11 Answer true or false to the following For credit where ne

1.1 Answer true or false to the following. For credit where necessary correct. 18 points a) In a flow net the hydraulic gradient is constant across all squares b) Determinations of the liquid limit and plastic limit are conducted to differentiate between a sand and a clay c) The smaller the coefficient of consolidation, the faster the consolidation process d) Ko is the ratio of total horizontal stress to the total vertical stress e) Terzaghi\'s consolidation theory relies on the hypothesis that the soil is fully saturated f The specific surface of clay particles is greater than that of sand particles g) The elastic solution for the stresses induced under the center of a uniformly loaded circular area indicates that the vertical stress increment increases with the Young\'s modulus of the elastic medium a) Compaction specifications can require values of the relative compaction (RC) greater than 100% b) For a given soil the discharge velocity is always smaller than the seepage velocity c) An oedometer test typically lasts several days d) The greater the drainage height, the faster the consolidation process e) The stiffer a soil, the greater its coefficient of consolidation f) ? The rate at which the consolidation settlement develops increases with the magnitude of the load applied at the surface Page 1 of8

Solution

a) False

This is because the flow net is comprised of squares, but they are not of same dimension. The head drop is constant between two adjacent equipotential lines, but the path travelled differs because the square dimension differ. So for a larger square, hydraulic gradient will be smaller than that for a smaller square.

b) True

when the Plasticity Index(PI) which is found by Liquid Limit and Plastic Limit\'s difference, is above the A-line in plasticity chart, it is clay, if it is below, then it is silt, but the particle size must be lesser than 0.075 mm.

c) False,

Cv(Co-efficient of consolidation) is the rate at which water can be expelled out or the compression of the soil can occur and is directly proportional to the permeability, so clearly, larger the co-efficient of consolidation, faster will be the compression.

d) True

The co-efficient of earth pressure at rest is the ratio of the effective horizontal stress to effective vertical stress.

f) True

Specific surface of the clay particle is larger than that of the sand because smaller the size, larger is the surface area. This is a simple property of shapes.