Soft surrounding rock double-sleeve drilling coring device and coring method

Abstract

The invention relates to the technical field of surrounding rock drilling, in particular to a soft surrounding rock double-sleeve drilling coring device and a coring method.The soft surrounding rock double-sleeve drilling coring device comprises a coring drill bit, a connecting sleeve, a coring sleeve and a drilling machine connecting base, the connecting sleeve and the coring sleeve are of an inner-outer double-sleeve structure, and drilling and rock breaking are achieved through rotation of an outer pipe; the inner pipe is kept static through magnetic force provided by the magnetic steel. By means of the magnetic force fixing technology, equipment abrasion and failure caused by traditional mechanical friction or hydraulic limiting are avoided, and torsional force transmitted to a rock core by a coring pipe is effectively reduced so as to keep the rock core stable; on the basis of the magnetic attraction force requirement, a coring and magnetic steel selecting method is provided, and a calculation formula of the area needed by magnetic steel is deduced by analyzing parameters such as disturbance torque, an inclination angle and gravity distribution so as to optimize the magnetic adaptation performance of the device; the method can be widely applied to rock core collection of complex stratums such as coal mines, petroleum shale and soft surrounding rocks in geological exploration, the rock core breakage rate is greatly reduced, and the coring integrity is improved.

Description

Technical Field

[0001] The invention relates to the technical field of surrounding rock drilling, and in particular to a double-casing coring device and a coring method for soft surrounding rock. Background Art

[0002] Drilling and coring of surrounding rocks is a key link in geological exploration, mining area structural analysis and surrounding rock mechanical testing. However, under complex working conditions, especially in soft surrounding rocks, due to the loose and broken characteristics of the surrounding rock structure, conventional coring tools have the following main problems:

[0003] During the coring process, the coring tube and the core rotate together, which will cause the core to be disturbed by additional torsional or radial forces, resulting in internal fragmentation or even pulverization, making it difficult to effectively retain the original distribution state of the core. The currently commonly used single-axis rotary drilling design only separates the inner and outer casings by mechanical limiting or lubrication, but under high rotation speed and complex impact conditions, the mechanism has a high probability of failure and insufficient stability. The ideal double-casing structure in a soft surrounding rock environment should achieve a design of "the outer casing rotates to complete drilling and core collection, while the inner tube remains stationary to reduce core loss". However, most of the existing devices have not solved the technical problem of inner tube fixation, and in particular have not proposed a dynamic adaptation mechanism for changes in coring angle, core length and weight. Summary of the invention

[0004] In view of the above problems, the present invention adopts the following technical solutions to achieve the above objectives:

[0005] The invention discloses a double-casing coring device for soft surrounding rock, comprising a coring drill located in a tunnel, a drilling rig connection seat, a connecting casing, a coring casing and a coring drill bit are sequentially installed on the coring drill rig, and the coring casing and the coring drill bit are used to drive into the surrounding rock for sampling;

[0006] The drilling rig connection seat comprises a casing connection shaft, an outer casing connection seat, an inner casing connection seat, and a magnetic steel fixing seat; wherein the casing connection shaft and the outer casing connection seat are fixedly connected by a plurality of connecting plates, the inner casing connection seat is located in the outer casing connection seat, and is coaxially arranged; the magnetic steel fixing seat is located on the coring drilling rig, the magnetic steel fixing seat is provided with a magnetic steel connection lower seat and a magnet on the magnetic steel connection lower seat, a plurality of connecting plates are provided with a magnetic steel connection upper seat and another magnet on the magnetic steel connection upper seat, the two magnets are magnetically attracted to each other, and the magnetic steel connection upper seat is fixedly connected to the inner casing connection seat;

[0007] The connecting sleeve comprises an outer connecting sleeve outer tube and an inner connecting sleeve inner tube, one end of the connecting sleeve outer tube is connected to the outer sleeve connecting seat, and one end of the connecting sleeve inner tube is connected to the inner sleeve connecting seat;

[0008] The coring casing comprises an outer coring casing outer tube and an inner coring casing inner tube, one end of the outer coring casing outer tube is connected to the other end of the connecting casing outer tube, and one end of the inner coring casing inner tube is connected to the other end of the connecting casing inner tube; a flexible sealing member is arranged inside the inner coring casing inner tube;

[0009] The coring drill bit is connected to the other end of the outer tube of the coring casing, and a through hole corresponding to the other end of the inner tube of the coring casing and having the same inner diameter as that of the inner tube of the coring casing is arranged in the middle of the coring drill bit.

[0010] As a further preferred solution, thrust ball bearings are respectively provided between the outer sleeve connecting seat and the inner sleeve connecting seat, between the connecting sleeve outer tube and the connecting sleeve inner tube, and between the coring sleeve outer tube and the coring sleeve inner tube.

[0011] As a further preferred scheme, the outer tube of the connecting casing and the outer casing connecting seat, the inner tube of the connecting casing and the inner casing connecting seat, the outer tube of the coring casing and the outer tube of the connecting casing, the inner tube of the coring casing and the inner tube of the connecting casing, the coring drill bit and the outer tube of the coring casing, the magnet and the magnetic steel connecting lower seat, and the magnet and the magnetic steel connecting upper seat are respectively fixedly connected by connecting threads.

[0012] As a further preferred solution, cutting edges are distributed on the outer surface of the core drill bit, and a cutting groove is formed between two adjacent cutting edges, and the cutting groove gradually becomes shallower away from the excavation direction.

[0013] As a further preferred embodiment, the magnetic steel is a neodymium iron boron permanent magnet.

[0014] A coring method for a double-casing coring device for soft surrounding rock, comprising the following steps:

[0015] S1. Connect the connecting sleeve to the drilling rig connection seat, connect an appropriate number of connecting sleeves according to the drilling situation, connect the coring sleeve to the connecting sleeve, connect the coring drill bit to the coring sleeve, and extend the coring sleeve into the surrounding rock borehole;

[0016] S2. Calculate the appropriate size of the magnet, connect the two magnets to the upper magnet connection seat and the lower magnet connection seat through the connecting threads, and prepare for drilling and coring;

[0017] S3, start the coring drill, the coring drill bit drives the coring casing to continuously advance, and the obtained core enters the inner tube of the coring casing. When the core reaches the flexible sealing member, the coring drill is closed;

[0018] S4. Remove the two magnetic steels, and then remove the connecting casings and coring casings in turn, slowly take out the core in the inner tube of the coring casing, put the taken out core into the core box in time, complete the coring, and transport it to the laboratory for relevant experiments.

[0019] As a further preferred solution, due to the magnetic attraction force F磁 It is mainly determined by the area A of the action surface and the magnetic field strength B. Therefore, under the condition that the inner diameter of the magnetic steel connection thread remains unchanged, the magnetic attraction of the magnetic steel is increased by adjusting the area A of the magnetic steel used according to the need of coring to meet the need of fixing each inner tube during coring;

[0020] The steps to calculate the area A of the magnetic steel are as follows:

[0021] a. Calculate the gravity component moment caused by gravity, T 重 =(m 管 +m 岩 +nm 连 )gsinθr 内 ;

[0022] Among them, m 管 is the mass of the coring casing, m 岩 The quality of the core can be estimated based on the geological conditions, m 连 is the mass of the connecting casing, n is the number of connecting casings, g is the acceleration of gravity, θ is the coring angle, r 内 is the core casing radius;

[0023] b. Calculate the torque caused by friction, T 摩 =(m 管 +m 岩 +nm 连 )μgr 内 ;

[0024] Among them, m 管 is the mass of the coring casing, m 岩 The quality of the core can be estimated based on the geological conditions, m 连 is the mass of the connecting sleeve, n is the number of connecting sleeves, g is the acceleration of gravity, μ is the friction coefficient, r 内 is the radius of the coring casing;

[0025] c. Calculate the total disturbance torque, T 总 =T 重 +T 摩 ;

[0026] d. Calculate the required magnetic attraction:

[0027] Among them, r 磁 The radial distance from the center of the core casing section to the magnetic steel;

[0028] e. Calculate the area required for the magnetic steel:

[0029] Among them, h is the distance between the two magnets, μ0 is the magnetic permeability of vacuum, and B is the magnetic induction intensity of the magnet material.

[0030] The beneficial effects of the present invention are as follows: the present invention has a simple structure and is easy to deploy. It does not require an additional power source to support the magnetic equipment and is suitable for underground coal mine operations and other complex strata drilling and coring scenarios. During the drilling and coring process, the outer tube of the device can continuously rotate to complete drilling or chip removal, while the inner tube is fixed by magnetic force and will not rotate. Even if it is subjected to complex torque or overload impact transmitted by the core, it can ensure that the inner layer coring function is not offset, and meet the high stability when working in the broken surrounding rock of the coal mine; the non-contact locking technology of neodymium iron boron magnets is introduced to achieve reliable fixation of the inner tube of the coring casing during the sampling process, and reduce the failure caused by equipment vibration and impact in traditional mechanical limit assemblies or hydraulic fixing solutions; a set of scientific magnetic steel selection methods are proposed, combined with the magnetic suction torque requirements under the conditions of broken surrounding rock in coal mines, and the inclination angle, friction force, accumulated gravity and other variables of the adaptive device when working are improved. The automation and intelligence level of coal mine equipment is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the operation of a double-casing coring device provided in an embodiment of the present invention;

[0032] Figure 2 A schematic diagram of a drilling rig connection base provided in an embodiment of the present invention;

[0033] Figure 3 A front view of a drilling rig connection base provided by an embodiment of the present invention;

[0034] Figure 4 A schematic diagram of the structure of a drilling rig connection base provided by an embodiment of the present invention;

[0035] Figure 5 A schematic diagram of a connecting sleeve provided in an embodiment of the present invention;

[0036] Figure 6 A schematic diagram of the connecting sleeve structure provided by an embodiment of the present invention;

[0037] Figure 7 A schematic diagram of a coring casing provided in an embodiment of the present invention;

[0038] Figure 8 A schematic diagram of the structure of a coring casing provided in an embodiment of the present invention;

[0039] Fig. 9 A schematic diagram of a coring drill bit provided in an embodiment of the present invention;

[0040] Fig.10 A schematic diagram of the structure of a coring drill bit provided in an embodiment of the present invention;

[0041] Fig.11 A schematic diagram of a magnetic steel structure provided in an embodiment of the present invention;

[0042] Among them: 1. Tunnel; 2. Coring drill; 3. Drilling rig connecting seat; 4. Connecting casing; 5. Coring casing; 6. Coring drill bit; 7. Surrounding rock; 8. Casing connecting shaft; 9. Connecting plate; 10. Magnetic steel connecting upper seat; 11. Magnetic steel; 12. Outer casing connecting seat; 13. Inner casing connecting seat; 14. Connecting thread; 15. Magnetic steel connecting lower seat; 16. Magnetic steel fixing seat; 17. Thrust ball bearing; 18. Connecting casing outer tube; 19. Connecting casing inner tube; 20. Coring casing outer tube; 21. Coring casing inner tube; 22. Flexible seal; 23. Cutting edge; 24. Cutting groove. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention;

[0044] The invention discloses a soft surrounding rock double-casing coring device and a use method thereof, which are used to obtain high-integrity, non-broken cores under soft surrounding rock conditions and simultaneously improve the reliability and adaptability of the coring device under special working conditions.

[0045] Figure 1 The schematic diagram of the operation of the double-casing coring device provided in the embodiment of the present invention includes a drilling rig connection seat 3, a connection sleeve 4, a coring sleeve 5 and a coring drill bit. When the device performs a drilling and coring operation in a tunnel 1, the coring drill bit 6 is connected to the front end of the coring sleeve 5 so that the core drilled by the coring drill bit 6 can be retained in the coring sleeve 5. The coring sleeve 5 is connected to the front end of the connection sleeve 4. The connection sleeve 4 only plays a connecting role and does not store the core. The connection sleeve 4 is connected to the drilling rig 2 through the drilling rig connection seat 3. The drilling rig 2 provides the power required for coring. The double-casing coring device can be operated through the drilling rig connection seat 3;

[0046] like Figures 2 to 4 As shown, the left end of the drilling rig connection seat 3 is fixedly connected to the drilling rig, and the right end can be connected to the coring casing 5 (when the connecting casing 4 is not used) or the connecting casing 4 according to the coring progress;

[0047] Further, in the drilling rig connection seat 3, the casing connection shaft 8 is connected to the rotating part of the coring rig 2, and the casing connection shaft 8 is connected to the outer casing connection seat 12 through the connecting piece 9. The outer casing connection seat 12 can be connected to the coring casing outer tube 20 of the coring casing 5 or the connecting casing outer tube 18 of the connecting casing 4 through the internal connecting thread 14, thereby completing the rotational power transmission of each outer tube to meet the coring requirements;

[0048] Further, in the drilling rig connection seat 3, the magnetic steel fixing seat 16 is connected to the non-rotating fixed part of the coring drilling rig 2, the magnetic steel 11 is connected to the magnetic steel fixing seat 16 through the magnetic steel connection lower seat 15, and another identical magnetic steel 11 is connected to the inner casing connection seat 13 through the magnetic steel connection upper seat 10. The two magnetic steels 11 have the same size and properties and are arranged in a mirror image. The inner casing connection seat 13 is fixed by magnetic force, and a gap is left between the two magnetic steels 11, which does not affect the movement of the connecting piece 9 in the gap. The inner casing connection seat 13 can be connected to the coring casing inner tube 21 of the coring casing 5 or the connecting casing inner tube 19 of the connecting casing 4 through the internal connecting thread 14, thereby completing the fixation of each inner tube, meeting the requirement that the inner tube remains fixed while the outer tube rotates;

[0049] Furthermore, there is a thrust ball bearing 17 between the outer sleeve connection seat 12 and the inner sleeve connection seat 13. The thrust ball bearing 17 can be used very reliably to freely separate the rotational movement between the inner and outer tubes, meeting the requirement that the inner tube remains fixed while the outer tube rotates;

[0050] Furthermore, the magnetic steel 11 is a neodymium iron boron permanent magnet, which has strong magnetic properties and can generate high-strength magnetic force in a small size. The connecting piece 9 is an aluminum alloy. Even if the connecting piece 9 dynamically passes through the gap between the magnetic steels 11, due to its aluminum alloy material, the core magnetic field distribution and the direction of the magnetic force lines will not be changed, and the impact is very weak, which will not significantly affect the magnetic properties and equipment stability. It has the advantages of corrosion resistance, light weight and high strength, and is particularly suitable for mine environments;

[0051] like Figures 5 and 6 As shown, the connecting sleeve outer tube 18 in the connecting sleeve 4 can be connected to the outer sleeve connecting seat 12 at the left end and the core sleeve outer tube 20 at the right end through the connecting thread 14;

[0052] Further, the connecting sleeve inner tube 19 in the connecting sleeve 4 can be connected to the left end inner sleeve connecting seat 13 and the right end core sleeve inner tube 21 through the connecting thread 14;

[0053] Further, a thrust ball bearing 17 is provided between the connecting sleeve outer tube 18 and the connecting sleeve inner tube 19;

[0054] like Figures 7 and 8 As shown, the coring casing outer tube 20 in the coring casing 5 can be connected to the left end connecting casing outer tube 18 and the right end coring drill bit 5 through the connecting thread 14;

[0055] Further, the core casing inner tube 21 in the core casing 5 can be connected to the left end connecting casing inner tube 19 through the connecting thread 14;

[0056] Further, a thrust ball bearing 17 is provided between the coring casing outer tube 20 and the coring casing inner tube 21, and a flexible seal 22 is provided near the left end to close the left end to store the obtained core;

[0057] like Figures 9 and 10 As shown, the coring drill bit 6 has a cutting edge 23 and a cutting groove 24 arranged to crush the surrounding rock 7, and the cutting groove 24 gradually becomes shallower in the longitudinal direction to facilitate the discharge of mud and the like and reduce resistance;

[0058] Furthermore, the coring drill bit 6 is connected to the outer tube 20 of the coring casing by connecting the thread 14, and the interior of the coring drill bit 6 is not connected to the inner tube 21 of the coring casing and a certain gap is left, but the inner diameter of the coring drill bit 6 is consistent with the inner tube 21 of the coring casing, and the core obtained by the coring drill bit 6 can be directly stored in the inner tube 21 of the coring casing; Fig.11 As shown, the magnet 11 is connected to the magnet connection upper seat 10 and the magnet connection lower seat 15 by the connecting thread 14. The magnetic force of the two magnets 11 ensures that the inner tubes do not rotate with the rotation of the outer tube.

[0059] Each outer tube in the present invention achieves drilling and rock breaking by rotating, and each inner tube is kept stationary by the magnetic force provided by the magnetic steel. The magnetic fixing technology is used to avoid equipment wear and failure caused by traditional mechanical friction or hydraulic limit, and effectively reduce the torsional force transmitted to the core by the coring tube to keep the core stable.

[0060] The new structure of the NdFeB magnet non-contact fixing technology introduced in the present invention reduces the damage of the core caused by mechanical interference such as rotation and overload, improves the integrity of core sampling, provides a magnetic fixing solution without physical contact, avoids excessive friction loss of equipment, and proposes a method for selecting the required magnets, thereby improving adaptability and reliability under different inclination angles and load conditions.

[0061] A coring method of a double-casing coring device for drilling soft surrounding rocks of the present invention comprises the following steps:

[0062] S1, connect the connecting sleeve 4 to the drilling rig connecting seat 3, connect an appropriate number of connecting sleeves 4 according to the drilling situation, connect the coring sleeve 5 to the connecting sleeve 4, connect the coring drill bit 6 to the coring sleeve (5), and extend the coring sleeve 5 into the borehole of the surrounding rock 7;

[0063] S2, calculate the appropriate size of the magnetic steel 11, connect the two magnetic steels 11 to the magnetic steel connection upper seat 10 and the magnetic steel connection lower seat 15 through the connecting thread 14, and prepare for drilling and coring;

[0064] S3, start the coring drill 2, the coring drill bit 6 drives the coring casing 5 to continuously advance, and the obtained core enters the inner tube 21 of the coring casing. When the core reaches the flexible sealing member 22, close the coring drill 2;

[0065] S4, remove the two magnetic steels 11, then remove the connecting sleeves 4 and the coring sleeves 5 in turn, slowly take out the core in the inner tube 21 of the coring sleeve, put the taken out core into the core box in time, complete the coring, and transport it to the laboratory for relevant experiments.

[0066] In the coring method of the present invention, by analyzing parameters such as disturbance torque, inclination angle and gravity distribution, the calculation formula for the required area of ​​the magnetic steel is derived to optimize the magnetic adaptability of the device; a thrust ball bearing is combined as an inner and outer tube connection to separate the rotation and improve the overall performance of the structure;

[0067] Due to the magnetic attraction F of the magnet 11 磁 It is mainly determined by the area A of the action surface and the magnetic field strength B. Therefore, under the condition that the inner diameter of the connection thread 14 of the magnetic steel 11 remains unchanged, the magnetic attraction of the magnetic steel (11) is increased by adjusting the area A of the magnetic steel 11 used according to the need of coring, so as to meet the need of fixing each inner tube during coring;

[0068] The steps for calculating the area A of the magnetic steel 11 are as follows:

[0069] a. Calculate the gravity component moment caused by gravity, T 重 =(m 管 +m 岩 +nm 连 )gsinθr 内 ;

[0070] Among them, m 管 is the mass of the core casing 5, m 岩 The quality of the core can be estimated based on the geological conditions, m 连 is the mass of the connecting sleeve 4, n is the number of connecting sleeves 4, g is the acceleration of gravity, θ is the coring angle, r 内 is the radius of the coring casing 5;

[0071] b. Calculate the torque caused by friction, T 摩 =(m 管 +m 岩 +nm 连 )μgr 内 ;

[0072] Among them, m 管 is the mass of the core casing 5, m 岩 The quality of the core can be estimated based on the geological conditions, m 连 is the mass of the connecting sleeve 4, n is the number of connecting sleeves 4, g is the acceleration of gravity, μ is the friction coefficient, r 内 is the radius of the coring casing 5;

[0073] c. Calculate the total disturbance torque, T 总 =T 重 +T摩 ;

[0074] d. Calculate the required magnetic attraction:

[0075] Among them, r 磁 The radial distance from the center of the cross section of the core casing 5 to the magnetic steel;

[0076] e. Calculate the area required for the magnetic steel:

[0077] Wherein, h is the distance between the two magnetic steels 11 , μ0 is the magnetic permeability of vacuum, and B is the magnetic induction intensity of the material of the magnetic steel 11 .

[0078] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A double-casing coring device for soft surrounding rock, characterized by: The invention comprises a coring drill (2) located in a tunnel (1), wherein a drill connection seat (3), a connecting sleeve (4), a coring sleeve (5) and a coring drill bit (6) are sequentially installed on the coring drill (2), wherein the coring sleeve (5) and the coring drill bit (6) are used to drive into surrounding rock (7) for sampling; The drilling rig connection seat (3) comprises a casing connection shaft (8), an outer casing connection seat (12), an inner casing connection seat (13), and a magnetic steel fixing seat (16); wherein the casing connection shaft (8) and the outer casing connection seat (12) are fixedly connected via a plurality of connection plates (9); the inner casing connection seat (13) is located inside the outer casing connection seat (12) and is coaxially arranged; the magnetic steel fixing seat (16) is located on the coring drilling rig (2); a magnetic steel connection lower seat (15) and a magnetic steel (11) on the magnetic steel connection lower seat (15) are provided on the magnetic steel fixing seat (16); a magnetic steel connection upper seat (10) and another magnetic steel (11) on the magnetic steel connection upper seat (10) are provided inside the plurality of connection plates (9); the two magnetic steels (11) are mutually magnetically attracted; the magnetic steel connection upper seat (10) and the inner casing connection seat (13) are fixedly connected; The connecting sleeve (4) comprises an external connecting sleeve outer tube (18) and an internal connecting sleeve inner tube (19), one end of the connecting sleeve outer tube (18) is connected to the outer sleeve connecting seat (12), and one end of the connecting sleeve inner tube (19) is connected to the inner sleeve connecting seat (13); The coring sleeve (5) comprises an outer coring sleeve outer tube (20) and an inner coring sleeve inner tube (21), one end of the outer coring sleeve outer tube (20) is connected to the other end of the connecting sleeve outer tube (18), and one end of the inner coring sleeve inner tube (21) is connected to the other end of the connecting sleeve inner tube (19); a flexible sealing member (22) is provided inside the inner coring sleeve inner tube (21); The coring drill bit (6) is connected to the other end of the coring sleeve outer tube (20), and a through hole corresponding to the other end of the coring sleeve inner tube (21) and having the same inner diameter as that of the other end is provided in the middle of the coring drill bit (6).

2. A double-casing coring device for soft surrounding rock according to claim 1, characterized in that: Thrust ball bearings (17) are respectively provided between the outer sleeve connecting seat (12) and the inner sleeve connecting seat (13), between the connecting sleeve outer tube (18) and the connecting sleeve inner tube (19), and between the coring sleeve outer tube (20) and the coring sleeve inner tube (21).

3. The double-casing coring device for soft surrounding rock according to claim 1, characterized in that: The connecting sleeve outer tube (18) and the outer sleeve connecting seat (12), the connecting sleeve inner tube (19) and the inner sleeve connecting seat (13), the coring sleeve outer tube (20) and the connecting sleeve outer tube (18), the coring sleeve inner tube (21) and the connecting sleeve inner tube (19), the coring drill bit (6) and the coring sleeve outer tube (20), the magnetic steel (11) and the magnetic steel connecting lower seat (15), and the magnetic steel (11) and the magnetic steel connecting upper seat (10) are fixedly connected via connecting threads (14).

4. The double-casing coring device for soft surrounding rock according to claim 1, characterized in that: The outer surface of the core drill bit (6) is provided with cutting edges (23), and a cutting groove (24) is provided between two adjacent cutting edges (23), and the cutting groove (24) gradually becomes shallower as it deviates from the excavation direction.

5. The double-casing coring device for soft surrounding rock according to claim 1, characterized in that: The magnetic steel (11) is a neodymium iron boron permanent magnet.

6. A coring method for a double-casing coring device for soft surrounding rock according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, connecting the connecting sleeve (4) to the drilling rig connecting seat (3), connecting an appropriate number of connecting sleeves (4) according to the drilling situation, connecting the coring sleeve (5) to the connecting sleeve (4), connecting the coring drill bit (6) to the coring sleeve (5), and extending the coring sleeve (5) into the borehole of the surrounding rock (7); S2, calculate the appropriate size of the magnetic steel (11), connect the two magnetic steels (11) to the magnetic steel connection upper seat (10) and the magnetic steel connection lower seat (15) through the connecting thread (14), and prepare for drilling and coring; S3, starting the coring drill (2), the coring drill bit (6) drives the coring casing (5) to continuously advance, and the obtained rock core enters the inner tube (21) of the coring casing. When the rock core reaches the flexible sealing member (22), the coring drill (2) is closed; S4, remove the two magnetic steels (11), then remove the connecting sleeves (4) and the coring sleeves (5) in turn, slowly take out the core in the inner tube (21) of the coring sleeve, put the taken out core into the core box in time, complete the coring, and transport it to the laboratory for relevant experiments.

7. A coring method for a double-casing coring device for soft surrounding rock according to claim 6, characterized in that: Due to the magnetic attraction F of the magnet (11) 磁 It is mainly determined by the area A of the action surface and the magnetic field strength B. Therefore, according to the need of coring, the magnetic attraction of the magnetic steel (11) is increased by adjusting the area A of the magnetic steel (11) used to meet the need of fixing each inner tube during coring; The steps for calculating the area A of the magnetic steel (11) are as follows: a. Calculate the gravity component moment caused by gravity, T 重 =(m 管 +m 岩 +nm 连 )gsinθr 内 ; Among them, m 管 is the mass of the coring casing (5), m 岩 The quality of the core can be estimated based on the geological conditions, m 连 is the mass of the connecting sleeve (4), n is the number of connecting sleeves (4), g is the acceleration of gravity, θ is the coring angle, r 内 is the radius of the coring casing (5); b. Calculate the torque caused by friction, T 摩 =(m 管 +m 岩 +nm 连 )μgr 内 ; Among them, m 管 is the mass of the coring casing (5), m 岩 The quality of the core can be estimated based on the geological conditions, m 连 is the mass of the connecting sleeve (4), n is the number of connecting sleeves (4), g is the acceleration of gravity, μ is the friction coefficient, r 内 is the radius of the coring casing (5); c. Calculate the total disturbance torque, T 总 =T 重 +T 摩 ; d. Calculate the required magnetic attraction: Among them, r 磁 is the radial distance from the center of the cross section of the core casing (5) to the magnetic steel; e. Calculate the area required for the magnetic steel: Wherein, h is the distance between the two magnetic steels (11), μ0 is the magnetic permeability of vacuum, and B is the magnetic induction intensity of the material of the magnetic steel (11).

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