Longer-term performance of grouted bolts in different lithologies in the Illinois coal basin mines

摘要

This paper assesses anchorage performance of fully grouted bolts in different lithologies in two coal mines in Illinois using the Short Encapsulation Pull Test (SEPT). These tests were done at two different times after bolt installation. Additional testing is planned after much longer periods (180 and 270 days). A borehole was also drilled in each test area about 2.6m above the coal seam prior to bolts installation and examined with a camera to document changes in delaminations. Load cells monitored changes in few selected bolts. In addition to Grip Factor (GF), anchorage stiffness data is also developed that provides interesting insights. GF values for all lithologies are similar to those reported in literature. GF values typically increased after time. Several findings corroborate the observations in the field on roof falls.