Working Method of In-situ Stress Testing System for Tunnel Engineering Excavation Compensation and Prevention and Control

Abstract

The present invention belongs to a in-situ stress testing system, and discloses a working method of an in-situ stress testing system for tunnel engineering excavation compensation prevention and control, comprising the following steps: pushing a drill pipe and a plugging test head into a specified depth of a test hole; controlling the arc-shaped outer supports on the front plugging head and the rear plugging head to expand outwards until they form a top support contact with the inner wall surface of the test hole; further injecting water into the water injection expansion rubber rings on the front plugging head and the rear plugging head to fill the gaps to form a complete seal, injecting water into the cavity of the plugging test head and continuously increasing the pressure until cracks occur on the rock mass wall surface in the cavity of the plugging test head, recording the pressure value when the cracks occur, and closing the pressure increasing water pump; controlling the pressure increasing water pump to adjust and control the water pressure in the cavity of the plugging test head according to the pressure regulation control equation through a calculation control terminal. The advantages of the present invention are: adopting a cooperative control mechanism, and constructing a control equation for water pressure regulation based on the seepage area, crack stiffness and leakage coefficient of the fracturing section.

Description

Technical Field

[0001] The present invention belongs to a in-situ stress testing system, and particularly relates to a working method of an in-situ stress testing system for tunnel engineering excavation compensation prevention and control. Background Art

[0002] The hydraulic fracturing method is one of the recommended methods for measuring rock mechanics and is currently the most reliable and direct method for measuring deep stress. This method is relatively simple to operate, the measured values are reliable, and multiple or repeated measurements can be carried out. It uses an expansion packer to seal a section of the borehole at a known depth, and then pressurizes the measured section by pumping fluid. The horizontal principal stress value is determined using the recorded breakdown pressure, instantaneous shut-in pressure, and reopening pressure. Currently, the main shortcoming is that the sealing and anti-seepage of the expansion packer are difficult to achieve an ideal level and it cannot adapt to rock masses with large pressures.

[0003] In addition, according to the mechanical characteristics of soft rock engineering, the hydraulic fracturing method faces unique technical challenges when measuring in-situ stress. Since soft rock has significant plastic deformation and rheological properties, the crack propagation mode formed during the fracturing process is essentially different from that of hard rock. Research shows that the seepage area of the fractured section, as an effective channel for fluid migration, directly affects the penetration rate of the fracturing fluid in the rock mass; the crack stiffness characterizes the ability of the crack wall to resist deformation, and its dynamic change will change the geometric shape of the crack; while the leakage coefficient reflects the ease of loss of the fracturing fluid along the primary fissures. The three together constitute the key parameters affecting the accuracy of in-situ stress 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. For this reason, this study established a non-linear function of the seepage area varying with the confining pressure, constructed a dynamic stiffness model considering the surface roughness of the fissures, 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 in-situ stress measurement in soft rock strata. Summary of the Invention

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

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A working method of an in-situ stress testing system for tunnel engineering excavation compensation prevention and control includes the following steps:

[0007] S1: Build a in-situ stress test system in the tunnel. The test system includes a drill pipe, a drill bit, a plugging test head, a water pump system, and a calculation and control terminal. Among them:

[0008] 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 fixing disk and a rear fixing disk respectively arranged at both ends of the connecting column. The front plugging head is arranged on the front fixing disk, and the rear plugging head is arranged on the rear fixing disk. The pressure sensor, the image observation device, and the water injection head are arranged on the connecting column.

[0009] The front plugging head and the rear plugging head have the same structure. The front plugging head includes 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 is driven to rotate by the driving mechanism. The number of the arc-shaped guide grooves is three and they are evenly distributed at equal angles on the rotating disk. The trajectory of the arc-shaped guide groove has a change from near to far in the radial distance from the central rotating shaft. The sliding groove is arranged radially and fixed on the front fixing disk. The sliding block is arranged behind the rotating disk and is slidably assembled on the sliding groove. The radial follower stud is inserted into the arc-shaped guide groove and the lower end is connected to the radial inner end of the sliding block. An arc-shaped outer support member is arranged at the radial outer end of the sliding block, and a water injection expansion rubber ring is embedded in the outer groove of the arc-shaped outer support member.

[0010] The water pump system includes a water storage tank, a booster pump, and a pump water pipeline. The water inlet of the booster pump is connected to the water storage tank, and the water outlet of the booster pump is connected to the pump water pipeline. The pump water pipeline includes a main pump water pipe and three pump water branch pipes branched from the main pump water pipe. The three pump water branch pipes 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.

[0011] The calculation and control terminal is connected to control the booster pump, the pressure sensor, and the image observation device.

[0012] S2: Install the drill bit at the front end of the drill pipe and drill obliquely upward on the tunnel face to form a test hole in the rock mass.

[0013] S3: After completing the drilling of the test hole, remove the drill bit from the drill pipe, install the plugging test head at the front end of the drill pipe, and then push the drill pipe and the plugging test head into the designated depth of the test hole. After being pushed into place, control the arc-shaped outer support member on the front plugging head to move radially until it forms a top support contact with the inner wall surface of the test hole, and control the arc-shaped outer support member on the rear plugging head to move radially until it also forms a top support contact with the inner wall surface of the test hole;

[0014] S4: Use the booster water pump to boost and pump the water in the water storage tank through the pump water pipeline. The pump water pipeline pumps water to three pump water branch pipes respectively. Two of the pump water branch pipes respectively inject water into the water injection expansion rubber rings on the front plugging head and the rear plugging head to expand and fill the gaps to form a complete seal. The remaining one pump water branch pipe injects water into the cavity of the plugging test head through the water injection head and continuously boosts the pressure until cracks occur on the inner wall surface of the test hole enclosed by the plugging test head. Record the occurrence time of the cracks through the image observation device and record the pressure value at the time of crack occurrence through the pressure sensor, and then turn off the booster water pump;

[0015] S5: The calculation and control terminal adjusts the water pressure. The pressure adjustment control equation of the water pressure is:

[0016]

[0017] In the formula:

[0018] is the fluid pressure in the crack;

[0019] P 0 refers to the initial actual pressure value in the crack after turning off the booster water pump, that is, the pressure value recorded at the time of crack occurrence in step S4;

[0020] is the rock porosity;

[0021] f t is the total formation compressibility and can be regarded as a constant;

[0022] m is the inherent permeability of the rock mass;

[0023] μ is the fluid viscosity;

[0024] is i the crack stiffness at the time step;

[0025] gt is the length of the measured section;

[0026] y c is the constant fracture height of the crack;

[0027] x c is 1 / 2 of the total crack length;

[0028] and are the pressures at the j-th and (j - 1)-th moments in a single time step;

[0029] is the leakage duration after the pump is turned off in a single time step;

[0030] i represents a time step;

[0031] j represents a moment.

[0032] The driving mechanism includes an electric telescopic rod mechanism and a straight rack. The electric telescopic rod mechanism is fixed on the front fixing disk. The ratchet on the straight rack meshes with the circular gear at the rear end of the central rotating shaft. The electric telescopic rod mechanism drives the straight rack to move reciprocally to drive the circular gear and the central rotating shaft to rotate.

[0033] The number of the sliding blocks on the front plug is the same as that of the arc-shaped guide grooves, both being three groups. The three arc-shaped outer support members on the radially outer ends of the three groups of sliding blocks jointly enclose to form an annular outer support member at the minimum radial stroke. When each arc-shaped outer support member moves radially outward along with the sliding block and abuts against the inner wall surface of the test hole, water is injected into the water injection expansion rubber ring through the water pump branch pipe to be pressurized and expanded to abut against the inner wall of the test hole to form a completely closed seal.

[0034] A rotating support is arranged at the central position of the front fixing 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.

[0035] A protective cover is sleeved on the front end of the central rotating shaft of the front plugging head. The center of the protective cover has a sleeving cylinder which is correspondingly sleeved on the front end of the central rotating shaft to form a clearance fit. A protective ring extends backward on the outer edge of the protective cover. Three guide rails are arranged on the protective cover and respectively correspond to the arrangement positions of the radial follower studs. The guide rails are in a slope shape within the radial movement path of the radial follower studs. The slope shape of the guide rails means that they extend from high to low in the radial direction, so as to enable the whole protective cover to move radially from the inside to the outside along with the radial follower studs, and the protective cover is gradually pushed upward under the guidance of the guide rails.

[0036] A rotary 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 rotary support and is axially limited.

[0037] The advantages of the present invention are as follows:

[0038] (1) By adopting a collaborative control mechanism, a control equation for water pressure regulation is constructed based on the seepage area, fracture stiffness, and leakage coefficient of the fracturing section, providing a new technical path for in-situ stress testing under complex geological conditions and avoiding the interference of secondary fractures caused by overpressure;

[0039] (2) The position of the inner wall surface of the test hole rock body is supported and fixed and preliminarily sealed through the arc-shaped outer support member, and further, the final seal with the inner wall surface of the test hole rock body is achieved by injecting water into and expanding the water-injecting and expanding rubber ring preset in the groove of the arc-shaped outer support member, so as to adapt to the fracturing test under high water pressure;

[0040] (3) The same water pump system can be used to complete the work of injecting water into and expanding the water-injecting and expanding rubber ring for sealing and the test of the water pressure fracturing value in the cavity of the plugging test head;

[0041] (4) A protective cover is sleeved on the front plugging head. Before work, the protective cover can cover the components on the front plugging head to prevent them from being collided 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 movement path of the arc-shaped outer support member. Description of the Drawings

[0042] Figure 1 It is a schematic diagram of drilling a test hole on the tunnel face with a drill bit installed on the drill pipe in the present invention;

[0043] Figure 2 It is a schematic diagram of obtaining the in-situ stress value by conducting a water pressure fracturing test with a plugging test head installed on the drill pipe in the present invention;

[0044] Figure 3 It is a schematic diagram of the plugging test head in the present invention;

[0045] Figure 4 Schematic front end face view of the front plugging head in the present invention (the protective cover is omitted);

[0046] Figure 5 Schematic view of the rotation of the rotating disk on the front plugging head in the present invention to drive the radial follower stud and the associated sliding block and arc-shaped outer support member to move radially outwards;

[0047] Figure 6 Schematic view of the arc-shaped outer support member on the front plugging head moving radially outwards and then further injecting water into the water injection expansion rubber ring to expand and fit and seal with the inner wall surface of the test hole;

[0048] Figure 7 Schematic rear end face view of the front plugging head in the present invention;

[0049] Figure 8 In the present invention Figure 7 Cross-sectional view A0A;

[0050] Figure 9 Schematic view of the process of the protective cover provided on the front plugging head being lifted under the drive of the radial follower stud;

[0051] Figure 10 Schematic view of the process of the water injection expansion rubber ring expanding and sealing;

[0052] Figure 11 Schematic view of the crack geometry in an infinite plane in the present invention.

[0053] Such as Figures 1-11 , the respective marks in the figure are:

[0054] Tunnel 1, heading face 2, drill pipe 3, drill bit 4, plugging test head 5, water storage tank 6, booster pump 7, calculation and control terminal 8, pump water pipeline 9;

[0055] Front plugging head 51, rotating disk 511, first central rotating shaft 512, arc-shaped guide groove 513, radial follower stud 514, sliding block 515, sliding groove 516, arc-shaped outer support member 517, water injection expansion rubber ring 518, electric telescopic rod mechanism 519a, straight rack 519b;

[0056] Rear plugging head 52, second central rotating shaft 521;

[0057] Connecting column mechanism 53, connecting column 531, front fixing plate 532, rear fixing plate 533;

[0058] Protective cover 54, cover plate 541, sleeve cylinder 542, guide rail 543, protective ring 544;

[0059] Pressure sensor 55;

[0060] Imaging observation device 56;

[0061] Water injection head 57. Specific implementation manner

[0062] The features of the present invention and other related features will be further described in detail below in conjunction with the accompanying drawings through embodiments, so as to facilitate the understanding of those skilled in the same industry:

[0063] Embodiment: As Figures 1-11 shown, this embodiment specifically relates to a working method of a ground stress testing system for tunnel engineering excavation compensation and prevention and control. This working method includes the following steps:

[0064] (S1) Construct a ground stress testing system in tunnel 1, including a drill pipe 3, a drill bit 4, a plugging test head 5, a water pump system, and a calculation and control terminal 8.

[0065] As Figure 1 , 2 shown, in the stage of drilling a test hole, the front end of the drill pipe 3 is detachably installed with a drill bit 4 to drill a test hole in the rock mass of the tunnel face 2; in the stage of hydraulic fracturing test, the front end of the drill pipe 3 is detachably installed with a plugging test head 5.

[0066] As Figures 1-10 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 imaging observation device 56, and a water injection head 57; the connecting column mechanism 53 includes a connecting column 531 and a front fixing disk 532 and a rear fixing disk 533 respectively arranged at both ends of the connecting column 531. The diameters of the front fixing disk 532 and the rear fixing disk 533 should ensure that they are smaller than the aperture of the test hole; the front plugging head 51 is arranged on the front fixing disk 532, and the rear plugging head 52 is arranged on the rear fixing disk 533; the pressure sensor 55, the imaging observation device 56, and the water injection head 57 are all arranged at different positions on the connecting column 531. It should be noted that a 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.

[0067] As Figures 1-10As shown in the figure, the front plug 51 includes a rotating disk 511, a first central rotating shaft 512, a driving mechanism, an arc-shaped 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 is driven to rotate (reciprocating rotation) by the driving mechanism. The number of arc-shaped guide grooves 513 is three groups and they are evenly distributed on the rotating disk 511 at equal angles. The trajectory of the arc-shaped guide groove 513 has a change from near to far in the radial distance from the first central rotating shaft 512. The sliding groove 516 is arranged radially and is 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 into the arc-shaped guide groove 513 and the lower end is connected to the radial inner end of the sliding block 515. An arc-shaped outer support member 517 is arranged at the radial outer end of the sliding block 515, and a water injection expansion rubber ring 518 is embedded in the outer groove of the arc-shaped outer support member 517.

[0068] As Figures 1-10 shown in the figure, the driving mechanism includes an electric telescopic rod mechanism 519a and a straight rack 519b. The electric telescopic rod mechanism 519a is fixed on the front fixed disk 532. The teeth on the straight rack 519b are engaged with the circular gear on the rear end of the first central rotating shaft 512. The electric telescopic rod mechanism 519a drives the straight rack 519b to make a reciprocating motion, so as 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.

[0069] As Figures 1-10 shown in the figure, the number of sliding blocks 515 on the front plug 51 is the same as the number of arc-shaped guide grooves 513, both are three groups. The three arc-shaped outer support members 517 on the radial outer ends of the three groups of sliding blocks 515 jointly enclose a ring-shaped outer support member at the minimum radial stroke, and the arc-shaped outer support members 517 are in contact with each other. When each arc-shaped outer support member 517 moves outward in the radial direction with the sliding block 515 and abuts against the inner wall surface of the test hole, water is injected into the water injection expansion rubber ring 518 through the pump water branch pipe to be pressurized and expand to abut against the inner wall of the test hole to form a completely closed seal.

[0070] It should be noted that the front plug 51 and the rear plug 52 have the same structure, so the structure of the rear plug 52 will not be elaborated here. The main difference between the two lies in the connection structure between the second central rotating shaft 521 in the rear plug 52 and the front end of the drill pipe 3. A rotating support is provided at the central position of the rear fixed disk 533 and is connected to one end of the second central rotating shaft 521 of the rear plug 52. The end of the second central rotating shaft 521 rotates on the rotating support and is axially limited. A limiting ring groove is provided at the other end of the second central rotating shaft 521 of the rear plug 52, and a limiting inner convex ring is provided at the front end of the drill pipe 3. By assembling the limiting inner convex ring of the drill pipe 3 into the limiting ring groove, the relative rotation and axial limitation between the second central rotating shaft 521 of the rear plug 52 and the drill pipe 3 are realized.

[0071] In addition, in order to provide protection during the process of the plugging test head 5 extending into the test hole, a protective cover 54 is further provided at the front end of the first central rotating shaft 512 of the front plug 51. A sleeve 542 is provided at the center of the cover plate 541 of the protective cover 54 and is correspondingly sleeved on the front end of the first central rotating shaft 512 to form a clearance fit. A protective ring 544 extends backward from the outer edge of the cover plate 541. Three guide rails 543 are provided on the cover plate 541 and respectively correspond to the positions of the radial follower studs 514. The guide rails 543 are in a ramp shape within the radial movement path of the radial follower studs 514. The ramp shape of the guide rails 543 means that it extends from high to low in the radial direction from the inside to the outside, so as to realize the overall upward movement of the protective cover 54 following the radial movement of the radial follower studs 514 from the inside to the outside. Under the guidance of the guide rails 543, the protective cover 54 gradually extends upward to make way for the radial outward movement of the arc-shaped outer support member 517. A rotating support is provided at the central position 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.

[0072] As Figures 2-9 shown, the water pump system includes a water storage tank 6, a booster water pump 7, and a pump water 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 pump water pipeline 9; the pump water pipeline 9 includes a main pump water pipe and three pump water branch pipes branched from the main pump water pipe. The three pump water branch pipes are respectively connected to the injection head 57, the injection expansion rubber ring 518 on the front plug 51, and the injection expansion rubber ring on the rear plug 52. In addition, the calculation control terminal 8 is connected to control the booster water pump 7, the pressure sensor 55, and the image observation device 56.

[0073] (S2)Install a drill bit 4 at the front end of the drill pipe 3 and drill obliquely upward on the tunnel face 2 of the tunnel 1 to form a test hole in the rock mass.

[0074] After the drilling of the test hole is completed in (S3), the drill bit 4 is removed from the front end of the drill pipe 3, and the plugging test head 5 is installed at the front end of the drill pipe 3. Then, the drill pipe 3 and the plugging test head 5 are pushed into the designated depth of the test hole. After being pushed into place, control the arc-shaped outer support member 517 on the front plugging head 51 to move radially until it forms a top support contact with the inner wall surface of the test hole, and control the arc-shaped outer support member 517 on the rear plugging head 52 to move radially until it also forms a top support contact with the inner wall surface of the test hole, so as to form a preliminary fixed position and a preliminary seal.

[0075] In (S4), the water in the water storage tank 6 is pressurized and pumped through the pump water pipeline 9 by the booster water pump 7. The pump water pipeline 9 pumps water to three pump water branch pipes respectively. Two of the pump water branch pipes inject water into and expand the water injection expansion rubber rings 518 on the front plugging head 51 and the water injection expansion rubber rings on the rear plugging head 52 respectively to fill the gaps and form a complete seal. The remaining one pump water branch pipe injects water into the cavity of the plugging test head 5 through the water injection head 57 and continuously pressurizes until cracks occur on the inner wall surface of the test hole enclosed by the plugging test head 5 (as Figure 11 shown). The image observation device 56 records the occurrence time of the cracks and the pressure sensor 55 records the pressure value when the cracks occur, and the booster water pump 7 is synchronously closed.

[0076] In (S5), as Figure 11 shown, then a pressure regulation and control equation is constructed based on the seepage area, crack stiffness and leakage coefficient of the fracturing section. The calculation control terminal 8 adjusts the cavity pressure in the plugging test head 5 according to this pressure regulation and control equation. This pressure regulation and control equation is:

[0077]

[0078] In the formula:

[0079] is the fluid pressure in the crack;

[0080] P 0 refers to the initial actual pressure value in the crack after the booster water pump 7 is closed, that is, the pressure value recorded when the cracks occur in step S4;

[0081] is the rock porosity;

[0082] f t is the total formation compressibility coefficient and can be regarded as a constant;

[0083] m is the intrinsic permeability of the rock mass;

[0084] μ is the fluid viscosity;

[0085] is i the fracture stiffness at the time step;

[0086] g t is the length of the measurement section;

[0087] y c is the constant fracture height of the fracture;

[0088] x c is 1 / 2 of the total fracture length, the unilateral fracture length at the base;

[0089] and are the pressures at the j-th and (j - 1)-th moments in a single time step;

[0090] is the leakage duration after the pump is shut off in a single time step;

[0091] i represents the time step, and the time step divides a period of time into n time periods;

[0092] j represents the moment.

[0093] In the hydraulic fracturing method for in-situ stress testing in this embodiment, the interaction between the regulation system of the booster pump and the pressure regulation control equation constitutes a closed-loop feedback mechanism, significantly improving the reliability of the test data and the analysis accuracy, and avoiding the interference of secondary fractures caused by overpressure.

[0094] The beneficial effects of this embodiment are as follows:

[0095] (1) Adopting a collaborative control mechanism, constructing a control equation for water pressure regulation based on the seepage area, fracture stiffness, and leakage coefficient of the fracturing section, providing a new technical path for in-situ stress testing under complex geological conditions, and avoiding the interference of secondary fractures caused by overpressure;

[0096] (2) Forming position support fixation and preliminary sealing between the arc-shaped outer support and the inner wall surface of the test hole rock body through the arc-shaped outer support, and further realizing the final sealing between the arc-shaped outer support and the inner wall surface of the test hole rock body by injecting water into the water-inflatable rubber ring preset in the groove of the arc-shaped outer support, adapting to the fracturing test under high water pressure;

[0097] (3) The same water pump system can be used to complete the water injection and inflation sealing work of the water-inflatable rubber ring and the test of the hydraulic fracturing value in the test head cavity;

[0098] (4)A protective cover is sleeved on the front plug head. Before operation, the protective cover can cover the components on the front plug head to protect them from 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 calculation control terminal adjusts the water pressure, and the pressure regulation control equation of the water pressure is: ； 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; φ 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; , For a single time step j Moment and j-1 The pressure of the moment; △t i 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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