Supporting structure for tunnel to pass through soft water-rich stratum and construction method of supporting structure

Abstract

The invention provides a supporting structure for a tunnel to pass through a soft water-rich stratum and a construction method of the supporting structure, belongs to the technical field of tunnel engineering supporting and lining, and solves the problems that in the prior art, the supporting rigidity is insufficient, a waterproof blind area exists, and cooperative stress is poor. According to the forepoling system, the outer-layer and inner-layer horizontal jet grouting piles and the large pipe shed are combined to form a closed reinforcing and waterproof curtain; the composite lining system sequentially comprises a primary support, a waterproof layer and a secondary lining layer from outside to inside. The connection collaborative structure takes a pipe shed end part supporting sleeve arch as a core to realize integrated connection and collaborative stress of an advance support and a lining system; the construction method comprises the steps of double-layer jet grouting pile construction, large pipe shed insertion and grouting, tunnel excavation, composite lining construction and whole-process monitoring. The method is suitable for tunnel construction of various soft water-rich stratums, tunnel construction safety and structural stability are remarkably improved, and remarkable safety benefits, economic benefits and social benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering support and lining technology, and particularly relates to a support structure and construction method that combines double-layer horizontal jet grouting piles, Φ108mm large pipe roof multi-layer advanced support and composite lining when tunnels pass through soft water-rich strata and other complex terrain and geological conditions such as soft water-rich strata and shallow buried biased pressure sections. Background Technology

[0002] In tunnel construction, when traversing soft, water-rich strata (such as water-rich sand layers, silty soil, and completely weathered silty mudstone), engineering challenges are often encountered, including poor self-stabilizing ability of the surrounding rock, susceptibility to water and sand inrush, collapse, and excessive surface settlement, which seriously threaten construction safety and project quality. Among existing advanced support technologies for tunnels traversing soft, water-rich strata, while single horizontal jet grouting piles can form a consolidated curtain, their system stiffness is insufficient in extremely soft strata, resulting in limited deformation resistance. While single Φ108mm large pipe roofs offer greater stiffness, the strata between the pipe roofs are prone to reinforcement blind spots, leading to poor waterproofing and seepage prevention, and thus failing to meet the support requirements for soft, water-rich strata.

[0003] Meanwhile, traditional composite lining for tunnel support often adopts a structure of "initial support + waterproof layer + secondary lining". When the tunnel passes through soft, water-rich strata, the initial support and the pre-support have poor synergistic stress resistance, which can easily lead to problems such as disintegration of the support system, damage to the waterproof layer, and excessive deformation in the later stages. For example, in existing technologies, horizontal jet grouting piles and pipe roofs are mostly arranged in a single layer or in a simple combination, without forming a double-layer synergistic reinforcement system, which cannot effectively resist the lateral pressure and seepage damage of soft, water-rich strata; moreover, the connection reliability between the lining structure and the pre-support is insufficient, resulting in poor load transfer and affecting the stability and long-term safety of the system during the tunnel's passage through soft, water-rich strata.

[0004] Furthermore, existing construction methods for tunnels traversing soft, water-rich strata suffer from inadequate coordination between pre-support and lining construction processes. This leads to problems such as insufficient verification of reinforcement effectiveness and untimely closure of the support ring, reducing construction efficiency and significantly increasing safety risks associated with tunnels traversing soft, water-rich strata. Therefore, there is an urgent need for a support structure and construction method that is adaptable to the conditions of tunnels traversing soft, water-rich strata, achieves coordinated stress distribution between pre-support and lining structures, and provides excellent waterproofing and seepage prevention. This will address the shortcomings of existing technologies and ensure the safety and quality of tunnel construction in soft, water-rich strata. Summary of the Invention

[0005] This invention aims to solve the technical problems of insufficient stiffness of pre-support, blind spots in reinforcement and waterproofing, poor synergistic stress distribution of lining structures, and high risks of deformation and leakage in the later stages when tunnels pass through soft and water-rich strata. It provides a support structure and construction method for tunnels passing through soft and water-rich strata. By optimizing the combination of the pre-support system and the composite lining structure, it achieves integrated and coordinated work of pre-reinforcement and lining structure, significantly improving the stability of the system and the reliability of waterproofing during tunnel passage through soft and water-rich strata, ensuring construction safety, improving construction efficiency, and reducing later maintenance costs.

[0006] The technical solution of this invention is: a support structure for tunnels traversing soft, water-rich strata, comprising an advanced support system, a composite lining system, and a connecting and coordinating structure; the advanced support system is arranged along the outer side of the tunnel excavation outline and adopts a combination structure of double-layer horizontal jet grouting piles and large pipe roofs to form a closed reinforcement and water-stop curtain; the composite lining system includes, from the outside to the inside, an initial support, a waterproof layer, and a secondary lining layer, for coordinating load bearing with the advanced support system; the connecting and coordinating structure is used to realize the coordinated stress bearing of the advanced support system and the composite lining system.

[0007] As a further improvement of the present invention, the double-layer horizontal jet grouting pile includes an outer layer of horizontal jet grouting piles and an inner layer of horizontal jet grouting piles. The outer layer of horizontal jet grouting piles has a pile diameter of 500-800mm, a pile length of 15-30m, a circumferential spacing of 400-600mm, a pile body interlocking of 100-300mm, and an outward insertion angle of 1-3°. The inner layer of horizontal jet grouting piles has the same pile diameter, pile length, and circumferential spacing as the outer layer, a pile body interlocking of 100-300mm, and an outward insertion angle matching the outer layer, forming a continuous closed reinforcement ring.

[0008] As a further improvement of the present invention, the large pipe shed adopts Φ108mm seamless steel pipe with a wall thickness of 6-8mm and a length consistent with the horizontal jet grouting pile. Each large pipe shed is inserted into the gap between the inner layer of horizontal jet grouting pile and the outer layer of horizontal jet grouting pile. Grouting holes are provided on the side wall of the pipe shed, with a spacing of 300-500mm and a hole diameter of 8-10mm.

[0009] As a further improvement of the present invention, the initial support adopts a combination structure of C25 shotcrete + I20b-I25b type steel arch frame and double-layer steel mesh. The shotcrete thickness is 26-31cm, the steel arch frame spacing is 0.6-0.8m, the steel mesh adopts Φ8mm steel bars, the mesh spacing is 200×200mm, and the initial support is closely attached to the end of the inner layer of horizontal jet grouting piles.

[0010] As a further improvement of the present invention, the secondary lining is made of C35 reinforced concrete cast in place with a thickness of 50-60cm. It is equipped with double-layer bidirectional reinforcing bars inside, with circumferential reinforcing bars of Φ22-25mm and a spacing of 200mm, and longitudinal reinforcing bars of Φ16-20mm and a spacing of 250mm.

[0011] As a further improvement of the present invention, the connecting and coordinating structure includes a pipe shed end support arch, an orifice pipe, fixed reinforcing bars, and a reinforcing cage; the pipe shed end support arch adopts a steel-concrete arch structure with a steel arch frame inside, and the inner edge of the arch is closely attached to the outer edge of the secondary lining; the orifice pipe is a Φ127mm seamless steel pipe, which is welded to the steel arch frame by fixed reinforcing bars at a spacing of 40cm; the large pipe shed passes through the orifice pipe and is driven between the two layers of jet grouting piles; the reinforcing cage is made of three Φ22mm threaded steel bars connected by steel rings and inserted into the large pipe shed.

[0012] A construction method for a tunnel support structure traversing soft, water-rich strata, comprising the following steps: Step 1: Construction preparation and geological survey, clarify the core parameters of the soft and water-rich strata, and arrange construction equipment; construct double-layer horizontal jet grouting piles, first construct the outer layer of horizontal jet grouting piles, and then construct the inner layer of horizontal jet grouting piles after an interval of 24 hours. After the construction is completed, inspect the strength and integrity of the pile body. Step 2: Before the grout of the inner layer of horizontal jet grouting piles initially sets, insert a large pipe roof into the gap between the two layers of jet grouting piles. After completion, supplement the grouting through the grouting holes of the pipe roof. Step 3: Excavate the tunnel using the three-step method or CRD method, advancing 0.5-1.0m per cycle to avoid disturbing the soft, water-rich strata; Step 4: Construct the initial support, waterproof layer, and secondary lining layer in sequence to ensure reliable connection of each structure; monitor the arch settlement, perimeter convergence, ground surface settlement, and water leakage throughout the process, and dynamically adjust construction parameters.

[0013] As a further improvement of the present invention, in step one, the horizontal jet grouting pile uses cement-water glass double liquid grout with a jetting pressure ≥35MPa and a grout setting time of 15-30min; the Φ108mm large pipe shed grouting uses cement grout with a grouting pressure of 1.5-2.0MPa.

[0014] As a further improvement of the present invention, in step four, the initial support is constructed within 2 hours after the excavation is completed, and the secondary lining layer lags behind the working face by ≤50m; the monitoring data control standards are: the arch settlement rate ≤3mm / d, the peripheral convergence rate ≤2mm / d, and the surface settlement controlled within ±10mm.

[0015] The beneficial effects of this invention are as follows: 1. Enhanced Advanced Support and Waterproofing Effects: The advanced support system combines double-layer horizontal jet grouting piles with Φ108mm large pipe roofs. The outer layer of jet grouting piles forms a large-area closed reinforcement ring and waterproof barrier, while the inner layer of jet grouting piles and Φ108mm large pipe roofs work together to enhance local rigidity. This completely solves the problems of insufficient rigidity of single support structures, reinforcement blind spots, and poor waterproofing. It can effectively resist the lateral pressure and seepage damage of soft, water-rich strata, prevent water and sand inrush and collapse accidents from the root, and ensure the safety of tunnel construction through soft, water-rich strata. 2. Excellent system synergy and load-bearing performance: By connecting the synergistic structures (pipe roof end support arch, orifice pipe, fixed steel bars, etc.), the advanced support system and the composite lining system are integrated, and a synergistic load-bearing system of "advanced support-initial support-secondary lining" is constructed. This ensures that the load is smoothly transferred from the advanced support to each lining structure, avoids the disconnection of the support system, significantly reduces the later structural deformation after the tunnel passes through soft and water-rich strata, and improves the stability and long-term safety of the tunnel system. 3. High reliability in waterproofing and seepage prevention: The double-layer horizontal jet grouting piles form a continuous closed water-stop curtain, which is supplemented by grouting with Φ108mm large pipe roof to completely block the groundwater seepage channel; at the same time, the waterproof layer is set between the initial support and the secondary lining, which avoids the deformation of the initial support during the tunnel crossing the soft and water-rich strata from damaging the waterproof layer. It achieves dual protection of "advanced water-stopping + drainage system", which greatly reduces the risk of leakage in the later stage and reduces maintenance costs. 4. High adaptability and high construction efficiency: The support structure and construction method of this invention are specifically adapted to tunnels traversing soft and water-rich strata. The construction process follows the principles of "short advance, fast closure, and frequent monitoring". The process is reasonably connected, and the advanced support and lining construction are promoted in tandem. This not only ensures construction safety, but also avoids the problems of cumbersome procedures and slow progress in traditional methods. It is applicable to the construction of tunnels in various soft and water-rich strata such as water-rich sand, silty soil, and completely weathered rock, as well as shallow buried biased pressure sections. It has a wide range of applications and strong practicality. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of the support structure of the present invention; Figure 2 This is a longitudinal cross-sectional schematic diagram of the support structure of the present invention; Figure 3 This is a schematic cross-sectional view of the arch support structure of the present invention; Figure 4 This is a schematic cross-sectional view of the large pipe shed support structure of the present invention; Figure 5 This is a schematic diagram of the cross-section of the large pipe shed supporting structure of the present invention; Figure 6 This is a schematic diagram of the steel cage connection inside the large pipe shed of the support structure of the present invention; Figure 7This is a schematic diagram of the fixed connection of the large pipe shed orifice pipe in the support structure of the present invention; Figure 8 This is a schematic diagram of the initial support structure of the present invention.

[0017] In the diagram: 1-Horizontal jet grouting pile; 1a-Outer layer horizontal jet grouting pile; 1b-Inner layer horizontal jet grouting pile; 2-Large pipe shed; 2a-Grouting hole; 3a-Reinforcing cage reinforcement; 3b-Reinforcing cage steel ring; 4-Arch; 4a-Arch steel frame; 4b-Breakhole pipe; 4c-Fixing reinforcement; 5-Initial support; 5a-Shotcrete; 5b-Steel arch frame; 5c-Double-layer steel mesh; 5d-Anchor pipe; 6-Waterproof layer; 7-Secondary lining layer. Detailed Implementation

[0018] The process method of the present invention will be described in detail through specific embodiments. The purpose of the embodiments is to support and explain the claims. Their content is a concretization of the foregoing technical solutions and should be consistent with the content of the technical solutions, but should not be construed as a limitation of the present invention.

[0019] like Figures 1-8 As shown, a support structure for tunnels traversing soft, water-rich strata is characterized by comprising an advanced support system, a composite lining system, and a connecting and coordinating structure, as detailed below: 1. Advanced support system The advanced support system is arranged along the outer side of the tunnel excavation outline. It is the core pre-protection structure when the tunnel passes through soft and water-rich strata. It adopts a combination of double-layer horizontal jet grouting piles 1 and Φ108mm large pipe sheds 2 to form a closed reinforcement and water-stopping curtain, which effectively restrains the deformation of soft and water-rich strata and blocks groundwater infiltration. The double-layer horizontal jet grouting pile 1 includes an outer layer of horizontal jet grouting piles 1a and an inner layer of horizontal jet grouting piles 1b. The outer layer of horizontal jet grouting piles 1a is arranged along the outer edge of the tunnel excavation outline to form a large-scale primary reinforcement ring and water-stop barrier. The pile diameter is 500-800mm, the pile length is 15-30m, the circumferential spacing is 400-600mm, the pile body interlocking is 100-300mm, and the outward insertion angle is 1-3°. The inner layer of horizontal jet grouting piles 1b is located inside the outer layer of horizontal jet grouting piles 1a and is arranged concentrically with the outer layer of horizontal jet grouting piles 1a. It is used to enhance the reinforcement effect and provide an installation foundation for the Φ108mm large pipe shed 2. The pile diameter, pile length, and circumferential spacing are the same as those of the outer layer of horizontal jet grouting piles 1a. The pile body interlocking is 100-300mm, and the outward insertion angle matches that of the outer layer of horizontal jet grouting piles 1a, ensuring that the double-layer piles form a continuous and closed reinforcement ring without reinforcement blind spots. The Φ108mm large pipe shed 2 uses Φ108mm seamless steel pipe with a wall thickness of 6-8mm and a length consistent with the horizontal jet grouting pile 1. Each Φ108mm large pipe shed 2 is inserted into the gap between the inner layer horizontal jet grouting pile 1b and the outer layer horizontal jet grouting pile 1a to form a "pile-pipe" collaborative force-bearing unit. The end of the large pipe shed 2 is supported by the sleeve arch 4. The side wall of the large pipe shed 2 is provided with grouting holes 2a with a spacing of 300-500mm and a diameter of 8-10mm for subsequent supplementary grouting, which further strengthens the bonding between the large pipe shed 2 and the jet grouting pile body and the surrounding soft and water-rich soil layer. The horizontal jet grouting pile 1 uses cement-water glass dual-liquid grout with a jetting pressure ≥35MPa and a grout setting time controlled within 15-30min to ensure rapid solidification of the pile body into a high-strength consolidated body, meeting the rapid support requirements when the tunnel passes through soft and water-rich strata; the grouting inside the Φ108mm large pipe roof 2 uses cement grout with a grouting pressure of 1.5-2.0MPa to ensure a tight bond between the pipe roof and the jet grouting pile body, forming a system-wide load-bearing structure.

[0020] 2. Composite lining system The composite lining system consists of an initial support 5, a waterproof layer 6, and a secondary lining layer 7, arranged from the outside to the inside. It is closely attached to the tunnel excavation face and works in conjunction with the advanced support system to bear the load and resist the pressure of soft, water-rich strata and groundwater erosion. The initial support 5 is arranged close to the tunnel excavation face and serves as the immediate load-bearing structure when the tunnel passes through soft, water-rich strata. It adopts a combination structure of C25 shotcrete 5a + I20b-I25b type steel arch frame 5b + double-layer steel mesh 5c. The shotcrete 5a is 26-31cm thick, the steel arch frame 5b is spaced 0.6-0.8m apart, and the steel mesh uses Φ8mm steel bars with a mesh spacing of 200×200mm. The initial support 5 is tightly attached to the ends of the inner layer horizontal jet grouting piles 1b to achieve rapid load transfer. Anchor pipes 5d are also installed on the shotcrete 5a, steel arch frame 5b, and double-layer steel mesh 5c.

[0021] Waterproof layer 6 is laid inside the initial support 5. It adopts a composite structure of polymer waterproof board + geotextile. The thickness of the waterproof board is ≥1.5mm, the geotextile specification is ≥20kN / m, the overlap width of waterproof layer 6 is ≥100mm, and it is sealed by hot welding. Waterproof layer 6 is fixed to the initial support by fixing nails to avoid damage to waterproof layer 6 due to deformation of the initial support during the tunnel crossing soft and water-rich strata, thus ensuring the reliability of waterproofing. The secondary lining layer 7 is located inside the waterproof layer 6 and is the core structure for long-term load-bearing and protection after the tunnel passes through soft and water-rich strata. It is made of C35 reinforced concrete and cast in place, with a thickness of 50-60cm. It is equipped with double-layer bidirectional reinforcing bars inside, with circumferential bars of Φ22-25mm and a spacing of 200mm, and longitudinal bars of Φ16-20mm and a spacing of 250mm. The secondary lining layer 7 lags behind the tunnel face by ≤50m to ensure rapid closure into a ring and control the long-term deformation of the soft and water-rich strata.

[0022] 3. Connection and Collaboration Structure The core of the connecting and coordinating structure is the end support arch 4 of the large pipe shed 2. The arch 4 is closely attached to the secondary lining layer 7 to realize a reliable connection between the advanced support system and the composite lining system, ensuring that the two are coordinated in bearing the force, and adapting to the complex stress conditions of the tunnel passing through soft and water-rich strata. The end support arch 4 of the large pipe shed 2 adopts a steel-concrete arch structure. The steel arch frame 5b and the orifice pipe 4b are set in the concrete. The orifice pipe 4b is fixed with fixed steel bars, which are welded to the steel arch frame 5b at a spacing of 40cm. The Φ108mm large pipe shed 2 passes through the orifice pipe and is driven between the two layers of jet grouting piles. The inner edge of the arch 4 is closely attached to the outer edge of the secondary lining layer 7 to ensure that the large pipe shed 2, the arch 4 and the lining structure form an effective synergistic force-bearing system and ensure the stable transmission of pressure in the soft and water-rich stratum. The Φ108mm large pipe shed 2 is equipped with a steel cage. The steel cage is made of three Φ22mm threaded steel cage steel bars 3a connected by steel rings and inserted into the Φ108mm large pipe shed 2 to improve the support rigidity of the pipe shed, ensure effective stress, and avoid structural bending deformation or breakage when the tunnel passes through soft and water-rich strata. This invention also provides a construction method for the above-mentioned tunnel support structure through soft, water-rich strata, ensuring reasonable connection between each process and adapting to the construction requirements of soft, water-rich strata, including the following steps: Step 1: Construction preparation and geological survey A detailed geological survey was conducted on the soft, water-rich strata in the tunnel crossing area to clarify the distribution range, water content, permeability coefficient, compressive strength, and other core parameters of the soft, water-rich strata. Based on the survey results, specific parameters for the double-layer horizontal jet grouting pile 1 and composite lining were designed. The construction site was cleared, and construction equipment suitable for the soft, water-rich strata was deployed, including horizontal rocker drilling rigs, high-pressure grouting pumps, shotcrete machines, formwork trolleys, and automated monitoring equipment.

[0023] Step 2: Construction of Double-Layer Horizontal Jet Grouting Piles Along the outer edge of the tunnel excavation outline, a horizontal rocker drilling rig was used to sequentially construct the outer layer of horizontal jet grouting piles 1a and the inner layer of horizontal jet grouting piles 1b. During construction, drilling accuracy and injection parameters were strictly controlled to avoid disturbing the surrounding soft, water-rich strata. After drilling to the designed depth, cement-water glass grout was injected at a pressure of ≥35MPa, while the drill rod rotated and was pulled out at a low speed to ensure thorough mixing of the grout with the soft soil. After the drill rod was pulled out, a Φ42mm guide pipe was inserted into the center of the jet grouting pile for grouting. After the outer layer of horizontal jet grouting piles 1a was completed, the inner layer of horizontal jet grouting piles 1b was constructed after a 24-hour interval to ensure the initial solidification of the outer pile body and to avoid damage to the pile body due to construction disturbance. After each jet grouting pile was completed, its strength and integrity were promptly inspected. The pile compressive strength was ≥2.5MPa, and the permeability coefficient was ≤1×10⁻⁶. -6 cm / s, meeting the requirements for support and water-stopping when tunnels pass through soft, water-rich strata.

[0024] Step 3: Insertion and grouting of Φ108mm large pipe roof Before the grout of the inner layer horizontal jet grouting pile 1b initially sets, the Φ108mm seamless steel pipe (Φ108mm large pipe shed 2) is statically pushed into the gap between the inner and outer layers of horizontal jet grouting piles with the help of the working arm of the horizontal rocker drilling rig. This avoids violent insertion that could disturb the soft, water-rich strata and the already constructed jet grouting piles, ensuring that the large pipe shed 2 fits tightly with the jet grouting pile body after it is in place. After the large pipe shed 2 is installed, additional grouting is performed through the grouting hole 2a on the side wall of the large pipe shed 2, injecting cement grout. The grouting pressure is controlled at 1.5-2.0MPa. During the grouting process, the grouting volume and pressure are monitored in real time to ensure that the grout is filled evenly. After the grouting is completed, the grouting hole 2a is sealed, so that the large pipe shed 2 and the jet grouting pile body form a system reinforcement structure.

[0025] Step 4: Tunnel Excavation Construction After the pre-support system is completed and reaches the design strength, tunnel excavation is carried out. Considering the poor self-stabilizing ability of soft and water-rich strata, the three-stage method or CRD method is adopted for excavation, following the principle of "short advance, weak disturbance, and fast closure". Each cycle advances 0.5-1.0m. Over-excavation and under-excavation are avoided during the excavation process. After excavation, the loose soil at the working face is removed in time to prevent the soft and water-rich strata from collapsing.

[0026] Step 5: Composite Lining Construction 5.1 Initial support 5 construction: The initial support 5 construction shall be completed within 2 hours after the excavation is completed. First, spray 5cm thick C25 concrete to seal the excavation face to prevent the soft and water-rich strata from being exposed and weathered. Then, install I20b-I25b type steel arch frame 5b to ensure reliable connection. Then, lay double layer steel mesh 5v. Finally, spray the remaining C25 concrete to the design thickness of 26-31cm. During the spraying process, ensure that the concrete is dense. 5.2 Construction of Waterproof Layer 6: After the initial support 5 reaches 70% of the design strength, a composite waterproof layer of polymer waterproof board + geotextile is laid. The waterproof board is hot-welded with an overlap width of ≥100mm. After welding, an air tightness test is performed to ensure no leakage. The waterproof layer 6 is fixed to the initial support 5 with fixing nails to ensure that the waterproof layer 6 is flat and undamaged. 5.3 Construction of secondary lining layer 7: After the waterproof layer 6 is completed, install the formwork trolley for secondary lining layer 7, and pour C35 reinforced concrete in place with a thickness of 50-60cm. The distance between the secondary lining layer 7 and the working face should be ≤50m to ensure rapid closure into a ring. After pouring and curing to the design strength, remove the formwork.

[0027] Step 6: Monitoring and Dynamic Adjustment Throughout the construction process, the settlement of the arch crown, peripheral convergence, surface settlement, and water seepage were monitored in real time, and the monitoring data were transmitted to the control center in real time. For tunnels traversing soft, water-rich strata, the monitoring and control standards were: arch crown settlement rate controlled at ≤3mm / d, peripheral convergence rate controlled at ≤2mm / d, and surface settlement controlled within ±10mm. If abnormal monitoring data was detected, emergency measures such as increased support density, shortened tunnel advance, and supplementary grouting were promptly implemented to ensure construction safety and structural stability during tunnel passage through soft, water-rich strata. Example 1 A railway tunnel traverses a water-rich sandy layer (soft, water-rich strata), with a surrounding rock grade of VI. The tunnel has a cross-sectional span of 12m, a height of 8m, a burial depth of 15m, a stratum water content of 30%, and a permeability coefficient of 5×10⁻⁶. -4 The specific parameters and construction process for the support structure and construction method of this invention, using cm / s, are as follows: 1. Design of support structure parameters Advanced support system: Outer layer horizontal jet grouting pile 1a has a pile diameter of 700mm, a pile length of 20m, a circumferential spacing of 500mm, a pile body interlocking of 250mm, and an outward insertion angle of 1-3°; Inner layer horizontal jet grouting pile 1b has the same pile diameter, pile length, and circumferential spacing as the outer layer (700mm, 20m, and 500mm respectively), a pile body interlocking of 180mm, and an outward insertion angle matching the outer layer of 1-3°; Φ108mm large pipe shed 2 uses Φ108mm seamless steel pipe with a wall thickness of 7mm and a length of 20m (consistent with the horizontal jet grouting piles), inserted into the gap between the inner and outer layer jet grouting piles, and the grouting holes 2a on the side wall of the large pipe shed 2 are spaced 400mm apart and have a hole diameter of 9mm; Composite lining system: Initial support 5 uses C25 shotcrete (28cm thick) + I22b type steel arch frame 5b (0.7m spacing) + double layer Φ8mm steel mesh (200×200mm mesh); Waterproof layer 6 uses 1.5mm thick polymer waterproof board + 20kN / m specification geotextile; Secondary lining layer 7 uses C35 reinforced concrete (55cm thick), with circumferential reinforcement Φ22-25mm, spacing 200mm, and longitudinal reinforcement Φ16mm, spacing 250mm. Connecting and coordinating structure: The end support arch 4 of the large pipe shed 2 is made of C30 concrete and is equipped with an I22b type arch steel frame 4a inside. The orifice pipe 4b is made of Φ127mm seamless steel pipe and is fixed to the steel arch frame 5b by welding Φ16mm fixed steel bars at a spacing of 40cm. The steel cage inside the Φ108mm large pipe shed 2 is made of three Φ22mm threaded steel bars connected by Φ20mm steel rings with a spacing of 200cm between the steel rings.

[0028] 2. Construction process Step 1: Construction preparation, detailed survey of the distribution range and core parameters of water-rich sand layers, and deployment of horizontal rocker drilling rigs, high-pressure grouting pumps, automated monitoring equipment, etc. Step 2: Construct the outer layer of horizontal jet grouting piles 1a, with a jetting pressure of 38MPa and a cement-water glass grout setting time of 20min. After construction, the pile strength is tested and found to be 3.2MPa, with a permeability coefficient of 8×10⁻⁶. -7 cm / s; After a 24-hour interval, apply the inner layer horizontal jet spraying 1b, with parameters matching the outer layer; Step 3: Before the initial setting of the inner layer horizontal jet grouting 1b grout, insert a Φ108mm large pipe roof 2 between the two layers of jet grouting piles. After completion, inject cement grout through the grouting hole 2a at a grouting pressure of 1.8MPa to ensure uniform grout filling. Step 4: Use the CRD method for excavation, advancing 0.5m per cycle. Remove loose soil promptly after excavation to prevent the collapse of the water-rich sand layer. Step 5: Complete the initial support 5 within 1.5 hours after excavation to ensure that all components are firmly connected; after the initial support 5 has stabilized, lay the waterproof layer 6 and test its airtightness; finally, construct the secondary lining layer 7, 18m after the working face. Step 6: Monitor the entire process. The settlement rate of the arch is controlled at 2 mm / d, the convergence rate of the perimeter is 1.5 mm / d, the surface settlement is controlled at +5 mm to -8 mm, and there is no water leakage.

[0029] 3. Implementation Results No water inrush, sand inrush, or collapse occurred during the construction of the tunnel through the water-rich sand layer (soft, water-rich stratum), ensuring effective construction safety. Monitoring data six months after tunnel completion showed that the cumulative settlement of the arch crown was 12mm, the cumulative convergence of the perimeter was 8mm, and there was no water leakage. The structural stability and waterproof reliability both met the design requirements. Compared with traditional support technology, the construction efficiency was increased by 40%, and the subsequent maintenance cost was reduced by 60%, fully verifying the superiority of this invention in tunneling through soft, water-rich strata.

[0030] Example 2 A highway tunnel traverses a section of loose, collapsible loess (soft, water-rich strata). The surrounding rock is classified as Class V. The tunnel has a cross-sectional span of 12m, a height of 8m, a burial depth of 10m, a soil moisture content of 40%, and a permeability coefficient of 2×10⁻⁶. -3 The construction was carried out using the technology of this invention. The parameters of the support structure were adjusted according to the characteristics of the loess strata (the circumferential spacing of the inner layer horizontal jet grouting piles 1b is consistent with that of the outer layer, which is suitable for a range of 400-600mm; the spacing of the steel arch frame 5b is 0.65m, which is suitable for a range of 0.6-0.8m). The construction process was smooth and there were no safety accidents. After completion, the structural deformation and leakage were controlled within the allowable range of the specifications, which further verified the adaptability and reliability of the structure and construction method of this invention to various soft and water-rich strata.

Claims

1. A support structure for tunnels traversing soft, water-rich strata, characterized in that: The structure includes an advanced support system, a composite lining system, and a connecting and coordinating structure. The advanced support system is arranged along the outer side of the tunnel excavation outline and adopts a combination structure of double-layer horizontal jet grouting piles (1) and large pipe sheds (2) to form a closed reinforcement and water-stop curtain. The composite lining system includes an initial support (5), a waterproof layer (6), and a secondary lining layer (7) from the outside to the inside, which are used to cooperate with the advanced support system in bearing load. The connecting and coordinating structure is used to realize the coordinated force bearing of the advanced support system and the composite lining system.

2. The tunnel support structure for traversing soft, water-rich strata according to claim 1, characterized in that: The double-layer horizontal jet grouting pile (1) includes an outer layer horizontal jet grouting pile (1a) and an inner layer horizontal jet grouting pile (1b). The outer layer horizontal jet grouting pile (1a) has a pile diameter of 500-800mm, a pile length of 15-30m, a circumferential spacing of 400-600mm, a pile body interlocking of 100-300mm, and an external insertion angle of 1-3°. The inner layer horizontal jet grouting pile (1b) has the same pile diameter, pile length, and circumferential spacing as the outer layer, a pile body interlocking of 100-300mm, and an external insertion angle matching the outer layer, forming a continuous closed reinforcement ring.

3. The support structure for tunnels traversing soft, water-rich strata according to claim 1, characterized in that: The large pipe shed (2) is made of Φ108mm seamless steel pipe with a wall thickness of 6-8mm and a length consistent with the horizontal jet grouting pile (1). Each large pipe shed (2) is inserted into the gap between the inner layer horizontal jet grouting pile (1b) and the outer layer horizontal jet grouting pile (1a). Grouting holes (2a) are set on the side wall of the large pipe shed (2). The spacing between the grouting holes (2a) is 300-500mm and the hole diameter is 8-10mm.

4. The support structure for tunnels traversing soft, water-rich strata according to claim 1, characterized in that: The initial support (5) adopts a combination structure of C25 shotcrete 5a + I20b-I25b type steel arch frame (5b) plus double-layer steel mesh (5c). The shotcrete (5a) is 26-31cm thick, the steel arch frame (5b) is spaced 0.6-0.8m apart, and the double-layer steel mesh (5c) uses Φ8mm steel bars with a mesh spacing of 200×200mm. The initial support is closely attached to the end of the inner layer horizontal jet grouting pile (1b).

5. The support structure for tunnels traversing soft, water-rich strata according to claim 1, characterized in that: The secondary lining layer (7) is made of C35 reinforced concrete cast in place, with a thickness of 50-60cm. It is equipped with double-layer bidirectional reinforcing bars inside, with circumferential reinforcing bars of Φ22-25mm and a spacing of 200mm, and longitudinal reinforcing bars of Φ16-20mm and a spacing of 250mm.

6. The support structure for tunnels traversing soft, water-rich strata according to claim 1, characterized in that: The connecting and coordinating structure includes a supporting arch (4) at the end of the large pipe shed (2), an orifice pipe (4b), a fixed reinforcing bar (4c), and a reinforcing cage; the arch (4) adopts a steel-concrete arch structure, with an arch steel frame (4a) inside, and the inner edge of the arch (4) is closely attached to the outer edge of the secondary lining layer (7); the orifice pipe (4b) is made of Φ127mm seamless steel pipe, which is welded to the arch steel frame (4a) by the fixed reinforcing bar (4c) at a spacing of 40cm; the large pipe shed (2) passes through the orifice pipe (4b) and is driven between the two layers of jet grouting piles; the reinforcing cage is made of three Φ22mm threaded steel bars connected by a reinforcing cage steel ring (3b) and inserted into the large pipe shed (2).

7. A construction method for a tunnel support structure traversing soft, water-rich strata according to any one of claims 1-6, characterized in that: The construction method includes the following steps: Step 1: Construction preparation and geological survey, clarify the core parameters of the soft and water-rich strata, and arrange construction equipment; construct double-layer horizontal jet grouting piles (1), first construct the outer layer horizontal jet grouting piles (1a), and construct the inner layer horizontal jet grouting piles (1b) after an interval of 24 hours. After the construction is completed, check the strength and integrity of the pile body. Step 2: Before the grout of the inner layer horizontal jet grouting pile (1b) initially sets, insert the large pipe roof (2) into the gap between the two layers of jet grouting piles. After completion, supplement the grouting through the pipe roof grouting hole (2a). Step 3: Excavate the tunnel using the three-step method or CRD method, advancing 0.5-1.0m per cycle to avoid disturbing the soft, water-rich strata; Step 4: Construct the initial support (5), waterproof layer (6), and secondary lining layer (7) in sequence to ensure reliable connection of each structure; monitor the settlement of the arch, the convergence of the perimeter, the settlement of the ground surface and the water leakage throughout the process, and dynamically adjust the construction parameters.

8. The construction method for a tunnel support structure traversing soft, water-rich strata according to claim 7, characterized in that: In step one, the horizontal jet grouting pile (1) uses cement-water glass double liquid grout with a jetting pressure ≥35MPa and a grout setting time of 15-30min; the Φ108mm large pipe shed (2) uses cement grout with a grouting pressure of 1.5-2.0MPa.

9. A construction method for a tunnel support structure traversing soft, water-rich strata according to claim 7, characterized in that: In step four, the initial support (5) is to be constructed within 2 hours after the excavation is completed, and the secondary lining layer (7) is to be ≤50m behind the face. The monitoring data control standards are: the settlement rate of the arch is ≤3mm / d, the peripheral convergence rate is ≤2mm / d, and the surface settlement is controlled within ±10mm.

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