Hydrostatic Force on a Retaining Wall
Hydrostatic Force on a Retaining Wall
Water pressure increases linearly with depth, so a wall holding back water feels a triangular pressure distribution. This worksheet computes the total horizontal force on the wall and the height at which it acts — the starting point for overturning and sliding checks on dams and tank walls.
The resultant force per unit width is F = ½ρgH², acting at H/3 above the base.
Inputs
A vertical wall of width b retaining water to depth H.
rho := 1000 kg/m^3=1000 kg/m^3
g := 9.81 m/s^2=9.81 m/s^2
H := 4 m=4 m
b := 5 m=5 m
Resultant force and line of action
F := 0.5·rho·g·H^2·b=392400 N
y_bar := H/3=1.33 m
Results
The resultant grows with the square of depth, so the bottom of a deep wall dominates. Because the force acts low (at H/3 from the base) it produces a large overturning moment about the toe — check sliding and overturning stability, not just the wall’s bending strength.
Assumptions & limitations
- Still water (hydrostatic) against a vertical face.
- Single fluid; no uplift or seepage pressure included.
- Atmospheric pressure acts on both sides and cancels.