1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
BE SEMESTER-V(New) • EXAMINATION WINTER 2016
Subject Code:2150609 Date:30/11/2016
Subject Name:Soil Mechanics
Time: 10:30 AM to 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1
Short Questions
14
1
Consolidation of soil is performed on type of soils.
2
If degree of saturation of a partially saturated soil is then its air content is
40%
60%
80%
100%
3
The coefficient of active earth pressure for a loose sand having an angle of internal friction of is
1/3
3
1
1/2
4
Select the incorrect statement
In a direct shear box test, plane of shear failure is predetermined
Better control is achieved on drainage of soil in triaxial compression test
Stress distribution on failure plane in case of triaxial compression test is uniform
Unconfined compression test can be carried out on all types of soils.
5
Bishop's method of stability analysis
Is more conservative
Neglects effect of forces acting on sides of the slices
Assumes slip surface as an arc of a circle
All of the above
2
6
Time factor for a clay layer is
A dimensional parameter
A dimensionless parameter
Inversely proportional to drainage path
Independent of thickness of clay layer
7
Rankine's theory of earth pressure assumes that the back of the wall is
Plane and smooth
Plane and rough
Vertical and smooth
Vertical and rough
8
Which of the following is the most accurate method of determination of water content
Calcium Carbide Method
Alcohol method
Oven Drying method
Sand Bath Method
9
Unconfined Compressive strength test is
Undrained test
Drained test
Consolidated test
Consolidated undrained test
10
Give full forms for CU CD test
11
Define Earth Pressure at rest
12
Coarse grained soils are best compacted by a
Drum roller
Rubber tyred roller
Sheep Foot Roller
Vibratory Roller
13
With increase in the amount of compaction energy
OMC increases but MDD decreases
OMC decreases but MDD increases
Both OMC and MDD increase
Both OMC and MDD remain the same.
14
What is pore water pressure?
Q.2

Differentiate between standard proctor and modified proctor test.
03

Explain the various factors affecting compaction.
04

A soil is compacted in a cylindrical mold with a volume of 1000 cc at
07
3
six different water contents, using the same compactive effort (Test 1). After compaction, the samples were extruded and weighed. The same test was repeated with a larger compactive effort (Test 2). The water contents and wet masses of the samples from the two tests are given below. All readings of weight are for wet mass in grams. Plot the water content vs dry density curves and compute MDD and OMC for the two and comment on your findings.
w
11
13
15
17
19
21
Test 1
1867
1956
2044
2106
2090
2036
Test 2
1937
2034
2108
2118
2097
2055
OR

Differentiate between the process of consolidation and compaction.
07
Q.3

Explain One Dimensional Consolidation using Spring Analogy?
03

Explain with the help of a neat sketch the procedure for determination of preconsolidation pressure?
04

The following readings were obtained from a consolidation test. Plot the values using square root of time fitting method and calculate the value of coefficient of consolidation if the initial specimen height is 20mm.

DDGR

DDGR

DDGR
0
500
3
133
9
63
0.5
442
4
110
10
51
1
211
5
95
11
40
1.5
178
6
84
12
33
2
154
7
80
13
23
2.5
142
8
76
14
14
07
OR
Q.3

Derive equation for stress distribution of soil under a point load as per Boussinesq's theory.
03

A water tank is supported by a ring foundation having outer diameter of 10m and inner diameter of 7.5m. The ring foundation transmits uniform load intensity of 160 kN/m2. Compute the vertical stress induced at a depth of 4m, below the centre of ring foundation, using
04
4
Boussinesq analysis, and Westergaard's analysis, taking

Explain Newmark's Chart and its application.
07
Q.4

Explain Modified Mohr Coulomb failure theory for shear strength?
03

Differentiate between Direct Shear Box and Triaxial Test.
04

A series of direct shear tests was conducted on a soil till failure occurred. The following are the results obtained. Find the shear strength parameters for the soil and find the values of principal stress and angle of principal planes for the normal stress of 0.2kg/cm2.
Sample No.
Normal Stress
Shear Stress
1
0.25
0.28
2
0.35
0.34
3
0.45
0.38
07
OR
Q.4

Explain various steps in selection of type of foundation for different structures.
03

Discuss in detail Rehbann's graphical method for determination of earth pressure
04

Give various objectives for carrying out subsurface exploration. Explain any one type of geophysical exploration method used in field alongwith its applications.
07
Q.5

Derive with the help of a neat sketch the factor of safety for infinite slopes for cohesionless soils (sand).
03

Explain Taylor's Stability Number in relevant terms.
04

Explain stepwise procedure for determination of FOS for finite slopes using method of slices
07
OR
5
Q.5

Differentiate between active and passive earth pressure with relevant examples.
03

A masonry retaining wall is 4m high. It has a vertical back with a horizontal sandy backfill upto the top, with a surcharge of 0.85kg/cm2. Determine the active pressure on the wall for the following condition: water table 1mt below the fill, with sand dry density of 1.85g/cc, moisture content above water table angle of internal friction 30 degree, specific gravity of sand 2.5, porosity of 30%
04

Explain Rankine's earth pressure theory for determination of lateral earth pressure under different conditions?
07