Design and optimisation of drainage systems for fractured slopes using the XFEM and FEM

The reliable and optimised design of a drainage system for saturated slopes is often a challenging geotechnical task. Such a task becomes even more challenging when a slope contains pre-existing joints and discontinuities. In saturated and semi-saturated conditions, the existence of joints may lead to a complex distribution of pore water pressure within the slope, affecting the effective stress distribution and the stability of the slope. This paper aims to study the effect of horizontal borehole drainage systems with different arrangements on pore water pressure distributions within a saturated fractured slope. In this study, several coupled pore fluid diffusion and stress-strain analyses were conducted using the e-Xtended Finite Element Method (XFEM) in conjunction with the Finite Element Method (FEM) to simulate the efficiency of a drainage system of a deep slope at the second largest open-cut mine in Australia. As one of the objectives of this study, the effect of water flow inside a joint and normal to the joint surface (normal flow) is considered as an essential simulation component. The results show that the pore water pressure distribution at the vicinity of the joint is considerably influenced by the magnitude of normal flow. Such influence should be taken into account when designing a drainage system, as the magnitude of normal flow and the performance of the drainage system may affect each other directly.