Drilled mining hole testing tool - has spring inside tube with arms bearing against hole walls when released

摘要

The testing tool measures the length and alterations on cross-section of a drilled hole, being particularly for monitoring working areas subject to rock falls in coal mines. It comprises a tube inserted in the hole for virtually its entire length and distorted by the rock pressure. An insert is secured in the bottom of the hole and can be coupled to the tube, and a set of probe bars of different diameters can be inserted in the tube. Inside the tube (1) and/or the insert (2) and fixed near the bottom (3) of the hole is a spring (4), held under tension so as to extend in the lengthwise direction of the tube by a locking device (5). When the latter is released, the two or more spring arms (6) extend through the tube and bear against the walls of the hole.