Water-rich soft overlying strata ultrasonic cracking pressure relief method based on in-hole argillization degree

Abstract

The invention discloses a water-rich soft overlying strata ultrasonic cracking pressure relief method based on in-hole argillization degrees, which mainly comprises the following steps of: before cracking, drilling a peephole with the depth equal to that of a cracking hole at an implementation site, then cleaning and peeping the peephole in sections, calculating the in-hole argillization degrees of each section of the peephole, and calculating the in-hole argillization degree of each section of the peephole according to the in-hole argillization degree of each section of the peephole; taking the result as the in-hole argillization degree of each section of all the cracking holes in the implementation site, designing ultrasonic parameters of each section of the cracking holes according to the in-hole argillization degree of each section of the cracking holes, and then performing ultrasonic cracking on the water-rich soft overlying strata by utilizing ultrasonic waves with periodic cycle characteristics; and an evaluation index for the ultrasonic cracking effect of the water-rich soft overlying strata is established, so that effective guidance is provided for field application of a subsequent ultrasonic cracking pressure relief technology. According to the method, the influence of the argillization effect in the drill hole on the ultrasonic cracking pressure relief effect under the actual engineering condition is considered, and a basis is provided for safe cracking in the hole under the water-rich soft overlying strata condition.

Description

Technical Field

[0001] The invention belongs to the technical field of mine production safety, and in particular relates to an ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of mud in a hole. Background Art

[0002] As the mining of coal resources in the shallow and central and eastern regions is exhausted, the mining of coal resources has gradually shifted to the deep and western regions. Since the coal-bearing strata in the western mining area are mainly Mesozoic Jurassic Cretaceous, the overlying strata of the coal seams have multiple layers of strong water-bearing strata, and a large number of roof drainage projects will be carried out before the coal mining process. However, due to the special diagenetic environment of the western mining area, the overlying strata of the coal seams are mostly weak strata, which causes water-rock coupling after the water-bearing strata are drained, and the mudification of the strata is serious. At the same time, when the mine enters deep mining, the load transmitted from the far-field rock strata to the near-field tunnel surrounding rock increases significantly, and the tunnel surrounding rock is severely deformed. Overburden unloading technology is an effective measure to reduce the bearing strength of the near-field surrounding rock and control the deformation of the tunnel surrounding rock.

[0003] At present, there are roughly two types of overburden pressure relief technologies. One type is hydraulic fracturing pressure relief technology that injects high-pressure liquid into the overburden to generate new or expand existing cracks in the overburden. For example, Chinese patent document CN118517266A discloses a hydraulic fracturing construction method for coal seam working face. This method uses long and short holes to carry out multi-dimensional hydraulic fracturing, and performs all fracturing pressure relief on the overburden on the working face, solving the problem of "large blocks becoming small blocks" around the tunnel to control the range and strength of overburden activity. The other type is blasting fracturing pressure relief technology that increases rock cracks and destroys rock integrity through blasting. For example, Chinese patent document CN117846593A discloses a method for arranging long drilling holes for blasting the top plate of an artificial pressure relief layer. This method reduces the elastic strain energy accumulated in the key layer of inducing impact by blasting, so that it cannot reach the minimum energy required for coal seam impact, and reduces the possibility of impact damage to the working face from the source. These technologies have achieved good application results in weakly water-bearing and hard overburden. However, with the application of hydraulic fracturing, blasting fracturing and other technologies in deep water-rich soft overburden conditions, due to the serious mudification of the rock mass around the borehole and the weakening of residual water, the hydraulic fracturing pressure cannot reach the expected value due to poor sealing effect, and the blasting cannot effectively fracture the overburden due to poor sealing effect and the energy of the blast wave is partially consumed by water. These problems frequently occur, seriously affecting the safe and efficient production of mines.

[0004] When ultrasonic waves propagate in rock formations, they will produce mechanical vibration effects with rocks and generate heat, which will cause the microcracks inside the rock formation to expand and deteriorate the physical and mechanical properties of the rock, eventually leading to rock fracture. Therefore, ultrasonic fracturing technology has been applied in the fields of coalbed methane production increase and hard rock fracturing in mines. However, this method is mostly used for harder rock formations or low-permeability coal seams, and ultrasonic waves are rarely used to crack and decompress water-rich soft overburden. This is because harder rock formations or low-permeability coal seams rarely produce mud effects due to their own physical characteristics, while weak coal or water-rich soft overburden contains more clay minerals, which will cause mud effects inside the borehole. The mud effects inside the borehole have a greater impact on the effect of ultrasonic cracking of weak coal or water-rich soft overburden, and scientific and rigorous methods are needed to strictly design the fracturing parameters. Summary of the invention

[0005] In order to safely and effectively crack water-rich soft overburden and give full play to the advantages of ultrasonic fracturing, the present invention provides an ultrasonic cracking and pressure relief method for water-rich soft overburden based on the mud degree in the hole. The mud degree of each segment in the hole is used to scientifically identify the mud effect of the key bearing layer of the overburden, and the segmented ultrasonic cracking in the hole under the conditions of water-rich soft overburden is realized, thereby effectively destroying the integrity of the key bearing layer of the overburden, reducing the load strength of the near-field surrounding rock, and controlling the deformation of the tunnel surrounding rock.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for ultrasonic cracking and decompression of water-rich soft overburden based on the degree of mud in the hole, characterized in that the method comprises the following steps:

[0008] Step 1: Obtain geomechanical information of the implementation site

[0009] Determine the implementation site of the ultrasonic cracking decompression method and obtain the geomechanical information of the implementation site to facilitate the subsequent determination of the key bearing layer of the overburden;

[0010] Step 2: Determine the key bearing layer of the overburden

[0011] Carry out implementation at the implementation site in sections, calculate the load borne by each layer of overburden at a certain section of the implementation site based on the overburden characteristics of the section of the implementation site, and determine the overburden layer with the largest load at the section of the implementation site as the key bearing layer of the overburden at the section of the implementation site;

[0012] Step 3: Identify the degree of mud in cracking holes

[0013] A peephole with the same depth as the cracking hole is constructed vertically upward at each implementation site, and the peephole is cleaned and peeped in sections. The mud degree of each section of the peephole is determined according to the section cleaning and peeping in the hole. The determined mud degree of each section of the peephole is the mud degree of each section of all cracking holes at the implementation site of the section. The mud degree represents a quantitative index of the mud effect degree of each section of the rock formation on the inner wall of the hole;

[0014] Step 4: Determine the location of the pre-crack fracture line of the overburden rock

[0015] Determine the location of the pre-crack fracture line of the water-rich soft overburden rock based on the mining characteristics of the working face, the use of the tunnel and the load characteristics of the surrounding rock;

[0016] Step 5: Design key parameters of ultrasonic cracking pressure relief technology

[0017] Designing cracking hole parameters within the key bearing layer of the overburden, and determining ultrasonic vibration parameters of each section of the cracking hole based on the mud degree of each section of the cracking hole, wherein the ultrasonic vibration parameters mainly include vibration frequency, amplitude and vertical vibration range, wherein the vibration frequency and amplitude are related to the mud degree of each section of the cracking hole, if the mud degree of a certain section of the cracking hole is large, then the vibration frequency and amplitude of the ultrasonic vibration parameters of the section of the cracking hole are also large, if the mud degree of a certain section of the cracking hole is small, then the vibration frequency and amplitude of the section of the cracking hole are also small;

[0018] Step 6: Implement ultrasonic cracking drilling

[0019] Use geological drilling rigs and supporting drilling platforms to carry out drilling construction according to the designed cracking hole parameters;

[0020] Step 7: Ultrasonic cracking of water-rich soft overburden

[0021] The in-hole segmented ultrasonic cracking of the key bearing layer of the water-rich weak overburden rock requires that the ultrasonic vibration wave has a periodic cycle characteristic and can cause fatigue damage to the rock; based on the characteristic that the ultrasonic vibration wave can propagate in both solid and liquid states, the ultrasonic vibration wave and the rock produce mechanical resonance and thermal damage effects, thereby cracking the rock and causing damage to the internal structure, physical and mechanical properties of the rock;

[0022] Step 8: Evaluate the ultrasonic cracking effect

[0023] An ultrasonic CT instrument was used to perform transmission CT imaging between cracking holes, and the inter-hole crack penetration rate was used as an indicator to evaluate the ultrasonic cracking effect at the first implementation site, providing a basis for adjusting key parameters of ultrasonic cracking pressure relief technology at the next implementation site.

[0024] The above steps 2 to 8 are repeated to sequentially complete the ultrasonic cracking depressurization at each implementation location.

[0025] Furthermore, the method for determining the key bearing layer of the overburden in step 2 is:

[0026] Calculate the load Q borne by each rock layer above the working face and identify it from bottom to top. If the i-th rock layer is the key bearing layer, the bearing relationship satisfied by the i+1-th rock layer is:

[0027] Q i >Q i+1

[0028] In the formula, Q i , Q i+1 are the loads borne by the i-th and i+1-th rock layers respectively.

[0029] Further, the specific method of step three is:

[0030] 3.1: Determine the mud degree of each section of the peephole at the implementation site

[0031] First, a peephole is constructed vertically upward at the implementation site. The depth of the peephole is equal to the depth of the cracking hole and the diameter is greater than 38mm. Then, the peephole is cleaned and peeped in sections from bottom to top within the vertical range of vibration. When cleaning the hole, the length of the cleaning hole and the amount of water for cleaning the hole must be consistent. Before cleaning the hole, a collection bucket must be placed under the peephole to collect the water sample flowing out during the cleaning, and a high-precision electronic weighing instrument must be used to test the weight of the water sample flowing out. After a section of the peephole is cleaned, the peephole is drilled and peeped at. The purpose of the peeping is to obtain the hole length of the hole wall of the section of the peephole with mud characteristics, and then the mud degree K of the i-th section of the peephole is calculated according to the following formula: i To identify,

[0032]

[0033] In the formula, B 0i is the length of the i-th segment of the peephole, B 1i is the length of the hole with mud characteristics in the i-th section of the peephole wall, W 0i is the weight of the water sample used for cleaning the peephole in section i, W 1i The weight of the water sample collected after the peephole section i is cleaned;

[0034] 3.2: Based on the mud degree of each section of the peephole at the implementation site, determine the mud degree K of each section in all cracking holes at the implementation site j , that is, K j =K i , j represents the segment number of each segment in the cracking hole, and j = i, which means that the mud degree of each segment of the cracking hole is equal to the mud degree of the corresponding segment of the peephole;

[0035] When 0≤K jWhen K<0.5, it indicates that the mudification phenomenon in the jth section of the cracking hole is relatively slight; when 0.5≤K j When 0.8≤K j When <1, it indicates that the mudification phenomenon in the jth section of the cracking hole is serious.

[0036] Further, the specific method of step 4 is:

[0037] According to the mining characteristics of the working face and the use of the tunnel, the load characteristics of the near-field surrounding rock are analyzed in three cases where the overburden pre-cracking fracture line is located above the coal body of the working face, above the tunnel, and above the goaf. The position of the overburden pre-cracking fracture line corresponding to the minimum peak value of the near-field surrounding rock load is taken as the final overburden pre-cracking fracture line position.

[0038] Furthermore, the cracking hole parameters in step 5 include the inclination angle θ, length and spacing of the cracking holes, wherein:

[0039] The cracking hole inclination angle θ is determined according to the position of the pre-crack fracture line of the overburden rock and the on-site drilling rig construction conditions. The cracking hole inclination angle θ needs to be the maximum angle under the on-site drilling rig construction conditions, and θ < 90°;

[0040] The cracking hole length L is determined by the vertical depth H and the inclination angle θ of the key bearing layer of the overburden, that is:

[0041]

[0042] In the formula, α is the coal seam inclination, θ is the angle between the cracking hole and the horizontal direction;

[0043] The cracking hole spacing C is:

[0044]

[0045] Where ξ is the ultrasonic vibration correction coefficient, which can be between 0 and 2.0, d is the cracking hole diameter, m is the coal seam thickness, f is the overburden rock strength coefficient, and M is the coal seam burial depth.

[0046] Furthermore, in step five, the vibration frequency can be selected between 20 and 40 kHz, and the amplitude can be selected between 30 and 60 μm; to ensure the ultrasonic cracking effect, the vertical range of vibration is set to 1.2 to 1.3 times the thickness of the key bearing layer of the overburden.

[0047] Further, in step seven, an ultrasonic vibration platform with coal mine safety certification is used to implement the ultrasonic cracking method.

[0048] Furthermore, the ultrasonic vibration platform includes a control system, an ultrasonic generator, a transducer, a horn, a toroidal exciter, a power supply device and a monitoring system; the control system is respectively connected to the power supply device and the ultrasonic generator, and is used to control and adjust the required ultrasonic vibration parameters; the monitoring system is used to monitor in real time the ultrasonic vibration wave characteristics output by the horn and the toroidal exciter; a transducer is arranged on the upper side of the ultrasonic generator, a horn is arranged on the top of the transducer, the horn is connected to the toroidal exciter, and the horn and the toroidal exciter are respectively connected to the monitoring system; the working method of the ultrasonic vibration platform is: first, the transducer, the horn and the toroidal exciter are delivered to the set position in the cracking hole through the geological drilling rig platform, and then the ultrasonic generator The control system controls the industrial current transmitted from the power supply device to be converted into a high-frequency electrical signal that meets the vibration frequency and amplitude of each section of the cracking hole. The transducer converts the high-frequency electrical signal into an ultrasonic vibration wave. The ultrasonic vibration wave is enhanced by the amplitude transformer and then passes through the annular exciter to produce mechanical resonance and thermal damage effects with the rock, which cracks the rock in sections and causes damage to the internal structure and physical and mechanical properties of the rock, effectively destroying the integrity of the key bearing layer of the overburden, reducing the ability to transmit the overburden load, blocking the source of the load on the near-field surrounding rock, thereby reducing the load strength of the surrounding rock and controlling the deformation of the tunnel surrounding rock; the ultrasonic vibration wave is a sine wave or a cosine wave, which has a periodic cycle characteristic, causes fatigue damage to the rock, and effectively reduces the cracking strength of the key bearing layer of the overburden;

[0049] Further, the specific method of step eight is:

[0050] Transmission CT imaging was performed between the first and last crack holes at each construction site to obtain the crack extension area between the first and last crack holes. The ratio of the crack extension area between the first and last crack holes to the ultrasonic vibration range area was defined as the inter-hole crack penetration rate at each construction site, that is:

[0051]

[0052] Where R is the crack penetration rate between holes, S is the area of ​​the crack extension region between the first and last crack holes, h is the vertical range of ultrasonic vibration, n is the number of crack holes, and C is the crack hole spacing;

[0053] When 0≤R<0.6, it indicates that the ultrasonic cracking effect is poor, and it is necessary to reduce the cracking hole spacing and enhance the vibration frequency and amplitude of the ultrasonic vibration wave before construction can be carried out at the next implementation site;

[0054] When 0.6≤R<0.8, the ultrasonic cracking effect is moderate, and the cracking hole spacing, vibration frequency and amplitude parameters of the ultrasonic cracking pressure relief technology can be adjusted according to the actual needs of the site to meet the construction requirements of the next implementation site;

[0055] When 0.8≤R<1, the ultrasonic cracking effect is better, indicating that the ultrasonic cracking pressure relief technical parameter is the optimal parameter under this condition. This parameter can be used as the ultrasonic cracking pressure relief technical parameter for the next implementation site.

[0056] The beneficial effects of the present invention are:

[0057] 1. The present invention constructs an in-hole mud degree that can directly reflect the mud effect inside the borehole, and scientifically evaluates and quantitatively characterizes the mud effect of each segment inside the borehole.

[0058] 2. The present invention takes into account the influence of the mud effect inside the borehole on the ultrasonic cracking pressure relief effect under actual engineering conditions, realizes the segmented ultrasonic cracking in the hole under the conditions of water-rich soft overburden, and utilizes the mechanical vibration effect generated by ultrasonic vibration waves and rocks to effectively destroy the integrity of the key bearing layer of the overburden, reduce the ability to transmit the overburden load, block the source of load on the near-field surrounding rock, weaken the load strength of the surrounding rock, and control the deformation of the tunnel surrounding rock.

[0059] 3. The ultrasonic vibration waves in the present invention have periodic cycle characteristics, causing fatigue damage to the rock, effectively reducing the cracking strength of the key bearing layer of the overburden, and having relatively low requirements on equipment power and power supply.

[0060] 4. The present invention establishes an evaluation index R for ultrasonic cracking effect of water-rich soft overburden, scientifically evaluates the implementation effect of ultrasonic cracking pressure relief technology, and can provide effective guidance for the on-site application of ultrasonic cracking pressure relief technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0062] Figure 1 A schematic flow chart of a method for ultrasonic cracking and decompression of water-rich soft overburden based on the degree of mud in the hole provided by an embodiment of the present invention;

[0063] Figure 2 A schematic diagram of load characteristics of the near-field surrounding rock above the coal body at the working face provided by the embodiment of the present invention;

[0064] Figure 3 A schematic diagram of load characteristics of the near-field surrounding rock where the pre-splitting fracture line is located above the tunnel provided by an embodiment of the present invention;

[0065] Figure 4 A schematic diagram of load characteristics of the near-field surrounding rock where the pre-splitting fracture line is located above the goaf provided by an embodiment of the present invention;

[0066] Figure 5 A schematic diagram of cracking hole parameter design provided by an embodiment of the present invention;

[0067] Figure 6 A schematic diagram of a method for ultrasonic cracking and decompression of water-rich soft overburden based on the degree of mud in the hole provided by an embodiment of the present invention;

[0068] Figure 7 A schematic diagram of an ultrasonic vibration platform provided in an embodiment of the present invention;

[0069] In the figure, 1, tunnel, 2, direct bottom, 3, basic bottom, 4, coal body of working face, 5, coal pillar, 6, goaf, 7, direct top, 8, basic top, 9, near-field surrounding rock load, 10, overburden load, 11, pre-splitting fracture line, 12, coal seam, 13, key bearing layer of overburden, 14, cracking hole, 15, ultrasonic vibration platform, 16, control system, 17, ultrasonic generator, 18, transducer, 19, amplitude transformer, 20, annular intensifier, 21, power supply device, 22, monitoring system, 23, ultrasonic vibration wave. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical scheme and beneficial effects of the present invention more clear, the following is combined with the current situation of a mine in Yuanyang Lake Mine Field, Ningxia Hui Autonomous Region and with reference to the attached Figure 1-7 , the present invention is further described in detail.

[0071] A certain mine is one of the main mines in Yuanyang Lake Mine Field, Ningxia Hui Autonomous Region. Due to its special diagenetic environment and sedimentary process, the overburden of the main mining coal seam 12 is mostly water-rich and weak overburden, and the thickness and other characteristics of the overburden vary greatly along the roadway. The direct roof 7 is composed of siltstone, the basic roof 8 is composed of mudstone, the direct bottom 2 is composed of fine sandstone, and the basic bottom 3 is composed of medium sandstone. In order to reduce the impact of water on the mining of coal seam 12, the mine has implemented a large number of overburden drainage projects, but the project only effectively drains most of the water in the overburden, and some water remains in the rock layer. This part of water and the weak overburden have water-rock coupling, causing serious mudification. At the same time, with the increase in mining intensity year by year, after the mine enters deep mining, the near-field surrounding rock of the roadway 1 is affected by the overburden load 10, and the surrounding rock is severely deformed, which restricts the safe and efficient production of the mine. To this end, the mine has successively adopted hydraulic fracturing, blasting fracturing and other technologies to destroy the integrity of the key bearing layer 13 of the overburden. However, due to the failure to scientifically identify the degree of mud in the hole, these technologies cannot achieve the expected results after implementation, and the deformation effect of the tunnel surrounding rock is not good. Therefore, in order to safely and effectively crack the water-rich soft overburden rock and give full play to the advantages of ultrasonic fracturing, the ultrasonic cracking pressure relief method of water-rich soft overburden rock based on the degree of mud in the hole is provided.

[0072] Reference Figure 1-Figure 7 The present invention provides a method for ultrasonic cracking pressure relief of water-rich soft overburden based on the degree of mud in the hole, which comprises the following steps:

[0073] Step 1: Obtain geomechanical information of the implementation site

[0074] Determine the implementation location of the ultrasonic cracking pressure relief method, and obtain the borehole columnar and overburden mechanical properties at the implementation location, in preparation for step 2 of determining the overburden key bearing layer 13;

[0075] Step 2: Determine the key bearing layer of the overburden 13

[0076] The implementation site is constructed in sections. First, the load Q borne by each rock layer above the working surface is calculated based on the overburden characteristics of each implementation site and identified from bottom to top. If the i-th layer is the key bearing layer 13 of the overburden, the bearing relationship satisfied by the i+1-th layer is:

[0077] Q i >Q i+1

[0078] In the formula, Q i , Q i+1 is the load borne by the i-th and i+1-th rock layers;

[0079] That is to say, the rock layer that bears the largest load at each implementation site is determined as the key bearing layer of the overburden at each implementation site.

[0080] Step 3: Identify the degree of mudification of cracking hole 14

[0081] First, a peephole with a diameter of 38-45 mm and a hole depth equal to the depth of cracking hole 14 is constructed vertically upward at a certain implementation site, and then the peephole is cleaned and drilled in sections from bottom to top within the vertical range of vibration; the length of the cleaning hole and the amount of water for cleaning the hole must be consistent during the cleaning, and a collection bucket must be placed under the peephole before cleaning to collect water samples flowing out during the cleaning, and a high-precision electronic weighing instrument is used to test the weight of the flowing water sample; for example, after the first section of the peephole is cleaned, the first section of the peephole is drilled and peeped to obtain the mud characteristics in the first section of the peephole, and then the mud degree K of the first section of the peephole 14 is measured. 1 To identify,

[0082]

[0083] In the formula, B 01 is the length of the first section of the peephole, B 11 W is the length of the hole with mud characteristics in the first section of the peephole wall, 01 is the weight of the water sample used for the first cleaning of the peephole, W 11The weight of the water sample collected after the first section of the peephole cleaning is completed;

[0084] When 0≤K 1 When <0.5, the mudding phenomenon in the borehole is relatively slight; 0.5≤K 1 When K<0.8, the mudding phenomenon in the borehole is serious; 0.8≤K 1 When <1, the mudding phenomenon in the borehole is serious;

[0085] The mud degree K of the first section of the peephole is determined 1 The mud degree of the first stage of all cracking holes at the first stage implementation site;

[0086] Using the same method, the mud degree of the remaining sections of the cracking hole was identified one by one.

[0087] Step 4: Determine the location of the pre-crack fracture line 11 of the overburden rock

[0088] like Figures 2 to 4 As shown, according to the mining characteristics of the working face and the need to preserve the tunnel 1, the characteristics of the load 9 borne by the near-field surrounding rock of the tunnel 1 are analyzed when the overburden pre-splitting fracture line 11 is located above the coal body 4 of the working face, above the tunnel 1, and above the goaf 6. It is found that when the overburden pre-splitting fracture line 11 is located above the goaf 6, the peak value of the load 9 borne by the near-field surrounding rock such as the coal body 4 and the coal pillar 5 of the working face is the smallest, and it is determined that the position of the overburden pre-splitting fracture line 11 is located above the goaf 6.

[0089] Step 5: Design key parameters of ultrasonic cracking pressure relief technology

[0090] The key parameters of ultrasonic cracking pressure relief technology include cracking hole parameters and ultrasonic vibration parameters, among which:

[0091] (1) The parameters of the cracking holes 14 include the inclination angle, length, spacing, etc. of the cracking holes 14. The inclination angle θ of the cracking holes 14 is determined according to the position of the pre-crack fracture line 11 of the overburden and the on-site drilling rig construction conditions. The inclination angle θ of the cracking holes 14 needs to be the maximum angle under the on-site drilling rig construction conditions, and θ < 90°.

[0092] The length L of the cracking hole 14 is determined by the vertical depth H and the inclination angle θ of the overburden key bearing layer 13, that is:

[0093]

[0094] Wherein, α is the inclination angle of the coal seam 12, and θ is the angle between the cracking hole 14 and the horizontal direction.

[0095] The spacing between the crack holes 14 is:

[0096]

[0097] Wherein, C is the spacing between cracking holes 14, ξ is the ultrasonic vibration correction coefficient, ξ can be between 0-2.0, d is the diameter of cracking hole 14, m is the thickness of coal seam 12, f is the overburden solidity coefficient, and M is the burial depth of coal seam 12.

[0098] (2) Ultrasonic vibration parameters mainly include vibration frequency, amplitude and vibration vertical range;

[0099] Based on the mud degree of each section of the cracking hole, the vibration frequency and amplitude of each section of the cracking hole are designed. When the mud degree of a section of the cracking hole is large, the vibration frequency and amplitude of the ultrasonic cracking construction site of this section are also large; when the mud degree of a section of the cracking hole is small, the vibration frequency and amplitude of the ultrasonic cracking construction site of this section are also small. Usually, the vibration frequency can be selected between 20 and 40 kHz, and the amplitude setting can be selected between 30 and 60 μm; to ensure the ultrasonic cracking effect, the vertical range of vibration is set to 1.2 to 1.3 times the thickness of 13 layers of the key bearing layer of the overburden.

[0100] Step 6: Implement ultrasonic cracking drilling

[0101] Use geological drilling rigs and supporting drilling platforms to carry out drilling construction according to the designed cracking hole parameters.

[0102] Step 7: Ultrasonic cracking of deep water-rich soft overburden

[0103] The ultrasonic vibration platform 15 with coal safety certification qualification is used to perform in-hole segmented ultrasonic cracking on the deep water-rich soft overburden key bearing layer 13. The ultrasonic vibration platform structure layout is shown in Figure 7 The overall system includes a control system 16, an ultrasonic generator 17, a transducer 18, an horn 19, a toroidal exciter 20, a power supply device 21 and a monitoring system 22. The power supply device 21 is connected to the control system 16, and the control system 16 is connected to the ultrasonic generator 17 to control and adjust the required ultrasonic vibration parameters in real time. The transducer 18 is arranged on the upper side of the ultrasonic generator 17, and the horn 19 is arranged on the top of the transducer 18. The toroidal exciter 20 is connected to the horn 19. The monitoring system 22 is connected to the horn 19 and the toroidal exciter 20 to monitor the characteristics of the output ultrasonic vibration wave 23 in real time.

[0104] The working method of the ultrasonic vibration platform 15 is as follows: first, the transducer 18, the horn 19 and the annular exciter 20 reach the set position in the cracking hole 14 through the geological drilling rig platform to perform ultrasonic cracking. The ultrasonic generator 17 is controlled by the control system to convert the industrial current transmitted by the power supply device 21 into a high-frequency electrical signal, the transducer 18 converts the high-frequency electrical signal into an ultrasonic vibration wave 23, and the horn 19 enhances the ultrasonic vibration wave 23. The enhanced ultrasonic vibration wave 23 undergoes mechanical resonance and thermal damage effects with the rock through the annular exciter 20, cracking the rock in sections and causing damage to the internal structure, physical and mechanical properties of the rock, effectively destroying the integrity of the overburden key bearing layer 13, reducing the ability to transmit the overburden load, and blocking the source of the near-field surrounding rock bearing the load 9, thereby reducing the surrounding rock load strength and controlling the deformation of the tunnel surrounding rock.

[0105] The ultrasonic vibration wave 23 in the embodiment of the present invention is preferably a sine / cosine wave, which has a periodic cycle characteristic, causes fatigue damage to the rock, and effectively reduces the cracking strength of the key bearing layer 13 of the overburden.

[0106] Step 8: Evaluate the ultrasonic cracking effect

[0107] Transmission CT imaging is performed between the first and last crack holes 14 of the construction site that has just been constructed to obtain the area of ​​the crack extension region between the first and last crack holes 14. The ratio of the crack extension region area between the first and last crack holes to the ultrasonic vibration range area is defined as the inter-hole crack penetration rate of the construction site, that is:

[0108]

[0109] Where, R is the crack penetration rate between holes at the construction site, S is the area of ​​the crack extension region between the first and last crack holes at the construction site, h is the vertical range of ultrasonic vibration at the construction site, n is the number of crack holes at the construction site, and C is the crack hole spacing at the construction site.

[0110] When 0≤R<0.6, it means that the ultrasonic cracking effect at the current construction site is poor, and it is necessary to reduce the cracking hole spacing and enhance the vibration frequency and amplitude of the ultrasonic vibration wave 23 before construction can be carried out at the next implementation site; when 0.6≤R<0.8, it means that the ultrasonic cracking effect at the current construction site is medium, and the cracking hole spacing, vibration frequency and amplitude parameters of the ultrasonic cracking pressure relief technology can be adjusted according to the actual needs of the site to meet the construction requirements of the next implementation site; when 0.8≤R<1, it means that the ultrasonic cracking effect at the current construction site is good, indicating that the ultrasonic cracking pressure relief technical parameters are the optimal parameters under this condition, and this parameter can be used as the ultrasonic cracking pressure relief technical parameters for the next implementation site.

[0111] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for ultrasonic cracking and pressure relief of water-rich soft overburden based on the degree of mud in the hole, characterized in that: The method comprises the following steps: Step 1: Obtain geomechanical information of the implementation site Determine the location for the ultrasonic fracturing decompression method and obtain geomechanical information to determine the key bearing layers of the overburden; Step 2: Determine the key bearing layer of the overburden Carry out implementation at the implementation site in sections, and determine the key bearing layer of the overburden rock at a certain section of the implementation site based on the overburden rock characteristics of the implementation site; Step 3: Identify the degree of mud in cracking holes A peephole with the same hole depth as the cracking hole is constructed vertically upward at each implementation site, and the peephole is cleaned and peeped in sections. The mud degree of each section of the peephole is determined according to the section cleaning and peeping in the hole. The determined mud degree of each section of the peephole is the mud degree of each section of all cracking holes at the implementation site of the section. The mud degree represents a quantitative index of the mud effect degree of each section of the rock formation on the inner wall of the hole; Step 4: Determine the location of the pre-crack fracture line of the overburden rock Determine the location of the pre-crack fracture line of the water-rich soft overburden rock based on the mining characteristics of the working face, the use of the tunnel and the load characteristics of the surrounding rock; Step 5: Design key parameters of ultrasonic cracking pressure relief technology Designing cracking hole parameters within the key bearing layer of the overburden, and determining ultrasonic vibration parameters of each section of the cracking hole based on the mud degree of each section of the cracking hole, wherein the ultrasonic vibration parameters mainly include vibration frequency, amplitude and vertical vibration range, wherein the vibration frequency and amplitude are related to the mud degree of each section of the cracking hole, the greater the mud degree, the greater the vibration frequency and amplitude, and vice versa; Step 6: Implement ultrasonic cracking drilling Carry out drilling construction according to the designed cracking hole parameters at the implementation site; Step 7: Ultrasonic cracking of water-rich soft overburden The in-hole segmented ultrasonic cracking of the key bearing layer of the water-rich weak overburden rock requires the ultrasonic vibration wave to have a periodic cycle characteristic and to produce fatigue damage to the rock; Step 8: Evaluate the ultrasonic cracking effect Transmission CT imaging was performed between the cracking holes, and the crack penetration rate between holes was used as an indicator to evaluate the ultrasonic cracking effect at the first implementation site, providing a basis for adjusting the key parameters of the ultrasonic cracking pressure relief technology at the next implementation site.

2. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: The method for determining the key bearing layer of the overburden in step 2 is: Calculate the load Q borne by each rock layer above the working face and identify it from bottom to top. If the i-th rock layer is the key bearing layer, the bearing relationship satisfied by the i+1-th rock layer is: Q i >Q i+1 In the formula, Q i , Q i+1 are the loads borne by the i-th and i+1-th rock layers respectively.

3. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: The specific method of step three is: 3.1: Determine the mud degree of each section of the peephole at the implementation site First, construct a peephole vertically upward at the implementation site. The depth of the peephole is equal to the depth of the cracking hole. Then, the peephole is cleaned and peeked in sections from bottom to top within the vertical range of vibration. The length of the sectioned cleaning hole and the amount of water for cleaning the hole must be consistent. Collect the water sample flowing out during the cleaning and conduct a weight test. After a section of the peephole is cleaned, the length of the hole with mud characteristics in the wall of the peephole is obtained, and then the mud degree K of the i-th section of the peephole is calculated according to the following formula: i To identify, In the formula, B 0i is the length of the i-th segment of the peephole, B 1i is the length of the hole with mud characteristics in the i-th section of the peephole wall, W 0i is the weight of the water sample used for cleaning the peephole in section i, W 1i The weight of the water sample collected after the peephole section i is cleaned; 3.2: Based on the mud degree of each section of the peephole at the implementation site, determine the mud degree K of each section in all cracking holes at the implementation site j , that is, K j =K i , j represents the segment number of each segment in the cracking hole, and j = i; When 0≤K j When K<0.5, it indicates that the mudification phenomenon in the jth section of the cracking hole is relatively slight; when 0.5≤K j When 0.8≤K j When <1, it indicates that the mudding phenomenon in the jth section of the cracking hole is serious.

4. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: The specific method of step 4 is: According to the mining characteristics of the working face and the use of the tunnel, the load characteristics of the near-field surrounding rock are analyzed in three cases where the overburden pre-cracking fracture line is located above the coal body of the working face, above the tunnel, and above the goaf. The position of the overburden pre-cracking fracture line corresponding to the minimum peak value of the near-field surrounding rock load is taken as the final overburden pre-cracking fracture line position.

5. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: The cracking hole parameters in step 5 include the inclination angle θ, length and spacing of the cracking holes, wherein: The cracking hole inclination angle θ needs to be the maximum angle under the on-site drilling rig construction conditions, and θ < 90°; The cracking hole length L is determined by the vertical depth H and the inclination angle θ of the key bearing layer of the overburden, that is: In the formula, α is the coal seam inclination, θ is the angle between the cracking hole and the horizontal direction; The cracking hole spacing C is: Where ξ is the ultrasonic vibration correction coefficient, ξ ranges from 0 to 2.0, d is the cracking hole diameter, m is the coal seam thickness, f is the overburden rock strength coefficient, and M is the coal seam burial depth.

6. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 5, characterized in that: The vibration frequency is selected between 20 and 40 KHz, the amplitude is selected between 30 and 60 μm, and the vertical range of vibration is set to 1.2 to 1.3 times the thickness of the key bearing layer of the overburden.

7. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: In the step seven, an ultrasonic cracking method is implemented using an ultrasonic vibration platform with coal mine safety certification.

8. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: The ultrasonic vibration platform mainly includes a control system, an ultrasonic generator, a transducer, a horn, a toroidal exciter, a power supply device and a monitoring system; the control system is respectively connected to the power supply device and the ultrasonic generator, and is used to control and adjust the required ultrasonic vibration parameters; the monitoring system is used to monitor in real time the ultrasonic vibration wave characteristics output by the horn and the toroidal exciter; a transducer is arranged on the upper side of the ultrasonic generator, a horn is arranged on the top of the transducer, the horn is connected to the toroidal exciter, and the horn and the toroidal exciter are respectively connected to the monitoring system; the ultrasonic vibration wave is a sine wave or a cosine wave, and has a periodic cycle characteristic.

9. The ultrasonic cracking pressure relief method for water-rich soft overburden based on the degree of shale in the pore according to claim 1, characterized in that: The specific method of step eight is: Transmission CT imaging was performed between the first and last crack holes at each construction site to obtain the crack extension area between the first and last crack holes. The ratio of the crack extension area between the first and last crack holes to the ultrasonic vibration range area was defined as the inter-hole crack penetration rate at each construction site, that is: Where R is the crack penetration rate between holes, S is the area of ​​the crack extension region between the first and last crack holes, h is the vertical range of ultrasonic vibration, n is the number of crack holes, and C is the crack hole spacing; When 0≤R<0.6, it indicates that the ultrasonic cracking effect is poor, and it is necessary to reduce the cracking hole spacing and enhance the vibration frequency and amplitude of the ultrasonic vibration wave before construction can be carried out at the next implementation site; When 0.6≤R<0.8, the ultrasonic cracking effect is moderate, and the cracking hole spacing, vibration frequency and amplitude of the ultrasonic cracking pressure relief technology need to be adjusted according to the actual needs of the site to meet the construction requirements of the next implementation site; When 0.8≤R<1, the ultrasonic cracking effect is better, indicating that the ultrasonic cracking pressure relief technical parameters are the optimal parameters under this condition, and this parameter can be used as the ultrasonic cracking pressure relief technical parameters for the next implementation site.

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