A method and system for early warning of settlement trend of a shield construction crossing a levee

Abstract

The application belongs to the technical field of shield construction, and discloses a method and system for early warning of settlement trend of shield construction crossing a dam; the method comprises the following steps: collecting silt layer geological data before the shield crosses the dam, and analyzing to obtain the distribution range and sensitivity level of the silt layer; collecting the tunneling parameters in real time in units of each ring when the shield machine crosses the silt layer section, and analyzing to obtain the disturbance index; collecting the real-time tunneling speed and the cutter head rotating speed, and recording the shutdown parameters when the complete shutdown condition is met; collecting the slurry tank pressure and the shutdown duration during shutdown, and calculating the pressure data; for the current sensitivity level, the preset hierarchical early warning rule is adopted, the current disturbance index basic threshold is corrected to obtain the corresponding dynamic threshold, the pressure data is compared with the dynamic threshold, and the early warning is issued according to the preset trigger logic classification; and the application improves the safety of shield construction crossing the dam.

Description

Technical Field

[0001] This application relates to the field of tunnel boring machine (TBM) construction technology, and more specifically, to a method and system for early warning of settlement trends during TBM tunneling through a levee. Background Technology

[0002] Chinese patent application CN118189889A discloses a method for monitoring lakebed settlement during tunnel boring machine (TBM) crossing an artificial lake: Step A: Establish a benchmark control network, including elevation benchmarks, working benchmarks, and monitoring points; Step B: Set up monitoring points along the tunnel main line within the lakebed area, with one monitoring point buried every 20m along the route; Step C: Monitor lakebed settlement using electronic distance measurement trigonometric leveling, employing a Leica TCRP1201+ total station mounted between the elevation benchmarks and monitoring points to measure the elevation differences from the benchmarks to the station and from the monitoring points, respectively, according to a set monitoring frequency. The data is automatically transmitted to the database management system. Step D: Collect the distance before and after the tunnel boring machine (TBM) reaches the artificial lake. The monitoring frequency changes with the distance: when the distance before and after the TBM reaches the artificial lake is >50m, the data monitoring frequency is once every 3 days; when the distance before and after the TBM reaches the artificial lake is ≥20m and <50m, the data monitoring frequency is twice every day; when the distance before and after the TBM reaches the artificial lake is <20m, the data monitoring frequency is three times every day. Here, d represents days. Step E: The database management system verifies and organizes the original elevation data, calculates and saves the elevations of the monitoring points, and uses comparative and graphical methods to analyze the magnitude, variation patterns, and development trends of the elevation data values ​​of each monitoring point in order to assess the safety status of the project and make decisions on the measures to be taken.

[0003] The aforementioned methods monitor surface subsidence, tracking lakebed deformation through high-frequency or low-frequency elevation measurements. However, in the special case of shield tunneling through silty sand layers, these layers exhibit significant thixotropic properties. When the tunnel boring machine (TBM) stops completely for any reason, the soil in front of the tunnel face may experience structural strength loss or even instantaneous liquefaction within minutes to tens of minutes. During this process, surface subsidence often shows no significant change due to the arching effect of the soil. In other words, surface subsidence is a lagging indicator after ground deformation occurs and cannot provide effective mechanical precursor information at the ignition stage of liquefaction risk. Consequently, by the time the system detects abnormal subsidence, the liquefaction event may have already occurred or is about to occur, rendering the early warning function essentially ineffective.

[0004] In summary, existing technologies lack specific design considerations for the thixotropic properties of soil when dealing with the shutdown situation of shield tunneling through silty sand layers, resulting in a lack of early warning capabilities for the risk of instantaneous liquefaction.

[0005] In view of this, this application proposes a method and system for early warning of settlement trends during shield tunneling through embankments to solve the above problems. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method and system for early warning of settlement trends during shield tunneling through embankments. This method involves obtaining the sensitivity level of the silty sand layer before the shield tunnels pass through it, calculating the tunneling disturbance index in real time during the tunneling process, and collecting high-frequency data on the pressure in the slurry chamber during a complete shutdown to obtain the instantaneous pressure change rate and cumulative pressure drop. Based on the sensitivity level, disturbance index, and shutdown duration, the pre-calibrated foundation threshold is dynamically corrected. After comparing the pressure characteristic quantities with the dynamic threshold, a graded warning is issued. This transforms the warning basis from lagging surface settlement to real-time slurry chamber pressure response, and enables the warning threshold to dynamically and adaptively adjust according to the degree of soil disturbance and thixotropic recovery state. This allows for accurate identification of risks at the pre-thixotropic liquefaction stage of the silty sand layer, effectively avoiding false alarms under low-disturbance conditions and missed alarms under high-disturbance conditions, thus improving the technical effect of enhancing the safety of shield tunneling through embankments.

[0007] This application provides the following technical solution: a method and system for early warning of settlement trends during shield tunneling through a levee, comprising:

[0008] Before the shield tunnel passes through the embankment, geological data of the silty sand layer is collected and analyzed to obtain the distribution range and sensitivity level of the silty sand layer.

[0009] Based on the distribution range, when the tunnel boring machine passes through the silty sand layer, the tunneling parameters are collected in real time on a per-ring basis, and the disturbance index of each ring is calculated based on the tunneling parameters.

[0010] During the tunnel boring machine's passage through the silty sand layer, the tunneling speed and cutterhead rotation speed are collected in real time. When the tunneling speed and cutterhead rotation speed meet the preset complete shutdown conditions, the shutdown time, the pressure of the slurry chamber before shutdown, the current sensitivity level, and the current disturbance index are recorded. During the shutdown, the pressure of the slurry chamber is collected, the shutdown duration is calculated based on the shutdown time, the cumulative pressure drop is calculated based on the difference between the pressure of the slurry chamber before shutdown and the current pressure of the slurry chamber, and the instantaneous pressure change rate is calculated based on the pressure difference of the slurry chamber at adjacent times.

[0011] For the current sensitivity level, the pre-calibrated basic threshold is corrected once based on the current disturbance index to obtain the corrected threshold. Then, the corrected threshold is corrected a second time based on the downtime to obtain the dynamic threshold. The instantaneous pressure change rate and cumulative pressure drop are compared with the corresponding dynamic thresholds, and warnings are issued in stages according to the preset trigger logic.

[0012] A system for early warning of settlement trends during shield tunneling through a levee, comprising the implementation of a method for early warning of settlement trends during shield tunneling through a levee, including:

[0013] Sensitivity Analysis Module: Before the shield tunnel passes through the embankment, geological data of the silty sand layer is collected and analyzed to obtain the distribution range and sensitivity level of the silty sand layer;

[0014] Disturbance analysis module: When the tunnel boring machine passes through the silty sand layer, the tunneling parameters are collected in real time on a ring-by-ring basis, and the disturbance index of each ring is calculated based on the tunneling parameters;

[0015] Pressure Analysis Module: During the tunnel boring machine's passage through silty sand layers, the module collects the tunneling speed and cutterhead rotation speed in real time. When the tunneling speed and cutterhead rotation speed meet the preset complete shutdown conditions, it records the shutdown time, the slurry chamber pressure before shutdown, the current sensitivity level, and the current disturbance index. During shutdown, the module collects the slurry chamber pressure, calculates the shutdown duration based on the shutdown time, calculates the cumulative pressure drop based on the difference between the slurry chamber pressure before shutdown and the current slurry chamber pressure, and calculates the instantaneous pressure change rate based on the pressure difference between adjacent slurry chamber times.

[0016] Early warning analysis module: For the current sensitivity level, the pre-calibrated basic threshold is corrected once based on the current disturbance index to obtain the corrected threshold. Then, the corrected threshold is corrected a second time based on the downtime to obtain the dynamic threshold. The instantaneous pressure change rate and cumulative pressure drop are compared with the corresponding dynamic thresholds, and early warnings are issued according to the preset trigger logic.

[0017] The technical effects and advantages of the method and system for early warning of settlement trends during shield tunneling through embankments, as described in this application, are as follows:

[0018] By conducting high-frequency continuous monitoring of the pressure in the mud-water chamber during shutdown and calculating the instantaneous pressure change rate and cumulative pressure drop, the lagging monitoring of surface subsidence in the prior art can be transformed into real-time monitoring of the pressure inside the chamber. Since pressure drop is a direct precursor to the loss of structural strength of silt layers, this application enables risk signals to be captured before liquefaction occurs, avoiding the early warning lag problem caused by relying solely on surface subsidence monitoring in the prior art, thereby improving the timeliness of risk identification.

[0019] By automatically triggering the monitoring program at the moment of shutdown and recording pressure changes in real time at a basic sampling interval, and by encrypting the sampling when the data fluctuation exceeds the standard, it can cover the risk window from the initiation to the development of thixotropic liquefaction in silt layer. This design can compress the monitoring cycle of days in the existing technology to minutes, solve the problem that low-frequency monitoring cannot capture the breakpoint of instantaneous changes, and enable the early warning system to truly have the ability to respond to short-term risks.

[0020] By introducing sensitivity level correction, disturbance index correction, and downtime correction, a multi-factor fusion dynamic threshold generation mechanism is constructed. Specifically, based on the basic threshold calibrated by indoor tests, the sensitivity level is first corrected according to the current face sensitivity level, then the disturbance level is corrected according to the degree of previous tunneling disturbance, and finally the downtime correction is made according to the soil strength recovery characteristics during downtime. This allows the warning threshold to be dynamically adjusted with the risk level. This avoids the shortcomings of existing technologies where static thresholds are prone to false alarms under low disturbance conditions and prone to missed alarms under high disturbance conditions, thus improving the accuracy of warning judgment.

[0021] By storing the disturbance correction parameters and thixotropic recovery parameters calibrated indoors as initial values ​​into the system, and then dynamically calibrating the parameters using measured data during subsequent construction, a closed-loop processing chain of calibration, application, feedback, and optimization is formed. This mechanism enables the early warning rules to be continuously iterated and optimized as the project progresses, avoiding the problem of model parameters being out of sync with the actual site conditions, and enhancing the adaptability and stability of the method in different projects.

[0022] In summary, this application is not merely a simple improvement on traditional settlement monitoring methods, but rather, focusing on the specific scenario of liquefaction risk during shutdown of silty sand layers, it constructs a complete processing chain encompassing pressure precursor capture, instantaneous response monitoring, dynamic threshold correction, and parameter closed-loop optimization. This enables the early warning results to accurately reflect the real-time state of the soil, thereby improving the safety of shield tunneling through embankments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a method for early warning of settlement trend during shield tunneling through a levee, as described in this application.

[0024] Figure 2 This is a schematic diagram of the method for obtaining the dynamic threshold in this application;

[0025] Figure 3 This is a schematic diagram of the method for issuing early warnings according to preset triggering logic levels in this application;

[0026] Figure 4 This is a schematic diagram of a shield tunneling settlement trend early warning system for crossing a levee, as described in this application. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Example 1

[0029] Please see Figure 1 As shown in the figure, this embodiment provides a method for early warning of settlement trend during shield tunneling through a levee, including:

[0030] Before the shield tunnel passes through the embankment, geological data of the silty sand layer is collected and analyzed to obtain the distribution range and sensitivity level of the silty sand layer.

[0031] In one specific implementation, boreholes are drilled and sampled, and exploration boreholes are laid out according to the requirements of relevant geotechnical engineering investigation specifications, with increased density of boreholes at the interface between the silt layer and adjacent strata. Geological logging is performed on the borehole cores to determine the top and bottom burial depths of the silt layer in each borehole, and the thickness of the silt layer at each borehole location is calculated. Based on the top and bottom burial depth data of each borehole, an interpolation method is used to draw a geological profile along the shield tunneling axis, determining the continuous distribution range, thickness variation, and burial depth variation of the silt layer along the tunneling direction. Unconfined silt samples are taken, and unconfined compressive strength tests are conducted according to relevant geotechnical testing method standards. The unconfined compressive strength of undisturbed soil and remolded soil is measured separately, and the ratio of the unconfined compressive strength of undisturbed soil to that of remolded soil is calculated as the thixotropic sensitivity.

[0032] Based on sensitivity, silty sand layers are divided into three sensitivity levels. Specifically, when the sensitivity is below the first sensitivity threshold, it is classified as low sensitivity; when the sensitivity is not lower than the first sensitivity threshold and not higher than the second sensitivity threshold, it is classified as medium sensitivity; and when the sensitivity is higher than the second sensitivity threshold, it is classified as high sensitivity. The method for setting the first and second sensitivity thresholds is as follows: the critical pressure drop of liquefaction of soil samples with different sensitivities is measured through laboratory tests. The sensitivity threshold at which a significant change in liquefaction risk occurs is used as the classification threshold. The critical pressure drop of liquefaction measured by laboratory tests is used as the indicator. When the change in sensitivity causes a change in the critical pressure drop of liquefaction exceeding ±15%, or other engineering experience values, such as ±20%, it is judged as a significant change, and this is used as the basis for the sensitivity level classification. The silty sand layer segment classification results and sensitivity levels are entered into the geological database of the shield tunneling construction management system.

[0033] Based on the distribution range, when the tunnel boring machine passes through the silty sand layer, the tunneling parameters are collected in real time on a per-ring basis, and the disturbance index of each ring is calculated based on the tunneling parameters.

[0034] In a specific implementation, tunneling parameters are collected in real time on a per-ring basis, and torque and speed data are collected synchronously at the same time. The tunneling parameters include cutterhead torque, cutterhead speed, and total thrust. The tunneling parameters are normalized to obtain normalized tunneling parameters, and the ratio of the tunneling parameters to the standard tunneling parameters is used as the normalized tunneling parameters.

[0035] The actual cutting power of the cutter head is calculated based on the cutter head torque and speed; for example, at the current moment... Actual cutting power ,in, For the first The torque of the ring cutter head; For the first Rotation speed of the ring cutter head;

[0036] The reference cutting power is calculated based on the normalized cutter head torque and normalized cutter head speed; such as the reference cutting power ,in, This is the normalized cutterhead torque; This is the normalized cutter head speed;

[0037] The single-ring disturbance index is calculated based on the actual cutting power of the cutter head, the reference cutting power, the total thrust, and the normalized total thrust. Specifically, the ratio of the actual cutting power of the cutter head to the reference cutting power is calculated to obtain the power ratio; the ratio of the total thrust to the normalized total thrust is calculated to obtain the thrust ratio; and the weighted sum of the power ratio and the thrust ratio is calculated to obtain the single-ring disturbance index.

[0038] The sum of the weighted weights of the power ratio and thrust ratio is 1, and these weights can be obtained through experimental statistics. Specifically, a shield tunneling shutdown liquefaction simulation test system is used. Through statistical analysis of experimental data, multiple regression is performed with the normalized values ​​of shear power and thrust as independent variables and the critical liquefaction intensity as the dependent variable. After normalizing the regression coefficients, the weighted coefficients of the power ratio and thrust ratio are obtained. For different sensitivity levels, the weighted coefficients can be calibrated through targeted tests. Specifically, undisturbed silty sand samples from the shield tunneling section are taken, and their basic physical and mechanical parameters are measured. Based on the dry density at the site, the soil samples are layered and filled into the model box to prepare three groups of soil samples: low sensitivity, medium sensitivity, and high sensitivity, with no less than three samples in each group. A penetrometer is used to simulate shield tunneling disturbances at different frequencies and penetration depths, and the cutterhead torque, cutterhead speed, total thrust, and corresponding normalized values ​​are recorded for each group of tests. Multiple disturbance intensities were set, each repeated three times. After each disturbance, a certain period of time was stopped, and the pore water pressure buried in the soil sample was monitored in real time. When the pore pressure drop rate continuously exceeded the pore pressure drop rate threshold for a preset duration, such as 5 seconds, and the cumulative drop exceeded the cumulative drop threshold, it was determined that the critical liquefaction state had been reached. The corresponding power ratio and thrust ratio were recorded. Using the power ratio Pratio and thrust ratio Tratio at the critical liquefaction state as independent variables and the critical liquefaction intensity Scrit as the dependent variable, a multiple linear regression model was established: Scrit = a × Pratio + b × Tratio + ε; where a and b are regression coefficients, and ε is the error term. The regression coefficients of the multiple linear regression model were solved and... Normalization is performed to obtain A and B, which are the normalized regression coefficients. Based on A and B, the power ratio weighting coefficient and thrust ratio weighting coefficient are calculated. The power ratio weighting coefficient is the ratio of |A| to |A|+|B|, and the thrust ratio weighting coefficient is the ratio of |B| to |A|+|B|. Where |A| is the absolute value of A, and |B| is the absolute value of B. The above steps are repeated for soil samples with low, medium, and high sensitivity levels to obtain three sets of weighting coefficients. The calibration results are stored in the shield tunneling construction management system. In actual early warning, the corresponding weighting coefficient is called according to the current sensitivity level of the tunnel face.

[0039] The disturbance index of each ring is continuously recorded, and the moving average of the disturbance index of the most recent preset number of rings is taken as the disturbance index at the current moment. The preset number of rings is set by collecting the disturbance index data of each ring when the tunnel boring machine is tunneling normally in the silty sand layer and calculating its autocorrelation coefficient. ,in, For the first The single-ring perturbation index of the ring; The mean of the sequence. For the number of lag rings, Let be the total number of rings in the sample. At a significance level of 0.05, the critical value is... Take the satisfied The largest The value serves as the upper limit of the significantly correlated ring number range for the disturbance index. Based on the tunneling speed v and the segment ring width L, the ratio of the segment ring width to the tunneling speed is calculated to obtain the single-ring tunneling time. The formation disturbance response time is obtained by calibration using on-site pore water pressure monitoring data. The ratio of the formation disturbance response time to the single-ring tunneling time is calculated to obtain the response ring number. The preset ring number is set to the value 3, the upper limit of the significantly correlated ring number range, and the maximum value among the response ring numbers to ensure that the moving average can smooth short-term fluctuations and reflect recent changes in disturbance trends in a timely manner.

[0040] The relationship between the tunnel boring machine's excavation speed and the ground disturbance response time is determined to ensure that the moving average can smooth short-term fluctuations while reflecting recent changes in disturbance trends in a timely manner. The ground disturbance response time is defined as the time interval from the change in the tunnel boring machine's excavation parameters to the occurrence of a measurable response in the ground pressure or displacement. This time interval can be obtained through inversion of field monitoring data or numerical simulation, and can be taken as 5 to 15 minutes, and adjusted according to actual geological conditions.

[0041] During the tunnel boring machine's passage through the silty sand layer, the tunneling speed and cutterhead rotation speed are collected in real time. When the tunneling speed and cutterhead rotation speed meet the preset complete shutdown conditions, the shutdown time, the pressure of the slurry chamber before shutdown, the current sensitivity level, and the current disturbance index are recorded. During the shutdown, the pressure of the slurry chamber is collected, the shutdown duration is calculated based on the shutdown time, the cumulative pressure drop is calculated based on the difference between the pressure of the slurry chamber before shutdown and the current pressure of the slurry chamber, and the instantaneous pressure change rate is calculated based on the pressure difference of the slurry chamber at adjacent times.

[0042] In one specific implementation, the shutdown defined in this embodiment specifically refers to a complete shutdown state, that is, a working condition in which both propulsion and rotation have stopped; when the complete shutdown condition is met, it is determined to be a complete shutdown; the method for setting the complete shutdown condition is as follows: the tunneling speed is continuously lower than a preset speed threshold for a preset duration, and the cutterhead rotation speed is zero; wherein, the method for setting the preset duration and the preset speed threshold is as follows: determined based on the duration of the normal shutdown process of the tunnel boring machine and the measurement accuracy of the speed sensor, such as statistically analyzing the distribution of the duration from deceleration to complete stop during the normal shutdown process of the tunnel boring machine, and taking the 95th percentile as the preset duration; combined with the measurement accuracy of the speed sensor, the speed threshold is set to 3 times the upper limit of the sensor noise; to ensure that the complete shutdown state can be accurately identified, and to avoid misjudging short pauses or speed fluctuations as shutdown.

[0043] Once a shutdown is determined, the system automatically triggers the shutdown liquefaction risk warning procedure and performs the following initialization operations: records the shutdown time; records the slurry chamber pressure at the last moment before shutdown; obtains the sensitivity level of the silt layer at the current working face location; obtains the current disturbance index; starts the pressure monitoring timer during shutdown and sets the sampling interval; the sampling interval is set according to the evolution rate of the thixotropic liquefaction risk of the silt layer. For example, the initial sampling interval can be set to 1-5 seconds, and then dynamically adjusted according to the actual pressure change rate. If the instantaneous pressure change rate exceeds 50% of the basic threshold for three consecutive sampling moments, it will be automatically encrypted to 0.5-1 seconds; if the pressure change rate is consistently lower than 10% of the basic threshold, it can be relaxed to 10-30 seconds to ensure that early signals of pressure changes can be captured.

[0044] The pressure in the slurry tank is continuously recorded at preset sampling intervals. For each sampling moment, two characteristic quantities are calculated: the instantaneous pressure change rate and the cumulative pressure drop. Specifically, the pressure difference between the current sampling moment and the previous sampling moment, as well as the time difference between the current sampling moment and the previous sampling moment, are calculated. The ratio of the pressure difference to the time difference is calculated to obtain the instantaneous pressure change rate. The difference between the slurry tank pressure at the last moment before shutdown and the slurry tank pressure at the current sampling moment is calculated to obtain the cumulative pressure drop. All calculation results are stored in the monitoring database in real time.

[0045] For the current sensitivity level, the pre-calibrated basic threshold is corrected once based on the current disturbance index to obtain the corrected threshold. Then, the corrected threshold is corrected a second time based on the downtime to obtain the dynamic threshold. The instantaneous pressure change rate and cumulative pressure drop are compared with the corresponding dynamic thresholds, and warnings are issued in stages according to the preset trigger logic.

[0046] In one specific implementation, the basic threshold includes a primary basic threshold, a secondary basic threshold, and a tertiary basic threshold; the method for pre-calibrating the basic threshold includes:

[0047] The basic threshold values ​​for low-sensitivity, medium-sensitivity, and high-sensitivity silty sand layers were calibrated through indoor thixotropic liquefaction simulation tests. The test procedure was as follows: using a shield tunneling machine shutdown liquefaction simulation test system, undisturbed silty sand soil samples were taken from the site and layered in a model box according to the dry density at the site; pore water pressure gauges were installed at different depths; the soil was penetrated by a penetrometer at a preset frequency, and the number of penetrations was adjusted to simulate different disturbance intensities; after each round of disturbance, the soil was stopped for a certain period of time, and the pore pressure changes were recorded; when the pore pressure drop rate exceeded the pore pressure drop rate threshold within a preset duration, and the cumulative drop exceeded the cumulative threshold value, the liquefaction threshold was determined. When the pressure drop threshold is reached, it is considered to have reached the critical liquefaction state. The instantaneous pressure change rate corresponding to the critical liquefaction state is used as the first-level basic threshold, and the corresponding cumulative pressure drop is used as the first-level cumulative pressure drop basic threshold. The first-level basic threshold is expanded by a preset multiple to obtain the second-level and third-level basic thresholds. The preset duration is set as follows: the preset duration should include at least 3-5 consecutive sampling intervals to ensure that a stable downward trend can be identified. The preset multiple is set as follows: based on experimental statistics, the average pressure change multiple required to trigger a higher level of liquefaction risk is taken.

[0048] In one specific implementation, refer to Figure 2 Methods for obtaining dynamic thresholds include:

[0049] Obtain the base threshold corresponding to the current working face based on the current sensitivity level of the working face;

[0050] Based on the current disturbance index, a preset disturbance correction function is used to calculate the disturbance correction coefficient. The product of the disturbance correction coefficient and the base threshold is then calculated to obtain the correction threshold. A preset disturbance correction function is used to describe the relationship between the disturbance correction coefficient and the disturbance index, ensuring that the disturbance correction coefficient is within a reasonable range. For example, an S-shaped curve function can be used to describe the disturbance correction coefficient. With Disturbance Index The relationship between the disturbance correction coefficients ;in, The parameters are adjusted to control the curve steepness. The inflection point of the function, i.e. corresponding Value; Parameter , The pre-defined disturbance correction function was determined by fitting data from indoor model tests. The method for setting the form and parameters of the pre-defined disturbance correction function was as follows: Multiple sets of tests with different disturbance intensities were conducted using indoor model tests. The disturbance index and the pressure drop threshold multiple required to trigger liquefaction were recorded for each set of tests. The pre-defined disturbance correction function curve was fitted using a nonlinear least squares method, with the goodness of fit not lower than the pre-defined threshold. The pre-defined threshold was set based on statistical or engineering experience. Simultaneously, a lower limit for the disturbance index was set, determined by selecting a value where the impact of tunneling disturbance on liquefaction risk is negligible when the disturbance index is below the lower limit, based on experimental statistics. The critical point is negligible. For example, through indoor tests, the pressure drop threshold multiple required to trigger liquefaction under different disturbance indices is measured. When the disturbance index is below a certain critical value, the pressure drop threshold multiple no longer increases significantly as the disturbance index decreases. For example, if the rate of change is less than or equal to 5%, the critical value at this time is the lower limit of the disturbance index, with a typical range of 0.2-0.4. When the current disturbance index is not greater than the lower limit of the disturbance index, the disturbance correction coefficient is directly set to the preset relaxation value. The preset relaxation value is set by determining the threshold amplification multiple measured by the liquefaction risk test under extremely low disturbance conditions, with a general range of 1.0-1.5.

[0051] During the shutdown, the shear strength of the disturbed silty sand layer will gradually recover with the resting time due to its thixotropic properties, thereby reducing the risk of liquefaction; by using the shutdown duration correction coefficient, the correction threshold is further corrected to make the early warning rules more in line with the actual evolution of the soil.

[0052] Original silty soil samples were taken from the shield tunnel section, and multiple sets of reshaped samples were prepared. After being left to stand for different durations, unconfined compressive strength tests were conducted. The strength recovery ratio for each standing time was calculated based on the strength within a preset time after the disturbance ended.

[0053] Retention time and intensity recovery ratio The experimental data are fitted to a strength recovery ratio function, preferably an exponential decay function, whose parameters are obtained through nonlinear regression. Alternatively, the data can be fitted to a hyperbola or exponential function, such as the strength recovery ratio function. ;in, The downtime is calculated from the moment of downtime. The limiting recovery ratio represents the maximum multiple by which the soil strength recovers relative to its initial strength after a sufficiently long settling time. This reflects the thixotropic recovery potential of the soil. It is a mathematical constant; The recovery rate coefficient controls how fast the intensity recovers; the larger the value, the faster the recovery. At the moment of shutdown, the strength recovery ratio is 1, meaning there is no recovery. The least squares method is used to perform nonlinear regression on the experimental data to obtain parameter estimates for the silt layer, specifically including the limiting recovery ratio and the recovery rate coefficient. The goodness of fit is required to be no less than a preset threshold, and the relative standard error of the parameters is required to be no greater than a preset error threshold. The relative standard error of the parameters is the ratio of the parameter standard error to the absolute value of the parameter estimate. The preset threshold and its setting method are based on statistical or engineering experience. The shutdown duration correction coefficient is defined as the strength recovery ratio. The product of the correction threshold and the shutdown duration correction coefficient is calculated to obtain the dynamic threshold.

[0054] Reference Figure 3 The methods for issuing warnings according to preset trigger logic include:

[0055] At each sampling time, the instantaneous pressure change rate is calculated. and cumulative pressure reduction The dynamic threshold is compared with the instantaneous pressure change rate dynamic threshold and the cumulative pressure drop dynamic threshold, and an early warning is triggered according to the early warning logic. In this embodiment, the term "dynamic threshold" is a general term, specifically including the instantaneous pressure change rate dynamic threshold and the cumulative pressure drop dynamic threshold, and specifically including a first instantaneous pressure change rate threshold, a second instantaneous pressure change rate threshold, a first cumulative pressure drop threshold, a second cumulative pressure drop threshold, and a third cumulative pressure drop threshold. The third instantaneous pressure change rate dynamic threshold is not included in the dynamic threshold because the instantaneous pressure change rate... Instead of comparing with dynamic thresholds, using trend judgment, in the extreme and dangerous stage where liquefaction is about to occur, the pressure change rate may have already far exceeded the normal range. The continuous accelerating downward trend itself is the most urgent signal, and it is more reasonable to directly trigger a level three warning.

[0056] Specifically, when the instantaneous pressure change rate When the pressure change rate exceeds the threshold of the first instantaneous pressure for N1 consecutive sampling times, or when the cumulative pressure drop... When the pressure drop is greater than or equal to the first cumulative pressure drop threshold, it is marked as a Level 1 warning. The method for setting N1 is as follows: based on the signal-to-noise ratio of the pressure sensor and the system's allowable false alarm rate, a statistical hypothesis testing method is used to determine it. Specifically, the pressure change rate data when the tunnel boring machine is normally shut down and there is no risk of liquefaction is collected, its standard deviation is calculated, and N1 is set so that the probability of N1 consecutive points exceeding the threshold due to random noise is lower than the preset false alarm rate threshold, thereby effectively suppressing single-point noise false triggering while ensuring the sensitivity of the warning.

[0057] When the instantaneous pressure change rate If the pressure change rate is greater than the second instantaneous pressure change rate threshold for N2 consecutive sampling times, or the cumulative pressure drop... When the pressure drop is greater than or equal to the second cumulative pressure drop threshold, a second-level warning is triggered regardless of whether a first-level warning has already been triggered. The method for setting N2 is as follows: based on the higher urgency of the second-level warning compared to the first-level warning, N2 can be set to a value less than or equal to N1. This is specifically determined through simulating the rapid development of liquefaction, ensuring that a higher-level warning is triggered more quickly when the pressure change rate accelerates. Typically, this is obtained by measuring the time from the start of a rapid pressure drop to reaching a dangerous state through indoor liquefaction simulation tests, dividing by the sampling interval, and rounding down.

[0058] A Level 3 warning is triggered when any of the Level 3 conditions are met: the rate of pressure decrease continues to increase, i.e., the instantaneous pressure change rate over N3 consecutive sampling times... Both are less than the instantaneous pressure change rate of the previous moment. At that time, or the cumulative pressure decreased When the pressure drop exceeds the third cumulative pressure drop threshold, or when the pressure in the slurry tank drops below a preset percentage of the slurry tank pressure before shutdown; N3 is set as follows: based on the physical law that the pressure drop rate before liquefaction usually exhibits a monotonically accelerating trend, N3 must be able to identify a clear monotonically increasing trend rather than short-term fluctuations; by analyzing measured pressure data from historical liquefaction events, the monotonic segment length of the instantaneous pressure change rate sequence is calculated. The monotonic segment length is defined as continuously satisfying the current instantaneous pressure change rate. Greater than the instantaneous pressure change rate of the previous moment The number of sampling points; the method for calculating the length of the monotonic segment is as follows: initialize the length counter to 0; traverse the instantaneous pressure change rate sequence, if the current value is greater than the previous value, then the length is increased by 1, otherwise it is reset to 0; take the lower quartile of the length values ​​of all monotonic segments as the reference value of N3, and adjust it in combination with the sampling interval.

[0059] The early warning system sends warning information to construction management personnel via the control room alarm screen, SMS, and APP, based on the trigger level. The information includes: warning level; shutdown location, sensitivity level, current disturbance index, and shutdown duration; pressure change curve and key data; and the currently used correction coefficient. Simultaneously, the system automatically pushes corresponding handling suggestions. For example, a yellow warning level prompts increased monitoring frequency and preparation of emergency supplies; an orange warning level prompts immediate proactive pressure-maintaining measures and attempts to resume tunneling; and a red warning level prompts immediate activation of the emergency plan and rapid grouting reinforcement.

[0060] Example 2

[0061] Please see Figure 4 As shown in the figure, this embodiment provides an early warning system for settlement trends during shield tunneling through a levee, including:

[0062] Sensitivity Analysis Module: Before the shield tunnel passes through the embankment, geological data of the silty sand layer is collected and analyzed to obtain the distribution range and sensitivity level of the silty sand layer;

[0063] Disturbance analysis module: Based on the distribution range, when the tunnel boring machine passes through the silty sand layer, the tunneling parameters are collected in real time on a ring-by-ring basis, and the disturbance index of each ring is calculated based on the tunneling parameters;

[0064] Pressure Analysis Module: During the tunnel boring machine's passage through silty sand layers, the module collects the tunneling speed and cutterhead rotation speed in real time. When the tunneling speed and cutterhead rotation speed meet the preset complete shutdown conditions, it records the shutdown time, the slurry chamber pressure before shutdown, the current sensitivity level, and the current disturbance index. During shutdown, the module collects the slurry chamber pressure, calculates the shutdown duration based on the shutdown time, calculates the cumulative pressure drop based on the difference between the slurry chamber pressure before shutdown and the current slurry chamber pressure, and calculates the instantaneous pressure change rate based on the pressure difference between adjacent slurry chamber times.

[0065] Early warning analysis module: For the current sensitivity level, the pre-calibrated basic threshold is corrected once based on the current disturbance index to obtain the corrected threshold. Then, the corrected threshold is corrected a second time based on the downtime to obtain the dynamic threshold. The instantaneous pressure change rate and cumulative pressure drop are compared with the corresponding dynamic thresholds, and early warnings are issued according to the preset trigger logic.

[0066] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0067] Finally: The above description is only a preferred embodiment of this application and is not intended to limit this application. 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 method for early warning of settlement trends during shield tunneling through a levee, characterized in that, include: Before the shield tunnel passes through the embankment, geological data of the silty sand layer is collected and analyzed to obtain the distribution range and sensitivity level of the silty sand layer. Based on the distribution range, when the tunnel boring machine passes through the silty sand layer, the tunneling parameters are collected in real time on a per-ring basis, and the disturbance index of each ring is calculated based on the tunneling parameters. During the tunnel boring machine's passage through the silty sand layer, the tunneling speed and cutterhead rotation speed are collected in real time. When the tunneling speed and cutterhead rotation speed meet the preset complete shutdown conditions, the shutdown time, the pressure of the slurry chamber before shutdown, the current sensitivity level, and the current disturbance index are recorded. During the shutdown, the pressure of the slurry chamber is collected, the shutdown duration is calculated based on the shutdown time, the cumulative pressure drop is calculated based on the difference between the pressure of the slurry chamber before shutdown and the current pressure of the slurry chamber, and the instantaneous pressure change rate is calculated based on the pressure difference of the slurry chamber at adjacent times. For the current sensitivity level, the pre-calibrated basic threshold is corrected once based on the current disturbance index to obtain the corrected threshold. Then, the corrected threshold is corrected a second time based on the downtime to obtain the dynamic threshold. The instantaneous pressure change rate and cumulative pressure drop are compared with the corresponding dynamic thresholds, and warnings are issued in stages according to the preset trigger logic.

2. The method for early warning of settlement trend during shield tunneling through a levee according to claim 1, characterized in that, Methods for obtaining dynamic thresholds include: Pre-calibrate the base thresholds for all sensitivity levels, and obtain the corresponding base thresholds for the current working face based on the current sensitivity level of the working face; Based on the current disturbance index, the disturbance correction coefficient is calculated using a preset disturbance correction function, and the basic warning threshold is dynamically corrected for the first time. Based on the downtime, a downtime correction coefficient is calculated using a preset intensity recovery ratio function. The threshold that has undergone the first dynamic correction is then dynamically corrected a second time to obtain a dynamic threshold that varies with downtime.

3. The method for early warning of settlement trend during shield tunneling through a levee according to claim 2, characterized in that, During the first dynamic correction process, when the current disturbance index is lower than the preset lower limit of the disturbance index, the disturbance correction coefficient is directly set to the preset relaxation value.

4. The method for early warning of settlement trend during shield tunneling through a levee according to claim 1, characterized in that, Methods for obtaining the disturbance index include: The tunneling parameters are normalized to obtain normalized tunneling parameters, and the ratio of the tunneling parameters to the standard tunneling parameters is used as the normalized tunneling parameters. The actual cutting power of the cutter head is calculated based on the cutter head torque and cutter head speed. The reference cutting power is calculated based on the normalized cutter head torque and normalized cutter head speed; The single-ring disturbance index is calculated based on the actual cutting power of the cutter head, the reference cutting power, the total thrust, and the normalized total thrust. The single-ring disturbance index of each ring is continuously recorded, and the moving average of the single-ring disturbance index of the most recent preset ring number is taken as the disturbance index at the current moment.

5. The method for early warning of settlement trend during shield tunneling through a levee according to claim 4, characterized in that, Methods for calculating the single-loop perturbation index include: Calculate the ratio of the actual cutting power of the cutter head to the reference cutting power to obtain the power ratio; Calculate the ratio of total thrust to normalized total thrust to obtain the thrust ratio, and calculate the weighted sum of power ratio and thrust ratio to obtain the single-loop disturbance index.

6. The method for early warning of settlement trend during shield tunneling through a levee according to claim 1, characterized in that, The method for setting the shutdown conditions is as follows: the tunneling speed is continuously lower than a preset speed threshold for a preset time period, and the cutterhead rotation speed is zero.

7. The method for early warning of settlement trend during shield tunneling through a levee according to claim 1, characterized in that, Methods for obtaining the instantaneous rate of change of pressure include: Calculate the pressure difference between the current sampling time and the previous sampling time in the mud chamber, as well as the time difference between the current sampling time and the previous sampling time. Calculate the ratio of the pressure difference to the time difference to obtain the instantaneous pressure change rate.

8. The method for early warning of settlement trend during shield tunneling through a levee according to claim 1, characterized in that, Methods for obtaining cumulative pressure drop include: Calculate the difference between the pressure in the mud chamber at the last moment before shutdown and the pressure in the mud chamber at the current sampling moment to obtain the cumulative pressure drop.

9. A method for early warning of settlement trend during shield tunneling through a levee, as described in claim 1, characterized in that, The methods for issuing warnings in tiers based on preset trigger logic include: When the instantaneous pressure change rate is greater than the first instantaneous pressure change rate threshold for N1 consecutive sampling times, or when the cumulative pressure drop is greater than or equal to the first cumulative pressure drop threshold, a level one warning is triggered.

10. A method for early warning of settlement trend during shield tunneling through a levee, as described in claim 9, is characterized in that... The method of issuing warnings in a tiered manner based on preset trigger logic also includes: When the instantaneous pressure change rate is greater than the second instantaneous pressure change rate threshold for N2 consecutive sampling times, or when the cumulative pressure drop is greater than or equal to the second cumulative pressure drop threshold, a second-level warning will be triggered regardless of whether a first-level warning has been triggered.

11. A method for early warning of settlement trend during shield tunneling through a levee, as described in claim 9, is characterized in that... The method of issuing warnings according to the preset trigger logic also includes: when the pressure drop rate continues to increase, that is, when the instantaneous pressure change rate of N3 consecutive sampling times is less than the instantaneous pressure change rate of the previous time, or when the cumulative pressure drop is greater than the third cumulative pressure drop threshold, or when the pressure in the mud and water tank drops to below the preset proportion of the pressure in the mud and water tank before shutdown, a level 3 warning is triggered.

12. A settlement trend early warning system for shield tunneling through a levee, implementing the settlement trend early warning method for shield tunneling through a levee as described in any one of claims 1-11, characterized in that, include: Sensitivity Analysis Module: Before the shield tunnel passes through the embankment, geological data of the silty sand layer is collected and analyzed to obtain the distribution range and sensitivity level of the silty sand layer; Disturbance analysis module: When the tunnel boring machine passes through the silty sand layer, the tunneling parameters are collected in real time on a ring-by-ring basis, and the disturbance index of each ring is calculated based on the tunneling parameters; Pressure Analysis Module: During the tunnel boring machine's passage through silty sand layers, the module collects the tunneling speed and cutterhead rotation speed in real time. When the tunneling speed and cutterhead rotation speed meet the preset complete shutdown conditions, it records the shutdown time, the slurry chamber pressure before shutdown, the current sensitivity level, and the current disturbance index. During shutdown, the module collects the slurry chamber pressure, calculates the shutdown duration based on the shutdown time, calculates the cumulative pressure drop based on the difference between the slurry chamber pressure before shutdown and the current slurry chamber pressure, and calculates the instantaneous pressure change rate based on the pressure difference between adjacent slurry chamber times. Early warning analysis module: For the current sensitivity level, the pre-calibrated basic threshold is corrected once based on the current disturbance index to obtain the corrected threshold, and then the corrected threshold is corrected a second time based on the downtime to obtain the dynamic threshold; the instantaneous pressure change rate and cumulative pressure drop are compared with the corresponding dynamic thresholds respectively, and early warnings are issued according to the preset trigger logic.

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