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Rock mass classification in highway tunnel engineering during exploration phase and case study

Yanqiang Du, Bing Xie

Archives of Civil Engineering

2023

Vol. 69, nr 2

141--153

It is the foundation of tunnel engineering to classify the rock mass surrounding tunnels. However, it is not easy to precisely determine the class of rock mass in practice as sufficient geological exploration need to be completed before rock mass classification, and there exists some disputes referring to the rationalization of dozens of methods for rock mass classification through the world. The principles and procedures of the basic quality method, which are widely used in China, are presented in this paper, and the application process of the basic quality method is showed with a project case of Zhongnanshan highway tunnel which has operated in safety for nearly a decade. Then, both the advantages and disadvantages of the basic quality method are analyzed in terms of practical engineering applications. In consideration of the defects of the basic quality method, the concept of the subclassing of surrounding rock in grade III-V is developed in the end and the criterion is given to determine the subclass of rock mass. This study is aimed at providing some useful ideas and a reference for rock classification in highway tunnel engineering.

Calculation model and analysis for lay-by spacing in highway tunnel

Liang Bo, Xiao Yao

Archives of Civil Engineering

2022

Vol. 68, nr 4

347--357

Tunnel lay-by spacing is directly related to traffic safety and engineering investment. Nevertheless, its mechanism is not clear, and the rationality of the exiting norms with respect to tunnel lay-by spacing needs to demonstrate. A calculation model for tunnel lay-by spacing was derived by considering the headway and the physical kinematics of the two vehicles chasing and encountering. With it, the influence of various parameters on lay-by spacing were analysed and the rationality of the model were discussed through comparing with existing norms. Results shows longitudinal gradient rate, daily average traffic flow, rolling resistance coefficient, posted speed limit are significant to determine the lay-by spacing, and the most important parameter is longitudinal gradient rate. Existing tunnel lay-by spacing norm values are not reasonable enough, either too strict or too loose. These findings provide scientific support for how to select tunnel lay-by spacing value, which can improve tunnel traffic safety and make engineering investment reasonable.