Part I: Selection and Design of Rigid Inclusions-Article

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This forum paper presents industry commentary guidelines for selecting and designing cementitious, cast-in-place rigid inclusions (RIs), a ground-improvement method used to reduce settlement beneath structures, slabs, embankments, and retaining walls on weak or compressible soils. RIs are typically discrete vertical columns separated from the supported structure by a load-transfer platform (LTP), which distributes loads between columns and surrounding soil. The authors note that no industry-wide U.S. standard currently governs RI selection, design, or verification; construction and verification are reserved for a planned Part II.<br /><br />The paper reviews load transfer, structural and geotechnical capacity, and settlement. Design should account for forces at the neutral plane, downdrag, column resistance, LTP behavior, and settlement of both the inclusion group and underlying bearing stratum. Foundation stiffness differences can create stress concentrations, making coordination between geotechnical and structural designers essential.<br /><br />For embankments and MSE walls, arching and load transfer through the LTP are central to performance. Global stability should reflect the reduction in stress carried by foundation soils—not treat RIs as added composite shear strength, since columns may fail in bending. Lateral deformation and column integrity also require evaluation.<br /><br />The authors discuss tensile and lateral loading, seismic-induced soil movements and column flexure, and risks from reduced confinement due to scour, liquefaction, karst, or long-term ground settlement. Where confinement may be lost, buckling and alternative LTP materials or reinforcement may need consideration. Overall, the paper emphasizes project-specific analysis, appropriate load-transfer assumptions, and careful assessment of both structural and geotechnical limit states.

Keywords

rigid inclusions

cementitious columns

ground improvement

load transfer platform

settlement reduction

geotechnical design

structural capacity

load transfer

embankment stability

lateral deformation