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

Abstract

In this study, the ASTM flatjack methodology was modified in several ways. The overlapping borehole slot was replaced with a ‘standard’ saw cut slot which produced a smooth semi oval opening for the installation of various shapes and sizes of flatjack without the need for grout. This methodology was tested initially in the field at Pioneer Coal in Stellarton and later in a lab program. Lab tests were conducted on specially prepared concrete blocks to evaluate the ratio between flatjack pressure and applied load. The lab tests results were used along with numerical modeling to develop correction factors to compensate for the difference in shape and size between the different flatjacks and the slot shapes used. Finally, a relationship was established between slot closure and the applied stress for the tested geometries.