_A_{10}_ × 90 1
_P_{h}_ = --------------- + _D_{W1}_ × 62--- × 0.4 =
tan. [phi] 2

_A_{10}_ × 90
--------------- + _D_{W1}_ × 25.
tan. [phi]

The only question of serious doubt is at just what depth the sand is
incapable of arching itself, but, for purposes of safety, the writer has
put this at the point, _F_, as noted above, = _D_{X}_, although he
believes that experiments on a large scale would show it to be nearer
0.67·_D_{X}_, above which the placing of additional back-fill will
lighten the load on the structure.

We have, then, for _D_{E}_ < _D_{X}_, the weight of the total prism of
the earth plus the water in the voids, plus the added pressure of the
water above the earth prism, that is:

The pressure per square foot at the base of any vertical ordinate =
_V_{P}_

1
_V_{P}_ = _D_{E}_ × 90 + _D_{E}_ × 62--- × 0.40 +
2

1
( _D_{W}_ - _D_{E}_ ) × 62---.
2