QUESTION $2$

$($a$)$ A sample of soil $($soil A$)$ is retrieved from the ground to be tested. The soil is saturated. A cylindrical specimen of soil A is prepared, measuring $37\mathrm{.}9mm$ diameter and $76\mathrm{.}1mm$ height. The specimen is saturated, and weighs $164\mathrm{.}4g.$ It is then placed in an oven at $105C$ for $24$ hours to dry and weighed again; the dry mass of the soil specimen is $116\mathrm{.}7g.$ The specific gravity of the soil was determined as $2\mathrm{.}71.$

TURN OVER

CEGE$0100$

Page $3$ of $6$

Determine:

$($i$)$ The soil's water content $($w$)$

$[3$ marks$]$

$($ii$)$ Its dry unit weight $(d)$

$[3$ marks$]$

$($iii$)$ Its saturated unit weight $({}_{\text{s}\text{a}\text{t}})$

$[3$ marks$]$

$($iv$)$ The average void ratio of the soil sample and its accuracy.

$[4$ marks$]$

$($b$)$ The sample of soil A for which you determined the void ratio above was retrieved from $5m$ depth in the soil profile shown in Figure Q$2.$ Using the unit weight determined in $($a$)$ and assuming hydrostatic conditions, answer the following:

i$)$ Plot the profiles of total stress, pore water pressure and effective stress for depths between $0m$ and $11\mathrm{.}6m$ below the ground surface.

$[6$ marks$]$

ii$)$ Soil A has a friction angle ${}^{\text{'}}=31\mathrm{.}5.$ Assuming the horizontal effective stress is related to the vertical effective stress by: ${}_{h^{\text{'}}}=K_0{}_v^{\text{'}},$ with $K_0=1-sin{}^{\text{'}},$ determine the horizontal effective stress and horizontal total stress at $5m$ depth.

$[4$ marks$]$

iii$)$ What would be the effect of lowering the water table to the top of the gravel layer on the effective stresses at a point $5m$ beneath the ground surface? Justify your answer.

$[2$ marks$]$

FIGURE $02$