Analysis of the influence of groundwater and the stress regime on bolt behaviour in underground coal mines

摘要

The service failure of rock bolts and cable bolts are frequently reported issues in underground coal mines.Whilst numerous experimental investigations concerned with the service failure of bolts have been conducted,numerical modelling offers an alternative approach in evaluating the factors contributing to service failures of bolts in underground mines.In this study,analysis of the influence of groundwater and tensile stress on bolts in underground coal mines was studied through the numerical modelling of a grouted bolt in the immediate roadway roof.Bolt tensile stress and groundwater dripping rates in the immediate roadway roof were analysed using a package based on finite element method to assess the effect of coal roof thickness and claystone bands,as main contributors of known service failures of bolts in roadways of underground coal mines.Increasing coal roof thickness was found to increase bolt dripping rates.Probable location of stress corrosion cracking (SCC) occurrence was established through examining the shift and increase in maximum bolt tensile stress that was exhibited along the bolt length with increasing coal roof thickness.Claystone bands situated at the top and centre horizon of a grouted bolt produced lower bolt dripping rates compared with scenarios with no claystone bands.Intersecting claystone bands at the centre horizon of a bolt for a fully grouted bolt could increase the likelihood of SCC corrosion and bolt failure by contributing to microbial corrosion processes and grout fracturing by tensile stress.This study improves the understanding the bolt failure associated with the presence of groundwater and changing stress environments,which in turn is imperative in formulating strategies to mitigate support element failures and improve the ground support viability.