Jointed rock mass large-span tunnel multi-stage supporting method based on space coupling mechanism

Abstract

The invention provides a jointed rock mass large-span tunnel multi-stage supporting method based on a space coupling mechanism, and relates to the technical field of large-span tunnel engineering. In order to solve the problem of low supporting efficiency in the prior art, according to a surrounding rock damage field caused by stress redistribution after a target large-span tunnel is excavated, the target large-span tunnel is divided into a far-field primary rock stress area, a middle-field bearing arch forming area and a near-field loosening area; in the near-field loose area, a free face is excavated in a closed mode through flexible net spraying concrete, and a stable base body is provided for the middle-field bearing arch forming area; in the midfield bearing arch forming area, a chain type crack resisting mechanism is adopted to construct a force chain network so as to mobilize the rock self-supporting potential in the midfield bearing arch forming area, and the load of the near-field loosening area is dredged to the far-field primary rock stress area; and in the far-field primary rock stress area, a deep anchoring point is established by adopting a deep anchoring mechanism, and the hole periphery load transmitted by the middle-field bearing arch forming area is converted into axial tension to be transferred to a deep stable rock mass. The supporting method disclosed by the invention has relatively high supporting efficiency.

Description

Technical Field

[0001] This invention relates to the field of large-span tunnel engineering technology, and in particular to a multi-stage support method for large-span tunnels in jointed rock masses based on a spatial coupling mechanism. Background Technology

[0002] As national energy, transportation, and other infrastructure projects extend to areas with complex geological conditions, the number of long-span tunnel projects is increasing. After excavation, long-span tunnels experience a wide and concentrated redistribution of stress in the surrounding rock, making them prone to loosening and collapse due to rock mass dispersion. Support technology is essential to control deformation and ensure stability. The effectiveness of the support directly determines the safety and economy of the project and is a core guarantee for tunnel construction under complex geological conditions.

[0003] Current support methods for long-span tunnels include using plain shotcrete, ordinary anchor bolts and cables, or steel arch frames. In terms of design, they mostly adopt the concept of passive load-bearing and uniform distribution, treating the surrounding rock as a source of load rather than part of the load-bearing structure, which leads to inherent limitations in dealing with long-span jointed rock masses.

[0004] The existing passive support system cannot actively build and strengthen the load-bearing structure formed by the rock mass itself. Moreover, it lacks a clear mechanism to effectively transfer the load around the tunnel to the deep, stable rock mass, resulting in low support efficiency.

[0005] Therefore, developing a multi-stage support method for large-span tunnels in jointed rock masses based on a spatial coupling mechanism is of great significance for improving support efficiency. Summary of the Invention

[0006] To address the problem of low support efficiency in existing technologies, this invention proposes a multi-stage support method for large-span tunnels in jointed rock masses based on a spatial coupling mechanism, specifically including the following steps: S1. Based on the surrounding rock damage field caused by stress redistribution after the excavation of the target large-span tunnel, the target large-span tunnel is divided into the far-field original rock stress zone, the mid-field bearing arch formation zone, and the near-field loosening zone. S2. In the near-field loosened area, flexible mesh shotcrete is used to seal the excavation face to provide a stable base for the mid-field bearing arch formation zone; S3. In the mid-field bearing arch formation zone, a chain-type fracture prevention mechanism is used to construct a force chain network to mobilize the self-supporting potential of the rock mass in the mid-field bearing arch formation zone and divert the load of the near-field loosened zone to the far-field original rock stress zone. S4. In the far-field original rock stress zone, a deep anchoring mechanism is adopted to establish deep anchoring points, which transform the tunnel perimeter load transmitted from the mid-field bearing arch formation zone into axial tensile force and transfer it to the deep stable rock mass.

[0007] Furthermore, in S3, the method of constructing a force chain network using a chain-like fracture prevention mechanism to mobilize the self-supporting potential of the rock mass within the mid-field bearing arch formation zone includes: actively constructing a continuous force chain network in the jointed rock mass through a first pre-tightening force element; establishing a continuous stress transmission path between dispersed rock blocks through the pre-tightening force generated by the first pre-tightening force element, connecting the dispersed rock blocks into an integral force-bearing unit, thereby mobilizing the self-supporting potential of the rock mass within the mid-field bearing arch formation zone.

[0008] Furthermore, the first prestressing element includes a prestressed anchor rod.

[0009] Furthermore, in step S4, the establishment of deep anchoring points using a deep anchoring mechanism includes: The second pre-tightening element crosses the mid-field bearing arch formation zone and the far-field original rock stress zone, and sets the anchoring end of the second pre-tightening element in the far-field original rock stress zone, anchoring the anchoring end to the rock mass in the far-field original rock stress zone, forming a stable deep anchoring point.

[0010] Furthermore, the second prestressing element includes a prestressed anchor cable.

[0011] Furthermore, anchoring the anchoring end to the stable rock mass in the far-field original rock stress zone includes injecting cementing material into the contact gap between the anchoring end and the rock mass in the far-field original rock stress zone, so that the deep anchoring point can stably bear the tunnel perimeter load transmitted from the mid-field bearing arch formation zone.

[0012] Furthermore, in S2, the flexible mesh shotcrete includes a flexible mesh and shotcrete. The flexible mesh shotcrete is used to seal the excavation free face, including: laying the flexible mesh against the excavation free face and fixing it at the joint intersections in the near-field loosened area to bind the loose rock blocks in the near-field loosened area into a whole; and tightly covering the flexible mesh and the rock surface with the shotcrete to seal the joint fissures in the near-field loosened area.

[0013] Furthermore, in S1, the surrounding rock damage field is a discontinuous and non-uniform damage field.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, based on the stress redistribution-induced surrounding rock damage field after the excavation of a target large-span tunnel, divides the tunnel into a far-field original rock stress zone, a mid-field bearing arch formation zone, and a near-field loosening zone. In the near-field loosening zone, flexible mesh shotcrete is used to seal the excavation face, providing a stable matrix for the mid-field bearing arch formation zone. In the mid-field bearing arch formation zone, a chain-like fracture-prevention mechanism is used to construct a force chain network to mobilize the self-supporting potential of the rock mass within the mid-field bearing arch formation zone, diverting the load from the near-field loosening zone to the far-field original rock stress zone. In the far-field original rock stress zone, a deep anchoring mechanism is used to establish deep anchoring points, converting the tunnel perimeter load transmitted from the mid-field bearing arch formation zone into axial tensile force and transferring it to the deep, stable rock mass. Specifically, the force chain network constructed through the chain-like fracture-prevention mechanism in the mid-field bearing arch formation zone connects discrete rock blocks within the jointed rock mass into a unified load-bearing unit, actively utilizing the rock mass's own compressive strength and the frictional interlocking ability between rock blocks to form a self-supporting arch within the mid-field bearing arch formation zone. This significantly reduces reliance on manual support structures, lowering material usage and construction costs while avoiding the risk of cavern instability due to support structure overload failure. Simultaneously, the flexible mesh sprayed concrete sealing the free face in the near-field loosened zone prevents weathering and loosening of the near-field rock mass, providing a stable matrix for the formation of the self-supporting arch in the mid-field bearing arch formation zone, further ensuring the continued realization of self-supporting potential and improving support efficiency.

[0015] Furthermore, the load in the near-field loosened zone is first directionally diverted to the far-field original rock stress zone through the force chain network of the mid-field bearing arch formation zone. Then, the deep anchoring mechanism used in the far-field original rock stress zone converts the load into axial tensile force, which is then transferred to the deep stable rock mass. This prevents the concentrated load around the tunnel from accumulating in the support structure or shallow rock mass, but instead completely transfers it to the stable rock mass through an appropriate spatial path, significantly reducing the stress concentration around the tunnel and improving support efficiency. By transferring loads through an appropriate spatial path, the risks of support structure cracking and rock mass collapse are reduced at the source, which is particularly suitable for the characteristics of large-span tunnels with wide stress distribution and high concentration. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a multi-stage support method for large-span jointed rock tunnels based on a spatial coupling mechanism, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of a multi-level support structure for a large-span tunnel in jointed rock mass provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] The specific embodiments of the present invention will be described below.

[0020] To address the low support efficiency of existing technologies, this invention divides the target large-span tunnel into a far-field original rock stress zone, a mid-field bearing arch formation zone, and a near-field loosening zone based on the stress redistribution and surrounding rock damage field caused by the excavation of the tunnel. In the near-field loosening zone, flexible mesh shotcrete is used to seal the excavation face, providing a stable matrix for the mid-field bearing arch formation zone. In the mid-field bearing arch formation zone, a chain-like fracture prevention mechanism is used to construct a force chain network to mobilize the self-supporting potential of the rock mass within the mid-field bearing arch formation zone, diverting the load from the near-field loosening zone to the far-field original rock stress zone. In the far-field original rock stress zone, a deep anchoring mechanism is used to establish deep anchoring points, converting the tunnel perimeter load transmitted from the mid-field bearing arch formation zone into axial tensile force and transferring it to the deep, stable rock mass. The support method of this invention has high support efficiency.

[0021] This invention provides a multi-level support method for large-span tunnels in jointed rock masses based on a spatial coupling mechanism. The spatial coupling mechanism refers to the technical logic of accurately matching support measures according to the characteristics of spatial partitions, while allowing the support functions of each partition to support each other and form a global linkage. Figure 1 This is a flowchart of a multi-stage support method for large-span jointed rock tunnels based on a spatial coupling mechanism, provided by an embodiment of the present invention. Figure 1 As shown, the specific steps include the following: S1. Based on the surrounding rock damage field caused by stress redistribution after the excavation of the target large-span tunnel, the target large-span tunnel is divided into the far-field original rock stress zone, the mid-field bearing arch formation zone, and the near-field loosening zone.

[0022] Large-span tunnels are engineering objects requiring support, situated in jointed rock mass geological conditions. After excavation, they are prone to instability due to stress concentration and rock mass dispersion. Before excavation, the rock mass is in a state of original stress equilibrium. After excavation, the surrounding rock mass is unloaded, and the original stress is redistributed. This manifests as reduced stress in the shallow rock mass, stress concentration in the middle layer, and the retention of original stress in the deeper layers. This stress redistribution after excavation is the direct cause of surrounding rock damage. The surrounding rock damage field refers to the discontinuous and non-uniform damage area in the surrounding rock mass after stress redistribution due to stress adjustment. Specifically, it manifests as joint fissure expansion, rock block loosening, and decreased integrity.

[0023] The far-field original rock stress zone is the area furthest from the excavation face. Its rock mass remains unaffected by the stress redistribution caused by excavation, maintaining its original stress state. This zone exhibits high integrity and stability, possessing the ability to bear and disperse the load around the tunnel. The near-field loosened zone is the area immediately adjacent to the excavation face. It is most affected by the excavation unloading, resulting in a significant reduction in rock stress, full expansion of joints and fissures, and a loose or semi-loose state of rock blocks, making it prone to detachment or collapse. The mid-field bearing arch formation zone is located between the near and far fields. While the rock mass has suffered some damage from excavation, it is not completely loosened and possesses the potential to form a self-supporting arch through active restraint.

[0024] Specifically, the division of the above three functional zones needs to be based on the mechanical state and damage degree of the surrounding rock, and determined through quantitative indicators to ensure the scientific nature and feasibility of the zoning design. The specific division thresholds and standards are as follows: Near-field loosened zone: This area is adjacent to the excavation face, where the rock mass is severely loosened and has lost its self-supporting capacity. Its determination requires meeting one or more of the following core indicators: Spatial range, typically extending from the excavation face into the rock mass from 0 to 1.0 times the equivalent diameter of the tunnel; Rock mass integrity index, with a rock mass integrity coefficient not exceeding 0.35, or a decrease in the longitudinal wave velocity of the rock mass compared to the undisturbed original rock exceeding 30%; Geological exploration characteristics, with ground-penetrating radar images showing strong and discontinuous chaotic reflections, and borehole television showing numerous open fractures or loosened rock blocks.

[0025] Mid-field load-bearing arch formation zone: This area is located outside the near-field loosened zone. The rock mass is damaged but not completely loosened, and has the potential to form a load-bearing structure through engineering reinforcement. Its determination requires meeting one or more of the following core indicators: Spatial range, typically located within a ring-shaped area of ​​1.0 to 3.0 times the equivalent diameter of the tunnel; Rock mass integrity index, with a rock mass integrity coefficient between 0.35 and 0.75, or a decrease in the longitudinal wave velocity of the rock mass compared to the undisturbed original rock between 10% and 30%; Geological exploration characteristics, with ground-penetrating radar images showing moderate-intensity, basically continuous, in-phase axial reflections, borehole television showing joints that are mainly closed or compacted, and core samples showing signs of stress concentration such as disc-like fractures.

[0026] Far-field original rock stress zone: This area is slightly affected by excavation disturbance and has a stable mechanical state, serving as the basis for providing deep anchorage. Its determination requires meeting one or more of the following core indicators: Spatial range, typically located outside 3.0 times the equivalent diameter of the tunnel; Rock mass integrity index, with a rock mass integrity coefficient greater than 0.75, or a decrease in the longitudinal wave velocity of the rock mass compared to the undisturbed original rock of less than 10%; Geological exploration characteristics, with ground-penetrating radar images showing uniform, weak, and calm reflections, and borehole television showing intact rock mass, closed primary joints, and no traces of excavation disturbance.

[0027] After excavation, stress redistribution occurs in the surrounding rock mass. Shallow rock loosens due to unloading, mid-layer stress concentrates, and deep rock retains its original stress, ultimately forming a discontinuous and non-uniform surrounding rock damage field. Geological exploration methods, such as high-frequency ground-penetrating radar scanning of the free face and borehole imaging to obtain rock mass integrity data, are used to identify the damage degree boundaries of the surrounding rock damage field. Based on the differences in damage degree, the surrounding rock mass is precisely divided into three spatial regions: a near-field loosening zone, a mid-field bearing arch formation zone, and a far-field original rock stress zone. By dividing these three regions with different characteristics, differentiated support measures are designed for each region, avoiding both over-support of the stable rock mass in the far field and under-support of the loose rock mass in the near field.

[0028] S2. In the near-field loosened area, flexible sprayed concrete is used to seal the excavation face, providing a stable base for the mid-field bearing arch formation zone.

[0029] Flexible mesh shotcrete is a composite material composed of flexible mesh and shotcrete. The flexible mesh, often made of steel wire or synthetic fiber, possesses a certain degree of flexibility, allowing it to conform to the undulating shape of the free face and bind loose rock blocks to prevent localized detachment. Shotcrete refers to concrete applied to both the flexible mesh and the rock mass surface using a spraying process, quickly sealing joints and fissures to form a continuous protective layer. The free face refers to the exposed rock mass surface after tunnel excavation. It is the unsupported interface between the rock mass and air and water, and is also the main risk point for rock block detachment in the near-field loosened area, requiring support and sealing. The stable matrix refers to the continuous, complete, and non-loose rock mass support surface formed after support in the near-field loosened area. It is the stable rock mass carrier provided by the combination of flexible mesh shotcrete and the near-field loosened rock mass, preventing rock block detachment and fissure propagation during mid-field construction.

[0030] Specifically, the flexible mesh shotcrete is used to seal the excavation face, including: laying the flexible mesh against the excavation face and fixing it at the joint intersections in the near-field loosened area to bind the loose rock blocks in the near-field loosened area into a whole; and tightly covering the flexible mesh and the rock surface with the shotcrete to seal the joints and fissures in the near-field loosened area.

[0031] Joint intersections are the meeting points of natural fissures in a rock mass. Compared to a single fissure surface, fixing a flexible mesh at the joint intersection can result in a higher degree of interlocking of rock blocks and greater stability.

[0032] The flexible mesh is laid along the undulating shape of the excavated free face, with overlaps between mesh panels. The overlap width must be greater than or equal to the side length of the mesh opening, ensuring no gaps. Anchors or other fixing elements are used to secure the mesh at joint intersections, with the spacing between each fixing point appropriate to the size of the rock block, ensuring the mesh is taut and secure. Wet spraying is then used to spray concrete onto the flexible mesh and rock surface, filling the gaps in the flexible mesh and joint fissures. After the concrete has initially set, the integrity of the coverage is checked, and any missed areas or gaps are repaired. Finally, a flexible mesh-sprayed concrete sealing layer is formed, completing the sealing of the free face. By binding loose rock blocks, rock block detachment is prevented, thus preventing construction safety accidents. Sealing joint fissures blocks water and air erosion paths, preventing rock weathering and softening. This addresses the risk of near-field instability. Simultaneously, the flexible mesh-sprayed concrete sealing layer formed in the near field, along with the bound rock block units, together constitute a stable matrix for the mid-field bearing arch formation zone, providing cross-zone support for the spatial coupling mechanism and ensuring the realization of the mid-field function.

[0033] S3. In the mid-field bearing arch formation zone, a chain-type fracture prevention mechanism is used to construct a force chain network to mobilize the self-supporting potential of the rock mass in the mid-field bearing arch formation zone and divert the load of the near-field loosened zone to the far-field original rock stress zone.

[0034] Specifically, this includes: actively constructing a continuous force chain network in the jointed rock mass through a first prestressing element; establishing a continuous stress transmission path between dispersed rock blocks through the prestressing force generated by the first prestressing element, connecting the dispersed rock blocks into an integral load-bearing unit, thereby mobilizing the self-supporting potential of the rock mass within the mid-field bearing arch formation zone. The first prestressing element includes a prestressed anchor rod.

[0035] Figure 2 This is a schematic diagram of a multi-stage support structure for a large-span tunnel in jointed rock mass provided in an embodiment of the present invention, as shown below. Figure 2 As shown, large-span tunnels in jointed rock masses are prone to forming collapse arch structures that progress from shallow to deep, including shallow and deep collapse arches, leading to chain-like failure. Prestressed anchor structures can effectively curb the expansion of shallow collapse arches and interrupt the chain-like failure path from near to far.

[0036] The first prestressing element is the core physical component for constructing the force chain network in the mid-field bearing arch formation zone. It possesses the characteristic of actively applying prestressing force, transmitting constraints to the rock mass through this force. It serves as both the node carrier of the force chain network and the source of the prestressing force. A continuous force chain network refers to a system of continuous stress across the entire domain, with the first prestressing element acting as the force chain node and the rock mass stress induced by the prestressing force acting as the chain link. The prestressing force is an active tensile force applied and locked by the first prestressing element. This tensile force is transmitted to the rock blocks through prestressed anchor bolts, forcing the discrete rock blocks to compress and interlock with each other, forming a stable stress transmission relationship.

[0037] By employing methods such as borehole imaging and geological logging, the distribution of joints and fractures and the size of dispersed rock blocks in the mid-field bearing arch formation zone were identified, providing a basis for selecting the spacing and length of the first prestressing element. Based on the survey results, anchor holes were drilled circumferentially (i.e., along the tunnel perimeter) and axially (i.e., along the tunnel length) along the mid-field bearing arch formation zone, and prestressed anchors were implanted. The circumferential spacing matched the joint density, the axial spacing adapted to the tunnel excavation cycle length, and the prestressed anchor depth ensured that one end was anchored into a stable rock block in the mid-field, while the other end extended beyond the rock surface for easy application of prestressing force. The prestressed anchors were subjected to the designed prestressing force using tensioning equipment, and locked with anchorages after the required tension was achieved. The prestressing force was transmitted through the anchor rod body to the rock block at the bottom of the anchor hole, forcing the dispersed rock blocks around the anchor hole to compress each other, establishing a continuous compressive stress transmission path between the rock blocks. When all prestressed anchors are prestressed, the local stress paths formed by each prestressed anchor are interconnected, constructing a continuous force chain network covering the mid-field bearing arch formation zone. Dispersed rock blocks are linked together into a continuous force chain network to form an integral force-bearing unit, thereby activating the rock mass's own compressive and anti-sliding capabilities and mobilizing its self-supporting potential.

[0038] By transforming discrete rock blocks into integral load-bearing units through a force chain network, the rock mass can bear most of the load in the mid-field bearing arch formation zone, eliminating the need for extensive steel supports and thick linings. This addresses the economic and durability shortcomings of existing passive support technologies that rely solely on artificial structures for load bearing. Simultaneously, the force chain network ensures that stress can be transferred throughout the rock blocks, rather than being confined to the vicinity of a single anchor, preventing stress concentration and support failure due to localized rock block loosening.

[0039] S4. In the far-field original rock stress zone, a deep anchoring mechanism is adopted to establish deep anchoring points, which transform the tunnel perimeter load transmitted from the mid-field bearing arch formation zone into axial tensile force and transfer it to the deep stable rock mass.

[0040] Specifically, this includes: using a second prestressing element to span the mid-field bearing arch formation zone and the far-field original rock stress zone, and setting the anchoring end of the second prestressing element in the far-field original rock stress zone, anchoring the anchoring end to the rock mass in the far-field original rock stress zone to form a stable deep anchoring point. The second prestressing element includes a prestressed anchor cable.

[0041] The second prestressing element is the core component for constructing the deep anchoring point in the far-field original rock stress zone. It has the ability to cross both the mid-field and far-field zones, transferring loads to the deep, stable rock mass. The anchoring end refers to the end of the second prestressing element (i.e., the prestressed anchor cable) that penetrates into the far-field original rock stress zone; it is the core part where the prestressed anchor cable firmly bonds with the stable rock mass in the far-field original rock stress zone. The deep anchoring point is the stable stress-bearing node formed by the anchoring end and the rock mass in the far-field original rock stress zone through anchoring action. It is a load transfer node jointly formed by the prestressed anchor cable anchoring end and the surrounding stable rock mass, capable of withstanding axial tensile forces for a long time, serving as the end point of the entire tunnel load transfer chain.

[0042] Anchor cable holes are drilled from the tunnel face or the rock mass in the mid-field bearing arch formation zone towards the far-field original rock stress zone. The drilling depth must penetrate the mid-field bearing arch formation zone and reach the anchoring position in the far-field original rock stress zone. Prestressed anchor cables are inserted along the anchor cable holes, ensuring that the anchoring end of the prestressed anchor cable reaches the anchoring position in the far-field original rock stress zone. The tensioning end of the prestressed anchor cable remains outside the rock mass to facilitate subsequent application of preload. Cementing material is injected into the contact gap between the anchoring end and the rock mass in the far-field original rock stress zone to ensure that the deep anchoring point can stably withstand the tunnel perimeter load transmitted from the mid-field bearing arch formation zone. After the cementing material reaches its design strength, preload is applied to the tensioning end of the prestressed anchor cable and locked. At this point, the anchoring end and the rock mass in the far-field original rock stress zone together constitute a deep anchoring point capable of withstanding axial tensile forces. By using the deep anchoring point as the load transfer endpoint, the circumferential load transferred from the mid-field bearing arch formation zone is transformed into axial tensile force and transferred to the deep stable rock mass, thus completely transferring the load to the far-field stable rock mass and achieving effective load transfer to the deep stable rock mass. While providing deep anchoring in the far-field, the anchor cable structure further reinforces the deep rock mass, effectively curbing the formation of deep collapse arches.

[0043] This embodiment divides the target large-span tunnel into three zones based on the stress redistribution caused by the excavation of the target large-span tunnel: a far-field original rock stress zone, a mid-field bearing arch formation zone, and a near-field loosening zone. In the near-field loosening zone, flexible mesh shotcrete is used to seal the excavation face, providing a stable matrix for the mid-field bearing arch formation zone. In the mid-field bearing arch formation zone, a chain-like fracture prevention mechanism is used to construct a force chain network to mobilize the self-supporting potential of the rock mass within the mid-field bearing arch formation zone, diverting the load from the near-field loosening zone to the far-field original rock stress zone. In the far-field original rock stress zone, a deep anchoring mechanism is used to establish deep anchoring points, converting the tunnel perimeter load transmitted from the mid-field bearing arch formation zone into axial tensile force and transferring it to the deep, stable rock mass. Specifically, the force chain network constructed through the chain-like fracture prevention mechanism in the mid-field bearing arch formation zone connects discrete rock blocks within the jointed rock mass into a unified load-bearing unit, actively utilizing the rock mass's own compressive strength and the frictional interlocking ability between rock blocks to form a self-supporting arch within the mid-field bearing arch formation zone. This significantly reduces reliance on manual support structures, lowering material usage and construction costs while avoiding the risk of cavern instability due to support structure overload failure. Simultaneously, the flexible mesh sprayed concrete sealing the free face in the near-field loosened zone prevents weathering and loosening of the near-field rock mass, providing a stable matrix for the formation of the self-supporting arch in the mid-field bearing arch formation zone, further ensuring the continued realization of self-supporting potential and improving support efficiency.

[0044] Furthermore, the load in the near-field loosened zone is first directionally diverted to the far-field original rock stress zone through the force chain network of the mid-field bearing arch formation zone. Then, the deep anchoring mechanism used in the far-field original rock stress zone converts the load into axial tensile force, which is then transferred to the deep stable rock mass. This prevents the concentrated load around the tunnel from accumulating in the support structure or shallow rock mass, but instead completely transfers it to the stable rock mass through an appropriate spatial path, significantly reducing the stress concentration around the tunnel and improving support efficiency. By transferring loads through an appropriate spatial path, the risks of support structure cracking and rock mass collapse are reduced at the source, which is particularly suitable for the characteristics of large-span tunnels with wide stress distribution and high concentration.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A multi-stage support method for large-span tunnels in jointed rock masses based on a spatial coupling mechanism, characterized in that, include: S1. Based on the surrounding rock damage field caused by stress redistribution after the excavation of the target large-span tunnel, the target large-span tunnel is divided into the far-field original rock stress zone, the mid-field bearing arch formation zone, and the near-field loosening zone. S2. In the near-field loosened area, flexible mesh sprayed concrete is used to seal the excavation face to provide a stable base for the mid-field bearing arch formation zone; S3. In the mid-field bearing arch formation zone, a chain-type fracture prevention mechanism is used to construct a force chain network to mobilize the self-supporting potential of the rock mass in the mid-field bearing arch formation zone and divert the load of the near-field loosened zone to the far-field original rock stress zone. S4. In the far-field original rock stress zone, a deep anchoring mechanism is adopted to establish deep anchoring points, which transform the tunnel perimeter load transmitted from the mid-field bearing arch formation zone into axial tensile force and transfer it to the deep stable rock mass.

2. The multi-stage support method for large-span tunnels in jointed rock mass based on spatial coupling mechanism according to claim 1, characterized in that, In S3, the construction of a force chain network using a chain-like fracturing mechanism to mobilize the self-supporting potential of the rock mass within the mid-field bearing arch formation zone includes: A continuous force chain network is actively constructed in the jointed rock mass through the first pre-tightening force element; The pre-tightening force generated by the first pre-tightening element establishes a continuous stress transmission path between the dispersed rock blocks, connecting the dispersed rock blocks into an integral force-bearing unit, thereby mobilizing the self-supporting potential of the rock mass in the mid-field bearing arch formation zone.

3. The multi-stage support method for large-span tunnels in jointed rock mass based on spatial coupling mechanism according to claim 2, characterized in that, The first prestressing element includes a prestressed anchor rod.

4. The multi-stage support method for large-span jointed rock mass tunnels based on spatial coupling mechanism according to claim 1, characterized in that, In step S4, establishing deep anchoring points using a deep anchoring mechanism includes: The second pre-tightening element crosses the mid-field bearing arch formation zone and the far-field original rock stress zone, and sets the anchoring end of the second pre-tightening element in the far-field original rock stress zone, anchoring the anchoring end to the rock mass in the far-field original rock stress zone, forming a stable deep anchoring point.

5. The multi-stage support method for large-span jointed rock mass tunnels based on spatial coupling mechanism according to claim 4, characterized in that, The second prestressing element includes a prestressed anchor cable.

6. The multi-stage support method for large-span jointed rock mass tunnels based on spatial coupling mechanism according to claim 4, characterized in that, Anchoring the anchoring end to the stable rock mass in the far-field original rock stress zone includes: injecting cementing material into the contact gap between the anchoring end and the rock mass in the far-field original rock stress zone so that the deep anchoring point can stably bear the tunnel perimeter load transmitted from the mid-field bearing arch formation zone.

7. The multi-stage support method for large-span tunnels in jointed rock mass based on spatial coupling mechanism according to claim 1, characterized in that, In S2, the flexible mesh shotcrete includes a flexible mesh and shotcrete. The flexible mesh shotcrete is used to seal the excavated exposed surface, including: The flexible mesh is laid on the excavated free face and fixed at the joint intersections of the near-field loosened zone to bind the loose rock blocks in the near-field loosened zone into a whole; The sprayed concrete is used to tightly cover the flexible mesh and the rock surface, sealing the joints and fissures in the near-field loosened zone.

8. The multi-stage support method for large-span tunnels in jointed rock mass based on spatial coupling mechanism according to claim 1, characterized in that, In S1, the surrounding rock damage field is a discontinuous and non-uniform damage field.

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