What is Underpinning?

Underpinning is the process of repairing and stabilizing an existing foundation system by transferring its bearing load to subsurface strata that is deeper and more stable than the near surface soil that supports the existing foundation system. Ram Jack uses push piers that are deep-driven, against the bottom of the existing foundation, until they reach an engineered level of resistance, through friction or contact with bedrock, call "refusal", where the structure's weight can no longer drive the pier deeper. At this point the structure's weight is transferred directly onto the piers.

The Purpose of Underpinning

Many of the houses that forensic engineers and repair contractors are asked to evaluate were constructed with foundations that are inadequate for the conditions existing on site. Because of the lack of suitable land, homes often built on marginal land that has insufficient bearing capacity to support the substantial weight of a structure. In addition, there are many areas of the country where the near surface soils consist predominantly of expansive clays that shrink and swell as their moisture content changes. As a result, underpinning is required to extend the foundation support to depths that provide greater bearing capacity and/or are less affected by climate, soil conditions and/or homeowners actions. This underpinning, if properly designed and installed, provides the basis to lift the structure to a more acceptable elevation and provides vertical support to prevent the underpinned area from settling.