EVALUATION OF IN-SITU STRESSES FROM MODIFIED FLATJACK TESTING METHODOLOGY IN THE NEAR SURFACE ENVIRONMENT

摘要

In-situ stresses can play a major role in the stability of large open pits and quarry floors in high-stress regions. Measuring these stresses is often costly and difficult. The flatjack method is a low-cost in-situ stress measurement technique; however, there is potential for cost reduction with minor changes from the typical approach without significantly compromising measurement quality. A ‘standard’ saw cut slot was used producing various smooth semi-oval openings for the installation of different flatjack shapes. Laboratory tests were conducted on specially prepared concrete blocks and the results were used along with numerical modelling to develop correction factors to compensate for the difference in shape and size between the flatjack and the slot. The smoothness and thickness of the saw cut slots eliminated the requirement for grout, decreasing installation time and allowed for recovery and reuse of the flatjack. These proposed modifications to the flatjack methodology significantly reduce the cost and time to measure in-situ stresses while appropriate correction factors account for discrepancies arising from differences in the slot and flatjack footprint. These modifications make in-situ stress measurement more accessible for smaller budget projects and practical to take a larger number of measurements improving the confidence of the results.