A permanent and temporary combined U-BIT excavation support system and construction method

Abstract

The present application belongs to the field of rail transit construction technology, and provides a permanent and temporary combined U-BIT excavation support system and construction method, which comprises: the system comprises a temporary support unit, a permanent connection unit and a gap filling and force transmission reinforcing unit. The construction method comprises end reinforcement and portal construction, U-shaped open pipe roof jacking, horizontal MJS temporary transverse support, top gap freezing reinforcement, upper layer soil excavation and temporary steel corbel installation, gap high strength filling, longitudinal concrete corbel construction, permanent and temporary conversion, layered excavation and structure backfilling and transfer floor construction. For the problems of upward floating or lateral instability in the pipe roof jacking stage, the jacking reaction force, displacement and grouting pressure data are collected in real time, the weight value is determined and quantitatively calculated as needed, the safety retest distance is dynamically determined, and the posture prediction model is combined to realize the active pre-control and closed-loop iterative adjustment of the weight strategy.

Description

Technical Field

[0001] This invention belongs to the field of rail transit construction technology, specifically a permanent and temporary combined U-BIT excavation support system and construction method. Background Technology

[0002] With the continuous expansion of urban rail transit networks, convenient transfers have become an important indicator for measuring service levels. However, due to the phased construction of the network and insufficient early planning, many existing operating stations lack provisions for platform-to-platform transfers to later lines. To achieve the construction of new stations that pass directly beneath existing operating stations and create transfer nodes without prior planning, the U-shaped open-top bundled tube jack (U-BIT) construction method has been developed in existing technologies. This method uses longitudinal jacking of square steel tubes and applies prestress laterally to form an integral load-bearing structure, offering advantages such as flexible cross-sections and minimal disturbance.

[0003] However, because the top of the U-shaped open-ended bundled tube curtain is not closed, the top tube section lacks upper restraint during jacking, making it highly susceptible to floating or tilting instability. The traditional approach is to add temporary counterweights to the top of the tube section to suppress instability, but this approach has significant shortcomings: firstly, whether to add counterweights and how much to add often relies on experience and lacks quantitative basis, leading to instability even with insufficient counterweights, or excessive counterweights wasting resources and affecting jacking efficiency; secondly, the lack of dynamic monitoring and advance prediction mechanisms for attitude changes during jacking makes it impossible to adjust the counterweight strategy according to real-time working conditions, and it is also difficult to determine a reasonable retesting step length, resulting in low construction control accuracy and delayed risk response.

[0004] Therefore, the present invention provides a permanent and temporary combined U-BIT excavation support system and construction method. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0006] The technical solution adopted by this invention to solve its technical problem is: a construction method for a permanent and temporary combined U-BIT excavation support system, which involves sequentially jacking in square steel pipe sections to form a U-shaped pipe curtain structure with an open upper part and a closed bottom, including the following steps: Step 1: Collect real-time data during the jacking process of the top pipe section, calculate the jacking reaction force fluctuation coefficient, vertical displacement rate and horizontal displacement rate, and determine whether temporary counterweights need to be added by comparing thresholds. The process for determining whether temporary counterweights need to be added is as follows: Based on real-time data, the jacking reaction force fluctuation coefficient, vertical displacement rate and horizontal displacement rate are calculated with a sliding window of 1m. If the jacking reaction force fluctuation coefficient is greater than 0.25 and meets the condition for two consecutive windows, or the vertical displacement rate is greater than 2 mm / m, or the horizontal displacement rate is greater than 1.5 mm / m, it is determined that temporary counterweights need to be added; otherwise, it is determined that they are not needed. Step 2: If necessary, calculate the required counterweight value based on the stress data of the top pipe section and apply the initial counterweight; Step 3: Based on real-time data during the jacking process of the top pipe section, determine the safe retest distance through stability analysis, which will serve as the benchmark step size for the next retest iteration; Step 4: After the jacking is completed according to the safe retest distance, retest the attitude of the pipe section, establish a displacement-jacking distance regression model, and predict whether the attitude deviation of the top pipe section exceeds the preset threshold before the end of jacking. If it exceeds the threshold, readjust the counterweight value according to the excess amount. Step 5: After each safe retest distance is advanced, repeat steps 2 to 4 to achieve dual dynamic closed-loop adjustment of the pressure value and the retest step length.

[0007] As a further aspect of the present invention: In step one, the real-time data includes jacking reaction force, vertical displacement of pipe section, horizontal displacement of pipe section, and grouting pressure; the jacking reaction force is collected by the pressure sensor of the main jacking cylinder, the vertical displacement is collected by the static level or laser displacement sensor, the horizontal displacement is collected by the laser target or the wire displacement gauge, and the grouting pressure is collected by the pressure sensor of the grouting hole.

[0008] As a further aspect of the present invention: in step two, the force data includes the self-weight of the pipe section, buoyancy, and grouting lifting force; The required counterweight value is calculated based on the equilibrium equations of the vertical force system established by Newton's first law, and the formula is: Required counterweight value ,in For the weight of the pipe section, It is the sum of buoyancy and grouting lifting force. For safety factor; Counterweights are applied by placing counterweights inside the pipe section, installing jacks between the top of the pipe section and the existing base plate, or by using prestressed tendons for tensioning.

[0009] As a further aspect of the present invention: in step three, the process of determining the safe retest distance is as follows: Calculate the acceleration of the displacement rate using a 1m sliding window; if the acceleration is not greater than zero, take the maximum value of 6m for the safe remeasurement distance; if the acceleration is greater than zero, calculate the safe remeasurement distance according to the kinematic equation; calculate the safe remeasurement distance according to the vertical and horizontal displacement rates respectively, and take the smaller value, limiting the range to 1.5m to 6m.

[0010] As a further aspect of the present invention: In step four, the process of predicting the attitude deviation of the top pipe section before the jacking is completed is as follows: After the jacking is completed according to the safety re-measurement distance, the attitude of the pipe section is re-measured, and the jacking distance and attitude deviation are added to the historical data; the correlation is determined according to the Pearson correlation coefficient of the jacking distance and deviation data, and vertical and horizontal displacement-jacking distance regression models are established respectively; the total jacking distance is substituted into the model to predict the final vertical and horizontal deviations before the end of jacking; when the predicted deviation is within ±20mm, the current pressure is maintained, and when it exceeds, adjustment is initiated.

[0011] As a further aspect of the present invention: In step four, if the predicted vertical deviation exceeds the threshold, the vertical excess amount is calculated, and the vertical excess amount is calculated when the upward deviation exceeds the limit. = Submersion exceeding the limit = ; If the predicted level deviation exceeds the threshold, calculate the level excess. ; The counterweight adjustment amount is: ,in, Vertical stiffness Horizontal stiffness; The new weight value is: ,in, Current weight value New weight value.

[0012] As a further aspect of the present invention: In step four, if only the vertical deviation exceeds the limit, the counterweight adjustment amount... When the upward movement exceeds the limit, the counterweight is increased; when the downward movement exceeds the limit, the counterweight is decreased; if only the horizontal movement exceeds the limit, the counterweight adjustment is [not specified]. If only the counterweight is increased; if both limits are exceeded, the counterweight adjustment is the sum of the two. The adjusted weight limit is between 0 and the maximum allowable value for the structure.

[0013] As a further aspect of the present invention: In step five, after each safe retest distance is advanced, steps two through four are repeated. Based on the current real-time data, it is re-determined whether additional weight is needed. If so, the initial weight is recalculated and applied. The safe retest distance is recalculated as the reference step size for the next iteration. The attitude is retested and the final deviation is predicted before adjusting the weight. Each iteration uses the latest data as the reference to form a dual dynamic closed-loop adjustment of the weight value and the retest step size.

[0014] A permanent-temporary combined U-BIT excavation support system includes: Temporary support unit: At a distance of 2 m below the station floor slab, a row of continuous horizontal MJS reinforcement bodies is installed along the entire length of the tunnel section. Its lateral width covers the pipe curtain structure and extends 3 m outward, serving as lateral support during the excavation of the upper layer of earthwork to prevent lateral displacement of the top pipe curtain. During the excavation of the upper layer of earthwork, temporary steel corbels are installed at intervals along the longitudinal direction. One end is fixed to the top steel pipe section of the pipe curtain, and the other end is pressed against the lower surface of the existing station floor slab. They are supported as excavation progresses, providing vertical support and directly controlling the settlement of the existing floor slab. Permanent connection unit: After the upper layer of earthwork excavation is completed and the temporary steel corbels are put into service, a reinforced concrete longitudinal corbel is constructed. The corbels are arranged along the entire length of the tunnel section and connect the top pipe section of U-BIT to the existing station floor slab to form a rigid permanent connection. Void filling and force transmission reinforcement unit: Freezing pipes are installed in the 500 mm thick soil between the top pipe curtain and the existing station floor slab to form a frozen reinforcement layer; high-strength cement grout or C45 or higher self-compacting concrete is injected into the remaining gap between the top steel pipe section and the existing floor slab to form a dense permanent force transmission layer; after the filling material reaches the design strength, the prestressed tendons in the vertical pipe curtain near the top can be tensioned to compress the filling layer.

[0015] The beneficial effects of this invention are as follows: By collecting real-time data on jacking reaction force, displacement, and grouting pressure, calculating the jacking reaction force fluctuation coefficient, vertical displacement rate, and horizontal displacement rate, and comparing them with preset thresholds, quantitative identification and on-demand triggering of instability risk are achieved, avoiding inefficiency caused by blindly adding counterweight or structural instability caused by insufficient counterweight; the required counterweight value is calculated based on physical parameters such as the self-weight of the pipe section, buoyancy, and grouting lifting force, so that the counterweight size matches the actual stress state of the pipe section, avoiding structural instability caused by insufficient or excessive counterweight; the safe retest distance is dynamically determined based on dynamic response theory, extending the step length to reduce the number of retests when stable, and shortening the step length to increase monitoring density when unstable, achieving adaptive matching between retest frequency and construction risk; a displacement-jacking distance regression model is established to predict the final deviation, and the counterweight adjustment value is quantitatively calculated based on the excess, and steps two to four are repeated after each safe retest distance is jacked, forming a dual dynamic closed-loop iterative mechanism of counterweight value and retest step length, so that the counterweight adjustment has both theoretical basis and can accurately respond to actual deviations. Attached Figure Description

[0016] The invention will now be further described with reference to the accompanying drawings.

[0017] Figure 1 This is a modular unit diagram of a permanent-temporary combined U-BIT excavation support system as described in Embodiment 1 of the present invention; Figure 2 This is a flowchart of the construction method steps for a permanent-temporary combined U-BIT excavation support system as described in Embodiment 2 of the present invention; Figure 3 This is a flowchart of the construction method steps for a permanent-temporary combined U-BIT excavation support system as described in Embodiment 3 of the present invention; Figure 4 This is a logic diagram of the construction method of a permanent and temporary combined U-BIT excavation support system as described in Embodiment 3 of the present invention. Detailed Implementation

[0018] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0019] Example 1: Please refer to Figure 1 As shown in the embodiment of the present invention, a permanent-temporary combined U-BIT excavation support system includes: Temporary support unit: At a distance of 2.0 m below the station floor slab, a row of continuous horizontal MJS reinforcement bodies is installed along the entire length (25.6 m) of the cut-and-cover section. Its transverse width covers the pipe curtain structure and extends 3 m outward, serving as transverse support during the excavation of the upper layer of earthwork to prevent lateral displacement of the top pipe curtain. During the excavation of the upper layer of earthwork, temporary steel corbels are installed at longitudinal intervals (e.g., every 1.5~2.0 m). One end is fixed to the top steel pipe section of the pipe curtain, and the other end is pressed against the lower surface of the existing station floor slab. They are supported as excavation progresses, providing vertical support and directly controlling the settlement of the existing floor slab. Permanent connection unit: After the upper layer of earthwork excavation is completed and the temporary steel corbels are put into service, a reinforced concrete longitudinal corbel is constructed. The corbels are arranged along the entire length of the tunnel section and connect the top pipe section of U-BIT to the existing station floor slab to form a rigid permanent connection, so as to realize the reliable transmission of vertical loads and horizontal forces. Void filling and force transmission reinforcement unit: A freezing pipe is installed in the 500 mm thick soil between the top pipe curtain and the existing station floor slab to form a frozen reinforcement layer. The frozen layer can ensure the self-stability of the soil during construction and also serve as a temporary force transmission medium to reduce void compression deformation. In the remaining void between the top steel pipe section and the existing floor slab, high-strength cement grout is injected or C45 or higher self-compacting concrete is poured to form a dense permanent force transmission layer. The filling material has micro-expansion, high compressive strength (≥45 MPa), and low shrinkage characteristics to ensure tight adhesion with the existing floor slab and steel pipe section. After the filling material reaches the design strength, the prestressed tendons in the vertical pipe curtain near the top can be additionally tensioned to compress the filling layer and improve the overall stiffness.

[0020] Example 2, please refer to Figure 2 As shown in the embodiment of the present invention, a construction method for a permanent-temporary combined U-BIT excavation support system includes the following steps: Step S1: End reinforcement and portal construction: In the pipe jacking launching shaft (North Zone C foundation pit) and receiving shaft (South Zone D foundation pit), horizontal MJS is used to reinforce the entrance and exit areas (longitudinal length 3 m, transverse expansion 3 m), and the portal structure is constructed and the jacking steel ring is pre-embedded. Step S2: U-shaped open pipe curtain jacking construction: Square steel pipe sections (A1 / A2 / A3 standard pipe sections and B1 / B2 / B3 working chamber pipe sections) are jacked in sequence to form a U-shaped pipe curtain structure with an open top and a closed bottom; the pipe sections are connected by CT-type locking buckles and filled with grease to stop water. Step S3: Construction of temporary horizontal MJS support: At a distance of 2.0 m below the existing station floor slab, a row of continuous horizontal MJS reinforcement bodies is constructed along the entire length of the tunnel section as temporary horizontal support; Step S4: Top void freezing reinforcement: Freezing pipes are installed in the 500 mm thick soil between the top pipe curtain and the existing base slab. The freezing system is activated to form a frozen reinforcement body, stabilize the void soil and initially transfer the solid. Step S5: Excavation of the upper soil layer and installation of temporary steel brackets: Excavate the upper soil layer in layers (each layer is 0.5~1.0m thick), and install temporary steel brackets as the excavation progresses; the steel brackets are arranged at intervals along the longitudinal direction, with the upper end pressed against the existing base plate and the lower end supported on the steel pipe section at the top of the pipe curtain, and prestress is applied in a timely manner as the excavation progresses; Step S6: High-strength filling construction of voids: Under the joint support of temporary steel brackets and frozen layer, high-pressure grouting or self-compacting concrete is poured into the remaining voids between the top steel pipe section and the existing base plate; the filling material should be injected from the reserved grouting hole or the working chamber of the pipe section to ensure that it is dense and without voids. Freezing can be stopped after the filling layer reaches the design strength. Step S7: Construction of longitudinal concrete corbels: After the infill layer reaches its strength, erect formwork and pour reinforced concrete longitudinal corbels. The corbels are connected to the existing base slab by rebar anchoring and welded or bolted to the steel pipe sections at the top of the pipe curtain to form permanent rigid support. Step S8: Temporary-permanent conversion: After the concrete corbel reaches the design strength, the temporary steel corbel is removed, and the top load is transferred to the lower structure through the infill layer → concrete corbel → pipe curtain, thus completing the temporary-permanent conversion; Step S9: Layered excavation and structural backfilling of the central and left / right compartments: Excavate the remaining soil in the order of first the central compartment and then the left / right compartments, and first the upper part and then the lower part. After the central compartment is excavated, the main structure is backfilled in time. Then the left and right compartments are excavated symmetrically and backfilled to finally form a complete transfer node. Step S10; Construction of transfer stairs: After the main structure is completed, the existing station floor slab is cut and transfer stairs are constructed to achieve zero-distance transfer.

[0021] Example 3, please refer to Figures 3-4As shown in the embodiment of the present invention, a construction method for a permanent-temporary combined U-BIT excavation support system mainly solves the instability problem in construction step S2, where the U-shaped open bundled pipe curtain is prone to floating or tilting due to the lack of closure at the top and the lack of upper restraint during jacking. Its core improvement lies in changing the traditional practice of blindly adding temporary counterweights. By collecting data such as jacking reaction force, displacement, and grouting pressure in real time, it first determines whether counterweight is indeed needed. When it is determined to be needed, the required counterweight value is quantitatively calculated based on real-time parameters such as buoyancy, self-weight, and friction. Simultaneously, the safe re-measurement distance is dynamically determined based on data such as jacking force fluctuation and displacement rate. After each jacking segment, the attitude prediction model is used to predict in advance whether the limits will be exceeded, thereby achieving proactive pre-control and closed-loop iterative adjustment of the counterweight strategy. Ultimately, unnecessary counterweight application is avoided while ensuring the stability of the pipe section, improving construction efficiency and control accuracy. Specifically, it includes the following steps: Step 1: Collect real-time data during the jacking process of the top pipe section, calculate the jacking reaction force fluctuation coefficient, vertical displacement rate and horizontal displacement rate, and determine whether temporary counterweights need to be added by comparing thresholds. In step one, the real-time data during the jacking process of the top pipe section includes: jacking reaction force, vertical displacement of the pipe section, horizontal displacement of the pipe section, and grouting pressure. The real-time data can be acquired in the following ways: During the jacking process of the top pipe section, four types of data are collected in real time at a sampling frequency of 1Hz: jacking reaction force, vertical displacement of the pipe section, horizontal displacement of the pipe section, and grouting pressure. Among them, the jacking reaction force is collected by the pressure sensor of the main jacking cylinder installed at the main jacking cylinder of the pipe jacking machine; the vertical displacement of the pipe section is collected by the static level or laser displacement sensor installed at the center of the top of the pipe section; the horizontal displacement of the pipe section is collected by the laser target + total station or wire displacement gauge installed on the side wall of the pipe section; and the grouting pressure is collected by the pressure sensor installed near the grouting hole on the outer wall of the pipe section. In step one, the process of calculating the jacking reaction force fluctuation coefficient, vertical displacement rate, and horizontal displacement rate is as follows: The sliding window length is set to 1m (corresponding to the jacking distance). After each 1m of jacking is completed, all real-time data is extracted, and the jacking reaction force fluctuation coefficient, vertical displacement rate, and horizontal displacement rate are calculated, specifically as follows: jacking reaction force fluctuation coefficient : ,in, : The maximum jacking reaction force within the current 1m window, : The minimum jacking reaction force within the current 1m window, : The average jacking reaction force within the current 1m window; Vertical displacement rate : ,in, Vertical displacement of the pipe segment at the end of the current window. Vertical displacement of the pipe section at the end of the previous window; Horizontal displacement rate : ,in, : Horizontal displacement of the pipe segment at the end of the current window : Horizontal displacement of the pipe section at the end of the previous window; In step one, the process of determining whether temporary counterweights need to be added is as follows: The jacking reaction force fluctuation coefficient Vertical displacement rate and horizontal displacement rate The values ​​are compared with preset thresholds, and the conditions for adding temporary counterweights are set as follows: Judgment Criterion 1: Fluctuation Coefficient of Jacking Reaction Force >0.25 and both consecutive windows satisfy this condition; Judgment condition two: Vertical displacement rate >2mm / m; Judgment condition three: Horizontal displacement rate >1.5mm / m; If any of the above judgment conditions are met, it is determined that temporary counterweights need to be added; otherwise, if none of them are met, it is determined that temporary counterweights do not need to be added. Understandably, the significance of step one lies in the following: by collecting data such as jacking reaction force, pipe section displacement, and grouting pressure in real time, and calculating the jacking reaction force fluctuation coefficient, vertical displacement rate, and horizontal displacement rate, and comparing them with preset thresholds, quantitative identification and on-demand triggering of pipe section instability risk are achieved. This changes the traditional experience-based approach of blindly adding weight, and provides an objective and quantifiable basis for subsequent weight decision-making. Step 2: If necessary, calculate the required counterweight value based on the stress data of the top pipe section and apply the initial counterweight; In step two, the stress data of the top pipe section includes the pipe section's self-weight, buoyancy, and grouting lifting force. The stress data is obtained as follows: Pipe section self-weight : ,in, For steel density, For the cross-sectional area of ​​the pipe section, It is the acceleration due to gravity; Buoyancy and grouting lifting force : ,in, For the density of water, The volume of water drained from the pipe section, For real-time grouting pressure, This represents the projected area at the bottom of the pipe section; In step two, the required weight value is calculated. The process is as follows: Establish the equilibrium equations for the vertical force system based on Newton's first law, taking upward as the positive direction. The equilibrium condition is: Introducing a safety factor (Based on the principle of variable load partial factors in the "Code for Design of Building Structures" GB 50009, the values ​​are taken as 1.2 to 1.5): Required weight The calculation formula is as follows: ; In step two, the process of applying initial weight includes, but is not limited to: placing precast concrete blocks or steel ingots inside the pipe section (if the internal space of the pipe section allows), setting jacks between the top of the pipe section and the existing base plate to apply reaction force (if the top space is limited and precise control is required), and applying downward locking force using the prestressed tendons inside the pipe section (if the existing prestressed system is applicable). Understandably, the significance of step two is that when step one determines that ballast is needed, a vertical force system equilibrium equation is established based on Newton's first law. The required ballast value is quantitatively calculated and applied based on physical parameters such as the self-weight of the pipe section, buoyancy, and grouting lifting force. This ensures that the ballast size matches the actual stress state of the pipe section, avoiding structural instability or resource waste caused by insufficient or excessive ballast, and achieving precision and theoretical application of ballast. Step 3: Based on real-time data during the jacking process of the top pipe section, determine the safe retest distance through stability analysis, which will serve as the benchmark step size for the next retest iteration; In step three, the real-time data during the jacking process of the top pipe section includes the jacking reaction force fluctuation coefficient, vertical displacement rate, horizontal displacement rate, and grouting pressure, all of which are obtained from step one. In step three, the process of determining the safe re-measurement distance is as follows: Calculate the displacement rate of the current window, using a sliding window of 1m. Displacement rate compared to the previous window ,according to (Given a 1m window) Calculate the acceleration of the displacement rate; like If the value is ≤0, it indicates that the rate has no upward trend, and the safe retest distance is the maximum allowable value of the safe retest distance (e.g., 6m). like <0, calculate the safe remeasurement distance based on the kinematic equations. : ,in, For the maximum allowable displacement rate, The average jacking speed; Calculate based on vertical and horizontal displacement rates respectively The smaller of the two values ​​is taken as the safe remeasurement distance, and the calculation result is subject to engineering amplitude limitation to obtain the final safe remeasurement distance: ,in, It is 6m. It is 1.5m; It should be noted that, The basis for choosing 6.0m is as follows: the attitude adjustment capability of the pipe jacking machine in soft soil is limited, and the maximum deflection rate per meter is about 0.1°. If the deviation is not re-measured after 6m, the cumulative deviation may exceed 0.6°, which is beyond the range of the pipe jacking machine's correction capability. At the same time, the maximum allowable differential deformation of the CT lock is 5mm. When the differential deformation rate does not exceed 1mm / m, the cumulative differential deformation corresponding to 6m is 6mm, which is close to the lock limit. Therefore, 6m is the upper limit value based on the dual constraints of attitude control and lock deformation. The basis for choosing 1.5m is that the minimum effective jacking distance of the pipe jacking machine is about 1m, plus a safety margin of 0.5m to ensure data acquisition and response time. At the same time, too short a retesting distance (such as less than 1.5m) will lead to frequent shutdowns for retesting, which will increase construction disturbance and the risk of pipe section instability. Understandably, the significance of step three lies in the following: based on real-time data during the jacking process, the acceleration of the displacement rate is calculated through dynamic response theory, and the safe retest distance is dynamically determined. This allows the retest step length to be automatically adjusted according to the stability of the current working conditions—extending the step length to reduce the number of retests when stable, and shortening the step length to increase monitoring density when unstable. This achieves an adaptive match between the retest frequency and construction risk, avoiding the inefficiency or monitoring blind spots caused by a fixed step length. Step 4: After the jacking is completed according to the safe retest distance, retest the attitude of the pipe section, establish a displacement-jacking distance regression model, and predict whether the attitude deviation of the top pipe section exceeds the preset threshold before the end of jacking. If it exceeds the threshold, readjust the counterweight value according to the excess amount. In step four, after the jacking is completed according to the safe re-measurement distance, the attitude of the pipe section is re-measured, and the process of establishing the displacement-jacking distance regression model is as follows: After the safe re-measurement distance jacking is completed, the vertical deviation, horizontal deviation and jacking distance of the pipe section are re-measured, and historical data is added. The historical data includes the jacking distance, vertical deviation and horizontal deviation of the pipe section jacking process in the past. Based on historical data on jacking distance and deviation (including vertical and horizontal deviation), the correlation between jacking distance and deviation data is determined using the Pearson correlation coefficient method: if the Pearson correlation coefficient is greater than or equal to a preset threshold of 0.7, it is linear; otherwise, it is nonlinear. If the relationship is linear, the least squares method is used to fit the jacking distance data and the deviation data to obtain the displacement-jacking distance regression model. If the relationship is nonlinear, nonlinear fitting is performed on the jacking distance data and deviation data, including but not limited to quadratic function fitting, exponential function fitting and power function fitting, and the model with the highest goodness of fit after fitting is selected as the displacement-jacking distance regression model. It should be noted that when establishing the displacement-jacking distance regression model, the jacking distance and vertical deviation are constructed independently, and the jacking distance and horizontal deviation are constructed independently. Therefore, there are two displacement-jacking distance regression models. In step four, the process of predicting whether the attitude deviation of the top section exceeds a preset threshold before the jacking is completed is as follows: The current total jacking distance is collected and substituted into the displacement-jacking distance regression model to obtain the attitude deviation of the top section (including horizontal deviation). and vertical deviation If the horizontal or vertical deviation is not within the preset deviation range (-20mm~20mm), it means that the attitude deviation of the top pipe section exceeds the preset threshold before the jacking ends; otherwise, it does not exceed the threshold. In step four, the process of readjusting the weight value based on the excess is as follows: Calculate the vertical and horizontal exceedance limits separately, as follows: Vertical over-limit:

[0022] Horizontal excess:

[0023] If only the vertical deviation exceeds the limit, the counterweight adjustment amount is: ; If only the horizontal limit is exceeded, the counterweight adjustment amount is: ; If both the vertical and horizontal dimensions exceed the limits, the counterweight adjustment amount is: ; in, Vertical stiffness is taken as positive when floating and negative when sinking. Horizontal stiffness is always taken as positive; the calculation method is as follows: The new weight value is: ,in, Current weight value New weight value; It should be noted that vertical stiffness The calculation method is as follows: ,in, The elastic modulus of steel is known. : Moment of inertia of cross section (calculated for design dimensions) Pipe section length, : Foundation reaction coefficient; Horizontal stiffness The calculation method is as follows: ,in, Soil compression modulus : coefficient of friction Pipe section width, : Pipe section shape factor; Understandably, the significance of step four lies in: re-measuring the pipe section attitude after jacking at the safe re-measurement distance, establishing a displacement-jacking distance regression model to predict the final deviation, and quantitatively calculating the counterweight adjustment value based on the excess, thus realizing the transformation from post-event correction to pre-event control. By directly linking the adjustment amount to the excess, and determining the stiffness coefficient based on the elastic foundation beam theory and Coulomb's friction law, the counterweight adjustment has both a theoretical basis and can accurately respond to actual deviations, effectively controlling the cumulative risk of exceeding the limits in the pipe section attitude. Step 5: After each safe retest distance is advanced, repeat steps 2 to 4 to achieve dual dynamic closed-loop adjustment of the pressure value and the retest step length; In step five, after each safe remeasurement distance is advanced, steps two through four are repeated to determine whether additional weight is needed (based on the current jacking reaction force fluctuation coefficient, displacement rate, etc.). If needed, the initial weight is calculated and applied, and the safe remeasurement distance is recalculated based on the current real-time data. As the baseline step size for the next iteration, the pipe section attitude is re-measured, the pipe section attitude deviation is predicted, and the pressure is adjusted according to the excess. Understandably, the significance of step five lies in repeating steps two through four after each safe re-measurement distance, forming a dual dynamic closed-loop iterative mechanism of weight value and re-measurement step length. The weight value is adjusted in real time according to the attitude deviation, and the re-measurement step length is dynamically updated according to the stability of the working conditions. The two are coupled and continuously optimized, ensuring that the entire jacking process is always in an adaptive optimal control state, which not only ensures the stability of the pipe section and the operational safety of the existing station, but also improves construction efficiency and control accuracy.

[0024] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A construction method for a permanent-temporary combined U-BIT excavation support system, comprising sequentially jacking in square steel pipe sections to form a U-shaped pipe curtain structure with an open upper section and a closed bottom, characterized in that: Includes the following steps: Step 1: Collect real-time data during the jacking process of the top pipe section, calculate the jacking reaction force fluctuation coefficient, vertical displacement rate and horizontal displacement rate, and determine whether temporary counterweights need to be added by comparing thresholds. The process for determining whether temporary counterweights need to be added is as follows: Based on real-time data, the jacking reaction force fluctuation coefficient, vertical displacement rate and horizontal displacement rate are calculated with a sliding window of 1m. If the jacking reaction force fluctuation coefficient is greater than 0.25 and meets the condition for two consecutive windows, or the vertical displacement rate is greater than 2 mm / m, or the horizontal displacement rate is greater than 1.5 mm / m, it is determined that temporary counterweights need to be added; otherwise, it is determined that they are not needed. Step 2: If necessary, calculate the required counterweight value based on the stress data of the top pipe section and apply the initial counterweight; Step 3: Based on real-time data during the jacking process of the top pipe section, determine the safe retest distance through stability analysis, which will serve as the benchmark step size for the next retest iteration; Step 4: After the jacking is completed according to the safe retest distance, retest the attitude of the pipe section, establish a displacement-jacking distance regression model, and predict whether the attitude deviation of the top pipe section exceeds the preset threshold before the end of jacking. If it exceeds the threshold, readjust the counterweight value according to the excess amount. Step 5: After each safe retest distance is advanced, repeat steps 2 to 4 to achieve dual dynamic closed-loop adjustment of the pressure value and the retest step length.

2. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 1, characterized in that: In step one, the real-time data includes jacking reaction force, vertical displacement of pipe section, horizontal displacement of pipe section, and grouting pressure. Jacking reaction force is collected by the pressure sensor of the main jacking cylinder, vertical displacement is collected by the static level or laser displacement sensor, horizontal displacement is collected by the laser target or wire displacement gauge, and grouting pressure is collected by the pressure sensor of the grouting hole.

3. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 1, characterized in that: In step two, the force data includes the self-weight of the pipe section, buoyancy, and grouting lifting force; The required counterweight value is calculated based on the equilibrium equations of the vertical force system established by Newton's first law, and the formula is: Required counterweight value ,in For the weight of the pipe section, It is the sum of buoyancy and grouting lifting force. For safety factor; Counterweights are applied by placing counterweights inside the pipe section, installing jacks between the top of the pipe section and the existing base plate, or by using prestressed tendons for tensioning.

4. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 3, characterized in that: In step three, the process of determining the safe re-measurement distance is as follows: Calculate the acceleration of the displacement rate using a 1m sliding window; if the acceleration is not greater than zero, take the maximum value of 6m for the safe remeasurement distance; if the acceleration is greater than zero, calculate the safe remeasurement distance according to the kinematic equation; calculate the safe remeasurement distance according to the vertical and horizontal displacement rates respectively, and take the smaller value, limiting the range to 1.5m to 6m.

5. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 1, characterized in that: In step four, the process of predicting the attitude deviation of the top pipe section before the jacking is completed is as follows: After the jacking is completed according to the safety re-measurement distance, the attitude of the pipe section is re-measured, and the jacking distance and attitude deviation are added to the historical data; the correlation is determined according to the Pearson correlation coefficient of the jacking distance and deviation data, and vertical and horizontal displacement-jacking distance regression models are established respectively; the total jacking distance is substituted into the model to predict the final vertical and horizontal deviations before the end of jacking; when the predicted deviation is within ±20mm, the current pressure is maintained, and when it exceeds, adjustment is initiated.

6. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 5, characterized in that: In step four, if the predicted vertical deviation exceeds the threshold, calculate the vertical excess amount; when the upward deviation exceeds the limit, calculate the vertical excess amount. = Submersion exceeding the limit = ; If the predicted level deviation exceeds the threshold, calculate the level excess. ; The counterweight adjustment amount is: ,in, Vertical stiffness Horizontal stiffness; The new weight value is: ,in, Current weight value New weight value.

7. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 6, characterized in that: In step four, if only the vertical deviation exceeds the limit, adjust the counterweight accordingly. When the upward movement exceeds the limit, the counterweight is increased; when the downward movement exceeds the limit, the counterweight is decreased; if only the horizontal movement exceeds the limit, the counterweight adjustment is [not specified]. If only the counterweight is increased; if both limits are exceeded, the counterweight adjustment is the sum of the two. The adjusted weight constraint is between 0 and the maximum allowable value for the structure.

8. The construction method of a permanent-temporary combined U-BIT excavation support system according to claim 1, characterized in that: In step five, after each safe retest distance is advanced, steps two through four are repeated: Based on the current real-time data, it is re-determined whether additional weight is needed. If so, the initial weight is recalculated and applied. The safe retest distance is recalculated as the reference step size for the next iteration. The attitude is retested and the final deviation is predicted before adjusting the weight. Each iteration uses the latest data as the reference to form a dual dynamic closed-loop adjustment of the weight value and the retest step size.

9. A permanent-temporary combined U-BIT excavation support system, manufactured by the construction method of any one of claims 1-8, characterized in that, include: Temporary support unit: At a distance of 2m below the station floor slab, a row of continuous horizontal MJS reinforcement bodies is set along the entire length of the tunnel section. Its transverse width covers the pipe curtain structure and extends 3m outward. It serves as transverse support during the excavation of the upper layer of earthwork to prevent lateral displacement of the top pipe curtain. During the excavation of the upper layer of earthwork, temporary steel corbels are set at intervals along the longitudinal direction. One end is fixed to the top steel pipe section of the pipe curtain, and the other end is pressed against the lower surface of the existing station floor slab. They are supported as excavation progresses, providing vertical support and directly controlling the settlement of the existing floor slab. Permanent connection unit: After the upper layer of earthwork excavation is completed and the temporary steel corbels are put into service, a reinforced concrete longitudinal corbel is constructed. The corbels are arranged along the entire length of the tunnel section and connect the top pipe section of U-BIT to the existing station floor slab to form a rigid permanent connection. Void filling and force transmission reinforcement unit: Freezing pipes are installed in the 500 mm thick soil between the top pipe curtain and the existing station floor slab to form a frozen reinforcement layer; high-strength cement grout or C45 or higher self-compacting concrete is injected into the remaining gap between the top steel pipe section and the existing floor slab to form a dense permanent force transmission layer; after the filling material reaches the design strength, the prestressed tendons in the vertical pipe curtain near the top can be tensioned to compress the filling layer.

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