$3\mathrm{.}9$ A coeis ona permable foundation las a lewes floor of nogligible thickness and is lom long in the direction of Aow. At the two endi of the floor $2\mathrm{.}5in$ deep piles are prooided. using thana's theory calculate. the uplft pressure at the mid$-$length of the flecr and at Quarter point. The effective Head of cuater can be assumed to be $2m.$