RU2532817C1 - Method of determining change of stress state of rock mass in vicinity of working - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to mining and is designed to determine the change in the stress state of the rock mass. The method comprises placement in the well of the hollow cylindrical acoustic line, receiving and analysis of parameters of ultrasonic signals propagating in it by means of the acoustic emission transducers mounted on its end surfaces. Preliminarily on the acoustic line coaxially with it and at some distance from each other at least two rings of textolite are fixed, which inner diameter coincides with the diameter of the acoustic line, and the outer - with the well diameter. Deformation of the well due to the shift of the reference pressure zone, results in deformation of the respective textolite rings and, respectively, the growth of acoustic-emission activity in these discs. The difference in time of arrival to the receiving transducers of those acoustic emission signals is measured, the amplitude of which is maximum of all incoming signals, and the depth of the zone of the reference pressure and its change in time is judged by the above mentioned time difference, the known length of the acoustic line and the measured rate of propagation of ultrasound in it.

EFFECT: increase in duration of the definition of changes in the stress state of rock mass in the vicinity of working during continuous monitoring acoustic-emission measurements of movement deeper into the solid mass of the zone of reference pressure.

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Description

The invention relates to mining and is intended to determine changes in the stress state of the rock mass in the vicinity of the mine.

A known method for determining the stress state of a rock mass, including sounding with ultrasonic pulses sections of the massif located between parallel wells at different depths, measuring the duration of the leading edge of each of the received ultrasonic pulses, the relative change of which with depth judges the voltage distribution in the vicinity of the mine, the depth at which the minimum duration of the leading edge of the ultrasonic pulse is noted corresponds to a maximum reference pressure zone [1].

The disadvantage of this method is the low accuracy of determining the displacement of the zone of reference pressure deep into the array during the destruction of its marginal area. Indeed, for such a definition, periodic repeated sounding of the sections of the array between parallel wells along their depth is necessary, which is accompanied by an inevitable change in the contact conditions of downhole acoustic transducers with the array. This, in turn, can lead to a change in the duration of the leading edge of the ultrasonic pulse even greater than the influence of the directly stressed state.

Closest to the technical nature of the present invention is a method for determining changes in the stress state of a rock mass in the vicinity of a mine, comprising placing in a measuring well passed from a mine circuit a cylindrical sound duct with two or more textolite rings installed along its length at some distance from each other, inner diameter which coincides with the diameter of the sound duct, and the external one with the diameter of the well, receiving an acoustic transducer fixed to t the front surface of the sound duct, acoustic emission signals propagating in it, arising in the rings of textolite [2].

In this method, each of the textolite rings is subjected to preliminary mechanical loading in the same direction that coincides with the diameter, and changes in the stress state of the near-surface array are judged by spasmodic increases in the steepness of the increase in the total count of acoustic emission signals received by the acoustic transducer.

The disadvantage of this method is the impossibility of its use during long-term monitoring observations of changes in the stress state in the vicinity of the mine. This is due to the fact that it is based on the acoustic emission effect of memory, which manifests itself in textolite rings over a time interval not exceeding 30 days. Therefore, it is precisely this period that limits the possibility of determining changes in the stress state of the massif. In practice, the change in stresses in the vicinity of the mine workings as they break and lose stability can occur for many months and even years.

This application solves the problem of creating a method that provides an increase in the duration of determining changes in the stress state of a rock mass in the vicinity of workings during continuous monitoring acoustic emission measurements of movement inland of a reference pressure zone array.

To solve the problem in a method for determining changes in the stress state of a rock mass in the vicinity of a mine, which includes placing a cylindrical sound duct in the measuring well passed from the mine’s contour with two or more textolite rings installed along its length at some distance from each other, whose inner diameter coincides with the diameter the sound duct, and the outer one with the diameter of the well, reception by an acoustic transducer mounted on the end surface of the sound duct, spread acoustic emission signals arising in it, arising in textolite rings, use a pipe of a given length as a sound pipe, in the walls of which the propagation speed of ultrasonic vibrations is preliminarily measured, acoustic emission signals are additionally received by a second acoustic converter mounted on the end surface of the sound pipe opposite to the first transducer, an electrical signal which is removed using a cable placed inside the sound duct, the time difference is measured ene arrival of the receiving transducers of the acoustic emission signals, the maximum amplitude of all the incoming signals, wherein the depth of the reference pressure zone and its time change is judged by the aforementioned time difference, a known length of the acoustic line and the measured ultrasound propagation velocity therein.

The proposed method is based on the experimentally established high acoustic emission stress sensitivity of the PCB, during deformation of which the resulting acoustic emission is characterized by high amplitude values. Moreover, the coefficient of strain sensitivity of the PCB nonlinearly increases with the increase in the deformations it experiences, which allows one to isolate the one from the PCB disks located along the control well that is currently in the reference pressure zone, i.e. experiencing maximum deformation.

A method for determining changes in the stress state of a rock mass in the vicinity of a mine is illustrated in FIG. 1, FIG. 2, FIG. 3, and FIG. 4, where FIG. 1 is a diagram of acoustic emission measurements in a control well; FIG. 2, FIG. 3 and 4 - amplitude values of acoustic emission signals arising in textolite rings at times t ₁ , t ₂ > t ₁ and t ₃ > t _2, respectively.

The scheme shown in Fig. 1 includes a measuring well 1, in which a pipe 2 of length l _T , which is acting as a sound pipe, is placed, for example, made of steel, textolite rings 3, 4, 5, receiving acoustic transducers 6 and 7, which are electrically cables 8 and 9 are connected to equipment for measuring acoustic emission parameters (not shown conditionally in FIG. 1).

Figure 2 shows the amplitude values of the acoustic emission signals 10, 11 and 12 occurring in the textolite rings 3, 4 and 5, respectively, at a fixed point in time t ₁ , when the reference pressure zone in the side array is located at a depth l _{1 of the} placement of the textolite ring 3.

Figure 3 shows the amplitude values of the acoustic emission signals 13, 14, and 15 occurring in textolite rings 4, 3, and 5, respectively, at a fixed point in time t ₂ > t ₁ , when the reference pressure zone in the contour array has shifted to a textolite placement depth l ₂ rings 4.

Figure 4 shows the amplitude values of the acoustic emission signals 16, 17, and 18 occurring in textolite rings 5, 4, and 3, respectively, at a fixed point in time t ₁ > t ₂ , when the reference pressure zone in the contour array is located at a depth l _{3 of} the textolite placement rings 5.

The method for determining changes in the stress state of the rock mass in the vicinity of the mine is as follows. In the walls of a metal sound duct 2 made in the form of a pipe with a length l _{T, the} propagation velocity ν of ultrasonic vibrations is measured. Then, on the sound duct 2, textolite rings 3, 4, 5 are fixed at a certain distance from each other, the total number of which can be several tens and depends on the maximum depth to which it is necessary to control the displacement of the reference pressure zone. Moreover, between textolite rings 3, 4, 5 and sound duct 2 provide reliable acoustic contact, for example, due to adhesive bonding. On the opposite end surfaces of the sound duct 2, the acoustic transducers 6 and 7 are fixed using an adhesive connection that provides reliable contact. In this case, the acoustic transducer 6 is connected using an electric cable 8 to one of the inputs of the multichannel acoustic emission measuring complex (in Fig. 1, conventionally shown), and the acoustic transducer 7 using an electric cable 9, passing inside the sound duct 2, to the second input of the multi-channel acoustic emission measure nogo complex. As the latter, for example, the commercially available A-Line 32D complex can be used. Next, the sound duct 2 with textolite rings 3, 4, 5 and receiving acoustic transducers 6 and 7 is placed in the measuring well 1 so that one of the end surfaces of the sound duct coincides with the production plane in which the well 1 is passed. Under the influence of stresses in the vicinity of the mine, the measuring well 1 is deformed, and maximum in the zone of reference pressure. So, for example, if at time t _{1 the} position of the zone of reference pressure is at a depth l ₁ where the textolite ring 3 is located, then this ring will experience maximum deformation. As a result, acoustic emission signals of maximum amplitude 10 will appear in the textolite ring 3, as shown in FIG. 2. As you move away from the zone of reference pressure into the interior of the array and move to the zone of natural stresses, the magnitude of the latter decreases. Accordingly, the measuring well is less deformed at a depth of l ₂ > l ₁ where the textolite ring 4 is located, in which acoustic emission signals with an amplitude of 11 will be smaller than the amplitude of the acoustic emission signals from the textolite ring 3. Similarly, the amplitude of 12 acoustic emission signals from textolite ring 5, located at a depth l ₃ > l _{2 of the} measuring well 1, will be less than the amplitude 11.

As the disturbance of the rocks of the near-mass array increases under the influence of natural and technogenic factors (for example, weathering), the reference pressure zone will shift deeper into the massif. At the same time, at some point in time t ₂ > t ₁ , the reference pressure zone will reach the depth l ₂ at which the textolite ring 4 is placed. Since the textolite ring 4 will experience maximum deformations with respect to rings 3 and 5 from the side of well 1, signals will appear in it acoustic emission with an amplitude of 13, which will exceed the amplitudes 14 and 15 of the acoustic emission signals arising in rings 3 and 5 (figure 3).

With further destruction of the rocks of the near-mass array at time t ₃ > t ₂ , the reference pressure zone will shift by a distance t ₃ > t ₂ and, as a result, the textolite ring 5 will experience maximum deformations, which will generate the acoustic emission signals shown in Fig. 4 with amplitude 16, which will exceed the amplitudes 17 and 18 of the acoustic emission signals arising in textolite rings 3 and 4.

Acoustic emission signals arising in textolite rings 3, 4, 5, through a sound pipe 2, are supplied to acoustic transducers 6 and 7 and then through the corresponding cables 8 and 9 to separate inputs of the acoustic emission measuring complex, the threshold of which is configured for the maximum amplitudes of these signals . Thus, the acoustic emission measuring complex receives acoustic emission signals from only one of the textolite rings that is currently closest to the reference pressure zone, generating, accordingly, a signal with maximum amplitude. Next, using the acoustic emission measuring complex, the difference Δt of the arrival times of the specified signal to the acoustic transducers 6 and 7 is measured, and the distance L from the output circuit to the location of the reference pressure zone is determined by the formula

. $$L=\frac{l_T-\Delta t\cdot \mathrm{<figure-callout\; id="2"\; label="\nu "\; filenames="00000002.png"\; state="\{\{state\}\}">\nu </figure-callout>}}{2}$$

.

Moreover, if the L value remains constant during long-term monitoring measurements, this indicates the invariability of the stress-strain state of the rock mass in the vicinity of the mine. If the value of L increases with time, then this indicates a shift of the zone of reference pressure inland, i.e. a change in his stress-strain state.

The described method was tested in natural conditions during underground mining of the Solikamsk potash deposit in the treatment zone. A hollow steel sound pipe with an external diameter of 10 mm, an internal 6 mm and a length of 2000 mm, with three textolite rings with an inner diameter of 10 mm, mounted on it at a distance of 10 cm from each other, was placed in a measuring hole, 42 mm in diameter, drilled perpendicular to the axis of the mine in the tape pillar mm, outer 42 mm and 12 mm thick. Before placing the sound duct in a hole on its end surfaces, acoustic emission transducers GT-200 were fixed, connected through preamplifiers to the A-Line 32D acoustic emission measuring complex. The measurements were carried out in a monitoring mode for a month and a half, while the shift of the reference pressure zone deep into the pillar occurred under the influence of the redistribution of rock pressure as a result of the movement of the face in the direction from the measurement zone deep into the massif. During measurements, the A-Line 32D complex identified a specific textolite ring, which is a source of maximum acoustic emission in an automated mode in accordance with the algorithm described above. The displacement of the reference pressure zone was recorded from the disk closest to the wellhead, located at a distance of 1 m to the disk farthest from the wellhead, at a depth of 1.2 m. The indicated displacement of the reference pressure zone was confirmed by measurements made by ultrasonic sounding.

Thus, the proposed method allows to solve the problem of increasing the duration of determining changes in the stress state of the rock mass, expressed in the displacement of the zone of reference pressure inland.

Sources taken into account when drawing up an application for an invention

1. USSR author's certificate No. 1149010, cl. E21C 39/00, publ. in BI No. 13 dated 04/07/85

2. A method for determining changes in the stress state of a mountain massif: application 2011147713/03 (071550), Ros. Federation: IPC E21C 39/00 / Skuratnik V.L., Nikolenko P.V., Korchak A.V. (Ros. Federation), applicant FSBEI HPE MGSU; declared 11/24/2011; priority November 24, 2011 (Decision on the grant of a patent for an invention dated February 4, 2013).

Claims (1)

A method for determining the change in the stress state of an array in the vicinity of a mine, including the placement of a cylindrical sound duct in a measuring well passed from a workout contour with two or more textolite rings installed along its length at some distance from each other, the inner diameter of which coincides with the diameter of the sound duct and borehole diameter, reception by an acoustic transducer mounted on the end surface of the sound duct, acoustic signals propagating in it Issues arising in textolite rings, characterized in that they use a pipe of a given length as a sound pipe, in the walls of which the propagation speed of ultrasonic vibrations is preliminarily measured, acoustic emission signals are additionally received by a second acoustic transducer installed on the end surface of the sound pipe opposite to the first transducer, an electrical signal with which is removed using a cable located inside the sound duct, measure the difference in arrival times at the reception converters of those acoustic emission signals, the amplitude of which is the maximum of all incoming signals, moreover, the depth of the reference pressure zone and its change in time are judged by the above time difference, the known length of the sound duct and the measured velocity of ultrasound propagation in it.

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