_h_ = exterior height, _l_ = exterior width,

{ [delta] = depth of cover, that is,
{ _D_{E}_ = earth, and _D_{W}_ = water depth,

[phi] = angle of repose, and, for tunnels _D_{W}_ > _D_{E}_ a depth

_l_ [phi]
= ----- ( 45° + ------- )
2 2

_W_{E}_ = weight of 1 cu. ft. of earth = 90 lb.; _W_{W}_ = weight of 1
cu. ft. of water = 62½ lb.

Conditions: 1 = normal sand, 2 = dry sand, 3 = supersaturated firm sand
with 40% of voids, 4 = supersaturated semi-aqueous material, 60%
aqueous, that is, 60% water and aqueous material.


_______________________________________________________
| | | | |
Combined | | | | |
assumed | _h_ | _l_ | [phi] | _D_{E}_ |
conditions. | | | | |
______________|________|________|________|____________|
| | | | |
I_{1} | 20 | 30 | 45° | 40 |
I_{2} | 20 | 30 | 30° | 40 |
II_{1} | 15 | 15 | 45° | 40 |
II_{2} | 15 | 15 | 30° | 40 |