Pipe ramming is a trenchless construction technique used to install underground utilities, pipes, ducts, conduits, and culverts. It involves using a pneumatic or hydraulically powered ramming tool, or piston, to drive an open-ended steel casing from the launch pit to the exit pit of a job site.
During this process, a ramming tool delivers high-frequency percussive blows which essentially hammer the steel casing through the earth to its final destination. (Read 5 Pipe Ramming Methods Used in HDD.)
As the casing moves through the soil, the wall thickness of the pipe is displaced, while the rest of the soil remains in the casing. Upon completion of ramming operations, the soil is removed from the inside of the casing by auguring, water jetting, or by flushing with compressed air.
The use of steel casings during pipe ramming operations is due primarily to the magnitude of the driving forces involved. The ramming tool needs to apply direct, high-impact forces to the casing in order to overcome skin friction and soil shear forces. As such, a casing material with sufficient strength properties must be used to avoid failure during application of the blows.
Steel, which is an alloy of iron and carbon, exhibits desirable behavior when subjected to impact loading. The ductility, yield strength, compressive strength, and strain rate of steel allow it to undergo the rigorous ramming process with little to no deformation.
In addition to the ability to withstand impacts, steel casings also possess a relatively low coefficient of friction; thus minimizing resistive forces as the casing is driven through the soil. The ring stiffness of the casing also provides adequate support for the upper layers of soil to reduce the probability of subsidence or settlement.