Subsidence, Bed Separation and Stress Change during Longwall Mining

A comprehensive field geotechnical monitoring program was carried out at West Cliff Colliery, Australia, which included one deep hole extensometer, two piezometers and two near-surface biaxial stressmeters installed at the bottom of a small valley above Longwall 32. A subsidence survey was carried out along two cross lines centered at the deep hole extensometer. The aim of this study was to determine the strata movement in the overburden rock mass in order to determine the injection horizons and evaluate injection efficiency for using the overburden grout injection technology to control subsidence. It was also aimed to monitor the near-surface stress change to understand the mechanism of river bed fracturing and valley closure. This paper presents the new findings from this field monitoring study.