Large excavations and their effect on displacement of land boundaries

A study to estimate land surface movement caused by large surface excavations in sedimentary strata is presented. In stratified or jointed strata the stress relief driven movement adjacent to large excavations can be significantly larger than expected. High lateral stresses measured in Australia and other places around the world indicate that the ratio of horizontal to vertical stress has been particularly high at shallow depths. The in situ strata is in compression and during excavation, stress is relieved towards the opening causing strata movement. Large excavations such as, open cut mines or highway cuttings, can initiate an extensive horizontal slide of surface layers towards the excavation. These ground movements can be damaging to surface structures such as water storage dams and large buildings. Based on stress measurements at shallow depths in Australian coal mines the study presented here calculates and models the extent of potential ground movement along the bedding surface adjacent to large excavations and provides a new prediction tool of land movement at the excavation boundary that can benefit the geotechnical practitioners in the mining industry.