Evaluation of Seismic Earth Pressure Acting on Footing Embedded in Cohesive Soil Based on Centrifuge Tests

Abstract eng:
This paper presents centrifuge test results for the seismic earth pressure acting on a footing embedded in cohesive soil. To clarify the effects of clay cohesion on the seismic earth pressure at the active and passive sides, two dynamic centrifuge tests were performed on a footing model supported by 2 × 2 piles embedded in an oil-based clay layer overlying a dense sand deposit. The cohesive soils were oil-based clays with cohesion values of 35 and 60 kN/m2. The study results indicate that the passive earth pressure of a clay can be estimated approximately based on Rankine’s theory. The relative displacement needed for the earth thrust at the passive side to reach a peak value was approximately 4%–6% of the embedment depth. The earth thrust at the active side acted on the footing in the form of a tensile force during strong shakings. However, the active earth pressure of a clay cannot be estimated by Rankine’s theory. The active earth pressure was smaller than the theoretical value probably because the ultimate extension force between the clay and footing was smaller than that caused by the failure of the clay, that is, the Mohr circle of the clay touched the Mohr–Coulomb failure envelope. The relative displacement needed for the earth thrust to reach the active state was approximately 1%–2% of the embedment depth.

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