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Cyclic shear loading response of Fraser River delta silt

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Title: Cyclic shear loading response of Fraser River delta silt
Author: Sanin, Maria Victoria
Degree Doctor of Philosophy - PhD
Program Civil Engineering
Copyright Date: 2010
Publicly Available in cIRcle 2010-11-22
Abstract: The cyclic shear response of low-plastic Fraser River silt was investigated using constant-volume direct simple shear testing. Silt specimens, initially consolidated to stress levels at or above the preconsolidation stress, displayed cyclic mobility type strain development during cyclic loading. Liquefaction in the form of strain softening accompanied by loss of shear strength did not manifest regardless of the applied cyclic stress ratio (CSR), or the level of induced excess pore water pressure (Δu). Cyclic mobility type stress-strain behaviour was observed in spite of the initial static shear stress bias. The potential for excess pore water pressure generation and associated shear strain development during cyclic loading was observed to increase with increasing level of initial static shear. Tests on specimens of undisturbed field samples and specimens reconstituted using the same silt material showed that undisturbed silt, despite having a looser density under identical consolidation stress conditions, exhibited more dilative response and larger shear resistance compared to those displayed by reconstituted specimens. In addition to consolidation stress conditions and resulting void ratios, it appears that other naturally inherited parameters such as soil fabric and aging effects would influence the shear response of natural silt. Studies were also conducted to examine the post-cyclic reconsolidation response of low-plastic silt using specimens of undisturbed and reconstituted Fraser River silt and reconstituted quartz powder initially subjected to constant volume cyclic loading at different CSR values and then reconsolidated to their initial effective stresses. The volumetric strains during post-cyclic reconsolidation (εv-ps) were noted to increase with the maximum Δu and maximum cyclic shear strain experienced during cyclic loading. The values of εv-ps and maximum excess cyclic pore water pressure ratio (ru max) were observed to form a coherent relationship regardless of overconsolidation effects, particle fabric, and initial void ratio of the soil. The specimens with high ru-max suffered significantly higher post-cyclic reconsolidation strains. The observed εv-ps versus ru-max relationship, when combined with the observed dependence of ru on CSR and number of load cycles, seems to provide a reasonable approach to estimate post-cyclic reconsolidation strains of low-plastic silt.
URI: http://hdl.handle.net/2429/30064
Scholarly Level: Graduate

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