BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI HYDERBAD CAMPUS
Second Semester 2014-‘15 TEST 1 (CLOSED BOOK) - SOLUTIONS
Course No: CE F243 Course Name: Soil Mechanics Date: 21.02.2015 Maximum Marks: 45 Max Duration: 60 Min. Component Weightage: 15%
PART – I
I. Answer all the following questions on the main answer script [20x0.5=10]
1. ___________________ is popularly known as Father of Soil Mechanics (Karl Terzaghi)
2. Intrusive igneous rocks will have _________________ structure (Crystalline)
3. Desilication can be classified as ___________________ type of weathering (Chemical)
4. Fill the following
Type of the Soil Genesis
Alluvial Soils Running water
Lacustrine Soils Deposited in quiet lakes
Marine Soils Deposited in sea water
Aeolian Soils Wind
Colluvial Soils Gravitational force, as in land slides
Glacial Soils Deposited by Glaciers
5. If maximum portion of shear strength of the soil is contributed by angle of internal
friction, then that soil could be classified as ____________ (Sandy soils or sand or
cohesion less soils)
6. Specific Gravity of Clay is always ____________ than the specific gravity of sands
(More)
7. The index, which is defined as a ratio (LL – NMC)/(LL-PL) where LL is Liquid Limit, NMC
is Natural Moisture Content of the soil, PL is Plastic Limit; is known as ______________
(Consistency Index)
8. The ratio between dry density achieved in the field and that obtained in the laboratory is
usually known as ______________________ (Relative Compaction Density)
9. Show pictorially the densest particle arrangement possible for spherical shaped particles
10. During the conduct of plate load test, what is the standard size of the plate used (75cm
dia)
11. Write the expansion for SPT (Standard Penetration Test)
12. The fourth group of clay miners apart from Illite, Kaolinite, Montmorrilonite is
______________ (playgorskite)
13. Clay particles suspended as colloids are controlled by _____________ energy(Surface
Energy)
14. Unsymmetrical distribution of _____________crystals in clays make them polar
(Silicate)
15. It was found that the CBR at 5mm penetration is greater than CBR at 2.5mm penetration
levels in all the three trials being attempted, CBR at _____mm shall be considered as
the design CBR. (5mm)
PART II
Answer the following questions briefly [5x4=20]
1. Compare the variation of dry density with water content for cohesion-less soil (no fines),
and a well graded soil sample. Justify the reasons for the variations in the curves
S.No Compaction Curve of Well graded soil
Compaction Curve of Cohesion less soil (no fines)
1 (0.5)
(0.5)
2 Dry density is a function of water
content (0.5)
Little influence of water content on dry
density(0.5)
3 The dry density is maximum at
Optimum water content and it
varies with soil type
The maximum dry density is achieved at
fully saturated condition. Max. Bulking at
4% - 5% water content
3 Dry density increases with
increase in water content dry of
Optimum because the air voids
get reduced and Attractive forces
due to surface charges of soil are
predominant (0.5)
Dry Density reduces initially due to Bulking
of soil particles (there is an increase in
volume of voids and corresponding
reduction of dry density) (0.5)
4 For water contents wet of
Optimum compaction does not
reduce the air voids appreciably,
but the volume of voids filled with
water increases due to which the
dry density reduces. Repulsive
forces due to surface tension of
water is predominant in the soil
structure (0.5)
As the water content is further increased,
the bulking effect is reduced and the
increase in compactive effort breaks the
capillary tension and hydrostatic forces
overcome the effective pressure between
the soil particles. (0.5)
2. Define Zero air voids line and state the expression relating dry unit weight with water
content and degree of saturation. Compare the 10% air content line and 90% saturation
line using a suitable illustration
Zero Air Voids Line:
The theoretical curve which represents the fully saturated condition (S = 100 %), gives
the relation between water content and dry density for no air voids. It cannot be reached
by compaction (1)
Derivation: (2)
Wע d = Gע
(1+e)
Wע d = Gע
(1+Gw/S) Where G – Specific Gravity
e- Voids ratio w- water content S – Degree of Saturation
3. Discuss various states of the soil (with respect to consistency and volumetric changes)
with varied levels of water contents using a suitable illustration
Zero Air voids line
(0.5)
80% Saturation line
or 20% Air content
line (0.5)
4. Draw a neat diagram of dispersed structure and the usual structure of Montmorrilonite
minerals
5. Define briefly and write formulae for bulk density, dry density, density of solids, saturated
density and submerged density of soils.
PART III
Solve the following Numerical
1. A core cutter, 12.6 cm in height and 10.2 cm in diameter weighs 1071g when empty. It is
used to determine the in-situ unit weight of an embankment. The weight of the core
cutter full of soil is 2970g. If the moisture content is 6%, what are the in-situ dry weight
and porosity? If the embankment gets fully saturated due to heavy rains, what will be the
increase in water content and the bulk unit weight, if no volume change occurs. The
specific gravity of the soil solids is 2.69. [7.5]
2. Classify the composite soil having soil fractions as follows using textural classification
system. The Chart is appended with the paper [4.5]
Soil fraction with sizes ranging from 2mm to 4.75mm = 200gm
Soil fraction passing 0.05mm sieve and retained on 0.002mm sieve = 400gm
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