Evaluation of Shear Modulus and Damping Ratio of Granular Materials Using Discrete Element Approach

Abstract

In this paper, an attempt has been made to highlight the influence of different parameters such as number of cycles, confining pressure, void ratio, gradation, initial anisotropy and stress path on the dynamic properties of granular materials using Discrete Element Method (DEM). A series of strain controlled cyclic triaxial numerical simulations using three dimensional DEM have been carried out on an assembly of spheres. Dynamic properties such shear modulus (G) and damping ratio (D) were determined from the typical hysteresis loop obtained during cyclic triaxial test simulation. It has been observed from the test results that the numerical simulation using DEM has captured the variation of dynamic properties over a wide range of shear strain values for different parameters considered for the current investigation. Maximum shear modulus (G max ) was found to be influenced by initial confining pressure, void ratio, gradation and initial anisotropy. Whereas, the damping ratio (D) was found to be influenced by number of cycles, initial confining pressure, gradation and stress path. Further it has been shown that the variation of shear modulus with shear strain can be divided into three distinct zones such as Isotropic Zone (IZ), Anisotropic Zone (AZ) and Stable Anisotropic Zone (SAZ). A drastic reduction of shear modulus with shear strain has been observed in the Anisotropic Zone (AZ). In addition, the results obtained using numerical simulations have been compared with the laboratory experimental values.

Analysis of wave propagation in dry granular soils using DEM simulations

“…9b). These observations are consistent with reported experimental results in the literature (e.g., [25,50,51,54,60]). Figure 10 shows the profile of low strain shear modulus and corresponding shear wave velocity extracted from cyclic shear stress-strain loops for different soil deposits.…”

“…Finally, at a b = 0.4 g, the range of strain increased significantly resulting in a considerable decrease in the shear wave velocity for all three soil deposits that is far from resonance and amplification factors that are less than 2. By increasing the shaking amplitude, the amplification factors reduce due to nonlinear soil behavior in the form of modulus degradation and increased damping that has been observed in several experimental work (e.g., [23,50,51,60]). Table 2 demonstrates a comparison between the amplification factor resulting from DEM simulations and the amplification factor computed from analytical method that employs transfer functions [34].…”

Microscale Energy Dissipation Mechanisms in Cyclically-Loaded Granular Soils

“…The concept of fabric is very useful for understanding the microstructure properties of granular assemblies. It has been effectively employed to characterize anisotropy while shearing granular materials using DEM simulations (Sitharam and Vinod 2010). The fabric tensor, / ij , for spherical particles is given by (e.g., Thornton 2000):…”

Energy dissipation in soil samples during drained triaxial shearing

“…A wide range of energy-based approaches have been proposed to predict the seismic liquefaction potential of a sand (e.g., Berrill & Davis, 1985;Law et al, 1990;Figueroa et al, 1994;Trifunac, 1995). The damping ratio, which quantifies the energy dissipated during cyclic loading, is often computed using the areas underneath and enclosed by a hysteresis loop on a stress-strain plot (e.g., experiments of Seed et al, 1986;Vucetic & Dobry, 1991; simulations of Sitharam & Vinod, 2010;El Shamy & Denissen, 2012). This method of computing energy terms is limited to distinguishing energy dissipated during the loading cycle and the maximum elastic energy stored during the cycle for the entire system.…”