In-situ dynamic testing of rock support at LKAB Kiirunavaara mine

A series of large scale dynamic tests were conducted at the LKAB Kiirunavaara mine using explosives to generate the dynamic load on the support system. This was done with the aim of developing a testing methodology for in-situ testing of ground support. Furthermore, the response of the installed rock support system to strong dynamic loading was evaluated. The results of the Tests 1, 2, 3, 4 and 5 indicated that the relation between the burden and the used amount of explosive had a vital role in either reducing or involving the effect of the detonation gases in the test results. Higher peak particle velocities were measured compared to those of similar large scale tests carried out in other countries. However, the level of induced damage in Tests 1 and 2 was limited to a fractured zone behind the support system while in Tests 4 and 5 the burden was unexpectedly destroyed. Based on the test results and preliminary numerical analysis, a modified test (Test 6) was designed at the same mine. The aim was to avoid the unexpected damage of burden as was observed in earlier tests, and to modify the dynamic loading leading to increase the depth of fractured zone and if possible pushing the support system beyond its limit. Results indicated that a larger fractured zone compare to earlier tests was developed behind the support system while the installed support system was still functional. Evidence from the damage to the tested cross-cuts in Test 6 indicated a reduction of radial cracks that provide access for the gas expansion. The results indicated that the installed support system, designed for dynamic conditions, performed well under the loading conditions which can cause ejection.