OasisLMS

Abstract: Rigid Inclusions (RIs), typically fully-grouted concrete columns, used to reduce settlement and increase bearing capacity, are versatile ground improvement elements widely used to support structures. RIs supporting buildings are often located under footings and slabs (referred to as foundations), separated by a load transfer platform (LTP). The purpose of the LTP is to create a physical separation between the RIs and the foundations and to distribute the load from the RI to the bottom of the foundation. RI-supported foundations are typically designed for uniform bearing. However, RIs do create stress concentrations on foundations, the magnitude of which varies based on applied loading, soil conditions, the quantity of RIs, the thickness of the LTP, and more. The impact of these stress concentrations on the supported foundations is a major question within industry. The purpose of this paper is to identify conditions that require further evaluation of the foundation’ s structural design and establish thresholds beyond which uniform conditions may be assumed for structural design.

While the impact of these stresses may require redesign of the foundations, it is rare in cases where the RI design follows traditional ground improvement methodology. Where the RIs act more like deep foundation elements than ground improvement, small changes may be required to the structural foundation design. In these cases, the stress concentrations should be evaluated by the RI designer and the structural engineer.

In this paper, we will show the results of 2D and 3D Plaxis models evaluating the conditions beneath RI-supported foundations. The slab models will evaluate the bending moment in the slab with changes in soil profile and LTP thickness. The footing models compare the bending moment and shear in the footing supported by RIs with those in the footing supported by a composite (uniform) soil for various numbers and layouts of RIs. Recommendations for thresholds beyond which uniform conditions may be assumed will be provided, as well as potential modifications to RI designs to achieve more uniform conditions.

Ms. Sonia Swift; Mr. Jules Petrella

Annual Conference Proceedings