface.

(a) Determine, with the aid of separate profiles, the variation of stressed with depth.

(15 marks)

(b) Illustrate the importance and use of this data, and analysis, to the Geotechnical Engineer.

(5 marks)



Question 3

In a Standard Compaction test on a soil, of specific gravity 2.67, the following results were

obtained:

Water content (%) Mass (g)

12.8 1890

14.5 2130

15.6 2200

16.8 2210

19.2 2160

The volume of the mould is 1000 cm3.

(a) Determine:

i. The maximum dry density obtainable under standard test conditions and the water

content at which this occurs. (10 marks)

ii. The percentage air voids and degree of saturation at optimum water content.

(5 marks)

(b) Discuss the techniques of quality control for field compaction of a highway, including the

part played by these results. (5 marks)



Question 4

A set of particle size distribution analyses on 3 soils, A, B and C, gave the following results:

Seive size (mm) Percentage passing

Soil A Soil B Soil c

20 100

10 97.2

6.3 91.5

2 76.5

0.6 55.0 90

0.425 35.8 75

0.300 24.3 10

0.212 16.7 3

0.150 7.0 0 100

0.063 2.0 1 91

A pipette analysis on Soil C gave the following results:

Particle sizes (mm) Percentage passing

Soil c

0.04 77

0.02 63

0.006 50

0.002 40

Soil C was found to have a liquid limit of 35 % and a plastic limit of 20 %.

Plot the particle size distribution curves and classify each soil. (20 marks)



Question 5

In an oedometer test on a specimen of saturated clay (Gs = 2.72), the applied pressure was

increased from 200 to 400 kPa and the following compression readings recorded:

Time (min) Gauge (mm)

0 7.82

1/4 7.42

1/2 7.32

1 7.21

2 1/4 6.99

4 6.78

6 ¼ 6.61

9 6.49

16 6.37

25 6.29

36 6.24

49 6.21

64 6.18

81 6.16

100 6.15

300 6.10

1440 6.02

After 1440 min, the thickness of the specimen was 16.25mm and the water content 24.8%.

Determine the values of the:

Coefficient of consolidation (10 marks)

Compression ratios (6 marks)

Coefficient of volume compressibility (2 marks)

Coefficient of permeability (2 marks)

Question 6

(a) A long embankment 30 m wide is to be built on layered ground as shown below. The net

vertical pressure applied by the embankment if 90 kPa. The soil profile and stress

distribution beneath the center of the embankment are shown below. The value of mv

for the upper clay is 0.35 m2/MN, and for the lower clay mv = 0.13 m2/MN.

Determine the final settlement under the center of the embankment due to consolidation of the

clay. State all assumptions. (10 marks)

(b) Give a detailed (with sketches) practical field solution to accelerate the rate of

consolidation. (5 marks)

(c) (c) Give a detailed (with sketches) practical field solution to compensate for the very

compressible ground. (5 marks)



Question 7

(a) Sketch the shearing force/deformation curves one would expect from shear box tests on

(i) loose sand

(ii) compacted sand. (2 marks)

(b) Shear box tests on compacted sand gave the following results:

Normal Load

(N)

Shear Load Peak

Value (N)

Shear Load Ultimate Value

(N)

90 85.6 55.1

225 215.4 143.0

350 343 230

The shear box measured 60 mm square.

Find the angle of shearing resistance of the sand

(i) in the compacted state

(ii) when loosened by the shearing action. (16 marks)

(c) Explain why compaction alters the angle of shearing resistance of sand. (2 marks)

Figure 1 Question 6



Question 8

(a) The results shown were obtained for peak failure in a series of triaxial tests on specimens

of saturated clay. Determine the values of the stress parameters.

Cell Pressure during

consolidation and

shear

(kN/m2)

Deviator Stress

(kN/m2)

Pore Water Pressure

(kN/m2)

200 117 110

400 242 227

800 468 455

(8 marks)

(b) List and explain in detail the principal types of triaxial tests. (6 marks)

(c) Outline a practical field application of each test. (6 marks)



Formulae Sheet



Particle Size Distribution Paper



Semi-log Graph Paper

2014_geot2005_geotechnicalengineering1_december 2014.pdf

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