Effect of Overburden Stress and Plasticity on the Cyclic Resistance of Silts

The effect of vertical effective consolidation stress, sigma vc ', on the cyclic resistance of nonplastic to plastic normally consolidated (NC) and overconsolidated (OC) intact and NC reconstituted silt was investigated using a series of constant-volume, stress-controlled cyclic direct simple shear (CDSS) tests. The results were interpreted considering the changes of specimen properties [e.g., void ratio, e, and overconsolidation ratio (OCR)] associated with the increased sigma vc '. Despite increasing density, all specimens exhibited a reduction in cyclic resistance as sigma vc ' increased. The reduction in cyclic resistance for intact specimens occurred due to the detrimental effect of yielding of the natural soil fabric, reduction in OCR, and the potential suppression of dilative tendencies, which outweighed the beneficial effect of reduced e. Tests of uniformly prepared reconstituted NC specimens reduced the number of factors contributing to the reduction of cyclic resistance (i.e., destruction of natural soil fabric, and reduction of OCR) with increased sigma vc ', and were used to confirm the sensitivity of cyclic resistance to sigma vc ', in which the detrimental effect of suppressed dilative tendencies on cyclic resistance dominated the beneficial effect of reduced e. The overburden correction factor, K sigma, was observed to decrease with increased plasticity index, PI, highlighting the role of compressibility on cyclic resistance.