A collapsible cooperative support system and construction method for coping with asymmetric load of a solution cavity

Abstract

The application discloses a collapsible cooperative supporting system for asymmetric load of a solution cavity and a construction method, and belongs to the technical field of tunnel and underground engineering supporting. In view of the engineering problems of unilateral suspension of a tunnel, asymmetric bias and brittle fracture of a traditional rigid support caused by a large solution cavity of a cross-hole type, the application provides a novel supporting system of "yielding-energy-absorbing-fixed-end cooperation". The system comprises asymmetrically arranged primary support arches, and "collapsible connecting nodes" with a constant resistance sliding mechanism are implanted in high stress concentration areas of the primary support arches to release the initial peak bias through a reserved yielding gap; on the suspended side of the solution cavity, a concrete protective arch with a bottom embedded in a deep groove of a bedrock is constructed, and a composite energy-absorbing backfill layer with mixed waste tire rubber particles is pumped between the protective arch and the primary arch. The application breaks the shackles of the traditional "rigid against rigid", realizes flexible release of surrounding rock stress and self-adaptive reconstruction of the supporting system, and fundamentally solves the tunnel structure instability disaster problem under the asymmetric geology of a large-span solution cavity.

Description

Technical Field

[0001] This invention relates to the field of deep-buried tunnel and underground engineering support and disaster prevention technology, and in particular to a retractable collaborative support system and construction method for tunnels passing through large cross-cavity karst caves under extreme geological loads such as unilateral suspension and asymmetric bias pressure. Background Technology

[0002] In the karst landform development areas of southwestern my country, the construction of long-base, deep-buried tunnels for high-speed railways and highways often encounters hidden large karst caves or underground river systems. Among them, "large karst cavities spanning multiple caves" is a particularly challenging geological condition. The typical characteristic of this type of geology is that the tunnel excavation outline is not entirely within the intact rock mass, but rather presents an asymmetrical pattern of "one side tightly attached to the rock wall, while the other side is completely exposed in a huge cavity."

[0003] In the traditional New Austrian Tunneling Method (NATM) construction theory, the assumed in-situ stress field is relatively symmetrical and uniform. Therefore, symmetrical, rigid closed steel arches (such as full-section I18 or I20 I-beams) combined with shotcrete are typically used as initial support. However, when faced with the ultimate "asymmetric eccentric pressure" caused by cross-tunnel cavities, the traditional rigid support scheme reveals fatal flaws: (1) “Using rigidity to overcome rigidity” leads to brittle fracture failure: The single-sided suspension of the tunnel breaks the stress balance of the original rock, and the lateral unloading of the cavity will cause the roof and the upper surrounding rock to generate a huge bias thrust. If the rigidity of the steel arch frame is increased indiscriminately (for example, by increasing the type of steel), when the bias thrust exceeds the support limit, the arch frame cannot undergo adaptive deformation, and the stress will be concentrated instantaneously at the arch foot and arch top, causing the rigid arch frame to undergo catastrophic torsion, buckling shear or even sudden bursting and collapse.

[0004] (2) The suspended side arch foot lacks a reliable "point of support": The premise of the traditional arch frame is that the arch foot must be placed on a solid rock foundation. However, in the cross-cavity karst cavity, the area below the suspended side is often a cavity or loose deposits, and the arch frame is like "stepping on cotton". Once the pressure from above is biased and downward, the suspended side arch frame will experience overall sinking and lateral slippage instability.

[0005] (3) Lack of energy absorption buffer for eccentric impact loads: Large karst caves are often accompanied by roof rockfalls or cave wall rockbursts due to weathering and erosion. The instantaneous collapse impact loads directly hit the rigid support, and since there is no buffer layer, the shock wave can easily cause penetrating damage to the support structure.

[0006] Therefore, breaking away from the traditional mindset of absolutely rigid support and developing a new type of asymmetric collaborative support system that can "be flexible first and then rigid, allow pressure to dissipate energy, and allow irregular shapes to take root" is an urgent task to ensure the safe and smooth completion of cross-cavity karst tunnels. Summary of the Invention

[0007] The purpose of this invention is to overcome the vulnerability of traditional rigid symmetrical support systems in the face of large-scale karst caves spanning tunnels, and to provide a retractable collaborative support system and construction method for coping with asymmetrical loads in karst caves. This system, through the coupling of three major technologies—"retractable node resistance limiting and pressure relief," "deep chiseling and embedding of fixed supports," and "modified rubber concrete damping and energy absorption"—changes the traditional passive load-bearing mode from a mechanical constitutive perspective, effectively solving the problem of disasters caused by eccentric pressure.

[0008] To achieve the above objectives, the overall structural design and principle of this invention are as follows: This invention discloses a retractable collaborative support system for coping with asymmetric loads in cavities, applicable to tunnels where one side is tightly attached to the surrounding rock and the other side is suspended in the cavity. It mainly consists of four collaborative modules: Firstly, the main arch is supported by asymmetric initial support. Breaking away from the conventional uniform cross-section design, based on numerical calculations, a conventional cross-section is used on the bearing side of the rock wall, while the cross-sectional stiffness is significantly increased on the suspended and biased side of the karst cavity (using large-sized I-beams), so that the material distribution perfectly matches the asymmetric stress envelope diagram.

[0009] Secondly, the retractable connection node (the core of this invention). At the segment point where the main arch bears the largest eccentric bending moment, a retractable node based on the friction limiting principle is inserted in series. It has a built-in reserved "pressure-yielding sliding gap". In the early stage of tunnel excavation, when the surrounding rock releases huge deformation energy and peak stress, the frictional resistance generated by the high-strength bolts is overcome, and the U-shaped steel undergoes relative slippage (shortening). This "taking a step back to open up a wider world" pressure-yielding mechanism effectively dissipates the peak energy that is enough to destroy the rigid arch frame; when the sliding gap closes, the node is locked, and the support system is converted to an absolutely rigid bearing state, preventing the surrounding rock from loosening further.

[0010] Thirdly, the deeply embedded, rooted concrete arch support (the fixed-end core of this invention). Addressing the challenge of the lack of lateral restraint on the suspended side and the immense overturning moment, this invention forcibly excavates a "deep locking groove" in the stable bedrock below the karst cavity side, embedding and casting the thick concrete arch support at its root within it. In a mechanical model, this constructs a "fixed-support anchorage end" with extremely strong shear and overturning resistance, effectively resisting the enormous asymmetric pressure and lateral shear force transmitted from the main arch.

[0011] Fourth, the flexible energy-absorbing backfill layer (the damping core of this invention). In the gap between the main arch and the protective arch, modified concrete incorporating waste tire rubber particles was innovatively pumped in. The extremely high Poisson's ratio and elasticity of the rubber particles transform this concrete layer into a "giant elastoplastic damping buffer." Whether it's asymmetric compression or rockfall impact, this layer can dissipate impact energy through micro-compression of its volume.

[0012] Furthermore, this invention also provides a construction method based on dynamic feedback. This method strictly adheres to the New Austrian Tunneling Method's (NATM) concept of "dynamic design and information-based construction," systematically integrating "trench excavation - arch support anchoring - retractable main arch assembly - energy-absorbing layer pouring" through precise construction of S1 to S5. It also specifies technical rules for setting the initial stroke of the yielding gap by calculating the maximum expected intrusion displacement ΔU of the surrounding rock using numerical simulation, and a dynamic dry prevention line based on a slip rate of 5 mm / d.

[0013] The beneficial technical effects of the present invention are as follows: 1. "Soft-then-hard" approach to mitigate peak bias pressure: Traditional support systems, which rigidly resist the pressure, are prone to failure. The retractable nodes of this invention allow the support system to yield in a controlled manner within a small stroke of 50-150mm. According to the law of conservation of energy, under the numerical simulation conditions of this embodiment, this yielding action releases up to approximately 70% of the distorted strain energy accumulated in the surrounding rock, successfully avoiding buckling and bursting of the main arch, and greatly reducing steel consumption and support costs.

[0014] 2. "Rock-embedded rooting" to resist overturning and sliding: By chiseling deep grooves and using long anchor bolts to pour concrete at the base of the arch support, the originally fragile lateral sliding boundary on the suspended side is reconstructed into an extremely stable "rigid embedded boundary". This deeply embedded anchor joint can effectively resist the huge shear force and overturning moment brought about by lateral unloading, ensuring the overall root stability of the asymmetric support system.

[0015] 3. "Rubber energy absorption" achieves shock absorption: The introduction of waste tires-concrete not only realizes the low-carbon and environmentally friendly utilization of solid waste resources, but also gives the support system a function similar to the "independent suspension shock absorber" of a car. When subjected to a sudden increase in asymmetric bias pressure or impact from falling rocks in the cavities, the rubber particles attenuate the strong shock wave through local elastic deformation, significantly reducing the risk of cracking in the main tunnel lining.

[0016] 4. "Dynamic monitoring" guides closed-loop construction: The construction method uses the sliding gap and sliding rate of the retractable connection nodes as intuitive stress feedback indicators. Combined with conventional monitoring and measurement methods, it can effectively assess the release state and stability of the surrounding rock deformation energy, providing quantitative data to assist in the timing of secondary lining construction and improving the reliability of engineering practice. Attached Figure Description

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

[0018] Figure 1This is a macroscopic cross-sectional view of the collaborative support system for dealing with asymmetric loads in the cavities according to the present invention (Note: the microscopic details of the energy-absorbing backfill layer are omitted in the figure to highlight the relationship between the main arch and the backfill).

[0019] Figure 2 This is a cross-sectional view of the retractable connection node (pressure relief mechanism) of the present invention, its rigid connection with the main arch, and its internal operating principle.

[0020] Figure 3 This is a closed-loop flowchart of the construction method for retractable collaborative support based on dynamic pressure feedback, as described in this invention.

[0021] Figure 4 This is a partially enlarged cross-sectional view of the composite structure consisting of the main arch, energy-absorbing layer, and protective arch, as well as the shear-resistant spikes of the present invention.

[0022] Figure 5 This is a diagram illustrating the "flexible first, rigid later" constant resistance pressure relief mechanism and the characteristic curve of surrounding rock stress release in the support system of this invention.

[0023] The attached diagram lists the components represented by each number as follows: 1-Asymmetric initial support main arch; 1a-Rock wall bearing side; 1b-Suspended cavity side; 12-Shear-resistant claws; 2-Retractable connection node; 21-Pressure-yielding sliding gap; 22-Sleeve U-shaped steel; 23-Inserted U-shaped steel; 24-Constant resistance limiting high-strength bolt; 25-Limiting clamp plate; 26-End face connecting steel plate; 3-Deeply embedded rooted concrete arch; 31-Bottom arch foot; 32-Long anchor bolt for locking foot; 4-Flexible energy-absorbing backfill layer; 5-Stable surrounding rock wall; 7-Large cavitary cavity spanning the tunnel; 8-Deep locking foot groove. Detailed Implementation

[0024] The following is in conjunction with the appendix Figures 1 to 5 The technical solution of the present invention is described through four engineering and technical embodiments of different depths.

[0025] (It should be noted that the specific dimensions, material ratios, and other parameters involved in the following embodiments are optimized values ​​based on typical karst tunnels in Southwest China, and are only used to illustrate the best engineering practices of the present invention, rather than as an absolute limitation on the protection boundaries of the claims of the present invention.) Example 1: Overall Spatial Topology and Rooting Construction of Asymmetric Cooperative Support System This embodiment relies on a particularly long, deeply buried trunk railway tunnel. When the tunnel was excavated to section DK12+450, a giant sinkhole with a volume of approximately 50,000 cubic meters was exposed on the right side. The left side of the tunnel is intact limestone, while the upper and middle parts of the right side are completely suspended, resulting in a huge eccentric thrust on the overlying rock to the right, forming an extremely severe asymmetric stress field.

[0026] Overall structural implementation (see) Figure 1 ): On the left side of the stable rock wall (5), the main arch on the rock wall bearing side (1a) adopts conventional I18 I-beams with a spacing of 0.8m / beam; On the right side of the suspended cavity (1b), due to the lack of surrounding rock and the presence of enormous eccentric pressure, the main arch model was upgraded to I22b I-beam.

[0027] In response to the problem of missing surrounding rock and suspended roof in the upper and middle part of the right side, this embodiment poured a 1.0m thick deep-embedded concrete arch (3) at a distance of 1.0m to 2.0m from the outer edge of the tunnel excavation outline (the specific distance depends on the over-excavation and impact resistance design of the cavity; in this example, it is 1.5m).

[0028] The core of the rooting process (see Figure 3 ): On the bedrock at the bottom of the cavity, a 1.5m deep and 1m wide anchor groove (8) was mechanically excavated. The bottom arch foot (31) was integrally cast into the deep groove, and 35 anchor bolts (32) with a length of 4.0m to 6.0m (5.0m in this example) were driven into the deep bedrock in a fan shape (attached). Figure 1 The length of the anchor bolts shown in the diagram is for illustrative purposes only; the actual length is 4 to 5 times the thickness of the arch support. This design transforms the original "sliding instability boundary" into a "fixed and embedded rock boundary".

[0029] Example 2: Breakthrough "Flexible-to-Rigid" Compact Node Design and Implementation This embodiment elaborates in detail the core energy dissipation component supporting the present invention—the retractable connection node (2).

[0030] In the above embodiment, if the I-beams on the left and right sides are directly rigidly spliced ​​together, when the huge pressure of the top plate is suddenly released, the rigid arch frame may buckle, twist and even collapse within minutes.

[0031] To solve this problem, such as Figure 1 As shown, the present invention cuts off the rigid arch frame in the middle of the arch crown (the area of ​​maximum bending moment and eccentric pressure concentration) and the right arch line (not shown in the figure), and implants a retractable connection node (2) in series.

[0032] The mechanical connections and internal mechanisms of nodes (see...) Figure 2 ): In terms of the connection method, the two ends of the node are directly and rigidly welded to the end faces of the cut main arch (1a) and main arch (1b) respectively through end face connecting steel plates (26), so that the retractable connection node (2) becomes the load-bearing bridge of the main arch. In terms of the mechanical direction arrangement, based on the mechanical relationship between active compression and passive guidance, the sleeve U-shaped steel (22) which serves as the passive guidance base is welded to the rock wall bearing side (1a) which is in a stable state; the inserted U-shaped steel (23) which serves as the active compression push rod is welded to the suspended side (1b) of the molten cavity which bears huge bias pressure.

[0033] The node is internally composed of a slightly larger cross-section sleeve U-shaped steel (22) and a slightly smaller cross-section insert U-shaped steel (23). Most importantly, during assembly, a pressure-relieving sliding gap (21) is reserved between the end of the insert U-shaped steel and the bottom wall of the sleeve U-shaped steel, and its stroke is determined according to L=k×ΔU as described in Example 4 (ΔU is relatively small in this section, and is taken as about 100mm in the example).

[0034] To ensure effective transmission of the normal clamping force, the height (vertical extension height) of the U-shaped flange of the inserted U-shaped steel (23) is slightly higher than that of the sleeved U-shaped steel (22), so that the external limiting clamp (25) is preferentially pressed against the protruding side edge of the inserted U-shaped steel during assembly, preventing the clamp from failing due to being suspended. The outer sides of the overlapping flanges on both sides are locked through by constant resistance limiting high-strength bolts (24) with disc spring washers and parallel limiting clamps (25). During on-site construction, a precise torque T is applied using a torque wrench, which is converted into a normal clamping force F on the U-shaped steel flange; based on the steel friction coefficient μ, this clamping force generates a preset sliding friction resistance f = μ × n × F, where n is the number of friction surfaces. By setting T, the constant resistance threshold of 300kN can be accurately reproduced. The elastic compensation effect of the disc spring washers ensures that the clamping force does not decrease during subsequent slippage and steel plate wear, achieving "constant resistance" pressure relief.

[0035] Mechanical evolution process (combined) Figure 5 (the curve) From the perspective of rock mechanics principles, before tunnel excavation, the deeply buried original rock is in a state of high ground stress equilibrium. The excavation and unloading momentarily breaks the original equilibrium, and the extremely high elastic strain energy accumulated inside the surrounding rock is released transiently, generating strong compressive deformation towards the free face (i.e., the transient peak bias pressure in the early stage of construction).

[0036] Stage 1 (Flexible Pressure Relief): When the transient peak pressure is >300kN, the frictional resistance of the bolt clamp is overcome, and the inserted U-shaped steel (23) slowly slides and retracts into the sleeved U-shaped steel (22), and the sliding gap gradually decreases. This invention actively provides deformation space for the surrounding rock through the moderate sliding and retraction of the node, and completely consumes this huge distortion strain energy through mechanical friction. When the energy is dissipated, the surrounding rock enters the stress redistribution stage and achieves a new steady-state equilibrium. Since this process releases the initial high ground stress caused by excavation, its energy release is a single and irreversible plastic physical process, and its unidirectional self-locking sliding characteristic makes it impossible to reverse reset. For the extremely rare subsequent reverse stress impact, the design has reserved construction space for installing reinforcing anchor rods or prestressed anchor cables near the retractable node (2) as a secondary reinforcement plan to ensure structural safety throughout the entire life cycle.

[0037] Stage Two (Rigid Locking): When the slippage reaches 100mm, the sliding gap (21) is reduced to zero, and the ends of the two steel sections are mechanically locked. At this time, the node returns to a rigid bearing state with extremely high stiffness, completely suppressing the residual creep of the surrounding rock.

[0038] Example 3: Formulation and Implementation of Flexible Energy-Absorbing Backfill Layer (Modified Waste Tires) Between the main arch and the protective arch, in this embodiment, a flexible energy-absorbing backfill layer (4) with disruptive damping characteristics was pumped and poured.

[0039] Material Preparation: Waste car tires are recycled and crushed into rubber granules with a particle size of 10-15mm using liquid nitrogen cryogenic pulverization technology. The granules are then soaked and stirred in a 5% sodium hydroxide solution for 24 hours to remove surface grease and roughen the surface, improving their bonding strength with cement slurry. Treatment with NaOH solution within this concentration range, compared to untreated or low-concentration treatment, effectively removes release agents such as zinc stearate from the rubber surface, forming micro-etched pits and increasing the rubber-cement interfacial bond strength by more than 50%. If the concentration is too high (>10%), it will corrode the rubber matrix and reduce its elasticity; if the treatment time is too long (>48h), the treatment effect tends to saturate, and the economic efficiency decreases. The rubber granules are added to C25 concrete at a volume ratio of 20%, replacing part of the coarse aggregate.

[0040] Synergistic mechanism: Rubber particles have an extremely high Poisson's ratio and an extremely low elastic modulus. This transforms the originally brittle concrete into a "recoverable" elasto-plastic buffer.

[0041] Anti-dynamic load recovery mechanism: As mentioned earlier, the slippage and pressure relief of the compressible connection node is an irreversible unidirectional plastic deformation. After the pressure relief gap is closed and locked, if the top plate of the cavity is subjected to weathering, water erosion, etc., and local rock collapse occurs later, forming a long-term, repeated impact dynamic load, the rigidly locked steel arch frame can no longer retreat. For this working condition, the flexible energy-absorbing backfill layer containing waste tire particles has a significant elastic recovery capability.

[0042] At the same time, in order to prevent interlayer peeling and slippage failure between the smooth steel frame and the rubber layer, such as Figure 4 As shown, on the outer edge of the suspended side (1b) of the main arch cavity, shear spikes (12) with a length of 150 mm are welded in a quincunx pattern at intervals of 0.5 m to 1.0 m along the circumferential and longitudinal directions. The shear spikes (12) are preferably made of threaded steel bars with ribs on the surface or wedge-shaped steel plates to enhance their mechanical interlocking force with the rubber concrete. The shear spikes (12) are deeply embedded and completely wrapped inside the energy-absorbing backfill layer, acting as shear anchors to prevent interlayer peeling and slippage. Since the design thickness of the flexible energy-absorbing backfill layer (4) (e.g., 0.3 m) is significantly greater than the length of the shear spikes (12) (0.15 m), it is ensured at the structural dimension boundary that the spike tips will never make physical contact with the outermost rigid concrete arch support (3), so as to prevent the inner main steel frame from being pierced in the opposite direction due to local stress concentration when rocks fall. When a partial collapse of the cavity roof impacts the outer protective arch, the rubber particles within the backfill layer undergo microscopic volumetric elastic compression, acting like thousands of tiny springs absorbing the shock wave and then returning to their original position. The shear-resistant spikes ensure that the main arch and the energy-absorbing layer deform synchronously and in tandem.

[0043] Example 4: Intelligent Construction Method with Closed-Loop Control Excellent structures rely on scientific construction methods. The construction method provided by this invention (see...) Figure 3 It strictly adheres to the dynamic design concept.

[0044] In steps S1 and S2, after using ground-penetrating radar to determine the bias range, the arch support and rooting are implemented.

[0045] Step S3, the main arch assembly, is the core. How to set the initial stroke of the pressure relief gap (21)? Before construction, a FLAC3D three-dimensional numerical model is established, the cavity volume obtained by radar is input, and the maximum expected intrusion displacement ΔU of the surrounding rock caused by asymmetric unloading of the section is calculated (assuming it is 80mm). Based on this, the initial pressure relief stroke is set according to the formula L = k × ΔU, where k is the safety redundancy coefficient, and the value range is 1.1~1.3. After a large number of numerical simulations and field tests, when k<1.1, it cannot fully accommodate the unexpected deformation caused by geological condition fluctuations, and there is a risk that the compressible connection node (2) will close prematurely and be unable to fully release the peak bias pressure, which may cause the main arch to buckle locally; when k>1.3, the excessive pressure relief stroke will cause the surrounding rock loosening zone to develop excessively, and the node closure time will be too long, affecting the construction progress and the mechanical opportunity for the support system to form a closed loop as early as possible, increasing the risk of surrounding rock instability. In this embodiment, given that the integrity of the surrounding rock in the cross section is still acceptable, the intermediate value k=1.2 is selected, that is, the initial pressure relief stroke is 1.2×80 = 96mm.

[0046] After the energy-absorbing backfill layer is poured in step S4, the dynamic pressure relief feedback stage begins in step S5.

[0047] On-site technicians use vernier calipers to accurately read the reduction in sliding clearance (21) every day.

[0048] Stable state: Slip rate <2mm / d. Subsequent operations can proceed normally.

[0049] Red Alert Status: When the daily slip rate is detected to be >5mm / d, or microcracks are visually observed at the root of the deep-embedded concrete arch (3), the system immediately issues an intervention command: suspend the excavation of the working face; urgently install three horizontal prestressed anchor cables on the suspended side of the cavity, one end of which is anchored to the deep-embedded concrete arch (3), and the other end is connected to the main arch (1b) on the suspended side of the cavity and applies active tension to forcibly provide external constraint resistance and curb the acceleration of slip.

[0050] After the gap is completely closed and the settlement tends to stabilize (deformation <0.2mm / d for 3 consecutive days), the waterproof membrane can be laid and the secondary lining can be poured across the entire cross section (6) to complete the final rigid closed loop of the entire asymmetric support system.

[0051] In summary, the retractable collaborative support system and construction method provided by this invention creatively integrates three cutting-edge technologies: "flexible-to-rigid resistance and pressure relief," "deeply embedded rock mass consolidation and rooting," and "waste tire rubber composite energy absorption." This completely eliminates the fatal asymmetric pressure curse in cross-tunnel karst cavities, significantly extending the service life of deeply buried tunnels in complex karst environments while ensuring the absolute safety of construction personnel.

[0052] The above descriptions are merely several preferred embodiments of the present invention, but the design concept and protection scope of the present invention are not limited thereto. Any equivalent component replacements or parameter optimizations made by those skilled in the art of deep-buried tunnel support, based on actual geological conditions, without departing from the mechanical principles and technical framework disclosed in this invention, should undoubtedly be included within the protection scope of this patent.

Claims

1. A retractable collaborative support system for coping with asymmetric loads in a karst cavity, applied to a tunnel section where one side is tightly attached to the surrounding rock and the other side is suspended above a large, cross-cavity karst cavity, characterized in that, The retractable collaborative support system includes: The asymmetric initial support main arch (1) is assembled along the tunnel excavation outline. The asymmetric initial support main arch (1) is divided into a rock wall bearing side (1a) and a cavity suspended side (1b). The cross-sectional stiffness of the cavity suspended side (1b) is greater than that of the rock wall bearing side (1a). The retractable connection node (2) is connected in series at the high stress concentration section of the asymmetric initial support main arch (1). The retractable connection node (2) is provided with a pressure relief sliding gap (21) with a predetermined stroke inside, which is used to perform relative sliding and shrinkage when the asymmetric bias pressure of the surrounding rock reaches the peak value, so as to release the deformation energy of the surrounding rock. The deep-embedded concrete arch (3) is set on the periphery of the suspended side (1b) of the cavity. The bottom arch foot (31) of the deep-embedded concrete arch (3) is embedded in the locking foot deep groove (8) excavated in the stable bedrock below, forming a fixed end support. The flexible energy-absorbing backfill layer (4) is poured between the deeply embedded and rooted concrete arch (3) and the suspended side (1b) of the cavity. The flexible energy-absorbing backfill layer (4) is made of modified concrete with waste tire rubber particles mixed in, and is used to buffer and absorb the dynamic bias impact generated by the collapse of the cavity top plate or lateral unloading.

2. The retractable collaborative support system for coping with asymmetric loads in a solution cavity according to claim 1, characterized in that: The two ends of the retractable connection node (2) are rigidly welded to the end faces of the cut rock wall bearing side (1a) and the cavity suspended side (1b) respectively through end face connecting steel plates (26); the retractable connection node (2) includes a sleeve U-shaped steel (22), an insert U-shaped steel (23) and a constant resistance limiting high-strength bolt (24) set on the outer side of the overlapping flange of the two; the end of the insert U-shaped steel (23) and the bottom wall of the sleeve U-shaped steel (22) form the pressure relief sliding gap (21), and the constant resistance limiting high-strength bolt (24) cooperates with the external limiting clamp (25) to provide constant sliding friction resistance.

3. The retractable collaborative support system for coping with asymmetric loads in a solution cavity according to claim 2, characterized in that: The preset length of the pressure-relief sliding gap (21) is 50mm~150mm. To ensure effective transmission of the normal clamping force, the height of the U-shaped section flange of the inserted U-shaped steel (23) is slightly greater than the height of the flange of the sleeved U-shaped steel (22), so that the flange edge of the inserted U-shaped steel (23) protrudes beyond the flange edge of the sleeved U-shaped steel (22) after assembly, thereby ensuring that the limiting clamp (25) is preferentially pressed against the protruding side edge of the inserted U-shaped steel (23) to prevent the clamp from causing a failure of the sleeved U-shaped steel (22) to be suspended. When the inserted U-shaped steel (23) slides to abut against the bottom wall of the sleeved U-shaped steel (22), the pressure-relief sliding gap (21) closes, and the retractable connection node (2) changes from the pressure-relief ductile state to the rigid bearing state.

4. The retractable collaborative support system for coping with asymmetric loads in a solution cavity according to claim 1, characterized in that: The embedding depth D of the bottom arch foot (31) into the locking foot deep groove (8) is ≥1.0m; and 3 to 5 locking foot long anchor rods (32) that penetrate deep into the bedrock are driven into the bottom of the bottom arch foot (31) in a fan shape, and the tail end of the locking foot long anchor rod (32) is welded to the steel reinforcement skeleton inside the bottom arch foot (31) as a whole.

5. A retractable collaborative support system for coping with asymmetric loads in a solution cavity according to claim 1, characterized in that: The suspended side (1b) of the asymmetric initial support main arch (1) is made of I20a or higher grade I-beams or H-beams, and its outer edge is welded with normally extending anti-shear spikes (12) in a quincunx pattern. The length of the anti-shear spikes (12) is less than the thickness of the flexible energy-absorbing backfill layer (4), so that the anti-shear spikes (12) are deeply buried and completely wrapped inside the flexible energy-absorbing backfill layer (4) and do not contact the deeply embedded and rooted concrete arch (3) at the spatial boundary, thereby strengthening the interface between layers to cooperate in bearing the force.

6. The retractable collaborative support system for coping with asymmetric loads in a solution cavity according to claim 1, characterized in that: The aggregate of the flexible energy-absorbing backfill layer (4) contains 15% to 30% waste tire rubber particles by volume, with a particle size of 5 mm to 20 mm, and is subjected to surface roughening and activation treatment by soaking and stirring in a 3% to 8% NaOH solution for 12 to 36 hours.

7. A construction method for a retractable collaborative support system for coping with asymmetric loads in a solution cavity, based on any one of claims 1-6, characterized in that, Includes the following steps: S1: Precise milling and trench reconstruction of asymmetric geological contour: Based on the bias boundary detected by three-dimensional ground radar, conventional excavation is carried out on the rock wall side; on the stable bedrock below the suspended side of the cavity, mechanical milling or weak blasting is used to excavate a deep trench with a depth and width of ≥1.0m (8). S2: Arch support and spatial construction: Several long anchor rods (32) are driven into the deep groove (8) of the anchor rod in a fan shape, and then steel bars are tied and early strength concrete is poured to form the deep embedded concrete arch support (3). S3: Main arch segment assembly and initial pre-tightening: Assemble the asymmetric initial support main arch (1), install the retractable connection node (2) at the arch top and the concentrated pressure part; lock the node flange by constant resistance limiting high strength bolt (24), adjust its torque, and set the initial stroke of the pressure relief sliding gap (21); S4: Pumping and micro-expansion bonding of energy-absorbing backfill layer: A mold is formed between the asymmetric initial support main arch (1) and the deep-embedded concrete arch (3), and the flexible energy-absorbing backfill layer (4) is pumped and poured to wrap the shear barbs (12) welded to the outer edge of the main arch and bonded tightly and cured. S5: Dynamic pressure relief feedback and support closed loop: During construction and stress redistribution of surrounding rock, the slippage of the compressible connection node (2) and the arch stress are monitored in real time; when the deformation energy of the surrounding rock is released, causing the pressure relief sliding gap (21) to be completely closed, the full-section secondary lining is constructed to achieve the final rigid closed loop of the support system.

8. The construction method according to claim 7, characterized in that: In step S3, the initial stroke of the pressure-relief sliding gap (21) is set based on the following: the maximum expected intrusion displacement ΔU of the surrounding rock of the section is calculated by numerical simulation, and the initial stroke L = (1.1~1.3) × ΔU is set to ensure that the main arch does not buckle during the pressure-relief period.

9. The construction method according to claim 7, characterized in that: In step S5, the monitoring threshold for the dynamic pressure feedback is set as follows: when the daily slip rate is detected to be >5mm / d, or when microcracks appear at the root of the deep-embedded concrete arch (3), active control intervention is immediately triggered, and horizontal prestressed tie anchors are added on the suspended side to forcibly suppress the eccentric deformation rate.

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