Construction method of tunnel crossing quick supporting structure

Abstract

The present application relates to the technical field of tunnel and underground engineering construction, in particular to a kind of tunnel level crossing quick supporting structure construction method, comprising the following steps: S100: excavation and temporary support arrangement;S200: hoisting positioning of conversion node;S300: main and slave arch frame quick assembly;S400: double-control pressure stress relief conversion.The present application couples the limiting friction slip yielding mechanism and the pressure-displacement double-control self-adaptive unloading method, not only provides quantitative flexible energy-absorbing space for soft surrounding rock in the initial stage of supporting stress to release high ground stress, but also realizes intelligent and staged smooth transfer of load in the system conversion stage of temporary support removal, effectively avoids stress mutation and settlement out of control caused by single nonlinear unloading, greatly improves the efficiency of supporting construction, and ensures the absolute safety and reliability of three-dimensional stress system conversion of high ground stress soft rock tunnel level crossing.

Description

Technical Field

[0001] This invention relates to the field of tunnel and underground engineering construction technology, specifically to a method for constructing a rapid support structure at tunnel intersections. Background Technology

[0002] In the field of tunnel and underground engineering construction, tunnel intersections (where the main tunnel and the cross passage meet) under conditions of high ground stress and weak surrounding rock have always been high-risk areas for deformation and instability of the support system due to the surge in excavation cross-sectional area and the complex three-dimensional spatial stress. Existing tunnel intersection support technologies mainly suffer from the following two core problems: First, the support node connection mode is simple and lacks a deformation and pressure relief mechanism.

[0003] Traditional initial support frameworks for level crossings often employ steel arch frames that are welded together or rigidly joined on-site inside the tunnel. This method not only results in lengthy assembly times and prolonged exposure of the surrounding rock, but also makes stress concentrations highly likely at the welded joints. More seriously, when subjected to large deformation compression from soft rock under high ground stress, the purely rigid support system cannot provide adequate stress release space, causing the deformation pressure of the surrounding rock to act directly on the rigid framework, which can easily lead to shear failure of the arch frame or overall buckling instability at the level crossing intersection.

[0004] Second, the system transformation process during the temporary support unloading phase is uncontrollable and can easily trigger secondary settlement.

[0005] In existing construction methods for level crossings, rigid temporary supports are typically installed in the central area to control the initial deformation of large-span sections. However, when removing these temporary supports after the initial support is closed into a ring, current technologies often employ either a one-time cut or a discontinuous, large-scale depressurization removal method. This transient unloading action triggers a severe redistribution of stress in the surrounding rock of the level crossing roof. Because the temporary support system lacks dynamic feedback and adaptive adjustment capabilities based on pressure and displacement monitoring data, the stress transfer in the surrounding rock during the unloading process is extremely uneven, often leading to sudden accelerated settlement of the level crossing arch, seriously threatening project safety. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for constructing a rapid support structure for a tunnel intersection, comprising the following steps: S100: Excavation and temporary support layout: The tunnel intersection section is excavated in stages while retaining the central core soil, and a hydraulic servo adaptive temporary support system is laid on the core soil; S200: Conversion Node Lifting and Positioning: The prefabricated assembled variable cross-section master-slave node conversion component is lifted to the design elevation using the hydraulic servo adaptive temporary support system and an initial support force is applied to it for clamping and positioning. S300: Quick assembly of master-slave arch frame: Using the master-slave node conversion component after positioning as the interface center, quickly lock-type steel arch frames are assembled radially towards the main tunnel and cross passage to form the initial support skeleton, and then sprayed concrete for sealing. S400: Dual-control stress relief conversion: Based on the pressure-displacement dual-control logic, the hydraulic servo adaptive temporary support system is adjusted to perform graded stress relief, transferring the surrounding rock load to the closed initial support frame. After the surrounding rock deformation converges, the hydraulic servo adaptive temporary support system is dismantled and the core soil is excavated.

[0007] Furthermore, in step S100, before the staged excavation of the tunnel intersection section, an advanced support process is also included: An advanced pipe roof with guiding function is installed into the rock mass along the design outline of the tunnel intersection section, and the advanced pipe roof is reinforced by grouting to form a pre-reinforced protection zone outside the design outline.

[0008] Furthermore, the step-by-step excavation of the tunnel intersection section while retaining the central core soil specifically includes: The surrounding rock mass is stripped in stages using micro-vibration blasting or mechanical excavation to control the central core soil to be truncated conical in shape, and to ensure that the top surface elevation of the central core soil is 0.5m to 1.5m lower than the installation bottom elevation of the prefabricated variable cross-section master-slave node conversion component, so as to construct the bearing platform of the hydraulic servo adaptive temporary support system.

[0009] Furthermore, the hydraulic servo adaptive temporary support system includes a base, a support jack, a ball joint tray, and a sensing component; The specific implementation of the hydraulic servo adaptive temporary support system deployed on the core soil is as follows: the base is leveled and anchored to the top surface of the central core soil, the ball joint tray is vertically lifted by the support jack, and the sensing components are synchronously connected to the PLC servo control terminal outside the tunnel to collect the pressure data and settlement displacement data at the ball joint tray in real time.

[0010] Furthermore, the assembled variable cross-section master-slave node conversion component is a high-strength steel structure in the form of multiple passages, which includes a central converging shell and multiple flange interfaces extending outwards; The process of using the hydraulic servo adaptive temporary support system to hoist the prefabricated assembled variable cross-section master-slave node conversion component to the design elevation and applying initial support force to it for clamping and positioning specifically includes an attitude adaptive adjustment process: A 3D laser scanner is introduced to verify the actual excavation profile of the intersection section, and the spatial inclination angle of the ball joint tray at the top of the temporary support system is adjusted according to the profile deviation data, so that the multiple flange interfaces are precisely aligned with the axial directions of the main tunnel and the transverse passage; then the temporary support system is driven to apply an initial thrust upward until the top of the central confluence shell is completely in close contact with the surrounding rock or advanced support system of the intersection arch.

[0011] Furthermore, before hoisting and positioning the prefabricated variable cross-section master-slave node conversion component, a pre-assembly process for the pressure relief structure is also included: Limiting friction sliding pressure relief joints are pre-assembled at the outer ends of the multiple flange interfaces. The limiting friction sliding pressure relief joint includes a U-shaped guide sleeve, a sliding disc with an elongated hole, and a polymer damping rubber pad. During pre-assembly, the sliding disc is locked at the initial limiting end of the elongated hole by a high-strength bolt with a fixed torque, so that it has a static friction threshold to resist the initial deformation pressure of the surrounding rock.

[0012] Furthermore, the process of assembling a quick-locking steel arch frame radially towards the main opening and transverse passage, with the positioned master-slave node conversion component as the interface center, includes mechanical quick-locking and symmetrical assembly processes. The connecting ends of each section of the quick-locking steel arch frame are seamlessly inserted into the U-shaped guide sleeve of the limiting friction sliding pressure relief joint, and mechanically and quickly locked without welding by the preset self-locking groove and the high-strength pin shaft. In terms of assembly sequence, the splicing is strictly carried out in accordance with the principle of first the main tunnel direction, then the transverse passage direction, and symmetrically and alternately radiating outward from the main and slave node conversion parts as the center, so as to construct an umbrella-shaped initial support frame.

[0013] Furthermore, the shotcrete is sealed off, specifically using a layered symmetrical spraying process to prevent eccentric loading: Starting from the arch foot of the umbrella-shaped initial support frame, concrete is sprayed layer by layer and section by section along the circumferential direction towards the center intersection of the master and slave node conversion components. During the spraying process, the amount of concrete sprayed on both sides of the symmetrical cross-section of the intersection is monitored in real time and the solidification rate is kept basically consistent to eliminate sudden loads on one side and prevent the hydraulic servo adaptive temporary support system from deflecting or becoming unstable due to eccentric stress, until the sprayed concrete completely wraps around and closes the quick-locking steel arch frame and node conversion components into a ring.

[0014] Furthermore, the hydraulic servo adaptive temporary support system, adjusted based on pressure-displacement dual control logic, performs staged pressure relief. The specific automatic control process includes: The single depressurization step size is set to 5% to 10% of the initial support force, and the support jack is driven by the PLC servo control terminal to perform the first stage of depressurization. After the first stage of depressurization is completed, the settlement displacement data at the ball joint tray is collected at high frequency by the sensing component, and the real-time settlement rate is calculated. If the real-time settlement rate within the continuous observation window is less than the preset convergence safety threshold, the surrounding rock at the current decompression level is determined to be stable, and the next level of decompression is automatically triggered. If, at any decompression level, the real-time settlement rate exceeds the warning threshold or a sudden settlement occurs, the PLC servo control terminal will instantly control the support jack to perform adaptive pressure replenishment and lock, forcibly interrupting the unloading process. After the surrounding rock stress is redistributed and tends to stabilize, the judgment loop will be entered again.

[0015] Furthermore, the process of transferring the surrounding rock load to the initial support frame after closure due to the staged pressure relief includes a synergistic pressure relief mechanism: When the large deformation extrusion pressure of soft rock borne by the initial support frame exceeds the static friction threshold set by the limiting friction sliding pressure relief joint, the sliding disc overcomes the pre-tightening friction force and slides directionally along the elongated hole, and simultaneously squeezes the polymer damping rubber pad to physically absorb energy. The sliding process allows the tunnel intersection section to generate moderate flexible convergence to release the high ground stress accumulation until the sliding disk abuts against the end limit point of the elongated hole, so that the initial support frame is transformed from a flexible pressure relief state to a fully rigid bearing state.

[0016] Beneficial effects This invention eliminates the complex in-tunnel welding process by introducing prefabricated modular variable cross-section master-slave node conversion components and quick-locking steel arch frames, significantly shortening the assembly and closure time of the initial support frame at the intersection. Simultaneously, this invention couples a limiting frictional sliding pressure-relief mechanism with a pressure-displacement dual-control adaptive unloading method. This not only provides a quantitative flexible energy-absorbing space for the weak surrounding rock to release high ground stress in the initial stage of support stress, but also achieves intelligent, graded, and smooth load transfer during the system transition stage of temporary support removal. This effectively avoids stress mutations and settlement runaway caused by single nonlinear unloading, significantly improving support construction efficiency while ensuring the absolute safety and reliability of the three-dimensional stress system conversion at the intersection of high-stress soft rock tunnels. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the rapid support construction method for tunnel intersections according to the present invention. Figure 2 This is a detailed flowchart of the excavation and temporary support layout of the present invention; Figure 3 Detailed flowchart of hoisting and positioning of conversion nodes. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0019] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but includes other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings: Example: like Figures 1-3 As shown, a construction method for a rapid support structure at a tunnel intersection includes the following steps: S100: Excavation and temporary support layout: The tunnel intersection section is excavated in stages while retaining the central core soil. A hydraulic servo adaptive temporary support system is then deployed on the core soil. S200: Conversion Node Lifting and Positioning: The prefabricated assembled variable cross-section master-slave node conversion component is lifted to the design elevation using a hydraulic servo adaptive temporary support system, and an initial support force is applied to it for clamping and positioning. S300: Quick assembly of master-slave arch frame: Using the master-slave node conversion component after positioning as the interface center, quickly lock-type steel arch frames are assembled radially towards the main tunnel and cross passage to form the initial support skeleton, and then shotcrete is sprayed to seal it. S400: Dual-control stress relief conversion: Based on the pressure-displacement dual-control logic adjustment of the hydraulic servo adaptive temporary support system, the pressure is relieved in stages, and the surrounding rock load is transferred to the closed initial support frame. After the surrounding rock deformation converges, the hydraulic servo adaptive temporary support system is removed and the core soil is excavated.

[0021] Furthermore, the specific implementation process of step S100 is as follows: Before carrying out substantive excavation of the tunnel intersection section, pre-grouting and pre-reinforcement are first carried out in the rock mass along the design outline of the tunnel intersection section.

[0022] Construction workers drilled pre-reinforced pipe roof boreholes using a down-the-hole drill rig, extending 3 to 5 degrees outward from the design outline. Seamless hot-rolled steel pipes with an outer diameter of 108 mm and a wall thickness of 6 mm were used for the pre-reinforced pipe roof, with grouting holes drilled in a staggered pattern along the pipe body. The circumferential spacing between the pipes was controlled between 40 and 60 cm. After the pipes were in place, a dual-liquid grouting pump was connected to inject cement-water glass grout into the pipes. The initial grouting pressure was set at 0.5 MPa to 1.0 MPa, and the final pressure was controlled between 1.5 MPa and 2.0 MPa. Grouting continued until the grout overflowed from adjacent pipe holes or reached the upper limit of the design grouting volume, thereby consolidating in the weak surrounding rock outside the design outline to form a ring-shaped pre-reinforced protective zone with a thickness of 2 to 3 meters.

[0023] After the advanced support system reaches its initial setting strength, the stage of stepped excavation and core soil retention begins.

[0024] Below the pre-reinforced retaining area, micro-vibration blasting combined with a cantilever tunneling machine was used to peel away the surrounding rock in stages. During the peeling and cutting process, operators deliberately avoided the geometric center of the intersection area based on a pre-set 3D BIM excavation model, thus preserving a large volume of central core soil in the spatial center. The cutting head of the cantilever tunneling machine was used to trim and contour the sidewalls of the preserved central core soil, strictly controlling the 3D geometric entity of the central core soil to be a truncated cone structure. Specifically, the bottom diameter of the truncated cone structure was controlled between 6 and 8 meters, the top diameter between 3 and 5 meters, and the sidewall slope was controlled between 1:0.75 and 1:1. Simultaneously, a total station was used to monitor the elevation of the horizontal top surface of the truncated cone structure in real time. Mechanical milling ensured that the elevation of the horizontal top surface of the truncated cone structure was precisely 0.5 to 1.5 meters lower than the installation bottom elevation of the prefabricated modular variable cross-section master-slave node conversion component. After milling, a single layer of steel mesh is tied to the horizontal top surface of the truncated cone structure, and a C25 early-strength concrete cushion layer with a thickness of 20 cm to 30 cm is poured to seal and solidify the central core soil, forming a load-bearing platform.

[0025] Once the C25 early-strength concrete cushion layer reaches more than 75% of its design strength, a hydraulic servo adaptive temporary support system is deployed on the bearing platform. This system comprises a high-strength steel base, multi-stage hydraulic jacks, a ball-and-socket tray, and sensor components. A small crawler crane is used to lift the high-strength steel base, marked with a crosshair, to the center of the bearing platform, aligning the crosshair with the center coordinates of the intersection. Holes are then drilled at pre-drilled locations on the high-strength steel base, and 4 to 8 M24 chemical anchors are inserted to rigidly anchor the base to the C25 early-strength concrete cushion layer. After anchoring, high-strength bolts are used to vertically connect the high-strength steel base to the bottom of the multi-stage hydraulic jack cylinder at its upper flange interface.

[0026] The piston rod of the multi-stage hydraulic jack is mechanically connected to a ball joint tray via a pin. The ball joint tray includes a concave ball seat and an convex universal ball plate fitted within the concave ball seat. Fiber optic pressure sensors are embedded in the pressure-bearing flange surface of the multi-stage hydraulic jack and the horizontal top surface of the convex universal ball plate, respectively. A laser displacement sensor is vertically arranged on the side edge of the convex universal ball plate. These sensors together constitute the sensing component.

[0027] After the sensor components are installed, armored communication cables are laid along the tunnel sidewall, and the signal output ports of the fiber optic pressure sensor and laser displacement sensor are hardwired to the PLC servo control terminal installed outside the tunnel. After the wiring is completed, the PLC servo control terminal is started and an start command is sent to the hydraulic pump station. The hydraulic pump station injects hydraulic oil into the rodless chamber of the multi-stage hydraulic jack through high-pressure oil pipes.

[0028] The piston rod of the multi-stage hydraulic jack extends vertically upward, driving the top ball joint tray to rise until the tray reaches the designed docking elevation. At this point, a pressure-holding command is input to the PLC servo control terminal, the hydraulic pump station locks the circuit valves, the hydraulic servo adaptive temporary support system enters standby support mode, and continuously transmits zero-point calibration data.

[0029] Furthermore, the specific implementation process of step S200 is as follows: Before hoisting the prefabricated variable cross-section master-slave node conversion component into place, the limiting friction sliding pressure relief joint is first pre-assembled on the ground at the outer ends of the multiple flange interfaces extending outward from the prefabricated variable cross-section master-slave node conversion component. The prefabricated variable cross-section master-slave node conversion component includes a central confluence shell welded from high-strength steel plates. The central confluence shell has 20 mm thick longitudinal and transverse stiffening ribs welded interlaced inside. The outer periphery of the central confluence shell radiates outwards to the main cavity flange interface for connecting to the main cavity arch frame and the transverse channel flange interface for connecting to the transverse channel arch frame. During pre-assembly, the fixed end of the U-shaped guide sleeve of the limiting friction sliding pressure relief joint is rigidly fastened to the main cavity flange interface and the transverse channel flange interface with bolts. Then, a sliding disc with an elongated hole is inserted into the slide rail of the U-shaped guide sleeve, and a 30 mm thick polymer damping rubber pad is clamped between the sliding disc and the bottom surface of the U-shaped guide sleeve. The length direction of the elongated hole is parallel to the sliding axis of the U-shaped guide sleeve. Use a digital torque wrench to tighten the high-strength bolt through the oblong hole. Set the tightening torque of the high-strength bolt to 350 N·m to 400 N·m, so that the sliding disc is firmly pressed against the initial limiting end of the oblong hole near the center confluence of the housing. In this way, the bolt preload is used to establish a static friction threshold between the sliding disc and the U-shaped guide sleeve to resist the initial deformation pressure of the surrounding rock.

[0030] After ground pre-assembly, a stationary 3D laser scanner is erected below the center of the tunnel intersection section. The scanner is then activated to perform a full-section dense point cloud scan of the exposed rock surface and benchmark points after excavation at the intersection section, acquiring 3D spatial point cloud data of the actual excavation contour. This 3D spatial point cloud data is transmitted in real-time via a wireless local area network to an external PLC servo control terminal. The PLC servo control terminal's internal geometric comparison software performs spatial 3D fitting and stitching between the actual excavation contour and the design standard BIM model, calculating the axial deviation, elevation deviation, and 3D spatial tilt angle change of the intersection arch, and generating spatial attitude adjustment command parameters for the ball-and-socket tray.

[0031] The hydraulic robotic arm of the tunnel multi-functional scaffolding machine grabs the pre-assembled variable cross-section master-slave node conversion component, which is equipped with a pressure relief joint, and smoothly lifts it above the hydraulic servo adaptive temporary support system deployed on the top surface of the central core soil. The base structure of the central confluence shell is then placed flat on the ball joint tray at the top of the hydraulic servo adaptive temporary support system, so that the positioning pin hole of the central confluence shell is mechanically engaged and locked with the positioning pin on the upper convex universal ball plate of the ball joint tray at the top of the hydraulic servo adaptive temporary support system.

[0032] Based on the spatial attitude adjustment command parameters generated by the PLC servo control terminal, the operator uses a micro-motion hydraulic jack to move the upper convex universal ball plate, causing it to rotate omnidirectionally within the concave ball seat of the ball hinge tray. This adjusts the spatial tilt angle of the ball hinge tray, thereby driving the assembled variable cross-section master-slave node conversion component to rotate slightly in three-dimensional space until the axis of the main tunnel flange interface is completely parallel to the design axis of the tunnel main tunnel and the axis of the transverse passage flange interface is completely parallel to the design axis of the tunnel transverse passage.

[0033] After the attitude alignment is completed, the PLC servo control terminal is activated to control the hydraulic pump station, continuously injecting high-pressure hydraulic oil into the rodless chamber of the multi-stage hydraulic jacks in the hydraulic servo adaptive temporary support system. The piston rod of the multi-stage hydraulic jack pushes the ball joint tray and the assembled variable cross-section master-slave node conversion component vertically upward until the top outer surface of the central confluence shell is completely in contact with the bottom surface of the pre-reinforced shed protection area at the intersection arch or the exposed surrounding rock surface. The hydraulic pump station continues to be driven to pressurize until the resultant force value fed back by the fiber optic grating pressure sensor embedded in the horizontal top surface of the upper convex universal ball plate reaches the preset initial support force range of 100kN to 150kN. At this time, the PLC servo control terminal automatically closes the oil inlet valve of the hydraulic pump station and locks the hydraulic oil circuit, so that the assembled variable cross-section master-slave node conversion component is firmly pressed and positioned at the design elevation, completing the entire implementation process of step S200.

[0034] Furthermore, the specific implementation process of step S300 is as follows: After the prefabricated variable cross-section master-slave node conversion component is clamped and positioned by the hydraulic servo adaptive temporary support system, the mechanical fast locking and symmetrical assembly of the quick-locking steel arch frame is carried out with the prefabricated variable cross-section master-slave node conversion component as the interface center. The operator starts the tunnel multi-functional scaffolding machine and grabs the first segment of the quick-locking steel arch frame in the main tunnel direction. The connecting end of the quick-locking steel arch frame in the main tunnel direction is seamlessly inserted into the U-shaped guide sleeve of the limiting friction sliding pressure relief joint pre-assembled on the outer end of the main tunnel flange interface. The surface of the connecting end is milled with a self-locking groove, and the side wall of the U-shaped guide sleeve has a through pin hole. When the connecting end is inserted to 100% of the depth of the U-shaped guide sleeve, the self-locking groove and the through pin hole are spatially coaxially aligned. The operator drives a cylindrical high-strength pin into the through pin hole and uses a cotter pin to pass through the anti-disengagement hole at the end of the high-strength pin for mechanical locking, completing the welding-free mechanical fastening. In terms of assembly sequence, the principle of assembling the steel arch frames in the main tunnel direction first and then assembling the steel arch frames in the transverse passage direction is strictly followed. In terms of spatial expansion logic, the prefabricated variable cross-section master-slave node conversion component is used as the absolute center, and the next segment of quick-locking steel arch frames is symmetrically and alternately spliced ​​outwards from the level intersection in a radial manner until the bottom end of each quick-locking steel arch frame extends to the reserved bedrock surface at the arch foot of the tunnel level intersection, thus constructing a fully stressed and closed umbrella-shaped initial support skeleton.

[0035] After the umbrella-shaped initial support frame is assembled, the layered symmetrical shotcrete sealing process to prevent eccentric loading is immediately initiated.

[0036] A dual-arm wet spraying robot was used for the spraying operation, and C25 early-strength shotcrete with added accelerator was selected as the spraying material. The spraying route started simultaneously from the arch feet on both sides of the umbrella-shaped initial support frame, and proceeded along the tunnel circumference from bottom to top towards the center intersection of the prefabricated variable cross-section master-slave node conversion component, and was sprayed in layers and sections.

[0037] The thickness of each layer of concrete sprayed in a single application is strictly controlled between 5 and 8 centimeters. During the re-spraying process, technicians installed pipeline flow meters and ultrasonic thickness gauges at the symmetrical cross-sections on both sides of the intersection to monitor and compare the cumulative volume of concrete sprayed, instantaneous spray thickness, and initial setting and curing speed on the symmetrical cross-sections in real time.

[0038] If the difference in the weight of the concrete on both sides of the cross section exceeds 10%, the control system will immediately reduce the spraying volume of the wet spraying robot on the side with the greater weight to keep the spraying volume and solidification speed on both sides absolutely consistent, so as to eliminate the eccentric stress caused by the sudden increase in weight on one side and prevent the hydraulic servo adaptive temporary support system from deflecting or becoming unstable due to uneven force.

[0039] Continue to perform layered symmetrical spraying until the sprayed concrete layer completely encloses all the quick-locking steel arch frames, limiting friction sliding pressure relief joints, and prefabricated variable cross-section master-slave node conversion parts, and closes into a ring at the inner edge of the design outline to form a dense and continuous permanent initial support shell.

[0040] Furthermore, the specific implementation process of step S400 is as follows: After the shotcrete layer has initially set and reached the set strength, the pressure-displacement dual-control decompression execution program built into the PLC servo control terminal located outside the tunnel is activated. The operator inputs and sets the single decompression step size parameter on the control interface of the PLC servo control terminal; the specific value is defined within the range of 5% to 10% of the preset initial support force. Simultaneously, the convergence safety threshold is set to 0.2 mm per day, the warning threshold to 1.0 mm per day, and the continuous observation window is set to 4 hours on the control interface.

[0041] After the parameters are set, the PLC servo control terminal outputs a control electrical signal to the proportional unloading valve of the hydraulic pump station. The hydraulic pump station extracts an appropriate amount of hydraulic oil from the rodless chamber of the multi-stage hydraulic jack according to the set step size, executing the first stage of pressure relief. After the first stage of pressure relief is completed, the PLC servo control terminal activates the laser displacement sensor and fiber optic pressure sensor in the sensing component to perform high-frequency data acquisition. The laser displacement sensor reads the absolute settlement displacement coordinate data at the ball joint tray at a frequency of 50 to 100 times per second and transmits it back to the microprocessor in the PLC servo control terminal to calculate the real-time settlement rate. If the microprocessor determines that the real-time settlement rate within the continuous observation window is always less than the preset convergence safety threshold, the PLC servo control terminal automatically sends the next stage of pressure relief command to the hydraulic pump station, and cyclically executes the staged unloading steps.

[0042] If, during any depressurization stage, the microprocessor detects that the real-time settlement rate exceeds the preset warning threshold, or that a non-linear settlement abrupt change occurs in the settlement displacement coordinate data, the PLC servo control terminal instantly and forcibly closes the proportional unloading valve and simultaneously opens the oil inlet valve to control the multi-stage hydraulic jacks to perform adaptive pressure compensation, physically locking the piston rods of the multi-stage hydraulic jacks. The control system forcibly interrupts the current unloading stage, maintaining the hydraulic jacking and locking state until the surrounding rock stress is redistributed. Once the settlement rate returned by the sensing components falls below the convergence safety threshold, the depressurization judgment loop program is restarted.

[0043] Within the stress range where the surrounding rock load gradually shifts from the hydraulic servo adaptive temporary support system to the initial closure support skeleton due to graded pressure relief, the limiting friction sliding pressure relief joint synchronously triggers a physical collaborative pressure relief mechanism. As the hydraulic support force gradually weakens, the large deformation compressive stress on the soft rock borne by the initial closure support skeleton increases in a gradient. When the normal component of the compressive stress exceeds the pre-set static friction threshold of the limiting friction sliding pressure relief joint, the sliding disc in the limiting friction sliding pressure relief joint overcomes the pre-tightening friction force applied by the high-strength bolts and generates directional mechanical sliding along the elongated hole in the U-shaped guide sleeve towards the tunnel's central axis. As the sliding disc moves, it simultaneously compresses the polymer damping rubber pad arranged at the end of the elongated hole, resulting in physical deformation and energy absorption. The relative displacement between the U-shaped guide sleeve and the sliding disc causes the initial closure support skeleton to generate a flexible convergent displacement towards the inside of the tunnel, releasing some of the accumulated high ground stress.

[0044] The sliding disc continuously presses inward against the polymer damping rubber pad until its end face abuts against the physical limit point at the end of the elongated hole. At this point, the mechanical gap within the U-shaped guide sleeve is completely closed, and the support frame transitions from a relatively flexible sliding and pressure-releasing state to a fully rigid, locked bearing state during the initial closure phase. The sensing components continue monitoring until it is confirmed that the deformation of the support frame during the initial closure phase has completely converged and no longer produces relative displacement. Then, the PLC servo control unit controls the multi-stage hydraulic jacks to completely release the residual internal pressure. Operators remove the chemical anchors that anchor the high-strength steel base to the bearing platform, remove all components of the hydraulic servo adaptive temporary support system, and coordinate excavation machinery to remove the core soil in the center, completing the rapid support and system conversion construction at the tunnel intersection.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing a rapid support structure at a tunnel intersection, characterized in that, Includes the following steps: S100: Excavation and temporary support layout: The tunnel intersection section is excavated in stages while retaining the central core soil. A hydraulic servo adaptive temporary support system is then deployed on the core soil. S200: Conversion Node Lifting and Positioning: The prefabricated assembled variable cross-section master-slave node conversion component is lifted to the design elevation using the hydraulic servo adaptive temporary support system and an initial support force is applied to it for clamping and positioning. S300: Quick assembly of master-slave arch frame: Using the master-slave node conversion component after positioning as the interface center, quickly lock-type steel arch frames are assembled radially towards the main tunnel and cross passage to form the initial support skeleton, and then sprayed concrete for sealing. S400: Dual-control stress relief conversion: Based on the pressure-displacement dual-control logic, the hydraulic servo adaptive temporary support system is adjusted to perform graded stress relief, transferring the surrounding rock load to the closed initial support frame. After the surrounding rock deformation converges, the hydraulic servo adaptive temporary support system is dismantled and the core soil is excavated.

2. The construction method for a rapid support structure at a tunnel intersection according to claim 1, characterized in that, In step S100, before the staged excavation of the tunnel intersection section, an advanced support process is also included: An advanced pipe roof with guiding function is installed into the rock mass along the design outline of the tunnel intersection section, and the advanced pipe roof is reinforced by grouting to form a pre-reinforced protection zone outside the design outline.

3. The construction method for a rapid support structure at a tunnel intersection according to claim 2, characterized in that, The step-by-step excavation of the tunnel intersection section while retaining the central core soil specifically includes: The surrounding rock mass is stripped in stages using micro-vibration blasting or mechanical excavation to control the central core soil to be truncated conical in shape, and to ensure that the top surface elevation of the central core soil is 0.5m to 1.5m lower than the installation bottom elevation of the prefabricated variable cross-section master-slave node conversion component, so as to construct the bearing platform of the hydraulic servo adaptive temporary support system.

4. The construction method for a rapid support structure at a tunnel intersection according to claim 3, characterized in that, The hydraulic servo adaptive temporary support system includes a base, a support jack, a ball joint tray, and a sensing component. The specific implementation of the hydraulic servo adaptive temporary support system deployed on the core soil is as follows: the base is leveled and anchored to the top surface of the central core soil, the ball joint tray is vertically lifted by the support jack, and the sensing components are synchronously connected to the PLC servo control terminal outside the tunnel to collect the pressure data and settlement displacement data at the ball joint tray in real time.

5. The construction method for a rapid support structure at a tunnel intersection according to claim 4, characterized in that, The prefabricated variable cross-section master-slave node conversion component is a high-strength steel structure with multiple passages, which includes a central converging shell and multiple flange interfaces extending outward. The process of using the hydraulic servo adaptive temporary support system to hoist the prefabricated assembled variable cross-section master-slave node conversion component to the design elevation and applying initial support force to it for clamping and positioning specifically includes an attitude adaptive adjustment process: A 3D laser scanner is introduced to verify the actual excavation profile of the intersection section, and the spatial inclination angle of the ball joint tray at the top of the temporary support system is adjusted according to the profile deviation data, so that the multiple flange interfaces are precisely aligned with the axial directions of the main tunnel and the transverse passage; then the temporary support system is driven to apply an initial thrust upward until the top of the central confluence shell is completely in close contact with the surrounding rock or advanced support system of the intersection arch.

6. The construction method for a rapid support structure at a tunnel intersection according to claim 5, characterized in that, Before hoisting and positioning the prefabricated variable cross-section master-slave node conversion component, a pre-assembly process for the pressure relief structure is also included: Limiting friction sliding pressure relief joints are pre-assembled at the outer ends of the multiple flange interfaces. The limiting friction sliding pressure relief joint includes a U-shaped guide sleeve, a sliding disc with an elongated hole, and a polymer damping rubber pad. During pre-assembly, the sliding disc is locked at the initial limiting end of the elongated hole by a high-strength bolt with a fixed torque, so that it has a static friction threshold to resist the initial deformation pressure of the surrounding rock.

7. A construction method for a rapid support structure at a tunnel intersection according to claim 6, characterized in that, The process of assembling a quick-locking steel arch frame radially towards the main opening and transverse passage, with the positioned master-slave node conversion component as the interface center, includes mechanical quick-locking and symmetrical assembly processes. The connecting ends of each section of the quick-locking steel arch frame are seamlessly inserted into the U-shaped guide sleeve of the limiting friction sliding pressure relief joint, and mechanically and quickly locked without welding by the preset self-locking groove and the high-strength pin shaft. In terms of assembly sequence, the splicing is strictly carried out in accordance with the principle of first the main tunnel direction, then the transverse passage direction, and symmetrically and alternately radiating outward from the main and slave node conversion parts as the center, so as to construct an umbrella-shaped initial support frame.

8. The construction method for a rapid support structure at a tunnel intersection according to claim 7, characterized in that, The shotcrete is used for sealing, specifically employing a layered symmetrical shotcrete process to prevent eccentric loading. Starting from the arch foot of the umbrella-shaped initial support frame, concrete is sprayed layer by layer and section by section along the circumferential direction towards the center intersection of the master and slave node conversion components. During the spraying process, the amount of concrete sprayed on both sides of the symmetrical cross-section of the intersection is monitored in real time and the solidification rate is kept basically consistent to eliminate sudden loads on one side and prevent the hydraulic servo adaptive temporary support system from deflecting or becoming unstable due to eccentric stress, until the sprayed concrete completely wraps around and closes the quick-locking steel arch frame and node conversion components into a ring.

9. A construction method for a rapid support structure at a tunnel intersection according to claim 8, characterized in that, The automatic control process for staged depressurization of the hydraulic servo adaptive temporary support system based on pressure-displacement dual control logic includes: The single depressurization step size is set to 5% to 10% of the initial support force, and the support jack is driven by the PLC servo control terminal to perform the first stage of depressurization. After the first stage of depressurization is completed, the settlement displacement data at the ball joint tray is collected at high frequency by the sensing component, and the real-time settlement rate is calculated. If the real-time settlement rate within the continuous observation window is less than the preset convergence safety threshold, the surrounding rock at the current decompression level is determined to be stable, and the next level of decompression is automatically triggered. If, at any decompression level, the real-time settlement rate exceeds the warning threshold or a sudden settlement occurs, the PLC servo control terminal will instantly control the support jack to perform adaptive pressure replenishment and lock, forcibly interrupting the unloading process. After the surrounding rock stress is redistributed and tends to stabilize, the judgment loop will be entered again.

10. A construction method for a rapid support structure at a tunnel intersection according to claim 9, characterized in that, The process of transferring the surrounding rock load to the initial support frame after closure due to the staged pressure relief includes a synergistic pressure relief mechanism: When the large deformation extrusion pressure of soft rock borne by the initial support frame exceeds the static friction threshold set by the limiting friction sliding pressure relief joint, the sliding disc overcomes the pre-tightening friction force and slides directionally along the elongated hole, and simultaneously squeezes the polymer damping rubber pad to physically absorb energy. The sliding process allows the tunnel intersection section to generate moderate flexible convergence to release the high ground stress accumulation until the sliding disk abuts against the end limit point of the elongated hole, so that the initial support frame is transformed from a flexible pressure relief state to a fully rigid bearing state.

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