Draft

2.4OtherLoads 47

2.4 OtherLoads.

2.4.1 HydrostaticandEarth

39 Structuresbelow groundmustresistlateralearthpressure.

q=K
h (2.28)

where is thesoildensity,K=

1 sin

1+sin

is thepressurecoecient,his theheight.

40 For sandandgravel = 120lb=ft

3

, and 30



.

41 If thestructureis partiallysubmerged,it mustalsoresisthydrostaticpressureof water,

Fig.2.10.

Figure2.10:EarthandHydrostaticLoadsonStructures

q= (^) Wh (2.29)
where (^) W= 62: 4 lbs=ft
3
.
Example2-5: HydrostaticLoad
Thebasement of a buildingis 12 ft below grade.Groundwateris located9 ft below grade,
whatthicknessconcreteslabis requiredto exactlybalancethehydrostaticuplift?
Solution:
Thehydrostaticpressuremustbe counteredby thepressurecausedby theweight of concrete.
Sincep =
hwe equatethe two pressuresandsolve forhthe height of theconcrete slab
(62:4)lbs=ft
3
(129)ft
| {z }
water
= (150)lbs=ft
3
h
| {z }
concrete
)h=
(62:4)lbs=ft
3
(150)lbs=ft
3 (3)ft(12)in/ft= 14:^976 in'
15.0inch