Toward Understanding the Seismic Performance of Rigid Inclusions-Paper

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Rigid inclusions (RIs) are stiff grout columns used in arrays to support foundations and embankments, usually without structural connection to the supported structure. Because they are lightly reinforced or unreinforced, they have limited ductility and may be vulnerable to earthquake-induced bending. The paper examines two seismic loading mechanisms: inertial forces transmitted from the structure and kinematic forces caused by soil movement, including shear-wave passage and permanent ground deformation.<br /><br />The authors propose a simplified assessment using a pseudostatic beam-on-nonlinear-Winkler-foundation (“p-y”) analysis. Ground-response estimates provide soil-displacement profiles, while structural inertia is represented through loads at the RI head and additional ground shearing. If analysis predicts hinging, designers should assess potential settlement, lateral displacement, and loss of bearing capacity.<br /><br />A hypothetical Los Angeles Basin example illustrates the approach. Both unreinforced RIs and RIs with a central reinforcing bar developed hinges under the combined loading. Kinematic loading was substantially more influential than structural inertial loading; ignoring it would significantly underestimate demand. Although the example foundation retained adequate bearing capacity, hinge damage could cause settlement through crushing or bulging. The study also cautions that RIs may be unsuitable at sites with moderate to severe liquefaction or lateral-spreading hazards unless rigorous analysis demonstrates acceptable performance.<br /><br />The authors emphasize that RI seismic behavior remains poorly documented, with little field evidence or physical testing. They recommend further research and careful seismic design that accounts for both loading mechanisms and evaluates post-earthquake system performance.

Keywords

rigid inclusions

seismic loading

kinematic forces

inertial forces

p-y analysis

beam-on-nonlinear-Winkler-foundation

ground deformation

earthquake design

lateral spreading

liquefaction hazards