This paper presents the results of 3D discrete element modeling of monotonic constant volume simple shear test on Pea gravel. 3D DEM simulations were validated using results from large-scale stacked-ring simple shear laboratory tests on real soils, where each particle was accounted for and was characterized by size and shape using the translucent segregation table (TST) test. To acknowledge and incorporate both the irregularity and non-uniformity of particle shapes in real soil specimen and providing a realistic representation of soil assembly in the numerical simulations, a non-uniform distribution of rolling resistance (obtained from the particle shape characterization using TST) was assigned to the spherical particles in the simulated specimens. Different aspects of soil behavior at micro- and mesoscale such as non-coaxiality, stress-induced fabric anisotropy and validity of boundary measurements in evaluating the soil response were investigated. It is shown that boundary measurements (as generally done in laboratory) lead to a conservative estimate of the soil strength and generated pore pressure inside the specimen.

Most recent tunnel designs rely on more thorough analyses of the intricate rock interactions. The three principal techniques for excavating rock tunneling are drill-and-blast for complete or partial cross-sections, TBM only for circular cross-sections with full faces, and road header for small portions. Tunnel-boring machines (TBM) are being utilized to excavate an increasing number of tunnels. Newer studies have demonstrated that subterranean structures such as tunnels produce a variety of consequences during and after ground shaking, challenging the long-held belief that they are among the most earthquake-resistant structures. Consequently, engineering assessment has become crucial for these unique structures from both the geotechnical and structural engineering standpoints. The designer should evaluate the underground structure's safety to ensure it can sustain various applied loads, considering both seismic loads and temporary and permanent static loads. This paper investigates how adding elastic, soft material between a circular tunnel and the surrounding rock affects seismic response. To conduct the study, Midas/GTS-NX was used to model the TBM tunnel and the nearby rock using the finite element (F.E.) method to simulate the soil-tunnel interactions. A time-history analysis of the El Centro (1940) earthquake was used to calculated the stresses accumulated in the tunnels during seismic episodes. Peak ground accelerations of 0.10-0.30 g, relative to the tunnel axis, were used for excitation. The analysis utilized a time step of 0.02 s, and the duration of the seismic event was set at 10 s. Numerical models were developed to represent tunnels passing through rock, with the traditional grout pea gravel vs. isolation layer. A parametric study determined how isolation material characteristics like shear modulus, Poisson's ratio, and unit weight affect tunnel-induced stresses. In the meantime, this paper details the effects of various seismic isolation materials, such as geofoam, foam concrete, and silicon-based isolation material, to improve protection against seismic shaking. The analysis's findings are discussed, and how seismic isolation affects these important structures' performance and safety requirements is explained.