The Fracture Mechanisms Of Rock Mass Under Stress?Seepage?Temperature And Damage Coupling Condition And Numerical Simulations By Using The General Particle Dynamics(GPD) Algorithm

A novel meshless numerical method, which is called general particle dynamics, is proposed to simulate samples of rock-like brittle heterogeneous material under seepage, temperature and stress coupling conditions, the numerical simulations are conducted to investigate the initiation and growth and coalescence of cracks by using a General Particle Dynamics code(GPD).(1)An elasto-brittle damage model based on the extension of the Hoek-Brown strength criterion is applied to reflect the initiation, growth and crack coalescence and the macro-failure of the rock-like materials. The particle is damaged when its stresses satisfy the Hoek-Brown strength criterion. Then, growth path of cracks is captured through the sequence of such damaged particles.(2)The GPD numerical method is adopted to establish the system of seepage and stress- damage coupling model. The displacement of the surrounding rock and fissure extension rule of underground tunnel after excavation under conditions of containing water and without water are studied. The influence of seepage on stress field and damage field are studied.(3)A novel numerical model of the coupling effects between the vertical stress and the internal hydraulic pressure on the stress field around the tips of the flaw and the propagation and coalescence of cracks in the framework of General Particle Dynamics is proposed, in which interaction among discrete particles is formulated using the virtual-bond method. Fractures of the virtual bonds among particles are determined by the Hoek-Brown damage evolution law of rock. The fractured virtual bonds can only bear the compressive and frictional behaviors between two particles. While, the completed virtual bonds can bear the tensile, shear and compressive behaviors.Furthermore, a novel generated particle method is proposed to simulate the flow of fissure water. The numerical results show that the water pressure plays a key role in the stress fields around flaw tips as well as the propagation paths and the coalescence pattern of wing cracks and secondary cracks.(4)If the thermal expansion coefficient of the inlaid grain is larger than that of the surrounding media,radial-cracks will be generated in the surrounding media,and theta-cracks emerge if the thermal expansion coefficient of inlaid grain is smaller than that of the surrounding media. The results agree well with the experimental results.(5)The seepage coefficient of rock mass is decreased when the temperature of surrounding rock is reduced. Crack seepage velocity obviously decrease due to the effect of temperature decrease.Temperature has a larger effect on seepage field, at the same time, the seepage field is also has great effect on temperature field. The temperature field around the crack is uneven due to difference of specific heat between rock and water.(6)The damaged zone above the vault and below the floor is decreasing when the the lateral pressure coefficient is reducing under the condition of seepage- temperature- stress coupling. The tension stress zone is also decreasing when the the lateral pressure coefficient is increasing.