Question

A layer of clay of 8 m thickness is located between two sand layers. The coefficient of consolidation of the clay is $5\times {10}^{-4}c{m}^2/sec$ . The fill material was placed over a very large area above the top sand layer . After 3 years, the percentage of additional pressure due to fill material will be carried by the soil grains at the middle of clay layer

• A. 58%
• B. 43.4%
• C. 60.9%
• D. 78.2%

Answer 1

The correct option is C 60.9%

Given:

H = 8 m
$d=\frac{H}{2}$ = 4m (Double drainage)

$C_v=5\times {10}^{-4}c{m}^2/sec$
$t=3years$

$T_v=\frac{C_{v}t}{d^2}$

$T_v=\frac{5\times {10}^{-4}\times 3\times 365\times 24\times 60\times 60}{(400{)}^2}$

$T_v=0.296$

$\therefore T_v@U=60\%\Rightarrow 0.283$

$\therefore T_v=0.296>0.283,(U>60\%)$

% of Additional pressure carried by soil grains is degree of consolidation, U %

$U>60\%\Rightarrow T_v=1.781-0.933lo{g}_{10}(100-U\%)$

$0.296=1.781-0.933lo{g}_{10}(100-U\%)$

U % = 60.95 %