Each wheel pass pushes stone down and squeezes water and fines up into the voids of the base, which soon becomes a muddy mix that ruts and loses strength. Pumping is common on haul roads, rail beds and unpaved yards over clayey soils. A separation geotextile under the base, plus drainage to keep the subgrade drier, is the standard cure.
Heard on the job
Base is pumping on every truck pass, mud's coming up through the stone, it needed fabric under it.
Also heard as
- subgrade pumping
- fines migration
Related terms
Separation
Keeping two different soil layers, such as an aggregate base and a soft subgrade, from mixing under load.
Subgrade
Native or prepared soil surface on which a pavement, aggregate base or liner system is built.
Stabilization
Improving how soft ground or an aggregate base carries traffic by adding geogrids or geotextiles.