Figure $9\mathrm{.}28$

$9\mathrm{.}9$ Refer to Figure $9\mathrm{.}28.$ What would be the maximum permissible depth of cut before heaving would occur?

$9\mathrm{.}10$ Refer to Problem $9\mathrm{.}9.$ Water may be introduced into the cut to improve the stability against heaving. Assuming that a cut is made up to the maximum permissible depth calculated in Problem $9\mathrm{.}9,$ what would be the required height of water inside the cut in order to ensure a factor of safety of $1\mathrm{.}5?$

$($Solve $9\mathrm{.}10$ only $)$