Method for predicting dynamic exposure time of mine roof by considering structural creep of rock mass

Abstract

The invention discloses a mine roof dynamic exposure time prediction method considering rock mass structural creep, and belongs to the technical field of mining safety, and the method specifically comprises the following steps: S1, carrying out rock mass structure measurement on a roof rock mass, and obtaining a rock mass integrity coefficient of the roof rock mass; s2, testing rock samples of roof rock masses with different burial depths are drilled on site, an indoor creep-fatigue interaction mechanical test is carried out on the testing rock samples, stress disturbance is applied in the indoor creep mechanical test, time corresponding to a creep stable stage and a creep unstable stage of the testing rock samples is determined, and a dynamic exposure time interval of the mine roof is preliminarily obtained; and S3, revising the initial mine roof dynamic exposure time interval according to the rock mass integrity coefficient to obtain predicted mine roof dynamic exposure time. The prediction precision is high, the prediction is shortened from the month level to the day level, and the mine roof management work can be conveniently guided.

Description

Technical Field

[0001] The invention relates to the technical field of mine mining safety, and in particular to a method for predicting the dynamic exposure time of a mine top considering rock mass structural creep. Background Art

[0002] In underground mining of metal mines, the physical and mechanical properties of the rock mass on the roof of the mine are closely related to the differences in the composition of the rock itself and the rock mass structure. To a large extent, the rock mass structure plays a vital role in the stability of the mine roof. There are many weak surfaces such as faults, joints, and fissures of different sizes and directions in the rock strata. The existence of these weak surfaces causes the extreme unevenness of the rock mass quality, making the mechanical parameters of each part of the rock mass different. In addition, in a complex rock mechanics environment, continuous mine excavation will continuously change the stress conditions and states of the mine roof and surrounding rock, and the original balanced stress field will be changed again, generating a new secondary stress field. Among them, the tensile stress at the center of the roof is the largest, and its magnitude exceeds the breaking strength of the rock mass, and tensile failure will occur; at the corners of the roof and the side walls, the rock is subjected to the largest shear stress, and when its magnitude exceeds the shear strength, the rock will be sheared. Since the mine roof is affected by the gravity of the overlying rock strata, the creep characteristics of the rock, and other factors, the mine roof exposure area is too large or the time is too long, the roof support strength is not strong enough or the support is not timely enough, and the mine structure parameter design is not reasonable. All these are prone to roof collapse accidents. According to relevant statistics, roof accidents in metal mines account for 46.5% of all types of accidents underground, ranking first in casualties. Mining should always put safety issues first. The current mine roof stability evaluation method and monitoring and early warning means have conducted a relatively systematic study on the mine explosion rate area. If a long exposure time is given during the roof management process, if the roof cannot be scientifically managed during this period, the roof risk will increase and cause mine safety accidents. Therefore, the accurate prediction of the exposure time of the top of the metal mine is of great significance for guiding the safe mining of mine blasting, mining, filling and connection.

[0003] At present, the research on the exposure time of the mine mostly adopts numerical simulation, instrument monitoring and empirical formula method. The position of the roof studied by such methods is usually fixed, and the deformation law of the stress and displacement of the roof over time is obtained by numerical simulation analysis; the monitoring instrument is installed on the roof of the tunnel, and the stress or deformation is used as the warning value to record the time from stability to destruction. The exposure time obtained by these two methods corresponds to the limit time when the roof is destroyed. It is ex post facto data, and it is difficult to predict the exposure time and cannot guide the management of the mine roof; the empirical formula mostly uses stability images and introduces time factors to give a larger time span for the stability of the roof, and the accuracy needs to be improved. The above research methods are aimed at the situation where the position of the mine roof is fixed. However, when the position of the mine roof changes with the mining height, such as the upward horizontal layered filling mining method, it is relatively difficult to obtain the exposure time of the roof. For this reason, it is urgent to find a method to predict the exposure time of the roof in advance. At present, there are many studies on the mechanism of roof rock caving in metal mines. Although it explains the roof caving phenomenon in mines to a certain extent, it reflects that the roof caving is related to the stress distribution and rock structure characteristics. Therefore, the rock structure elements are crucial in the study of roof stability and cannot be ignored. In the evaluation of the stability of mine roof, it mainly includes field monitoring method, theoretical calculation and numerical simulation method and multivariate statistical method. When evaluating the stability, the exposure area and limit span that affect the stability of the mine are calculated by many methods. However, the influence of time factors on the stability of the roof, that is, the exposure time of the roof, is not considered. Foreign scholars analyzed the exposure time of the roof by statistical probability method, and corrected the stability number in the MATHEWS stability diagram by introducing time factors, and gave the recommended value of roof exposure. The exposure time span is in months, which is divided into four types: greater than 12 months, 5 to 12 months, 3 to 5 months, and less than 3 months. This approach artificially amplifies the stability state of the roof to a certain extent, and cannot reflect the actual stress state of the roof, which has great safety hazards. Moreover, the MATHEWS stability diagram of stability isoprobability lines does not consider the influence of rock mass structural creep on the stability of the roof. As the roof of the mining area is affected by factors such as the gravity of the overlying rock strata, rock creep, and mining disturbance characteristics, it is urgent to carry out the evaluation of the roof's aging stability and the prediction of the exposure time. Summary of the invention

[0004] The purpose of the present invention is to provide a method for predicting the dynamic exposure time of a mine roof taking into account the structural creep of rock mass, so as to solve the above technical problems.

[0005] To achieve the above object, the present invention provides a method for predicting the dynamic exposure time of a mine roof taking into account the structural creep of rock mass, and the specific steps are as follows: Step S1: measuring the rock mass structure of the roof rock mass to obtain the rock mass integrity coefficient of the roof rock mass; Step S2: Drill test rock samples of roof rock masses with different buried depths on site, conduct indoor creep-fatigue interactive mechanical tests on the test rock samples, apply stress disturbances during the indoor creep mechanical tests, and determine the time corresponding to the stable creep stage and the unstable creep stage of the test rock samples, so as to obtain a preliminary dynamic exposure time interval of the mine roof; Step S3: Revise the preliminary mine top dynamic exposure time interval according to the rock mass integrity coefficient to obtain the predicted mine top dynamic exposure time.

[0006] Preferably, in step S1, the rock mass integrity coefficient calculation formula is as follows: ; in, is the wave velocity coefficient, is the joint coefficient, is the rock quality index of the current roof rock mass, It is the maximum value of rock quality index of roof rock mass in the whole mining area; ; in, is the wave velocity of the roof rock mass, is the rock wave velocity; ; in, The number of regional joints obtained by non-contact measurement of the roof rock mass and digital panoramic borehole photography; is the rock volume in the measurement area.

[0007] Preferably, step S2 is specifically as follows: Step S21: obtaining test rock samples at different burial depths by drilling; Step S22: installing a disturbance stress monitoring system at the mining site, extracting the disturbance stress amplitude and disturbance frequency according to the disturbance stress wave data collected in real time; converting the disturbance stress wave into a sine wave by using a rain flow counting method or an equivalent amplitude method, and obtaining the frequency spectrum characteristic parameters of the disturbance stress wave; Step S23: Perform indoor graded creep loading on the test rock samples with different burial depths. Considering the difference between the sample size and the on-site rock mass, the field measured data is converted into laboratory data for graded creep loading. The time of each creep stage of the mechanical test is 48 hours. The disturbance is loaded during the graded creep loading according to the frequency spectrum characteristic parameters of the disturbance stress wave. The time calculation formula is as follows: ; in, is the disturbance loading time, is the disturbance frequency, The number of cycles for the disturbance loading; The loading parameters of field disturbance stress to indoor disturbance stress are transformed by introducing stress similarity ratio. The stress similarity ratio kc is defined as: kc= C L ×C ρ C L is the geometric similarity ratio, C ρ is the density similarity ratio; The calculation formula for the loading amplitude of indoor mechanical tests is as follows: ; in, is the loading amplitude, is the stress similarity ratio, is the recorded stress wave amplitude; After the test, the strain-time curve is obtained; Step S24: constructing a creep model; Step S25: Use the damped least square method to fit the creep curve of the creep model parameters according to the strain-time curve to obtain the time interval [T1, T2] of the creep stable stage and the creep unstable stage; T1 is the creep time corresponding to the loading stage corresponding to the deformation rate of 0, and T2 is the creep time corresponding to the nxth loading stage; n is the stage number when the test rock sample is destroyed, and x is the safety factor; Step S26: Determine the initial mine top dynamic exposure time interval .

[0008] Preferably, the creep model adopts the Burgers model, and the creep time is calculated when it is not greater than the rock yield stress. The constitutive equation, creep equation, unloading equation and relaxation equation of the Burgers model are as follows: ; ; ; ; in, , as well as are stress, first-order derivative of stress with respect to time, and second-order derivative of stress with respect to time, respectively; , as well as are strain, first-order derivative of strain with respect to time, and second-order derivative of strain with respect to time, respectively; and are the first spring elastic modulus and the second spring elastic modulus respectively; and are the viscosity coefficient of the first viscosity pot element and the viscosity coefficient of the second viscosity pot element respectively; For uninstallation time, and are the first and second integration constants related to the initial conditions, respectively; and are the first relaxation parameter and the second relaxation parameter respectively related to the variation characteristics of material stress-strain; For time.

[0009] Preferably, the stress function after loading disturbance is as follows: ; in, The stress function after loading disturbance, is the angular frequency of the disturbance wave.

[0010] Preferably, in step S3, the revised formula of the preliminary mine top dynamic exposure time interval is as follows: ; in, To predict the dynamic exposure time of mine roof.

[0011] Therefore, the present invention adopts the above-mentioned method for predicting the dynamic exposure time of the mine top considering the structural creep of the rock mass, which has the following beneficial effects: (1) The preliminary mine roof dynamic exposure time interval was revised based on the rock mass integrity coefficient that characterizes the structural characteristics of the roof rock mass. The introduced rock mass integrity coefficient is determined by the volume joint density and rock mass wave velocity to improve the prediction accuracy.

[0012] (2) During the indoor creep mechanics test, disturbances were loaded and the mining blasting disturbance was taken into account. The disturbance frequency and amplitude were equivalently reduced according to the stress wave characteristics of the mine blasting vibration record. The Burgers model was used to determine the time difference between the creep stability stage and the creep instability stage of the test rock sample, and the preliminary dynamic exposure time interval of the mine roof was obtained, revealing the evolution characteristics of the whole process of fault zone activation and tunnel instability.

[0013] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the roof position map of the west mining area of ​​Section 4059 of the present invention; Figure 2 This is the roof position map of the East Mining Area of ​​Section 4059 of the present invention; Figure 3 The present invention is a flow chart of a method for predicting the dynamic exposure time of a mine top taking into account the structural creep of rock mass. DETAILED DESCRIPTION

[0015] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "setting", "installation", and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0016] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0017] The research object is the east-west mining area of ​​the 4059m section of Hongniu Copper Mine, and the height of the middle section from 4059m to 4097m is 38 meters. Figure 1 and Figure 2 As shown, 12 meters have been mined in the west mining area. The mining area has a large span and a long empty roof time, which poses a serious safety risk. It is necessary to predict the roof exposure time at different mining depths for upward mining. The ore body is mined in layers with a thickness of 6 meters.

[0018] like Figure 3 As shown in FIG. 1 , a method for predicting the dynamic exposure time of a mine roof considering the structural creep of rock mass is described. The specific steps are as follows: Step S1: rock mass structure measurement is performed on the roof rock mass, and rock mass structure data is obtained by combining structural surface photography imaging, borehole television and ultrasonic testing to obtain the rock mass integrity coefficient of the roof rock mass.

[0019] The calculation formula of rock mass integrity coefficient is as follows: ; in, is the wave velocity coefficient, is the joint coefficient, is the rock quality index of the current roof rock mass, It is the maximum value of rock quality index of roof rock mass in the whole mining area; ; in, is the wave velocity of the roof rock mass, is the rock wave velocity; ; in, The number of regional joints obtained by non-contact measurement of the roof rock mass and digital panoramic borehole photography; is the rock volume in the measurement area.

[0020] Step S2: Drill test rock samples of roof rock masses with different buried depths on site, conduct indoor creep-fatigue interactive mechanical tests on the test rock samples, load stress disturbances during the indoor creep mechanical tests, and determine the time corresponding to the stable creep stage and the unstable creep stage of the test rock samples to obtain a preliminary dynamic exposure time interval of the mine roof.

[0021] Step S2 is specifically as follows: Step S21: Drilling is used to obtain test rock samples at different roof burial depths. In this embodiment, the west mining area and the east mining area obtain test rock samples at burial depths of 0 meters, 6 meters, 12 meters, 18 meters and 24 meters. At least 5 test rock samples are drilled at each burial depth to eliminate the discreteness of the rock test results at the same layer height as much as possible.

[0022] Step S22: Install a disturbance stress monitoring system at the mining site, extract the disturbance stress amplitude and disturbance frequency based on the disturbance stress wave data collected in real time; convert the disturbance stress wave into a sine wave using a rain flow counting method or an equivalent amplitude method to obtain the frequency spectrum characteristic parameters of the disturbance stress wave.

[0023] Step S23: Perform indoor graded creep loading on the test rock samples with different burial depths. Considering the difference between the sample size and the on-site rock mass, the field measured data is converted into laboratory data for graded creep loading. The time of each creep stage of the mechanical test is 48 hours. The disturbance is loaded during the graded creep loading according to the frequency spectrum characteristic parameters of the disturbance stress wave. The time calculation formula is as follows: ; in, is the disturbance loading time, is the disturbance frequency, The number of cycles for the disturbance loading.

[0024] The loading parameters of field disturbance stress to indoor disturbance stress are transformed by introducing stress similarity ratio. The stress similarity ratio kc is defined as: kc = CL × Cρ; CL is the geometric similarity ratio, and Cρ is the density similarity ratio.

[0025] The calculation formula for the loading amplitude of indoor mechanical tests is as follows: ; in, is the loading amplitude, is the stress similarity ratio, is the recorded stress wave amplitude.

[0026] After the test, the strain-time curve was obtained.

[0027] Step S24: construct a creep model; the creep model adopts the Burgers model, and the constitutive equation, creep equation, unloading equation and relaxation equation of the Burgers model are as follows: ; ; ; ; in, , as well as are stress, first-order derivative of stress with respect to time, and second-order derivative of stress with respect to time, respectively; , as well as are strain, first-order derivative of strain with respect to time, and second-order derivative of strain with respect to time, respectively; and are the first spring elastic modulus and the second spring elastic modulus respectively; and are the viscosity coefficient of the first viscosity pot element and the viscosity coefficient of the second viscosity pot element respectively; For uninstallation time, and are the first and second integration constants related to the initial conditions, respectively; and are the first relaxation parameter and the second relaxation parameter respectively related to the variation characteristics of material stress-strain; For time.

[0028] When t=0, only the spring works. , when t→∞, →∞, the strain change rate tends to a constant, which belongs to the metastable creep type. Similarly, the unloading equation of the Burgers body can be obtained by superimposing the unloading equations of the Maxwell body and the Kelvin body. When t→∞, , after unloading, some permanent deformation remains. When t→∞, σ→0, the stress can relax to 0, and the relaxation curve is a descending exponential curve. Through the graded loading creep test, it is found that the creep curve of the rock sample shows two forms of stable creep and unstable creep at different stress levels. For the prediction of the roof exposure time, for the sake of conservatism, the Burgers model is used not to calculate the time corresponding to the unstable creep, but to calculate the creep time corresponding to the creep deformation rate of zero and the xth creep loading stage from the end, which is the preliminarily determined roof exposure time interval. x can be set according to actual needs. The larger the x, the higher the safety factor.

[0029] The stress function after loading disturbance is as follows: ; in, The stress function after loading disturbance, is the angular frequency of the disturbance wave.

[0030] Step S25: Use the damped least squares method to fit the creep curve of the creep model parameters according to the strain-time curve to obtain the time interval [T1, T2] of the creep stable stage and the creep unstable stage; T1 is the creep time corresponding to the loading stage corresponding to the deformation rate of 0, and T2 is the creep time corresponding to the nxth loading stage; n is the stage number when the test rock sample is destroyed, and x is the safety factor.

[0031] Step S26: Determine the initial mine top dynamic exposure time interval .

[0032] Step S3: Revise the preliminary mine top dynamic exposure time interval according to the rock mass integrity coefficient to obtain the predicted mine top dynamic exposure time.

[0033] The revised formula for the dynamic exposure time interval of the preliminary mine roof is as follows: ; in, To predict the dynamic exposure time of mine roof.

[0034] In order to verify the effectiveness of the technical solution of this embodiment, it is verified with the existing prediction solution, which uses the MATHEWS stability diagram with added stability isoprobability lines.

[0035] Table 1 Calculated values ​​of roof creep parameters and exposure time at different burial depths in the west mining area ;

[0036] Table 2 Calculated values ​​of roof creep parameters and exposure time at different burial depths in the East Mining Area ;

[0037] Table 3 Roof exposure time at different burial depths in the western mining area based on stability isoprobability lines ;

[0038] Table 4 Roof exposure time at different burial depths in the East Mining Area based on stability isoprobability lines ;

[0039] In Tables 3 and 4, and f represent the corrected stable number and predicted probability value respectively.

[0040] Compared with the above results, the predicted dynamic exposure time of the mine roof falls within the scope of the existing technical solutions, which illustrates the effectiveness of the prediction results of the present application. The roof exposure time interval predicted by structural creep is short, and the roof exposure time prediction is shortened from "monthly level" to "day level", with smaller errors and more accurate results, which can well guide the management of mine roofs.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for predicting the dynamic exposure time of a mine roof considering rock mass structural creep, characterized in that: The specific steps are as follows: Step S1: measuring the rock mass structure of the roof rock mass to obtain the rock mass integrity coefficient of the roof rock mass; Step S2: Drill test rock samples of roof rock masses with different buried depths on site, conduct indoor creep-fatigue interactive mechanical tests on the test rock samples, apply stress disturbances during the indoor creep mechanical tests, and determine the time corresponding to the stable creep stage and the unstable creep stage of the test rock samples, so as to obtain a preliminary dynamic exposure time interval of the mine roof; Step S3: Revise the preliminary mine top dynamic exposure time interval according to the rock mass integrity coefficient to obtain the predicted mine top dynamic exposure time.

2. A method for predicting the dynamic exposure time of a mine top considering rock mass structural creep according to claim 1, characterized in that: In step S1, the rock mass integrity coefficient is calculated as follows: ； in, is the wave velocity coefficient, is the joint coefficient, is the rock quality index of the current roof rock mass, It is the maximum value of rock quality index of roof rock mass in the whole mining area; ； in, is the wave velocity of the roof rock mass, is the rock wave velocity; ； in, The number of regional joints obtained by non-contact measurement of the roof rock mass and digital panoramic borehole photography; is the rock volume in the measurement area.

3. A method for predicting the dynamic exposure time of a mine roof considering rock mass structural creep according to claim 2, characterized in that: Step S2 is specifically as follows: Step S21: obtaining test rock samples at different burial depths by drilling; Step S22: installing a disturbance stress monitoring system at the mining site, extracting the disturbance stress amplitude and disturbance frequency according to the disturbance stress wave data collected in real time; converting the disturbance stress wave into a sine wave by using a rain flow counting method or an equivalent amplitude method, and obtaining the frequency spectrum characteristic parameters of the disturbance stress wave; Step S23: Perform indoor graded creep loading on the test rock samples with different burial depths. Considering the difference between the sample size and the on-site rock mass, the field measured data is converted into laboratory data for graded creep loading. The time of each creep stage of the mechanical test is 48 hours. The disturbance is loaded during the graded creep loading according to the frequency spectrum characteristic parameters of the disturbance stress wave. The time calculation formula is as follows: ； in, is the disturbance loading time, is the disturbance frequency, The number of cycles for the disturbance loading; The loading parameters of field disturbance stress to indoor disturbance stress are transformed by introducing stress similarity ratio. The stress similarity ratio kc is defined as: kc= C L ×C ρ； C L is the geometric similarity ratio, C ρ is the density similarity ratio; The calculation formula for the loading amplitude of indoor mechanical tests is as follows: ； in, is the loading amplitude, is the stress similarity ratio, is the recorded stress wave amplitude; After the test, the strain-time curve is obtained; Step S24: constructing a creep model; Step S25: Use the damped least square method to fit the creep curve of the creep model parameters according to the strain-time curve to obtain the time interval [T1, T2] of the creep stable stage and the creep unstable stage; T1 is the creep time corresponding to the loading stage corresponding to the deformation rate of 0, and T2 is the creep time corresponding to the nxth loading stage; n is the stage number when the test rock sample is destroyed, and x is the safety factor; Step S26: Determine the initial mine top dynamic exposure time interval .

4. A method for predicting the dynamic exposure time of a mine roof considering rock mass structural creep according to claim 3, characterized in that: The creep model adopts the Burgers model. The creep time is calculated when it is not greater than the rock yield stress. The constitutive equation, creep equation, unloading equation and relaxation equation of the Burgers model are as follows: ； ； ； ； in, , as well as are stress, first-order derivative of stress with respect to time, and second-order derivative of stress with respect to time, respectively; , as well as are strain, first-order derivative of strain with respect to time, and second-order derivative of strain with respect to time, respectively; and are the first spring elastic modulus and the second spring elastic modulus respectively; and are the viscosity coefficient of the first viscosity pot element and the viscosity coefficient of the second viscosity pot element respectively; For uninstallation time, and are the first and second integration constants related to the initial conditions, respectively; and are the first relaxation parameter and the second relaxation parameter respectively related to the variation characteristics of material stress-strain; For time.

5. The method for predicting the dynamic exposure time of a mine roof considering rock mass structural creep according to claim 4, characterized in that: The stress function after loading disturbance is as follows: ； in, The stress function after loading disturbance, is the angular frequency of the disturbance wave.

6. A method for predicting the dynamic exposure time of a mine roof considering rock mass structural creep according to claim 4, characterized in that: In step S3, the revised formula for the dynamic exposure time interval of the preliminary mine top is as follows: ； in, To predict the dynamic exposure time of mine roof.

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