Professor Ernesto Villaescusa, Industry Chair in Mining Rock Mechanics, Western Australian School of Mines, Curtin University of Technology notes that he “read with interest the article entitled Strata control” in International Mining’s May issue. He comments: “Leading photo. It raises a lot of questions… For example if this would be a typical installation practice, the position of the operator leaves a lot to be desired. In unsupported ground, on a typical development face, it means that the operator is indeed exposed to instability from above.

“The statement ‘hard rocks mines are moving from mechanical to resin anchor bolts to improve ground support efficiency’ needs qualification. In Australia, most mines rely on frictional bolts and there is documented evidence of problems with the efficient installation of resin bolts.”

In the paper by Villaescusa E, et al, . Quantifying the performance of resin anchored rock bolts in the Australian underground hard rock mining industry. Int J Rock Mech Mining Sci (2007), doi:10.1016/j.ijrmms.2007.03.004, the authors conclude: “The overcoring data show that for the majority of the current bolt–hole size combinations, reinforcement systems and installation practices used in the Australian hard rock mining industry, the best resin mixing and bolt encapsulation occurs within the middle region of the bolt. In all cases of low load transfer, poor resin mixing was identified as the main cause. In addition, the majority of the overcored bolts had no resin at the collar region, indicating that effective plating of the bolts is very important for long-term effectiveness. The worst conditions in terms of encapsulation and load transfer are found towards the toe region of the bolts.”

Villaescusa continues: “However, the biggest issue I have is with the shotcrete section of this article.

“First of all, shotcrete does not provide active support ‘within minutes’, and the fibres are not designed to secure a ‘good bond’ with the rock. Most importantly, the suggestion that ‘most mining fatalities are caused by small stones weighting less than 1 kg’ is plainly wrong. This is a dangerous statement that is clearly designed to discredit the role of wire/chain link mesh in rock support (in favour of shotcrete). Our experience and research outcomes clearly show that mesh is a critical component of a ground support strategy, specially when deformations exceeding 50 mm are likely to be experienced when the shotcrete is no longer effective.

“Furthermore, the statement that TSL can be used as ‘a replacement for wire mesh’ is also not correct or scientifically justified. Our research shows that the current TSL products have serious force-displacement deficiences.”

John Chadwick responds: “Both Mike Rispin and I were able to discuss these points with Professor Villaescusa at the recent MassMin conference in Sweden and the other contributor to the shotcrete discussion has been made aware of Villaescusa’s points.

Michael Rispin, Head of Mining, UGC International, BASF Construction Chemicals Europe: “In response to Dr. Villaescusa’s concerns regarding the article, I will first and foremost address his concern with respect to the part on TSL as contributed by BASF. He and I had the opportunity to speak about this face-to-face at MassMin and I believe that we came amicably to an equilibrium regarding the issue and attributed it primarily to interpretation and semantics.

“The passage in the article reads: ‘Largely designed to be a rapidly applied, temporary ground support or as a replacement for wire mesh in conjunction with rock reinforcement, TSLs offer …’. We stand fully behind this statement.

“The interpretation of the effectiveness of TSL or that of wire mesh is not represented by the statement and is, of course and as with other means of ground support, dependent upon local conditions, application specifics, thickness of TSL, gauge of wire mesh, etc. Notwithstanding that, the statement as published is maintained to be accurate.”

Further comment and contributions are welcomed.