Intermediate rock support for reconstruction and extension of small-clear-distance tunnel and construction method

Abstract

The invention belongs to the field of tunnel support, and discloses a middle rock support for reconstruction and extension of a small-clear-distance tunnel and a construction method, and the construction method comprises the following steps: constructing a stable temporary steel support in an existing tunnel; the lining segment and the primary support spraying layer which are close to the interlayer rock are removed, and then disintegrating slag on the surface of the interlayer rock is cleaned; drilling holes in the middle clamping rock, driving a plurality of hollow grouting anchor rods, and then pouring an underground diaphragm wall; after the hardening of the underground diaphragm wall reaches the standard, first filler is injected behind the underground diaphragm wall, second filler is injected through the hollow grouting anchor rod, and the first filler and the second filler are in contact to form a bolting-grouting composite body; trays are additionally arranged at the two ends of the hollow grouting anchor rod, and the trays are locked on the outer surface of the underground diaphragm wall through locks. By means of the safe, efficient and environment-friendly supporting structure and the construction method, the problems that in the small-clear-distance tunnel reconstruction and extension process, the stability of interlaid rocks is poor, and construction disturbance is large are effectively solved, and remarkable engineering application value and technical innovation are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel support, and particularly to a support and construction method for the middle rock mass in the reconstruction and expansion of small clear - distance tunnels. Background Art

[0002] In the field of tunnel engineering, with the continuous advancement of transportation infrastructure construction, the demand for the reconstruction and expansion of existing small clear - distance tunnels is becoming increasingly strong. In such projects, the support and stability of the middle rock mass are the key to ensuring the safety and quality of the project.

[0003] In the construction of the reconstruction and expansion of existing tunnels, traditional methods have obvious deficiencies: the middle rock mass deteriorates due to multiple disturbances, resulting in poor stability; excessive use of anchor bolts and cable bolts not only increases costs but also exacerbates rock mass fracture due to drilling. Although blasting demolition is efficient, it will seriously disturb the middle rock mass, causing deformation and damage to the existing lining; existing support technologies (such as ordinary anchor bolts and shotcrete) are difficult to effectively control the deformation of the middle rock mass and cannot form a stable support system; in addition, insufficient protection of the existing tunnel during construction is likely to cause cracks or deformation, threatening the structural safety; these problems seriously restrict the engineering effect of the reconstruction and expansion of small clear - distance tunnels.

[0004] Therefore, this application designs a support and construction method for the middle rock mass in the reconstruction and expansion of small clear - distance tunnels to solve the above - mentioned technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a support and construction method for the middle rock mass in the reconstruction and expansion of small clear - distance tunnels, so as to solve the problems existing in the prior art, reduce the disturbance to the middle rock mass during construction, enhance the stability of the rock mass, reduce construction costs, improve construction efficiency, and ensure the safety and quality of the reconstruction and expansion project of small clear - distance tunnels.

[0006] To achieve the above - mentioned purpose, the present invention provides the following solution: The present invention provides a support and construction method for the middle rock mass in the reconstruction and expansion of small clear - distance tunnels, including the following steps:

[0007] Construct a stable temporary steel support in the existing tunnel;

[0008] Demolish the lining segments and the initial support shotcrete layer adjacent to the rock mass, and then clean the debris on the surface of the middle rock mass;

[0009] Drill holes in the middle rock mass and drive several hollow grouting anchor bolts, and then pour concrete to form a diaphragm wall that fits the surface of the middle rock mass;

[0010] After the diaphragm wall hardens to the standard, inject a first filler behind the diaphragm wall, and at the same time inject a second filler through the hollow grouting anchor bolts. The first filler and the second filler come into contact to form an anchor - grouting complex;

[0011] Install trays at both ends of the hollow grouting bolt, and use locking devices to lock the trays on the outer surface of the diaphragm wall.

[0012] Preferably, in the step of demolishing the lining segments and the primary shotcrete layer adjacent to the intermediate rock, mechanical equipment is used to cut and demolish the lining segments and the primary shotcrete layer on the side of the existing tunnel close to the intermediate rock, so as to reduce the disturbance impact on the undemolished tunnel lining structure in the existing tunnel.

[0013] Preferably, in the step of constructing the diaphragm wall, after the construction of the hollow grouting bolt is completed, reinforcement cages are erected on both sides of the intermediate rock in a fitting manner. The reinforcement cages are adapted to the demolished lining segments and the primary shotcrete layer, and the reinforcement cages are fixedly connected to the ends of the hollow grouting bolts.

[0014] Preferably, in the step of constructing the diaphragm wall, concrete is poured and filled at the position of the reinforcement cage to form the diaphragm wall, and the diaphragm wall is parallel to the existing tunnel and fits on the side wall of the intermediate rock.

[0015] Preferably, the position of drilling in the intermediate rock starts from the arch waist of the existing tunnel close to the side of the intermediate rock in the existing tunnel, and penetrates the intermediate rock to reach the arch waist of the other existing tunnel.

[0016] Preferably, the hollow grouting bolts are arranged axially and uniformly along the intermediate rock, and both ends of the hollow grouting bolts extend into the two existing tunnels respectively.

[0017] Preferably, the first filler includes concrete slurry, and the concrete slurry is injected into the gap between the diaphragm wall and the intermediate rock.

[0018] Preferably, the second filler includes thixotropic polyurethane slurry, and the thixotropic polyurethane slurry is injected into the space between the two diaphragm walls through the hollow grouting bolts.

[0019] Preferably, the hollow grouting bolt includes a hollow full-thread bolt body, and the hollow full-thread bolt body is embedded in the drilled hole of the intermediate rock in a penetrating manner; both ends of the hollow full-thread bolt body are locked and fixed in the drilled hole of the intermediate rock by nuts connected by threads.

[0020] Preferably, the hollow grouting bolts are distributed circumferentially along the cross-section of the existing tunnel.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects: The present invention discloses a method for supporting and constructing the middle rock stratum in the reconstruction and expansion of small clear distance tunnels. A stable temporary steel support is erected in the existing tunnel to provide safety guarantee for subsequent construction and maintain the stability of the existing lining. The lining segments and the primary shotcrete layer adjacent to the middle rock stratum are removed in a specific manner, and then the crushed slag on the surface of the middle rock stratum is cleaned up to create conditions for subsequent support operations, effectively avoiding the disturbance of the middle rock stratum during blasting construction, reducing the degree of rock mass deterioration, and ensuring the stability of the middle rock stratum. A number of hollow grouting bolts are drilled and driven into the middle rock stratum, and then concrete is poured to form a diaphragm wall that fits the surface of the middle rock stratum, initially constructing a support structure. Reducing the use of bolts saves material costs, simplifies the construction process, reduces the amount of drilling operations, reduces the number of bolts used, reduces the risk of rock mass rupture caused by a large number of drill holes, protects the integrity of the rock mass structure, and speeds up the construction progress. After the diaphragm wall is hardened to the standard, the first filler is injected behind its wall, and at the same time, the second filler is injected through the hollow grouting bolts. The two fillers come into contact to form an anchor grouting complex. The bolts reinforce the broken area and grout behind the wall, and together with the diaphragm wall, they serve as part of the lining of the expanded tunnel, forming an integrated support system, improving the bearing capacity and stability of the tunnel, and further enhancing the support effect. Trays are installed at both ends of the hollow grouting bolts, and the trays are locked on the outer surface of the diaphragm wall with locks to stabilize the bolts and improve the reliability of the overall support.

[0022] Through a safe, efficient, and environmentally friendly support structure and construction method, the present invention effectively solves the problems of poor stability of the middle rock stratum and large construction disturbance during the reconstruction and expansion of small clear distance tunnels, and has significant engineering application value and technical innovation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0024] Figure 1 It is a schematic diagram of the construction of the diaphragm wall adjacent to the middle rock stratum in the present invention;

[0025] Figure 2 It is a schematic diagram of the lining of the expanded tunnel in the present invention;

[0026] Figure 3 It is a schematic diagram of the layout of the reinforcement cage of the diaphragm wall in the present invention;

[0027] Figure 4 It is a flow chart of the construction method in the present invention;

[0028] In the figure: 1. Existing tunnel; 2. Temporary steel support; 3. Diaphragm wall; 4. Hollow grouting bolt; 5. Waist of the existing tunnel arch; 6. Springing of the existing tunnel arch; 7. Outline of the existing tunnel; 8. Intermediate rock; 9. Crown of the existing tunnel; 10. Lining of the extended tunnel; 11. Steel reinforcement cage. Specific implementation manner

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0031] Referring to Figures 1-4 As shown, this embodiment provides a support and construction method for the intermediate rock in the reconstruction and expansion of a small clear distance tunnel, including the following steps:

[0032] Construct a stable temporary steel support 2 in the existing tunnel 1; on the premise of ensuring the stability of the existing tunnel 1, erect a temporary steel support 2 in the existing tunnel 1 to ensure the stability of the existing lining and construction safety. Based on this premise, the safety construction requirements can be met;

[0033] Demolish the lining segments and the initial support shotcrete layer adjacent to the intermediate rock 8, and then clean the debris on the surface of the intermediate rock 8; demolish the lining segments and the initial support shotcrete layer adjacent to the intermediate rock 8 on two adjacent existing tunnels 1 to reduce the disturbance impact on the lining structure of the un-demolished tunnel, expose the intermediate rock 8, and then clean the debris structure with loose surface structure on the intermediate rock 8;

[0034] Drill holes in the intermediate rock 8 and drive in a number of hollow grouting bolts 4, and then pour concrete to form a diaphragm wall 3 that fits the surface of the intermediate rock 8; use a drilling machine to horizontally drill a number of holes through the intermediate rock 8, and connect the two adjacent existing tunnels 1 through the holes; then pour the diaphragm wall 3 with concrete closely against the intermediate rock 8, and then cure the diaphragm wall 3 made of concrete to make the concrete harden normally;

[0035] After the diaphragm wall 3 has hardened to meet the standards, inject the first filler behind the diaphragm wall 3, and at the same time inject the second filler through the hollow grouting bolt 4. The first filler and the second filler come into contact to form an anchor grouting composite body. After the hardness of the diaphragm wall 3 reaches the set index, inject the first filler between the middle rock stratum 8 and the diaphragm wall 3 through the grouting equipment to fill the gap between the middle rock stratum 8 and the diaphragm wall 3 and bond the two together. At the same time, the hollow grouting bolt 4 is connected to another grouting equipment to inject the second filler around the central control grouting bolt. The second filler fills the gap of the middle rock stratum 8 to fix the hollow grouting bolt 4 and the middle rock stratum 8 together. At the same time, the second filler and the first filler come into contact and penetrate and combine with each other to form an anchor grouting composite body under physical action, improving the overall stability of the rock mass.

[0036] Install trays at both ends of the hollow grouting bolt 4 and use locking devices to lock the trays on the outer surface of the diaphragm wall 3. By abutting the trays against the outer wall of the diaphragm wall 3, the hollow grouting bolt 4 and the diaphragm wall 3 are further locked together, improving the strength of the overall support structure.

[0037] The present invention discloses a support and construction method for the middle rock stratum in the reconstruction and expansion of a small clear distance tunnel. A stable temporary steel support 2 is built in the existing tunnel 1 to provide safety guarantee for subsequent construction and maintain the stability of the existing lining. The lining segments and the primary support shotcrete layer adjacent to the middle rock stratum 8 are removed in a specific manner, and then the crushed slag on the surface of the middle rock stratum 8 is cleaned up to create conditions for subsequent support operations, effectively avoiding the disturbance of the middle rock stratum 8 during blasting construction, reducing the degree of rock mass deterioration, and ensuring the stability of the middle rock stratum 8. Drill holes in the middle rock stratum 8 and drive several hollow grouting bolts 4, and then pour concrete to form a diaphragm wall 3 that fits the surface of the middle rock stratum 8, initially constructing a support structure, reducing the use of bolts, saving material costs, simplifying the construction process, reducing the amount of drilling operations, reducing the number of bolts used, reducing the risk of rock mass rupture caused by a large number of drill holes, protecting the integrity of the rock mass structure, and accelerating the construction progress. After the diaphragm wall 3 has hardened to meet the standards, inject the first filler behind its wall, and at the same time inject the second filler through the hollow grouting bolt 4. The two fillers come into contact to form an anchor grouting composite body. The bolt reinforces the broken area and grouts behind the wall, and together with the diaphragm wall 3, serves as part of the lining 10 of the expanded tunnel, forming an integrated support system, improving the bearing capacity and stability of the tunnel, and further enhancing the support effect. Install trays at both ends of the hollow grouting bolt 4 and use locking devices to lock the trays on the outer surface of the diaphragm wall 3 to stabilize the bolts and improve the reliability of the overall support. The present invention effectively solves the problems of poor stability of the middle rock stratum 8 and large construction disturbance during the reconstruction and expansion of small clear distance tunnels through a safe, efficient, and environmentally friendly support structure and construction method, and has significant engineering application value and technical innovation.

[0038] In an embodiment of the present application, the existing tunnel contour line 7 of the existing tunnel 1 includes parts such as the existing tunnel arch springing 6, the existing tunnel arch waist 5, and the existing tunnel crown 9, forming an overall support on the existing tunnel 1.

[0039] In an embodiment of the present application, the bottom end of the temporary steel support 2 is fixed on the stable existing tunnel arch springing 6 to ensure the stability of the support; while the top end of the temporary steel support 2 supports on the existing tunnel crown 9 to achieve the support of the existing tunnel 1.

[0040] For a further optimized solution, in the step of demolishing the lining segments and the primary shotcrete layer adjacent to the intermediate rock, mechanical equipment is used to cut and demolish the lining segments and the primary shotcrete layer on the side of the existing tunnel 1 close to the intermediate rock 8, reducing the disturbance effect on the un-demolished tunnel lining structure in the existing tunnel 1. Use mechanical cutting to demolish the lining segments and the primary shotcrete layer adjacent to the intermediate rock 8, and clean the debris on the surface of the intermediate rock 8; use a diamond saw blade cutting machine to cut the lining segments adjacent to the intermediate rock 8. During the cutting process, the depth of cutting the lining segments should be controlled to avoid unnecessary damage to the surrounding structures; also ensure that the cutting surface is flat for subsequent cleaning work.

[0041] For a further optimized solution, in the step of constructing the diaphragm wall 3, after the construction of the hollow grouting anchor rod 4 is completed, a steel reinforcement cage 11 is erected on both sides of the intermediate rock 8 in a fitting manner. The steel reinforcement cage 11 is adapted to the demolished lining segments and the primary shotcrete layer, and the end of the steel reinforcement cage 11 is fixedly connected to the end of the hollow grouting anchor rod 4. The steel reinforcement cage 11 is tied with steel bars, and then the steel reinforcement cage 11 is erected on the excavated part of the existing tunnel 1 and tied to the end of the hollow grouting anchor rod 4 by binding wires or other means to form an overall support framework, improving the integrity of the subsequent support.

[0042] For a further optimized solution, in the step of constructing the diaphragm wall 3, concrete is poured and filled at the location of the steel reinforcement cage 11 to form the diaphragm wall 3. The diaphragm wall 3 is parallel to the existing tunnel 1 and fits against the side wall of the intermediate rock 8. During construction, a support formwork is set on the outer surface of the steel reinforcement cage 11, and then concrete is poured into the support formwork through a pouring device to form the diaphragm wall 3, which is parallel to the tunnel and fits against the intermediate rock 8.

[0043] For a further optimized solution, the drilling position in the intermediate rock 8 starts from the existing tunnel arch waist 5 on the side of the existing tunnel 1 close to the intermediate rock 8 and penetrates through the intermediate rock 8 to reach the existing tunnel arch waist 5 of another existing tunnel 1. The drilling in the intermediate rock 8 penetrates from the arch waist on the side of the existing tunnel 1 close to the intermediate rock 8 to the arch waist of another existing tunnel 1, enabling the hollow grouting anchor rod 4 to effectively penetrate through the key part of the intermediate rock 8, anchoring the intermediate rock 8 from both sides of the arch waist, improving the anchoring effect of the anchor rod on the intermediate rock 8, and enhancing the overall stability and bearing capacity of the intermediate rock 8.

[0044] For a further optimized solution, the hollow grouting bolts 4 are arranged axially and uniformly along the middle rock stratum 8, and both ends of the hollow grouting bolts 4 extend into the two existing tunnels 1 respectively. The hollow grouting bolts 4 are arranged axially and uniformly along the middle rock stratum 8, and both ends extend into the two existing tunnels 1 respectively. The uniformly distributed bolts form a stable anchoring system in the middle rock stratum 8, sharing the rock mass stress evenly; both ends of the hollow grouting bolts 4 extend into the existing tunnels 1, strengthening the connection between the middle rock stratum 8 and the existing tunnels 1, making the whole structure a stable entity and improving the stability of the tunnel.

[0045] For a further optimized solution, the first filler includes concrete slurry, and the concrete slurry is injected into the gap between the diaphragm wall 3 and the middle rock stratum 8; the second filler includes thixotropic polyurethane slurry, and the thixotropic polyurethane slurry is injected into the space between the two diaphragm walls 3 through the hollow grouting bolts 4. The first filler uses concrete slurry and is injected into the gap between the diaphragm wall 3 and the middle rock stratum 8 for filling, enhancing the bonding force and integrity between the diaphragm wall 3 and the middle rock stratum 8, strengthening the constraint of the support structure on the middle rock stratum 8, and improving the stability of the middle rock stratum 8; the second filler uses thixotropic polyurethane slurry and is injected into the space between the two diaphragm walls 3 through the hollow grouting bolts 4. The thixotropic polyurethane slurry fills the pores of the rock mass and reinforces the broken rock mass, forming an anchor grouting complex with the concrete slurry, further improving the strength, stability, impermeability and durability of the middle rock stratum 8.

[0046] In an embodiment of the present application, the thixotropic polyurethane slurry is selected from high molecular thixotropic materials and is made by mixing component A and component B in a volume ratio of 1:1.

[0047] In an embodiment of the present application, component A includes sodium silicate solution and potassium silicate solution, and the volume ratio of the sodium silicate solution to the potassium silicate solution is 4:1.

[0048] In an embodiment of the present application, component B includes one or more of diphenylmethane diisocyanate and toluene diisocyanate, the terminal amino resin is polyaspartate, the thixotropic agent is fumed silica, and the solubilizer includes one or more of ethylene glycol diacetate, tributyl citrate and dioctyl phthalate.

[0049] In an embodiment of the present application, the main component of the thixotropic polyurethane slurry is polyurethane, and its chemical properties are relatively stable; the main components of concrete include cement, sand and gravel, water, etc. The alkaline environment formed after the hydration of cement is an important manifestation of its chemical characteristics. Polyurethane itself has a certain tolerance to the alkaline environment and will not react chemically with alkaline substances and be corroded or deteriorated like some materials; therefore, from a chemical perspective, the thixotropic polyurethane slurry and concrete basically do not react chemically.

[0050] In an embodiment of the present application, the thixotropic polyurethane grout has good fluidity and filling properties. After being injected into the anchor bolts in projects such as the reconstruction and expansion of small clear - distance tunnels, it can penetrate into the pores and cracks of the concrete. As time goes by, the polyurethane grout solidifies and forms a tight physical bond with the concrete. This bond enhances the density of the concrete and improves its performance such as impermeability and crack resistance. In the support project of the middle rock stratum 8, after the thixotropic polyurethane grout is injected into the anchor bolts, it acts together with the surrounding concrete to enhance the overall stability of the rock mass, and no chemical reaction occurs.

[0051] In an embodiment of the present application, in some extreme or special cases, the thixotropic polyurethane grout and the concrete may interact with each other. If the concrete contains certain special additives or impurities, it may change the surface properties of the concrete and affect the penetration and adhesion effects of the polyurethane grout. However, this influence is not a chemical reaction but a change in physical interaction.

[0052] For a further optimized solution, the hollow grouting anchor bolt 4 includes a hollow full - thread anchor bolt body, and the hollow full - thread anchor bolt body is embedded in the drill hole of the middle rock stratum 8 in a penetrating manner; both ends of the hollow full - thread anchor bolt body are locked and fixed in the drill hole of the middle rock stratum 8 by nuts connected by threads. The hollow grouting anchor bolt 4 includes an anchor head, a hollow full - thread anchor bolt body, a grouting exhaust ring, a grout stopper, a backing plate, and a nut. The hollow full - thread anchor bolt body penetrates the drill hole of the middle rock stratum 8, and both ends are locked and tightened by nuts connected by threads. The hollow full - thread anchor bolt body is convenient for grouting, enabling the grout to spread evenly and enhancing the anchoring effect, while the nut connected by threads ensures that the anchor bolt is stable in the drill hole, prevents loosening, guarantees the continuous effectiveness of the anchoring function, and improves the reliability of the support structure.

[0053] In an embodiment of the present application, the length of the hollow full - thread anchor bolt body is 3 - 6 m, the diameter is 25 mm, and the wall thickness is 8 mm.

[0054] For a further optimized solution, the hollow grouting anchor bolts 4 are circumferentially distributed along the cross - section of the existing tunnel 1. The hollow grouting anchor bolts 4 are circumferentially distributed along the cross - section of the existing tunnel 1, forming an annular anchoring system in the cross - section direction of the existing tunnel 1, further enhancing the connection and stability between the middle rock stratum 8 and the existing tunnel 1, anchoring the middle rock stratum 8 from multiple directions, and improving the stability and bearing capacity of the entire support structure.

[0055] In an embodiment of the present application, the circumferential spacing between the hollow grouting anchor bolts 4 between the crown 9 of the existing tunnel and the waist 5 of the existing tunnel is 200 cm.

[0056] In an embodiment of the present application, the circumferential spacing between the hollow grouting anchor bolts 4 between the waist 5 of the existing tunnel and the toe 6 of the existing tunnel is 100 cm.

[0057] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0058] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A support and construction method for the middle rock stratum in the reconstruction and expansion of a small clear distance tunnel, characterized in that It includes the following steps: Construct a stable temporary steel support (2) in the existing tunnel (1); Demolish the lining segments and the initial shotcrete layer adjacent to the intermediate rock, and then clean the debris on the surface of the intermediate rock (8); Drill holes in the intermediate rock (8) and drive several hollow grouting bolts (4), and then pour concrete to form a diaphragm wall (3) arranged in conformity with the surface of the intermediate rock (8); After the diaphragm wall (3) has hardened to the standard, inject a first filler behind the diaphragm wall (3), and at the same time inject a second filler through the hollow grouting bolts (4). The first filler and the second filler come into contact to form an anchor grouting complex; Install trays at both ends of the hollow grouting bolts (4), and use locking devices to lock the trays on the outer surface of the diaphragm wall (3).

2. The middle rock support and construction method for the reconstruction and expansion of small clear distance tunnels according to claim 1, characterized in that: In the step of demolishing the lining segments and the initial shotcrete layer adjacent to the intermediate rock, use mechanical equipment to cut and demolish the lining segments and the initial shotcrete layer on the side of the existing tunnel (1) close to the intermediate rock (8), so as to reduce the disturbance effect on the undemolished tunnel lining structure in the existing tunnel (1).

3. The middle rock pillar support and construction method for the reconstruction and expansion of the small clear distance tunnel according to claim 1, characterized in that: In the step of constructing the diaphragm wall (3), after the construction of the hollow grouting bolts (4) is completed, reinforcement cages (11) are erected on both sides of the intermediate rock (8) in conformity. The reinforcement cages (11) are adapted to the demolished lining segments and the initial shotcrete layer, and the reinforcement cages (11) are fixedly connected to the ends of the hollow grouting bolts (4).

4. The middle rock pillar support and construction method for the reconstruction and expansion of closely spaced tunnels according to claim 3, characterized in that: In the step of constructing the diaphragm wall (3), pour concrete filling at the position of the reinforcement cages (11) to form the diaphragm wall (3). The diaphragm wall (3) is parallel to the existing tunnel (1) and is attached to the side wall of the intermediate rock (8).

5. The middle rock pillar support and construction method for the reconstruction and expansion of closely spaced tunnels according to claim 1, characterized in that: The positions of the drill holes in the intermediate rock (8) start from the existing tunnel springing (5) on the side of the existing tunnel (1) close to the intermediate rock (8), penetrate the intermediate rock (8) and reach the existing tunnel springing (5) of the other existing tunnel (1).

6. The middle rock pillar support and construction method for the reconstruction and expansion of small clear distance tunnels according to claim 5, characterized in that: The hollow grouting bolts (4) are arranged axially and uniformly along the intermediate rock (8), and both ends of the hollow grouting bolts (4) extend into the two existing tunnels (1).

7. The middle rock support and construction method for the reconstruction and expansion of small clear distance tunnels according to claim 1, characterized in that: The first filler includes concrete slurry, and the concrete slurry is injected into the gap between the diaphragm wall (3) and the intermediate rock (8).

8. The middle rock support and construction method for the reconstruction and expansion of small clear distance tunnels according to claim 7, characterized in that: The second filler includes thixotropic polyurethane slurry, and the thixotropic polyurethane slurry is injected into the space between the two diaphragm walls (3) through the hollow grouting bolts (4).

9. The middle rock support and construction method for reconstruction and expansion of closely spaced tunnels according to claim 1, characterized in that: The hollow grouting bolt (4) includes a hollow full-thread bolt body, and the hollow full-thread bolt body is embedded in the drill hole of the intermediate rock (8) in a penetrating manner; both ends of the hollow full-thread bolt body are locked and fixed in the drill hole of the intermediate rock (8) by nuts connected by threads.

10. The middle rock pillar support and construction method for the reconstruction and expansion of closely spaced tunnels according to claim 9, characterized in that: The hollow grouting bolts (4) are distributed circumferentially along the cross section of the existing tunnel (1).

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