Robust equivalent tunnelling Mohr–Coulomb strength parameters for generalised Hoek–Brown media

A novel robust method for estimating equivalent tunnelling Mohr-Coulomb strength parameters in elastic-plastic or elasto-brittle-plastic media satisfying Hoek-Brown failure criterion is proposed. Based on the best uniform approximation technique, this method consists of explicit and closed-form formulae in terms of elementary functions, making the estimation of equivalent parameters more convenient than other methods. A simple code is provided and a series of benchmark test cases are performed for validation. When the tunnel support is accurately known, the performance estimates of this method are better than estimates of best fitting in an artificial stress range and best fitting in the existing range methods, but not as accurate as the performance of equating model responses method and that proposed by Jimenez et al. However, when the estimation of support pressure is poor, this method is the most robust among all methods. In elasto-brittle-plastic rock mass, the advantage of robustness of this method is even more obvious. Considering both accuracy and robustness, this method can be employed as a preferable alternative.