An ultrasonic cracking pressure relief method for water-rich soft overburden rock based on hole mud content

Abstract

The application discloses a water-rich soft overburden rock ultrasonic cracking pressure relief method based on hole mudification degree, which mainly comprises the following steps: drilling a peeping hole with the same depth as the cracking hole at the implementation site before cracking; segmentally cleaning and segmentally peeping the peeping hole; calculating the hole mudification degree of each segment of the peeping hole and taking the hole mudification degree as the hole mudification degree of each segment of all cracking holes at the implementation site; designing the ultrasonic wave parameters of each segment of the cracking hole according to the hole mudification degree of each segment of the cracking hole; and using ultrasonic waves with periodic cycle characteristics to crack the water-rich soft overburden rock; and establishing an ultrasonic cracking effect evaluation index to effectively guide the field application of the subsequent ultrasonic cracking pressure relief technology. The application considers the influence of the hole internal mudification effect on the ultrasonic cracking pressure relief effect under the actual engineering conditions, and provides a basis for the hole safety cracking under the water-rich soft overburden rock condition.

Description

Technical Field

[0001] The present 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 coal resources in the shallow, central and eastern regions are depleted, mining is gradually shifting to deeper, western regions. Because the coal-bearing strata in the western mining area are primarily Jurassic-Cretaceous in the Mesozoic Era, the overlying strata contain multiple layers of highly aquiferous rock. Therefore, extensive roof drainage is performed prior to coal mining. However, due to the unique diagenetic environment of the western mining area, the overlying strata are mostly weak, causing water-rock coupling after drainage, resulting in severe mudification. Furthermore, as the mine enters deeper mining, the load transferred from the far-field strata to the near-field roadway surrounding rock increases significantly, causing severe deformation of the roadway surrounding rock. Overburden unloading technology is an effective measure to reduce the bearing strength of the near-field surrounding rock and control deformation of the roadway surrounding rock.

[0003] Currently, there are two main types of overburden pressure relief technologies. One involves hydraulic fracturing, which involves injecting high-pressure liquid into the overburden to create new or expand existing fractures. Publication No. CN118517266A, for example, discloses a method for hydraulic fracturing at a coal seam working face. This method employs a combination of long and short holes for multi-dimensional hydraulic fracturing, completely fracturing and relieving the overburden at the working face. This solves the problem of controlling the range and strength of the overburden by reducing large blocks to smaller ones around the roadway. Another type of blasting-induced fracturing pressure relief involves increasing fractures in the rock formation and destroying its integrity. Publication No. CN117846593A, for example, discloses a method for arranging long drill holes for blasting in the roof of an artificial pressure relief layer. This method reduces the elastic strain energy accumulated in the key induced impact layer through blasting, preventing it from reaching the minimum energy required for coal seam impact, thereby reducing the likelihood of impact damage to the working face. These technologies have achieved good results in weakly water-bearing, 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, problems such as hydraulic fracturing failing to reach the expected pressure due to poor sealing effect, and blasting failing to effectively fracture the overburden due to poor sealing effect and partial consumption of blast wave energy by water have frequently occurred, seriously affecting the safe and efficient production of mines.

[0004] When ultrasonic waves propagate in rock formations, they produce mechanical vibration effects on the 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 enhancement 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 mudification effects due to their own physical properties, while weak coal or water-rich soft overburden contains more clay minerals, which will cause mudification effects inside the borehole. The mudification effect inside the borehole has a greater impact on the effect of ultrasonic cracking of weak coal or water-rich soft overburden, and it is necessary to adopt a scientific and rigorous method 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 content in the hole. The mud content of each segment in the hole is used to scientifically identify the mud effect of the key bearing layer of the overburden, thereby realizing segmented ultrasonic cracking in the hole under the conditions of water-rich soft overburden, 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 pressure relief of water-rich weak overburden based on the degree of in-hole mud, characterized in that the method comprises the following steps:

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

[0009] Determine the implementation location of the ultrasonic cracking pressure relief method and obtain geomechanical information of the implementation location 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. Based on the overburden characteristics of a certain section of the implementation site, calculate the load borne by each overburden layer at that section of the implementation site. Determine the overburden layer that bears the largest load at that section of the implementation site as the key bearing layer of the overburden at that section of the implementation site.

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

[0013] At each implementation site, a peephole with a depth equal to that of the cracking hole is constructed vertically upwards, and the peephole is cleaned and peeped in sections. The mud degree of each section of the peephole is determined based on the results of the section cleaning and peeping in the hole. The mud degree of each section of the peephole determined is the mud degree of each section of all cracking holes at the implementation site of the section. The mud degree represents a quantitative indicator of the degree of mud effect produced in 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-cracking fracture line of the water-rich soft overburden based on the mining characteristics of the working face, the use of the roadway, 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 argillaceousness 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 argillaceousness of each section of the cracking hole. If the argillaceousness of a certain section of the cracking hole is greater, the ultrasonic vibration parameter vibration frequency and amplitude of this section of the cracking hole are also greater. If the argillaceousness of a certain section of the cracking hole is less, the vibration frequency and amplitude of this section of the cracking hole are also smaller.

[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] In-hole segmented ultrasonic cracking of the key bearing layer of water-rich weak overburden requires that the ultrasonic vibration wave has periodic cyclic characteristics and can cause fatigue damage to the rock. Based on the characteristic that ultrasonic vibration waves 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 damaging its internal structure, physical and mechanical properties.

[0022] Step 8: Evaluate the ultrasonic cracking effect

[0023] An acoustic CT instrument was used to perform transmission CT imaging between the 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 the key parameters of the ultrasonic cracking unloading technology at the next implementation site.

[0024] The above steps 2 to 8 are repeated to complete the ultrasonic cracking pressure relief at each implementation location in sequence.

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

[0029] Furthermore, 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 peeked in sections from bottom to top within the vertical range of vibration. The cleaning length and water volume of each section must be consistent. Before cleaning, a collection bucket must be placed under the peephole to collect water samples flowing out during cleaning. A high-precision electronic weighing instrument is used to test the weight of the water samples flowing out. After a section of the peephole is cleaned, the section is drilled and peeked. The purpose of the peephole is to obtain the length of the hole with mud characteristics on the wall of the section, and then the mud degree K of the i-th section of the peephole is calculated according to the following formula: i To identify, that is

[0032]

[0033] Where B 0i is the length of the peephole segment i, 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 mild; when 0.5≤K j When K<0.8, it indicates that the mudification phenomenon in the jth section of the cracking hole is more serious; when 0.8≤K j When <1, it indicates that the mudification phenomenon in the jth section of the cracking hole is serious.

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

[0037] According to the mining characteristics of the working face and the usage of the roadway, the load characteristics of the near-field surrounding rock are analyzed in three cases: the overburden pre-cracking fracture line is located above the coal body of the working face, above the roadway, 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 conditions. The cracking hole inclination angle θ needs to be the maximum angle under the on-site drilling 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] Where 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 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 vibration range is set to 1.2 to 1.3 times the thickness of the key bearing layer of the overburden.

[0047] Furthermore, 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 circumferential exciter, a power supply device and a monitoring system; the control system is connected to the power supply device and the ultrasonic generator respectively, 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 circumferential exciter; a transducer is provided on the upper side of the ultrasonic generator, a horn is provided on the top of the transducer, the horn is connected to the circumferential exciter, and the horn and the circumferential exciter are respectively connected to the monitoring system; the working method of the ultrasonic vibration platform is: first, the transducer, horn and circumferential 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 conversion of the industrial current transmitted from the power supply device 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 amplified by the amplitude transformer and then passes through the annular exciter to produce mechanical resonance and thermal damage effects with the rock, cracking the rock in sections and causing 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 borne by the near-field surrounding rock, thereby weakening 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 with a periodic cycle characteristic, causing fatigue damage to the rock and effectively reducing the cracking strength of the key bearing layer of the overburden;

[0049] Furthermore, 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 the holes, S is the area of ​​the crack propagation 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 increase 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 parameters are the optimal parameters under this condition. This parameter can be used as the ultrasonic cracking pressure relief technical parameters 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 uses 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 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 weak 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 following briefly introduces the drawings required for use in the description of the embodiments. 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 paying any creative work.

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

[0063] Figure 2 A schematic diagram of the load-bearing characteristics of the near-field surrounding rock with the pre-splitting fracture line located above the coal body at the working face provided by an embodiment of the present invention;

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

[0065] Figure 4 A schematic diagram of load-bearing characteristics of the near-field surrounding rock with the pre-splitting fracture line 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 pressure relief of water-rich weak overburden based on in-hole argillaceity 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 roof, 8. basic roof, 9. near-field surrounding rock load, 10. overburden load, 11. pre-crack 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. toroidal intensifier, 21. power supply device, 22. monitoring system, 23. ultrasonic vibration wave. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical solutions 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 described in further detail.

[0071] A certain mine is one of the main mines in the Yuanyang Lake mining area of ​​the Ningxia Hui Autonomous Region. Due to its unique diagenetic environment and sedimentary processes, the overburden of the main mining seam 12 is mostly water-rich and weak overburden. The thickness and other characteristics of the overburden vary significantly along the roadway strike. The immediate roof 7 is composed of siltstone, the basic roof 8 is composed of mudstone, the immediate bottom 2 is composed of fine sandstone, and the basic bottom 3 is composed of medium sandstone. To reduce the impact of water on the mining of coal seam 12, the mine implemented extensive overburden drainage projects. However, these projects only effectively drained most of the water in the overburden, leaving some water remaining in the rock strata. This water-rock coupling with the weak overburden caused severe mudification. Furthermore, with the increasing mining intensity and the mine's deep mining, the load 9 borne by the near-field surrounding rock of the roadway 1 was affected by the overburden load 10, resulting in severe deformation of the surrounding rock, which hampered safe and efficient production. To address this issue, the mine adopted hydraulic fracturing and explosive fracturing techniques to destroy the integrity of the critical bearing layer 13 of the overburden. However, due to factors such as the inability to scientifically identify the degree of in-hole argillaceousness, these technologies have failed to achieve the desired results after implementation, resulting in poor deformation of the surrounding rock in the tunnel. Therefore, to safely and effectively crack water-rich, weak overburden and leverage the advantages of ultrasonic fracturing, the present invention provides a method for ultrasonic cracking and pressure relief of water-rich, weak overburden based on the degree of in-hole argillaceousness.

[0072] Reference Figure 1-Figure 7 The present invention provides a method for ultrasonic cracking and pressure relief of water-rich weak overburden based on the degree of in-hole mud, comprising 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 to prepare 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 construction site is constructed in sections. First, the load Q borne by each rock layer above the working face is calculated based on the overburden characteristics of each section of the construction 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] Where 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 mud degree of cracking hole 14

[0081] First, a peephole with a diameter of 38 to 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 cleaning length and the amount of water for each section must be consistent when cleaning the hole, and a collection bucket must be placed under the peephole before cleaning to collect water samples flowing out during cleaning, and a high-precision electronic weighing instrument is used to test the weight of the water samples flowing out; 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 K1 of the first section of the peephole 14 is identified, that is,

[0082]

[0083] Where 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 W is the weight of the water sample used for the first stage of peephole cleaning. 11 The weight of the water sample collected after the first section of the peephole cleaning is completed;

[0084] When 0≤K1<0.5, the mudification phenomenon in the borehole is relatively mild; when 0.5≤K1<0.8, the mudification phenomenon in the borehole is relatively serious; when 0.8≤K1<1, the mudification phenomenon in the borehole is severe;

[0085] The mud degree K1 of the first section of the peephole determined is used as the mud degree of the first section of all cracking holes at the first section implementation location;

[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 overburden pre-crack fracture line 11

[0088] like Figures 2 to 4 As shown in the figure, according to the mining characteristics of the working face and the need to preserve the roadway 1, the load 9 characteristics of the near-field surrounding rock of the roadway 1 are analyzed when the overburden pre-splitting fracture line 11 is located above the coal body 4 of the working face, above the roadway 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 of 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 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, and spacing 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 conditions. The inclination angle θ of the cracking holes 14 must be the maximum angle under the on-site drilling 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 cracking holes 14 is:

[0096]

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

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

[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 the 13-layer 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 weak overburden

[0103] The ultrasonic vibration platform 15 with coal safety certification is used to perform in-hole segmented ultrasonic cracking on the deep water-rich weak 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, a horn 19, a toroidal exciter 20, a power supply 21, and a monitoring system 22. The power supply 21 is connected to the control system 16, which is connected to the ultrasonic generator 17 to control and adjust the required ultrasonic vibration parameters in real time. The transducer 18 is provided on the upper side of the ultrasonic generator 17, and the horn 19 is provided 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 ultrasonic vibration platform 15 operates as follows: first, the transducer 18, horn 19, and annular exciter 20 are sent through the geological drilling platform to a set position within the cracking hole 14 for ultrasonic cracking. The ultrasonic generator 17, controlled by a control system, converts industrial current transmitted from the power supply 21 into a high-frequency electrical signal. The transducer 18 converts the high-frequency electrical signal into an ultrasonic vibration wave 23. The horn 19 amplifies the ultrasonic vibration wave 23. The amplified ultrasonic vibration wave 23, passing through the annular exciter 20, mechanically resonates with the rock and produces a thermal damage effect. This cracks the rock in sections and damages its internal structure, physical and mechanical properties. This effectively destroys the integrity of the critical bearing layer 13 of the overburden, reduces its ability to transmit overburden loads, and blocks the source of the load 9 borne by the near-field surrounding rock, thereby reducing the surrounding rock's load strength and controlling deformation of the roadway 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 at the construction site that has just been completed to obtain the area of ​​the crack propagation region between the first and last crack holes 14. The ratio of the crack propagation region area between the first and last crack holes to the ultrasonic vibration range area is defined as the inter-hole crack penetration rate at this 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 propagation 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 spacing between crack holes at the construction site.

[0110] When 0≤R<0.6, it indicates 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 indicates 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 actual needs on site to meet the construction requirements of the next implementation site; when 0.8≤R<1, it indicates 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 scope of protection of the present invention.

Claims

1. A method for ultrasonic cracking and pressure relief of water-rich soft overburden based on the degree of argillaceousness 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 implementing the ultrasonic cracking pressure relief method and obtain geomechanical information to identify the key bearing layers of the overburden; Step 2: Determine the key bearing layer of the overburden Carry out implementation at each implementation site in sections, and determine the key bearing layer of the overburden at a certain implementation site based on the overburden characteristics of that implementation site; Step 3: Identify the mud degree of cracking hole At each implementation site, a peephole with the same depth as the cracking hole is constructed vertically upwards, and the peephole is cleaned and peeped in sections. The mud degree of each section of the peephole is determined based on the results of 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 this section. The mud degree represents a quantitative indicator of the degree of mud effect produced in 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 and weak overburden rock based on the mining characteristics of the working face, the use of the roadway 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 argillaceousness of each section of the cracking hole. The ultrasonic vibration parameters mainly include vibration frequency, amplitude, and vertical vibration range. The vibration frequency and amplitude are related to the argillaceousness of each section of the cracking hole. The greater the argillaceousness, 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 In-hole segmented ultrasonic cracking of key bearing layers of water-rich weak overburden requires that the ultrasonic vibration wave has periodic cyclic characteristics and can cause fatigue damage to the rock; Step 8: Evaluate the ultrasonic cracking effect Transmission CT imaging was performed between the 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 the key parameters of the ultrasonic cracking unloading technology at the next implementation site.

2. The ultrasonic cracking pressure relief method for water-rich weak overburden based on in-hole mud content according to claim 1, characterized in that: The method for determining the key bearing layer of 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 Where 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 weak overburden based on in-hole mud content 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 and water volume of each section must be consistent during cleaning. Collect water samples flowing out during cleaning and perform weight testing. 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, that is Where B 0i is the length of the peephole segment i, 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 mild; when 0.5≤K j When K<0.8, it indicates that the mudification phenomenon in the jth section of the cracking hole is more serious; when 0.8≤K j When <1, it indicates that the mudification phenomenon in the jth section of the cracking hole is serious.

4. The ultrasonic cracking pressure relief method for water-rich weak overburden based on in-hole mud content 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 usage of the roadway, the load characteristics of the near-field surrounding rock are analyzed in three cases: the overburden pre-cracking fracture line is located above the coal body of the working face, above the roadway, 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 weak overburden based on in-hole mud content 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 must be the maximum angle under on-site drilling 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: Where 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, which ranges from 0 to 2.0, d is the cracking hole diameter, m is the coal seam thickness, f is the overburden strength coefficient, and M is the coal seam burial depth.

6. The ultrasonic cracking pressure relief method for water-rich weak overburden based on in-hole mud content 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 vibration range 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 weak overburden based on in-hole mud content according to claim 1, characterized in that: In the step seven, an ultrasonic vibration platform with coal mine safety certification is used to implement the ultrasonic cracking method.

8. The ultrasonic cracking pressure relief method for water-rich weak overburden based on in-hole mud content according to claim 7, characterized in that: The ultrasonic vibration platform mainly includes a control system, an ultrasonic generator, a transducer, a horn, a circumferential 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 characteristics of the ultrasonic vibration waves output by the horn and the circumferential exciter; a transducer is provided on the upper side of the ultrasonic generator, a horn is provided on the top of the transducer, the horn is connected to the circumferential exciter, and the horn and the circumferential 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 weak overburden based on in-hole mud content 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 propagation area between the first and last crack holes. The ratio of the crack propagation 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 the holes, S is the area of ​​the crack propagation 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 increase 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 for the current implementation site, and this parameter can be used as the ultrasonic cracking pressure relief technical parameters for the next implementation site.

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