Non-centering connected-arch tunnel asymmetric load structure coordination system and design method

Abstract

The application discloses a non-guided continuous-arch tunnel asymmetric load structure coordination system and a design method, and solves the problems of instability of a preceding hole base, cracking of an inverted arch, instability of a middle wall and collapse of a supporting hole of a following hole caused by close construction. Through disturbance degree and plastic zone analysis of surrounding rock, an asymmetric load model is established in combination with Fenner theory; hierarchical construction procedures are formulated according to differences in surrounding rock conditions, and a distance between a working face and lining is controlled; load adaptability design is realized by adopting structural measures such as reinforcing supporting parameters of the preceding hole, expanding arch feet of the middle wall and deepening the inverted arch; a differential monitoring system with the middle wall pressure stress of the preceding hole and settlement of a maintenance passage as indexes is constructed, and a key monitoring range is determined based on a three-dimensional numerical model. The application realizes quantization of asymmetric load, process interference control, matching of supporting parameters and establishment of a monitoring benchmark, significantly improves stability of a tunnel structure and safety of construction, and is suitable for non-guided continuous-arch tunnel engineering under terrain limited conditions.

Description

Technical Field

[0001] This invention belongs to the field of tunnel and underground engineering design and construction technology, specifically relating to a collaborative system and design method for asymmetric load structures of tunnels without a central guide arch, suitable for complex mountainous terrain and urban underground interchanges under confined space conditions. Background Technology

[0002] As an effective solution for highway tunnel construction facing challenges such as narrow terrain, steep slopes, difficult route planning, connections between large bridges and tunnels, and strict land constraints, the non-centralized arch tunnel has been widely used in recent years in mountainous areas of southwest my country and urban underground interchange projects. However, due to significant differences in structural system, stress mode, and construction organization requirements compared to traditional arch tunnels, problems such as instability of the foundation of the preceding tunnel, cracking of the invert arch, instability and failure of the lining wall, and traction-type collapse of the initial support of the following tunnel often occur during close-proximity construction, seriously affecting tunnel structural safety and construction progress.

[0003] Currently, the design and construction of tunnels without a central guide arch mainly rely on empirical methods used for conventional tunnels or separated tunnels, lacking systematic asymmetric load analysis models and collaborative design theories. Specifically, existing technologies have significant shortcomings in the following key aspects:

[0004] 1. Difficulty in quantifying asymmetric loads: Traditional methods for calculating surrounding rock pressure do not take into account the secondary disturbance and deterioration of the surrounding rock of the preceding tunnel by the subsequent tunnel excavation, making it difficult to accurately reflect the actual load distribution characteristics and easily leading to conservative or insufficient design of support parameters.

[0005] 2. Inaccurate control of construction procedures: The current construction methods do not fully distinguish the differences in mechanical response under soft rock and hard rock conditions, and the control standards for the distance between the tunnel face and the secondary lining are vague, which can easily lead to structural traction failure.

[0006] 3. Inappropriate matching of support structure: The support parameters mostly adopt a uniform strengthening strategy, ignoring the changes in the stress mode of the structure under asymmetric loads, especially the stability risk brought about by the transformation of the central wall from small eccentric compression to large eccentric compression;

[0007] 4. The monitoring system lacks specificity: the existing monitoring items and early warning thresholds fail to reflect the dynamic disturbance impact of subsequent tunnel construction on the structure of the preceding tunnel, making it difficult to achieve early identification and effective intervention of risks.

[0008] In summary, current technologies have not yet developed a systematic solution to effectively address the challenges of asymmetric load distribution, structural response imbalance, and construction disturbance control caused by close-proximity construction of tunnels without a central guide arch. Therefore, there is an urgent need to propose a scientific and practical asymmetric load-structure co-design method to improve the design level and construction safety assurance capabilities of tunnels without a central guide arch. Summary of the Invention

[0009] To address the aforementioned issues, this invention provides a collaborative system and design method for asymmetric load structures in tunnels without a central guide arch. The aim is to construct a complete collaborative control system from four dimensions: load calculation, construction organization, support design, and monitoring and early warning. This system solves key technical problems such as difficulty in quantifying surrounding rock disturbance, structural stress imbalance, severe process interference, and delayed monitoring and early warning under close-construction conditions.

[0010] The technical solution adopted in this invention is as follows:

[0011] A collaborative system for asymmetric load structures in a tunnel without a central guide arch includes: a load asymmetric system, a process asymmetric system, a support asymmetric system, and a monitoring asymmetric system.

[0012] The load asymmetric system is a functional module that realizes dynamic evaluation and accurate modeling of the asymmetric load of the surrounding rock under close construction conditions in tunnels without a central guide arch by quantifying the surrounding rock disturbance, identifying the plastic zone, correcting the strength parameters, and calculating using elastoplastic theory.

[0013] The process asymmetric system is a collaborative construction control module that distinguishes the surrounding rock grade and lithological characteristics, adopts differentiated chemical methods, and controls key construction steps to suppress the propagation of disturbances from nearby construction and ensure structural stability.

[0014] The asymmetric support system enhances the load-bearing capacity of the preceding tunnel structure and matches the standard support of the subsequent tunnel through differentiated support design, forming an asymmetric support system with coordinated stiffness to adapt to the asymmetric load distribution caused by close-proximity construction.

[0015] The monitoring asymmetric system, by configuring differentiated monitoring items and dynamic thresholds and combining numerical simulation to determine the range of disturbance impact, achieves full-process perception and risk identification of the structural state of tunnels without a central guide arch.

[0016] Furthermore, the load asymmetric system includes a surrounding rock disturbance quantification module, a plastic zone identification module, a strength and damage parameter correction module, and an asymmetric load calculation module;

[0017] The surrounding rock disturbance quantification module obtains elastic wave velocities at different stages through single-hole acoustic wave testing, and quantitatively assesses the degree of construction disturbance to the surrounding rock.

[0018] The plastic zone identification module uses cross-hole CT or acoustic wave method combined with differential / threshold analysis to determine the range of plastic failure of the surrounding rock;

[0019] The strength damage parameter correction module dynamically corrects the cohesion and internal friction angle based on the surrounding rock disturbance degree, reflecting the characteristics of surrounding rock strength deterioration.

[0020] The asymmetric load calculation module combines Fenner's elastoplastic theory with the ratio of support forces before and after disturbance to calculate the load increment and asymmetric distribution of the surrounding rock of the tunnel.

[0021] Furthermore, the asymmetric process system includes a pre-tunneling process module, a post-tunneling process module, and a face spacing control module;

[0022] The preliminary tunnel construction module selects an appropriate excavation method based on different surrounding rock grades;

[0023] The subsequent tunneling process module employs either mechanical excavation or controlled blasting methods depending on the lithological differences.

[0024] The face spacing control module limits the reasonable spacing between the face of the subsequent tunnel and the secondary lining of the preceding and subsequent tunnels.

[0025] Furthermore, the asymmetric support system includes a pre-tunnel reinforced support module and a post-tunnel conventional support module;

[0026] The pre-tunnel reinforcement support module enhances the overall stiffness of the structure under asymmetric loads by increasing the initial support thickness, upgrading the steel frame specifications, densifying the anchor bolt arrangement, and adopting the construction method of expanding the arch foot of the central wall and deepening the invert arch.

[0027] The conventional support module for the secondary tunnel adopts standard support parameters that match the surrounding rock grade, forming a stiffness transition relationship with the primary tunnel and coordinating the mechanical response of the support system between the two tunnels.

[0028] Furthermore, the asymmetric monitoring system includes a symmetric monitoring module, an asymmetric monitoring module, and a monitoring range control module;

[0029] The symmetrical monitoring module integrates conventional monitoring parameters such as crown settlement, surrounding displacement, surrounding rock pressure, and support internal forces for overall structural condition assessment.

[0030] The asymmetric monitoring module focuses on collecting data on compressive stress in the walls of the pilot tunnel and settlement of the maintenance passage, and sets early warning thresholds to identify local stress anomalies.

[0031] The monitoring range control module, based on three-dimensional numerical simulation and stress change analysis, delineates the spatial range of the impact of subsequent tunnel construction on structural disturbance.

[0032] A collaborative design method for asymmetric load structures of tunnels without a central connecting arch, based on the aforementioned collaborative system for asymmetric load structures of tunnels without a central connecting arch, includes the following steps:

[0033] Step 1, Asymmetric load calculation: Based on the surrounding rock disturbance degree and plastic zone identification, the model is modified using elastoplastic theory to dynamically quantify the asymmetric surrounding rock pressure distribution between the first tunnel and the second tunnel;

[0034] Step 2, Asymmetric construction sequence design: Based on the grade and lithological differences of the surrounding rock, formulate a graded excavation plan and control the distance between the working face and the secondary lining to suppress the superimposed disturbance effect caused by close-contact construction;

[0035] Step 3, Asymmetric support structure design: By differentiating and enhancing the support parameters of the pilot tunnel, and optimizing the structural form of the central wall arch foot and invert arch, the structure's resistance to eccentric pressure under asymmetric loads is improved.

[0036] Step 4, Construction of an asymmetric monitoring system: Combining a dual-threshold early warning mechanism with three-dimensional numerical simulation, key monitoring items and the scope of disturbance impact are determined to achieve dynamic perception and control of structural risks.

[0037] Further, step 1, the asymmetric load calculation, includes the following steps:

[0038] Step 1.1, Obtain elastic wave velocity data: The elastic wave velocity data includes the initial wave velocity V0 in the undisturbed state, the first disturbance wave velocity V1 after the excavation of the first tunnel, and the second disturbance wave velocity V2 after the excavation of the subsequent tunnel.

[0039] Step 1.2, calculate the surrounding rock disturbance degree:

[0040]

[0041] In the formula, D i D1 represents the degree of disturbance to the surrounding rock caused by the excavation of the first tunnel; D2 represents the degree of secondary disturbance to the surrounding rock caused by the excavation of the subsequent tunnel.

[0042] Step 1.3, Determine the radius of the plastic zone: Use the cross-hole CT method or the single-hole acoustic wave method to set up measuring points along the radial direction of the tunnel to conduct wave velocity tests. Analyze the test results according to the differential method or the threshold method to determine the radius RP of the plastic zone;

[0043] Step 1.4 Correcting the surrounding rock strength parameters: Based on the definition of surrounding rock disturbance degree by elastic wave velocity and empirical statistical relationships, calculate the cohesion c and internal friction angle of the surrounding rock of the pilot tunnel after one and two disturbances.

[0044] c i =f(c0,D i ), (i = 1, 2);

[0045]

[0046] In the formula, c0, The cohesion and internal friction angle of the undisturbed surrounding rock of the initial tunnel; c1, The cohesion and internal friction angle of the surrounding rock after the initial tunnel excavation and subsequent disturbance; c2, The cohesion and internal friction angle of the surrounding rock after one disturbance following the excavation of the pilot tunnel; f(c0,D) i () represents the empirical statistical relationship between cohesion and the degree of disturbance of the surrounding rock; Empirical statistical relationship between friction angle and surrounding rock disturbance degree;

[0047] Step 1.5, Calculate the increase in surrounding rock pressure: Based on the modified formula of Fenner's elastoplastic theory, calculate the coefficient of the increase in secondary disturbance load of the surrounding rock of the pilot tunnel.

[0048] ξ = P2 / P1;

[0049]

[0050] In the formula, ξ is the incremental coefficient of secondary disturbance load of the surrounding rock of the pilot tunnel; P1 and P2 are the minimum support forces required for the surrounding rock of the pilot tunnel to reach a stable state after primary and secondary disturbances; σ0 is the initial ground stress; R0 is the single-unit radius of the tunnel. The radius of the plastic zone corresponding to the primary and secondary disturbances of the surrounding rock of the tunnel.

[0051] Thus, the pressure increment Δq of the surrounding rock in the pilot tunnel is calculated; Δq = ξq, where q is the standard surrounding rock pressure.

[0052] Furthermore, step 2, the asymmetric construction sequence design, includes the following steps:

[0053] Step 2.1, Preliminary tunnel construction procedures: For Class V surrounding rock, a three-stage pre-reserved core soil method is adopted; for Class IV surrounding rock, a two-stage method is adopted.

[0054] Step 2.2, subsequent tunnel construction procedures: For Class V soft rock, mechanical block excavation is used; for Class III–IV hard rock, vibration damping holes and controlled blasting are used.

[0055] Step 2.3, Construction distance control: For Class V surrounding rock, the distance between the tunnel face and the secondary lining of the first and second tunnels should be no less than 30m and no more than 40m; for Class IV surrounding rock, appropriate adjustments should be made based on the site conditions to ensure the stability of the secondary lining and initial support structure of the first and second tunnels during the excavation of the second tunnel.

[0056] Further, step 3, the design of the asymmetric support structure, includes the following steps:

[0057] Step 3.1, Enhanced support for the initial tunnel: Enhance the support parameters for the initial tunnel, including: initial support thickness, steel frame type and spacing, radial reinforcement anchor length and spacing; the initial tunnel adopts enlarged central wall arch foot size, while eliminating the cable trench to increase the structural bearing area; the initial tunnel adopts deepened invert arch to improve foundation stability and rise-to-span ratio;

[0058] Step 3.2, Conventional support for the subsequent tunnel: The subsequent tunnel is designed with support parameters according to standard loads, forming a stiffness gradient with the preceding tunnel;

[0059] Step 3.3, Structural stress mode adaptation: When the tunnel is excavated and the secondary lining is not constructed into a ring, the central wall changes from small eccentricity to large eccentricity under pressure. At this time, the bearing capacity of the connection parts is strengthened.

[0060] Furthermore, step 4, the construction of the asymmetric monitoring system, includes the following steps:

[0061] Step 4.1, Determination of monitoring items for the asymmetric monitoring system of the tunnel without a central guide arch:

[0062] The monitoring items of the asymmetric monitoring system for tunnels without a central guide arch include both symmetric and asymmetric monitoring items;

[0063] Symmetrical monitoring items are those monitored in both the initial and subsequent tunnels, including mandatory and optional items: Mandatory items are: geological and support condition observation, surface subsidence, blasting vibration, surrounding displacement, arch subsidence, steel frame and reinforcing steel internal forces, displacement within the surrounding rock, surrounding rock pressure, contact pressure, and initial support and secondary lining concrete stress; Optional items are: displacement within the surrounding rock and anchor bolt axial force.

[0064] The asymmetric monitoring items are those for monitoring the pre-tunnel during the subsequent tunnel excavation stage, including: compressive stress on the surface of the wall lining of the pre-tunnel and settlement of the maintenance passage on the side of the wall of the pre-tunnel;

[0065] Step 4.2, Determination of monitoring benchmarks for the asymmetric monitoring system of the tunnel without a central guide arch:

[0066] For the monitoring items, monitoring benchmarks should be set with reference to current standards and engineering experience;

[0067] For asymmetric monitoring projects, the main components include: monitoring of compressive stress on the surface of the central wall lining and monitoring of settlement of the central wall side inspection passage;

[0068] Monitoring of compressive stress on the surface of the middle wall lining: Based on the Kent-Park constitutive model, the compressive stress control threshold is set to 50% of the standard value of concrete compressive strength, i.e., 0.5fc;

[0069] Settlement monitoring of the maintenance access road on the middle wall: By establishing a two-dimensional numerical model to simulate the entire construction process, applying stepwise displacement boundary conditions, extracting the maximum compressive stress change curve of the lining, and taking the settlement value δ corresponding to the first time the compressive stress reaches 0.5fc as the settlement monitoring control benchmark;

[0070] Step 4.3, Determining the monitoring range of the asymmetric monitoring system for tunnels without a central guide arch:

[0071] Step 4.3.1 Establish a three-dimensional numerical model: Based on the tunnel lining cross-section design drawings, establish a three-dimensional numerical calculation model of the stratum-structure method for a tunnel without a central guide arch; simulate the excavation process of the subsequent tunnel under the condition that the preceding tunnel has been completed in the model;

[0072] Step 4.3.2 Determine the monitoring range from the tunnel face to its secondary lining: Extract the maximum compressive stress on the surface of the wall lining of the preceding tunnel corresponding to the section between the tunnel face and the secondary lining, and plot the variation law of the subsequent tunnel excavation step distance; determine the monitoring range L1 from the tunnel face to its own secondary lining based on the principle that the compressive stress does not exceed 0.5fc.

[0073] Step 4.3.3 Recalculate the tunnel after modeling, maintaining a distance of L1 between the secondary lining and the tunnel face, and simulate the actual construction rhythm in the model; verify and optimize the rationality of L1;

[0074] Step 4.3.4 Determine the range of disturbance impact of the subsequent tunnel on the preceding tunnel:

[0075] First, extract the compressive stress on the surface of the wall lining of the pilot tunnel corresponding to the section between the secondary lining of the pilot tunnel and the working face of the subsequent tunnel along the longitudinal direction of the model, and analyze its variation with the construction step distance.

[0076] Then, determine the rearward disturbance range L at the end of the secondary lining of the pilot tunnel. 21 Disturbance range L in front of the back cave face 22 ; through stress increment ΔP(x) j The criterion of ≤5% is determined iteratively;

[0077] Stress increment ΔP(x) j The formula for calculating ) is:

[0078]

[0079] In the formula, P(x i ) represents a certain position x i The compressive stress value on the lining surface at x is expressed as the compressive stress value at a certain measuring point behind the end of the secondary lining of the tunnel; i P(x) represents the distance from the secondary lining of the pilot tunnel. i+1 ),P(x i+2 ...,P(x j () represents the compressive stress values ​​at multiple subsequent locations, indicating the stress from x... i+1 To x j Compressive stress data at each measuring point within the interval; {P(x i+1 ),P(x i+2 ...,P(x j )} min This is the minimum value among multiple subsequent compressive stress values; x jTo monitor the end position of the section, i.e. the location of the tunnel face of the subsequent tunnel; i is the index of the current analysis point, i = d1 or j - d2, d1 is the range of significant changes in compressive stress from the end of the secondary lining of the preceding tunnel towards the tunnel face of the subsequent tunnel, and d2 is the range of significant changes in compressive stress in front of the tunnel face of the subsequent tunnel; j is the index of the final analysis point, j = s0 - s, s0 is the initial distance of the tunnel face of the subsequent tunnel from the secondary lining of the preceding tunnel, and s is the excavation distance of the tunnel face of the subsequent tunnel;

[0080] Step 4.3.5 Final Monitoring Scope Determination: The routine monitoring scope of the subsequent tunnel is the same as that of a traditional tunnel; the key monitoring scope of the pilot tunnel is: L1 behind the working face of the subsequent tunnel, and L behind the secondary lining of the pilot tunnel. 21 L in front of the back cave 22 .

[0081] The beneficial effects of this invention are:

[0082] This invention proposes a collaborative system and design method for asymmetric load structures in tunnels without a central guide arch. By constructing a four-tiered asymmetric collaborative system of "load-process-support-monitoring," it achieves systematic innovation in theoretical modeling, construction organization, structural response, and risk control. This effectively solves four key technical challenges faced by tunnels without a central guide arch under close-proximity construction conditions: difficulty in quantifying asymmetric loads, difficulty in controlling process interference, difficulty in matching support parameters, and difficulty in establishing monitoring benchmarks. Specific beneficial effects are as follows:

[0083] 1. Constructing an asymmetric load system to solve the problem of quantifying surrounding rock disturbance: This invention proposes for the first time a load increment calculation model based on the degree of surrounding rock disturbance and the radius of the plastic zone. Combining dynamic testing of elastic wave velocity and Fenner's elastic-plastic theory correction method, it scientifically quantifies the secondary disturbance effect and bias pressure effect of the excavation of the secondary tunnel on the surrounding rock of the primary tunnel, realizing the accurate calculation of asymmetric load and avoiding the problem of insufficient support stiffness caused by underestimation of load in traditional methods.

[0084] 2. Establish an asymmetric process system to effectively suppress the propagation of construction disturbances: Develop differentiated construction plans for different surrounding rock conditions, and optimize the excavation sequence and step distance control standards for the first and subsequent tunnels. By strictly limiting the reasonable distance between the tunnel face of the subsequent tunnel and the secondary lining of the first and subsequent tunnels, structural instability phenomena such as traction collapse caused by overlapping processes are effectively prevented, thus improving construction safety.

[0085] 3. Forming an asymmetric support system to achieve coordinated load and structural response: Based on the characteristics of asymmetric load distribution, the initial tunnel support parameters are specifically enhanced, including increasing the initial support thickness, steel frame specifications, and anchor bolt density. Simultaneously, structural reinforcement measures such as expanding the central wall arch foot and deepening the invert arch are introduced to significantly improve the central wall's resistance to eccentric pressure and effectively suppress typical defects such as invert arch cracking and central wall collapse.

[0086] 4. Constructing an asymmetric monitoring system for dynamic risk identification and early warning: This invention innovatively establishes an asymmetric monitoring system that includes a dual-threshold early warning mechanism for compressive stress in the central wall and settlement of the maintenance passage. It also dynamically identifies key structural sections affected by disturbances using three-dimensional numerical simulation technology. By setting a compressive stress limit of 0.5fc and a settlement threshold δ determined based on the stress change curve, the scientific rigor and effectiveness of the monitoring are improved, enabling dynamic risk management throughout the entire construction process.

[0087] In summary, this invention provides a complete and systematic asymmetric collaborative design and construction control technology system for tunnels without a central guide arch, exhibiting significant technological advancements and engineering practicality. This system not only enhances the safety and stability of tunnel structures but also provides a replicable and scalable technical solution for the design and construction of proximity tunnels under complex geological conditions. Attached Figure Description

[0088] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0089] Figure 1 This is a schematic diagram of the four-fold asymmetric technology system of the present invention;

[0090] Figure 2 A schematic diagram of the construction process for a cross-section of a Class V surrounding rock tunnel without a central guide arch.

[0091] Figure 3 A schematic diagram of the construction process for a cross-section of a Class IV surrounding rock tunnel without a central guide arch.

[0092] Figure 4 Schematic diagram of step distance control during construction of Class V surrounding rock in a tunnel without a central guide arch;

[0093] Figure 5 This is a schematic diagram illustrating the change in the stress mode of the wall during the stage of subsequent tunnel excavation before the secondary lining is constructed into a ring.

[0094] Figure 6 Schematic diagram of the design for expanding the arch foot of the central wall and deepening the inverted arch in the pilot tunnel;

[0095] Figure 7 A two-dimensional numerical calculation model of the lining strata-structure method for a SL5a type tunnel without a central guide arch;

[0096] Figure 8 The variation law of maximum compressive stress in the lining of the pilot tunnel with the settlement of the maintenance tunnel;

[0097] Figure 9 A three-dimensional numerical calculation model of the lining strata-structure method for a SL5a type tunnel without a central guide arch;

[0098] Figure 10 for Figure 9 Schematic diagram of the tunnel section in the initial state of the three-dimensional numerical calculation model;

[0099] Figure 11 The variation law of the maximum compressive stress on the surface of the wall lining in the tunnel before the excavation step distance of the tunnel is shown.

[0100] Figure 12 The variation law of compressive stress on the surface of the wall lining in the tunnel before the excavation step distance of the tunnel;

[0101] Figure 13 Schematic diagram of the monitoring range of a pilot tunnel with SL5a lining for a non-centralized arch tunnel;

[0102] Figure 14 This is a schematic diagram of monitoring points for special monitoring projects;

[0103] In the diagram, 1-Preliminary tunnel; 2-Initial support of the preliminary tunnel; 3-Secondary lining of the preliminary tunnel; 4-Subsequent tunnel; 5-Initial support of the subsequent tunnel; 6-Secondary lining of the subsequent tunnel; 7-Working face of the preliminary tunnel; 8-Working face of the subsequent tunnel; A-Monitoring point for compressive stress on the surface of the wall lining of the preliminary tunnel; B-Settlement monitoring point for the side inspection road of the wall lining of the preliminary tunnel; C-Enlarged arch foot of the wall lining of the preliminary tunnel; D-Dimension of the deepened invert arch of the preliminary tunnel; L A - The distance between the working face of the rear tunnel and the secondary lining of the preceding tunnel; L B - The distance between the tunnel face and its secondary lining; L1 - The monitoring range between the tunnel face and its secondary lining; L2 - The monitoring range between the tunnel face and the secondary lining of the tunnel ahead; L 21 --The range of significant changes in compressive stress from the end of the secondary lining of the pilot tunnel towards the working face of the subsequent tunnel; L 22 - The range of significant changes in compressive stress in front of the tunnel face. Detailed Implementation

[0104] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0105] This embodiment provides an asymmetric load-structure synergy system for a centrally located connecting arch tunnel without a central guide. By establishing a four-fold asymmetric technical system of "load, process, support, and monitoring" for the centrally located connecting arch tunnel without a central guide, and proposing corresponding design methods, it solves the problems of surrounding rock disturbance, structural instability, and construction safety caused by close-proximity construction in current centrally located connecting arch tunnels without a central guide.

[0106] Specifically, such as Figure 1 As shown, the asymmetric load structure collaborative system of the tunnel without a central guide arch includes: a load asymmetric system, a process asymmetric system, a support asymmetric system, and a monitoring asymmetric system.

[0107] Asymmetric load systems:

[0108] The load asymmetric system is a functional module system for dynamic evaluation and precise modeling of the problems caused by the secondary disturbance of the surrounding rock of the preceding tunnel due to the excavation of the subsequent tunnel under close-proximity construction conditions in tunnels without a central guide arch. This system achieves scientific modeling and quantitative analysis of asymmetric loads through the quantification of surrounding rock disturbance, identification of plastic zones, correction of strength parameters, and calculation using elastoplastic theory.

[0109] The system specifically includes the following four functional modules:

[0110] (1) Quantification module for surrounding rock disturbance:

[0111] The elastic wave velocity of the surrounding rock of the pilot tunnel was tested using the single-hole acoustic wave method at different construction stages, including: initial wave velocity V0: the surrounding rock in an undisturbed state; primary disturbance wave velocity V1: the surrounding rock state after the pilot tunnel was excavated; and secondary disturbance wave velocity V2: the surrounding rock state after the subsequent tunnel was excavated.

[0112] Based on this, the degree of disturbance of the surrounding rock is calculated:

[0113]

[0114] Used to quantitatively assess the degree of disturbance to the surrounding rock caused by construction.

[0115] (2) Plastic Zone Identification Module:

[0116] The surrounding rock is tested using either cross-hole CT or single-hole acoustic wave method, and the extent of the plastic zone is identified by combining the following methods:

[0117] Differential method: Identify the boundary of the plastic zone by the abrupt change point of the first derivative of the wave velocity-depth curve;

[0118] Threshold method: using V i A value of ≥0.85V0 is used as the standard to determine whether the surrounding rock is in an elastic state, thereby determining the radius RP of the plastic zone.

[0119] (3) Strength and damage parameter correction module:

[0120] Based on the surrounding rock disturbance degree D, the surrounding rock strength parameters are dynamically corrected, specifically including:

[0121] Cohesion correction: c i =f(c0,D i Internal friction angle correction:

[0122] The above empirical formulas reflect the strength degradation characteristics of the surrounding rock under construction disturbance, providing accurate material parameters for load calculation.

[0123] (4) Asymmetric load calculation module:

[0124] Based on the modified formula of Fenner's elastoplastic theory, and combined with the ratio of the minimum support force required before and after the disturbance -ξ=P2 / P1, the load increment of the surrounding rock of the tunnel is calculated as follows: Δq=ξq; thus, an asymmetric load distribution model is established: vertical pressure of the tunnel before the disturbance: q1=q+Δq=q+ξq; vertical pressure of the tunnel after the disturbance: q2=q;

[0125] This module enables dynamic evaluation and asymmetric modeling of surrounding rock loads under near-construction conditions, providing a theoretical basis for subsequent support design and structural verification.

[0126] Asymmetric system of processes:

[0127] The asymmetric construction process system addresses the mechanical differences and disturbance propagation issues between the preceding and following tunnels during close-proximity construction of tunnels without a central guide arch. It proposes a collaborative construction control module that differentiates construction techniques based on surrounding rock grade and lithological characteristics, and controls key construction steps. This system aims to effectively suppress disturbance effects, ensure structural stability, and improve construction safety.

[0128] The system specifically includes the following three functional modules:

[0129] (1) Pre-tunneling process module:

[0130] like Figure 2 As shown, an appropriate excavation method is selected based on the surrounding rock grade to ensure the safety and structural stability of the initial tunnel construction:

[0131] Class V surrounding rock: The three-stage pre-reserved core soil method is adopted. The construction process is as follows: ring excavation → initial support ① → excavation section II → initial support ② → skip excavation section III → initial support ③ → excavation section IV → initial support ④ → skip excavation section V → invert construction ⑤ → excavation sections VI-1 and VI-2 → excavation section VII → initial support ⑥ → invert construction ⑦ → invert filling ⑧ → integral casting secondary lining ⑨.

[0132] Class IV surrounding rock: The two-stage method is adopted, and the construction process is as follows: upper section excavation Ⅰ → upper section initial support ① → lower section skip excavation Ⅱ → lower section initial support ② → excavation section Ⅲ → initial support ③ → excavation section Ⅳ → invert arch initial support ④ → invert arch construction ⑤ → invert arch filling ⑥ → integral formwork secondary lining ⑦.

[0133] (2) Post-tunneling process module:

[0134] like Figure 2 As shown, appropriate excavation methods should be selected based on lithological differences to minimize disturbance to the already constructed pilot tunnels:

[0135] Class V soft rock: Mechanical segmented excavation method is adopted, and the construction process is as follows: Circular excavation I → Initial support of the upper section ① → Step-by-step excavation of core soil II-1 and II-2 → Initial support of the lower section ② → Excavation section III → Initial support ③ → Excavation section IV → Initial support of the invert ④ → Excavation section V → Initial support of the lower section ④ → Invert construction ⑤ → Invert filling ⑥ → Overall casting and secondary lining ⑦. Among them, mechanical excavation is preferred for the surrounding rock on the side closer to the pilot tunnel to avoid blasting disturbance.

[0136] Grade III–IV hard rock: The construction process employs a combination of vibration-damping holes and controlled blasting. The sequence is as follows: Circular excavation I → Initial support of the upper section ① → Excavation section II → Initial support of the lower section ② → Excavation section III → Initial support ③ → Excavation section IV → Initial support of the invert ④ → Excavation section V → Initial support of the lower section ④ → Invert construction ⑤ → Invert filling ⑥ → Integral casting and secondary lining ⑦. Vibration-damping holes should be installed in the surrounding rock near the pilot tunnel before controlled blasting to minimize vibration impact.

[0137] (3) Tunnel face spacing control module:

[0138] like Figure 2 As shown, by strictly limiting the reasonable distance between the tunnel face of the subsequent tunnel and the secondary lining of the preceding and subsequent tunnels, structural instability such as traction collapse caused by overlapping processes is prevented.

[0139] Under Class V surrounding rock conditions, the distance between the working face of the subsequent tunnel and the secondary lining of the preceding tunnel should be no less than 30m and no more than 40m; under Class IV surrounding rock conditions, the distance can be adjusted appropriately according to the actual geological conditions, but the structural stability requirements still need to be met.

[0140] Asymmetric support system:

[0141] The asymmetric support system is a proposed asymmetric support structure system designed to address the asymmetric load distribution problem caused by the near-continuous construction of tunnels without a central connecting arch. This system enhances the bearing capacity of the preceding tunnel through differentiated support design and achieves a stiffness coordination relationship with the standard support of the subsequent tunnel. The aim of this system is to achieve a reasonable match between support parameters and structural stress state, thereby improving the overall structural stability.

[0142] The system specifically includes the following two functional modules:

[0143] (1) Pre-tunnel reinforcement support module:

[0144] To address the asymmetric load effects caused by disturbances during the construction of the subsequent tunnel, a reinforced support design scheme was adopted for the pilot tunnel, which mainly includes:

[0145] Improve initial support parameters: appropriately increase the thickness of shotcrete, upgrade the type and density of steel frames, and densify the arrangement of system anchor bolts to enhance the overall rigidity and bearing capacity of the initial support;

[0146] Expand the structure of the central wall arch foot: Eliminate the cable trench setting, increase the stress size of the central wall arch foot while meeting drainage requirements, enhance the connection strength between the central wall and the invert arch, and improve its resistance to eccentric pressure;

[0147] Deepen the invert arch structure design: Increase the invert arch burial depth by 30-40cm to effectively improve the invert arch rise-to-span ratio and the foundation embedment depth, thereby improving the stress state of the invert arch and enhancing the foundation stability.

[0148] The above measures significantly improved the overall stiffness and deformation resistance of the tunnel structure under asymmetric loads, effectively preventing typical defects such as central wall crushing and invert arch cracking.

[0149] (2) Conventional support module for the rear tunnel:

[0150] The secondary tunnel is designed with standard support parameters that match the surrounding rock grade to ensure sufficient structural stability under its own load. Simultaneously, its support stiffness is slightly lower than that of the primary tunnel, forming a reasonable stiffness gradient transition relationship with the primary tunnel, thus avoiding mechanical response imbalance caused by abrupt stiffness changes.

[0151] The design of this module enables coordinated response of the support system between the two tunnels during stress, ensuring the safety and stability of the overall tunnel structure under close-contact construction conditions.

[0152] Monitoring asymmetric systems:

[0153] The asymmetric monitoring system is a comprehensive structural state perception and risk identification system proposed to address the structural stress asymmetry and local instability risks caused by disturbances during the excavation of subsequent tunnels in tunnels without a central guide arch during near-continuous construction. This system utilizes differentiated monitoring item configuration, dynamic threshold setting, and numerical simulation to help determine the disturbance range. The system aims to achieve accurate monitoring and dynamic early warning of key structural components, thereby improving the level of construction safety control.

[0154] The system specifically includes the following three functional modules:

[0155] (1) Symmetry monitoring module

[0156] This system integrates commonly used monitoring items in conventional tunnel construction to provide a unified assessment of the overall structural condition of both the preceding and subsequent tunnels. These include: crown settlement, peripheral displacement, and surface settlement; surrounding rock pressure and contact pressure; and internal forces in the support structure, such as stress in the steel frame, anchor bolts, and concrete. These monitoring items are implemented in both the preceding and subsequent tunnels, forming a symmetrical monitoring foundation for the structural condition.

[0157] (2) Asymmetric monitoring module

[0158] Focusing on the local disturbance effects of subsequent tunnel construction on the preceding tunnel, targeted asymmetric monitoring projects are set up, mainly including:

[0159] Monitoring of compressive stress on the surface of the middle wall lining: Based on the Kent-Park constitutive model analysis, the compressive stress warning threshold is set to 50% of the standard value of concrete compressive strength, i.e. ≤0.5fc, to ensure that the structure is in an elastic stress state and prevent plastic damage;

[0160] Settlement monitoring of the maintenance access road on the middle wall: By establishing a two-dimensional stratum-structure method numerical model, the entire construction process is simulated, and stepwise displacement boundary conditions are applied to extract the maximum compressive stress change curve of the lining. The settlement value δ corresponding to the first time the compressive stress reaches 0.5fc is used as the settlement early warning benchmark.

[0161] This module enables differentiated monitoring and dynamic early warning of key stress-bearing parts of the structure.

[0162] (3) Monitoring range control module

[0163] Based on a three-dimensional numerical model of the construction stage, the disturbance propagation process of the subsequent tunnel under the condition that the preceding tunnel has been completed is simulated, and the key monitoring sections are determined by combining the stress change law:

[0164] L1: The monitoring range between the tunnel face and its secondary lining is determined by inversion based on the control standard that the compressive stress in the middle wall does not exceed 0.5fc;

[0165] L 21 : The range of impact of rearward disturbance at the end of the secondary lining of the pilot tunnel;

[0166] L 22 : The range of disturbance in front of the working face of the rear tunnel;

[0167] Using the stress increment formula:

[0168]

[0169] When ΔP(x) jWhen the stress percentage is ≤5%, the stress change is considered to be stable, and the corresponding distance is L. 21 With L 22 .

[0170] The final monitoring range is determined as follows: L1 behind the working face of the subsequent tunnel; L behind the secondary lining of the preceding tunnel. 21 ; L in front of the back cave entrance 22 The aforementioned sections are structural areas significantly affected by disturbances and should be included in the key monitoring scope.

[0171] Based on the aforementioned collaborative system of asymmetric load structures for tunnels without a central connecting arch, this embodiment also proposes a collaborative design method for asymmetric load structures of tunnels without a central connecting arch, the specific steps of which are as follows:

[0172] Step 1, Asymmetric load calculation:

[0173] Due to the close proximity of the tunnels during construction, tunnels without a central connecting arch are highly susceptible to secondary disturbance of the surrounding rock of the completed tunnel during the excavation of the subsequent tunnel. This leads to rock degradation and expansion of the plastic zone, significantly increasing the rock pressure acting on the support structure of the preceding tunnel. Therefore, step 1 proposes an asymmetric load calculation method based on the degree of rock disturbance and the identification of the plastic zone. By modifying the model using elastoplastic theory, a dynamic quantitative assessment of the difference in surrounding rock pressure between the preceding and subsequent tunnels can be achieved.

[0174] Step 1.1, Obtain elastic wave velocity data:

[0175] Single-hole acoustic wave velocity testing of surrounding rock was conducted at different construction stages, including:

[0176] Initial wave velocity V0: Wave velocity of the surrounding rock under undisturbed conditions; First disturbance wave velocity V1: Wave velocity after the excavation of the first tunnel and the application of initial support and secondary lining; Secondary disturbance wave velocity V2: Wave velocity of the surrounding rock at the same location after the excavation of the subsequent tunnel.

[0177] The wave velocity data mentioned above is used for subsequent calculation of surrounding rock disturbance.

[0178] Step 1.2, calculate the surrounding rock disturbance degree:

[0179] Define the degree of surrounding rock disturbance D i The quantitative index reflecting the degree of disturbance to the surrounding rock is calculated using the following formula:

[0180]

[0181] In the formula, D i D1 represents the degree of disturbance to the surrounding rock caused by the excavation of the first tunnel; D2 represents the degree of secondary disturbance to the surrounding rock caused by the excavation of the subsequent tunnel.

[0182] Step 1.3, determine the radius RP of the plastic zone:

[0183] Using either cross-hole CT or single-hole acoustic wave method, measuring points are laid out radially along the tunnel, with a spacing of 0.5–1 m between the measuring points, to conduct wave velocity tests. The extent of the plastic zone of the surrounding rock is then determined by combining the following two methods:

[0184] Differential method: The location of gradient abrupt change is determined by the peak point of the first derivative of the wave velocity-depth curve, which corresponds to the boundary of the plastic zone;

[0185] Threshold method: using V i ≥0.85V0 is used as the criterion for the surrounding rock to be in an elastic state, and the minimum radial depth that meets the condition is the radius RP of the plastic zone.

[0186] Step 1.4 Correct the surrounding rock strength parameters:

[0187] Based on the surrounding rock disturbance degree D i Based on empirical statistical relationships, the strength parameters of the surrounding rock are dynamically corrected:

[0188] Cohesion correction formula: c i =f(c0,D i ), (i = 1, 2);

[0189] Internal friction angle correction formula:

[0190] In the formula, c0, The cohesion and internal friction angle of the undisturbed surrounding rock of the initial tunnel; c1, The cohesion and internal friction angle of the surrounding rock after the initial tunnel excavation and subsequent disturbance; c2, The cohesion and internal friction angle of the surrounding rock after one disturbance following the excavation of the pilot tunnel; f(c0,D) i () represents the empirical statistical relationship between cohesion and the degree of disturbance of the surrounding rock; Empirical statistical relationship between friction angle and surrounding rock disturbance degree.

[0191] Step 1.5, calculate the increase in surrounding rock pressure Δq:

[0192] Based on the modified formula of Fenner's elastoplastic theory, and combined with the ratio of the minimum support force required by the surrounding rock before and after disturbance, the load increment coefficient ξ of the surrounding rock is calculated:

[0193] ξ = P2 / P1;

[0194] in:

[0195] In the formula, ξ is the incremental coefficient of secondary disturbance load of the surrounding rock of the pilot tunnel; P1 and P2 are the minimum support forces required for the surrounding rock of the pilot tunnel to reach a stable state after primary and secondary disturbances; σ0 is the initial ground stress; R0 is the single-unit radius of the tunnel. The radius of the plastic zone corresponding to the primary and secondary disturbances of the surrounding rock of the tunnel is given.

[0196] Therefore, we can conclude that: Δq = ξq;

[0197] The final results are as follows: Vertical surrounding rock pressure of the first tunnel: q1=q+Δq=q+ξq, horizontal surrounding rock pressure: e1=λq1; Vertical surrounding rock pressure of the second tunnel: q2=q, horizontal surrounding rock pressure: e2=λq2; q is the standard surrounding rock pressure; λ is the horizontal lateral pressure coefficient.

[0198] Step 1 constructs an asymmetric load calculation system that considers the effects of surrounding rock disturbance and plastic expansion by combining on-site measured data with theoretical models. This enables scientific modeling and accurate prediction of the difference in surrounding rock pressure between the pre-existing tunnel and the subsequent tunnel, providing an important basis for subsequent process control, support design, and monitoring and early warning.

[0199] Step 2, Asymmetric construction sequence design:

[0200] In tunnels without a central connecting arch, under close-proximity construction conditions, the excavation of the subsequent tunnel will significantly disturb the structure of the preceding tunnel that has already been constructed. To effectively suppress the propagation of disturbance and ensure structural safety, it is necessary to formulate differentiated construction procedures based on the surrounding rock grade and lithological characteristics, and strictly control key construction steps to form a collaborative construction control system with asymmetric characteristics.

[0201] Step 2.1, Construction procedures for the pilot tunnel:

[0202] During the initial tunnel excavation phase, before the subsequent tunnel construction begins, the construction method can refer to the conventional separated tunnel process, but should be selected based on the adaptability of the surrounding rock grade.

[0203] Class V soft surrounding rock: such as Figure 2 As shown, the three-stage pre-reserved core soil method is recommended, and the specific construction process is as follows:

[0204] 1. Circular excavation section I; 2. Initial support construction ①; 3. Excavation section II; 4. Initial support construction ②; 5. Skip-cut excavation section III; 6. Initial support construction ③; 7. Excavation section IV; 8. Initial support construction ④; 9. Skip-cut excavation section V; 10. Invert construction ⑤; 11. Excavation sections VI-1 and VI-2; 12. Excavation section VII; 13. Initial support construction ⑥; 14. Invert construction ⑦; 15. Invert filling ⑧; 16. Integral casting secondary lining ⑨.

[0205] Class IV medium-hard surrounding rock: such as Figure 3 As shown, the two-step method is recommended, and the specific construction process is as follows:

[0206] 1. Excavate the upper section I; 2. Construct the initial support of the upper section ①; 3. Excavate the lower section II in a skip-cut manner; 4. Construct the initial support of the lower section ②; 5. Excavate the lower section III; 6. Construct the initial support of the lower section ③; 7. Excavate the section IV; 8. Construct the initial support of the invert arch ④; 9. Construct the invert arch ⑤; 10. Construct the invert arch filling ⑥; 11. Construct the secondary lining in a monolithic formwork ⑦.

[0207] Step 2.2, Construction procedures for the subsequent tunnel:

[0208] Since the construction of the subsequent tunnel poses a risk of disturbing the structure of the preceding tunnel, the construction methods should adopt targeted measures based on the differences in lithology to reduce the disturbance effect of construction:

[0209] Class V soft surrounding rock: such as Figure 2 As shown, the mechanical block excavation method is recommended, and the specific process is as follows:

[0210] 1. Circular excavation section I; 2. Construction of initial support for the upper section ①; 3. Excavation section II-1; 4. Excavation section II-2; 5. Construction of initial support for the lower section ②; 6. Excavation section III; 7. Excavation section IV; 8. Construction of initial support for the invert ③; 9. Excavation section V; 10. Construction of initial support for the lower section ④; 11. Construction of the invert ⑤; 12. Construction of invert filling ⑥; 13. Integral casting and secondary lining ⑦.

[0211] For the surrounding rock V on the side of the lower step close to the pilot tunnel, in order to avoid disturbing the surrounding rock of the pilot tunnel during the excavation of this part, it is recommended to use mechanical excavation method to excavate this part of the surrounding rock.

[0212] Class III-IV hard surrounding rock: such as Figure 3 As shown, the recommended method is vibration damping holes + controlled blasting, and the specific process is as follows:

[0213] 1. Circular excavation section I; 2. Construction of initial support for the upper section ①; 3. Excavation section II; 4. Construction of initial support for the lower section ②; 5. Excavation section III; 6. Excavation section IV; 7. Construction of initial support for the invert ③; 8. Excavation section V; 9. Construction of initial support for the lower section ④; 10. Construction of the invert ⑤; 11. Construction of invert filling ⑥; 12. Integral casting and secondary lining ⑦.

[0214] For the surrounding rock V on the side of the lower step close to the pilot tunnel, in order to avoid disturbing the surrounding rock of the pilot tunnel during the excavation of this part, vibration damping holes can be drilled on the side close to the pilot tunnel first, and then controlled blasting can be used to excavate this part of the surrounding rock.

[0215] Step 2.3, Construction step distance control:

[0216] To prevent structural instability issues such as traction collapse caused by the cumulative effect of construction processes due to excessively small spacing between the tunnel face and the secondary lining, strict control should be exercised over key construction steps.

[0217] Under Class V surrounding rock conditions: such as Figure 4 As shown, the step distance L between the tunnel face 8 and the secondary lining 3 of the tunnel is... A The distance between the working face 8 and the secondary lining 6 of the subsequent tunnel should not be less than 30m and not more than 40m; at the same time, the step distance L between the working face 8 and the secondary lining 6 of the subsequent tunnel should be... B The above requirements should also be met.

[0218] Under Class IV surrounding rock conditions: adjustments can be made appropriately based on the actual geological conditions on site, but it is still necessary to ensure that the structural stability is not affected by construction disturbances.

[0219] By setting reasonable construction step distances, the disturbance effect of the subsequent tunnel 4 construction on the preceding tunnel 1 structure can be effectively mitigated, ensuring the safety and stability of the overall structural system.

[0220] Step 2 establishes an asymmetric construction procedure system based on surrounding rock classification and lithological differences, proposes construction methods and key construction parameter control standards for different surrounding rock conditions, effectively suppresses disturbances during close-proximity construction, and provides a good construction environment foundation for subsequent support design and monitoring and early warning.

[0221] Step 3, Asymmetric support structure design:

[0222] Due to the significant asymmetric load distribution characteristics in tunnels without a central connecting arch during close-proximity construction, the surrounding rock pressure borne by the preceding tunnel is typically significantly greater than that of the subsequent tunnel. Furthermore, during the construction phase of the subsequent tunnel, before its secondary lining is closed, the stress pattern of the central wall undergoes a significant change, shifting from small eccentric compression to large eccentric compression, posing a severe challenge to structural stability. Therefore, step 3 proposes a differentiated support structure design method based on asymmetric load response. By enhancing the support parameters of the preceding tunnel and optimizing the structural form of key components, the overall structure's bearing capacity and stability under asymmetric stress conditions are improved.

[0223] Step 3.1, Pre-existing tunnel reinforcement support:

[0224] To accommodate the structural stress requirements under asymmetric loads, the pilot tunnel adopts a reinforced support design, which mainly includes:

[0225] Improve initial support parameters: increase shotcrete thickness, select higher strength steel frame models, increase steel frame spacing, extend anchor bolt length and appropriately increase anchor bolt density;

[0226] Enlarging the size of the central wall arch: Eliminating the cable trench, and increasing the load-bearing area of ​​the central wall arch while meeting drainage requirements, such as... Figure 6 As shown at position C, the connection stiffness between the central wall and the invert arch is enhanced, thereby improving the stability of the eccentrically loaded short column and preventing defects such as central wall crushing and invert arch cracking caused by connection failure.

[0227] Deepen the inverted arch structure: such as Figure 6 As shown at location D, increasing the depth of the invert arch by 30-40cm improves the foundation embedment depth, effectively mitigating the foundation settlement problem caused by subsequent tunnel excavation in the weak surrounding rock section. Simultaneously, as... Figure 6 As shown, the rise-to-span ratio of the inverted arch and the roundness of the structure are improved, thus optimizing the overall stress performance.

[0228] The above measures work together to significantly improve the overall stiffness and deformation resistance of the tunnel structure under asymmetric loads.

[0229] Step 3.2, conventional support for the subsequent tunnel:

[0230] The secondary tunnel is designed with standard support parameters that match the surrounding rock grade to ensure sufficient structural safety under its own load. Simultaneously, its support stiffness is slightly lower than that of the primary tunnel, forming a reasonable stiffness gradient transition relationship with the primary tunnel, thus avoiding mechanical response imbalance caused by abrupt stiffness changes.

[0231] This design strategy not only ensures the structural safety of the rear tunnel itself, but also achieves coordinated response of the support system between the two tunnels during the stress process.

[0232] Step 3.3, Structural stress mode adaptation:

[0233] like Figure 5 and Figure 6 As shown, during the excavation of the secondary tunnel 4 but before its secondary lining has been closed into a ring, the wall of the primary tunnel 1 loses the "constraint and gripping" effect of the original surrounding rock. Its stress mode changes from a small eccentrically compressed short column with multiple elastic supports on one side to a large eccentrically compressed short column with weakened multiple elastic supports in the direction of eccentric load. This is the most dangerous working condition of the structure and is very likely to cause instability and cracking.

[0234] Therefore, in addition to strengthening the support parameters of the pilot tunnel, the stability of the central wall needs to be enhanced through the following structural measures: enlarge the arch foot design of the central wall: enhance the connection strength between the central wall and the invert arch, and improve its resistance to eccentric pressure; deepen the invert arch design: increase the embedment depth of the invert arch foundation, enhance the stability of the foundation, and improve the lateral stress environment of the central wall.

[0235] The above-mentioned structural reinforcement measures are based on the stress mechanism and effectively address adverse stress states that occur during construction, ensuring the safety and stability of the structure throughout the entire construction cycle.

[0236] Step 3 constructed a differentiated support structure system for asymmetric loads. By enhancing the support parameters of the pilot tunnel and optimizing the construction methods of the central wall arch foot and invert arch, dynamic adaptation of the structural stress mode and construction disturbance characteristics was achieved. This system not only improved the overall bearing capacity of the tunnel structure but also provided a solid structural foundation for subsequent monitoring and risk control.

[0237] Step 4, Construction of the asymmetric monitoring system:

[0238] In tunnels without a central connecting arch, under close-proximity construction conditions, the excavation of the subsequent tunnel can significantly disturb the already constructed structure of the preceding tunnel, particularly the central wall lining, which is prone to structural defects such as crushing and cracking. To achieve dynamic perception and risk warning of key structural components, a differentiated monitoring system needs to be constructed, covering three core aspects: monitoring item setting, monitoring benchmark setting, and monitoring scope determination. Step 4 proposes an asymmetric monitoring system based on a dual-threshold early warning mechanism and three-dimensional numerical simulation assistance to achieve full-process perception of the tunnel structural state and accurate identification of the scope of disturbance impact.

[0239] Step 4.1, Determination of monitoring items for the asymmetric monitoring system of the tunnel without a central guide arch:

[0240] Based on the tunnel construction stage and the characteristics of disturbance impact, monitoring items are divided into two categories: symmetrical monitoring items and asymmetrical monitoring items.

[0241] Symmetrical monitoring projects require monitoring of both the initial and subsequent tunnels:

[0242] Required test items: 1. Geological and support condition observation, 2. Surface subsidence, 3. Blasting vibration, 4. Surrounding displacement, 5. Arch subsidence, 6. Steel frame and steel reinforcement internal force, 7. Displacement of surrounding rock based on points set inside the tunnel, 8. Surrounding rock pressure, 9. Contact pressure, 10. Initial support and secondary lining concrete stress.

[0243] Optional measurement items: 1. Displacement within the surrounding rock mass based on surface-based monitoring points; 2. Axial force of anchor bolts.

[0244] Asymmetric monitoring projects, with a focus on monitoring the preceding tunnel during the later tunnel construction phase:

[0245] 1. Compressive stress on the surface of the wall lining in the initial tunnel; 2. Settlement of the maintenance access road on the side of the wall in the initial tunnel;

[0246] The aforementioned monitoring program provides comprehensive coverage of the tunnel's structural condition while highlighting key areas, particularly enhancing the monitoring capabilities for critical load-bearing components such as the central wall.

[0247] Step 4.2, Determination of monitoring benchmarks for the asymmetric monitoring system of the tunnel without a central guide arch:

[0248] Symmetrical monitoring project benchmark:

[0249] The monitoring data was set in accordance with the Technical Specifications for Highway Tunnel Construction (JTG / T-3660-2020) and combined with engineering practice experience to ensure that the monitoring data is comparable and operable.

[0250] Asymmetric monitoring project benchmark:

[0251] 1. Compressive stress benchmark for the surface of the central wall lining:

[0252] Based on the Kent-Park constitutive model analysis, if the compressive stress on the surface of the lining concrete is controlled within the range of 0 to 0.5fc, the concrete is in an elastic working state, which can avoid plastic deformation and structural defects. Therefore, the early warning threshold for compressive stress in the middle wall is set at 0.5fc.

[0253] 2. Settlement benchmark for the maintenance access road on the middle wall:

[0254] A two-dimensional stratum-structure method numerical model was established to simulate the entire construction process. A progressive displacement boundary condition was applied to the maintenance access road on the middle wall side, with a displacement step size of 1 mm. The maximum compressive stress variation curve of the lining was extracted. When the compressive stress first reached 0.5ffc, the corresponding settlement value δ became the settlement monitoring and control benchmark.

[0255] Step 4.3, Determining the monitoring range of the asymmetric monitoring system for tunnels without a central guide arch:

[0256] To accurately identify the areas affected by structural disturbances, a three-dimensional numerical simulation combined with stress change analysis was used to determine the key monitoring areas.

[0257] Step 4.3.1 Establish a three-dimensional numerical model:

[0258] Based on the tunnel lining section design drawings, a three-dimensional numerical calculation model based on the stratum-structure method was established to simulate the excavation process of the subsequent tunnel after the construction of the preceding tunnel has been completed.

[0259] In the model: the pilot tunnel has exceeded the front and rear tunnels by a certain distance, and the core soil and steps of the pilot tunnel face have been reserved, and the initial support and secondary lining have been constructed; the pilot tunnel will no longer be excavated during the construction of the rear tunnel.

[0260] The excavation and support sequence and excavation advance length of the model were strictly carried out in accordance with the design and construction procedures. During the calculation process, the tunnel face and initial support were slowly advanced until the model calculation was completed.

[0261] Step 4.3.2 Determine the monitoring range L1 from the tunnel face to its secondary lining:

[0262] Extract the compressive stress variation curve of the middle wall corresponding to the section between the tunnel face and its secondary lining. With the compressive stress not exceeding 0.5fc as the control principle, determine the reasonable monitoring range L1 between the tunnel face and the secondary lining.

[0263] Step 4.3.3: Recalculate L1 for the tunnel after modeling:

[0264] The process of synchronously advancing the secondary lining and the working face while maintaining a distance of L1 was simulated in the model to verify the rationality of the L1 setting and to optimize the construction rhythm and monitoring arrangements.

[0265] Step 4.3.4 Determine the disturbance influence range L2 of the subsequent tunnel on the preceding tunnel:

[0266] L 21 The extent of rearward disturbance at the end of the secondary lining of the pilot tunnel; L 22 The area affected by disturbance in front of the working face of the rear tunnel;

[0267] The specific determination method is as follows:

[0268] 1. Extract the compressive stress data of the wall lining surface along the longitudinal direction and plot its variation curve with the construction step distance;

[0269] 2. Preliminarily determine the starting and ending points of significant changes in compressive stress, corresponding to d1(L) respectively. 21 ) and d2(L 22 );

[0270] 3. Extract the compressive stress value of the wall lining surface in each construction step and compare it with the minimum value;

[0271] 4. Iterative judgment using the stress increment formula:

[0272]

[0273] In the formula, P(x i ) represents a certain position x i The compressive stress value on the lining surface at x is expressed as the compressive stress value at a certain measuring point behind the end of the secondary lining of the tunnel; i P(x) represents the distance from the secondary lining of the pilot tunnel. i+1 ),P(x i+2 ...,P(x j () represents the compressive stress values ​​at multiple subsequent locations, indicating the stress from x... i+1 To x j Compressive stress data at each measuring point within the interval; {P(x i+1 ),P(x i+2 )…,P(x j )} min This is the minimum value among multiple subsequent compressive stress values; x jTo monitor the end position of the section, i.e. the location of the tunnel face of the subsequent tunnel; i is the index of the current analysis point, i = d1 or j - d2, d1 is the range of significant changes in compressive stress from the end of the secondary lining of the preceding tunnel to the tunnel face of the subsequent tunnel, and d2 is the range of significant changes in compressive stress in front of the tunnel face of the subsequent tunnel; j is the index of the final analysis point, j = s0 - s, s0 is the distance from the tunnel face of the subsequent tunnel to the secondary lining of the preceding tunnel in the initial state of the model, and s is the excavation distance of the tunnel face of the subsequent tunnel.

[0274] If ΔP(x) j If the stress change is ≤5%, then the stress change is considered to be stable, and the corresponding distance is: L 21 =d1,L 22 =d2.

[0275] Step 4.3.5 Final monitoring range determination:

[0276] The monitoring range for the rear tunnel can be set with reference to the standards for traditional tunnels.

[0277] The key monitoring area for the pilot tunnel is: L1 behind the working face of the subsequent tunnel; L behind the secondary lining of the pilot tunnel. 21 ; L in front of the back cave entrance 22 .

[0278] The aforementioned area is a region significantly affected by the construction disturbance of the subsequent tunnel and should be included as a key monitoring target in order to achieve dynamic identification and timely early warning of structural risks.

[0279] Step 5 establishes an asymmetric monitoring system. Through differentiated monitoring project settings, scientific monitoring benchmark establishment, and the assistance of a three-dimensional numerical model to determine the scope of disturbance impact, this system enables full-process status perception and dynamic risk identification of key structural components in a tunnel without a central guide arch under near-continuous construction conditions. This system significantly improves the relevance of monitoring data and the timeliness of early warning responses, providing crucial technical support for ensuring construction safety.

[0280] Furthermore, to verify the effectiveness of the collaborative design method for asymmetric load structures in tunnels without a central guide arch, this embodiment also conducted the following practical engineering verifications:

[0281] Actual project verification 1:

[0282] Taking a Class V surrounding rock tunnel without a central guide arch as an example, calculate the load increment Δq of the pilot tunnel. The radius of the pilot tunnel is R0 = 6.5m, the initial ground stress is σ0 = 20MPa, the initial cohesion is c0 = 0.3MPa, and the internal friction angle is...

[0283] 1. Calculate the surrounding rock disturbance degree D:

[0284] Using the cross-hole CT method, the wave velocity of the surrounding rock in the triangular area after the disturbance of the first tunnel excavation was measured to be V1 = 2.1 km / s, and the wave velocity of the surrounding rock in the triangular area after the disturbance of the subsequent tunnel excavation was V2 = 1.85 km / s. V0 was taken as 2.5 km / s.

[0285]

[0286] 2. Determine the radius Rp of the plastic zone:

[0287] After the initial tunnel excavation and disturbance, the wave velocity was measured to be Rp1 = 5.1m, and after the subsequent tunnel excavation and disturbance, the wave velocity was measured to be Rp2 = 7.5m.

[0288] 3. Calculate strength and damage parameters:

[0289] Based on empirical statistical relationships, take...

[0290] The calculated value is c1 = 0.29 MPa. c2 = 0.27 MPa

[0291] 4. Calculate the increase in surrounding rock pressure:

[0292] Based on the modified formula of Fenner's elastoplastic theory, P1 = 16.24 MPa, P2 = 8.88 MPa, and ξ = P2 / P1 = 0.55.

[0293] Therefore, the pressure increment of the surrounding rock in the tunnel is Δq = 0.55q.

[0294] Actual Engineering Verification 2:

[0295] like Figure 14 As shown, in a Class V surrounding rock section of a tunnel without a central connecting arch, the initial support 2 of the pilot tunnel 1 has a C25 shotcrete thickness of 0.29m and a secondary lining of C35 concrete thickness of 0.7m. Similarly, the initial support 5 of the subsequent tunnel 4 has a C25 shotcrete thickness of 0.27m and a secondary lining of C35 concrete thickness of 0.65m. The parameters of the Class V surrounding rock and support structure are listed in Tables 1 and 2.

[0296] Table 1 Physical and mechanical parameters of Class V surrounding rock

[0297]

[0298] Table 2 Parameters of Support Structure for Class V Surrounding Rock

[0299]

[0300] Step 4.1, determining the monitoring items for the construction monitoring system of the tunnel without a central guide, and step 4.2, determining the monitoring benchmark for the construction monitoring system of the tunnel without a central guide, will not be repeated here;

[0301] For special monitoring items:

[0302] The monitoring points for compressive stress on the surface of the wall lining in the tunnel are as follows: Figure 14 At point A in the tunnel, the benchmark for monitoring compressive stress on the surface of the tunnel wall lining is 0.5fc = 11.7MPa, and the standard value of compressive strength of C35 concrete is fc = 23.4MPa.

[0303] The settlement monitoring point of the inspection roadway on the side of the tunnel wall is as follows: Figure 14 At point B in the diagram, the settlement monitoring benchmark δ for the maintenance tunnel on the side wall of the pilot tunnel is:

[0304] First, such as Figure 7 As shown, a two-dimensional numerical calculation model of the stratigraphy-structure method for tunnels without a central guide arch is established.

[0305] Then, as Figure 8 As shown, based on the stress state of the support structure and surrounding rock after construction, displacement boundary conditions are applied to the inspection passage on the side wall of the pilot tunnel in the model. The displacement step size is 1mm, and the maximum compressive stress of the pilot tunnel lining is calculated and extracted.

[0306] Depend on Figure 8 It can be seen that as the settlement value of the inspection passage on the side wall of the pilot tunnel increases, the maximum compressive stress of the pilot tunnel lining shows an approximately linear increasing trend.

[0307] When the settlement value of the maintenance tunnel reaches 6.4 mm, the maximum compressive stress of the lining of the pilot tunnel increases to 0.5fc, or 11.7 MPa. Therefore, the settlement monitoring benchmark for the maintenance tunnel of the pilot tunnel is determined to be δ = 6.4 mm.

[0308] Then, the monitoring range of the construction monitoring system for tunnels without a central guide arch was determined:

[0309] like Figure 9 As shown, a three-dimensional numerical calculation model of the stratigraphy-structure method for a tunnel without a central guide arch is established. Figure 10 and Figure 13 As shown in the model, the pilot tunnel has already exceeded the front and rear tunnels by a certain distance, and the core soil and steps of the pilot tunnel face have been reserved, and the initial support and secondary lining have been constructed. During the construction of the rear tunnel, the pilot tunnel will no longer be excavated, and the excavation advance length of each calculation step is taken as 0.5m.

[0310] like Figure 11 As shown, after the model calculation is completed, the maximum compressive stress on the surface of the wall lining of the preceding tunnel corresponding to the section between the tunnel face and the secondary lining is extracted, and the variation law of the stress on the surface of the wall lining of the preceding tunnel is plotted.

[0311] Depend on Figure 11It can be seen that as the tunnel face advances, the maximum compressive stress on the surface of the wall lining in the preceding tunnel exhibits a trend of initially rising rapidly and then gradually stabilizing. This is because the compressive stress on the surface of the wall lining in the preceding tunnel does not exceed 0.5f. c That is, based on the principle of 11.7MPa, the reasonable distance between the tunnel face and its secondary lining is approximately the distance corresponding to the 10th calculation step, at which point L1 = 35m.

[0312] During the model construction phase, the secondary lining was constructed in close succession as the tunnel face and initial support slowly advanced, maintaining a distance of L1 = 35m from the tunnel face until the model calculation was completed.

[0313] like Figure 12 and Figure 14 As shown, after the model calculation is completed, the grid node with the largest compressive stress on the surface of the wall lining of the first tunnel is selected on the cross section. The compressive stress on the surface of the wall lining of the first tunnel corresponding to the section between the secondary lining 3 of the first tunnel and the working face of the subsequent tunnel is extracted along the longitudinal direction of the model, and its variation law with the subsequent tunnel excavation step distance is plotted.

[0314] Depend on Figure 12 It can be preliminarily determined that the range of significant changes in compressive stress from the end of the secondary lining of the pilot tunnel towards the face of the subsequent tunnel is d1 = 10m, and the range of significant changes in compressive stress in front of the face of the subsequent tunnel is d2 = 15m.

[0315] Extract the compressive stress results of the inner wall lining surface of the pilot tunnel at d1 = 10m behind the third end of the secondary lining of the pilot tunnel and d2 = 15m in front of the tunnel face of the subsequent tunnel in each construction step, and compare them with the minimum compressive stress behind the third end of the secondary lining of the pilot tunnel. Calculate the stress increment ΔP(x) using the following formula. j The calculation results are shown in Tables 3 and 4.

[0316]

[0317] In the formula, x i The distance from the secondary lining of the first tunnel is 3, i = 10 or j - 15; j = 55 - s, where s is the excavation distance of the working face of the subsequent tunnel.

[0318] Table 3 Calculation results of compressive stress after secondary lining of the pilot tunnel.

[0319]

[0320] Table 4. Calculation results of compressive stress in front of the tunnel face.

[0321]

[0322] As shown in Tables 3 and 4, during the forward advancement of the tunnel face, the compressive stress on the surface of the secondary lining of the pilot tunnel within 10m from the end of the secondary lining of the pilot tunnel toward the tunnel face does not differ from the minimum compressive stress behind it by more than 3%. The compressive stress on the surface of the secondary lining of the pilot tunnel at 15m in front of the tunnel face does not differ from the minimum compressive stress in front of that position by more than 3%. Therefore, d1 = 10m and d2 = 15m can be determined.

[0323] like Figure 13 and Figure 14 As shown, when the tunnel without a central connecting arch is excavated, the monitoring range of the tunnel is relatively conventional and can be determined with reference to traditional tunnels. However, the monitoring range of the tunnel in front is the section between the two tunnels that is greatly disturbed by the excavation of the tunnel in front. That is, the area 35m forward of the secondary lining 6 of the tunnel in front, 10m backward of the secondary lining 3 of the tunnel in front, and 15m forward of the working face of the tunnel in front should all be included in the monitoring range.

[0324] like Figure 14 As shown, through the above design process, the special monitoring items and monitoring benchmarks for the SL5a lining section of the tunnel without a central guide arch in this project, in addition to the conventional monitoring items, are as follows: the compressive stress benchmark on the surface of the wall of the pilot tunnel is 11.7 MPa, and the settlement benchmark for the maintenance access road on the side of the wall of the pilot tunnel is 6.4 mm; the monitoring range is: 35 m behind the working face of the subsequent tunnel, 10 m behind the secondary lining 3 of the pilot tunnel, and 15 m in front of the working face of the subsequent tunnel. During the implementation of on-site construction monitoring, if the monitoring items reach or exceed their benchmark values, necessary reinforcement support and other treatment measures should be taken.

[0325] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A collaborative system for asymmetric load-bearing structures in a tunnel without a central connecting arch, characterized in that: The asymmetric load structure collaborative system of the tunnel without a central guide arch includes: asymmetric load system, asymmetric process system, asymmetric support system, and asymmetric monitoring system. The load asymmetric system is a functional module that realizes dynamic evaluation and accurate modeling of the asymmetric load of the surrounding rock under close construction conditions in tunnels without a central guide arch by quantifying the surrounding rock disturbance, identifying the plastic zone, correcting the strength parameters, and calculating using elastoplastic theory. The process asymmetric system is a collaborative construction control module that distinguishes the surrounding rock grade and lithological characteristics, adopts differentiated chemical methods, and controls key construction steps to suppress the propagation of disturbances from nearby construction and ensure structural stability. The asymmetric support system enhances the load-bearing capacity of the preceding tunnel structure and matches the standard support of the subsequent tunnel through differentiated support design, forming an asymmetric support system with coordinated stiffness to adapt to the asymmetric load distribution caused by close-proximity construction. The monitoring asymmetric system, by configuring differentiated monitoring items and dynamic thresholds and combining numerical simulation to determine the range of disturbance impact, achieves full-process perception and risk identification of the structural state of tunnels without a central guide arch.

2. The collaborative system of asymmetric load structure for a tunnel without a central guide arch as described in claim 1, characterized in that: The load asymmetric system includes a surrounding rock disturbance quantification module, a plastic zone identification module, a strength and damage parameter correction module, and an asymmetric load calculation module. The surrounding rock disturbance quantification module obtains elastic wave velocities at different stages through single-hole acoustic wave testing, and quantitatively assesses the degree of construction disturbance to the surrounding rock. The plastic zone identification module uses cross-hole CT or acoustic wave method combined with differential / threshold analysis to determine the range of plastic failure of the surrounding rock; The strength damage parameter correction module dynamically corrects the cohesion and internal friction angle based on the surrounding rock disturbance degree, reflecting the characteristics of surrounding rock strength deterioration. The asymmetric load calculation module combines Fenner's elastoplastic theory with the ratio of support forces before and after disturbance to calculate the load increment and asymmetric distribution of the surrounding rock of the tunnel.

3. The collaborative system of asymmetric load structure for a tunnel without a central guide arch as described in claim 1, characterized in that: The asymmetric system of the process includes a pre-tunneling process module, a post-tunneling process module, and a face spacing control module; The preliminary tunnel construction module selects an appropriate excavation method based on different surrounding rock grades; The subsequent tunneling process module employs either mechanical excavation or controlled blasting methods depending on the lithological differences. The face spacing control module limits the reasonable spacing between the face of the subsequent tunnel and the secondary lining of the preceding and subsequent tunnels.

4. The collaborative system of asymmetric load structure for a tunnel without a central guide arch as described in claim 1, characterized in that: The asymmetric support system includes a pre-tunnel reinforced support module and a post-tunnel conventional support module. The pre-tunnel reinforcement support module enhances the overall stiffness of the structure under asymmetric loads by increasing the initial support thickness, upgrading the steel frame specifications, densifying the anchor bolt arrangement, and adopting the construction method of expanding the arch foot of the central wall and deepening the invert arch. The conventional support module for the secondary tunnel adopts standard support parameters that match the surrounding rock grade, forming a stiffness transition relationship with the primary tunnel and coordinating the mechanical response of the support system between the two tunnels.

5. The collaborative system of asymmetric load structure for a tunnel without a central guide arch as described in claim 1, characterized in that: The asymmetric monitoring system includes a symmetric monitoring module, an asymmetric monitoring module, and a monitoring range control module; The symmetrical monitoring module integrates conventional monitoring parameters such as crown settlement, surrounding displacement, surrounding rock pressure, and support internal forces for overall structural condition assessment. The asymmetric monitoring module focuses on collecting data on compressive stress in the walls of the pilot tunnel and settlement of the maintenance passage, and sets early warning thresholds to identify local stress anomalies. The monitoring range control module, based on three-dimensional numerical simulation and stress change analysis, delineates the spatial range of the impact of subsequent tunnel construction on structural disturbance.

6. A collaborative design method for asymmetric load structures of tunnels without a central connecting arch, the collaborative design method being based on the collaborative system for asymmetric load structures of tunnels without a central connecting arch as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1, Asymmetric load calculation: Based on the surrounding rock disturbance degree and plastic zone identification, the model is modified using elastoplastic theory to dynamically quantify the asymmetric surrounding rock pressure distribution between the first tunnel and the second tunnel; Step 2, Asymmetric construction sequence design: Based on the grade and lithological differences of the surrounding rock, formulate a graded excavation plan and control the distance between the working face and the secondary lining to suppress the superimposed disturbance effect caused by close-contact construction; Step 3, Asymmetric support structure design: By differentiating and enhancing the support parameters of the pilot tunnel, and optimizing the structural form of the central wall arch foot and invert arch, the structure's resistance to eccentric pressure under asymmetric loads is improved. Step 4, Construction of an asymmetric monitoring system: Combining a dual-threshold early warning mechanism with three-dimensional numerical simulation, key monitoring items and the scope of disturbance impact are determined to achieve dynamic perception and control of structural risks.

7. The collaborative design method for asymmetric load structures of tunnels without intermediate guide arches according to claim 6, characterized in that: Step 1, Asymmetric load calculation, includes the following steps: Step 1.1, Obtain elastic wave velocity data: The elastic wave velocity data includes the initial wave velocity V0 in the undisturbed state, the first disturbance wave velocity V1 after the excavation of the first tunnel, and the second disturbance wave velocity V2 after the excavation of the subsequent tunnel. Step 1.2, calculate the surrounding rock disturbance degree: In the formula, D i D1 represents the degree of disturbance to the surrounding rock caused by the excavation of the first tunnel; D2 represents the degree of secondary disturbance to the surrounding rock caused by the excavation of the subsequent tunnel. Step 1.3, Determine the radius of the plastic zone: Use the cross-hole CT method or the single-hole acoustic wave method to set up measuring points along the radial direction of the tunnel to conduct wave velocity tests. Analyze the test results according to the differential method or the threshold method to determine the radius RP of the plastic zone; Step 1.4 Correcting the surrounding rock strength parameters: Based on the definition of surrounding rock disturbance degree by elastic wave velocity and empirical statistical relationships, calculate the cohesion c and internal friction angle of the surrounding rock of the pilot tunnel after one and two disturbances. c i =f(c0,D i ),(i=1,2); In the formula, c0, The cohesion and internal friction angle of the undisturbed surrounding rock of the initial tunnel; c1, The cohesion and internal friction angle of the surrounding rock after the initial tunnel excavation and subsequent disturbance; c2, The cohesion and internal friction angle of the surrounding rock after one disturbance following the excavation of the pilot tunnel; f(c0,D) i () represents the empirical statistical relationship between cohesion and the degree of disturbance of the surrounding rock; Empirical statistical relationship between friction angle and surrounding rock disturbance degree; Step 1.5, Calculate the increase in surrounding rock pressure: Based on the modified formula of Fenner's elastoplastic theory, calculate the coefficient of the increase in secondary disturbance load of the surrounding rock of the pilot tunnel. ξ = P2 / P1; In the formula, ξ is the incremental coefficient of secondary disturbance load of the surrounding rock of the pilot tunnel; P1 and P2 are the minimum support forces required for the surrounding rock of the pilot tunnel to reach a stable state after primary and secondary disturbances; σ0 is the initial ground stress; R0 is the single-unit radius of the tunnel. The radius of the plastic zone corresponding to the primary and secondary disturbances of the surrounding rock of the tunnel. Thus, the pressure increment Δq of the surrounding rock in the pilot tunnel is calculated; Δq = ξq, where q is the standard surrounding rock pressure.

8. The collaborative design method for asymmetric load structures of tunnels without intermediate guide arches according to claim 6, characterized in that: Step 2, asymmetric construction sequence design, includes the following steps: Step 2.1, Preliminary tunnel construction procedures: For Class V surrounding rock, a three-stage pre-reserved core soil method is adopted; for Class IV surrounding rock, a two-stage method is adopted. Step 2.2, subsequent tunnel construction procedures: For Class V soft rock, mechanical block excavation is used; for Class III–IV hard rock, vibration damping holes and controlled blasting are used. Step 2.3, Construction distance control: For Class V surrounding rock, the distance between the tunnel face and the secondary lining of the first and second tunnels should be no less than 30m and no more than 40m; for Class IV surrounding rock, appropriate adjustments should be made based on the site conditions to ensure the stability of the secondary lining and initial support structure of the first and second tunnels during the excavation of the second tunnel.

9. The collaborative design method for asymmetric load structures of tunnels without intermediate guide arches according to claim 6, characterized in that: Step 3, asymmetric support structure design, includes the following steps: Step 3.1, Enhanced support for the initial tunnel: Enhance the support parameters for the initial tunnel, including: initial support thickness, steel frame type and spacing, radial reinforcement anchor length and spacing; the initial tunnel adopts enlarged central wall arch foot size, while eliminating the cable trench to increase the structural bearing area; the initial tunnel adopts deepened invert arch to improve foundation stability and rise-to-span ratio; Step 3.2, Conventional support for the subsequent tunnel: The subsequent tunnel is designed with support parameters according to standard loads, forming a stiffness gradient with the preceding tunnel; Step 3.3, Structural stress mode adaptation: When the tunnel is excavated and the secondary lining is not constructed into a ring, the central wall changes from small eccentricity to large eccentricity under pressure. At this time, the bearing capacity of the connection parts is strengthened.

10. The collaborative design method for asymmetric load structures of tunnels without intermediate guide arches according to claim 6, characterized in that: Step 4, Construction of the asymmetric monitoring system, including the following steps: Step 4.1, Determination of monitoring items for the asymmetric monitoring system of the tunnel without a central guide arch: The monitoring items of the asymmetric monitoring system for tunnels without a central guide arch include both symmetric and asymmetric monitoring items; Symmetrical monitoring items are those monitored in both the initial and subsequent tunnels, including mandatory and optional items: Mandatory items are: geological and support condition observation, surface subsidence, blasting vibration, surrounding displacement, arch subsidence, steel frame and reinforcing steel internal forces, displacement within the surrounding rock, surrounding rock pressure, contact pressure, and initial support and secondary lining concrete stress; Optional items are: displacement within the surrounding rock and anchor bolt axial force. The asymmetric monitoring items are those for monitoring the pre-tunnel during the subsequent tunnel excavation stage, including: compressive stress on the surface of the wall lining of the pre-tunnel and settlement of the maintenance passage on the side of the wall of the pre-tunnel; Step 4.2, Determination of monitoring benchmarks for the asymmetric monitoring system of the tunnel without a central guide arch: For the monitoring items, monitoring benchmarks should be set with reference to current standards and engineering experience; For asymmetric monitoring projects, the main components include: monitoring of compressive stress on the surface of the central wall lining and monitoring of settlement of the central wall side inspection passage; Monitoring of compressive stress on the surface of the middle wall lining: Based on the Kent-Park constitutive model, the compressive stress control threshold is set to 50% of the standard value of concrete compressive strength, i.e., 0.5fc; Settlement monitoring of the maintenance access road on the middle wall: By establishing a two-dimensional numerical model to simulate the entire construction process, applying stepwise displacement boundary conditions, extracting the maximum compressive stress change curve of the lining, and taking the settlement value δ corresponding to the first time the compressive stress reaches 0.5fc as the settlement monitoring control benchmark; Step 4.3, Determining the monitoring range of the asymmetric monitoring system for tunnels without a central guide arch: Step 4.3.1 Establish a three-dimensional numerical model: Based on the tunnel lining cross-section design drawings, establish a three-dimensional numerical calculation model of the stratum-structure method for a tunnel without a central guide arch; simulate the excavation process of the subsequent tunnel under the condition that the preceding tunnel has been completed in the model; Step 4.3.2 Determine the monitoring range from the tunnel face to its secondary lining: Extract the maximum compressive stress on the surface of the wall lining of the preceding tunnel corresponding to the section between the tunnel face and the secondary lining, and plot the variation law of the subsequent tunnel excavation step distance; determine the monitoring range L1 from the tunnel face to its own secondary lining based on the principle that the compressive stress does not exceed 0.5fc. Step 4.3.3 Recalculate the tunnel after modeling, maintaining a distance of L1 between the secondary lining and the tunnel face, and simulate the actual construction rhythm in the model; verify and optimize the rationality of L1; Step 4.3.4 Determine the range of disturbance impact of the subsequent tunnel on the preceding tunnel: First, extract the compressive stress on the surface of the wall lining of the pilot tunnel corresponding to the section between the secondary lining of the pilot tunnel and the working face of the subsequent tunnel along the longitudinal direction of the model, and analyze its variation with the construction step distance. Then, determine the rearward disturbance range L at the end of the secondary lining of the pilot tunnel. 21 Disturbance range L in front of the back cave face 22 ; through stress increment ΔP(x) j The criterion of ≤5% is determined iteratively; Stress increment ΔP(x) j The formula for calculating ) is: In the formula, P(x i ) represents a certain position x i The compressive stress value on the lining surface at x is expressed as the compressive stress value at a certain measuring point behind the end of the secondary lining of the tunnel; i P(x) represents the distance from the secondary lining of the pilot tunnel. i+1 ),P(x i+2 ...,P(x j () represents the compressive stress values ​​at multiple subsequent locations, indicating the stress from x... i+1 To x j Compressive stress data at each measuring point within the interval; {P(x i+1 ),P(x i+2 ...,P(x j )} min This is the minimum value among multiple subsequent compressive stress values; x j To monitor the end position of the section, i.e. the location of the tunnel face of the subsequent tunnel; i is the index of the current analysis point, i = d1 or j - d2, d1 is the range of significant changes in compressive stress from the end of the secondary lining of the preceding tunnel towards the tunnel face of the subsequent tunnel, and d2 is the range of significant changes in compressive stress in front of the tunnel face of the subsequent tunnel; j is the index of the final analysis point, j = s0 - s, s0 is the initial distance of the tunnel face of the subsequent tunnel from the secondary lining of the preceding tunnel, and s is the excavation distance of the tunnel face of the subsequent tunnel; Step 4.3.5 Final Monitoring Scope Determination: The routine monitoring scope of the subsequent tunnel is the same as that of a traditional tunnel; the key monitoring scope of the pilot tunnel is: L1 behind the working face of the subsequent tunnel, and L behind the secondary lining of the pilot tunnel. 21 L in front of the back cave 22 .

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