Two problems in rock mechanics arising out of the working of deep ore or coal deposits

Abstract

Research of the stress-strain state of extensive rock masses, including that in the neighborhood of systems of underground workings, is becoming important as deep coal and ore deposits are being opened up, deep mines being planned and constructed, and systems for mining at great depths being created.This research is being done by geophysicists, mechanical engineers, and mining engineers, both in order to refine our basic ideas on the state of stress of the earth's crust and for practical purposes associated with mining at great depths. Depths have already been reached at which the stresses in the undisturbed rock are comparable with its strength (we arbitrarily call such depths "great").At these depths such dangerous phenomena as shock bumps are more frequent and more hazardous; here we must reexamine the question of the "optimim" technology (e.g., work with continuous stowing).We can distinguish two main groups of problems in rock mechanics, the first of which involves assessing the initial state of the rock (before disturbance by human agency), estimating its stresses and principal displacements; the second involves strength calculations on the structural elements of systems of workings (development and main workings and the influence of extraction operations).

On the loss of stability of rock around workings and holes

“…Despite the fact that this model yielded good results in solving a specific special problem, it is, nevertheless, logically incomplete, since there remain unanswered questions concerning the relation between the model in question and the already familiar classical theories [8,9], correspondence with experimental results, and the load surface and gradient law. These questions are answered rather fully from positions of the experimentally proven plasticity theory, which is proposed by Kovrizhnykh [i,2] and which is used below to solve specific problems.…”

“…The dimensions and shape of this zone will depend on the geometric shape of the working, the elastoplastic properties of the rock, and the stress state in the intact mass. It is convenient to study the inelastic deformation of rock in problems with cylindrical and spherical sym~netry for a circular working in a hydrostatic stress field.Simple analytic solutions can be frequently obtained in these cases; this makes it possible to conduct a detailed theoretical analysis and obtain a simple quantitative evaluation of the parameters required in practice.An examination of these problems with allowance for correction factors and more precise definitions of classical theories is proposed, for example, in [3][4][5][6][7][8].It is well known that for the majority of rocks in a "rigid" loading regime [7], the stress-strain curve increases to a maximum with the specimen in compression -sublimiting deformation -and then begins to drop -translimiting deformation.In plasticity theory, the first segment beyond the elastic limit is called hardening, and the second softening. Using experimental data for uniaxial compression and being based on some variant of plasticity theory, it is possible to obtain a stress-strain curve for an arbitrary form of stress state, and, in turn, to formulate a complete system of equations for the problem of a working.…”

Constructing composite diagrams for the mechanical states of rocks and ideal materials

“…

From the literature and from the proceedings of congresses and conferences on mining geomechanics, we see that there has recently been a rapid accumulation of experimental data on the strength and deformation properties of rocks and that significant experimental and theoretical work has been undertaken in this field [1][2][3]. This has covered a broad front and has yielded copious observational data, which have acquired increasing value owing to the general transition of mining operations to deeper horizons and the opening-up of new mineral deposits.

A knowledge of the laws of deformation and fracture of rocks in underground mineral working enables the engineer to predict rock pressure manifestations and to make an intelligent choice of the controllable factors so as to obtain the greatest productive effect in the support and maintenance of the workings throughout their service lives with the minimum expenditure of effort.

The strength and deformation properties of rocks, measured on specimens of given shape and size, correspond to concrete but particular schemes of forces.

…”

“…In research on rock mechanics, a popular approach regards the undisturbed rock as a homogeneous isotropic elastic half-space loaded by its own weight; to study its state of stress one usually assumes that the horizontal and vertical components of the stress are related by dependences corresponding to the hypotheses of hydrostatic [2][3][4] or empirically nonhydrostatic [5] stress distributions.…”

The state of stress in undisturbed stratified rocks with steeply dipping strata of various thicknesses

“…An important problem in mining geomechanics, especially in connection with the opening-up of deep ore and coal deposits, is to determine the state of stress of the rock before mining operations begin [1]. Without a knowledge of the natural state of stress of the rocks, it is impossible, e.g., to determine the mechanism and nature of such dangerous phenomena as shock bumps and gas bursts.…”