The rock mass' seepage property which is different from homogeneous material is very complex because of the cracks. Using new theory and method to research seepage-stress coupling character of rock mass becomes an attracted and challengeable difficulty in the domain of rock hydraulics. In this paper the particle flow code (PFC) theory is introduced to research rock mass' complex seepage property in mesoscopic aspect. To different water pressure and lateral compression the cracks' propagation rule is not identical. The rack's dip angle and distance of two cracks also affect propagation rule. These factors how to influence two cracks' initial extending angle and direction under different condition are researched by PFC. These propagation rule is very important to understand rock mass' seepage-stress coupling process.


There are many cracks which offer good condition for groundwater's motion, rest and storage in the crack rock mass[1]. The cracks cause rock mass' complex mechanic and seepage property which is different from homogeneous material. The seepage-stress coupling of crack rock mass will cause crack's initiation and propagation. This is a prominent characteristic of fractured rock[2]. It is difficult to show the crack's propagation in the seepage-stress coupling process by traditional seepage theory[3]. The crack's initiation, propagation and runthrough are the reasons which cause rock mass' destabilization and damage. In this paper the theory of particle flow code(PFC) is used to research crack's initiation and propagation from the mesoscopic aspect in the seepage-stress coupling process. To different water pressure and lateral compression the cracks propagation rule is not identical. The crack's dip angle and distance of two cracks also affect propagation rule. In this paper these factor how to influence two cracks are researched by PFC.

Fluid Coupling Method of PFC2D

PFC2D is able to model a rock mass, by bonding every particle to its neighbor; the resulting assembly can be regard as a "solid" that has elastic-plastic properties. The geometry of the assembly of circular is regarded as "real material" (figure 1). The geometry and location of each microcrack are determined by the sizes and current locations of the two parent particles from which the microcrack originated. Each microcrack is assumed to be a cylinder whose axis lies in the modeling plane. The geometry and location are fully described by the thickness, radius, unitnormal, and centroid location. The thickness equals the gap between the two parent particles. The radius is given by the intersection of the cylinder bisection plane, with a membrane stretched tightly between the two parent particles (figure 2). Where c R is the cylinder radius, and c t is the cylinder thickness.

Flow formulation

As far as the fluid is concerned, the pipe is equivalent to a parallel-plate channel, with length(L), aperture(a) and unit depth.

Pressure Formulation

Each domain receives flows from the surrounding pipe:Σq. In one time step Ät, the increase in fluid pressure is given by the following equation, assuming that inflow is taken as positive.

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