RU2094831C1 - Method of prediction of dynamic manifestations of mountain pressure - Google Patents

Abstract

FIELD: geophysics. SUBSTANCE: method is based on analysis of change in concentration of radon measured continuously in air flow pumped out of rock mass. Data of at least two sensors are necessary for analysis. One of sensors is positioned at distance of not more than 100 m from shock- hazard zone, and the other is removed from that zone for at least 400 m. Probability of mountain shock is judged by reduction of radon concentration at measurement point located near shock-hazard zone and by increase in radon concentration at distant measurement point. EFFECT: more effective prediction. 4 dwg

Description

 The invention relates to geophysics and is intended for use in the operational forecasting of dynamic manifestations of rock pressure (rock blows) in deep mines, while ensuring safe mining operations in conditions under which the possibility of rock blows increases.

 The purpose of the invention to increase the reliability of the operational forecast of rock strikes in deep mines.

 This goal is achieved by the fact that in the method for predicting dynamic manifestations, the exhalation value (emission from minerals and rocks) of radon radioactive gas in the rock mass is used as a precursor, which varies depending on changes in the stress state of the rock mass. At the same time, for the purposes of short-term (at the level of hours) forecast, continuously varying short-term in the range from minute to one hour variations in the concentration of radon and thoron in a continuous stream of air (gas) pumped out of the rock mass at least in two observation points located at different distances from the shock hazard zone in the mine, both in the immediate vicinity of it and in the far zone, at a distance of not less than 400 m, moreover, the sensors are placed in the array at a depth that is sufficient to obtain significant measurements The decrease in the concentration of radon is the effective volume of rocks that are under the influence of altered rock pressure.

 Known methods for assessing the danger of mountain impacts, operational forecasting of mountain impacts using various geophysical phenomena as precursors (forecast parameters): seismoacoustic emission and electromagnetic radiation, the attenuation decrement of elastic waves passing through the array, the ratio of the velocities of longitudinal and transverse waves, etc. P. All known methods give positive results in specific different application conditions, however, all these methods are practically not applicable in a working mine, where there is a large number of technogenic interference in the form of seismic signals caused by the operation of vehicles, drilling rigs, explosions to destroy (dump) rocks, where there is a high level of electromagnetic interference caused by vehicles, drilling rigs and pumping units.

 Closest to the proposed method is a method for determining the danger of rock blows in a mine. In this method, the change in the permeability of the studied rock mass over time is measured, which is recorded by monitoring the rate of change in pressure in a well drilled in the rock mass. In this case, either a vacuum or an overpressure is created in the well and the time of pressure change to the initial, natural level in this part of the massif is controlled. This method has three significant drawbacks.

 Firstly, it has a very large temporal resolution (up to several days), secondly, insufficient sealing of the mouth of the measuring well can lead to significant distortion, and thirdly, it is almost impossible to automate the measurement process.

 The proposed method is based on the following well-known geophysical phenomena: the constant release (emanation) of rock radioactive gas of radon (thoron), as a decay product of the uranium-radium (thorium-radium) family, the accumulation of this gas inside the rock mass, the separation of radon from the massif in case of discontinuity last one. This phenomenon has been studied in detail, and the relationship between the intensity of seismic-acoustic emission and the concentration of radon released into the environment is shown.

 The essence of the method can be explained on the basis of the graphs of FIG. 1, which shows in a schematic form the main processes occurring in a mountain massif with a change in the stress state in any part of it.

With an increase in rock pressure P / 1 / in any part of the massif, deformation / 2 / of this mass occurs and two characteristic zones arise: the compression zone / 3 / and the unloading zone / 4 /. With increasing load (Fig. 1, b), intense cracking occurs in the compression zone with the accumulation of radon (toron) in these cracks. At the same time, these cracks deform and “squeeze” radon in direction 5 into the unloading zone 4. Therefore, in the compression zone / 3 /, the radon concentration decreases (Fig. 1c), and in the unloading zone / 4 / it increases (Fig. 1, d). A further increase in the load leads to a further decrease in the concentration of radon in the compression zone 3 and its increase in the unloading zone 4. When the load exceeds the tensile strength 6 (Fig. 1, b), rock shock 7 occurs. In this case, a sharp increase in cracks and radon occurs begins to move in the opposite direction of 5, increasing the concentration in the former compression zone 3, which after a mountain impact becomes almost the unloading zone. Gradually, the concentration of radon in both zones returns to its original state (CO, CO ₂ ), which is characterized by the content of natural radioactive elements in the rock mass and emanation coefficient.

 A qualitative analysis of the processes shows that there are two characteristic zones: a compression zone (or “near” zone to the place of a possible rockburst) and a discharge zone (or a “far” zone with respect to a possible rockburst), in which the behavior of the radon concentration curve differently. In the “near” zone, a harbinger of rockburst is a decrease in the concentration of radon in the massif, and in the “far” zone, on the contrary, an increase in concentration.

 To implement the method, at least two observation wells are drilled, one of which is located close to the working face, where rock strikes most often occur, the other well is drilled away from the bottom, as a rule, in a zone calm by mountain impacts. The wells are sealed and continuous air pumping is made from them, in the flow of which short-term variations in the concentration of radon (toron) are continuously measured. Based on the analysis of variations in the concentration of radon (thoron), they judge the possibility of a rock strike and the period of time until a rockburst.

 Example. The method was tested at the Severouralsk bauxite mine in an area with relatively frequent mountain impacts in mines at depths from 350 to 600 m. When measuring, equipment with a scintillation camera was used, and analog and digital recordings were used. Information was accumulated every 10 to 15 minutes. Data averaging during data processing was carried out as necessary for 0.5, 1 or 3 hours.

 Representative registration examples are shown in FIG. 2, 3 and 4. In FIG. 2 shows continuous measurements taken at two points in the shaft. The measurements showed that the concentration of radon in the mine air remains virtually unchanged (Fig. 2, graph 1). The "background" (in the absence of excess pressure) concentration of radon in the observation well drilled in the "near" zone (Fig. 2, graph 3) has characteristic large instantaneous variations in concentration with its average constant value. This type of curve is determined mainly by technogenic factors microseismic effects due to the working mine.

 Before a mountain impact (Fig. 2, curve 2), there is a decrease in instantaneous fluctuations and a decrease in the concentration of radon in the observation well. In limestone, this effect appears 50-70 minutes before the moment of a rock impact. After a mountain impact, an increase in the measured radon concentration is observed and its restoration to its initial state.

 In an observation well drilled in bauxite “in the near” zone, the considered effect is manifested 20-30 hours before the moment of rock impact.

 The imposition of processes of preparation for rockburst and explosive mining of an array (Fig. 3) leads to specific changes in concentration. The graph shows that the explosion in the face / 1 / causes an effect similar to rock impact a sharp increase in the concentration of radon. However, this explosion could not remove the completely stressed state of the massif. 30 minutes after the explosion, the concentration of radon began to decrease again and after another 30 minutes there was a rather powerful (2600 J) rockburst / 2 /. Probably, without an explosion, the process would have taken a different path (dashed curve).

 In the "far" zone, the behavior of the concentration of radon is significantly different (Fig. 4). Rock impact is not preceded by a decrease, but by a sharp increase in the concentration of radon and rock shock follows after passing the maximum on the concentration curve. When a series of mountain impacts occurs, a superposition of the curves typical of a single impact is observed, and the maximum concentration values for each subsequent impact are reduced.

 Thus, the proposed method for measuring variations in the concentration of radon in two observation wells located at different distances from the proposed epicenter of rock impact allows us to almost unambiguously predict the possibility of rock impact and the time of preparation of the impact about its possible energy.

 In addition, the proposed method is quite technological: firstly, the process of recording radon (toron) is continuous in time and there is no need to strictly control the sealing of observation wells, and secondly, the measurement process is easily automated.

Claims (1)

 A method for predicting dynamic manifestations of rock pressure in deep mines, including the study of changes in the stress state of a rock mass from the dynamics of radon emission from this mass, characterized in that at least at two measuring points, one of which is located at a distance of no more than 100 m, the other at a distance of at least 400 m from the shock hazard zone, the concentration of radon in the continuous flow of air pumped out of the rock mass is recorded, and the probability of a rock shock is judged by the decrease in the concentration of radon in the near minutes from udaroopasnost zone measurement point and the simultaneous increase in the concentration of radon in the farthest from udaroopasnost zone measurement point.

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