Sinking of vertical shafts and other mine workings by drilling and blasting leads to the development of roughheSS (projections and hollows) in the peripheral rock; with the usual type of drilling and blasting, these reach 50-70 cm in depth (Fig. 1). A number of recent analytical papem [1-3, etc.] show that these roughnesses have a marked influence on the stress distribution in the periphery of a working, especially an unsupported one. We have experimentally attacked the problem of the action of a sprayed-concrete support (lining) and its interaction with the surrounding solid rock weakened by curved apertures.Mathematically, the problem is analogous to that of the stress distribution in a weightless plate with a hole, the periphery of which simulates the roughnesses of the unsupported working, or in a plate supported by a ring which repeats these roughnesses, with uniform compressive stress at "infinity." We used the optical-polarization method of investigation, with plane models with "frozen-in" stresses. The scale of the models was 1:100.The models were disks, 175 mm in diameter and 10 mm thick At the center of each disk was a hole simulating a vertical working with a rough* or smooth periphery. In preparing models with supported contou~ we glued a ring into the hole, so that its external contour matched the internal contour of the hole. The models were made Disks simulating the solid rock were made from SD-10 resin, which has a modulus of elasticity of E = 140 kg/cm z at 'the freezing point. The model supports were made from SD-5 (E = 45 kg/cm~ or epoxy resin (E = 400 kg/cm~.

Most underground workings in ledge rocks, in coal and ore mines or constructed for transport and power requiremerits, are excavated by drilling and blasting. We therefore need information on the stress-deformation (mechanical) state of rock masses near these workings.Despite some differences of approach to the problems associated with determination of the characteristics of the state of this sector of rock masses, certain generally accepted ideas are held on the phenomena and processes characteristic of ledge rock when a mine working is driven through it; the essence of these ideas is as follows [1-4, etc.].When a mine working is driven through ledge rock in a state of natural stress, the stress-deformation state changes and the following regions are formed near the working: a) a region of artificially fissured rocks (weakened by driving the working) of reduced strength and stresses (in comparison with the undisturbed rock mass); b) a region of higher stresses, within which man-made fissuring is absent.It is assumed that the strength of uniform naturally undisturbed rocks hardly changes at all as one goes further away from the boundary of the region of higher stresses and deeper into the rock mass (the changes have a random character). However, as shown by our investigations. * these ideas do not give a complete picture of the actual state of rocks.The investigations were performed in several stages. In the first stage we investigated the state of the rocks in the immediate vicinity of the periphery of the working, i.e., the intensity of natural fissuring which occurred when the mine working was driven by drilling and blasting. The dimensions of this region and the fissuring intensity were established within specific intervals from the fall in the pressure of compressed air injected into the rock mass in various different isolated sectors of boreholes driven into the walls of the workings. The measurements were performed in boreholes of diameter 45-47 ram, up to 1.5 m long, in sandstones, siltstones, and clay shales.The investigations showed that at the periphery of the working, clay shales and siltstones underwent maximum disturbance. With increasing distance from the periphery into the rock mass, the degree of disturbance of the rocks decreases relatively rapidly (30-50 cm) and is practically stabilized at a distance of 1.0-1.3 m. The degree of disturbance of strong monolithic sandstones is very slight and is stabilized 15-20 cm from the periphery. Siltstones and clay shales exhibit greater disturbance near the periphery, but the degree of disturbance decreases fairly sharply as one goes further into the rock mass.Similar results were obtained in the Karaganda coalfield, in the mines of the Urals, the Kola Peninsula, and other regions.We must determine how erosion factors affect exposed rocks in order to establish the contribution made by these processes to the formation of a fissure region and its development as time passes. This problem was solved *E. B. Revzyuk helped with the experiments.All-Union Scientif...