Rigid Inclusion (RI) ground improvement elements, such as Geopier® GeoConcrete® Columns (GCCs), are often used to support conventional shallow footings in soft, unsuitable soil conditions. With reference to Figure 1 below, a granular load transfer layer (aka “Footing Pad”) is included between the footing and the RIs to: 1) help transfer vertical footing loads down into the RIs and 2) provide a “shear break” to separate the footing and the RIs.
Applied structural lateral forces (typically wind/seismic) are resisted by passive soil pressure on the face of the footing, side friction along the side of the footing, and base friction along the bottom of the footing. Having a granular Footing Pad between the footing and RIs helps reduce, but might not eliminate, applied shear forces to the RIs. Thus, some of the applied base shear force can place lateral load demand on the RIs. Given that RIs generally consist of unreinforced concrete or grout, their lateral load capacity can be relatively low. The Massachusetts State Building Code (MSBC) 10th edition section 1809.14.1.1 requires that the lateral capacity of RIs be evaluated during design. If you have questions on this, please do not hesitate to reach out to discuss further, we would be happy to help!
KEY TAKEAWAYS
- Footing Pads reduce, but may not eliminate, applied shear forces to Rigid Inclusions
- Rigid Inclusions are subject to shear and bending.
- The MSBC 10th edition section 1809.14.1.1 requires that the lateral capacity of Rigid Inclusions be evaluated during design.
- Please do not hesitate to reach out to discuss further, we would be happy to help!
