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Abstract
Civil engineering projects are located predominantly in urban environments. Conurbations have tended to develop in areas where there is access to arable land and water, generally associated with a lake or river system. Projects involving subsurface infrastructure such as sewer collection systems, water distribution networks or metro lines, frequently must deal with potentially unstable sediments, and a high water table. Civil infrastructure tends to be relatively shallow and therefore during the excavation phase there is considerable potential for settlement of adjacent structures, which are usually in close proximity in an urban environment. The methods developed by the civil engineering industry to construct shafts are therefore focused on controlling the ground and water, and limiting the potential for settlement.
Shafts to access mineral deposits are most generally located in hard rock and tend to be much deeper than those for civil infrastructure. Mining projects are almost always located in remote areas where the impact on communities is less. Thus there are different considerations in the shaft construction methods, with the focus more on speed and efficiency. Deep mining methods have some applications in civil engineering, most usually on hydro-electric schemes and storage caverns.
Multiple methods exist for excavating and supporting shafts on civil engineering projects. This paper reviews the available construction methods and offers a commentary on what they involve and when they are likely to be considered viable. This assessment is developed into a matrix that could be used as a guide for identifying potential shaft construction techniques for the conditions prevailing on a particular project.
1 . Introduction
Shafts are an integral part of almost all civil engineering projects involving underground construction (Fig. 1). Shafts can generally be categorised according to the support methods and excavation techniques used to construct them. The choices available to the constructor are in turn determined primarily by the prevailing ground conditions and the function of the shaft. In the latter case, the ultimate function of the shaft may not be the deciding factor as the initial function of the shaft, for instance in providing the means to launch a tunnel boring machine (TBM), may require a significantly larger excavation than the final structure to be built in the shaft.
Shafts in hard rock generally require...