A continuous monitoring device and method for concentrated stress areas in surrounding rock of underground engineering

Abstract

The present invention belongs to the field of geotechnical engineering and mining engineering technology, and specifically relates to a continuous monitoring device and method for concentrated stress areas in surrounding rocks of underground engineering projects, comprising a power supply and a voltage difference analyzer, and also comprising a plastic rod, a gold-plated sheet, an expansion hose, and a sodium chloride solution storage tank; the power supply is electrically connected to the gold-plated sheet, the voltage difference analyzer is electrically connected to the power supply, the gold-plated sheet is coaxially fixedly connected to the plastic rod, the plastic rod is matched with the expansion hose, the sodium chloride solution tank is provided with a valve, and the sodium chloride solution storage tank is connected to the expansion hose. The present invention solves the problem of not being able to provide true feedback on vertical concentrated stress in underground engineering projects by generating an electrical signal through the displacement between an ion node and a magnetic ring to generate an iron ion offset.

Description

Technical Field

[0001] The present invention is used in the fields of geotechnical engineering and mining engineering, and particularly relates to a device and method for continuously monitoring concentrated stress areas of surrounding rocks in underground engineering. Background Art

[0002] The concentrated stress in underground space projects has a great impact on project safety. Preparing to find the concentrated stress distribution area and then taking control measures is an effective measure to eliminate engineering disasters.

[0003] Currently, many technologies can be used to test or calculate the ground stress or three-dimensional ground stress state of underground engineering, such as the surrounding rock pressure monitoring device with patent number CN107462354A, which includes an arch frame (1) with an upward arch in the middle, the arch surface of the arch frame (1) is located in the left and right vertical directions, the arch frame (1) is made of steel, and a plurality of steel string pressure boxes (3) are provided on the arch outer surface (2) of the arch frame (1), the bases of the plurality of steel string pressure boxes (3) are installed and connected to the arch outer surface (2), the spacing between adjacent steel string pressure boxes (3) is 600mm-1000mm, and the pressure detection heads of the plurality of steel string pressure boxes (3) are along The arched outer surface (2) of the arch frame (1) is extended outward in a direction perpendicular to the arched outer surface (2). The outer side of the arched outer surface (2) of the arch frame (1) is provided with an arched force transmission steel plate (4) with the middle part arched upward. The arched surface of the arched force transmission steel plate (4) is located in the left and right vertical directions. The pressure detection heads of multiple steel string pressure boxes (3) are respectively placed on the arched force transmission steel plate (4). There is surrounding rock (5) above the arched force transmission steel plate (4). The gap between the surrounding rock (5) and the arched force transmission steel plate (4) is filled with concrete (6). There shall be no other supporting objects between the arched force transmission steel plate (4) and the arched outer surface (2) of the arch frame (1) except for the steel string pressure box (3). This solution can reduce or avoid the waste of construction materials, reduce construction costs, and is a very convenient surrounding rock pressure monitoring device for installation and use.

[0004] However, the following issues exist: 1. Geostress measurement focuses on drilling holes in intact rock masses. However, the surrounding rock is disturbed, with well-developed fractures and a highly discrete stress distribution. This makes stress measurement relatively difficult and inaccurate. 2. Disturbed geostress constantly changes with underground construction. Currently, conventional drilling methods can only measure stress at fixed locations, making it difficult to track dynamic changes in geostress in real time. 3. Numerical calculations simplify geological conditions and cannot truly reflect the three-dimensional geological stress environment. Furthermore, the results can only be used as a qualitative analysis under specific working conditions. Summary of the Invention

[0005] This solution provides a continuous monitoring device for concentrated stress areas in the surrounding rock of underground engineering to solve the problem of not being able to truly feedback the geological three-dimensional stress environment.

[0006] In order to achieve the above objectives, this program provides a continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering.

[0007] The device comprises a power supply and a voltage difference analyzer, and also comprises a plastic rod, a gold-plated sheet, an expansion hose and a sodium chloride solution storage box; the power supply is electrically connected to the gold-plated sheet, the voltage difference analyzer is electrically connected to the power supply, the gold-plated sheet is coaxially fixedly connected to the plastic rod, the plastic rod is matched with the expansion hose, the sodium chloride solution box is provided with a valve, and the sodium chloride solution storage box is connected to the expansion hose.

[0008] The principle of this solution is as follows: when monitoring surrounding rock stress, a pre-opened borehole is found. The operator wraps a plastic rod around gold-plated sheets at equal intervals, then uses the gold-plated sheets to pull a wire connected to a power source. The operator then inserts an expansion hose into the borehole and pushes the plastic rod into the hose. Once the hose reaches the specified depth, the valve of the sodium chloride solution tank is opened and sodium ion solution is poured into the hose until the hose contacts the rock wall. Finally, the operator seals the hose and connects the wire pulled from the gold-plated sheets to a voltage differential analyzer. The voltage changes are monitored to perform three-dimensional stress analysis on the geology.

[0009] The beneficial effect of this scheme is that the volume change of the sodium ion solution can accurately determine the concentrated stress area of ​​the surrounding rock of the underground space and quantitatively determine the pressure size, which is of great significance to the prevention and control of geological disasters in the surrounding rock of underground space projects.

[0010] Furthermore, the device further comprises an air pump connected to the sodium chloride solution tank, which discharges the sodium ion solution into the expansion hose through air pressure, thereby enabling the sodium chloride ion solution to better couple with the rock wall.

[0011] Furthermore, the air pump is equipped with a reversing valve connected to an expansion hose. After the operator places the expansion hose and the plastic rod into the hole, the reversing valve connects to the expansion hose and evacuates the air inside the expansion hose to prevent the presence of gas in the expansion hose, which could generate erroneous signals indicating surrounding rock movement.

[0012] Furthermore, it also includes a support ring, a fixed plate and an airbag. The support ring cooperates with the plastic rod. The airbag is located inside the support ring. The airbag cooperates with the expansion hose. The fixed plate is arranged to rotate coaxially with the plastic rod. The fixed plate is fixedly connected to the expansion hose. The fixed plate is used to seal the expansion hose and provide a support point at one end of the plastic rod. The support ring is first placed into the deepest part of the borehole, and then the expansion hose and plastic rod are placed into the borehole. The end of the plastic rod is placed on the support ring to support the plastic rod and prevent it from being suspended in the air for a long time, causing the end to sag and send out an erroneous signal. At the same time, the airbag is coupled to the liquid-filled expansion hose. When the temperature inside the surrounding rock changes, the airbag will change due to thermal expansion and contraction, affecting the volume change of the end of the sodium chloride solution. The operator judges the temperature change through the electrical signal received by the gold-plated sheet at the end, which can remind the operator that the temperature difference between the inside and outside of the rock has increased and protective measures are needed to prevent the rock from cracking.

[0013] Furthermore, the support ring is made of metal, which can more sensitively detect temperature changes and improve the accuracy of temperature detection.

[0014] Furthermore, the airbag is made of rubber, and carbon dioxide gas is introduced into the airbag. Rubber has good toughness and prevents the airbag from rupturing. The gas expansion coefficient of carbon dioxide is currently known, which facilitates the calculation of temperature conversion by staff.

[0015] Furthermore, it also includes a cylinder, a condenser, a first contact piece, a second contact piece, a gear and a half rack; the output shaft of the cylinder is fixedly connected to the half rack, the half rack cooperates with the gear, the gear is fixedly arranged coaxially with the plastic rod, the condenser cooperates with the cylinder, the plastic rod is provided with an electrode piece, the electrode piece is connected in series with the gold-plated piece, the first contact piece and the second contact piece are on the same horizontal line, the first contact piece and the second contact piece cooperate with the electrode piece, the first contact piece and the second contact piece are both connected in series with the voltage difference analyzer, and the first contact piece and the second contact piece are connected in parallel.

[0016] Since the plastic rod is in a suspended state, it is inevitable that it will bend in the middle and send out an error message, causing the staff to think that the surrounding rock has changed. In the initial state, the electrode piece is in contact with the first contact piece, and the voltage difference analyzer can collect data. There is an acetone solution with a boiling point of 56 degrees inside the cylinder. When there is sunlight during the day, the condenser collects sunlight on the cylinder, and the acetone solution boils and turns into gas, the volume increases, and the output shaft of the cylinder moves up, driving the half rack to move up and mesh with the gear. The plastic rod rotates, so that the electrode piece is no longer in contact with the first contact piece, and the voltage difference analyzer stops collecting. Collect data and exclude unnecessary data. After the plastic rod rotates 180 degrees, the electrode piece contacts the second contact piece, and the voltage difference analyzer continues to receive this electrical signal. Then the half rack continues to rise and no longer meshes with the gear. The plastic rod rotates exactly half a circle. At night, the temperature drops, the output shaft of the cylinder moves down, and the half rack meshes with the gear again. The plastic rod reverses 180 degrees and repeats the above steps. During the rotation, the voltage difference analyzer does not collect data because the electrode piece and the second contact piece are disconnected. After stopping, the electrode piece contacts the first contact piece, and the voltage difference analyzer continues to collect data. During the day, one side of the plastic rod is affected by gravity, and at night, the other side is affected by gravity. In this way, the effects of gravity on both sides of the plastic rod are offset, eliminating the problem of the plastic rod bending and deforming due to the influence of gravity, which ultimately causes inaccurate data.

[0017] Furthermore, the voltage difference analyzer is provided with a time delay switch and an alarm light. When the voltage difference analyzer is powered off for a short time, the voltage difference analyzer does not collect data. When the voltage difference analyzer is powered off for a long time, it indicates that there is a problem with the device and the alarm light is on.

[0018] This solution also discloses a method for continuously monitoring concentrated stress areas in surrounding rock of underground engineering, comprising the following steps:

[0019] A method for continuously monitoring equipment in a concentrated stress zone of surrounding rock of an underground engineering project comprises the following steps:

[0020] Step S10: First, drill a horizontal hole at the location to be tested, then prepare a plastic rod, install the microcontroller and ID on the ground, and fix gold-plated sheets at equal intervals on the plastic rod. Each gold-plated sheet is connected in series to a power supply outside the drilled hole through a wire;

[0021] Step S20: preparing an expansion hose with a circular cross section that matches the length of the drill hole, and pushing the expansion hose into the drill hole;

[0022] Step S30: Push the plastic rod with the gold-plated sheet into the expansion hose in the borehole, then fill the expansion hose with sodium chloride ion solution and increase the filling pressure to cause the expansion hose to expand and deform and couple with the rock mass of the borehole wall. Finally, seal the expansion hose, and extend the plastic rod and the wire connected to the gold-plated sheet from the outer end.

[0023] Step S40: When the surrounding rock of the borehole is compressed and deformed, the cross-section and volume of the expansion hose section decrease, resulting in a change in the AC impedance between each pair of gold-plated sheets, causing a change in the amplitude of the AC sine wave circuit between each pair of gold-plated sheets. The amplitude change is further analyzed to calculate the voltage change between the gold-plated sheets.

[0024] Step S50: Analyze the gold-plated sheet area where the voltage changes and determine the concentrated stress area. The greater the voltage change, the greater the ground stress. Based on the value of the voltage change and the physical and mechanical parameters of the surrounding rock, the concentrated pressure of the surrounding rock can be calibrated and calculated.

[0025] This method collects stress changes of surrounding rocks through volume changes of sodium ions, which is more accurate and precise. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the first state diagram of a continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering.

[0027] Figure 2 This is the second state diagram of a continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering.

[0028] Figure 3 This is an enlarged view of the anti-deformation device of a continuous monitoring equipment for concentrated stress areas in the surrounding rock of underground engineering. Specific implementation methods

[0029] The symbols in the drawings of the specification include: voltage difference analyzer 1, plastic rod 2, gold-plated sheet 3, power supply 4, surrounding rock 5, expansion hose 6, borehole 7, sodium chloride ion solution 8, air pump 9, catheter 10, sodium chloride solution tank 11, reversing valve 12, support ring 13, air bag 14, fixed plate 15, cylinder 16, condenser 17, half rack 18, gear 19, electrode sheet 20, first contact sheet 21 and second contact sheet 22.

[0030] The embodiment is basically as shown in the attached Figure 1 、 Figure 2 As shown:

[0031] This solution provides a continuous monitoring device for concentrated stress areas in surrounding rock of an underground project, comprising a voltage difference analyzer 1, a plastic rod 2, a gold-plated sheet 3, a power supply 4, surrounding rock 5, an expansion hose 6, a borehole 7, a sodium ion solution 8, an air pump 9, a conduit 10, a sodium chloride solution tank 11, a reversing valve 12, a support ring 13, and an air bag 14.

[0032] The diameter of the plastic rod 2 is much smaller than the drilled hole 7, and both ends of the plastic rod have rounded corners to prevent it from damaging the expansion hose 6. The gold-plated sheet 3 is made of standard copper wire, though silver wire can be used if available. Each gold-plated sheet 3 is then wound 7-10 times at 0.5-meter intervals. Each gold-plated sheet 3 is then connected to the copper wire, which is then led out and electrically connected to the power supply 4. The voltage differential analyzer 1 is connected to the copper wire. A sodium ion solution 8 is located within a sodium chloride solution tank 11, which then connects to the expansion hose 6 via a conduit 10. This sodium ion solution 8 is used because it generates electrical conductivity, a phenomenon caused by the migration of sodium ions in an electric field. A reversing valve 12 is connected to the sodium chloride solution tank 11 at one end and to the expansion hose 6 at the other. The support ring 13 is made of stainless steel with strong thermal sensitivity, and the airbag 14 is a highly resilient rubber airbag with carbon dioxide gas flowing inside. In its initial state, the airbag 14 is in a transitional fit with the support ring 13.

[0033] As attached Figure 1 、 Figure 2 As shown:

[0034] The operator moves the catheter 10 to the front of the borehole 7, starts the air pump 9 to generate air pressure, and removes the internal broken sand and gravel to prevent the sand and gravel from damaging the expansion hose 6. After cleaning, the air bag 14 is first placed in the support ring 13. The diameter of the support ring 13 is the same as the diameter of the borehole 7. The operator places the support ring 13 at the bottom of the borehole 7 and measures the initial temperature at the deepest part of the borehole 7 at the same time.

[0035] Prepare a circular plastic bag 6 , the length of which is the same as or slightly longer than the drill hole 7 . The bag 16 is expandable and deformable, and has a certain degree of toughness. Before deformation, its diameter is slightly smaller than the diameter of the drill hole 7 . An expansion hose is pushed into the drill hole. The operator then wraps and secures gold-plated sheets 3 at a fixed distance around a plastic rod 2 , which has a diameter much smaller than the drill hole 7. The sheets 3 cannot slide. The spacing can be set to 0.05-1m based on the required accuracy. The smaller the spacing, the higher the measurement accuracy. Each gold-plated sheet 3 is connected to the drill hole opening via a thin wire, and AC power is supplied to the sheets 3 via a removable power supply.

[0036] Insert the plastic rod 2, equipped with the gold-plated sheet 3, into the expansion hose 6 and place it on the support ring 13. This effectively prevents the end of the rod from sinking due to gravity due to prolonged suspension. Then, the air pump 9 is connected to the expansion hose 6 through the reversing valve 12. The air pump 9 drains the air inside the expansion hose 6 to prevent false signals from being generated when the air inside the expansion hose is free. Once preparations are complete, the reversing valve 12 is switched, connecting the air pump 9 to the sodium chloride solution tank 11. The sodium chloride solution tank 11 is then connected to the expansion hose 6 via the conduit 10.

[0037] The operator then activates the air pump, filling plastic bag 6 with sodium ion solution and increasing the pressure, causing it to expand and deform, coupling with the rock mass of borehole 7 and airbag 14. Finally, the bag is sealed to prevent the sodium ion solution from escaping. A plastic rod and a wire connected to the gold-plated sheet extend from the outer end. The wire extending from the outer end of plastic rod 2 and the wire connected to the gold-plated sheet 3 are electrically connected to a voltage differential analyzer.

[0038] When the borehole surrounding rock 5 is subjected to stress, it compresses and deforms, with the largest deformation occurring in the area of ​​concentrated stress. This deformation reduces the cross-section and volume of the plastic bag, which in turn affects the impedance of the sodium ion solution, causing changes in the current flowing through the closed-loop gold-plated sheet and, consequently, the voltage across the gold-plated sheets 3.

[0039] At the same time, when the temperature inside the rock changes due to environmental influences, the airbag 14 will squeeze the expansion hose due to the principle of thermal expansion and contraction, causing the volume of the sodium ions at the end to change. The gold-plated sheet 3 at the end will not be affected by the change of the surrounding rock because of the presence of the support ring 13. Therefore, when the electrical signal transmitted from the end changes, it means that the temperature of the surrounding rock has changed. The thermal expansion of carbon dioxide is calculated based on the gas expansion coefficient, and the specific temperature change is converted. The operator can effectively know the temperature difference between the inside and outside of the surrounding rock in advance, and can take effective precautions to prevent the surrounding rock from cracking due to the temperature difference between the inside and outside.

[0040] A single-chip microcomputer and an ID are used outside borehole 7 to collect voltage. The gold-plated areas where voltage changes are detected are analyzed to identify areas of concentrated stress. The greater the voltage change, the greater the ground stress. Furthermore, based on the magnitude of the voltage change and the physical and mechanical parameters of the surrounding rock 5, the pressure in the surrounding rock 5 can be calibrated and calculated, yielding a three-dimensional stress environment.

[0041] As attached Figure 2 、 Figure 3 As shown:

[0042] Because the plastic rod is a key component in monitoring signals, it ideally doesn't need to bend. However, gravity causes it to bend and deform, generating many erroneous signals of surrounding rock deformation. To eliminate this problem, this solution provides an anti-deformation device, which includes a fixed plate 15, a cylinder 16, a condenser lens 17, a half rack 18, a gear 19, an electrode sheet 20, a first contact sheet 21, and a second contact sheet 22.

[0043] The fixed plate 15 is secured to the drilled hole with expansion screws. The expansion hose is heat-sealed to the fixed plate, creating a sealed environment. The cylinder 16 is made of a metal surface with high thermal conductivity, specifically silver. The liquid inside is a low-boiling-point solution, such as acetone, which boils at 56°C, ensuring excellent sealing. The condenser 17 is a convex lens located next to the cylinder 16, focusing sunlight onto the cylinder 16 to provide heat. The half rack 18 is one-quarter toothed and three-quarters toothless. The toothed portion of the half rack 18 meshes with the gear 19. The electrode piece 20 and the contact piece 21 are connected in the absence of external force. The first contact piece 21 is electrically connected in series with the voltage difference analyzer 1, the second contact piece 22 is electrically connected in series with the voltage difference analyzer 1, and the first contact piece 21 and the second contact piece 22 are connected in parallel. When the electrode piece 20 contacts the first contact piece 21 or the second contact piece 22, the voltage difference analyzer collects data.

[0044] At noon, the temperature is high. The focusing effect of condenser lens 17 causes the acetone solution in cylinder 16 to rapidly boil and evaporate, transforming into a large volume of gas. Cylinder 16's output shaft moves upward, half rack 18 meshes with gear 19, and plastic rod 2 rotates half a turn. Simultaneously, due to the rotation of plastic rod 2, electrode 20 disconnects from first contact 21, and voltage differential analyzer 1 stops collecting this information. After plastic rod 2 rotates 180 degrees, electrode 20 contacts second contact 22, and voltage differential analyzer 1 continues to receive this electrical signal. Half rack 18 then continues to rise, disengaging from gear 19, and plastic rod 2 rotates exactly half a turn. At night, the temperature drops, and cylinder 16's output shaft moves downward, reengaging half rack 18 with gear 19. Plastic rod 2 rotates 180 degrees, and the above steps repeat. During the rotation, voltage differential analyzer 1 does not collect data because electrode 20 and second contact 22 are disconnected. After stopping, electrode 20 contacts first contact 21, and voltage differential analyzer 1 resumes collecting data. During the day, one side of the plastic rod 2 is affected by gravity, while at night, the other side is affected by gravity. Thus, the gravity effects on both sides of the plastic rod 2 are offset, eliminating the problem of bending and deformation of the plastic rod 2 due to gravity, which results in inaccurate data.

[0045] If the voltage difference analyzer 1 does not collect receipts for a long time, the delay switch is triggered, the delay switch is connected to the alarm light, and the alarm light is powered on, indicating that the equipment is abnormal and the staff can deal with it in time.

[0046] The above is only an embodiment of the present invention. Common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be considered as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for continuously monitoring equipment in concentrated stress areas of surrounding rock in underground engineering, comprising the following steps: step S10: First, drill a horizontal hole at the location to be tested, then prepare a plastic rod, install the microcontroller and ID on the ground, and fix gold-plated sheets at equal intervals on the plastic rod. Each gold-plated sheet is connected in series to a power supply outside the drilled hole through a wire; Step S20: preparing an expansion hose with a circular cross section that matches the length of the drill hole, and pushing the expansion hose into the drill hole; Step S30: Push the plastic rod with the gold-plated sheet into the expansion hose in the borehole, then fill the expansion hose with sodium chloride ion solution and increase the filling pressure to cause the expansion hose to expand and deform and couple with the rock mass of the borehole wall. Finally, seal the expansion hose, and extend the plastic rod and the wire connected to the gold-plated sheet from the outer end. Step S40: When the surrounding rock of the borehole is compressed and deformed, the cross-section and volume of the expansion hose section decrease, resulting in a change in the AC impedance between each pair of gold-plated sheets, causing a change in the amplitude of the AC sine wave circuit between each pair of gold-plated sheets. The amplitude change is further analyzed to calculate the voltage change between the gold-plated sheets. Step S50: Analyze the gold-plated sheet area where the voltage changes and determine the concentrated stress area. The greater the voltage change, the greater the ground stress. According to the numerical value of voltage change and the physical and mechanical parameters of the surrounding rock, the concentrated pressure of the surrounding rock can be calibrated and calculated.

2. A continuous monitoring device for concentrated stress areas in surrounding rock of an underground project, applied to the method for continuous monitoring device for concentrated stress areas in surrounding rock of an underground project according to claim 1, comprising a power supply and a voltage difference analyzer, characterized in that: It also includes a plastic rod, a gold-plated sheet, an expansion hose and a sodium chloride solution storage box; the power supply is electrically connected to the gold-plated sheet, the voltage difference analyzer is electrically connected to the power supply, the gold-plated sheet is coaxially fixedly connected to the plastic rod, the plastic rod is matched with the expansion hose, the sodium chloride solution box is provided with a valve, and the sodium chloride solution storage box is connected to the expansion hose.

3. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 2, characterized in that: The device also includes an air pump, which is connected to the sodium chloride solution tank.

4. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 3, characterized in that: The air pump is provided with a reversing valve, and the reversing valve is connected to the expansion hose.

5. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 3, characterized in that: It also includes a support ring, a fixed plate and an airbag, the support ring cooperates with the plastic rod, the airbag is located inside the support ring, the airbag cooperates with the expansion hose, the fixed plate is arranged to rotate coaxially with the plastic rod, and the fixed plate is fixedly connected to the expansion hose.

6. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 5, characterized in that: The support ring is made of metal.

7. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 5, characterized in that: The airbag is made of rubber, and carbon dioxide gas is introduced into the airbag.

8. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 2, characterized in that: It also includes a cylinder, a condenser, a first contact piece, a second contact piece, a gear and a half rack; the output shaft of the cylinder is fixedly connected to the half rack, the half rack cooperates with the gear, the gear is fixedly arranged coaxially with the plastic rod, the condenser cooperates with the cylinder, an electrode piece is provided on the plastic rod, the electrode piece is connected in series with the gold-plated piece, the first contact piece and the second contact piece are on the same horizontal line, the first contact piece and the second contact piece cooperate with the electrode piece, the first contact piece and the second contact piece are both connected in series with the voltage difference analyzer, and the first contact piece and the second contact piece are connected in parallel.

9. The continuous monitoring device for concentrated stress areas in surrounding rock of underground engineering according to claim 8, characterized in that: The voltage difference analyzer is provided with a time delay switch and an alarm light.

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