A fracture mechanics based slope stability analysis with application to reclaimed steep-slopes

Forestry reclamation approach (FRA) is a technique used in surface mining to reclaim already mined areas, which recommends that upper 1.3 m (≈ 4 ft) of reclaimed slope should be left as uncompacted as possible to facilitate successful tree root growth. However, the consequences of leaving upper 1.3 m of uncompacted material may lead to instability of reclaimed slopes that is not accurately simulated using traditional equilibrium limit methods. A numerical model for slope stability analysis based on the fracture mechanics approach is developed in this research. The interface slope region between the lower compacted and upper uncompacted material is assumed as a joint surface. Two-dimensional constant strength displacement discontinuity (DD) analysis of the joint surfaces is carried out for the dry and hydrostatic pressure conditions. The weight of the overlying material acts as boundary conditions on the joint surfaces. Once, the DDs over the joint surface(s) are estimated, then the stresses at the prescribed points on the slope are estimated and checked using Mohr-Coulomb criterion to locate potential failure surfaces. The advantage of applying the DD analysis is that it reduces the problem dimension by one degree and eliminates discretization of whole slope area. The fracture mechanics based slope analysis gives better estimate of stability, because it accounts for the local stress concentration in vicinity of the cracks. The analytical slope stability results using the DD model, GeoSlope/W model and field slope monitoring investigation results demonstrated that overall slope is stable. Hence, the FRA is applicable to steep-slopes provided the slope gradient is maintained through careful final grading.