Method and system for accurately evaluating freezing process of tunnel constructed by artificial freezing method

Abstract

The invention discloses a method and a system for accurately evaluating a freezing process of a tunnel constructed by an artificial freezing method, and belongs to the technical field of geotechnical engineering testing. The method comprises the following steps: acquiring geological exploration data and soil texture design parameters of a frozen area, and determining an underground area and an earth surface area which need to be artificially frozen; constructing a temperature measuring hole, and arranging a temperature monitoring part and a resistance monitoring part; sorting and analyzing the temperature monitoring data, the resistivity monitoring data and the data of the change condition of the freezing condition along with the number of days in the freezing process; the monitoring data and the underground freezing equipment arrangement information are added into a multi-physics field numerical simulation analysis part, and simulation parameters and other details are adjusted. Data monitored by the temperature monitoring part and the resistance monitoring part are input into the multi-physics field numerical simulation analysis part, numerical simulation is carried out on the freezing process, and visualization and accurate evaluation of the freezing process of the tunnel constructed through the manual freezing method are achieved through interactive verification with the monitored data.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering testing, and particularly relates to a method and system for accurately evaluating the freezing process of a tunnel constructed by the artificial freezing method. Background Art

[0002] With the rapid development of urbanization economy, a large number of construction projects in soft soil areas have emerged like mushrooms after rain, whether in water-rich areas of river basins or areas with soft soils (such as silt, silty soil or quicksand layers). When the groundwater level is shallow and there is soft soil under the foundation, traditional construction methods are difficult to ensure the stability of the foundation pit excavation at the construction site. Therefore, it is very important to carry out water isolation treatment and artificial freezing for the foundation pit. For the underground excavation process, if the artificial freezing treatment is improper, leakage may occur during the excavation process, causing excessive lateral deformation of the underground tunnel, and then resulting in overall instability, and even possibly causing the collapse of surrounding buildings (structures).

[0003] The artificial freezing technology is a commonly used method for strengthening and stabilizing soft soil foundations, and is used to ensure the stability and safety during tunnel construction. It was first used as a temporary support method, and later researchers discussed various factors affecting the selection of freezing temperature, the thickness of the frozen zone and the spacing of freezing pipes, providing a new direction for the application of the artificial freezing method.

[0004] However, when using the artificial freezing technology, problems such as soil expansion or other issues during the freeze-thaw process of the soil will seriously affect the construction process and even lead to serious accidents. Therefore, it is crucial to monitor the freeze-thaw situation of the soil and the development of the frozen wall during the freezing construction process. However, the single temperature sensor device has insufficient capabilities. At the same time, in the dim underground connection passage, workers are prone to damage the sensor lines during the construction process, and it cannot be guaranteed that each temperature sensor used is in good condition and the monitoring process is accurate. Also, due to a large number of buildings and various underground cables around the urban subway connection passage to be monitored, the stability of the formation process of the frozen area must be strictly controlled during the artificial freezing process. In summary, the existing artificial freezing detection methods are limited to only reflecting local conditions and have certain errors, and there are also defects in risk prediction.

[0005] Therefore, it is necessary to provide a method and system for accurately evaluating the freezing process of a tunnel constructed by the artificial freezing method. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and system for accurately evaluating the freezing process of a tunnel constructed by the artificial freezing method, so as to solve the problems that the existing artificial freezing detection methods are limited to only reflecting local conditions and have certain errors, and there are also defects in risk prediction.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] An accurate evaluation method for the freezing process of a tunnel constructed by the artificial freezing method, comprising:

[0009] S1. Obtain the geological exploration data of the freezing area and the soil quality design parameters, confirm the different wave velocities between the unfrozen soil and the frozen soil, and determine the underground area and the surface area that need to be artificially frozen;

[0010] S2. Construct temperature measurement holes in the underground area according to the design drawings, arrange a temperature monitoring unit and a resistivity monitoring unit, and ensure stable connection of the lines and equipment;

[0011] S3. Organize and analyze the temperature monitoring data, resistivity monitoring data, and data on the change of the freezing condition with the number of days during the freezing process;

[0012] S4. According to the construction drawings, add the monitoring data and the underground freezing equipment layout information to different modules of the multi-physical field numerical simulation analysis unit, and adjust the simulation parameters and other details;

[0013] S5. Through the interactive verification between the monitoring data and the simulation model, determine the relationship between the resistivity monitoring data and the freezing process, and realize the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method.

[0014] The present invention realizes the real-time monitoring and mutual verification of multi-physical field data through the temperature monitoring unit and the resistivity monitoring unit, inputs the monitored multi-physical field data into the multi-physical field numerical simulation analysis unit, conducts numerical simulation on the freezing process, determines the relationship between the resistivity monitoring data and the freezing process through the interactive verification with the monitoring data, and realizes the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method.

[0015] Furthermore, the monitoring methods of the temperature monitoring unit and the resistivity monitoring unit include:

[0016] S1. Reasonably arrange temperature measurement holes in the tunnel and install underground temperature sensors for temperature monitoring and calculating the wall thickness of the formed freezing wall;

[0017] S2. Conduct resistivity monitoring on the position where the freezing wall is formed in the frozen area stratum;

[0018] S3. Construct a "water-thermal-mechanical" tunnel freezing model according to the geological report;

[0019] S4. Evaluate the freezing process based on the feedback of the temperature monitoring data and the resistivity monitoring data;

[0020] S5. During the tunnel construction, verify and visualize the "water-thermal-mechanical" tunnel freezing model with the real-time monitoring data.

[0021] Further, in step S4, it is required to construct a three-dimensional artificial freezing model for the area to be measured, and the artificial freezing model and the mechanics, temperature, and seepage modules jointly construct a multi-physical field coupling model.

[0022] Further, the monitoring method of the resistance monitoring unit is an operation method based on high-density electrical detection of the artificial freezing process, including the following steps:

[0023] S1. Obtain geological exploration data and soil design parameters of the freezing area, and determine the high-density electrical method survey area;

[0024] S2. According to the principle of the four-electrode Wenner array, determine the total length L of the survey line, the electrode measurement point distance x, the electrode distance a, and the isolation coefficient n, and then determine the measurement point positions in the survey area, and calculate the maximum detection depth Hmax according to the following formula:

[0025] Hmax = a / 2 = nx / 2;

[0026] S3. Judge whether the maximum detection depth Hmax obtained by the traditional surface electrode arrangement method can meet the detection requirements. When Hmax is not less than the underground freezing area depth h, use the surface electrode arrangement method for electrode installation, and the surface electrodes are arranged along the top of the artificial freezing area; when Hmax is less than the freezing area depth h, use a combination of underground electrode arrangement and surface electrode arrangement for electrode installation, the surface electrodes are arranged along the top of the artificial freezing area, and the underground electrodes are located below the corresponding surface electrodes;

[0027] S4. Layout the survey line, install the electrodes at the measurement point positions to form a survey network;

[0028] S5. Connect the surface electrodes, underground electrodes, programmed multi-channel electrode conversion device, high-density electrical method host, and data acquisition system through cables to automatically collect apparent resistivity data at different depths in the artificial freezing area;

[0029] S6. Use the data processing system to process the collected apparent resistivity, then perform two-dimensional inversion calculation, analyze the apparent resistivity characteristics of the artificial freezing area at different depths, obtain the high-density electrical method apparent resistivity contour section distribution map of the artificial freezing area, and determine the distribution pattern of the apparent resistivity in the artificial freezing area;

[0030] S7. Regularly detect, compare the high-density electrical method detection images of different freezing days, analyze the inverted two-dimensional apparent resistivity contour section distribution map and formula, compare with the design drawings of the artificial freezing area at the construction site, and detect whether the freezing situation in the artificial freezing area meets the expectations according to the apparent resistivity contour section distribution map, and pay attention to the detected freezing problems during real-time detection.

[0031] Further, in step S4, both the number of survey lines and the number of electrodes are multiple, and the multiple survey lines and the multiple electrodes can be arbitrarily extended according to the survey area range, the working face size, and the detection accuracy.

[0032] Further, the data processing system includes a computer, a color printer, a color plotter, and a color display screen. The collected apparent resistivity data is transmitted to the computer by the high-density host, preprocessed by two-dimensional inversion calculation, and the apparent resistivity contour section distribution map is displayed. After going offline, various result drawings can be automatically drawn and printed.

[0033] Further, the working method of the multi-physical field numerical simulation analysis unit includes the following steps:

[0034] S1. Obtain the soil property parameters and the initial data of the initial equipment experiment monitoring according to the geological monitoring report, and construct a multi-physical field numerical simulation model;

[0035] S2. Add all the buildings and construction equipment that can affect the freezing process in the frozen construction area to the model according to the construction soil quality, add the positions of the freezing pipes to the model according to the drawings, and determine the refrigerant circulation path according to the working state of the refrigerating machine;

[0036] S3. Verify the operation accuracy of the model according to the temperature monitoring data and the resistivity monitoring data, and conduct a freezing process assessment;

[0037] S4. After the multi-physical field numerical simulation model is established accurately, the freezing state of the tunnel at each day can be monitored regardless of the real time according to the simulated results.

[0038] An accurate assessment system for the freezing process of a tunnel constructed by the artificial freezing method includes:

[0039] A temperature monitoring unit for collecting temperature data at different moments during the freezing process;

[0040] A resistance monitoring unit for recording the visual data of the gradual change of resistance caused by the freezing of moisture in the underground soil at different moments during the freezing process;

[0041] A multi-physical field numerical simulation analysis unit for establishing a simulation model by combining the texture report with the data collected by the temperature monitoring unit and the resistance monitoring unit, and predicting the freezing state of the tunnel at each day after freezing by using the simulation model in combination with the temperature and resistance trends.

[0042] Further, the temperature monitoring unit includes a temperature sensor, a moisture sensor, a pore pressure sensor, a temperature sensing data line, and a data collector; the resistance monitoring unit includes a resistivity test probe, a resistivity sensing data line, and a resistivity acquisition and analysis module; the multi-physical field numerical simulation analysis unit includes a physical parameter output module, a physical modeling module, and a data output module.

[0043] The present invention has the following beneficial effects:

[0044] The present invention refers to a comprehensive and all-round method for evaluating the freezing process of subway tunnels by combining a multi-physical field simulation model with temperature monitoring and resistance monitoring. Among them, temperature sensors are installed during underground construction, the thickness of the frozen wall is calculated according to the empirical formula, the thickness of the formed frozen wall and the depth of the underground frozen wall position are monitored by the resistance method, and then the change of resistivity during the freezing process is inferred by observing the change of resistivity in the visible image generated by the observation equipment, and at the same time, the established multi-physical field numerical simulation model is adjusted to fit the real-time data of temperature monitoring and resistance monitoring to adjust the simulation model. Finally, the results of each other are verified, and through the interactive verification of the simulation model and the monitoring data, the relationship between the resistivity monitoring data and the freezing process is determined, and the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method are realized. Description of the Drawings

[0045] Figure 1 It is a cross-sectional view of the positions of freezing holes, pressure relief holes and temperature measuring holes in on-site construction;

[0046] Figure 2 It is a flow chart of the operation method for detecting artificial freezing by the high-density electrical method;

[0047] Figure 3 It is a schematic diagram of data acquisition and processing of the high-density electrical method for the electrode installation technology (where the underground electrodes are installed or not according to the depth requirements);

[0048] Figure 4 It is a schematic diagram of the on-vehicle construction installation technology of underground electrodes;

[0049] Figure 5 It is a three-dimensional structure schematic diagram of the multi-physical field simulation model.

[0050] Among them: 1. Surface electrode; 2. Measuring line; 3. Freezing area; 4. Program-controlled multi-channel electrode conversion device; 5. High-density electrical method main machine; 6. Computer; 7. Color printer; 8. Color plotter; 9. Color display screen; 10. Data acquisition system; 11. Data processing system; 12. Underground electrode; 13. Rigid straight push rod; 14. Diamond drill bit; 15. On-vehicle servo hydraulic control system. Specific Embodiments

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] In order to realize the visualization and accurate evaluation of the freezing process of a tunnel constructed by the artificial freezing method, and at the same time to improve the detection accuracy and the reliability of risk assessment, the present invention comprehensively proposes that on the basis of predicting the formation of the frozen wall by temperature monitoring, the artificial tunnel freezing is detected by the resistance method, and then combined with the multi-physical field numerical simulation of the construction background, and the freezing process is evaluated according to the geological report analysis and the monitoring data of temperature and resistivity. The monitoring data of the three-party monitoring results are cross-validated to determine the relationship between the temperature and resistivity monitoring data and the freezing process, and the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method are realized by combining multi-physical field monitoring.

[0053] Please refer to Figures 1 to 5 , in a specific embodiment, an accurate evaluation method for the freezing process of a tunnel constructed by the artificial freezing method includes:

[0054] S1. Obtain the geological exploration data and soil design parameters of the freezing area 3, confirm the different wave velocities between the unfrozen soil and the frozen soil, and determine the underground area and surface area that need to be artificially frozen.

[0055] Specifically, the geological exploration data includes the formation distribution, the physical properties of the soil layer, and the change of water content, etc., and the construction freezing area 3 is pre-planned according to the construction drawings. The design parameters of the freezing area 3 include the freezing shape size, depth, etc. The freezing shape size of the underground construction tunnel determines the layout position of the temperature sensors.

[0056] S2. Construct temperature measurement holes in the underground area according to the design drawings, arrange the temperature monitoring part and the resistance monitoring part, and ensure the stable connection of the lines and equipment.

[0057] S3. Organize and analyze the temperature monitoring data, resistivity monitoring data, and data on the change of the freezing condition with the number of days during the freezing process.

[0058] S4. According to the construction drawings, add the monitoring data and the underground freezing equipment layout information to different modules of the multi-physical field numerical simulation analysis part, and adjust the simulation parameters and other details; while adjusting the detailed parameters of the multi-physical field numerical simulation model according to the geological monitoring report, the temperature monitoring data and the resistance monitoring data should also be combined.

[0059] S5. Through the cross-validation of the monitoring data and the simulation model, determine the relationship between the resistivity monitoring data and the freezing process, and realize the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method.

[0060] In the present invention, a comprehensive and all-round method for evaluating the freezing process of a subway tunnel by combining a multi-physical field simulation model with temperature monitoring and resistance monitoring is cited. Among them, temperature sensors are installed during underground construction, the thickness of the frozen wall is calculated according to an empirical formula, the thickness of the formed frozen wall and the depth of the underground frozen wall position are monitored by combining the resistance method, and then the change of resistivity during the freezing process is inferred from the visible graph generated by the observation equipment, thereby inferring the freezing process. At the same time, the established multi-physical field numerical simulation model is adjusted and matched with the real-time data of temperature monitoring and resistance monitoring to adjust the simulation model. Finally, the results of each other are verified, and the relationship between the resistivity monitoring data and the freezing process is determined through the interactive verification of the simulation model and the monitoring data, realizing the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method.

[0061] In one embodiment, the monitoring methods of the temperature monitoring unit and the resistance monitoring unit include:

[0062] S1, Reasonably arrange temperature measuring holes in the tunnel and install underground temperature sensors for temperature monitoring and calculating the thickness of the formed frozen wall.

[0063] Specifically, before constructing the underground temperature measuring holes, calculate the arrangement positions of the temperature sensors in advance, and predict the thickness of the formed frozen wall according to an accurate empirical formula; during construction, ensure that all components are intact, and at the same time require that the temperature sensors and lines have the characteristics of waterproof, low-temperature resistance and unaffected sensitivity in harsh environments.

[0064] S2, Conduct resistivity monitoring on the position where the frozen wall is formed in the frozen zone stratum.

[0065] Specifically, strictly control the arrangement interval of the surface electrodes 1 according to the monitoring depth to ensure the stable operation of the electrodes and the lines during the monitoring process. For the surface where manual construction is inconvenient, use large equipment to assist in the installation to ensure that the electrodes are in stable contact with the underground soil.

[0066] S3, Construct a "water-thermal-mechanical" tunnel freezing model according to the geological report.

[0067] S4, Evaluate the freezing process based on the feedback of temperature monitoring data and resistivity monitoring data.

[0068] Specifically, it is required to construct a three-dimensional artificial freezing model for the area to be measured, and the artificial freezing model and the mechanical, temperature and seepage modules jointly construct a multi-physical field coupling model.

[0069] S5, During tunnel construction, verify and visualize the "water-thermal-mechanical" tunnel freezing model with real-time monitoring data.

[0070] In one embodiment, the monitoring method of the resistance monitoring unit is an operation method based on high-density electrical detection of the artificial freezing process, including the following steps:

[0071] S1. Obtain the geological exploration data of the frozen area 3 and the soil design parameters, and determine the high-density resistivity survey area.

[0072] S2. According to the principle of the four-electrode Wenner array, determine the total length L of the survey line 2, the electrode measurement point distance x, the electrode distance a, and the isolation coefficient n, and then determine the measurement point positions in the survey area, and calculate the maximum detection depth Hmax according to the following formula:

[0073] Hmax = a / 2 = nx / 2.

[0074] Specifically, the construction freezing position determines the length of the single-sided survey line 2 arranged by the surface resistance method and the instrument installation position, etc. Among them, the main electrode distance a is the product of the measurement point distance x and the isolation coefficient n, and the corresponding detection depth H is a / 2. When the isolation coefficient n is the maximum value, the corresponding detection depth H is the largest.

[0075] S3. Judge whether the maximum detection depth Hmax obtained by the traditional surface electrode arrangement method can meet the detection requirements. When Hmax is not less than the depth h of the underground frozen area 3, use the surface electrode arrangement method for electrode installation, and the surface electrode 1 is arranged along the top of the artificial frozen area 3; when Hmax is less than the depth h of the frozen area 3, use a combination of underground electrode arrangement and surface electrode arrangement for electrode installation. The surface electrode 1 is arranged along the top of the artificial frozen area 3, and the underground electrode 12 is located below the corresponding surface electrode 1.

[0076] S4. Layout the survey line 2, install the electrodes at the measurement point positions to form a survey network.

[0077] It can be understood that the number of both the survey line 2 and the electrodes is multiple. The multiple survey lines 2 and multiple electrodes can be arbitrarily expanded according to the survey area range, the working face size, and the detection accuracy. To make the monitoring depth more accurate, the underground electrode installation technology can be used and the vertical jacking equipment can be used to install the electrodes. The underground electrode installation technology not only increases the detection depth, but also improves the resolution of the apparent resistivity profile at both ends of the survey line 2 and in the deep underground frozen area, and effectively avoids the phenomenon of shallow low-resistance shielding current at the same time. The vertical jacking equipment consists of a vehicle-mounted servo hydraulic control system 15, a rigid straight push rod 13, and a diamond drill bit 14.

[0078] S5. Connect the surface electrode 1, the underground electrode 12, the programmed multi-channel electrode conversion device 4, the high-density resistivity mainframe 5, and the data acquisition system 10 through cables, and automatically collect the apparent resistivity data at different depths of the artificial frozen area 3.

[0079] S6. Use the data processing system 11 to process the collected apparent resistivity, then perform two-dimensional inversion calculation, analyze the apparent resistivity characteristics of the artificial freezing area at different depths, obtain the sectional distribution map of the apparent resistivity isolines of the high-density electrical method in the artificial freezing area, and determine the distribution pattern of the apparent resistivity in the artificial freezing area.

[0080] Specifically, the data processing system 11 includes a computer 6, a color printer 7, a color plotter 8, and a color display 9. The collected apparent resistivity data is transmitted to the computer 6 through the high-density mainframe, preprocessed through two-dimensional inversion calculation, and the sectional distribution map of the apparent resistivity isolines is displayed. After going offline, various result drawings can be automatically drawn and printed.

[0081] S7. Regularly detect, compare the high-density electrical method detection images of different freezing days, analyze the sectional distribution map and distribution pattern of the inverted two-dimensional apparent resistivity isolines, compare with the design drawings of the artificial freezing area at the construction site, and detect whether the freezing situation in the artificial freezing area meets the expectations according to the sectional distribution map of the apparent resistivity isolines. Pay attention to the discovered freezing problems during real-time detection.

[0082] In this way, temperature sensors are relatively common, and the operation method is to drill temperature measurement holes underground for installing underground temperature sensors. In the present invention, resistance monitoring uses the high-density electrical method to detect the artificial freezing process of the subway tunnel. This device is a non-destructive testing technology represented by the resistivity method. Due to its advantages of non-destruction, accuracy, and high efficiency, it is widely used in the detection of the freezing construction industry. Usually, the resistivity of groundwater is only n×10 -1 ~n×10 Ω·m. When the soil reaches below the freezing point, the water in the soil freezes into ice, and the resistivity will increase sharply. The resistivity of frozen soil can be as high as n×10 2 ~n×10 4 Ω·m. Therefore, using resistivity to detect the freezing wall and freezing area 3 in the construction of underground tunnels is a new idea for the quality detection level. At the same time, with the rise of computers in recent years, various simulation software has become relatively more perfect and reliable. Therefore, the present invention combines temperature monitoring and resistivity monitoring with multi-physical field numerical simulation prediction and analysis. The results of each other are mutually verified. By cross-verifying with the monitoring data, the relationship between the resistivity monitoring data and the freezing process is determined, and the visualization and precise evaluation of the freezing process of the tunnel constructed by the artificial freezing method are realized.

[0083] After accurately establishing the multi-physical field numerical simulation in the present invention, the results of each other are mutually verified. By cross-verifying with the monitoring data, the relationship between the resistivity monitoring data and the freezing process is determined, and the visualization and precise evaluation of the freezing process of the tunnel constructed by the artificial freezing method are realized. In one embodiment, the working method of the multi-physical field numerical simulation analysis unit includes the following steps:

[0084] S1. Obtain the soil property parameters and the initial data of the initial equipment experiment monitoring according to the geological monitoring report, and construct a multi-physical field numerical simulation model; encrypt the grid of the freezing area 3 for the established multi-physical field numerical simulation model to increase the precision calculation.

[0085] S2. Add all the buildings and construction equipment that can affect the freezing process in the freezing construction area to the model according to the construction soil quality, add the positions of the freezing pipes to the model according to the drawings, and determine the refrigerant circulation path according to the working state of the refrigerator.

[0086] S3. Verify the operation accuracy of the model according to the temperature monitoring data and the resistivity monitoring data, and conduct an evaluation of the freezing process.

[0087] Specifically, after the temperature sensors are installed and the resistance monitoring equipment is fixed, geological monitoring can be carried out on the freezing area, and the results are introduced into the model of the multi-physical field numerical simulation analysis department, and it is required to be consistent with the initial detection results.

[0088] S4. After the multi-physical field numerical simulation model is established accurately, real-time monitoring can be carried out regardless of the tunnel freezing state of each simulated day.

[0089] In addition, the embodiment of the present invention also provides a precise evaluation system for the freezing process of a tunnel constructed by the artificial freezing method, including:

[0090] A temperature monitoring department, which is used to collect temperature data at different moments during the freezing process.

[0091] A resistance monitoring department, which is used to record the visual data of the gradual change of resistance caused by the freezing of moisture in the underground soil at different moments during the freezing process.

[0092] A multi-physical field numerical simulation analysis department, which is used to establish a simulation model by combining the texture report with the data collected by the temperature monitoring department and the resistance monitoring department, and use the simulation model to predict the tunnel freezing state of each day after freezing in combination with the temperature and resistance trends.

[0093] Among them, the temperature monitoring department includes temperature sensors, moisture sensors, pore pressure sensors, temperature sensing data lines and data acquisition instruments; the resistance monitoring department includes resistivity test probes, resistivity sensing data lines and resistivity acquisition and analysis modules; the multi-physical field numerical simulation analysis department includes a physical parameter output module, a physical modeling module and a data output module.

[0094] Since the precise evaluation system for the freezing process of a tunnel constructed by the artificial freezing method is the system corresponding to the above-mentioned precise evaluation method for the freezing process of a tunnel constructed by the artificial freezing method and has the same beneficial effects, the present invention will not elaborate on this.

[0095] The present invention relates to the artificial freezing process and method of subway connecting passages with multi-physical field monitoring in the field of geotechnical engineering testing. Specifically, it involves the traditional conventional operation of monitoring and calculating the formation of the freezing curtain by temperature sensors, and at the same time introducing a high-density electrical instrument and operation method for monitoring resistance changes. The innovation lies in using the data obtained from preliminary monitoring during the freezing process for simulation correction. After successfully establishing the simulation model, the complete tunnel freezing formation process can be predicted and analyzed by multi-physical field numerical simulation.

[0096] Implementation case:

[0097] In an inland clay urban area, there is rich groundwater storage and the depth of the groundwater level is moderate. Currently, large-scale underground traffic construction is underway. To relieve the traffic congestion brought about by urban development, the construction of subway tunnels is widely welcomed. Therefore, it is necessary to construct in the water-rich underground, so artificial freezing treatment is required before construction. For this purpose, not only the stable formation of the freezing wall needs to be ensured to achieve water isolation treatment, but also the progress of the freezing area 3 needs to be observed in real time. For this reason, an accurate evaluation method for the freezing process of tunnels constructed by the artificial freezing method is proposed, and its steps are as follows:

[0098] S1. Obtain the geological exploration data and soil design parameters of the freezing area 3, confirm the different wave velocities between the unfrozen soil and the frozen soil, and determine the underground area and surface area that need to be artificially frozen.

[0099] S2. Construct temperature measurement holes in the underground area according to the construction drawings, correctly operate and arrange temperature sensors, and ensure stable connection of the lines and equipment.

[0100] S3. When starting to freeze, in the surface area, according to the four-electrode Wenner array principle, determine the total length L of the measuring line 2, the electrode measurement point distance x, the electrode distance a, and the isolation coefficient n, determine the measuring area measurement point positions, predict the required detection depth Hmax, and select the pole arrangement method.

[0101] S4. Lay the measuring line 2 and install the electrodes at the measurement point positions. Connect the measuring line 2, the electrodes, the programmed multi-channel electrode conversion device 4, the high-density electrical method host 5, and the data acquisition system 10 through cables to automatically and quickly collect the apparent resistivity data of different depths in the artificial freezing area.

[0102] S5. Use the data processing system 11 to process the collected apparent resistivity, perform two-dimensional inversion calculation on the apparent resistivity, analyze the apparent resistivity characteristics of the artificial freezing area at different depths, and obtain the cross-sectional distribution map of the apparent resistivity isolines of the high-density electrical method in the artificial freezing area;

[0103] S6. Organize and analyze the temperature monitoring data, resistance monitoring data, and data on the change of the freezing condition with the number of days during the freezing process;

[0104] S7. According to the construction drawings, accurately add the monitoring data and the layout information of the underground freezing equipment into different modules of the simulation model, and adjust the simulation parameters and other details;

[0105] S8. Through the interactive verification between the simulation model and the monitoring data, determine the relationship between the resistivity monitoring data and the freezing process, and realize the visualization and accurate evaluation of the freezing process of the tunnel constructed by the artificial freezing method.

[0106] This embodiment provides a combination of the conventional method of monitoring and predicting the formation of the freezing curtain by temperature sensors and the resistance method, and introduces the evaluation and prediction of computer simulation software, which can achieve an unprecedented accurate and comprehensive monitoring. Moreover, the protection scope of the present invention is not limited to the described embodiment.

[0107] The above-described embodiments are only used to describe the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for accurately evaluating the freezing process of a tunnel constructed by an artificial freezing method, characterized in that: include: S1, obtain geological exploration data and soil design parameters of the frozen area, confirm the different wave velocities between unfrozen soil and frozen soil, and determine the underground area and surface area that need to be artificially frozen; S2: construct temperature measuring holes in the underground area according to the design drawings, lay out the temperature monitoring unit and the resistance monitoring unit, and ensure that the lines are stably connected to the equipment; S3, collating and analyzing the temperature monitoring data, resistivity monitoring data and data on the change of freezing conditions over the days during the freezing process; S4, according to the construction drawings, adding the monitoring data and underground freezing equipment layout information to different modules of the multi-physics field numerical simulation analysis unit, and adjusting the simulation parameters and other details; S5, through interactive verification of monitoring data and simulation model, the relationship between resistivity monitoring data and freezing process is determined, and the freezing process of tunnels constructed by artificial freezing method can be visualized and accurately evaluated.

2. The method for accurately evaluating the freezing process of a tunnel constructed by artificial freezing method according to claim 1 is characterized in that: The monitoring method of the temperature monitoring unit and the resistance monitoring unit includes: S1, reasonably arrange temperature measuring holes in the tunnel and install underground temperature sensors to monitor the temperature and calculate the thickness of the frozen wall; S2, conducting resistivity monitoring at the location where the frozen wall is formed in the frozen zone strata; S3, construct the "water-heat-force" tunnel freezing model according to the geological report; S4, evaluating the freezing process based on the temperature monitoring data and resistivity monitoring data feedback; S5, real-time monitoring data during tunnel construction to verify and visualize the "water-heat-force" tunnel freezing model.

3. The method for accurately evaluating the freezing process of a tunnel constructed by artificial freezing method according to claim 2 is characterized in that: In step S4, it is required to construct a three-dimensional artificial freezing model for the area to be tested, and the artificial freezing model and the mechanics, temperature and seepage modules jointly construct a multi-physics field simulation model.

4. The method for accurately evaluating the freezing process of a tunnel constructed by artificial freezing method according to claim 1 is characterized in that: The monitoring method of the resistance monitoring unit is an operation method based on high-density electrical detection of an artificial freezing process, comprising the following steps: S1, obtain geological exploration data and soil design parameters of the frozen area and determine the high-density electrical measurement area; S2, according to the principle of four-electrode Wenner array, determine the total length of the measuring line L, the electrode measuring point distance x, the electrode distance a and the isolation coefficient n, and then determine the location of the measuring point in the measuring area, and calculate the maximum detection depth Hmax according to the following formula: Hmax=a / 2=nx / 2; S3, judging whether the maximum detection depth Hmax obtained by the traditional surface electrode arrangement method can meet the detection requirements. When Hmax is not less than the depth h of the underground frozen area, the surface electrode arrangement method is used to install the electrodes, and the surface electrodes are arranged along the top of the artificial frozen area; when Hmax is less than the depth h of the frozen area, the underground electrode arrangement and the surface electrode arrangement method are combined to install the electrodes, and the surface electrodes are arranged along the top of the artificial frozen area, and the underground electrodes are located below the corresponding surface electrodes; S4, laying out the measuring lines and installing the electrodes at the measuring points to form a measuring network; S5, connect the surface electrodes, underground electrodes, program-controlled multi-channel electrode conversion device, high-density electrical method host and data acquisition system through cables to automatically collect apparent resistivity data at different depths in the artificial freezing area; S6, using a data processing system to process the acquired apparent resistivity, and then performing a two-dimensional inversion calculation, analyzing the apparent resistivity characteristics of artificially frozen areas at different depths, obtaining a high-density electrical method apparent resistivity contour line cross-section distribution map of the artificially frozen area, and determining a distribution pattern of the apparent resistivity in the artificially frozen area; S7, conduct regular inspections, compare high-density electrical detection images of different freezing days, analyze the inverted two-dimensional apparent resistivity contour line section distribution map and distribution pattern, compare with the design drawings of the artificial freezing area of ​​the construction site, and detect whether the freezing situation in the artificial freezing area meets expectations based on the apparent resistivity contour line section distribution map, and detect and pay attention to the freezing problems found in real time.

5. The method for accurately evaluating the freezing process of a tunnel constructed by the artificial freezing method according to claim 4 is characterized in that: In step S4, the number of the measuring lines and the number of the electrodes are both multiple, and the multiple measuring lines and the multiple electrodes can be arbitrarily expanded according to the measuring area range, the working surface size and the detection accuracy.

6. The method for accurately evaluating the freezing process of a tunnel constructed by artificial freezing method according to claim 4 is characterized in that: The data processing system includes a computer, a color printer, a color plotter and a color display screen. The collected apparent resistivity data is transmitted to the computer via a high-density host computer, pre-processed by two-dimensional inversion calculation and displayed as a distribution map of apparent resistivity contour lines. After being offline, various result drawings can be automatically drawn and printed.

7. The method for accurately evaluating the freezing process of a tunnel constructed by artificial freezing method according to claim 1 is characterized in that: The working method of the multi-physics field numerical simulation analysis unit, The following steps are involved: S1, based on the soil property parameters obtained from the geological monitoring report and the initial data from the initial equipment experimental monitoring, a multi-physics field numerical simulation model is constructed; S2, according to the construction soil, add all the buildings and construction equipment that can affect the freezing process in the freezing construction area to the model, add the freezing pipe position to the model according to the drawings, and determine the refrigerant circulation path according to the working status of the freezer; S3, verify the operation accuracy of the model based on the temperature monitoring data and resistivity monitoring data, and evaluate the freezing process; S4, after the multi-physics field numerical simulation model is established accurately, the freezing state of the tunnel on each simulated day can be used for real-time monitoring.

8. An accurate evaluation system for the freezing process of a tunnel constructed by artificial freezing method, characterized in that: include: The temperature monitoring unit is used to collect temperature data at different times during the freezing process; The resistance monitoring unit is used to record the visual data of the gradual change of resistance caused by the freezing of water in the underground soil at different times during the freezing process; The multi-physics field numerical simulation analysis unit is used to establish a simulation model by combining the texture report with the data collected by the temperature monitoring unit and the resistance monitoring unit, and to use the simulation model to predict the freezing state of the tunnel at various days after freezing in combination with the temperature and resistance trends.

9. The accurate evaluation system for freezing process of tunnels constructed by artificial freezing method according to claim 8 is characterized in that: The temperature monitoring unit includes a temperature sensor, a moisture sensor, a pore pressure sensor, a temperature sensing data line and a data acquisition instrument; the resistance monitoring unit includes a resistivity test probe, a resistivity sensing data line and a resistivity acquisition and analysis module; the multi-physical field numerical simulation and analysis unit includes a physical parameter output module, a physical modeling module and a data output module.

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