A comprehensive underground excavation design (CUED) methodology for geotechnical engineering design of deep underground mining and tunneling

Abstract

Underground excavation designs in mining and civil engineering projects are associated with a different geometric, complex ground structure, field–stresses, and groundwater conditions. Due to diverse influence factors and various requirements for each project, the design procedure should be customised based on the site-specific factors. The design procedure is only a direct and triggering process, while in a complex ground condition, mixed failure mechanisms may occur. The objective of this research is to present a new methodology "Comprehensive Underground Excavation Design" called CUED method with emphasis on diagnosis of ground behaviour and failure mechanism(s) in deep and hard rock conditions for long-term life expectations. The CUED method proposed in six steps including ground characterisation, diagnosis of ground behaviour, identifying failure mechanism, design analysis to manage ground behaviour, construction, field measurements/monitoring and design update. A procedure has been defined for each step by determination of input data, processing data and output data, so-called IPO approach. IPO is applied to determine parameters of the CUED method in each step. Based on the proposed method, rock mass composition provides sufficient information to the diagnosis of ground behaviour. Then, different types of failure modes and related mechanisms are evaluated following three main factors: rock mass structures, stress concentration and construction conditions/key features of the projects. In some cases, only one failure mechanism is dominant, but in many cases, may failure starts with one mechanism and then followed by other mechanism or combination of mechanisms. It makes the design more complicated and should be adjusted during operational stages. Design analysis to manage ground behaviour is carried out to determine appropriate strategy in an unstable ground such as selecting suitable excavation method, excavation sequences, and ground stabilisation methods regarding time-cost model of the projects. Meanwhile, the design parameters are implemented in the construction stage by excavation, loosening, depressurisation/stress management, quality control of materials and installing ground support systems. Optimisation of design parameters is performed through new acquired data in field measurements to reduce the risk of rock failures. The proposed design procedure was verified through several case studies from mining and underground excavation projects, and some typical cases were presented. The purpose of the proposed design method is to attempt to increase productivity, cost optimisation, safety improvement, and consequently diminish instability in underground excavations. The research results indicated that the proposed method efficiently increase safety and optimise the project's cost and time. The presented CUED method could be used as engineering tools for underground excavation design.