State the correct answer. Also, provide reasons to justify the statement in your

Question

State the correct answer. Also, provide reasons to justify the statement in your answer book along with the question number. (i) The submerged density, gamma_sub (or gamma) can be lower than the unit weight of water, gamma_w T F (ii) The liquid limit of a soil cannot be greater than 100%. T F (iii) A well graded soil has a higher coefficient of permeability than a poorly granded (or uniform) soil. T F (iv) The pore-water pressure in a normally consolidated clay sample is always positive. T F (v) The triaxial shear test apparatus is a versatile equipment and can be used for determining the shear strength of soils under different loading conditions for all soils including sands and clays (i.e., UU, CU and CD conditions) T F

Explanation / Answer

1.) FALSE.

Submerged unit weight cannot be less than unit weight of water.

when the soil exists below water, it is in submerged condition. A buoyant force acts on the soil solids. According to archimedes principle, the buoyant force is equal to the weight of water displaced by the solids. The net mass of the solids reduced. The reduced mass is known as Buoyant mass or submerged mass.

The weight of the water in the voids has a zero weight in water, as the weight of the water and the bouyant force just balance each other. When submerged all the voids are assumed to be filled with water. So if it is less than unit weight of water its going to float.

2.) TRUE (Case 1) FALSE (Case 2 )

Case 1. Definition of Liquid limit: Liquid limit is the water content at which the soil is sufficently fluid to flow when the device is given 25 blows.Water content may be greater than 100%

Case 2. It may be liquidity index 100% and liquidity index cannot be > 100% as it does not exist.

3.) FALSE

Well-graded soil means the soil sample consists of different sizes of particles (combination of different sized particles). As they contain different sized particles the voids between the large sized particles are filled by small sized particles and voids formed by them are filled by further small particles. In this way the voids are reduced in the case of well-graded soils which in turn reduces the coefficient of permeability. But this doesn't happens in the case of uniform soils as they all same sized particles.

Coefficient of permeability of Well Graded soils < Coefficient of permeability of Uniform Soils

4.) FALSE

What ever may be the soil pore water pressure is always negative except in case of porewater pressure due to wetting of soil above the GWL due to cappilarity.

Effective Stress = Total stresss - Pore water pressure

5.) TRUE

Yes, it suitable all conditions and all drainage conditions can be well controlled. It is a versatile appartus as it is a developement after other equipment.

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