Numerical simulation of stress-strain state in frozen wall during thawing

Abstract

Blasting and drilling operations during shaft sinking assume switching off the freezing columns which can lead to stability loss of a frozen wall and inrush of thawed soil into the stope. This work assesses safety of shaft sinking when freezing columns are turned off for a period of four days. It is assumed that the frozen wall loses its bearing capacity when displacement of its unfixed section exceeds 10 cm. Calculations are carried out for silt and sand stratums. Simulation was performed in finite-element software Comsol Multiphysics. Displacements of internal wall were obtained for two initial thicknesses of the frozen wall. In the first case the soil was frozen to the boundary of the future shaft, in the second case initial thickness corresponded to project documentation. It has been shown that frozen wall in silt stratum does not lose its bearing capacity even for complete defrosting. For sand stratum calculated time was equal to 85 days for the first thickness and 24 days for the second thickness of frozen wall.