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1. The authors have experimentally studied the parameters and characteristics of acoustic radiation in the operation of flame-jet burners. 2. The presence of powerful acoustic waves in the zone of thermal action promotes intensification of the thermal fracture of rocks, and this must be taken into account in choosing the best parameters for existing machines and in designing new rock-breaking units. 3. It is possible to model the process of rock breaking in flame broadening of boreholes by using low-power gas burners in conjunction with acoustic oscillators. Thus, by comparatively simple means, we can study the complex phenomena occurring in the borehole, and this gives us a rapid method for predicting the region of rational application of flame broadening of boreholes.

1. Direct impact of the striker mass on the rock can greatly increase the impact energy and the efficiency of the apparatus. 2. Automatic operation of the mechanism for opening the ports increases the frequency of impacts of the hydraulic drill. 3. A hazardous state which can occur in the absence of obstacles to impact can be avoided by appropriate design of the composite piston so as to brake the impact mass without expansion of the pneumatic spring. 4. In contrast with drilling and blasting, rock breaking by means of a high-energy hydraulic drill does not disturb the stratified structure of the rock and thus much reduces the possibility of rock falls and flooding of the working—this is especially important when cutting underwater tunnels and subways. 5. Our studies with high-energy hydraulic drills suggest that rock breaking with high impact energy may in the near future become the main method of making working in rocky ground, owing to its cheapness, universality, and capability of organization as a continuous process.

1. The forward thrust depends on the parameters of the perforator and bit and on the characteristics of the rock being drilled. 2. The optimal forward thrust should ensure that the perforator operates so that in each cycle the body drops on to the shoulder before the bit emerges to the level of the preceding impact, and the withdrawal of the body should be equal to the depth of penetration per impact. 3. The equations found above can be used to determine the forward thrust in the design of feed mechanisms, as well as to elucidate the laws of change of this thrust in drilling with a given perforator and various bits, or in various rocks: this may prove useful in the design of drilling machines with automated setting to optimal drilling conditions.

1. The breakdown voltages of the rocks studied are comparatively low and do not exceed 270 kV for a 1 cm thickness. This means that electrical methods based on technically available energy sources can be used for rock breaking. 2. With voltage durations of 2·10−7 to 2·10−6sec, the breakdown voltages of wet rocks do not exceed those of dry rocks by more than 25%. 3. Impregnating rocks with an insulating liquid (transformer oil) increases their breakdown voltages. The relative increase in breakdown voltage depends mainly on the structure and porosity of the rock.

1. The higher the impact energy, the lower is the value of the stresses which must be induced in a rock mass being broken. 2. The use of high impact energies creates more favorable stresses for the percussion tool. 3. In the case of high-energy impact, with increasing hardness of the rock the rate of rock breaking will either decrease very slightly (in contrast with fracture by a cutting tool or roller bit) or even increase.