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The intense increase in the volume of construction is making the problem of creating effective methods and means of nonblasting fracturing of materials quite urgent.The Institute of Hydrodynamics, Siberian Branch, Academy of Sciences of the USSR, has conducted theoretical and experimental investigations into the creation of means of fracturing solid materials by high-pressure pulsed jets. The jetting method of fracturing has a number of virtues: there is no outlay for an expensive tool, since the rock is fractured by water; dust does not form, which eliminates silicosis; the implement does not contact the working face; pulsed jets act on the face with a high instantaneous power. However, the results of testing the water-jet propelling devices created at the Institute of Hydrodynamics showed that although the high-pressure pulsed jets can fracture strong rocks the energy-output ratio of fracturing depends on the strength of the rock and natural discontinuity of the mass, and the economically effective area of use of such jets does not extend beyond rocks of average strength, (Fig, i). In the water-jet propelling devices, by means of which the results of fracturing rocks being analyzed were obtained, the pressure in the impact chamber gradually increases, due to which shooting of the jet and its spontaneous damping occur. At the same time there are suggestions [i] which permit eliminating the unfavorable features of the water-jet devices of the given design, which apparently can introduce certain corrections in the conclusions about the effectiveness of using pulsed jets.

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Owing to the huge reserves in the Kuzbass, in the immediate future the proportion of coal won by the opencur method will soon be doubled or trebled. Hydromechanization will be employed increasingly for overburden removal in the Kuzhass open-cut mines. In the past 3 years about 80 million m s of overburden has been excavated by this method. The cost of this work was only a half or a rhixd of that for power-shovel methods and other methods of transport. The advantages of continuous operation associated with hydromechanization have been clearly demonstrated (the labor efficiency has been increased by a factor of 2-2.5). However, despite the high efficiency of hydromechanization in comparison with other transport facilities, the performances of the giant jets in moderately plastic and highly plastic alluvial rocks are low. Thus, whereas the performance of a ZGM-2M hydraulic machine in light loams is 360-600 mS/h, in coarsely pelitic, silty, and sandy clays it is only 60 mS/h.Excavator performances in such rocks (with railway transport) are also poor, particularly in winter. At the Bacharsk//open-cut mine the capacity of the steam-driven trains in the case of hard rocks is 2300 mS/shift in summer and 2000 mS/shift in winter; in the case of plastic rocks these figures fall to 1800 and 1200 mS/shift in summer and winter, respectively. Furthermore, in the Kuzbass open-cut mines the amounts of rock which cannot be readily removed by hydraulic jets are very great and comprise nearly one third of the total amount of detrital deposits.in recent years great efforts have been made in the Kuzbass to develop new, more effective hydromechanization methods for working such rocks. The best results have been obtained with the use of preliminary mechanical loosening; this improved the hydromechanization indices in the case of rocks with higher plasticities, but they were still far below those for light and medium mantle rocks.To obtain a more effective procedure for working clay rocks, a study was made of the feasability of artificially modifying their physico-chernical properties. It was found that the plastic properties and swelling capacities of clay rocks can be modified by artificial dehydration followed by removal of the free water and then the lyosorbed (loosely combined) water.Experiments on highly plastic Kuzbass rocks revealed a change in r (the pIasticiry index) and the swelling time with changing moisture content W of the specimen (Table 1).However, the amount of energy which must be expended on drying rocks to an effective moisture content (W < 10) is great. Even if we allow for the fact that the energy expended on hydraulic transport of clay decreases with its moisture content, we cannot place much hope in working plastic rocks by heating to remove the moisture (see the figure).Considerable promise attaches to the method in which the permeahilities of clay rocks to water are increased by electroosmotic forces. The results of experiments on highly plastic rocks of the Bachatskii open-cut mine confirm the economic practic...