A $2400$ mm x $2400$ mm footing is to be installed with its base at a depth of $2\mathrm{.}00$ m below the surface, in an $7\mathrm{.}00$ m thick layer of soil. The unit weight of the soil is $18\mathrm{.}5$ kN$/$m$3.$ The water table is $10\mathrm{.}00$ m below the surface. After excavation, construction of foundation and backfill, the footing carries a net load of $1000$ kN$.$ What is the final effective stress at a depth of $3\mathrm{.}5$ m below the surface? Assume a vertical:horizontal stress dispersion angle of $2$:$1.$

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