Instability of boreholes with slurry

Drilling slurry has been widely used in the construction of wet-processed borehole excavation, and the stability of such an excavation is of great concern to engineers. In this short note, the problem of borehole stability is revisited using the finite element limit analysis. The study sets out to establish an undrained correlation between stability number and depth ratio of a borehole excavation under axisymmetric condition. To understand several observed phenomena, the effects of slurry pressure and the increasing undrained strength with depth are investigated. The overall aim of the note is to produce practical solutions in the form of design equations for engineer in the field to evaluate the borehole stability using a simple factor of safety