Share:
How It Works
When the water table rises above a buried pipe, the water exerts external hydrostatic pressure. The pressure equals the unit weight of water (typically 62.4 lb/ft³) multiplied by the height of water above the pipe crown. This load must be added to soil and wheel loads when checking pipe wall strength.
Example Problem
Water table is 3 ft above the top of a buried pipe. What is the hydrostatic pressure?
- P = 62.4 × 3 = 187.2 lb/ft²
Frequently Asked Questions
What is the unit weight of water?
Fresh water weighs about 62.4 lb/ft³ (9,810 N/m³). Salt water is about 64 lb/ft³. Use the correct value for your site conditions.
When does hydrostatic pressure matter for buried pipe?
It matters whenever the water table is above the pipe. In flood-prone areas or near rivers, seasonal high water can add hundreds of pounds per square foot of external pressure.
Can hydrostatic pressure float a pipe?
Yes. An empty pipe below the water table experiences buoyancy. If the upward force exceeds the pipe weight plus soil cover, the pipe can float upward. Anti-flotation anchors or heavy backfill prevent this.
Related Calculators
- Pipe Soil Pressure Calculator — soil weight and buoyancy factor.
- Pipe Vacuum Load Calculator — internal vacuum load on buried pipe.
- Pipe Vacuum Load Calculator — internal vacuum load on buried pipe.
- Pipe Wheel Loading Calculator — wheel loads at various cover depths.
- Fluid Pressure Calculator — calculate hydrostatic pressure at any depth.
- Pressure Unit Converter — convert between psi, kPa, and bar.
National Resources Conservation Service. National Engineering Handbook. 1995. USDA.