Dynamic and cyclic behavior of soils over the wide range of shear strains in NGI-type simple shear testing devices.

摘要

The response of civil engineering structures subjected to cyclic and dynamic loads depends to a large extent on the cyclic stress-strain behavior of foundation soil in shear. Due to the complexities of cyclic soil behavior and laboratory and field testing, some important behavioral aspects have still not been investigated to a satisfactory extent. The objective of the laboratory investigation described in this dissertation is to throw more light on these aspects and thus advance the state of knowledge on the cyclic behavior of soils in the range of very small and very large cyclic shear strain amplitudes, γ_c.; A total of 94 simple shear tests were conducted on 47 soils with their plasticity index, PI, ranging from 0 to 44, their cyclic shear strain amplitudes, γ _c, ranging from 0.00012% to 15%, and vertical stress, σ_v , ranging from 24 to 1700 kPa. The other relevant parameters and factors also ranged within the boundaries of interest. Such an extensive testing program yielded 12,500 recorded cyclic loops, which are organized in a computer database where they can be easily manipulated, compared and plotted in various useful formats.; The existing modulus reduction curves, G_s/G_max vs. γ_c, and the damping ratio curves, λ vs. γ _c, and their trends with plasticity index of the soil, PI, are refined in the domain of small γ_c and extended into the domain of large γ_c. The effects of PI, degree of saturation, S, void ratio, e, σ_v, γ_c, number of cycles, N, rate of straining, frequency, f, and the shape of cyclic straining, on the values of G_s, G_s/G_max and λ are examined. Some trends agree with previously published data, while some provide new insights into the above effects. The cyclic settlement, ϵ_v, of several different partially saturated soils was examined and modeled too, including the evaluation of the effect of f on ϵ_v. In addition to that, the volumetric cyclic threshold shear strain, γ_tv, for both cyclic settlement and pore water pressure buildup was examined for several different soils. This study of γ_tv represents the most comprehensive study of γ_tv for clayey soils conducted to date.