Please answer no$\mathrm{.}3$ and $4$

A $5-$m high road embankment is to be constructed on a $10-$m thick clay layer $($see Figure $1).$ The water table is at the top surface of the clay layer, which is underlain by a sand layer. Some key soil parameters obtained from preliminary ground investigation works are summarised below:

Sand

Figure $1$

$(1)$ What is the primary settlement of the clay layer under the weight of the road embankment?

$(2)$ What is the secondary settlement undergone by the clay layer $80$ years after the clay has completed the primary consolidation under the weight of the road embankment? $($The fill material for the embankment is sandy gravel. Assume the construction time of the embankment is short and can be taken as instantaneous loading$)$

The design engineer is concerned with the secondary settlement and would like to use surcharging to reduce it$.$ He considers two options.

In the first option, he plans to construct the $5-$m road embankment together with a $5-$m thick fill layer as surcharge $($see Figure $2).$ The $5-m$ surcharge fill will be removed $3\mathrm{.}33$ years after construction of the embankment.

$1$

$(3)$ At the time of surcharge removal, what is the effective surcharge ratio, $R_s\text{'},$ of the whole clay layer with respect to effective final vertical stress under the $5-m$ road embankment? The design engineer divides the clay layer into $4$ equal sublayers in his estimate of $R{s}^{\text{'}}.$ Please fill in the table with supporting calculations.

$\backslash$table$[[\backslash$table$[[$Thickness of$],[$Sublayer $($m$)]],\backslash$table$[[$Mid$-$depth of$],[$Sublayer $($m$)]],{}_{vo}^{\text{'}}(kPa),{}_{vm}^{\text{'}}(kPa),{}_{vf}^{\text{'}}(kPa),R_s^{\text{'}}$