Inside dimensions: h, w, l
Outside dimensions: h + 2t, w + 2t, l + 2t
where t is the wall thickness
Vc = (h + 2t)(w + 2t)(l + 2t)
- hwl
A = (w + 2t)(l + 2t)
Since there is 1 ft of soil over the top of tank,
z = (1 ft) + (h +2t) - d
where d is the water table.
γconcrete = 150 pcf
γsoil = 120 pcf
γwater = 62.4 pcf
To float, the buoyancy force acting on the bottom of
the tank must be greater than the weight of the tank and the soil on
top.
septic tank: h = 6 ft, w = 6 ft, l = 10 ft, t = 4 in.
Vc = 474.1 - 360 = 114.1 ft3
A
= 71.11 ft2
z = 7.67 - d
If the groundwater table depth is less than 1.89 ft, the septic tank
will float.
Recommendation to keep it from floating: use 6 in. walls instead of
4 in. |