Shear performance of yielding self-drilling anchors under controlled conditions

Abstract

The traditional installation of grouted rockbolts requires a support hole to be pre-drilled followed by the installation of a cementitious or resin grout. The rockbolt is then inserted into the grout. In highly stressed or poor ground, the presence of fractures, shear features and altered rock can lead to unravelling of the support hole and result in blockages and grout losses. Consequently, the support holes are often redrilled, resulting in oversized holes, increased installation times, and poor installation quality.Replacing the conventional drill string with a self-drilling anchor (SDA) improves both the quality and advancement rate of installation. These are critical considerations in poor ground. The SDA rockbolt is coupled to the rock drill, drilled to depth, then decoupled and post grouted. This one-step installation method overcomes the challenges of drilling into fractured rock where hole closures and grout losses are common. The operational advantages of the application of a one-step system using self-drilling anchors have recently been demonstrated in two caving operations, Oyu Tolgoi mine in Mongolia and Malmberget mine in Sweden.A yielding SDA offers additional performance benefits when in squeezing rock or seismic prone ground. There is limited data on the response of yielding self-drilling anchors to tensile and shear loading under controlled laboratory conditions. The undertaken experimental program has investigated the behaviour of a yielding SDA under tensile and shear loads. This contributes to an improved understanding of the response of self-drilling anchors under a single loading mechanism and can provide an indication of performance in highly stressed and fractured rock observed in caving operations and deep underground mines.

A review of ground support mesh testing around the world

“…Current testing is predominantly focused on lab testing for which tests are highly repeatable, and input parameters can be adjusted to gain an insight into how different parameters impact the capacity for single samples, e.g. Knox et al (2018), Knox & Berghorst (2019), Crompton & Knox (2022), Knox & Hadjigeorgiou (2022), and Abreu & Knox (2022). It is not possible to replicate certain underground conditions in the lab (installation quality etc.…”