Working method of ground stress test system for tunnel engineering excavation compensation prevention and control

Abstract

The invention belongs to a ground stress test system, and discloses a working method of a ground stress test system for tunnel engineering excavation compensation prevention and control, which comprises the following steps: pushing a drill rod and a plugging test head to a specified depth of a test hole; arc-shaped outer supporting pieces on the front plugging head and the rear plugging head are controlled to expand outwards until the inner wall face of the test hole is in top supporting contact; further injecting water into the water injection expansion rubber rings on the front plugging head and the rear plugging head to fill the gap to form complete sealing, injecting water into the cavity of the plugging testing head and continuously pressurizing until the wall surface of the rock body in the cavity of the plugging testing head cracks, recording the pressure value when the cracks occur, and closing the booster water pump; and controlling the booster water pump to adjust and control the water pressure of the cavity in the plugging test head through the calculation control terminal according to the pressure adjustment control equation. The method has the advantages that a cooperative control mechanism is adopted, and a control equation for water pressure adjustment is constructed based on the seepage area, the fracture rigidity and the leakage coefficient of the fracturing section.

Description

Technical Field

[0001] The invention belongs to a geostress testing system, and in particular relates to a working method of a geostress testing system for tunnel engineering excavation compensation prevention and control. Background Art

[0002] Hydraulic fracturing is one of the recommended methods for measuring rock mechanics. It is currently the most reliable and direct method for measuring deep stress. This method is relatively simple to operate, has reliable values, and can be used for multiple or repeated measurements. It uses an expansion packer to isolate a section of a borehole at a known depth, and then pressurizes the measuring section by pumping in fluid. The horizontal principal stress value is determined using the recorded failure pressure, instantaneous shut-in pressure, and reopening pressure. The main drawback at present is that the sealing and anti-seepage of the expansion packer is difficult to achieve the ideal level and cannot adapt to rock masses with high pressure.

[0003] In addition, according to the mechanical characteristics of soft rock engineering, hydraulic fracturing faces unique technical challenges when measuring geostress. Since soft rock has significant plastic deformation and rheological properties, the crack extension pattern formed during fracturing is essentially different from that of hard rock. Studies have shown that the seepage area of ​​the fracturing section, as an effective channel for fluid migration, directly affects the penetration rate of the fracturing fluid in the rock mass; the fracture stiffness characterizes the ability of the fracture wall to resist deformation, and its dynamic changes will change the geometric morphology of the fracture; and the leakage coefficient reflects the difficulty of the fracturing fluid to flow along the primary fracture. The three together constitute the key parameters affecting the accuracy of geostress measurement. The traditional hard rock model does not fully consider the time-varying characteristics of the above parameters, resulting in significant deviations in the soft rock stress measurement results. To this end, this study established a nonlinear function of the seepage area changing with the confining pressure, constructed a dynamic stiffness model considering the roughness of the fracture surface, and derived the correlation equation between the leakage coefficient and the pore pressure based on seepage mechanics. Finally, the coupling mechanism of the three is integrated to provide a new theoretical basis for the measurement of geostress in soft rock formations. Summary of the invention

[0004] The purpose of the present invention is to provide a working method of a geostress testing system for tunnel engineering excavation compensation and prevention based on the above-mentioned deficiencies of the prior art. The working method adopts a collaborative control mechanism to construct a control equation for water pressure regulation based on the seepage area, crack stiffness and leakage coefficient of the fracturing section, so as to adjust and control the cavity water pressure in the plugging test head through a booster water pump.

[0005] The purpose of the present invention is achieved by the following technical solutions: A working method of a geostress testing system for tunnel engineering excavation compensation prevention and control, comprising the following steps: S1: Construct a geostress testing system in the tunnel, the testing system comprising a drill rod, a drill bit, a plugging test head, a water pump system and a computing control terminal; wherein: The plugging test head includes a front plugging head, a rear plugging head, a connecting column mechanism, a pressure sensor, an image observation device and a water injection head; the connecting column mechanism includes a connecting column and a front fixed disk and a rear fixed disk respectively arranged at both ends of the connecting column; the front plugging head is arranged on the front fixed disk, and the rear plugging head is arranged on the rear fixed disk; the pressure sensor, the image observation device and the water injection head are arranged on the connecting column; The front plugging head has the same structure as the rear plugging head; the front plugging head comprises a rotating disk, a central rotating shaft, a driving mechanism, an arc-shaped guide groove, a radial follower stud, a sliding block and a sliding groove; the central rotating shaft is arranged at the center of the rotating disk and driven to rotate by the driving mechanism; the number of the arc-shaped guide grooves is three groups and they are evenly distributed on the rotating disk at equal angles; the trajectory of the arc-shaped guide groove and the radial distance of the central rotating shaft vary from near to far; the sliding groove is radially arranged and fixed on the front fixed disk; the sliding block is arranged at the rear of the rotating disk and slidably assembled on the sliding groove; the radial follower stud is inserted in the arc-shaped guide groove and the lower end is connected to the radial inner end of the sliding block; the radial outer end of the sliding block is provided with an arc-shaped outer support member, and a water-injected expansion rubber ring is embedded in the outer groove of the arc-shaped outer support member; The water pump system includes a water storage tank, a booster water pump and a water pump pipeline; the water inlet of the booster water pump is connected to the water storage tank, and the water outlet of the booster water pump is connected to the water pump pipeline; the water pump pipeline includes a water pump main pipe and three water pump branches branched from the water pump main pipe, and the three water pump branches are respectively connected to the water injection head, the water injection expansion rubber ring on the front plugging head, and the water injection expansion rubber ring on the rear plugging head; The computing control terminal is connected to control the booster pump, the pressure sensor, and the image observation device; S2: installing the drill bit at the front end of the drill rod and drilling obliquely upward on the tunnel face to form a test hole in the rock mass; S3: After the drilling of the test hole is completed, the drill bit is removed from the drill rod, the plugging test head is installed at the front end of the drill rod, and then the drill rod and the plugging test head are pushed into the specified depth of the test hole; after being pushed into place, the arc-shaped outer support member on the front plugging head is controlled to move radially until it forms a supporting contact with the inner wall surface of the test hole, and the arc-shaped outer support member on the rear plugging head is controlled to move radially until it also forms a supporting contact with the inner wall surface of the test hole; S4: The water in the water storage tank is pressurized and pumped through the water pumping pipeline by the booster water pump, and the water pumping pipeline is pumped to the three water pumping branches respectively, wherein two of the water pumping branches are respectively injected with water to the water injection expansion rubber ring on the front plugging head and the water injection expansion rubber ring on the rear plugging head to fill the gap and form a complete seal, and the remaining water pumping branch is injected with water into the cavity of the plugging test head through the water injection head and continuously pressurized until cracks occur on the inner wall of the test hole enclosed by the plugging test head, the time of occurrence of the cracks is recorded by the image observation device and the pressure value when the cracks occur is recorded by the pressure sensor, and the booster water pump is turned off; S5: The computing control terminal then adjusts the water pressure based on the following pressure regulation control equation:

[0006] Where: is the fluid pressure in the fracture; P 0 Refers to the initial actual pressure value in the crack after the booster water pump is turned off, that is, the pressure value recorded in step S4 when the crack occurs; is the rock mass porosity; f t is the total formation compressibility factor, which can be considered as a constant; m is the intrinsic permeability of the rock mass; μ is the fluid viscosity; for i Crack stiffness at the time step; g t is the length of the measuring section; y c is the constant crack height; x c 1 / 2 of the total seam length; , is the pressure at time j and time j-1 in a single time step; The leakage duration after the pump is turned off for a single time step; i represents the time step; j Represents the moment.

[0007] The driving mechanism includes an electric telescopic rod mechanism and a spur rack. The electric telescopic rod mechanism is fixed on the front fixed plate. The teeth on the spur rack are meshed with the circular gear on the rear end of the central rotating shaft. The electric telescopic rod mechanism drives the spur rack to make reciprocating motion to drive the circular gear and the central rotating shaft to rotate.

[0008] The number of the sliding blocks on the front plugging head is the same as the number of the arc-shaped guide grooves, both of which are three groups. The three arc-shaped external support members on the radial outer ends of the three groups of sliding blocks are jointly enclosed to form an annular external support member at the minimum radial stroke; when each arc-shaped external support member moves radially outward with the sliding block and supports the inner wall surface of the test hole, water is injected and pressurized into the water-injected expansion rubber ring through the water pump branch pipe to expand and support the inner wall of the test hole to form a completely closed seal.

[0009] A rotating support is arranged at the center of the front fixed disk and is connected to the rear end of the central rotating shaft. The rear end of the central rotating shaft rotates on the rotating support and is axially limited.

[0010] A protective cover is mounted on the front end portion of the central rotating shaft of the front plugging head, and the center of the protective cover has a sleeve which is correspondingly mounted on the front end portion of the central rotating shaft to form a clearance fit. A protective ring extends backward on the outer edge of the protective cover, and three guide rails are arranged on the protective cover and respectively correspond to the setting positions of the radial follow-up studs. The guide rails are sloped in the radial moving path of the radial follow-up studs. The slope of the guide rails refers to extending from high to low in the radial direction, so that the protective cover as a whole moves from inside to outside in the radial direction with the radial follow-up studs, and the protective cover gradually extends upward under the guidance of the guide rails.

[0011] A rotating support is arranged at the center of the rear fixed disk and is connected to one end of the central rotating shaft of the rear plugging head. The end of the central rotating shaft of the rear plugging head rotates on the rotating support and is axially limited.

[0012] The advantages of the present invention are: (1) A coordinated control mechanism is adopted to construct the control equation of water pressure regulation based on the seepage area, fracture stiffness and leakage coefficient of the fracturing section, which provides a new technical path for geostress testing under complex geological conditions and can avoid secondary fracture interference caused by overpressure; (2) The arc-shaped external support member is used to form a position support fixation and preliminary seal between the inner wall of the test hole rock body, and further a water injection expansion rubber ring preset in the groove of the arc-shaped external support member is used to expand water to achieve the final seal between the inner wall of the test hole rock body, so as to adapt to the high water pressure fracturing test; (3) The same water pump system can be used to complete the water injection expansion sealing work of the water injection expansion rubber ring and the test of the water pressure fracturing value in the plugging test head cavity; (4) A protective cover is mounted on the front plugging head. Before operation, the protective cover can cover the components on the front plugging head to avoid collision during the process of extending into the test hole, and can rise synchronously when the arc-shaped outer support member expands outward to avoid blocking the moving path of the arc-shaped outer support member. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of installing a drill bit on a drill rod and drilling a test hole on a tunnel face in the present invention; Figure 2 A schematic diagram of installing a plugging test head on a drill pipe to perform a hydraulic fracturing test to obtain a ground stress value in the present invention; Figure 3 is a schematic diagram of a plugging test head in the present invention; Figure 4 Schematic diagram of the front end face of the front plugging head in the present invention (protective cover omitted); Figure 5 It is a schematic diagram of the rotating disk on the front plugging head in the present invention rotating to drive the radial follower stud and the associated sliding block and arc-shaped outer support member to move radially outward; Figure 6 It is a schematic diagram of the arc-shaped outer support member on the front plugging head in the present invention moving radially outward and further injecting water to expand the water-injection expansion rubber ring so as to fit and seal with the inner wall surface of the test hole; Figure 7 It is a schematic diagram of the rear end face of the front plugging head in the present invention; Figure 8 For the present invention Figure 7 A0A section view in; Fig. 9 It is a schematic diagram of the process of the protective cover arranged on the front plugging head in the present invention being lifted up by the radial follower stud; Fig.10 It is a schematic diagram of the process of expansion and sealing of the water-injected expansion rubber ring in the present invention; Fig.11 Schematic diagram of the fracture geometry in an infinite plane in the present invention.

[0014] like Figure 1-11 , the marks in the figure are: Tunnel 1, face 2, drill rod 3, drill bit 4, plugging test head 5, water storage tank 6, booster pump 7, computing control terminal 8, pumping pipeline 9; Front plugging head 51, rotating disk 511, first central rotating shaft 512, arc guide groove 513, radial follower stud 514, sliding block 515, sliding groove 516, arc outer support member 517, water-injected expansion rubber ring 518, electric telescopic rod mechanism 519a, spur rack 519b; Rear plugging head 52, second central rotating shaft 521; Connecting column mechanism 53, connecting column 531, front fixing plate 532, rear fixing plate 533; Protective cover 54, cover plate 541, sleeve 542, guide rail 543, protective ring 544; Pressure sensor 55; Image observation device 56; Water injection head 57. DETAILED DESCRIPTION

[0015] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art: Example: Figure 1-11 As shown, this embodiment specifically relates to a working method of a ground stress testing system for tunnel engineering excavation compensation prevention and control, and the working method includes the following steps: (S1) Constructing a geostress testing system in the tunnel 1, including a drill rod 3, a drill bit 4, a plugging test head 5, a water pump system and a computing control terminal 8.

[0016] like Figure 1 , 2 As shown, during the test hole drilling stage, the front end of the drill rod 3 is detachably mounted with a drill bit 4 to drill a test hole in the rock mass of the tunnel face 2; during the hydraulic fracturing test stage, the front end of the drill rod 3 is detachably mounted with a plugging test head 5.

[0017] like Figure 1-10 As shown, the plugging test head 5 includes a front plugging head 51, a rear plugging head 52, a connecting column mechanism 53, a pressure sensor 55, an image observation device 56 and a water injection head 57; the connecting column mechanism 53 includes a connecting column 531 and a front fixed disk 532 and a rear fixed disk 533 respectively arranged at both ends of the connecting column 531, and the diameters of the front fixed disk 532 and the rear fixed disk 533 should be ensured to be smaller than the aperture of the test hole; the front plugging head 51 is arranged on the front fixed disk 532, and the rear plugging head 52 is arranged on the rear fixed disk 533; the pressure sensor 55, the image observation device 56 and the water injection head 57 are all arranged at different positions of the connecting column 531. It should be noted that the test cavity of the plugging test head 5 is formed under the enclosure of the front plugging head 51 and the rear plugging head 52.

[0018] like Figure 1-10As shown, the front plugging head 51 includes a rotating disk 511, a first central rotating shaft 512, a driving mechanism, an arc guide groove 513, a radial follower stud 514, a sliding block 515 and a sliding groove 516. The first central rotating shaft 512 is fixedly arranged at the center of the rotating disk 511 and driven to rotate (reciprocate) by the driving mechanism. The number of the arc guide grooves 513 is three groups and they are evenly distributed on the rotating disk 511 at equal angles. The radial distance between the trajectory of the arc guide grooves 513 and the first central rotating shaft 512 is The distance between them changes from near to far; the sliding groove 516 is radially arranged and fixed on the front fixed disk 532, the sliding block 515 is arranged behind the rotating disk 511 and is slidably assembled on the sliding groove 516, the radial follower stud 514 is inserted in the arc guide groove 513 and the lower end is connected to the radial inner end of the sliding block 515, the radial outer end of the sliding block 515 is provided with an arc-shaped outer support member 517, and a water-injected expansion rubber ring 518 is embedded in the outer groove of the arc-shaped outer support member 517.

[0019] like Figure 1-10 As shown, the driving mechanism includes an electric telescopic rod mechanism 519a and a spur rack 519b. The electric telescopic rod mechanism 519a is fixed on the front fixed plate 532. The teeth on the spur rack 519b are meshed with the circular gear on the rear end of the first central rotating shaft 512. The electric telescopic rod mechanism 519a drives the spur rack 519b to make reciprocating motion to drive the circular gear and the first central rotating shaft 512 to rotate. The first central rotating shaft 512 can drive the rotating disk 511 to rotate synchronously.

[0020] like Figure 1-10 As shown, the number of sliding blocks 515 on the front plugging head 51 is the same as the number of arc-shaped guide grooves 513, both of which are three groups. The three arc-shaped external support members 517 on the radial outer ends of the three groups of sliding blocks 515 are together enclosed to form a ring-shaped external support member at the minimum radial stroke, and the arc-shaped external support members 517 are in contact with each other. When each arc-shaped external support member 517 moves radially outward with the sliding block 515 and is supported against the inner wall surface of the test hole, water is injected and pressurized into the water-injected expansion rubber ring 518 through the water pump branch pipe to expand and support the inner wall of the test hole to form a completely closed seal.

[0021] It should be noted that the structures of the front plugging head 51 and the rear plugging head 52 are the same, so the structure of the rear plugging head 52 will not be described in detail. The main difference between the two is the connection structure between the second central rotating shaft 521 in the rear plugging head 52 and the front end of the drill rod 3. A rotating support is provided at the center position of the rear fixed plate 533 and is connected to one end of the second central rotating shaft 521 of the rear plugging head 52. The end of the second central rotating shaft 521 rotates on the rotating support and is axially limited. A limiting annular groove is provided on the other end of the second central rotating shaft 521 of the rear plugging head 52, and a limiting inner convex ring is provided at the front end of the drill rod 3. By assembling the limiting inner convex ring of the drill rod 3 in the limiting annular groove, the mutual rotation and axial limitation between the second central rotating shaft 521 of the rear plugging head 52 and the drill rod 3 can be achieved.

[0022] In addition, in order to provide protection during the process of the plugging test head 5 being inserted into the test hole, a protective cover 54 is further provided at the front end portion of the first central rotating shaft 512 of the front plugging head 51. The center of the cover plate 541 of the protective cover 54 has a sleeve 542 which is correspondingly sleeved on the front end portion of the first central rotating shaft 512 to form a clearance fit. A protective ring 544 extends backward on the outer edge of the cover plate 541. Three guide rails 543 are provided on the cover plate 541 and respectively correspond to the setting positions of the radial follow-up stud 514. The guide rails 543 are sloped within the radial movement path of the radial follow-up stud 514. The slope of the guide rails 543 refers to extending from high to low in the radial direction from the inside to the outside, so as to realize that the protective cover 54 as a whole moves from the inside to the outside in the radial direction along with the radial follow-up stud 514. The protective cover 54 gradually extends upward under the guidance of the guide rails 543 to make way for the radial outward movement of the arc-shaped outer support member 517. A rotating support is provided at the center of the front fixed disk 532 and is connected to the rear end of the first central rotating shaft 512. The rear end of the first central rotating shaft 512 rotates on the rotating support and is axially limited.

[0023] like Figure 2-9 As shown, the water pump system includes a water storage tank 6, a booster water pump 7 and a water pumping pipeline 9; the water inlet of the booster water pump 7 is connected to the water storage tank 6, and the water outlet of the booster water pump 7 is connected to the water pumping pipeline 9; the water pumping pipeline 9 includes a water pumping main pipe and three water pumping branches branched from the water pumping main pipe, and the three water pumping branches are respectively connected to the water injection head 57, the water injection expansion rubber ring 518 on the front plugging head 51, and the water injection expansion rubber ring on the rear plugging head 52. In addition, the computing control terminal 8 is connected to control the booster water pump 7, the pressure sensor 55, and the image observation device 56.

[0024] (S2) A drill bit 4 is installed at the front end of the drill rod 3 and drilling is performed obliquely upward on the tunnel face 2 of the tunnel 1 to form a test hole in the rock mass.

[0025] (S3) After completing the drilling of the test hole, remove the drill bit 4 from the front end of the drill rod 3, install the plugging test head 5 at the front end of the drill rod 3, and then push the drill rod 3 and the plugging test head 5 into the specified depth of the test hole; after being pushed into place, control the arc-shaped external support member 517 on the front plugging head 51 to move radially until it forms a supporting contact with the inner wall surface of the test hole, and control the arc-shaped external support member 517 on the rear plugging head 52 to move radially until it also forms a supporting contact with the inner wall surface of the test hole, so as to form a preliminary fixation in place and a preliminary seal.

[0026] (S4) The water in the water storage tank 6 is pressurized and pumped through the water pumping pipe 9 by the booster water pump 7. The water pumping pipe 9 pumps the water to the three water pumping branches respectively. Two of the water pumping branches are respectively filled with water to the water injection expansion rubber ring 518 on the front plugging head 51 and the water injection expansion rubber ring on the rear plugging head 52 to fill the gap and form a complete seal. The remaining water pumping branch is filled with water through the water injection head 57 into the cavity of the plugging test head 5 and continuously pressurized until cracks appear on the inner wall of the test hole enclosed by the plugging test head 5 (such as Fig.11 As shown), the moment of occurrence of the crack is recorded by the image observation device 56, the pressure value when the crack occurs is recorded by the pressure sensor 55, and the booster pump 7 is closed synchronously.

[0027] (S5) Fig.11 As shown, a pressure regulation control equation is then constructed based on the seepage area, fracture stiffness and leakage coefficient of the fracturing section, and the calculation control terminal 8 adjusts the cavity pressure in the plugging test head 5 according to the pressure regulation control equation. The pressure regulation control equation is:

[0028] Where: is the fluid pressure in the fracture; P 0 Refers to the initial actual pressure value in the crack after the booster pump 7 is turned off, that is, the pressure value recorded in step S4 when the crack occurs; is the rock mass porosity; f t is the total formation compressibility factor, which can be considered as a constant; m is the intrinsic permeability of the rock mass; μ is the fluid viscosity; for i Crack stiffness at the time step; g t is the length of the measuring section; y c is the constant crack height; x c It is 1 / 2 of the total seam length, based on the length of the seam on one side; , is the pressure at time j and time j-1 in a single time step; The leakage duration after the pump is turned off for a single time step; i Represents the time step, which divides a period of time into n time periods; j Represents the moment.

[0029] In the hydraulic fracturing geostress test of this embodiment, the interaction between the regulating system of the booster pump and the pressure regulation control equation constitutes a closed-loop feedback mechanism, which significantly improves the reliability and analysis accuracy of the test data and avoids secondary crack interference caused by overpressure.

[0030] The beneficial effects of this embodiment are: (1) A coordinated control mechanism is adopted to construct the control equation of water pressure regulation based on the seepage area, fracture stiffness and leakage coefficient of the fracturing section, which provides a new technical path for geostress testing under complex geological conditions and can avoid secondary fracture interference caused by overpressure; (2) The arc-shaped external support member is used to form a position support fixation and preliminary seal between the inner wall of the test hole rock body, and further a water injection expansion rubber ring preset in the groove of the arc-shaped external support member is used to expand water to achieve the final seal between the inner wall of the test hole rock body, so as to adapt to the high water pressure fracturing test; (3) The same water pump system can be used to complete the water injection expansion sealing work of the water injection expansion rubber ring and the test of the water pressure fracturing value in the plugging test head cavity; (4) A protective cover is mounted on the front plugging head. Before operation, the protective cover can cover the components on the front plugging head to avoid collision during the process of extending into the test hole, and can rise synchronously when the arc-shaped outer support member expands outward to avoid blocking the moving path of the arc-shaped outer support member.

Claims

1. A working method of a ground stress testing system for tunnel engineering excavation compensation prevention and control, characterized in that The working method comprises the following steps: S1: constructing a geostress testing system in a tunnel, the testing system comprising a drill rod, a drill bit, a plugging testing head, a water pump system and a computing control terminal; wherein: the plugging testing head comprises a connecting column mechanism and a front plugging head and a rear plugging head respectively arranged at two ends of the connecting column mechanism; S2: installing the drill bit at the front end of the drill rod and drilling obliquely upward on the tunnel face to form a test hole in the rock mass; S3: After the drilling of the test hole is completed, the drill bit is removed from the drill rod, the plugging test head is installed at the front end of the drill rod, and then the drill rod and the plugging test head are pushed into the specified depth of the test hole; after being pushed into place, the arc-shaped outer support member on the front plugging head is controlled to move radially until it forms a supporting contact with the inner wall surface of the test hole, and the arc-shaped outer support member on the rear plugging head is controlled to move radially until it also forms a supporting contact with the inner wall surface of the test hole; S4: The water pump pipeline in the water pump system has three water pump branches, two of which are respectively used to inject water into the water-injected expansion rubber ring on the front plugging head and the water-injected expansion rubber ring on the rear plugging head to fill the gap and form a complete seal, and the remaining water pump branch is used to inject water into the cavity of the plugging test head and continuously increase the pressure until cracks occur on the inner wall of the test hole enclosed by the plugging test head, and the time of occurrence of the cracks is recorded by an image observation device and the pressure value when the cracks occur is recorded by a pressure sensor, and the water pump system is shut down; S5: The computing control terminal then adjusts the water pressure based on the following pressure regulation control equation: Where: is the fluid pressure in the fracture; P 0 Refers to the initial actual pressure value in the crack after the booster water pump in the water pump system is turned off, that is, the pressure value recorded in step S4 when the crack occurs; is the rock mass porosity; f t is the total formation compressibility factor, which can be considered as a constant; m is the intrinsic permeability of the rock mass; μ is the fluid viscosity; for i Crack stiffness at the time step; g t is the length of the measuring section; y c is the constant crack height; x c 1 / 2 of the total seam length; , is the pressure at time j and time j-1 in a single time step; The leakage duration after the pump is turned off for a single time step; i represents the time step; j Represents the moment.

2. The working method of a ground stress testing system for tunnel engineering excavation compensation prevention and control according to claim 1 is characterized in that The plugging test head includes the front plugging head, the rear plugging head, the connecting column mechanism, a pressure sensor, an image observation device and a water injection head; the connecting column mechanism includes a connecting column and a front fixed disk and a rear fixed disk respectively arranged at both ends of the connecting column; the front plugging head is arranged on the front fixed disk, and the rear plugging head is arranged on the rear fixed disk; the pressure sensor, the image observation device and the water injection head are arranged on the connecting column; The front plugging head has the same structure as the rear plugging head; the front plugging head comprises a rotating disk, a central rotating shaft, a driving mechanism, an arc-shaped guide groove, a radial follower stud, a sliding block and a sliding groove; the central rotating shaft is arranged at the center of the rotating disk and driven to rotate by the driving mechanism; the number of the arc-shaped guide grooves is three groups and they are evenly distributed on the rotating disk at equal angles; the trajectory of the arc-shaped guide groove and the radial distance of the central rotating shaft vary from near to far; the sliding groove is radially arranged and fixed on the front fixed disk; the sliding block is arranged at the rear of the rotating disk and slidably assembled on the sliding groove; the radial follower stud is inserted in the arc-shaped guide groove and the lower end is connected to the radial inner end of the sliding block; the radial outer end of the sliding block is provided with an arc-shaped outer support member, and a water-injected expansion rubber ring is embedded in the outer groove of the arc-shaped outer support member; The water pump system includes a water storage tank, a booster water pump and the water pump pipeline; the water inlet of the booster water pump is connected to the water storage tank, and the water outlet of the booster water pump is connected to the water pump pipeline; the water pump pipeline includes a water pump main pipe and three water pump branches branched from the water pump main pipe, and the three water pump branches are respectively connected to the water injection head, the water injection expansion rubber ring on the front plugging head, and the water injection expansion rubber ring on the rear plugging head; The computing control terminal is connected to control the booster pump, the pressure sensor, and the image observation device; The driving mechanism includes an electric telescopic rod mechanism and a spur rack. The electric telescopic rod mechanism is fixed on the front fixed plate. The teeth on the spur rack are meshed with the circular gear on the rear end of the central rotating shaft. The electric telescopic rod mechanism drives the spur rack to make reciprocating motion to drive the circular gear and the central rotating shaft to rotate.

3. The working method of the ground stress testing system for tunnel engineering excavation compensation prevention and control according to claim 2 is characterized in that The number of the sliding blocks on the front plugging head is the same as the number of the arc-shaped guide grooves, both of which are three groups. The three arc-shaped external support members on the radial outer ends of the three groups of sliding blocks are jointly enclosed to form an annular external support member at the minimum radial stroke; when each arc-shaped external support member moves radially outward with the sliding block and supports the inner wall surface of the test hole, water is injected and pressurized into the water-injected expansion rubber ring through the water pump branch pipe to expand and support the inner wall of the test hole to form a completely closed seal.

4. The working method of the ground stress testing system for tunnel engineering excavation compensation prevention and control according to claim 2 is characterized in that A rotating support is arranged at the center of the front fixed disk and is connected to the rear end of the central rotating shaft. The rear end of the central rotating shaft rotates on the rotating support and is axially limited.

5. The working method of the ground stress testing system for tunnel engineering excavation compensation prevention and control according to claim 4 is characterized in that A protective cover is mounted on the front end portion of the central rotating shaft of the front plugging head, and the center of the protective cover has a sleeve which is correspondingly mounted on the front end portion of the central rotating shaft to form a clearance fit. A protective ring extends backward on the outer edge of the protective cover, and three guide rails are arranged on the protective cover and respectively correspond to the setting positions of the radial follow-up studs. The guide rails are sloped in the radial moving path of the radial follow-up studs. The slope of the guide rails refers to extending from high to low in the radial direction, so that the protective cover as a whole moves from inside to outside in the radial direction with the radial follow-up studs, and the protective cover gradually extends upward under the guidance of the guide rails.

6. The working method of the ground stress testing system for tunnel engineering excavation compensation prevention and control according to claim 2 is characterized in that A rotating support is arranged at the center of the rear fixed disk and is connected to one end of the central rotating shaft of the rear plugging head. The end of the central rotating shaft of the rear plugging head rotates on the rotating support and is axially limited.

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