Excavating and supporting process for large-section double-layer tunnel in weak surrounding rock

Abstract

The invention relates to the technical field of tunnel construction, in particular to an excavation supporting process for a large-section double-layer tunnel in weak surrounding rock. Comprising the steps of advanced pre-reinforcement supporting, upper-layer tunnel excavation and primary supporting, special bearing pile construction in the tunnel, upper-layer tunnel secondary lining and middle plate pouring, lower-layer tunnel partition excavation and primary supporting and lower-layer tunnel secondary lining pouring. According to the construction method, the complete construction process of advanced pre-reinforcement, layered supporting, partition excavation and permanent lining is constructed, the defects of a traditional technology in the aspects of advanced supporting, upper and lower layer construction interference and excavation disturbance control are effectively overcome, the stability of weak surrounding rock is guaranteed from the whole construction process, and the construction safety level is remarkably improved; and meanwhile, conflicts among procedures are greatly reduced through the block and zone excavation mode, the construction adaptability is also improved through special equipment matched with the space in the hole, and therefore dual optimization of the construction period and the engineering cost is achieved.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a large-section double-layer tunnel excavation and support process in soft surrounding rock. Background Technology

[0002] In engineering projects involving large-section double-layer tunnels, the tunnels often traverse areas of weak surrounding rock. Weak surrounding rock is characterized by poor stability, susceptibility to collapse, and large deformation after excavation. Large-section double-layer tunnels, due to their vertical layering and complex spatial structure, must withstand greater surrounding rock loads and structural self-weight during excavation. Traditional excavation and support techniques have several shortcomings: either insufficient pre-support measures make it difficult to control the risk of collapse in weak surrounding rock in advance; or the support structure has a single function (such as insufficient initial support arch foot bearing capacity), failing to meet the layered stress requirements of double-layer tunnels; or the excavation sequence lacks specificity, easily leading to secondary disturbance of the surrounding rock and causing structural deformation. These problems not only affect construction safety but may also prolong the construction period and increase project costs, necessitating a specialized excavation and support technique suitable for the "weak surrounding rock + large-section double-layer tunnel" scenario. Summary of the Invention

[0003] The purpose of this invention is to provide a large-section double-layer tunnel excavation and support technology in weak surrounding rock. Through the whole process design of "advanced pre-reinforcement - layered support - zoned excavation - load transfer - permanent lining", the invention achieves the goals of controllable deformation of weak surrounding rock, coordinated construction between upper and lower layers, and strong equipment adaptability, thus ensuring construction safety and engineering economy.

[0004] To achieve the above objectives, the technical solution provided by the present invention is as follows: A support technology for excavation of a large-section double-layer tunnel in weak surrounding rock includes the following steps: S1. Advanced pre-reinforcement support: An advanced support structure is constructed outside the tunnel excavation outline to form an advanced protective barrier and reinforce the weak surrounding rock in advance. S2. Excavation and initial support of the upper tunnel: The upper tunnel is excavated in sections. Initial and temporary support are immediately provided after excavation. At the same time, a hardening layer is laid at the bottom of the upper tunnel, and lateral reinforcement components are installed on the outside of the steel arch frame foot of the upper tunnel to stabilize the upper tunnel structure. S3. Construction of special load-bearing piles inside the tunnel: Special load-bearing components are constructed on both sides of the upper tunnel inside the tunnel. After the special load-bearing components are poured, the left and right special load-bearing components are connected into a whole by the cap beam. S4. Secondary lining and middle slab pouring of the upper tunnel: After the initial support of the upper tunnel is stable, the secondary lining of the upper tunnel is poured, and the middle slab of the tunnel is poured at the same time. One end of the middle slab is connected to the secondary lining, and the other end is connected to the cap beam. S5. Sectional Excavation and Initial Support of Lower Tunnel: The unexcavated weak surrounding rock of the lower tunnel is excavated in sections and steps according to the preset sequence. After the excavation of each section is completed, initial support and temporary support are carried out within the specified time to quickly seal the surrounding rock. S6. Secondary lining pouring of the lower tunnel: After the full-section excavation of the lower tunnel is completed and the initial support deformation is stable, the secondary lining of the lower tunnel is poured to form a permanent load-bearing structure.

[0005] Preferably, the advanced pre-reinforcement structure in step S1 is an advanced pipe shed.

[0006] Preferably, in step S2, the lateral reinforcement component is a grouting conduit, and the grouting conduit is a hot-rolled seamless steel perforated pipe with an outer diameter of 42mm, a wall thickness of 4mm, a length of 4.5m, and is set at intervals of 1.2m along the longitudinal direction of the upper tunnel.

[0007] Preferably, the hardening layer in step S2 is a C30 reinforced concrete layer, and the thickness of the hardening layer is 40cm. Preferably, the segmented excavation mode of the upper tunnel in step S2 is left and right segmented excavation.

[0008] Preferably, the load-bearing component in step S3 is a bored cast-in-place pile with a pile diameter of 800mm, a pile length embedded in the bedrock below the tunnel to a depth of ≥2m, and a pre-reserved steel bar at the top of the pile is anchored to the transition layer in step S3. The bored cast-in-place pile is constructed using a low-headroom rotary drilling rig.

[0009] Preferably, in step S5, the number of pre-defined zones for the unexcavated weak surrounding rock of the lower tunnel is 4, and the tunnel is excavated in stages according to the order of zones I to IV.

[0010] Preferably, the initial support in steps S2 and S5 includes anchor bolts, steel arch frames, and wet-sprayed concrete.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention effectively compensates for the shortcomings of traditional processes in terms of advanced support, interference between upper and lower layers during construction, and control of excavation disturbance by constructing a complete construction process of "advanced pre-reinforcement - layered support - zoned excavation - permanent lining". It ensures the stability of weak surrounding rock throughout the entire construction process and significantly improves the level of construction safety. Among them, the special load-bearing piles and the tunnel middle plate together build a collaborative load-bearing system of "upper layer bearing, middle layer transition, and lower layer protection", forming a stable load transfer path, which can effectively avoid the adverse disturbance of lower layer excavation to the upper structure. At the same time, the block-and-zone excavation method greatly reduces the conflict between processes, and the special equipment adapted to the tunnel space also improves the construction adaptability, thereby achieving the dual optimization of construction period and project cost. Attached Figure Description

[0012] 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.

[0013] Figure 1 This is a schematic diagram of the construction method of the support technology of the present invention; Figure 2 This is a schematic diagram of the specific structure of step S1 of the support process of the present invention; Figure 3 This is a schematic diagram of the specific structure of step S2 of the support process of the present invention; Figure 4 This is a schematic diagram of the specific structure of step S3 of the support process of the present invention; Figure 5 This is a schematic diagram of the specific structure of step S4 of the support process of the present invention; Figure 6 This is a schematic diagram of the specific structure of step S5 of the support process of the present invention.

[0014] The attached diagram lists the components represented by each number as follows: 1. Advanced support structure; 2. Initial support; 3. Temporary support; 4. Lateral reinforcement components; 5. Hardened layer; 6. Unexcavated weak surrounding rock; 7. Load-bearing components; 8. Crown beam; 9. Secondary lining of upper tunnel; 10. Intermediate slab; 11. Secondary lining of lower tunnel. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] like Figure 1-6 As shown: Embodiment 1 of the present invention is as follows: A support technology for excavation of a large-section double-layer tunnel in weak surrounding rock includes the following steps: S1. Advanced pre-reinforcement support: An advanced support structure 1 is constructed outside the tunnel excavation outline to form an advanced protective barrier and reinforce the weak surrounding rock in advance. S2. Excavation and initial support of the upper tunnel: The upper tunnel is excavated in sections. After excavation, initial support 2 and temporary support 3 are immediately installed. At the same time, a hardening layer 5 is laid at the bottom of the upper tunnel, and lateral reinforcement components 4 are installed on the outside of the steel arch frame foot of the upper tunnel to stabilize the upper tunnel structure. S3. Construction of Special Bearing Piles Inside the Tunnel: Special bearing components 7 are constructed on both sides of the upper tunnel inside the tunnel. After the special bearing components 7 are poured, the left and right special bearing components 7 are connected into a whole by a capping beam 8. The capping beam connects the bored piles on both sides into a whole, forming an "anti-lateral displacement frame" structure, which greatly improves the anti-lateral displacement stiffness of the pile body and can effectively resist the lateral pressure generated by the surrounding rock on the pile body during the excavation of the lower tunnel, preventing the pile body from tilting. Moreover, the capping beam is made of high-strength concrete and has strong bending resistance, which can stably bear lateral loads, ensure the overall stability of the special bearing system, and provide support for the safety of the upper structure. S4. Upper Tunnel Secondary Lining and Middle Slab Casting: After the initial support of the upper tunnel has stabilized, the upper tunnel secondary lining 9 is cast, and the tunnel middle slab 10 is cast simultaneously. One end of the middle slab 10 is connected to the secondary lining 9, and the other end is connected to the capping beam 8. The tunnel middle slab adopts a high-strength reinforced concrete structure, which has the dual functions of spatial separation and load transfer. It can clearly divide the upper and lower tunnel spaces, avoid the impact of upper construction debris and sewage on lower operations, and can evenly transfer the upper load to the dedicated load-bearing piles through reasonable connection design. At the same time, the reliable connection between the middle slab and the upper secondary lining and capping beam effectively controls the settlement of the upper structure and ensures the vertical stability of the double-layer tunnel structure. S5. Sectional excavation and initial support of the lower tunnel: The unexcavated weak surrounding rock 6 of the lower tunnel is excavated in sections and steps according to the preset sequence. After the excavation of each section is completed, initial support and temporary support are carried out within the specified time to quickly seal the surrounding rock. S6. Secondary lining pouring of the lower tunnel: After the full-section excavation of the lower tunnel is completed and the initial support deformation is stable, the secondary lining of the lower tunnel 11 is poured to form a permanent load-bearing structure.

[0017] Specifically, the advanced pre-reinforcement structure in step S1 is an advanced pipe shed.

[0018] As can be seen from the above description, compared with traditional advanced small pipes, it has a longer support length and stronger structural rigidity, which can form a rigid protective barrier outside the tunnel excavation outline and reinforce the weak surrounding rock in advance. At the same time, by injecting grout into the surrounding rock through the pipe roof, the bonding strength and self-stabilizing ability of the weak surrounding rock can be further improved, significantly reducing the risk of surrounding rock collapse during excavation and providing a stable construction environment for subsequent tunnel excavation operations.

[0019] Specifically, in step S2, the lateral reinforcement component 4 is a grouting conduit, and the grouting conduit is a hot-rolled seamless steel pipe with an outer diameter of 42mm, a wall thickness of 4mm, a length of 4.5m, and is set at intervals of 1.2m along the longitudinal direction of the upper tunnel.

[0020] As can be seen from the above description, the grouting pipe adopts a hot-rolled seamless steel perforated pipe structure, which has the dual functions of anchoring and grouting. It can specifically reinforce the surrounding rock at the foot of the upper tunnel steel arch, enhance the support stability of the bottom of the steel arch, and avoid the overturning problem of the steel arch due to the instability of the surrounding rock at the foot. Moreover, the pipe is arranged at specific intervals along the longitudinal direction of the upper tunnel, which can form a continuous foot reinforcement zone, which can adapt to the characteristics of uneven deformation of weak surrounding rock and ensure the stability of the temporary support structure of the upper tunnel.

[0021] Specifically, the hardening layer 5 in step S2 is a C30 reinforced concrete layer with a thickness of 40cm.

[0022] As can be seen from the above description, the C30 reinforced concrete hardened layer can serve as a temporary invert arch to bear the concentrated load of various types of machinery during the construction of the upper tunnel, avoiding the sinking problem of construction machinery due to insufficient bearing capacity of the weak surrounding rock, and ensuring the smooth progress of construction. At the same time, the surface of the hardened layer is flat, which can provide a standardized working surface for the subsequent construction of special load-bearing piles in the tunnel, improve the accuracy of pile construction, and reduce construction errors caused by uneven working surfaces.

[0023] Specifically, in step S2, the upper tunnel is excavated in blocks on the left and right.

[0024] As can be seen from the above description, the left and right block excavation mode adopted by the upper tunnel reduces the single excavation area by half, which greatly reduces the disturbance range of the surrounding rock caused by a single excavation and avoids the stress concentration problem of the surrounding rock caused by full-section excavation. In addition, the reasonable interval time set for excavation on both sides ensures that the initial support of the excavation area on one side is fully stressed and stable before the excavation operation on the other side is carried out, which further reduces the risk of secondary disturbance of the surrounding rock and ensures the stability of the surrounding rock during the excavation of the upper tunnel.

[0025] Specifically, in step S3, the load-bearing component 7 is a bored cast-in-place pile with a diameter of 800mm and a length that is embedded in the bedrock below the tunnel to a depth of ≥2m. The pile top is reinforced with steel bars and anchored to the transition layer in step S3. The bored cast-in-place pile is constructed using a low-headroom rotary drilling rig.

[0026] As described above, the system ensures sufficient vertical bearing capacity for the piles. Through reasonable pile diameter design and bedrock embedment depth requirements, the piles can stably withstand various loads transmitted from the upper tunnel, preventing settlement due to insufficient bearing capacity. Furthermore, the design of pre-reserved reinforcing bars at the pile top and anchorage to the middle plate achieves a rigid connection between the pile and the middle plate, improving load transfer efficiency and preventing load concentration issues caused by the separation of the middle plate from the pile. The low-headroom rotary drilling rig used is well-suited to the limited headroom after upper tunnel excavation, eliminating the need for additional tunnel cross-section enlargement for the equipment, reducing tunnel excavation volume, and lowering project costs. Additionally, this type of drilling rig has high hole-forming efficiency, shortening the construction time of bored piles, accelerating the construction progress of load-bearing structures within the tunnel, and further optimizing the overall project schedule. Specifically, in step S5, the number of preset zones for the unexcavated weak surrounding rock 6 of the lower tunnel is 4, and the excavation is carried out step by step in the order of zones I to IV.

[0027] As described above, by dividing the lower full-section into four independent small zones, the area of ​​a single excavation is significantly reduced, avoiding the stress concentration problem in the surrounding rock caused by traditional two-zone or full-section excavation. The disturbance range of the surrounding rock caused by a single excavation is significantly reduced. Furthermore, the excavation sequence of I to IV is designed based on the stress distribution law of weak surrounding rock, which can realize the gradual release and orderly transfer of surrounding rock stress, avoid stress superposition caused by disordered excavation, effectively control the total deformation of the lower surrounding rock, and prevent excessive deformation from affecting the stability of the upper-layer formed intermediate slab, secondary lining, and special load-bearing pile structure. At the same time, the small-zone excavation mode also creates favorable conditions for "timely support after excavation", which can quickly apply initial support to a small area of ​​the excavation face, significantly shorten the exposure time of weak surrounding rock, reduce the weathering and loosening problems caused by long-term exposure of the surrounding rock, and ultimately ensure the safety and structural stability of the lower tunnel excavation without causing adverse disturbance to the upper-layer constructed system.

[0028] Specifically, the initial support in steps S2 and S5 includes anchor bolts, steel arch frames, and wet shotcrete.

[0029] As described above, the initial support system employs a combination of "anchor bolts + steel arch frames + wet shotcrete." These three components work together to form a flexible support structure, which can quickly seal the excavation face of the surrounding rock, preventing weathering and loosening of the weak surrounding rock due to moisture loss. It can also adapt to minor deformations of the weak surrounding rock, preventing cracking due to excessive rigidity. Furthermore, this support system possesses strong load-bearing capacity, effectively constraining the plastic deformation of the surrounding rock and ensuring its short-term stability during tunnel excavation, thus creating conditions for subsequent permanent lining construction.

[0030] The specific construction process of the above embodiments is as follows: 1) Advanced pre-reinforcement support An advanced pipe roof is installed 50cm outside the tunnel excavation outline. The pipe roof uses φ108mm×6mm hot-rolled seamless steel pipes with a length of 15m and a circumferential spacing of 30cm. A horizontal directional drilling rig was used to drill the hole, with a diameter of 120mm. After the pipe roof is installed, cement-water glass dual-liquid grout (cement grout: water glass = 1:0.8, water-cement ratio 1:1) is injected into the surrounding rock through the pipe roof. The grouting pressure is 0.8-1.2MPa, and the grouting volume is controlled at 20L / m. After grouting, the cohesion c of the surrounding rock is increased to 28kPa.

[0031] 2) Excavation and initial support of the upper tunnel Segmented excavation: The excavation is carried out in segments on the left and right. First, the left half section (4.2m wide and 3.5m high) is excavated, with an excavation advance of 0.8m / cycle (consistent with the spacing of the steel arch frame). Initial support: Initial support shall be implemented immediately after excavation. ① Install φ25mm hollow grouting anchor rods (3.5m in length, 1.2m × 1.2m spacing), with a grouting pressure of 0.6MPa; ② Install I25b type steel arch frames (spacing 0.8m), and use φ22mm longitudinal connecting bars (spacing 1.0m) between the steel arch frames; ③ Wet spraying of C25 concrete (25cm thickness), spraying pressure 0.4MPa; Foot reinforcement and bottom hardening: φ42mm×4mm×4.5m hot-rolled seamless steel perforated pipes (longitudinal spacing 1.2m) are installed on the outside of the foot of the steel arch frame, and cement grout (water-cement ratio 1:1, pressure 0.8MPa) is injected; at the same time, a 40cm thick C30 reinforced concrete hardening layer is poured, and the hardening layer is cured for 7 days before proceeding to the next step.

[0032] 3) Construction of special bearing piles inside the tunnel Pile layout: Drilled cast-in-place piles with a diameter of 800mm and a spacing of 2.4m are laid on both sides of the upper tunnel (1.5m away from the tunnel sidewall), for a total of 334 piles (800m tunnel). Hole Formation and Pouring: A low-headroom rotary drilling rig (3.6m in height) was used to form a hole to a depth of 12m (including 3.5m embedded in moderately weathered mudstone); after cleaning the hole, the reinforcing cage was lowered, and a 50cm long φ25mm threaded steel bar was reserved at the top of the pile; C30 concrete (180mm slump) was poured using the tremie method to avoid pile breakage; Construction of the capping beam: After the pile body has been cured for 28 days, the C35 reinforced concrete capping beam is poured. The capping beam and the top of the pile are poured as a whole and cured for 14 days.

[0033] 4) Secondary lining and intermediate slab pouring of the upper tunnel Secondary lining: After monitoring the deformation rate of the upper initial support with the surrounding rock convergence instrument and confirming that it is ≤0.5mm / d, the upper secondary lining is poured: C35 reinforced concrete (40cm thick) is used, with a two-way steel mesh inside. The lining is poured using a hydraulic lining trolley, with a pouring length of 12m / cycle and a curing period of 14 days. Intermediate slab pouring: A C40 reinforced concrete intermediate slab is poured between the secondary lining and the capping beam. The connection between the intermediate slab and the secondary lining and the capping beam adopts a tongue and groove design, and φ18mm shear bars (spaced 30cm) are inserted. Curing time is 21 days.

[0034] 5) Sectional excavation and initial support of the lower tunnel Zoning: The lower tunnel is divided into four zones: I (left 1 / 4 section), II (right 1 / 4 section), III (left remaining 1 / 4 section), and IV (right remaining 1 / 4 section). Zoned excavation: Excavate in the order of I→II→III→IV, with an excavation advance of 0.8m / cycle in each zone and an excavation interval of ≥12h; Initial support: Initial support shall be implemented within 4 hours after excavation of each area (same as step S2), and monitoring shall show that the deformation of the underlying surrounding rock is ≤4mm.

[0035] 6) Secondary lining pouring of the lower tunnel After the lower layer is fully excavated, the initial support deformation rate is monitored to be ≤0.5mm / d. The lower secondary lining is then poured: C35 reinforced concrete (35cm thick) is used, with φ18mm@200mm bidirectional steel mesh laid inside. The lining is poured using a hydraulic lining trolley and cured for 14 days to complete the construction.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that variations may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A large cross-section double-deck tunnel excavation and support process in soft surrounding rock, characterized in that: The method comprises the following steps: S1, advance pre-reinforcement support: an advance support structure (1) is arranged outside the tunnel excavation contour line to form an advance protection barrier and reinforce the soft surrounding rock in advance; S2, upper tunnel excavation and initial support: the upper tunnel is excavated in blocks, and initial support (2) and temporary support (3) are arranged immediately after excavation, a hardening layer (5) is arranged at the bottom of the upper tunnel, and lateral reinforcing members (4) are arranged outside the feet of the steel arches of the upper tunnel to stabilize the structure of the upper tunnel; S3, in-hole special bearing pile construction: special bearing members (7) are arranged on both sides of the in-hole upper tunnel, the left and right special bearing members (7) are connected into a whole through a crown beam (8) after the special bearing members (7) are poured; S4, upper tunnel secondary lining and middle plate pouring: after the initial support of the upper tunnel is stable, the upper tunnel secondary lining (9) is poured, and the tunnel middle plate (10) is poured at the same time, one end of the middle plate (10) is connected with the secondary lining (9), and the other end is connected with the crown beam (8); S5, lower tunnel partition excavation and initial support: the unexcavated soft surrounding rock (6) of the lower tunnel is excavated in partitions and steps according to a preset order, and initial support and temporary support are arranged within a specified time after the excavation of each area is completed, so as to quickly close the surrounding rock; S6, lower tunnel secondary lining pouring: after the lower tunnel is completely excavated and the initial support is deformed and stable, the lower tunnel secondary lining (11) is poured to form a permanent bearing structure.

2. The large cross-section double-layer tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The advance pre-reinforcement structure in step S1 is an advance pipe shed.

3. The large cross-section double-layer tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The lateral reinforcing member (4) in step S2 is a grouting small pipe, and the grouting small pipe is a hot-rolled seamless steel pipe with an outer diameter of 42 mm, a wall thickness of 4 mm, and a length of 4.5 m, and is arranged along the longitudinal direction of the upper tunnel at an interval of 1.2 m.

4. The large cross-section double-deck tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The hardening layer (5) in step S2 is a C30 reinforced concrete layer, and the thickness of the hardening layer is 40 cm.

5. The large cross-section double-deck tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The block excavation mode of the upper tunnel in step S2 is left-right block excavation.

6. The large cross-section double-deck tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The bearing member (7) in step S3 is a bored pile, the pile diameter of the bored pile is 800 mm, the pile length is embedded in the rock below the tunnel to a depth of ≥2 m, the top steel reinforcement of the bored pile is connected with the transition layer anchor in step S3, and the construction of the bored pile is performed by a low-clearance rotary drilling rig.

7. The large cross-section double-deck tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The unexcavated soft surrounding rock (6) of the lower tunnel in step S5 is divided into four regions in sequence, and is excavated in steps.

8. The large cross-section double-deck tunnel excavation and support process in soft surrounding rock according to claim 1, characterized in that: The initial support in steps S2 and S5 both comprises an anchor rod, a steel arch and wet sprayed concrete.

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