The Impact of Rigid Inclusions on the Design of Footings and Slabs-PPT Presentation

PPT Presentation

Pdf Summary

The presentation explains how rigid inclusions (RIs), including controlled modulus columns (CMCs), affect the design of slabs and footings. RIs are typically unreinforced, grout- or cement-filled displacement elements used to improve soft, compressible, or variable soils. They share load with the surrounding soil, with load transfer influenced by negative and positive skin friction.<br /><br />The design approach depends on the project. Under a ground-improvement approach, soil and RIs share the load and foundation stresses are relatively uniform. Under a deep-foundation approach, RIs carry most of the load, producing more concentrated foundation stresses and requiring closer coordination between RI and structural designers.<br /><br />For slabs, a load-transfer platform (LTP) helps spread loads and reduce uneven stresses. Thinner LTPs increase the RIs’ effect on the slab, so slab tensile stresses should be checked, particularly where the LTP is relatively thin or soils are soft. Possible responses include increasing LTP thickness or slab moment capacity; solutions can be tailored to the project.<br /><br />For footings, RIs create stress concentrations, but load sharing can reduce their effects. The resulting footing moments and shear forces should be assessed. Recommendations include using circular RI layouts where possible, placing an RI near the footing center, and keeping RIs within one-quarter of the footing width from its center. Designing for uniform bearing is generally a conservative approach: with this layout, RI-induced moments should not exceed those associated with uniform support.<br /><br />The presentation emphasizes evaluating project-specific risks and having RI designers and structural engineers work together to select an appropriate design approach.

Keywords

rigid inclusions

controlled modulus columns

ground improvement

deep foundation

slab design

footing design

load transfer platform

soil-structure interaction

skin friction

stress concentration