QUESTION $1$

$[12]$

A $6m$ square concrete structure exerts a uniform pressure of $510k\frac{N}{m^2}$ to the ground. The proposed footing depth is $1\mathrm{.}6m.$ The soil profile of the proposed site consists of $5\mathrm{.}1m$ thick soft clay with a dry unit weight of $18\mathrm{.}4kN.m^3$ and saturated unit weight of $19\mathrm{.}3k\frac{N}{m^3}.$

Due to the sensitivity of the soft clay, a $2\mathrm{.}5m$ thick gravelly sand will be imported, placed, and compacted to a dry unit weight of $18\mathrm{.}6k\frac{N}{m^3}$ on top of the clay layer before construction occurs.

The soft clay is $100\%$ saturated and it is expected that the fill material will become saturated due to capillary action to a height of $1m.$ The fill material $($gravelly sand$)$ has a moisture content of $15\%.$

Calculate the total and effective vertical pressure at the bottom of the clay layer immediately after construction.

QUESTION $2$

$[10]$

A layer of clay lies under a $3\mathrm{.}8m$ thick gravel layer with a dry and saturated unit weight of $16\mathrm{.}5k\frac{N}{m^3}$ and $17\mathrm{.}8k\frac{N}{m^3}$ respectively, and on top of a $5\mathrm{.}2m$ thick sand with a saturated unit weight of $18\mathrm{.}9k\frac{N}{m^3}.$ The water table is $1\mathrm{.}8m$ below ground level. The sand is under artesian pressure, the piezometric surface being $3m$ above ground water level. The saturated unit weight of the clay is $19\mathrm{.}9k\frac{N}{m^3}.$

Calculate the thickness of the clay layer if the effective vertical pressure at the bottom of the clay layer is $50k\frac{N}{m^2}.$

QUESTION $3$

$[12]$

A footing $($strip$)$ is to be constructed on a pure clay soil. The footing is to support a wall that imposes a loading of $155kN$ per meter length of the wall and is founded at a depth of $0\mathrm{.}5m$ below the surface. What footing width should be provided to have a safety factor of $3,$ using Terzaghi's general bearing capacity equation. The clay has a unit weight of $17\mathrm{.}3k\frac{N}{m^3}\frac{?}{c_u}=72k\frac{N}{m^2}.$ There was no evidence of GWL upon investigation.

QUESTION $4$

$[28]$

A warehouse with a $3m$ wide footing is constructed in an $8m$ thick clay layer, at a depth $1\mathrm{.}5m$ below the ground surface. The clay has a dry and saturated unit weight of $16\mathrm{.}3k\frac{N}{m^3}$ and $17\mathrm{.}9k\frac{N}{m^3}$ respectively. The ground water table is $1m$ below the ground surface. Oedometer test results indicate that the coefficient of volume change may be taken as $310-4\frac{m^2}{k}N$ for the pressure range $75-415k\frac{N}{m^2}$

a$)$ If the warehouse should not settle more than $10\%$ of the depth of the footing, what is the required net and total bearing pressures to produce consolidation of this magnitude?

b$)$ If the coefficient of permeability is given as $3\mathrm{.}810-8\frac{m}{m}in,$ how long will it take $($in months$)$ for half of the specified settlement to occur?

c$)$ How much consolidation and settlement will occur over $12$ months?

QUESTION $5$

$[5]$

In a falling$-$head permeability test the initial head of $1m$ dropped to $0\mathrm{.}35m$ in $3$ hours, the diameter of the standpipe being $5mm.$ The soil specimen was $200mm$ long and $100mm$ in diameter. Determine the coefficient of permeability of the soil in $\frac{m}{s}.$