RU2191411C2 - Method controlling stressed state of rock mass - Google Patents

Abstract

FIELD: mining industry. SUBSTANCE: given method deals with control over stressed state of rock mass at early stage of formation of discontinuities leading to dynamic manifestations. Train of uniform pulses is used as sounding signal. Dispersion of components of spectrum of pulses passed through controlled section of rock mass is evaluated in addition. Its change in subsequent series is employed to make judgment on changes which occurred in rock mass. EFFECT: enhanced sensitivity of control over stressed-deformed state of rock mass. 2 cl, 2 dwg

Description

 The invention relates to geophysics and can be used in the mining industry to study and ensure control of nascent processes leading to softening of the massif.

 There is a passive method of geophysical monitoring of a mountain massif, in which the average value and variance of the received acoustic emission signals are estimated at different time and equal volume intervals at different levels in each microzone, and past physical changes in the mass are judged by the inequality [1] .

 The disadvantage of this method is that the flow of acoustic emission signals from natural sources has gaps due to the fault of technical means, which cannot be in constant operation, which cannot be eliminated in mine conditions. And any omission will cause data distortion, which can no longer be used in the method to obtain reliable results.

 A device is known that implements a method in which the array is sounded by seismic-acoustic pulses and the spectrum of pulses is determined, and geomechanical changes in the array are judged by comparing the spectra [2].

 The disadvantages include low sensitivity and inability to track weak changes in the stress-strain state of the rock mass, which is very necessary for predicting the destruction of hierarchically larger changes in it.

 Closer is the method in which a stationary noise signal having a normal distribution with an average value of zero is emitted into the ultrasound array. The transmitted noise signal is received and its dispersion and the period of the autocorrelation function are measured. It is believed that the position of the maximum of the reference pressure zone corresponds to an array point with maximum dispersion and a minimum period of the autocorrelation function of the received signal [3].

 The disadvantages include low sensitivity, because this method is integral and it estimates the variance of the entire signal as a whole.

 The claimed solution is aimed at increasing the sensitivity of monitoring changes in the stress state of the rock mass.

 This goal is achieved by the fact that in the known method consisting in sounding sections of the array with signals, determining the variance of the signal that has passed the controlled section of the rock mass, a series of several bursts of uniform pulses is used as the probing signal, and the variance of the components of the spectrum of the signal that passed the controlled section of the mountain massif, and the repetition rate of a series of pulses is determined by the speed of geomechanical processes in the massif, and the duration pulses per burst and porosity designate the same and are selected based on the detail of control.

 The essence of the proposed method is as follows.

When sounding the array as a radiating signal, use a series consisting of several packs of uniform pulses (figure 1). Such a signal, having passed the controlled section of the massif, will have features in its spectrum, i.e. characteristic changes in the amplitudes of individual harmonics. The spectrum of one burst of pulses that passed the controlled area of the rock mass is shown in Fig.2. Here, Aω ₁ ... Aωn is the amplitude at the corresponding frequencies ω ₁ ... ωn; ω ₀₁ ... ω _0k are the frequencies at which the spectral density function is zero. When passing the entire series through the controlled area, we get as many spectra as there are packs in the series. Each time, a signal that has passed the controlled section captures various changes in the spectral components in its spectrum, which corresponds to physical changes in the state of the rock mass. Moreover, higher harmonics are responsible for smaller changes in the structure of the massif, and vice versa.

где k - номер серии;
i - номер гармоники;
j - номер пачки в серии;
n - количество пачек в серии;

- оценка дисперсии амплитуды i-й гармоники k-й серии;

- среднее значение амплитуды i- гармоники k-й серии;
A_ij ^k - значение амплитуды i-й гармоники j-й пачки k-й серии.To achieve high control sensitivity, it is necessary to evaluate the variance of the amplitudes in the spectrum of the signal that has passed the controlled section of the rock mass, because she is more sensitive to change. The variance estimate is determined using the following expression:

where k is the series number;
i is the harmonic number;
j is the number of packs in the series;
n is the number of packs in the series;

- estimation of the variance of the amplitude of the i-th harmonic of the k-th series;

- the average value of the amplitude of the i-harmonic of the k-th series;
A _ij ^k is the amplitude value of the i-th harmonic of the j-th packet of the k-th series.

 So, when passing one series through a controlled section of a mountain massif, we obtain as many estimates of the variance of the amplitudes as many harmonics were chosen for control. When repeating a series, the frequency of which depends on the speed of geomechanical processes, we obtain new values of the variance estimates of the selected amplitudes, which are subject to comparison.

 The pulse duration and duty cycle in the pack should be the same. With a sufficiently detailed control, it is noteworthy that, at high duty cycle values, the signal spectrum contains a very large number of harmonics slowly decreasing in amplitude, which allows you to very carefully examine a particular section of the array or structure.

The zero of the spectrum envelope function ω _0i depends on the pulse duration τ (Fig. 2). So, when studying the higher-frequency part of the spectrum, which is responsible for very small physical changes in the structure of the array, ω ₀ should be shifted to the right along the axis ω, for which the duration τ is reduced.
Comparing, thus, the obtained estimates of the dispersion of the signals of the preceding with the subsequent ones, it is possible to estimate the change in the physical state of the monitored section of the massif with greater sensitivity by changing them.

 The experiments were carried out on rock samples with a cube side of 30, 50, 70 mm. Excitation and receiving sensors were recorded on the selected samples. The radiation was carried out in series consisting of packs of rectangular pulses with an amplitude of about 10 V. A spectrum analyzer with memory SWRl0ls from SIEMENS was connected to the output of the receiving sensor. Estimates of the variance were determined in the frequency range 0.2-2.0 MHz. With a slight change in the load on the samples, the dispersion estimate changed (increased), moreover, in the high-frequency region, more significantly, while the averaged signal spectrum remained unchanged.

Literature
1. RF patent 2090905 from 09/20/97, G 01 V 1/00 BI 26.

 2. Auth. St. Petersburg 1645511, 1991, E 21 C 39/00, BI 16.

 3. Auth. USSR Academy of Sciences 1452984, 1989, E 21 C 39/00, BI 3.

Claims (3)

1. A method of controlling changes in the stress state of a mountain massif, including sounding of sections of the massif with signals, determining the variance of the signal that has passed through a portion of the massif, characterized in that a series of several bursts of uniform pulses is used as the probing signal, and the variance of the components of the spectrum of the signal that passed the controlled portion is additionally array according to the formula

where k is the series number;
i is the harmonic number;
j is the number of packs in the series;
n is the number of packs in the series;

- estimation of the variance of the amplitude of the i-th harmonic of the k-th series;

- the average value of the amplitude of the i-th harmonic of the k-th series;
A _ij ^k is the value of the amplitude of the i-th harmonic of the j-th packet of the k-th series;
and by their change in subsequent series they judge the change in the stress state of the massif as a whole.  2. The method according to claim 1, characterized in that the repetition rate of a series of pulses is determined by the speed of geomechanical processes in the array.  3. The method according to claim 1, characterized in that the duration, amplitude, duty cycle of the pulses in the packet should be the same and are selected based on the control detail.

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