Three-dimensional discrete element modeling of tunneling in sand

This thesis uses three dimensional discrete element modeling (DEM) to examine: (1) laboratory triaxial tests on Ottawa sand; (2) centrifuge testing of a tunnel in Fontainebleau sand; and (3) surface settlement along a 6.5-m-diameter shallow tunnel in mixed face conditions where the upper layer was sand.; Laboratory triaxial tests on Ottawa sand were used to establish the micro-parameters, namely, particle elastic properties and contact friction, for the DEM used to simulate the centrifuge tests and the shallow tunnel. Assemblies of smooth spherical particles as well as 'clustered' particles at both dense and loose densities at different confining pressures were modeled. Both rigid single and segmental walls were used as lateral boundaries. It was found that while the size or scale effect can be minimized the particle shape influences the peak strength of the synthetic material. Perfectly spherical particles underestimated the peak strength. The volumetric response was found to be insensitive to either particle size or shape.; DEM, using smooth spherical particles, was used to simulate a centrifuge test of a shallow tunnel in sand. The collapse pressure and near face displacements from the DEM simulations were in close agreement with the results from the centrifuge test and analytical results.; Three-dimensional DEM was used to simulate surface settlement of a recently constructed 6.5-m-diameter tunnel excavated within the City of Edmonton. The tunnel was excavated by earth pressure balanced shield tunnel boring machine and traversed in both uniform and mixed face condition. The findings from the numerical modeling suggest that the geology of the mixed-face tunneling conditions was likely the controlling factor in reducing the surface settlements.