A construction method of open cut tunnel overpassing existing shield tunnel and open cut tunnel

Abstract

This application relates to a construction method for an open-cut tunnel crossing an existing shield tunnel and the open-cut tunnel itself, including: internal reinforcement of the section of the existing shield tunnel located within a pre-set area of ​​the new open-cut foundation pit; construction of a solidification body in the soil surrounding the foundation pit, wrapping the sidewalls and bottom of the pit to form a U-shaped constraint structure; installation of a steel pipe shed support structure along the longitudinal direction of the tunnel within the solidification body at the bottom of the pit; excavation of the foundation pit using the inverted shaft wall method combined with a compartmentalized skip-excavation sequence, construction of a bottom sealing grid and anchoring it to the steel pipe shed, followed by construction of the main structure; and automated monitoring throughout the entire process. Through the systematic synergy of five measures—internal annular steel component reinforcement, U-shaped stratum reinforcement, longitudinal steel pipe shed, inverted shaft wall compartmentalized skip-excavation, and automated monitoring—a three-layer protection system ("inner-middle-outer") and a multi-level load transfer chain are formed, effectively suppressing the uplift and deformation of the existing shield tunnel caused by foundation pit excavation unloading in soft soil strata, and significantly improving the safety and reliability of close-range overpass construction.

Description

Technical Field

[0001] This application relates to the field of tunnel boring machine (TBM) construction technology, and in particular to a method for constructing an open-cut tunnel that crosses an existing TBM tunnel and the open-cut tunnel itself. Background Technology

[0002] With the continuous acceleration of urbanization in my country, the development and utilization of underground space is becoming increasingly intensive, and urban rail transit networks are becoming more and more complex. In the soft soil strata areas of many large cities, new underground projects inevitably need to cross or be adjacent to existing operating tunnels. Among them, the situation of new cut-and-cover tunnels crossing over existing shield tunnels is particularly common and carries high risks.

[0003] In soft soil strata, the soil is characterized by high water content, high compressibility, and high sensitivity. When excavation work is carried out above a newly constructed open-cut foundation pit, the soil at the bottom of the pit is removed, resulting in a reduction in the overburden pressure above the existing shield tunnel and creating an unloading effect. This unloading effect can cause the soil at the bottom of the pit to rebound, thereby pushing the underlying existing shield tunnel to undergo vertical upward deformation. If the upward displacement is too large, it can lead to the opening of the joints of the existing tunnel segments, excessive bolt stress, and deviations in track geometry, and in severe cases, it can even threaten the structural and operational safety of the tunnel.

[0004] Currently, protective measures for such overpass construction typically involve internal reinforcement of existing tunnels, improvement of the surrounding soil, and optimization of the excavation sequence. However, existing construction methods still have shortcomings in practical application. On the one hand, various protective measures are often implemented independently, resulting in the reinforcement effect not being maximized. Especially in complex soft soil strata, single or simple combinations of measures are insufficient to effectively suppress the tunnel's upward deformation. On the other hand, the load transfer path during construction is not clearly defined, and the longitudinal stiffness distribution is uneven, easily leading to stress concentration at the boundary between reinforced and unreinforced zones. Furthermore, existing construction control relies heavily on post-construction monitoring and early warning, lacking real-time linkage and control with construction parameters, making it difficult to achieve forward-looking deformation control and resulting in low construction safety reserves. Summary of the Invention

[0005] This application provides a construction method for an open-cut tunnel to cross an existing shield tunnel, and an open-cut tunnel, to solve the problems in related technologies such as difficulty in controlling the upward deformation of existing shield tunnels due to upper excavation and unloading, lack of systematic coordination of protective measures, and low safety controllability during construction.

[0006] Firstly, a construction method for a cut-and-cover tunnel crossing an existing shield tunnel is provided, comprising the following steps: Internal reinforcement will be carried out on the sections of existing shield tunnels located within the pre-set area of ​​the newly constructed open-cut foundation pit; A solidification body is constructed in the surrounding soil of the newly built open-cut foundation pit. The solidification body wraps around the sidewalls and bottom of the pit to form a U-shaped constraint structure. A support structure is installed at the bottom of the U-shaped constraint structure along the longitudinal direction of the newly constructed open-cut foundation pit; The new open-cut foundation pit was excavated using the inverted well wall method combined with the compartmentalized skip excavation sequence. After the bottom of the foundation pit reached the design elevation, the bottom sealing grid was constructed and anchored to the supporting structure. Then the main structure of the open-cut tunnel was constructed. Existing shield tunnels are monitored, and construction parameters are adjusted based on the monitoring data.

[0007] In some embodiments, internal reinforcement is carried out on sections of existing shield tunnels located within a predetermined area of ​​a newly constructed open-cut excavation pit, including: Before constructing a new open-cut foundation pit, ring-shaped steel components are installed on the inner surface of the segments within the pre-defined section of the existing shield tunnel. The ring-shaped steel components are arranged at intervals along the longitudinal direction of the tunnel, and adjacent ring-shaped steel components are connected by longitudinal steel ribs. Structural bonding material is filled between the annular steel member and the pipe segment to bond the annular steel member and the pipe segment into an integral load-bearing structure.

[0008] In some embodiments, the projection section of the newly constructed open-cut excavation pit onto the existing shield tunnel is defined as the central section, and the area extending from the central section to both sides by a predetermined distance is defined as the transition section. Along the axial direction of the existing shield tunnel, the arrangement density of the annular steel components in the central section is greater than that in the transition section.

[0009] In some embodiments, the construction method for reinforcing the sidewalls of newly excavated open-cut foundation pits includes: Within a predetermined distance range outside the design boundary of the newly constructed open-cut foundation pit, extending below ground level to a predetermined depth below the bottom of the newly constructed open-cut foundation pit, high-pressure jet grouting piles or mixing piles are used to form lateral restraint walls along both sides of the newly constructed open-cut foundation pit.

[0010] In some embodiments, the construction method for reinforcing the bottom of a newly excavated open-cut foundation pit includes: High-pressure jet grouting piles are used to reinforce the soil above the existing shield tunnel and below the bottom slab of the newly built open-cut foundation pit, and are connected to the reinforced body of the sidewall of the newly built open-cut foundation pit to form the U-shaped constraint structure.

[0011] In some embodiments, the method for setting up the support structure includes: Within the solidified body of the newly constructed open-cut foundation pit, a steel pipe shed is drilled longitudinally along the newly constructed open-cut foundation pit. The steel pipe shed consists of multiple steel pipes arranged parallel to each other in the longitudinal direction. Grout is injected into the surrounding soil through grouting holes on the steel pipe walls, so that the steel pipes and the surrounding solidified body form a composite shed structure.

[0012] In some embodiments, the inverted well wall method is used for construction, including the following steps: First, construct the top locking ring beam, then excavate the soil layer by layer from top to bottom. After each layer is excavated, construct the side wall steel frame and anchor bolt support for that layer, and install internal steel supports at the steel frame location. The side wall support structure extends invertedly from the top down to the bottom of the foundation pit.

[0013] In some embodiments, dividing the newly constructed open-cut foundation pit longitudinally into several compartments and excavating them in a skip-excavation sequence includes: The newly constructed open-cut foundation pit is divided into multiple independent excavation sections along the longitudinal direction, and is divided into at least a first batch of excavation sections and a second batch of excavation sections by adopting an intermittent skip excavation sequence; First, construct the first batch of excavation chambers and the pit bottom sealing structure, and then connect the pit bottom sealing structure of the first batch of excavation chambers with the longitudinal support structure to form a load-bearing connection. After the main structure of the first batch of excavation chambers reaches the preset strength, the second batch of excavation chambers will be constructed.

[0014] In some embodiments, adjusting construction parameters based on monitoring data includes: Set multi-level early warning thresholds for deformation of existing shield tunnels; Real-time acquisition of vertical and horizontal displacement data of existing shield tunnels, and comparison with the multi-level early warning thresholds; When the monitoring data exceeds the warning threshold, construction control measures corresponding to the warning level are implemented. These measures include suspending construction, increasing load, or activating the emergency plan.

[0015] Secondly, a cut-and-cover tunnel is provided, which is constructed using the construction method described in the first aspect.

[0016] This application provides a construction method for an open-cut tunnel crossing an existing shield tunnel, and a systematic collaborative protection construction method for an open-cut tunnel crossing an existing shield tunnel at close range in soft soil strata. By forming a three-layer protection system of "inner-middle-outer" in the spatial dimension by reinforcing the existing shield tunnel with annular steel components inside, reinforcing the "U"-shaped stratum outside the open-cut tunnel, supporting the longitudinal steel pipe canopy, carrying out compartmentalized jump excavation construction with inverted shaft walls, and fully automated monitoring, five technical measures are implemented. This forms a multi-level load transfer chain in the mechanical path and a progressive collaborative logic of "reinforcement before excavation and monitoring while construction" in the construction sequence. Therefore, it realizes a full-dimensional systematic safety control from the existing shield tunnel body to the stratum environment and the construction process. It significantly suppresses the uplift, longitudinal uneven deformation and lateral convergence deformation of the existing shield tunnel caused by the excavation and unloading of the foundation pit in soft soil strata, and greatly improves the safety and reliability of close-range crossing construction. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the construction method of the open-cut tunnel crossing an existing shield tunnel in this application. Figure 2 A schematic diagram of a cut-and-cover tunnel crossing an existing shield tunnel. Figure 3 A schematic diagram of the longitudinal section of an open-cut tunnel crossing an existing shield tunnel. Figure 4 A schematic diagram of a cross-section for reinforcing the internal annular steel structure of an existing shield tunnel. Figure 5 for Figure 4 Detailed schematic diagram of the longitudinal connection of the central ring steel component; Figure 6 A schematic diagram of the cross-section of the side and bottom strata reinforcement of an open-cut tunnel; Figure 7 This is a schematic diagram of the longitudinal steel pipe shed layout at the bottom of an open-cut tunnel; Figure 8 A schematic diagram showing the division of open-cut foundation pits into compartments for skip-excavation. Figure 9 Schematic diagram of the layered excavation and main structure construction steps for the inverted well wall Figure I ; Figure 10 Schematic diagram of the layered excavation and main structure construction steps for the inverted well wall Figure II ; Figure 11 Schematic diagram of the layered excavation and main structure construction steps for the inverted well wall Figure III ; Figure 12 Schematic diagram of the layered excavation and main structure construction steps for the inverted well wall Figure IV ; Figure 13 This is a schematic diagram of the existing tunnel's automated monitoring section and the layout of monitoring points.

[0019] In the diagram: 1. Newly constructed open-cut tunnel; 2. Existing shield tunnel; 3. Open-cut tunnel roof slab; 4. Open-cut tunnel floor slab; 5. Open-cut tunnel sidewall; 6. Locking ring beam; 7. Shaft sidewall; 8. Circular steel component; 9. Longitudinal steel rib; 10. Anchor bolt; 11. Epoxy resin; 12. Anti-corrosion coating; 13. Lateral restraint wall; 14. Bottom reinforcement; 15. Steel pipe shed; 16. Steel frame; 17. Anchor bolt; 18. Internal support; 19. Bottom sealing grid; 20. Backfill; 21. Automated monitoring point. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] First, some of the technical terms used in this application will be explained to help those skilled in the art understand this application.

[0022] MJS: Metro Jet System is a high-pressure jet grouting reinforcement technology that can precisely control the ground pressure and effectively reduce the impact on the surrounding environment.

[0023] This application provides a construction method for an open-cut tunnel to cross an existing shield tunnel 2, which can solve the problems in related technologies such as difficulty in controlling the upward deformation of the existing shield tunnel 2 due to the unloading of the upper excavation, lack of systematic coordination of protective measures, and low safety controllability of the construction process.

[0024] Firstly, a construction method for a cut-and-cover tunnel crossing an existing shield tunnel 2 includes the following steps: S100: Internal reinforcement of the section of the existing shield tunnel 2 located within the pre-set area of ​​the newly constructed open-cut foundation pit.

[0025] In this embodiment, the preset range refers to the projection section of the newly constructed open-cut foundation pit onto the existing shield tunnel 2 and its two extended sections. This range is determined comprehensively based on the width of the foundation pit, the tunnel depth, and the geological conditions to ensure that the reinforced section can cover the entire tunnel area affected by construction.

[0026] S101: Determine the reinforcement section of the annular steel component 8 based on the projection range of the newly built open-cut tunnel 1 on the existing shield tunnel 2.

[0027] The scope of the reinforcement section is determined according to the following principles: the central section is the projection of the newly constructed open-cut tunnel 1 onto the existing shield tunnel 2, and a transition section extending from the central section to both sides is no less than 1.5 times the bottom width of the newly constructed open-cut tunnel 1. Along the longitudinal direction of the existing shield tunnel 2, the arrangement density of the annular steel members 8 in the central section is greater than that in the transition section, and the spacing of the annular steel members 8 in the transition section gradually increases to the normal spacing. For example, in the central section, the arrangement of each ring transitions to a one-ring interval, and then to a one-ring interval between two rings, forming a gradually changing stiffness reinforcement pattern of "dense in the middle and gradually sparse at both ends," avoiding abrupt stiffness changes at the boundary between the reinforced and unreinforced sections.

[0028] S102: Before the construction of the new open-cut tunnel 1, the existing shield tunnel 2 shall be internally reinforced.

[0029] Reference Figure 4 and Figure 5 The reinforcement work will be carried out during the subway's nighttime shutdown hours to minimize the impact on the operation of existing lines. The specific steps are as follows: Ring steel components 8 are installed on the inner surface of the segments in the pre-set section of the existing shield tunnel 2. The ring steel components 8 are arranged at intervals along the longitudinal direction of the tunnel. Adjacent ring steel components 8 are connected by longitudinal steel ribs 9 to form a spatial stiffness enhancement system of "ring rib joint". A structural bonding material, such as high-strength epoxy resin 11, is filled between the annular steel member 8 and the pipe segment to bond the annular steel member 8 and the pipe segment into an integral load-bearing structure.

[0030] Under the unloading action of the excavation, the existing shield tunnel 2 beneath it will tend to rise and bulge. The unreinforced segments are hinged flexible structures with weak bending stiffness at the circumferential and longitudinal joints. Under the rebound force of the base caused by external unloading, the segments are prone to lateral convergence deformation and longitudinal bending deformation. By installing annular steel members 8 on the inner surface of the segments and filling them with epoxy resin 11, the annular steel members 8 are bonded to the segments to form a composite structure, which significantly improves both the sectional bending stiffness and axial stiffness. The longitudinal steel ribs 9 connect the annular steel members 8 into a whole, so that the originally discrete reinforcement rings form a continuous spatial stiffness enhancement system in the longitudinal direction, effectively constraining the lateral expansion and longitudinal bending of the segments. At the same time, the gradual arrangement of the annular steel members 8 along the longitudinal direction with "dense in the middle and gradually sparse at both ends" ensures a smooth transition of stiffness between the reinforced and unreinforced sections, avoids additional stress concentration at the stiffness abrupt change, and prevents damage to the segments due to sudden increase in shear stress at the reinforcement boundary.

[0031] S200: Construct a solidification body in the surrounding soil of a newly built open-cut foundation pit. The solidification body wraps around the sidewalls and bottom of the pit, forming a U-shaped constraint structure.

[0032] Reference Figure 6This step includes reinforcing the lateral and bottom strata of the newly constructed open-cut excavation pit, specifically including the following steps: S201: Reinforcement of the surrounding strata of newly constructed open-cut foundation pit.

[0033] A lateral restraint wall 13 is formed by setting a predetermined distance interval, such as 5m, outside the design boundary of the open-cut excavation pit, and extending below ground level to a predetermined depth below the bottom of the open-cut excavation pit, such as not less than 1.5m. High-pressure jet grouting piles or soil mixing piles are used to form the lateral restraint wall 13 along both sides of the excavation pit. The predetermined distance interval and predetermined depth can be adjusted according to the excavation pit and the surrounding environment.

[0034] S202: Reinforcement of the ground stratum at the bottom of newly constructed open-cut foundation pit.

[0035] High-pressure jet grouting piles were used to reinforce the soil above the existing shield tunnel 2 and below the bottom slab 4 of the open-cut tunnel, and the reinforced soil was connected to the sidewall of the foundation pit to form a U-shaped confinement structure. The reinforcement depth was no less than 3m below the bottom slab 4 of the open-cut tunnel, and the net distance between the lower end of the reinforced area and the top of the existing shield tunnel 2 was no less than 1.5m.

[0036] The essence of foundation pit excavation is to unload the soil at the bottom of the pit, causing upward rebound deformation. Lateral restraint walls 13 are arranged on both sides of the foundation pit, and their main functions are: a) to cut off the horizontal connectivity between the soil inside and outside the foundation pit, restricting the lateral extrusion of the soil at the bottom of the pit after unloading, and reducing the vertical rebound of the soil at the bottom of the pit; b) to bear the earth pressure on the sidewalls of the foundation pit, reducing the horizontal displacement of the sidewalls into the pit. The bottom reinforcement body 14 improves the interlayer soil above the existing shield tunnel 2, increasing the compression modulus and shear strength of the interlayer soil, which is equivalent to increasing the stiffness of the load transfer path from the bottom of the pit to the tunnel arch. When rebound force is generated by unloading at the bottom of the pit, the bottom reinforcement body 14 acts as the first stress barrier, absorbing part of the rebound energy through its own compression deformation, and transferring the remaining load relatively evenly to the soil below in the form of a surface load, avoiding stress concentration directly acting on the arch of the existing shield tunnel 2. The lateral restraint wall 13 and the bottom reinforcement body 14 overlap and connect to form a "U"-shaped structure. Its overall stiffness is much greater than any single reinforcement measure. In space, it constitutes a semi-enclosed constraint on the newly built open-cut tunnel 1, effectively limiting the transmission of deformation of the bottom of the pit and the surrounding soil to the existing shield tunnel 2.

[0037] S300: Within the bottom portion of the U-shaped constraint structure, a support structure is installed along the longitudinal direction of the newly constructed open-cut foundation pit.

[0038] Reference Figure 7After the bottom reinforcement 14 reaches its design strength, the steel pipe shed 15 is constructed. Within the reinforcement of the pit bottom wall, the steel pipe shed 15 is drilled longitudinally along the newly constructed open-cut tunnel 1. The steel pipe shed 15 consists of multiple steel pipes arranged parallel to each other longitudinally. The outer diameter of the steel pipes is 159–219 mm, the wall thickness is not less than 8 mm, and the spacing between the steel pipes is 300–500 mm. It is positioned below the bottom surface of the bottom slab of the newly constructed open-cut tunnel 1, close to the bottom surface of the bottom slab. The length of the steel pipe shed 15 covers the entire newly constructed open-cut pit and extends at least 3 meters outwards from both ends of the pit.

[0039] After the steel pipe shed 15 is drilled, grout is injected into the soil around the pipe through the grouting holes on the steel pipe wall. The grouting pressure is controlled at 1.5 to 2.5 MPa, so that the steel pipe and the surrounding solidified body form a composite shed structure.

[0040] During the longitudinal excavation of an open-cut foundation pit, the unloading at the bottom of the pit is not completed all at once, but rather gradually progresses longitudinally. Under these conditions, the rebound force of the soil at the bottom of the excavated section is a longitudinally non-uniformly distributed load. The steel pipe shed 15 provides a load transfer path along the longitudinal direction of the tunnel. Its mechanical mechanism is as follows: the steel pipe shed 15 is located below the bottom surface of the foundation pit slab, close to the bottom surface of the slab. When a certain section is excavated, the soil at the bottom of the pit in that area experiences unloading rebound, and the rebound force is transferred to the steel pipe shed 15 through the bottom reinforcement 14. Each steel pipe in the steel pipe shed 15 is arranged along the longitudinal length of the foundation pit, possessing large bending stiffness and tensile strength, which can disperse and transfer the concentrated rebound force acting on the bottom of the excavated section to the unexcavated soil anchorage area at both ends of the steel pipe shed 15 (extending 3m beyond the foundation pit), forming a "multi-point dispersion, longitudinal transfer" force mode. Meanwhile, the composite scaffold structure formed by the grouted steel pipe and the surrounding soil, together with the U-shaped constraint structure in step S300, forms a gridded reinforcement system. Its equivalent bending stiffness is far greater than the simple superposition of any one scheme, further enhancing the load dispersion effect. The stress characteristics of this support structure determine that the upward load on each point above the existing shield tunnel 2 is averaged out, and the peak load is significantly reduced, thereby effectively controlling the differential settlement and local upward concentration of the existing shield tunnel 2.

[0041] S400: The new open-cut foundation pit is excavated using the inverted well wall method combined with the compartmentalized skip excavation sequence. After the bottom of the foundation pit reaches the design elevation, the bottom sealing grid 19 is constructed and anchored to the support structure. Then the main structure of the open-cut tunnel is constructed.

[0042] Reference Figures 8 to 12 Specifically, this includes: S401: Divide the foundation pit longitudinally into multiple independent excavation chambers, and use an intermittent skip-excavation sequence to divide it into at least a first batch of excavation chambers and a second batch of excavation chambers.

[0043] like Figure 8As shown, the newly constructed open-cut foundation pit is divided longitudinally into multiple independent excavation sections. The width of each section is determined comprehensively based on the pit width, tunnel depth, and monitoring and control requirements, generally ranging from 4 to 6 meters. An intermittent skip-excavation sequence is adopted, with all sections excavated in at least two batches. The first batch of excavation bins will be odd-numbered bins (such as #1, #3, #5, etc.), and will be constructed first. The second batch of excavated chambers will be even-numbered chambers (such as 2#, 4#, 6#, etc.). Excavation can only begin after the main structure of each chamber in the first batch has reached the design strength and the monitoring data has stabilized.

[0044] In some embodiments, the compartments can be divided into three or more batches for skip excavation based on the longitudinal length of the pit and site conditions, in order to further reduce the unloading area per batch. For example, the compartments can be divided into three batches in a "two-out-of-one" manner, and excavated in batches at intervals. The more batches there are, the smaller the unloading area per batch, but the construction period will be extended accordingly. It is necessary to select the appropriate batch based on the project schedule requirements.

[0045] S402: First, construct the first batch of excavation chambers and the bottom sealing structure of the pit, and then connect the bottom sealing structure of the first batch of excavation chambers with the supporting structure to form a load-bearing connection. Taking a sub-account as an example, the specific steps are as follows: S4021: As Figure 9 As shown, the top locking ring beam 6 is constructed first to form a closed structure at the top of the foundation pit; S4022: As Figure 10 As shown, the soil is excavated layer by layer from top to bottom, with each layer having a preset excavation depth, for example, 2.5m; S4023: After each layer is excavated, construct the steel frame 16 and anchor bolts 17 for the side wall support of that layer, and install steel internal support 18 at the position of steel frame 16; S4024: Repeat construction of S4022 and S4023, with the sidewall support structure extending downwards layer by layer from the top to the ground elevation at the bottom of the pit; S4025: As Figure 10 As shown, after the bottom of the foundation pit reaches the design elevation, the bottom sealing grid 19 is constructed and anchored to the supporting structure to combine the longitudinal force transmission function of the steel pipe shed 15 with the overall rigidity of the bottom sealing structure. Immediately afterwards, the bottom slab cushion layer and the open-cut tunnel bottom slab 4 are constructed. S4026: As Figure 11 As shown, the open-cut tunnel sidewall 5 and the roof slab are constructed sequentially from bottom to top.

[0046] S403: The second batch of excavation chambers will be constructed after the main structure of the first batch of excavation chambers has reached the preset strength.

[0047] The construction procedures for the second batch of excavation sections are the same as those for the first batch. A post-cast strip with a width of 800mm is set between the bottom slab of the second batch of excavation sections and the bottom slab of the adjacent first batch of excavation sections. C40 micro-expansion concrete is used for the post-cast strip, and the expansion rate is controlled between 0.03% and 0.05% to ensure that the bottom slabs of each section are connected as a whole.

[0048] In step S400, the core of the inverted shaft wall method lies in "excavation and protection immediately"—after each layer of soil is excavated, the sidewall steel frame 16, anchor bolts 17, and internal supports 18 are immediately constructed, so that the retaining structure forms a closed stress system after each excavation step is completed. Compared with the traditional open-cut method, which involves large-area exposure followed by unified support erection, the inverted shaft wall method significantly shortens the unsupported exposure time of the soil, reduces the time-history effect of ground stress release, and thus reduces the total amount of soil rebound at the bottom of the pit.

[0049] The mechanical significance of compartmentalized skip excavation lies in breaking down large-area continuous unloading into multiple small-area intermittent unloading processes. Taking 14 compartments as an example, if the traditional sequential excavation method is used, when the entire pit is excavated, the unloading area is equivalent to the entire pit area, meaning that the shield tunnel 2 bears a large-area unloading load in one go. However, with the interval skip excavation method, the area excavated in a single operation is only 1 / 7 of the entire pit area, significantly reducing the amount of unloading per operation. At the same time, the unexcavated soil from the even-numbered compartments is retained between adjacent odd-numbered compartments. These soil columns act as natural temporary supports, providing lateral restraint to the bottom soil of the excavated area and inhibiting the further expansion of the rebound range from the bottom of the pit.

[0050] The connection between the bottom sealing grid 19 and the longitudinal steel pipe shed 15 has a synergistic effect in terms of force distribution. The bottom sealing grid 19 provides a rigid constraint surface for the pit bottom. When the even-numbered compartments are excavated laterally, the bottom slabs of the odd-numbered compartments, whose structural construction has been completed, and the bottom sealing grid 19 constitute a lateral rigid support, forming a "cross-shaped" grid-like force system with the longitudinal steel pipe shed 15. The longitudinal force transmission effect of the steel pipe shed 15 is further distributed laterally through the bottom sealing grid 19, so that the upward load on the top of the existing shield tunnel 2 is effectively distributed in both longitudinal and lateral dimensions, realizing three-dimensional stress redistribution control.

[0051] S500: Monitor the existing shield tunnel 2 and adjust the construction parameters based on the monitoring data.

[0052] See Figure 13Specifically, throughout steps S100 to S400, automated real-time monitoring is implemented on the existing shield tunnel 2. The monitoring system includes automated monitoring points 21 deployed on the existing shield tunnel 2 within a range of no less than 5 times the depth of the new open-cut excavation pit. The longitudinal spacing of the monitoring sections is 5–10 m, and the spacing is increased to 2–3 m within the projection section of the new open-cut tunnel 1. Monitoring parameters include vertical displacement (settlement / heave), horizontal convergence, longitudinal uneven settlement, segment joint opening, and changes in the geometric dimensions of the track within the tunnel.

[0053] Data was collected every 2 hours during the reinforcement of the ring steel component; every 4 hours during the ground reinforcement; and continuously in real time during the compartmentalized excavation. The data transmission interval was 30 minutes. The monitoring data was transmitted to the construction control center in real time via wired or wireless means.

[0054] The following are the details of setting multi-level early warning thresholds for deformation of existing shield tunnel 2: A yellow warning is triggered when the displacement rate exceeds 0.5 mm / d or the cumulative displacement reaches 40% of the alarm value. An orange alert is triggered when the displacement rate exceeds 1.0 mm / d or the cumulative displacement reaches 70% of the alarm value. A red alert is triggered when the displacement rate exceeds 1.5 mm / d or the cumulative displacement reaches 90% of the alarm value.

[0055] Different warning levels correspond to different construction response measures: When a yellow alert is issued, construction at the current work site should be suspended, monitoring frequency should be increased, and the cause of deformation should be analyzed. When an orange alert is issued, construction of the affected compartment will be suspended, counterweights will be added to the base plate, and the monitoring frequency of adjacent compartments will be increased. When a red alert is issued, all construction work is halted, and emergency plans are activated, including measures such as backfilling and weighting, and adding temporary supports.

[0056] The monitoring data in step S500 is a quantitative verification of the stress effectiveness of each protective measure in steps S100 to S400. Specifically: the vertical displacement and horizontal convergence data of the arch directly reflect the effect of the internal annular steel component 8 on improving the rigidity of the tunnel itself—if the reinforcement is sufficient, the opening amount of the tunnel segment joints and the lateral deformation amount after loading should be significantly less than that in the unreinforced state; the rebound data of the pit bottom reflects the suppression effect of the bottom reinforcement 14 and the steel pipe shed 15 on unloading rebound—if the reinforcement and shed system effectively play the role of load distribution and transmission, the stress transmitted from the pit bottom rebound to the tunnel arch will be greatly reduced; the comparison of the change curves of monitoring data during different compartment excavation processes can evaluate the control effectiveness of compartment skip excavation on the single unloading amount.

[0057] Yellow alerts correspond to the warning line of the elastic deformation stage of the soil, orange alerts correspond to the warning line of the elasto-plastic transition stage, and red alerts correspond to the control line of the plastic failure stage. When monitoring data triggers different levels of alerts, the dynamic adjustment of construction parameters is equivalent to actively changing the mechanical boundary conditions, such as reducing the compartment width to reduce the single unloading amount and increasing the load to balance the rebound force, so that the stress state of the existing shield tunnel 2 is always within a controllable and safe range. Thus, step S500 not only plays a monitoring role, but also achieves a leap from "passive monitoring" to "active control" through active intervention in the mechanical behavior of construction, ensuring that the entire construction process is always in a safe and controllable state.

[0058] Secondly, this application provides an open-cut tunnel, constructed using the construction method described in the first aspect.

[0059] In summary, the beneficial effects of this application are as follows: The core innovation of this application lies in the deep synergy and system integration among the five technical measures, forming an integrated collaborative protection system. Its internal logical relationship is as follows: Spatial Dimensional Synergy: Step 1 involves forming a stiffening reinforcement layer inside the existing shield tunnel; Step 2 involves forming a retaining reinforcement body outside the newly constructed open-cut tunnel; and Step 3 involves forming a longitudinal canopy layer between the existing shield tunnel and the newly constructed open-cut tunnel. These three layers of protection spatially form an "inner-middle-outer" triple protection system, each with its own function while complementing each other—the annular steel structure provides segment stiffness, the external reinforcement body provides ground constraint, and the longitudinal steel pipe canopy provides a load transfer path.

[0060] Synergistic Mechanical Path: The mechanical essence of the upward movement of existing shield tunnels is that the unloading during excavation of the foundation pit causes the vertical stress release to exceed the resistance capacity of the tunnel-soil system. The synergistic mechanical path in this application is as follows: the steel pipe shed disperses and transfers the longitudinal unloading stress along the longitudinal direction of the newly built open-cut tunnel → the lateral restraint wall restricts the lateral extrusion of the soil → the bottom reinforcement zone increases the soil's deformation modulus → the annular steel component enhances the tunnel's own stiffness. These four elements form a complete multi-level mechanical transmission chain.

[0061] Coordination during construction: Step four, the compartmentalized skip excavation, works closely with Step three, the longitudinal steel pipe shed—the steel pipe shed is anchored during the construction of the bottom sealing structure in odd-numbered compartments, integrating the longitudinal force transmission function of the steel pipe shed with the overall integrity of the newly constructed open-cut tunnel support structure. Step five, the monitoring system, implements dynamic feedback control over the entire construction process from Step one to Step four, forming a closed loop of "construction-monitoring-adjustment".

[0062] The sequential coordination follows a logical progression: first, reinforce the existing structure; then, reinforce the strata; next, construct the scaffolding; and finally, excavate in sections. Step one is performed first to ensure that the existing shield tunnel has sufficient rigidity reserves. Step two follows immediately after, with strata reinforcement completed before excavation. Step three involves drilling steel pipe scaffolding in the reinforced area, utilizing the stability of the reinforced soil to ensure the construction accuracy of the steel pipe scaffolding. Step four involves precise section-by-section excavation after the entire protection system is in place. Step five is carried out throughout the entire process to ensure full control.

[0063] The construction process of this application is illustrated below with a specific example: This embodiment uses a case study of a newly constructed open-cut subway tunnel crossing an existing operational shield tunnel in a city. In this project, the new open-cut tunnel is a rectangular frame structure with a width of 8.1m and a height of 7m; the existing shield tunnel has an outer diameter of 6.2m, an inner diameter of 5.5m, a segment thickness of 350mm, and a ring width of 1.2m. The minimum clear distance between the bottom of the open-cut pit and the crown of the existing shield tunnel is 2.75m, and the total clear distance between the two tunnels is 9.2m. The site strata are typical soft soil layers, mainly composed of silty clay and silty clay, exhibiting engineering characteristics of high water content, high compressibility, and low strength. The construction method specifically includes the following steps: S100: Reinforcement of the internal annular steel structure of existing shield tunnels Based on the projection range of the newly constructed open-cut tunnel onto the existing shield tunnel, the total length of the annular steel component reinforcement section was determined to be 90m. The central section, comprising the projection section plus a 3m extension at each end, totaling 58m, will have one annular steel component installed for each ring of tunnel segments in this section. The transition sections at both ends will each have 10 rings, with one ring skipped between each pair of rings, before transitioning to one annular steel component every two rings. Construction of the annular steel components will be carried out during the subway's nighttime shutdown period, and the specific steps are as follows: (1) Pre-treatment of the segments within the reinforcement range of the existing shield tunnel, including pipeline relocation, leakage control, and crack repair; (2) Based on the actual deformation of the existing shield tunnel segments, prefabricated annular steel components are divided into blocks. The annular steel components are made of 20mm thick Q345 steel plates. (3) The ring steel components are anchored in the inner wall of the tunnel segment with anchor bolts. The whole ring reinforcement is adopted. The ring steel components are set in each ring along the longitudinal direction of the tunnel, and the closed ring steel components are formed by five ring steel components. (4) The gap between the annular steel member and the inner wall of the segment is filled with epoxy resin pressure grouting. (5) The surface of the ring steel component is sprayed with epoxy zinc-rich primer and polyurethane topcoat for corrosion protection.

[0064] Step S200: Reinforcement of the strata on the sides and bottom of the cut-and-cover tunnel (1) Side reinforcement: 5m outside the design boundary of the open excavation pit and 3m outside the inverted well wall, the side reinforcement is constructed by using three-axis mixing piles. The diameter of the mixing piles is 850mm, the pile overlap is 250mm, and the reinforcement depth extends from below the ground to below the bottom of the pit by no less than 1m.

[0065] (2) Ground Reinforcement at the Pit Bottom: In the interlayer soil area between the bottom of the open-cut pit and the existing shield tunnel arch, jet grouting was carried out using the MJS method to form a reinforced bottom layer. The thickness of the reinforced bottom layer was 2.5m, and the net distance between the bottom surface of the reinforced layer and the existing shield tunnel arch was 1.5m. MJS reinforcement construction parameters: The piles were constructed in a "four-at-a-time" staggered pile sequence, with a designed pile diameter ≥ 2.0m; overlap thickness ≥ 400mm; grouting pressure ≤ 40MPa; air pressure 0.7MPa; ground pressure control range 0.10~0.30MPa; cement grout usage approximately 40%; pumping speed 15min / m; rotation speed 4r / min; lifting step distance 25mm; grout flow rate 85~100L / min. After 28 days, the unconfined compressive strength of the reinforced layer reached 1.5MPa, and the permeability coefficient ≤ / cm / s. During construction, the soil pressure is automatically adjusted through the mud discharge valve to maintain it within the range of 1.2 to 1.5 times the in-situ soil pressure.

[0066] Step S300: Construction of longitudinal steel pipe shed at the bottom of open-cut tunnel After the bottom reinforcement reaches 80% of its design strength, the steel pipe shed construction begins. Horizontal holes with a diameter of 200mm are drilled longitudinally along the open-cut tunnel. Seamless steel pipes with an outer diameter of 159mm and a wall thickness of 10mm are inserted into each hole, spaced 400mm apart. A total of 38 steel pipe sheds are installed, covering the entire length of the excavation pit and extending 3m outwards from both ends. Grouting holes with a diameter of 8mm are pre-drilled on the steel pipe walls, arranged in a staggered pattern with a spacing of 300mm. After the steel pipes are drilled and positioned, cement-water glass grout is injected into the surrounding soil through the grouting holes at a pressure of 2.0MPa. The grout volume per hole is approximately 1.5 times the volume of the void space outside the steel pipe.

[0067] S400: Inverted shaft wall method for compartmentalized skip excavation construction The cut-and-cover tunnel is 70m long longitudinally and divided into 14 compartments, each 5m wide. These compartments are numbered sequentially from 1# to 14#. Each compartment is constructed using the inverted shaft wall method, with the foundation pit supported by reinforced steel grating, internal bracing, and external anchor bolts.

[0068] First, the inverted well wall construction of the odd-numbered compartments (1#, 3#, 5#, 7#, 9#, 11#, and 13#) will be carried out. Taking compartment 1# as an example, the specific steps are as follows: (1) Construction of the lock ring beam, with a cross-sectional dimension of 1200mm×1000mm; (2) Excavate the soil layer by layer from top to bottom, with each layer having an excavation depth of 2.5m; (3) Immediately after the excavation of each layer is completed, construct the sidewall grid steel frame and anchor bolt support for that layer, and set steel supports at the grid steel frame positions; the grid thickness is 350mm, specification φ25@500; the anchor bolts are φ42mm steel bars, 2.5m long, with a horizontal inclination angle of 25° and a vertical spacing of 1m. The supports are 28b / 32b I-beams.

[0069] (4) Repeat steps (2) and (3) to construct layer by layer downwards until the bottom elevation of the foundation pit is reached; (5) After the bottom of the foundation pit reaches the design elevation, the bottom sealing grid is constructed and connected to the longitudinal steel pipe shed. Then, the bottom slab cushion layer (C20 plain concrete, 200mm thick) and the open-cut tunnel bottom slab are constructed immediately.

[0070] (6) The sidewalls and roof of the open-cut tunnel are constructed from bottom to top.

[0071] Excavation of even-numbered compartments can only begin after the concrete strength of the main structure of the odd-numbered compartments reaches 100% of the design strength and the monitoring data is stable.

[0072] The construction procedures for even-numbered compartments are the same as those for odd-numbered compartments. A post-pouring strip with a width of 800mm is provided between the bottom slab of an even-numbered compartment and the bottom slab of an adjacent odd-numbered compartment. C40 micro-expansion concrete is used for pouring, and the expansion rate is controlled between 0.03% and 0.05% to ensure that the bottom slabs of each compartment are connected as a whole.

[0073] S500: Automated Monitoring and Dynamic Control of Construction The monitoring section layout plan is as follows: 15 monitoring sections will be set up in the 70m long section affected by construction. The monitoring sections will be spaced 3m apart in the projected section (approximately 58m), for a total of 20 sections; and 4 monitoring sections will be set up in each 20m extension range at both ends, with a spacing of 5m.

[0074] Five monitoring points were set up at each monitoring section, located at the tunnel arch crown, left arch waist, right arch waist, left arch bottom, and right arch bottom, respectively. The monitoring content included vertical displacement and horizontal convergence. The monitoring frequency was as follows: data was collected every 2 hours during the ring steel component reinforcement construction; data was collected every 4 hours during the stratum reinforcement construction; and data was collected continuously in real time during the compartmentalized skip excavation construction, with a data transmission interval of 30 minutes.

[0075] The warning thresholds are set to three levels: yellow warning – displacement rate 0.5 mm / d or cumulative displacement 5 mm; orange warning – displacement rate 1.0 mm / d or cumulative displacement 8 mm; red warning – displacement rate 1.5 mm / d or cumulative displacement 10 mm.

[0076] During the actual construction of this embodiment, the maximum cumulative vertical displacement of the existing shield tunnel was 2.3 mm, and the maximum horizontal convergence was 0.5 mm, which was far below the warning value, verifying the safety and effectiveness of the method in this application.

[0077] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0078] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0079] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A construction method for a cut-and-cover tunnel crossing an existing shield tunnel, characterized in that, Includes the following steps: Internal reinforcement will be carried out on the sections of existing shield tunnels located within the pre-set area of ​​the newly constructed open-cut foundation pit; A solidification body is constructed in the surrounding soil of the newly built open-cut foundation pit. The solidification body wraps around the sidewalls and bottom of the pit to form a U-shaped constraint structure. A support structure is installed at the bottom of the U-shaped constraint structure along the longitudinal direction of the newly constructed open-cut foundation pit; The new open-cut foundation pit was excavated using the inverted well wall method combined with the compartmentalized skip excavation sequence. After the bottom of the foundation pit reached the design elevation, the bottom sealing grid was constructed and anchored to the supporting structure. Then the main structure of the open-cut tunnel was constructed. Existing shield tunnels are monitored, and construction parameters are adjusted based on the monitoring data.

2. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, Internal reinforcement will be carried out on the sections of existing shield tunnels located within the pre-defined area of ​​the newly constructed open-cut excavation pit, including: Before constructing a new open-cut foundation pit, ring-shaped steel components are installed on the inner surface of the segments within the pre-defined section of the existing shield tunnel. The ring-shaped steel components are arranged at intervals along the longitudinal direction of the tunnel, and adjacent ring-shaped steel components are connected by longitudinal steel ribs. Structural bonding material is filled between the annular steel member and the pipe segment to bond the annular steel member and the pipe segment into an integral load-bearing structure.

3. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 2, characterized in that, The projection section of the newly constructed open-cut foundation pit onto the existing shield tunnel is defined as the central section, and the area extending from the central section to both sides by a predetermined distance is defined as the transition section. Along the axial direction of the existing shield tunnel, the arrangement density of the annular steel components in the central section is greater than that in the transition section.

4. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, The construction methods for reinforcing the sidewalls of newly constructed open-cut foundation pits include: Within a predetermined distance range outside the design boundary of the newly constructed open-cut foundation pit, extending below ground level to a predetermined depth below the bottom of the newly constructed open-cut foundation pit, high-pressure jet grouting piles or mixing piles are used to form lateral restraint walls along both sides of the newly constructed open-cut foundation pit.

5. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, The construction methods for reinforcing the bottom of newly excavated open-cut foundation pits include: High-pressure jet grouting piles are used to reinforce the soil above the existing shield tunnel and below the bottom slab of the newly built open-cut foundation pit, and are connected to the reinforced body of the sidewall of the newly built open-cut foundation pit to form the U-shaped constraint structure.

6. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, The methods for setting up the support structure include: Within the solidified body of the newly constructed open-cut foundation pit, a steel pipe shed is drilled longitudinally along the newly constructed open-cut foundation pit. The steel pipe shed consists of multiple steel pipes arranged parallel to each other in the longitudinal direction. Grout is injected into the surrounding soil through grouting holes on the steel pipe walls, so that the steel pipes and the surrounding solidified body form a composite shed structure.

7. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, The inverted well wall method is used for construction, including the following steps: First, construct the top locking ring beam, then excavate the soil layer by layer from top to bottom. After each layer is excavated, construct the side wall steel frame and anchor bolt support for that layer, and install internal steel supports at the steel frame location. The side wall support structure extends invertedly from the top down to the bottom of the foundation pit.

8. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, The newly constructed open-cut foundation pit is divided longitudinally into several compartments, and excavated in a skip-excavation sequence, including: The newly constructed open-cut foundation pit is divided into multiple independent excavation sections along the longitudinal direction, and is divided into at least a first batch of excavation sections and a second batch of excavation sections by adopting an intermittent skip excavation sequence; First, construct the first batch of excavation chambers and the pit bottom sealing structure, and then connect the pit bottom sealing structure of the first batch of excavation chambers with the longitudinal support structure to form a load-bearing connection. After the main structure of the first batch of excavation chambers reaches the preset strength, the second batch of excavation chambers will be constructed.

9. The construction method for an open-cut tunnel crossing an existing shield tunnel as described in claim 1, characterized in that, Adjusting construction parameters based on monitoring data includes: Set multi-level early warning thresholds for deformation of existing shield tunnels; Real-time acquisition of vertical and horizontal displacement data of existing shield tunnels, and comparison with the multi-level early warning thresholds; When the monitoring data exceeds the warning threshold, construction control measures corresponding to the warning level are implemented. These measures include suspending construction, increasing load, or activating the emergency plan.

10. A cut-and-cover tunnel, characterized in that, Obtained by using the construction method described in any one of claims 1-9.

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