Calculation of rock pressure in shafts and roadways of circular section

Abstract

In previous papers [1–4] the author has developed the theory of rock pressure on ring-shaped walls of circular section for the conditions when: 1. (a) around the shaft axis rotation symmetrical plane stresses have an influence 2. (b) in the surroundings of a roadway or circular cross section triaxial, but rotating symmetrically, geostatic stresses have an influence. This paper describes the calculation of rock pressure on ring-shaped walls of circular section for the conditions when: 1. (c) the geostatic stress condition around the shaft is rotational symmetrically but also a vertical stress appears. 2. (d) the geostatic stresses around the roadway of circular cross section are not rotation symmetrical. The origins of this paper are to be found in the following basic theses: 1. (1) The unsupported rock mantle of the roadway of circular cross section extends at right angles to the longitudinal axis of the roadway towards the inner space of the roadway when it becomes plastic under the influence of geostatic stresses. This displacement is residual in that it surpasses the degree of elastic displacement. 2. (2) The onset of plastic deformation around the roadway can be hindered by rotation symmetrical force systems acting from within and directed outwards, superposed on the roadway mantle. When the distortion potential of the resultant stresses of the geostatic stresses and the stresses of the superposed force systems are equal, even to the rock distortion (deformation) potential, then movement of the rock mantle ceases. Graphs showing the basic properties of rocks and metals under compressive loading are enclosed in the paper, which summarizes the general deduction of the distortion (deformation) potential. The relations by which to calculate the limit of the plastic and elastic ranges on the roadway edge, and the rock pressure on the linings of shafts and roadways of circular section, are described. A ring support built into the excavated cross-sectional area changes the original rock pressure distribution. The paper describes a test performed in the Ring Support Testing Laboratory of the Hungarian Mining Research Institute, based on which an approximate relation may be found for calculating the change in rock pressure. Finally some practical examples of the industrial application of theoretical results are included.