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How It Works
Surface vehicle loads spread through the soil at an angle. Shallow pipes (less fill) see a concentrated load, while deeper pipes benefit from greater load distribution. Two separate equations handle fill depths above and below a threshold. The wheel load per linear foot can then be converted to a pressure using the pipe diameter.
Example Problem
An H-20 truck wheel load of 16,000 lb acts on a pipe with 3 ft of cover and an impact factor of 1.5. Estimated wheel load per foot is highly dependent on the cover depth equation used. Increase cover depth to reduce the load reaching the pipe.
Frequently Asked Questions
What is an H-20 wheel load?
H-20 refers to the AASHTO standard 20-ton highway truck. The maximum single-wheel load is 16,000 lb. Heavier trucks (H-25, HL-93) require using correspondingly larger wheel loads in the calculation.
Why are there two equations for different depths?
At shallow depths (typically < 2–3 ft), the load spreads through a smaller soil prism and the impact factor is larger. At greater depths the load distributes more widely and the pressure on the pipe drops significantly.
What is the impact factor?
The impact factor accounts for dynamic effects from moving vehicles. It is typically 1.5 for highway loads and 1.0 for static loads. Heavier or faster traffic may warrant higher factors.
Related Calculators
- Pipe Soil Pressure Calculator — soil weight pressure and buoyancy.
- Buried Corrugated Pipe Calculator — combined design pressure and wall thrust.
- Pipe Hydrostatic Pressure Calculator — external water pressure on buried pipe.
- Pipe Vacuum Load Calculator — internal vacuum load on buried pipe.
- Pressure Unit Converter — convert wheel loading pressure between units.
National Resources Conservation Service. National Engineering Handbook. 1995. USDA.