Structural Steel Underpinning – Engineering
There are normally two phases of engineering assessment when dealing with a foundation settlement problem. The first step is to identify what is causing the problem. A Soils Engineer will typically employ a number of subsurface investigative techniques that can help identify a deficient or sub standard supporting soil condition.
In cases where a soil improvement technique is recommended, the soils engineer will typically outline a remedial program that will help address the subsurface conditions encountered.
When a building is significantly affected by settlement, a Structural Engineer should also be consulted to conduct a structural condition assessment to determine if additional remedial measures are required. This repair plan would consider the limitations of the existing building system and how it will respond to the repair without compromising the safety or integrity of the structure.
Penetrating Radar (GPR) – This testing method uses a high frequency electromagnetic pulse to reflect back and document buried subsurface anomalies. This test is typically conducted early on in the investigation to help improve the chances of finding sinkhole conditions or buried debris.
Electrical Resistivity Testing (ERT) – This approach is similar to the GPR but it measures how well the soil inhibits an electrical current flow. It has been used extensively in mineral exploration as well as engineering applications. Once the resistivity has been established it can be compared to known resistivity values for different earth materials and interpreted to provide horizontal layer mapping. When compared to the GPR test, this approach is better suited to penetrate a highly conductive material such as clay.
Hand Auger Boring (HA) – This manual test method retrieves soil samples in the upper soils (Typically the upper 5′ – 7′ feet). It will also provide classification data that can help identify inadequate supporting soils (Buried Organic or Shrink Swell Clay Soils). This shallow test method allows the engineer to get an overall perspective of the upper strata at a particular site. It also allows for limited soil testing in tight quarters where a drill rig may not be able access.
Standard Penetration Test Boring (SPT) – This deep boring test method typically requires a drill rig to help investigate, retrieve, and classify the deeper soil conditions at a test location. This information can be helpful in determining the specific engineering characteristics and expected performance of a particular soil type as it relates to the suitability of providing support to the structure. In addition to classifying the soil type, it can also help define loosened or raveled zones that may be indicative of sinkhole development.