Geotech Questions

8/13/2019 Geotech Questions

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GeotechExplain the term adsorbed water?Ans:- The layer of water which surrounding the clay crystal arecalled adsorbed water.

Discuss factors affecting compaction in the field?

Ans:- Factor affecting compaction are the following: -

i) Compaction effort

ii) Water content

iii) Method of compaction

iv) Type of soil

Explain Stoke s Law?

Ans Stokes law: - The constant terminal velocity of sphericalparticle settling through an infinitely large medium is given as :

V = (Ys Yl)xD2/ 18

Ys= unit weight of settling solidsYl = unit weight of liquid suspensionD =Diameter of settling solids= Dynamic coefficient of velocity


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Explain Earth pressure at rest?

Ans When the retaining wall is rigid and unyielding, the soil is in thestate of rest and there are no deformations and displacements theearth pressure corresponding to this state is called earth pressureat rest.

Explain the concept of OMC?

Ans The water content corresponding to the maximum dry unitweight is called optimum moisture content(OMC).When soil iscompacted at certain moisture content bulk density is found and atthat moisture content dry density is computed as OMC.

Q.8. What are the limitations of Direct Shear test?

Ans Limitations

1. The plane of failure is predetermined which may not be theweakest plane.2. The stress conditions are known only at failure hence it is difficultto plot the Mohrs circle.3. The distribution of the stress on failure plane is not uniform.4. There is no mechanism to measure pore pressure.5. There is no control over drainage conditions.6. The test is suitable for sands under drained conditions.


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Differentiate between Consolidation and compaction?

Ans Difference between compaction and consolidation:-

Compaction Consolidation

1. It is almost an instantaneous

phenomenon

1. It is a time depend

phenomenon2. Soil is always unsaturated 2. Soil is completely saturated

). Densification is due to a reductionin the volume of air at given water

content

3. Volume reduction is due toexpulsion of pore water from voids

(4). Specified compaction techniqueare used in this process

4. Consolidation occurs onaccount of a load placed

on the soil.

Write name of tests used for determination of in-situ unitweight?

Ans The following tests are used to determine in-situ unit weight

a) Core cutter methodb) Sand Replacement method

c) Water Displacement method.


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What are soil aggregate properties?

Ans-Soil aggregate properties are those properties which are

depends on the soil mass as a whole and, thus, represent the

collection behavior of a soil . Soil aggregate properties are

influenced by soil stress history, mode of soil formation and the

soil structure. Soil aggregate properties are of greater significance

in engineering practice, Since engineering structure are foundedon undisturbed, natural soil deposit.

Distinguish between normally consolidated and over-consolidated soil?Ans-Normally Consolidated Soil:-A soil is said to be normally consolidated when the existing effectivestress is the maximum that it has ever experienced in its stresshistory.

Over Consolidated Soil:-A soil is said to be over consolidated , if the existing effective stressis less than the pre consolidation stress.


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What is passive earth pressure?Ans- In retaining wall if the wall pushed towards the backfill theresultant pressure is passive earth pressure.

Define plastic limit?

Ans- Plastic limit: - In Plastic Limit consistency change from semisolid stage to plastic stage. If soil is rolled into threads of 3mm diathan at plastic limit crack just start to appear.

Give any two assumptions of wedge theory?Ans Assumptions:-1.Coulomb considered equilibrium of entire wedge.2.The backfill is dry, homogeneous, cohesionless and isotropic.

3.The backfill of wall assumed rough.

What is Flow index ?Ans The slope of curve between water content & no. of blows iscalled flow index.

What is Base Exchange Capacity?

Ans- Base (cation) Exchange capacity:- The ability of clay particleto adsorb ions on its surface or edge is called its base or cation


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exchange capacity which is foundation of the mineral structure ofthe clay and the size of the particle .

What is relative compaction?

Ans- Relative compaction is defined as the ratio of the field dry unitweight , yd(field)to the laboratory maximum dry unit weight, y(dmax)asper specified standard test, namely Indian standard light or heavycompaction test.

Relative compaction=Yd(field)/ Yd(max)

What is compaction of soil?

Ans- Compaction of soil :- Compaction is an instantaneous processin partially saturated soils by which density is increased byincreasing external pressure.

What is relative density?

Ans- Relative density : (Id) Relative is also called degree of densityor density index. It on index which quantifies the degree of packingb/w the loosest and densest possible state of coarse grain soil it isdetermine experimentally

emax = maximum void ratio

enat= natural void ratio

emin= minimum void ratio


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Name Methods to determine the water content?a) oven drying method

b) pycnometer method

c) calcium carbide method

d) sand bath method

e) alcohol method

f) torsion balance method

Q: - The atterberg limit of a clays soil are liquid limit 63%, plasticlimit 40%, and shrinkage limit 27% & natural moisture content is50%, determine shrinkage index, plasticity index, consistency index

, liquidity index.

Shrinkage index = Is= WpWs

= 40 -27


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= 13

Plasticity index Ip= Wl Wp

= 63 40

= 23%

Consistency index Ic= Wl Wn/ Wl Wp

= 63 50 / 63 40= 0.56

Liquid index IL= Wn Wp/ Wl Wp

= 50 40 / 63 40

= 0.434

3

.

, .

()

()

0.4 (11 ) 0.9 2.70

49 (33 ) 0.75 2.64

915 (44

)

0.60 2.70


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(1) (1) 9.81 13.94 /

3

(2) (2)

9.81 18.58 / 3

(3) (3)

9.81 19/ 3

(4) (4)

9.81 20.2 /3

(1) (1)

1 13.94 3 41.82 /2

0

41.82 0

41.82/2

(2) (2)

1+ 1 13.943+18.581 60


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9.81 1

9.81

60 9.81

50.59/2

(3) (3)

1+ 1 + 2

13.943+18.581+195

41.82 + 18.58 + 95

155.4/2

9.81 1 + 98.1 5

58.86

155.4 58.86

96.54/2

(4) (4)

41.82 + 18.58 + 95 + 20.2 6

276.6/2

58.86 + (9.81 6) 117.72


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( ) 276.6117.72/2

=158.88kn/m2

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