Shield tunnel advance water detection device and method based on ag / agcl electrode

Abstract

The application discloses a shield tunnel advanced water detection device and method based on an Ag / AgCl electrode, which comprises a water detection sensor arranged on a shield machine cutter disc spoke, the water detection sensor comprising an Ag / AgCl electrode and a wire connected with the Ag / AgCl electrode, and being used for measuring the soil potential difference at a shield tunnel face in a shield machine tunneling process; a water detection sensor protective sleeve covering the outer periphery of the Ag / AgCl electrode and being installed on the shield machine cutter disc spoke, and being used for preventing the broken rock in the soil from damaging the water detection sensor in the shield machine tunneling process; a kink and fracture prevention mechanism connected with the wire connected with the Ag / AgCl electrode, and being used for preventing the wire from being wound or knotted due to rotation in the shield machine cutter disc rotating tunneling process; and a data monitoring and early warning device connected with the Ag / AgCl electrode through the wire, and being used for collecting and analyzing the measured data. The application can predict the distribution and content of water in front of the shield tunnel face, thereby providing reliable technical guidance and prediction.

Description

Technical Field

[0001] This invention relates to the field of shield tunnel design and construction, and in particular to a shield tunnel advanced water detection device and method based on Ag / AgCl electrodes. Background Technology

[0002] With the booming development of urban rail transit construction in my country, the shield tunneling method, characterized by its "high efficiency, high quality, and high benefits," has become an important and widely used construction method. However, shield tunneling machines are vulnerable without geological risk warnings. Blindly tunneling into adverse geological structures can easily lead to major engineering accidents, causing incalculable personal and property losses. Relevant advanced prediction methods include: Germany's BEAM (Bore-Tunnelling Electrical Ahead Monitoring) technology based on the principle of focused frequency domain induced polarization; ISP (Integrated Seismic Prediction) technology based on a surface wave-transverse wave conversion model; Japan's advanced detection using tunneling parameters; and domestic methods such as three-dimensional induced polarization, HSP (Horizontal Sonic Profiling) acoustic reflection, TST (Tunnel Seismic Tomography), and CFC (Complex Frequency Conductivity) electromagnetic wave reflection. Most of these detection methods are for detecting geological structures, while methods for detecting water are rare. The main problems are as follows: 1. The shield cutterhead occupies the tunnel face, making it difficult to conduct observations on the tunnel face; 2. The complex electromagnetic environment generated by the large metal equipment makes conventional electrical resistivity tomography (OTT) detection less effective; 3. The tunnel lining segments separate the detection instruments from the soil and rock, making signal acquisition inconvenient.

[0003] Soil is a complex physicochemical system containing solid particles, water, and gases. Inorganic and organic matter, as well as microorganisms, generate stray currents in the soil due to ionization and electrochemical processes. These stray currents in soil mainly refer to currents that flow without a fixed order or pattern; they exist underground as a natural system and are a major cause of corrosion in underground metal structures. Simultaneously, because soil is a conductor with a certain resistance, a potential difference is generated when current flows through it. However, the potential difference generated by stray currents in soil is relatively small, making it difficult to measure with conventional potentiometers in the tunnel face environment of shield tunneling. Therefore, this invention proposes a shield tunnel pre-exploration water detection device and method based on Ag / AgCl electrodes. Summary of the Invention

[0004] To address the shortcomings and low accuracy of existing shield tunnel water detection technologies, this invention proposes a method and apparatus for shield tunnel water detection based on Ag / AgCl electrodes. This method and apparatus can predict the distribution and content of water ahead of the tunnel face without interfering with shield tunneling, thus providing reliable technical guidance and prediction, and ensuring the safety of shield construction.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a shield tunnel advanced water detection device based on Ag / AgCl electrodes, comprising:

[0006] A water detection sensor, installed on the spokes of the shield machine cutterhead, includes an Ag / AgCl electrode and a wire connected to the Ag / AgCl electrode, used to measure the soil potential difference at the tunnel face in real time during the shield machine's excavation process;

[0007] A protective sleeve for the water detection sensor covers the outer periphery of the Ag / AgCl electrode and is installed on the spokes of the tunnel boring machine cutterhead. It is used to prevent gravel in the soil from damaging the water detection sensor during the tunnel boring machine's excavation process.

[0008] An anti-kink and breakage mechanism is connected to the wires connecting the Ag / AgCl electrodes to prevent the wires from tangling or twisting and breaking during the tunnel boring machine cutterhead rotation process.

[0009] The data monitoring and early warning device is connected to the Ag / AgCl electrode via the wire and is used to collect and analyze the measured data. If the soil potential difference exceeds the set safety value, a safety alarm will be issued to achieve the early warning function.

[0010] Optionally, the number of water sensors is the same as the number of spokes on the tunnel boring machine cutterhead, and they are respectively installed at the ends of the spokes on the tunnel boring machine cutterhead.

[0011] Optionally, the protective sleeve for the water detection sensor is a metal mesh structure, covering the outer periphery of the Ag / AgCl electrode and fixed to the spokes of the tunnel boring machine cutterhead.

[0012] Optionally, the anti-kink breakage mechanism includes a wire support, a rotating disk, and a motor. The rotating disk has wire supports distributed around its outer circumference in the same number as the spokes of the tunnel boring machine cutterhead. Multiple wires connected to the Ag / AgCl electrode are fixed to the multiple wire supports one-to-one. A hole is pre-drilled in the center of the rotating disk, and the hole is fixedly connected to the output shaft of the motor. The motor is used to drive the rotating disk to rotate.

[0013] Furthermore, during the tunnel boring machine's excavation process, the motor power is adjusted to ensure that the angular velocity of the rotating disk is the same as and in the same direction as the angular velocity of the tunnel boring machine's cutterhead, in order to prevent the wire from breaking due to tangling or twisting caused by rotation.

[0014] A method for advanced water detection in shield tunnels based on Ag / AgCl electrodes, employing the aforementioned Ag / AgCl electrode-based advanced water detection device for shield tunnels, includes the following steps:

[0015] (1) The relationship between soil potential difference and soil moisture content was obtained through experiments. Based on the relationship between soil potential difference and soil moisture content, a safe value for soil moisture content was set, and the corresponding value of soil potential difference was obtained and set as the safe value of soil potential difference.

[0016] (2) Install Ag / AgCl electrodes at the ends of the cutterhead spokes of the tunnel boring machine, and wrap a water detection sensor protective sleeve around each Ag / AgCl electrode. Fix the water detection sensor protective sleeve to the ends of the cutterhead spokes. After multiple wires connecting the Ag / AgCl electrodes are fixed by the wire bracket on the rotating disk, they are connected to the data monitoring and early warning device.

[0017] (3) During the tunnel boring machine’s excavation process, the power of the motor of the anti-torsion fracture mechanism is adjusted so that the rotational angular velocity of the anti-torsion fracture mechanism is the same as the rotational angular velocity of the tunnel boring machine cutterhead and the direction is consistent.

[0018] (4) During the actual measurement stage, the anti-knotting fracture mechanism is placed on the ground in the pedestrian gate space of the shield machine. During the tunneling process of the shield machine, the potential difference on the face of the shield machine cutterhead can be monitored in real time through the water detection sensor.

[0019] (5) When the detected potential difference exceeds the preset soil potential difference safety value, the data monitoring and early warning device will issue an alarm. At this time, it is necessary to make a judgment on the subsequent construction to ensure the safety of the tunnel boring machine construction.

[0020] Optionally, in step (1), the experimental method is as follows: two Ag / AgCl electrodes are inserted into the soil. When the soil is dry, an appropriate amount of water is added to control different moisture contents in the soil. The two Ag / AgCl electrodes are 2-5 m apart. The potential difference between the two Ag / AgCl electrodes is measured and then divided by the distance between the two points to obtain the soil potential gradient, as shown in the following formula:

[0021] ΔG=ΔV / L

[0022] Where: ΔG—potential gradient, mV / m; ΔV—potential difference, mV; L—distance between two points, m.

[0023] Furthermore, by conducting similar tests on soil samples during the tunnel boring process, a linear equation can be obtained based on the test results. During the test, a safe value for soil moisture content is set, which yields the corresponding value for soil potential difference, and this value is set as the safe value for soil potential difference.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] (1) This invention employs a water detection sensor based on Ag / AgCl electrodes. Ag / AgCl electrodes are commonly used for marine electric field measurements and can achieve high-precision soil potential detection at the tunnel face of a shield tunnel. Combined with the influence of soil moisture content on soil potential, it enables advanced prediction of the distribution and content of water ahead of the tunnel face. Compared with conventional measurements using potentiometers, this device offers advantages such as high precision, ease of installation, and no interference with shield tunneling. The method and device for advanced prediction of water distribution and content ahead of the tunnel face can significantly improve the safety of shield tunneling construction.

[0026] (2) An anti-kink fracture mechanism was designed. Because the shield machine cutterhead rotates continuously during the tunneling process, the wires of the water detection sensors installed on the spokes of the shield machine cutterhead will twist together due to rotation and eventually break. Passing the wires of the water detection sensors through the anti-kink fracture mechanism can effectively solve this problem.

[0027] (3) The water detection sensor of the present invention can realize the real-time measurement of the soil potential difference at the tunnel face of the shield tunnel. A safety value is set at the data monitoring and early warning device. If the soil potential difference exceeds the set safety value, a safety alarm will be issued, realizing the early warning function of the advanced water detection device for the shield tunnel. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the installation position of a water detection sensor according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of a water detection sensor structure provided in one embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of a protective sleeve for a water detection sensor provided in one embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of an anti-kink fracture mechanism provided in one embodiment of the present invention;

[0033] Figure 5 This is a graph showing the relationship between soil potential difference and soil moisture content.

[0034] Reference numerals in the attached diagram: 1-Shield machine cutterhead; 2-Water detection sensor; 3-Shield machine cutterhead spokes; 4-Ag / AgCl electrode; 5-Wire; 6-Data monitoring and early warning device; 7-Water detection sensor protective sleeve; 8-Anti-kink and breakage mechanism; 9-Wire support; 10-Rotating disk; 11-Hole. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0037] In the description of this invention, it should also be noted that the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this application. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Soil moisture content is a crucial parameter during shield tunneling. Since soil is a conductor with a certain resistance, a potential difference is generated when current flows through it. This potential difference can be used to determine the severity of stray currents. Traditionally, this potential difference is measured using a potentiometer. However, during shield tunneling, the potential difference generated by stray currents in the soil is relatively small and difficult to measure in the tunnel face environment. To address these issues and measure soil moisture content, this invention, based on an analysis of the advantages and disadvantages of existing methods, provides a novel method for determining soil moisture content using a water sensor based on Ag / AgCl electrodes and the microelectroflow effect.

[0039] The core principle of this invention is to install a water-detecting sensor on the spokes of the tunnel boring machine cutterhead to couple it with the soil sample being tested. Then, a 100MHz high-frequency alternating current is applied to the water-detecting sensor, generating an alternating magnetic field. At this time, the electrons in the soil sample undergo spin polarization motion at the same frequency, thereby generating a micro-electron flow. The water content in the soil affects the frequency of the alternating current, which in turn affects the alternating magnetic field. The strength of the micro-electron flow varies depending on the water content, so the water content in the soil can be determined by the strength of the micro-electron flow.

[0040] A shield tunnel advanced water detection device based on Ag / AgCl electrodes, the device mainly consists of a water detection sensor, a protective sleeve for the water detection sensor, an anti-kink and fracture mechanism, and a data monitoring and early warning device, wherein:

[0041] The water detection sensor is based on Ag / AgCl electrodes and mainly consists of Ag / AgCl electrodes connected by wires. Its main advantage lies in its high-precision potential difference measurement capability. This water detection sensor can be used to measure stray currents at the tunnel face of a shield tunnel to accurately reflect the potential difference of the soil at the tunnel face. By placing the Ag / AgCl electrodes on the shield machine cutterhead and in contact with the soil at the tunnel face, the potential difference of the soil at the tunnel face can be directly measured. In practical implementations, the water detection sensors are installed on the spokes of the shield machine cutterhead, with the number of water detection sensors matching the number of spokes. During the tunnel boring machine's excavation process, the water detection sensors will measure the soil potential difference at the tunnel face in real time.

[0042] The primary function of the protective sleeve for the water detection sensor is to effectively protect the sensor. During the tunnel boring machine's excavation and soil removal process, the Ag / AgCl electrodes, mounted on the cutterhead spokes, are susceptible to damage from the pressure and friction caused by debris and stones in the soil. To prevent damage, the protective sleeve is designed with a metal mesh structure. This structure prevents damage from debris and stones while maintaining the sensor's ability to measure soil potential difference, ensuring accurate results. The sleeve also serves to secure the Ag / AgCl electrodes.

[0043] The anti-kink and anti-breakage mechanism connects to the wires of the water detection sensor. This mechanism rotates with the tunnel boring machine (TBM) cutterhead, preventing the wires from twisting and breaking during the TBM's rotation and excavation process. Multiple wires connected to the corresponding Ag / AgCl electrodes are secured together by the anti-kink and anti-breakage mechanism and then connected to the data monitoring and early warning device, enabling the measurement of soil potential difference at the tunnel face during TBM excavation.

[0044] The function of the data monitoring and early warning device is to collect and analyze the data measured by the water detection sensor. After setting a safety value for the data monitoring and early warning device, if the soil potential difference exceeds the set safety value, a safety alarm can be issued to realize the early warning function of the shield tunnel advanced water detection device.

[0045] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0046] Figure 1 The diagram shows the installation of a water-detecting sensor according to an embodiment of the present invention. The water-detecting sensor 2 is installed on the spokes of the cutterhead 1 of the tunnel boring machine (TBM). The number of water-detecting sensors 2 depends on the number of spokes 3 of the TBM cutterhead. That is, the number of water-detecting sensors 2 is the same as the number of spokes 3 of the TBM cutterhead. The water-detecting sensor 2 is installed at the end of the spokes 3 of the TBM cutterhead. The specific installation position can be selected in the gaps of the spokes 3 of the TBM cutterhead, as long as it does not affect the excavation of soil during the tunneling process. Figure 1The red circle indicates the installation location of the water detection sensor 2. In this embodiment, the shield machine cutterhead spokes 3 consist of 6 spokes, and the water detection sensors 2 are numbered sequentially as A, B, C, D, E, and F. Sensors 2 in the same direction are grouped together: A and D form one group; B and E form another; and C and F form yet another. Only by grouping sensors 2 in pairs can the strength of the micro-electron flow be measured. Furthermore, dividing the sensors 2 into different groups allows for accurate determination of the direction in which the micro-electron flow is strongest during monitoring, and also helps assess the highest probability of adverse seepage geology ahead, thus providing a clearer understanding of the soil moisture content distribution at the tunnel face. During shield machine excavation, the water detection sensor 2 will measure the soil potential difference at the tunnel face in real time.

[0047] Figure 2 The diagram shows a schematic of a water detection sensor structure according to an embodiment of the present invention. The water detection sensor 2 is mainly composed of an Ag / AgCl electrode 4 and a wire 5. Currently, there are various models of Ag / AgCl electrodes available on the market. The electrode model selected in this embodiment is the Bangxin Ag / AgCl electrode-BXCY-1, which has advantages such as high-temperature stability and electrochemical stability, and is generally used for marine electric field measurement. The Ag / AgCl electrode 4 can detect the soil potential at the tunnel face of a shield tunnel. The wire 5 can transmit the micro-current signal detected by the Ag / AgCl electrode 4 to the data monitoring and early warning device 6. The data monitoring and early warning device 6 can display the micro-current intensity detected by the Ag / AgCl electrode 4. If the detected micro-current intensity exceeds a preset safety value, an alarm will be issued to provide early warning.

[0048] Figure 3 The diagram shows a schematic of a water detection sensor protection device according to an embodiment of the present invention. The water detection sensor protective sleeve 7 is made of metal, specifically a metal mesh structure, and only needs to cover the Ag / AgCl electrode 4 in the water detection sensor 2. This structure can prevent the Ag / AgCl electrode 4 from being squeezed and rubbed by gravel in the soil during shield tunneling, thus protecting the Ag / AgCl electrode 4 in the water detection sensor 2. The water detection sensor protective sleeve 7 is fixed to the cutterhead spokes 3 of the shield machine by welding. The Ag / AgCl electrode 4 is covered by the water detection sensor protective sleeve 7, which, in addition to its protective function, also serves to fix it.

[0049] Figure 4The diagram shows a schematic of an anti-kink fracture mechanism provided in one embodiment of the present invention. The main function of the anti-kink fracture mechanism 8 is to connect with the wires 5 on the water detection sensor 2. The anti-kink fracture mechanism 8 can be rotated and adjusted to prevent the wires 5 on multiple water detection sensors 2 from twisting together and breaking due to rotation. This device can be placed on the ground in the pedestrian gate space of the tunnel boring machine. The specific location is not required as long as it does not affect construction. The anti-kink fracture mechanism 8 mainly consists of three parts: wire support 9, rotating disk 10, and motor. The outer circumference of the rotating disk 10 is evenly distributed with the same number of wire supports 9 as the spokes 3 of the tunnel boring machine cutterhead. This embodiment uses six wire supports 9 as an example for explanation. The six wires 5 connected to the Ag / AgCl electrode 4 are fixed one-to-one on the six wire supports 9. The rotating disk 10 has a hole 11 in the middle, which is fixed to the motor output shaft. The motor output shaft can drive the rotating disk 10 to rotate. During the tunnel boring machine (TBM) excavation process, the rotational speed of the TBM cutterhead is a controllable factor. Therefore, by controlling the power of the motor, the rotational speed of the rotating disk 10 can be controlled. Adjusting the motor power ensures that the angular velocity of the rotating disk 10 is the same as and in the same direction as the angular velocity of the TBM cutterhead, preventing the wire 5 from becoming entangled or twisted due to rotation and thus breaking.

[0050] Figure 5 The graph shows the relationship between soil potential difference and soil moisture content. The horizontal axis E represents the potential difference, and the vertical axis w represents the moisture content. Guilin red clay was selected as the test subject in the graph. Soil potential gradient is a parameter for assessing the degree of hazard from stray currents. Soil potential difference refers to the rate of change of soil potential per unit distance. Because soil is a conductor with a certain resistance, a potential difference is generated when current flows through it. During the experiment, two Ag / AgCl electrodes were inserted into the soil. When the soil was dry, an appropriate amount of water was added to control different moisture contents. The two Ag / AgCl electrodes were placed 2–5 m apart. The potential difference between the two Ag / AgCl electrodes was measured, and then divided by the distance between the two points to obtain the soil potential gradient. This can be expressed by the following formula:

[0051] ΔG=ΔV / L

[0052] Where: ΔG—potential gradient, mV / m; ΔV—potential difference, mV; L—distance between two points, m.

[0053] The measurement was performed vertically, meaning that after measuring along one direction, a measurement was taken perpendicular to that direction. The experimental curves show a strong linear relationship between soil potential difference and soil moisture content for different soil types. Therefore, if similar tests are conducted on soil samples during tunnel boring machine (TBM) excavation, a linear equation can be obtained from the test results. By setting a safe value for soil moisture content during the test, the corresponding value of soil potential difference can be obtained and set as the safe value for soil potential difference. Regarding the safe value for soil moisture content, based on soil mechanics knowledge, this invention suggests setting the limit moisture content of the soil as the safe value, for example, the plastic limit moisture content w of clay. p This indicates the water content at which clay is in a semi-solid state and a plastic state, typically around 30%. (w) p =0.3 is used as the safe value for primary soil moisture content; the liquid limit water content w of clay L This indicates the water content at which clay is in the plastic and fluid state, typically around 42%. (w) L =0.42 is taken as the safe value for secondary soil moisture content. According to Figure 5 The relationship between soil potential difference and soil moisture content can be used to determine the safe potential difference values ​​corresponding to the safe values ​​of soil moisture content at levels one and two. When the detected soil potential difference exceeds the preset safe value during tunnel boring machine (TBM) excavation, it indicates that the soil moisture content has reached a dangerous level, and the data monitoring and early warning device will issue an alarm to achieve the functions of advanced water detection and early warning.

[0054] The overall workflow of the device of this invention is briefly described below: Before the tunnel boring machine (TBM) begins excavation, Ag / AgCl electrodes 4 are installed at the ends of the spokes of the TBM cutterhead 1. A metal mesh structure water-detecting sensor protective sleeve 7 is wrapped around each Ag / AgCl electrode 4. The water-detecting sensor protective sleeve 7 is welded to the cutterhead spokes 3. The wires 5 connected to the Ag / AgCl electrodes 4 are fixed via wire brackets 9 on the rotating disk 10 and then connected to the data monitoring and early warning device 6. During the TBM's excavation, the rotational speed of the TBM cutterhead 1 is a controllable factor by engineers. By adjusting the power of the motor connected to the anti-kink fracture mechanism 8, the rotational angular velocity of the anti-kink fracture mechanism 8 is ensured to be the same as and in the same direction as the rotational angular velocity of the TBM cutterhead 1. It should be emphasized that the "same" angular velocity does not require strict requirements; it is sufficient to ensure that the wires do not become entangled or twisted. During the actual measurement phase, the anti-kink fracture mechanism 8 is placed on the ground in the pedestrian gate space of the tunnel boring machine. As the tunnel boring machine advances, the potential difference on the face of the cutterhead can be monitored in real time. When the detected potential difference exceeds the preset soil potential difference safety value, the data monitoring and early warning device 6 issues an alarm. At this time, it is necessary to make a judgment on the subsequent construction to ensure the safety of the tunnel boring construction.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A shield tunnel advanced water detection device based on Ag / AgCl electrodes, characterized in that, include: A water detection sensor, installed on the spokes of the shield machine cutterhead, includes an Ag / AgCl electrode and a wire connected to the Ag / AgCl electrode, used to measure the soil potential difference at the tunnel face in real time during the shield machine's excavation process; A protective sleeve for the water detection sensor covers the outer periphery of the Ag / AgCl electrode and is installed on the spokes of the tunnel boring machine cutterhead. It is used to prevent gravel in the soil from damaging the water detection sensor during the tunnel boring machine's excavation process. An anti-kink and breakage mechanism is connected to the wires connecting the Ag / AgCl electrodes to prevent the wires from tangling or twisting and breaking during the tunnel boring machine cutterhead rotation process. The data monitoring and early warning device is connected to the Ag / AgCl electrode via the wire and is used to collect and analyze the measured data. If the soil potential difference exceeds the set safety value, a safety alarm will be issued to achieve the early warning function.

2. The shield tunnel advanced water detection device based on Ag / AgCl electrodes according to claim 1, characterized in that, The number of water detection sensors is the same as the number of spokes on the tunnel boring machine cutterhead, and they are installed at the ends of the spokes.

3. The shield tunnel advanced water detection device based on Ag / AgCl electrodes according to claim 1, characterized in that, The protective sleeve for the water detection sensor is a metal mesh structure that covers the outer periphery of the Ag / AgCl electrode and is fixed to the spokes of the tunnel boring machine cutterhead.

4. The shield tunnel advanced water detection device based on Ag / AgCl electrodes according to claim 1, characterized in that, The anti-kink and breakage mechanism includes a wire support, a rotating disk, and a motor. The rotating disk has wire supports distributed around its outer circumference in the same number as the spokes of the tunnel boring machine cutterhead. Multiple wires connected to the Ag / AgCl electrode are fixed to the wire supports one-to-one. A hole is pre-drilled in the center of the rotating disk and is fixedly connected to the output shaft of the motor. The motor is used to drive the rotating disk to rotate.

5. The shield tunnel advanced water detection device based on Ag / AgCl electrodes according to claim 4, characterized in that, During the tunnel boring machine's excavation process, the motor power is adjusted to ensure that the angular velocity of the rotating disc is the same as and in the same direction as the angular velocity of the cutterhead of the tunnel boring machine. This is to prevent the wires from becoming tangled or twisted due to rotation, which could lead to breakage.

6. A method for advanced water detection in shield tunnels based on Ag / AgCl electrodes, employing the advanced water detection device for shield tunnels based on Ag / AgCl electrodes as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) The relationship between soil potential difference and soil moisture content was obtained through experiments. Based on the relationship between soil potential difference and soil moisture content, a safe value for soil moisture content was set, and the corresponding value of soil potential difference was obtained and set as the safe value of soil potential difference. (2) Install Ag / AgCl electrodes at the ends of the cutterhead spokes of the tunnel boring machine, and wrap a water detection sensor protective sleeve around each Ag / AgCl electrode. Fix the water detection sensor protective sleeve to the ends of the cutterhead spokes. After multiple wires connecting the Ag / AgCl electrodes are fixed by the wire bracket on the rotating disk, they are connected to the data monitoring and early warning device. (3) During the tunnel boring machine’s excavation process, the power of the motor of the anti-torsion fracture mechanism is adjusted so that the rotational angular velocity of the anti-torsion fracture mechanism is the same as the rotational angular velocity of the tunnel boring machine cutterhead and the direction is consistent. (4) During the actual measurement stage, the anti-knotting fracture mechanism is placed on the ground in the pedestrian gate space of the shield machine. During the tunneling process of the shield machine, the potential difference on the face of the shield machine cutterhead can be monitored in real time through the water detection sensor. (5) When the detected potential difference exceeds the preset soil potential difference safety value, the data monitoring and early warning device will issue an alarm. At this time, it is necessary to make a judgment on the subsequent construction to ensure the safety of the tunnel boring machine construction.

7. The method for advance water detection in shield tunnels based on Ag / AgCl electrodes according to claim 6, characterized in that, In step (1), the experimental method is as follows: two Ag / AgCl electrodes are inserted into the soil. When the soil is dry, an appropriate amount of water is added to control different moisture contents in the soil. The two Ag / AgCl electrodes are 2-5m apart. The potential difference between the two Ag / AgCl electrodes is measured and then divided by the distance between the two points to obtain the soil potential gradient, as shown in the following formula: ΔG=ΔV / L Where: ΔG - potential gradient, mV / m; ΔV - potential difference, mV; L - distance between two points, m.

8. The method for advance water detection in shield tunnels based on Ag / AgCl electrodes according to claim 7, characterized in that, By conducting similar tests on soil samples during the tunnel boring process, a linear equation can be obtained based on the test results. During the test, a safe value for soil moisture content is set, which yields the corresponding value for soil potential difference, and this value is set as the safe value for soil potential difference.

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