Degradation of Marine Clays under Cyclic Loading

Threshold Shear Strains for Cyclic Degradation and Cyclic Pore Water Pressure Generation in Two Clays

“…9 and 10 depend not only on σ 0 vc , OCR, and f (Mortezaie and Vucetic 2013), but also significantly on the magnitudes and sequence of γ c applied in a multistage test. These curves therefore differ from the t versus γ c curves obtained from a series of separate tests on the same soil conducted at the same σ 0 vc , OCR, and f, but just different γ c , such as those presented by Idriss et al (1978), Vucetic and Dobry (1988), and Tan and Vucetic (1989). Consequently, to draw conclusions about various cyclic degradation trends at γ c > γ td , the curves in Figs.…”

“…Previous studies show that both the degradation parameter, t, which measures the rate of cyclic degradation with N [defined below by Eq. (2)], and the cyclic pore water pressure, Δu N , depend on σ 0 vc , OCR, and f (e.g., Vucetic and Dobry 1988;Tan and Vucetic 1989;Mortezaie and Vucetic 2013). The above variations of parameters σ 0 vc , OCR, and f may, therefore, allow a preliminary, general evaluation of their effects on γ td and γ tp .…”

Effect of Frequency and Vertical Stress on Cyclic Degradation and Pore Water Pressure in Clay in the NGI Simple Shear Device

“…In this regard, it is interesting to mention another well-documented aspect of the cyclic behavior of clay that is also counterintuitive. In overconsolidated clays of higher plasticity, with OCR higher than 2, a significant cyclic degradation takes place despite a decrease of pore water pressure with N and associated increases of effective stress (Andersen 1976;Andersen et al 1980;Vucetic 1988;Tan and Vucetic 1989). The increase of the effective stress would suggest a strengthening of soil instead of its degradation, but that is apparently not the case.…”

“…They include, among others, a survey of the cyclic triaxial stress-controlled loading behavior of a number of different soils by Lee and Focht (1976), a detailed investigation of the cyclic triaxial and simple shear stress-controlled behavior of a marine plastic clay (PI 5 27) by Andersen (1976) and Andersen et al (1980), and the investigation and modeling of the cyclic triaxial strain-controlled behavior of a soft high plasticity clay (PI 5 49) by Idriss et al (1976Idriss et al ( , 1978 and Moriwaki and Doyle (1978). The cyclic strain-controlled behavior studies were followed by investigations of the effects of the type of soil and overconsolidation ratio (OCR) on the magnitude and rate of cyclic degradation and cyclic pore water pressure (e.g., Vucetic and Dobry 1988;Tan and Vucetic 1989;Matasovic and Vucetic 1995), and the studies about the cyclic threshold shear strain for cyclic degradation and cyclic pore water pressure in clays (e.g., Vucetic 1994b; Hsu and Vucetic 2006;Tabata and Vucetic 2010). The results of the cyclic strain-controlled investigations enabled the development of a computer model for the cyclic response of soil deposits (Idriss et al 1976) and modification of an existing computer model for the seismic response of soil deposits that incorporates the cyclic strain-controlled degradation and pore water pressure change (Matasovic and Vucetic 1993).…”

“…Idriss et al (1978) found that for many clays the relationship d versus N, in a loglog format is approximately a straight line. The slope of this line is the degradation parameter, t, which for a given g c describes the rate of cyclic degradation with N. For overconsolidated clays, d versus N in a log-log format is also approximately a straight line (Vucetic and Dobry 1988), while for sands it is typically curved (Dobry et al 1982;Mortezaie 2012). Note that cyclic degradation in the cyclic stress-controlled mode can also be expressed with a degradation index, d p , which also describes the reduction of the secant shear modulus with N. Its basic definition is the same…”