Meaning
Hydraulic transport of fine material under rigid pavements results from the rapid movement of water through the subbase during wheel passage. When subgrade pumping occurs, the saturated soil is ejected through joints or cracks in the concrete slab. This process removes the physical support for the pavement and leads to structural instability.
Erosion Mechanism
Dynamic loading from heavy vehicles creates high pore water pressure that forces a slurry of fines and water to the surface.
Void Development
Frequent repetition of the pumping cycle creates empty spaces beneath the concrete where the subgrade used to be. These voids allow the slab to deflect further under load, which accelerates the rate of material loss. Preventing subgrade pumping requires the use of non erodible base materials or the installation of effective drainage systems.
Geotextile layers can also act as a filter to keep the fines in place while allowing water to pass through. If the pumping is not stopped, the slab will eventually crack under its own weight or the weight of passing traffic.
Soil Base
Stabilizing the foundation with cement or lime reduces the availability of fine particles for transport. Failure to address the drainage issues results in the rapid deterioration of the entire road or floor section.
