Poster Presentation Australasian Groundwater Conference 2017

Modelling of groundwater flow and geomechanical stresses near rock bolts in an underground mine (#85)

Jack Smith 1 , Wendy Timms 1 , Chengguo Chengguo Zhang 1 , Hamed Lamei Ramandi , Serkan Saydam 1
  1. The University of New South Wales, UNSW Kensington Campus , Sydney, NEW SOUTH WALES, Australia

One of the major failure modes of bolts in underground mines is Stress Corrosion Cracking (SCC) in which bolts fail due to the combined influences of tensile stress and a corrosive environment. SCC of bolts is primarily driven by groundwater chemistry and biological activity that facilitate corrosion. To investigate the conditions promoting groundwater flow and stress near installed bolts, the groundwater flow and stress in grout surrounding bolts, and surrounding rock strata are modelled using a 2D finite element technique. The model domain (15 m width by 15 m thick, with ~11,0000 elements) include a single 2m grouted steel bolt in the roof of a 5 m2 roadway with coal, clay, sandstone, and shale as the major rock types. Forty seven different rock strata configurations and nine different grout conditions are studied. The parameters of the models are set based on data from a mine in New South Wales of Australia including material properties, hydraulic conductivity, joint properties, in-situ stresses and boundary conditions. Discharge flowrates are measured at the interface between the grouted bolt and the roof. The results indicate that coal strata contains the highest groundwater discharge flow and also existence of a clay band intersecting in the bolt results in a higher discharge flowrate. It is observed that grout failure and loss result in higher groundwater discharge and consequently enhanced SCC. It is also observed that the absence of grout in upper section of the bolt leads to a high tensile stress to the bolt suggesting that improper grouting and/or grout damage contributes to the tensile stresses and flowrate that cause SCC. The results of this study provide a better understanding on the conditions contributing to SCC failure in bolts and also assists in advancing solutions for preventing SCC bolt failure.

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