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Seismic Shear Deformation of Compliant Fine-Grained Soil

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Soil Yield Strength
Diagram of soil yield strength.

Critical State Definition of Soil Yield Strength:

Fine grained soil yield strength (q/Gamma symbol'h: strength/effective overburden stress) can be expressed as a function of the effective stress normalized-normally consolidated shear strength (Sn), overconsolidation ratio (OCR), and power function (Equivalent conductivity symbolo), where q/Gamma symbol'h =Sn•(OCR)Equivalent conductivity symbolo (Ladd and Foott, 1974). An idealized soil, on the left, has a cylindrical yield-surface in the zone of overconsolidation, and a conical yield surface in the zone of normal consolidation (Wood, 1990). Permanent plastic deformations can occur when transient earthquake and block-induced stresses exceed the mobilized yield stress of the soil.

Looking down the confining stress axis, below, are two circular yield-stress surfaces that show the difference between traditional displacement models and our multidimensional compliant model. Traditional models neglect the influence of strike motions and resonance within the displaced mass. The two models have the same slope-induced static stress and dip directed earthquake stress, but the resultant vectors are different due to our inclusion of the additional motions. In the case below, traditional Newmark analysis does not predict deformation, whereas, our method does. Strike-directed motions induce dip-directed deformations, and resonance can dramatically increase or reduce computed deformations.

Newmark analysis vs. multi-dimensional compliant deformation analysis.

Soil landslide diagram. Resonance period of ground.
Rigid analysis model.
Flexible analysis model.

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last modified 1 December 2003 (lzt)
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