Research On Mechanical Properties Of Methane Hydrate Soil And Rockfills Using DEM

Soil is composed of discrete soil particles. The discrete property of soil particlesmakes the mechanics characteristics very complex. Discrete element method (DEM) is anew numerical computation method, which uses discrete elements to simulate discretematerial such as soil. DEM code is used in this thesis to simulate methane hydrate androckfillsto study the mechanical characteristics.Methane hydrate is considered to be valuable resource to solve the currentworld energy crisis. However, in order to evaluate the safety of the submarinemethane hydrate production,we must understand the impact of methane hydratedecomposition on seabed soil. Two-dimensional discrete element method isoften used for qualitative analysis of material characters. PFC2D is used to buildmodel to study the mechanical property of soil containing methane hydrate.PFC2D model is used to simulate undrained biaxial compression test. The resultreflects the undrained shearing softening and hardening process and analyzesthe undrained shearing behavior of soil with different compactness. In addition,PFC2D could calculate the excess pore pressure produced by decomposition ofmethane hydrate, with Boyle’s law and effective stress principle, ignoring thechange of volume of soil particles and water. PFC2D is also used to assess theeffect of methane hydrate decomposition on undrained shearing characters ofsoil, and analyze the submarine slope stability.Many high-fill projects are constructed of rockfills. However, the particlesizes of rockfills are relatively large. The laboratory testing of rockfills requireslarge equipment, e.g. large triaxial apparatus, which are not commonly available.This paper discusses the possibility of using discrete element method(DEM) toinvestigate theshearingbehavior of rockfills along different stress paths. Usingdiscrete element method (DEM), a number of spherical units could be bondedtogether to form one non-spherical particle, to simulate crushable rockfillsparticles. A discrete element model is then built and calibrated against a set oflarge scale triaxial tests of rockfills subjected to different confining pressures.Model parameters are determined through comparing simulation results with the test results. The stress-strain behavior of rockfills loaded along different stresspaths are then predicted using the model with the same parameters.Bycomparing the simulation results with the large scale stress-path triaxialtesting data, it is verified that the DEM model can reasonably simulate themechanical properties ofcrushable rockfills.Meanwhile， the small strainstiffness property of rockfills is discussed here.