| Popis: |
This project aims to provide an insight into the behaviour of cemented sand under high pressures, and to further the understanding of the role of particle crushing. The discrete element method is used to investigate the micro mechanics of sand and cemented sand in high-pressure triaxial tests and one-dimensional normal compression. Using the software PFC3D, a new triaxial model has been developed, which features an effective flexible membrane that allows free deformation of the specimen and the natural failure mode to develop. The model is capable of exerting and sustaining high confining pressures. Cementation has been modelled using inter-particle bonds, and a full investigation of the bond properties is presented, highlighting their influence on the macroscopic behaviour (e.g. failure mode and volumetric response). A simple particle breakage mechanism is used to model the one-dimensional normal compression of sand. By considering the stresses induced in a particle due to multiple contacts, and allowing particles to fracture without the use of agglomerates, this work aims to explain the mechanics of normal compression. The influence of the mechanics of fracture on the slope of the normal compression line is investigated, and the normal compression is linked to the evolution of a fractal particle size distribution. A new equation for the one-dimensional normal compression line is proposed, which includes the size-effect on average particle strength, and demonstrates agreement with experimental results. It is shown that this new equation holds for a wide range of simulations. The time dependence of particle strength is incorporated in to this model to simulate one-dimensional creep tests, leading to a new creep law. The normal compression of cemented sand is investigated, and the results show that bonding reduces particle crushing, and that it is both the magnitude and distribution of bond strengths that influence the compression curve of the structured material. Simulations are also presented that show that it is possible to capture the effects of particle crushing in high-pressure triaxial tests on both sand and cemented sand. Particle crushing is shown to be essential for capturing realistic volumetric behaviour, and the intrusive capabilities of the discrete element method are used to gain insight into the effects that cementation has on the degree of crushing. |
