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# Underground Pipes - Earth Pressure

The pressure acting on an object in the ground - typical on the outside of a pipe can be calculated as

p = psoil + pwater + ptransport               (1)

where

p = pressure acting on object in the ground (Pa)

psoil = pressure caused by the weight of the soil above the object (Pa)

pwater = hydrostatic pressure caused by the weight of the water above the object (Pa)

ptransport = pressure caused by the transport load on surface of the soil (Pa)

• 1 Pa = 10-6 N/mm2 = 10-3 kPa = 1.450x10-4 psi (lbf/in2)

Pressure caused by soil

psoil = ρs g (h - hw) + ρsw g hw                 (2)

where

ρs = density of soil above the groundwater (typical 1800 - 1900 kg/m3)

g = acceleration of gravity (9.81 m/s2)

h = depth from surface to object (m)

hw = depth from groundwater level to object (m)

ρswdensity of soil below groundwater level (reduced due to Buoyancy of soil - typical value 1100 kg/m3)

Pressure caused by groundwater

pwater = ρw g hw                 (3)

where

ρsw = density water  (1000 kg/m3)

Pressure caused by transport

The pressure caused by transport depends on the force (weight) on each wheel. The figure below indicates the the pressure at different depths for wheel force 75 kN (7500 kg) with dynamic factor 1.75.

### Example - Pressure acting on an Underground Pipe

The pressure acting on pipe at buried at depth 2 m and 2 m below groundwater level can be calculated as

psoil = [(1800 kg/m3) (9.81 m/s2) ((2 m) - (1 m)) ] + [(1100 kg/m3) (9.81 m/s2) (1 m)]

= 28449 Pa

= 28.5 kPa

pwater = (1000 kg/m3) (9.81 m/s2) (1 m)

= 9810 Pa

= 9.8 kPa

ptransport = aprox. from the diagram  - 20 kPa

Total pressure

p = (28.5 kPa) + (9.8 kPa) + (20 kPa)

= 58 kPa

• 1 kPa = 1 kN/m2

### Underground Pressure Calculator

This calculator is based on the equations below and can used to estimate the underground pressure acting on objects relatively smaller than the depth they are buried - typically pipes with diameter less than 3-500 mm.

Pressure from transport is calculated for wheel force 75 kN (7500 kg) with dynamic factor 1.75.

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