Question $2$ hecture $(3)$

$($a$)$ At a reclamation project site, the seabed is $5m$ below the water surface. The subsurface

soil profile consists of $8m$ of clay underlain by highly permeable sandstone. Laboratory

tests were conducted on samples of the clay, and its saturated unit weight was found to be

$16\mathrm{.}5k\frac{N}{m^3}.$ Also, the clay was found to be normally$-$consolidated, with initial void ratio

of $1\mathrm{.}10,$ compression index $(C_c)$ and coefficient of consolidation $(c_v)$ of $0\mathrm{.}46$ and

$1\mathrm{.}65\frac{m^2}{y}$ear, respectively. According to the reclamation design, $11m$ of fill will be placed

over the clay layer. The unit weight of the fill above water table is $19k\frac{N}{m^3},$ and its

saturated unit weight is $20k\frac{N}{m^3}.$

i$.$ Determine the water pressure and effective vertical stress at the middle of clay layer,

immediately after the fill is placed and many years after the fill is placed.

ii$.$ Taking into consideration the construction period of $12$ months, estimate the

consolidation settlements after $6$ months, $24$ months and $48$ months.

$(5$ marks$)$

If the clay layer is divided into two sublayers, each being $4m$ thick, estimate the

corresponding coefficients of volume compressibility $(m_v)$ for each of the two sublayers,

stating the necessary assumptions.

$(6$ marks$)$