Stress State Change Monitoring Using Displacement Change Measurements

A method to back calculate stress state change was developed in Dynamic Control of Underground Mining Operations (DynaMine) research project. The purpose of this method is to provide real-time estimates of the stress state change caused by excavation. In this paper the method is evaluated with in situ data analysis and using two-dimensional modelling. The method is based on linearly elastic modelling and multiple linear regression between the modelled engineering strains and measured engineering strains. The measurements were done at the Kylylahti mine and using data from Posiva ́s ONKALO rock characterization facility as reference. The Kylylahti test site was instrumented with two 20 meter multipoint borehole extensometers. 2D modelling was used to analyse the test site conditions using both near field and far field models. The data obtained from the test site was used to track changes caused by an excavation approximately 30 meters from the test site. The resulting stress change estimates from both of the sites were generally too high. Possible reasons for the too high estimates are discussed and suggestions for future research are given.