Identification of discontinuities in resin layer of grouted rock bolts

摘要

The rock bolt support system is one of the major elements of safe maintenance of roof sections in coal mines almost all over the world. Leading coal producers such as the USA, South Africa, and Australia use the rock bolt system as practically the only one in roadways, room, and pillar sections. It has also been increasingly popular in other coal-producing countries including Poland. The function of the rock bolt support system is to anchor and reinforce the rock zone in the near field of an underground opening to deeper rock strata. In contrast to the conventional steel framework, the crucial part of the rock bolt support system is concealed from the observer. The developed method uses modal analysis procedures and is based on impact excitation. It consists of two main phases: experimental, which entails the measurement of modal characteristics of an investigated object; and theoretical involving reference to the Finite Element (FE) model databases. The main assumption of the method is that boundary conditions have to be such that the in situ bolt behaves like a cantilever. Since an installed rock bolt acts as an oscillator, different lengths of grouting discontinuity form different boundary conditions and change its modal parameters.