It is known that the rate of descent of the roof is the first derivative of the descent with respect to time. Knowing the dependence of the roof descent on the duration of sudden subsidences, we can easily find the dependence of the rate of descent on the duration:The dependences of the rate of descent on the duration of sudden subsidences of the roof for various faces are listed in Table 4, and are shown graphically in Fig. 3b; from the graphs we see that the greatest rate of descent of the roof occurs in the First Eastern face. In the Seventh and Sixteenth Eastern faces the rates of roof descent during the period of sudden subsidences were at approximately the same level. The maximum rates, found by investigating the function v = f(t) at the maximum, are 181, 87, and 86 mm/sec in the First, Seventh, and Sixteenth Eastern faces. The rates of roof descent found on a statistical--probability basis were in practically the same ranges.From the viewpoint of practical utilization of the subsidence parameters, one of the most pressing problems is to adapt hydraulic props to work in conditions liable to sudden roof subsidences. The new mechanized technology for mining the thin veins in Transbaikal developed at the Chita branch of VNIIPROzoloto together with the Dnepropetrovsk Mining Institute and the Tomsk Polytechnic Institute is based on the use of a movable mechanized extraction system for cutting ore in a vertical face [i]. The system consists of a light movable balloon support and a self-propelled drilling carriage which, during drilling and charging of the face, moves along guides fixed to the support sections. The ore is broken down onto the balloon support, which at the moment of blasting is close to the face (2.5-4 m from it). Therefore, in designing the support elements of the system it is necessary to determine their stability when exposed to blasting.Three types of loads arise during breaking-down of the ore, viz., seismic forces, impact of rock fragments, and the pressure in the air shock wave (ASW) fronts; preliminary calculations have revealed that the most dangerous load for the stability of the system is that due to the frontal action of the blast, formed mainly by the ASW. The principal supporting elements of the extraction system were DGI [Dnepropetrovsk Mining Institute] balloon chocks [2,3]. A balloon chock consists of three balloons of corded rubber material, 1.3xO.7x(0.1, ..., 0.3) m in size, connected by rubber bands. Below we discuss a design solution which transfers the explosion loads (directly or via the cutting shields) to the front walls of the balloons.Taking as an example the elastic balloon for which the theoretical scheme is shown in Fig. la, let us consider its interaction with the pressure at the ASW front. Under the load AP (the pressure in the ASW front), the front wall of the cylinder is pushed back through a distance AZ. This reduces the volume of the balloon and raises the pressure inside it, inVNllPROzoloto, Chita. Translated from No. 2,

The paper presents the results of numerical modeling of heat treatment of concrete of a monolithic floor using a heating wire in winter conditions, depending on factors such as ambient temperature, wind speed, isothermal curing temperature, and others. The following parameters were taken as the main parameters for calculating the heat treatment of concrete: the geometric dimensions of the concreting area, the type and dimensions of the thermal insulation layer to ensure thermal protection of the monolithic structure during the heat treatment of concrete, the type and characteristics of transformers that provide the necessary power for preheating and heating concrete of monolithic floors, as well as the class of concrete, cement consumption and type of heating wire. As a result of calculations, the values of the required power for heating concrete of monolithic structures, the number of transformers, the voltage on the transformer for heating the concrete, as well as the duration of the periods of heating, isothermal curing and cooling during the heat treatment of concrete were obtained. As a result of the performed numerical experiments, the modes of heat treatment of a monolithic floor were deter-mined, which ensure the achievement of the required strength of concrete of monolithic structures. This type of heat treatment of concrete during winter periods has established itself as energy efficient and versatile, since heating wires can be used in structures of any type, configuration and reinforcement. With the correct use of heating wires, it is possible to obtain high-quality reinforced concrete structures erected at negative ambient temperatures.

No abstract