THREE-DIMENSIONAL STRESS RELAXATION PROCESSES IN THE VICINITY OF THE TUNNELLING FACE
1978
The problems of tunnelling in unstable strata are substantially determined by the three-dimensional behaviour in the vicinity of the tunnel face, the method of advance and support and the rate of advance in relation to the time the rock is unsupported. The present paper represents a summary of two comprehensive experimental works, which arrive at some remarkable results partly by unconventional methods. Both the three-dimensional stress relaxation as well as the time-dependent structural behaviour of underground cavities were investigated by measurements in actual tunnel projects and also in comparable equivalent models. Some of the results of these investigations are A stress-relieved zone around the tunnel face, followed by stress concentrations or convergence discontinuities one or two diameters behind the face, an undulating stress distribution in the rock and an abrupt time-dependent relaxation of stress peaks in relation to the rate of advance and the time without support. The limits of the conceptual model of the mechanics of continua are revealed. (TRRL)
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