CN111896399B - Research CFRP (carbon fiber reinforced plastic) constrained heat damage coal sample creep-impact coupling test system and method - Google Patents

Abstract

The invention discloses a research CFRP (carbon fiber reinforced plastic) constrained thermal damage coal sample creep-impact coupling test system and a method, and belongs to the technical field of underground engineering and mining engineering. The method of the invention comprises the following steps: preparing a coal sample test piece, grouping the coal samples, heating the coal samples, pasting CFRP and strain gauges on the coal samples, and performing a uniaxial compression test; and (3) carrying out a creep impact test on the coal sample by adopting a creep-impact coupling test system, finally analyzing test data, obtaining the optimal CFRP wrapping layer number for resisting creep-impact disturbance according to the increment of the strength improvement of the test piece by different reinforcing layer numbers, and analyzing the influence of thermal damage on the mechanical property of the coal sample for resisting the creep-impact disturbance. The invention can provide reference for the design of the in-situ heat injection exploitation of coal underground gasification, coal underground liquefaction and coal bed gas, optimization of the roadway surrounding rock supporting scheme, and exploration of the aging rupture characteristics of deep coal rock under the action of impact load.

Description

Coupling creep-shock test system and method for studying CFRP-like confined thermally damaged coal samples

technical field

The invention relates to the technical field of underground engineering and mining engineering, in particular to a creep-shock coupling test system and method for studying CFRP-like confined thermal damage coal samples.

Background technique

As the mining depth of my country's coal mines is getting deeper and deeper, the deep surrounding rocks of coal mines are susceptible to the influence of the "three highs and one disturbance" environment, and there have been phenomena such as increased water pressure, increased ground temperature, coal and gas outbursts, and rock impacts. .

Temperature is one of the important factors affecting the physical and mechanical parameters of coal block. Compared with normal temperature, the mechanical parameters of coal rock under high temperature conditions, such as fracture toughness, strength, elastic modulus and Poisson's ratio, all have temperature effects. Mining projects related to temperature, such as underground coal gasification, underground coal liquefaction, and in-situ thermal injection mining of coalbed methane, have a common feature that underground coal is in a three-dimensional stress and high temperature environment. For example, in underground coal gasification, the gasification combustion zone acts as a heat source to generate heat on the surrounding coal and rock mass. Although the rock mass is a poor conductor of heat, after a long period of high temperature, the lithology of the top and bottom of the coal seam will change under the action of high temperature. change. CFRP is widely used in the field of reinforced concrete because of its high temperature resistance, high strength, and high modulus. Therefore, the use of CFRP to strengthen coal pillars can effectively enhance the mechanical properties of coal pillars.

During the mining of deep coal seams, coal rocks are easily affected by impacts such as blasting, excavation, and mechanical vibration, and coal rocks are more prone to creep deformation under long-term loads. Therefore, considering the environment of underground coal, underground coal pillars will be subjected to high temperature, ground stress brought by upper and lower rock strata, and impact force brought by blasting and excavation, so a method that can simulate high temperature, ground stress and impact load on coal pillars is needed. experiment method.

Contents of the invention

Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a creep-shock coupling test system and method for studying CFRP-like constrained thermal damage coal samples, which can be used for underground coal gasification, underground coal liquefaction and in-situ thermal injection mining of coalbed methane Program design provides reference.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A creep-shock coupling test system, including: top plate, counterweight, weight, weight, weight plate, supporting steel column, hydraulic jack, load sensor, load collector, bottom plate, hoist, strain gauge, strain acquisition instruments and computers.

The supporting steel column is provided with a chute, the three ends of the counterweight are provided with sliders, and the sliders on the counterweight are slidably connected with the chute on the supporting steel column.

The weight and the winch are connected through the central pulley and the steel rope fixed on the top plate; Increase or decrease the number of weights to control the counterweight to exert pressure on the test piece;

The three small pulleys are distributed around the central pulley in an equilateral triangle, corresponding to the three ends of the counterweight, and the large pulley is fixed on the top plate at the position corresponding to the weight plate; the large pulley and the hoist are on the opposite side of the central pulley, The center pulley, one of the three small pulleys and the large pulley are arranged in a straight line in order; in order to avoid crossing between the lines, the connection between the hoist and the center pulley does not pass through the small pulley.

The strain collector controls the strain gauges to collect strain data in real time, and transmits the data to the computer; the computer sends control instructions to the hoist by analyzing the strain data, and the hoist drives the weight to apply impact disturbance to the counterweight.

The middle part of the counterweight is a hemispherical groove, which is convenient for the test piece to be impacted uniformly.

The load sensor is arranged on the upper part of the hydraulic jack, and the test piece to be tested is placed on the load sensor; the load collector controls the load sensor to collect the load on the test piece, and transmits the load data to the computer for simulating different stages. working conditions.

On the other hand, the present invention also provides a method of using a creep-shock coupling test system to study the mechanical properties of CFRP-like confined thermally damaged coal samples, including the following steps:

Step 1: Collect and make coal samples under different thermal damages, and carry out different degrees of reinforcement treatment on the coal samples under different thermal damages. The process is as follows:

Step 1.1: Collect coal blocks from deep mines, first grind the coal blocks to standard coal samples, and the coal samples need to be polished smooth to ensure that the surface is clean and free of dirt;

Step 1.2: Divide the coal samples into several groups, the number of each group is the same, and heat the coal samples of different groups in the form of increasing temperature;

Step 1.3: After standing the heated coal samples to room temperature, paste different layers of CFRP strips on the outer surface of each group of coal samples for reinforcement.

The standard coal sample is any one of a standard cuboid with an aspect ratio of 1:1:2, or a standard cylinder with a height to diameter ratio of 2:1, and the specimen can be replaced by a concrete column, a rock column Specimen;

The temperature range for heating coal samples of different groups is 100°C to 500°C.

Step 2: Take a coal sample with the same number of CFRP layers from each group, apply pressure to it in the longitudinal direction until it is destroyed, obtain the stress-strain curve of each group of coal samples and obtain the peak strength σ _p on the curve;

Step 3: In order to simulate the working conditions at different stages, select three points on the stress-strain curve that are smaller than the peak strength σ _p , and record them as stress intensities σ _A , σ _B and σ _C ;

Step 4: Paste the strain gauge on the coal sample and place it on the load cell of the creep-shock coupling test system. Under the stress intensity σ _A obtained in step 3, carry out the creep test by step-by-step loading. In the constant-speed creep stage of creep, n cycles of impact disturbance with a frequency of f are applied until the coal sample is destabilized and destroyed after several creep stages, and the creep-shock disturbance intensity applied when the coal sample is destabilized and destroyed is recorded , the process is as follows:

Step 4.1: Paste several strain gauges vertically and circumferentially outside the CFRP strip of the coal sample, place the coal sample on the load cell, and raise the coal sample to the position where it touches the bottom of the counterweight lightly through a hydraulic jack to avoid coal sample Minor damage under load before the test;

Step 4.2: Reduce the weight on the weight plate to make the counterweight pressurize the coal sample. The load collector controls the load sensor to collect the load on the coal sample, and transmits the load data to the computer. At the same time, adjust the number of weights to make the coal sample The loading value on the sample is controlled at the stress σ _A ;

Step 4.3: The strain collector controls the strain gauge to collect the strain data of the coal sample in real time, and transmits the data to the computer, which analyzes the strain data;

Step 4.4: When the strain meets the constant-speed creep condition, the computer sends a control command to the hoist, and the hoist drives the weight to apply n cycles of impact disturbance with frequency f to the counterweight;

Said satisfying the constant-rate creep condition is satisfying dε/dt=Ω, ε is the strain value, t is the time, dε/dt is the strain value per unit time, and Ω is a constant;

Step 4.5: Continue to load after the completion of each level of creep, and after the same time after each loading, apply n cycles of impact disturbance with frequency f in the constant-speed creep stage.

Step 5: Repeat step 4 to obtain the stress-strain diagrams of coal samples with the same number of CFRP layers under stress intensities σ _A , σ _B and σ _C in different groups, that is, under different thermal damages, and the creep- impact disturbance intensity;

Step 6: Repeat steps 2 to 5 until the stress-strain diagram of the coal samples in the same group, that is, under the same thermal damage degree and different CFRP layers, and the creep-impact disturbance strength applied during the instability failure are obtained;

Step 7: Comparing the stress-strain diagrams of coal samples with different CFRP layers and the creep-impact disturbance strength applied at the time of instability failure in the same group, that is, under the same thermal damage degree and the same loading stress, according to the different reinforcement layers The increment of the strength of the specimen was increased to obtain the optimal number of CFRP wrapping layers for resisting creep-shock disturbance, and the influence of thermal damage on the mechanical properties of coal samples against creep-shock disturbance was analyzed.

The beneficial effects produced by adopting the above-mentioned technical scheme are: the method and system provided by the present invention are easy to operate, and can effectively measure the mechanical properties of CFRP-like passive confinement thermally damaged coal samples under creep-shock coupling, and also adopt the method of controlling variables, Experiments were carried out at different temperatures and with different numbers of CFRP layers, and the number of CFRP wrapping layers that optimally resisted creep-impact disturbances was obtained according to the increase in the strength of the specimen with different reinforcement layers. The invention can provide reference for underground coal gasification, underground coal liquefaction and in-situ heat injection mining of coalbed methane, optimized roadway surrounding rock support scheme design, and exploration of time-dependent fracture characteristics of deep coal and rock mass under impact load.

Description of drawings

Fig. 1 is the structural diagram of a kind of creep-shock coupling test system in the embodiment of the present invention;

Fig. 2 is a schematic diagram of the connection mode between the weight plate and the counterweight in the embodiment of the present invention;

Fig. 3 is the flowchart of the method for studying the mechanical properties of CFRP-like confined thermally damaged coal samples in an embodiment of the present invention;

Fig. 4 is a schematic diagram of coal sample CFRP package and strain gauge arrangement in the embodiment of the present invention;

Fig. 5 is the top view of Fig. 4 in the embodiment of the present invention;

Fig. 6 is the schematic diagram of stress-strain curve in the embodiment of the present invention;

Fig. 7 is a schematic diagram of the force situation of the coal sample in the embodiment of the present invention;

Fig. 8 is a schematic diagram of the loading situation of the step-by-step loading creep test in the embodiment of the present invention.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

In this embodiment, a creep-shock coupling test system, as shown in Figure 1, includes: a top plate 1, a counterweight 2, a weight 3, a weight 4, a weight plate 5, a supporting steel column 6, and a hydraulic jack 7. Load sensor 8, load collector 9, base plate 10, winch 11, strain gauge 12, strain collector 13 and computer 14.

The supporting steel column 6 has a chute 6-1, and the three ends of the counterweight 2 have sliders, and the slider on the counterweight is slidably connected with the chute 6-1 on the supporting steel column.

The weight 3 and hoist 11 are connected through the central pulley 1-1 fixed on the top plate and the steel rope; the weight plate 5 and the counterweight 2 are connected through three small pulleys 1-2 and a large pulley fixed on the top plate 1-3 are connected by steel rope, the connection situation is shown in Figure 2, by increasing or decreasing the number of weights 4 on the weight plate 5, the counterweight 2 exerts pressure on the test piece;

The three small pulleys 1-2 are distributed around the central pulley 1-1 in an equilateral triangle, corresponding to the three ends of the counterweight 2, and the large pulley 1-3 is fixed on the top plate at a position corresponding to the weight plate 5, As shown in Figure 2; the large pulley 1-3 and the winch 11 are on the opposite side of the central pulley 1-1, the central pulley 1-1, one of the three small pulleys 1-2 and the large pulley 1-3 are in order Arrange on the position of a straight line, as shown in Figure 2; For avoiding crossing between lines, hoisting machine 11 and center pulley 1-1 are connected on the plane and do not pass through small pulley 1-2.

The strain acquisition instrument 13 controls the strain gauge 12 to collect strain data in real time, and transmits the data to the computer 14; the computer 14 sends a control command to the hoist 11 by analyzing the strain data, and the hoist 11 drives the weight 3 to apply the weight to the counterweight 2. Shock disturbance.

The middle part of the counterweight 2 is a hemispherical groove, which is convenient for the test piece to be impacted uniformly.

The load sensor 8 is arranged on the top of the hydraulic jack 7, and the test piece to be detected is placed on the load sensor 8; the load collector 9 controls the load sensor 8 to collect the load on the test piece, and transmits the load data to the computer 14, Used to simulate working conditions in different stages.

On the other hand, the present invention also provides a method of using a creep-shock coupling test system to study the mechanical properties of a CFRP-like confined thermally damaged coal sample. The process is shown in Figure 3, including the following steps:

Step 1: Collect and make coal samples under different thermal damages, and carry out different degrees of reinforcement treatment on the coal samples under different thermal damages. The process is as follows:

Step 1.1: Collect coal blocks from deep mines, first grind the coal blocks to standard coal samples, and the coal samples need to be polished smooth to ensure that the surface is clean and free of dirt;

In this embodiment, the coal block is processed into a standard cylinder of 50 mm × 100 mm (diameter × height), and the specific implementation is to polish the protruding part on the surface of the coal sample specimen with an angle grinder, and remove the floating ash on the surface with sandpaper, The protruding part of the surface is smoothed with a cutting machine, and the corners are polished into an arc shape. The coal sample needs to be polished smooth and the surface is clean and free of dirt.

Step 1.2: Divide the coal samples into several groups, the number of each group is the same, and heat the coal samples of different groups in the form of increasing temperature;

In this embodiment, coal samples with similar densities are selected for grouping, and high-temperature reinforcement groups, high-temperature non-reinforcement groups, normal temperature reinforcement groups, and normal temperature non-reinforcement groups are set. Multiple high-temperature reinforcement groups and high-temperature non-reinforcement groups can be set according to temperature. The number of strip layers is set to a high temperature reinforcement group and a normal temperature reinforcement group, with at least 7 coal samples in each group. The coal samples in the high-temperature reinforcement group and the high-temperature non-reinforcement group were taken for heat treatment, and the specimens were heated by a resistance furnace. After putting the coal samples into the furnace in groups according to the temperature, turn on the power, adjust the temperature to the corresponding temperature value, wait for the temperature to rise to the set temperature, then keep the temperature for 4 hours, and cool it naturally in the furnace to room temperature.

Step 1.3: After standing the heated coal samples to room temperature, paste different layers of CFRP strips on the outer surface of each group of coal samples for reinforcement.

In this embodiment, the glue is evenly applied to both sides of the CFRP strip with a brush, and the CFRP strip is compacted and wrapped on the entire side of the coal sample, and the overlapping length of the CFRP is 50 mm.

Step 2: Take a coal sample with the same number of CFRP layers from each group, apply pressure to it in the longitudinal direction until it is destroyed, obtain the stress-strain curve of each group of coal samples and obtain the peak strength σ _p on the curve;

In this embodiment, one coal sample in all groups is taken, and the coal sample is pressed at 0.2mm/s on a universal testing machine until it is destroyed. The stress-strain curve of the specimen shown in Fig. 6 was obtained by actual measurement and the peak strength σ _p was obtained.

Step 3: In order to simulate the working conditions at different stages, select three points on the stress-strain curve that are smaller than the peak strength σ _p , and record them as stress intensities σ _A , σ _B and σ _C , as shown in Figure 6;

In this embodiment, σ _A = 50% σ _p , σ _B = 70% σ _p , σ _C = 90% σ _p , and the corresponding conversion is performed on the selected stress and the creep stress of each level and the weight of the weight. The conversion is determined by the following formula:

mg=σ×πr ²

Wherein, m is the mass of the weight corresponding to the loading stress, σ is the loading stress, π is 3.14, the radius r is 0.025m, and g is 9.8m/s ² .

Step 4: Paste the strain gauge on the coal sample and place it on the load cell of the creep-shock coupling test system. Under the stress intensity σ _A obtained in step 3, carry out the creep test by step-by-step loading. In the constant-speed creep stage of creep, n cycles of impact disturbance with a frequency of f are applied until the coal sample is destabilized and destroyed after several creep stages, and the creep-shock disturbance intensity applied when the coal sample is destabilized and destroyed is recorded , the process is as follows:

Step 4.1: Paste several strain gauges vertically and circumferentially outside the CFRP strip of the coal sample, place the coal sample on the load cell, and raise the coal sample to the position where it touches the bottom of the counterweight lightly through a hydraulic jack to avoid coal sample Minor damage under load before the test;

In this embodiment, a total of 12 strain gauges are arranged for each coal sample, and 3 strain gauges are evenly arranged in the height direction around the side of the coal sample. Detection of axial stress and axial fracture location. The strain gauges are evenly distributed around the sides of the coal sample. The central position of the strain gauges in the middle is at half the height of the coal sample. The center height difference of each strain gauge is 30mm. The specific layout of the strain gauges is shown in Figure 4 and Figure 5.

Step 4.2: Reduce the weight on the weight plate to make the counterweight pressurize the coal sample. The load collector controls the load sensor to collect the load on the coal sample, and transmits the load data to the computer. At the same time, adjust the number of weights to make the coal sample The loading value on the sample is controlled at the stress σ _A ;

Step 4.3: The strain collector controls the strain gauge to collect the strain data of the coal sample in real time, and transmits the data to the computer, which analyzes the strain data;

Step 4.4: When the strain meets the constant-speed creep condition, the computer sends a control command to the hoist, and the hoist drives the weight to apply n cycles of impact disturbance with frequency f to the counterweight;

Said satisfying the constant-rate creep condition is satisfying dε/dt=Ω, ε is the strain value, t is the time, dε/dt is the strain value per unit time, and Ω is a constant;

Step 4.5: After each level of creep is completed, continue to load. After the same time after each loading, apply n cycles of impact disturbance with frequency f in the constant-speed creep stage, as shown in Figure 8.

In this embodiment, a step-by-step creep test with a period of _t2 for each stage is carried out. At the same time, the hoist is used to lift the weight at a distance of 0.5m between the bottom of the weight and the bottom of the groove of the counterweight _. The n-cycle impact disturbance with frequency f is applied at all times until the coal sample loses stability and fails after about 4 to 5 creep stages.

Step 5 _: Repeat _step 4 to obtain the stress-strain diagrams and the _creep- impact disturbance intensity;

Step 6: Repeat steps 2 to 5 until the stress-strain diagram of the coal samples in the same group, that is, under the same thermal damage degree and different CFRP layers, and the creep-impact disturbance strength applied during the instability failure are obtained;

As shown in Figure 7, the coal sample is subjected to three forces in total, σ ₁ is the ground stress, the σ _side is the circumferential constraint force provided by the CFRP layer, and σ _d is the impact load. The impact energy of the falling weight is calculated according to the following formula:

E=m ₁ gh

Among them, the weight m ₁ is 10kg, and h is 0.5m.

Step 7: Comparing the stress-strain diagrams of coal samples with different CFRP layers and the creep-impact disturbance strength applied at the time of instability failure in the same group, that is, under the same thermal damage degree and the same loading stress, according to the different reinforcement layers The increment of the strength of the specimen was increased to obtain the optimal number of CFRP wrapping layers for resisting creep-shock disturbance, and the influence of thermal damage on the mechanical properties of coal samples against creep-shock disturbance was analyzed.

Claims (1)

1. A method for researching the mechanical properties of CFRP-like constrained heat damage coal samples is characterized in that,

a creep-impact coupling test system is adopted to realize a method for researching the mechanical properties of CFRP-like constrained heat damage coal samples;

the system comprises: the device comprises a top plate, a balance weight, a heavy hammer, a weight tray, a supporting steel column, a hydraulic jack, a load sensor, a load collector, a bottom plate, a winch, a strain gauge, a strain collector and a computer;

the support steel column is provided with a chute, three ends of the counter weight are provided with sliding blocks, and the sliding blocks on the counter weight are in sliding connection with the chute on the support steel column;

the heavy hammer is connected with the winch through a central pulley fixed on the top plate and a steel rope; the weight tray and the balance weight are connected through three small pulleys and a large pulley which are fixed on the top plate by steel ropes, and the balance weight is controlled to apply pressure to the test piece by increasing or decreasing the number of the weights on the weight tray;

the three small pulleys are distributed around the central pulley in a regular triangle shape, correspond to the three end parts of the balance weight, and are fixed at positions on the top plate, corresponding to the weight plates; the large pulley and the winch are arranged at the opposite side of the central pulley, and the central pulley, one small pulley of the three small pulleys and the large pulley are sequentially arranged at a straight line position; in order to avoid the intersection between the wires, the connecting wire between the winch and the central pulley on the plane does not pass through the small pulley;

the strain acquisition instrument controls the strain gauge to acquire strain data in real time and transmits the data to the computer; the computer sends a control instruction to the winch by analyzing the strain data, and the winch drives the heavy hammer to apply impact disturbance to the balance hammer;

the middle part of the balance weight is provided with a hemispherical groove, so that a test piece is convenient to be impacted uniformly;

the load sensor is arranged at the upper part of the hydraulic jack, and a test piece to be detected is placed on the load sensor; the load collector controls the load sensor to collect the load of the test piece, and transmits load data to the computer for simulating working conditions at different stages;

the method comprises the following steps:

step 1: collecting and manufacturing coal samples under different heat injuries, and carrying out reinforcing treatment on the coal samples under different heat injuries to different degrees, wherein the process of the step 1 is as follows:

step 1.1: collecting coal blocks from a deep mine, firstly polishing the coal blocks to a standard coal sample, wherein the coal sample is required to be polished smoothly, and the clean and pollution-free surface is ensured, and the standard coal sample is a standard cuboid with the length-to-width ratio of 1:1:2;

step 1.2: dividing coal samples into a plurality of groups, heating the coal samples of different groups in a mode of increasing temperature, wherein the coal samples of different groups are selected to be grouped, a high-temperature reinforcing group, a high-temperature non-reinforcing group, a normal-temperature reinforcing group and a normal-temperature non-reinforcing group are arranged, a plurality of high-temperature reinforcing groups and high-temperature non-reinforcing groups are arranged according to temperature, a high-temperature reinforcing group and a normal-temperature reinforcing group are arranged according to the number of layers of strips, at least 7 coal samples in each group are heated, the coal samples in the high-temperature reinforcing group and the high-temperature non-reinforcing group are taken for heating treatment, a test piece is heated by adopting a resistance furnace, a power supply is started after the coal samples are placed into the furnace according to the temperature groups, the temperature is regulated to be controlled to a corresponding temperature value, the temperature is kept constant for 4 hours after the temperature is increased to the set temperature, the furnace is naturally cooled to the room temperature, and the heating temperature range is 100-500 ℃;

step 1.3: standing the heated coal samples to normal temperature, and respectively pasting CFRP strips with different layers on the outer surfaces of each group of coal samples for reinforcement;

step 2: taking a coal sample with the same CFRP layer number from each group, applying pressure to the coal sample longitudinally until the coal sample is destroyed, actually measuring to obtain a stress-strain curve of each group of coal samples and obtaining peak intensity sigma on the curve _p ；

Step 3: to simulate the conditions of different stages, three values less than the peak strength sigma are chosen on the stress-strain curve _p Is denoted as stress intensity sigma _A 、σ _B Sum sigma _C Wherein σ is _A ＝50％σ _p ，σ _B ＝70％σ _p ，σ _C ＝90％σ _p For selected stress magnitude and eachThe level creep stress and the weight are correspondingly converted, and the conversion is determined by the following formula:

mg＝σ×πr ²

wherein m is the weight mass corresponding to the loading stress, sigma is the loading stress, pi is 3.14, the radius r is 0.025m, and g is 9.8m/s ² ；

Step 4: attaching strain gauge to coal sample and placing the strain gauge on load sensor of creep-impact coupling test system, and obtaining stress intensity sigma in step 3 _A Step-by-step loading creep test is carried out, n times of cyclic impact disturbance with the frequency f are applied at the constant-speed creep stage of each corresponding creep stage until the coal sample is subjected to instability damage after a plurality of creep stages, and the creep-impact disturbance strength applied when the coal sample is subjected to instability damage is recorded;

the process of the step 4 is as follows:

step 4.1: a plurality of strain gauges are vertically and circumferentially stuck outside a CFRP strip of a coal sample, the coal sample is placed on a load sensor, and the coal sample is lifted to the bottom of a light-touch balance weight through a hydraulic jack, so that the condition that the coal sample is subjected to load to generate fine damage before a test is avoided;

step 4.2: the weights on the weight tray are reduced, so that the balance weight pressurizes the coal sample, the load collector controls the load sensor to collect the load born by the coal sample, load data are transmitted to the computer, and meanwhile, the number of the weights is adjusted to control the loading value on the coal sample at the stress sigma _A ；

Step 4.3: the strain acquisition instrument controls the strain gauge to acquire strain data of the coal sample in real time, the data is transmitted to the computer, and the computer analyzes the strain data;

step 4.4: when the strain meets the constant-speed creep condition, a computer sends a control instruction to a winch, and the winch drives a heavy hammer to apply n times of cyclic impact disturbance with the frequency f to the balance hammer, wherein the constant-speed creep condition is met, dε/dt=Ω, ε is a strain value, t is time, dε/dt is a strain value in unit time, Ω is a constant;

step 4.5: continuously loading after each stage of creep is completed, applying n times of cyclic impact disturbance with the frequency f at the constant-speed creep stage after the same time is passed after each stage of creep is loaded;

step 5: repeating the step 4 to obtain the coal samples with the same CFRP layer number in different groups, namely under different heat damages, at the stress intensity sigma _A 、σ _B Sum sigma _C The stress-strain diagram below and the creep-impact disturbance strength applied when the instability is broken;

step 6: repeating the steps 2 to 5 until obtaining stress-strain images of the coal samples in the same group, namely under the same heat damage degree and different CFRP layer numbers, and creep-impact disturbance strength applied when the coal samples are unstable and damaged;

step 7: and comparing the stress-strain diagram of the coal samples with different CFRP layers and the creep-impact disturbance intensity applied during the destabilization damage under the same heat damage degree and the same loading stress in the same group, obtaining the CFRP wrapping layer number with optimal creep-impact disturbance resistance according to the increment of the strength improvement of the test piece by different reinforcing layers, and analyzing the influence of the heat damage on the mechanical property of the coal samples for resisting the creep-impact disturbance.