Period #$25$: In$--$class Assignment

A saturated, normally consolidated clay lies beneath $2$ m of sandy soil. In this period's pre$-$class assignment, you should have found that the undrained cohesion in the NC clay soil is given by the expression:

$c_u(z)=8\mathrm{.}95$kPa$+(3\mathrm{.}41kN*m^{-3})(z-2m),$ for zin$[2m,8m]$

For undrained conditions, the shear strength criterion in the soil is:

$|{}_{\text{m}\text{a}\text{x}}|=\sqrt[\phantom{2}]{(\frac{{}_x-{}_z}{2}{)}^2+({}_{xz}{)}^2}{c}_u$

a$.$ Use the undrained strength criterion at the center of the clay layer to compute how much shear stress ${}_{xz}$ would need to be applied at a point to cause shear failure.

b$.$ Assume that a pre$-$load surcharge $q=60$kPa is applied to the site. When the clay layer has completely consolidated under the surcharge, use the drained strength criterion to calculate the shear stress ${}_{xz}$ needed to cause shear failure at the center of the layer.

c$.$ Now assume that an undisturbed sample of soil is collected from the middle of the layer after pre$-$loading and brought into a laboratory. What would be its expected unconfined compressive strength?

d$.$ Estimate how many days to achieve $99\%$ average consolidation of the layer under the pre$-$loading.

Due on ICON, start of Period $26.$

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$q,$

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