3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Excavating through the kalahari group rock masses: practical experience from a small-scale shaft sinking project(2019) Mateveke, Raymond; Mateveke, RaymondTunnelling projects in the weak Kalahari rock masses of the Northern Cape, South Africa present significant design challenges for both large and small-scale excavations. Most of the design of tunnelling and support carried out at present in the Kalahari is based on experience, analytical and empirical methods. The approach typically makes use of limited geotechnical information from the project site.The Kalahari basin is a complex geotechnical environment. Tunnelling projects are sensitive to the variable ground and groundwater conditions. A detailed site investigation to establish the geological and geotechnical model is critical in the selection of the appropriate excavation method and tunnel design. A review of early tunnelling projects revealed that in situ stresses and water infiltration is a long-term stability concern for inadequately lined tunnels through the red clay and weathered rock masses.This project explores the use of numerical modelling to predict the expected failure modes of the weak rock masses, with emphasis placed on concrete liner support for maintaining stability. The support models are analysed using 2D numerical models to determine the Factor of Safety of the liner. A support design criterion for reinforced and unreinforced concrete is introduced and appliedto the models to evaluate the lining thickness. The effect of using 2D plane strain models instead of3D analysis was also investigated. The total displacement of numerical models built in RS2 wascompared to RS3 models.