As the ground support technology developed, it has been enabled access to more geotechnically challenging ground conditions, such as hard rock mining within high stress environments. This is achieved by improvements of the ground support elements as well as additional understanding of the failure mechanisms and related ground behavior. In this paper, the process of brittle, sudden failure due to stress increase has been tested in the laboratory scale for a number of rock types and various combination of ground support schemes. The rock mass behavior shows strong correlation with its uniaxial compressive strength and largely influences the ground support demand. The results show that surface support performance and energy dissipation depend upon the implementation of a tough layer that can transfer load to the reinforcing elements while controlling the overall displacement. The laboratory results have been confirmed with implementation of large-scale trials at a high-stress mining environment.
As mining progresses to increased depths, it has always been a challenge to manage the related deformations caused by the high stress. The main failure mechanisms under the high stress condition can be classified into violent spalling failure and structure-controlled violent failure (Villaescusa et al., 2016). The depth of failure of the violent spalling failure is relatively shallow (usually less than 0.5m) and it results in surface support damage. Violent failure occurring along the geological structures can cause deeper damage to the excavations (Fig. 1.).
Excavation behaviour under the high stress has been studied using different rock materials in a laboratory scale environment (Kusui, 2016). The main purpose of the tests was to investigate the failure process and the relationship between the rock mass strength and the maximum tangential stress at a number of failure stages. Fig. 2. shows a typical experimental set-up of a 200 mm diameter unsupported tunnel before and after testing. During the test, two types of sandstone and granite were used to investigate the effects of the rock strength subjected to an increased stress. The specimens were loaded until pillar crushing was experiences at the late stages of the failure processes.