A cooperative construction method of tunnel crossing through a fault fracture zone surface hole

Abstract

The application relates to a tunnel crossing fault fracture zone surface hole inside cooperative construction method, which can be used for the complex working conditions that the corresponding surface of the tunnel crossing fault fracture zone is a river ditch and the buried depth is relatively shallow, realizes the cooperative construction of the surface hole inside through the process modes of surface sleeve valve pipe grouting reinforcement, surface water interception and drainage and paving counterpressure, hole inside grading pipe shed advanced support, three-step temporary inverted arch method excavation and composite lining and full-ring closed waterproofing, forms the three-dimensional prevention and control of the shallow buried section of the fault fracture zone through the space lapping, stress transmission and process locking of the two sets of measures, and ensures the tunnel safety during the construction period and the operation period. In the construction process, the site construction safety is ensured through the increase of the surface monitoring and dam body stability monitoring, hole inside and outside hydrological monitoring and the like.

Description

Technical Field

[0001] This application relates to the field of tunnel construction technology, and more specifically, to a collaborative construction method for tunnels passing through surface tunnels in fault fracture zones. Background Technology

[0002] When tunnel projects cross fault fracture zones, if the fault zone overlaps with surface ditches and is shallow, construction faces a complex combination of challenges, including surface water infiltration, poor surrounding rock stability, and a high risk of water inrush and mudslide.

[0003] Existing technologies typically employ single in-tunnel pre-support or surface grouting reinforcement measures, but these have the following shortcomings: (1) Surface water seeps into the tunnel along the fracture zone of the fault, and the grouting slurry is difficult to retain effectively under the scouring of water flow, resulting in poor grouting reinforcement effect; (2) The surface backfill only plays a ballast role and does not consider the stress coordination with the in-tunnel support system, resulting in insufficient integrity of the support system; (3) The surface reinforcement and in-tunnel construction procedures lack systematic coordination, and each measure is implemented independently, failing to form a three-dimensional prevention and control system that runs through the entire construction process. Summary of the Invention

[0004] The purpose of this application is to provide a collaborative construction method for tunnels passing through surface tunnels in fault fracture zones. By coordinating surface drainage, paving and counterpressure, sleeve valve grouting, and in-tunnel advanced pipe roof, three-stage temporary invert arch excavation, composite lining, and full-ring waterproofing, the construction and operation safety of shallow buried sections in fault fracture zones can be achieved.

[0005] To achieve the above objectives, this application provides a collaborative construction method for a tunnel passing through a surface tunnel in a fault fracture zone. The surface of the fault fracture zone corresponds to a river ditch and is relatively shallow. The collaborative construction method includes the following steps: S1. Set up a temporary water-blocking cofferdam upstream of the surface river corresponding to the fault fracture zone, and lay drainage pipes to intercept and drain surface water. S2. Sleeve valve grouting is carried out in the corresponding area of ​​the ground surface where the tunnel passes through the fault fracture zone. The reinforcement depth is not less than 2m from the ground surface to the bottom of the tunnel, forming a surface grouting reinforcement ring. S3. Lay a reinforced concrete paving layer above the culvert at the bottom of the ditch, and backfill concrete above the paving layer to the top of the tunnel culvert excavation outline. The concrete thickness shall not be less than 5m above the top of the tunnel to form a surface counter-pressure backfill. At the same time, the initial support and secondary lining inside the tunnel on both sides of the gully shall form a stress-coordinated overall structure. S4. Construct advanced long pipe roofs at the tunnel face, including constructing the first pipe roof in the transition section of the fault fracture zone and the second pipe roof in the core section of the fault, to form a pipe roof reinforcement ring inside the tunnel. S5. After the pre-support is completed, the tunnel is excavated using the three-stage temporary invert arch method, and initial support and radial grouting are carried out. S6. Construct composite lining and a fully enclosed waterproof system; The surface grouting reinforcement ring and the tunnel pipe roof reinforcement ring are radially overlapped in the surrounding rock of the tunnel to form a closed three-dimensional reinforcement ring; the drainage of surface water runs continuously throughout the entire construction process; the tunnel construction is carried out after the surface grouting is completed and passes inspection.

[0006] In a further embodiment, in step S2, the reinforcement ring includes a reinforcement ring at the bottom of the ditch and a reinforcement ring around the tunnel. The reinforcement ring at the bottom of the ditch extends from 20m upstream of the tunnel to 15m downstream of the tunnel. The reinforcement width of the reinforcement ring around the tunnel is 7m outside the structures on both sides of the tunnel, and the reinforcement depth is not less than 2m from the ground surface to below the tunnel bottom.

[0007] In a further embodiment, in step S3, the top surface of the surface backfill adopts an asymmetric slope to ensure that the thickness of the overburden layer directly above the tunnel is not less than 5m, and gradually decreases towards the upstream and downstream. Anti-buoyancy anchors are installed, and the reinforced concrete side walls on both sides of the paving layer, backfill, and gully are continuously configured with steel mesh to form a U-shaped wall structure.

[0008] In a further embodiment, the grouting effect inspection standard in step S2 is as follows: the Pt curve shows an upward trend and the Qt curve shows a downward trend, the back-calculated grout filling coefficient is ≥80%, and the core sampling rate of the inspection hole is ≥80%.

[0009] In a further embodiment, the water-retaining cofferdam described in step S1 is a composite structure consisting of a gravity retaining wall, a foundation, and pile foundations. The retaining wall is embedded in the gully rock mass on both sides, the foundation is buried in the bottom of the gully, and the pile foundations are located at the bottom of the foundation.

[0010] In a further embodiment, in step S4, the first pipe roof adopts a Φ89mm pipe roof with a 10m ring, and the second pipe roof adopts a Φ108mm pipe roof, which is constructed in one go to cross the gully, with an overlap length of ≥3m between the two sections; a pipe roof working room with a 1m widening excavation is set up before the construction of the second pipe roof.

[0011] In a further implementation, in step S5, the excavation advance of the upper step in each cycle is no more than the spacing of one steel frame, the excavation support of the sidewall in each cycle is no more than two frames, the excavation advance of the invert arch in each cycle is no more than 3m, the closing position of the invert arch is no more than 35m from the working face, a temporary invert arch is set at the bottom of the middle and upper steps and sealed with shotcrete, and temporary steel frame cross bracing is added as necessary to increase overall stability based on monitoring and measurement.

[0012] In a further embodiment, after step S5 is completed, radial grouting is performed within the tunnel for 5m, with a grouting pressure of 1-1.5MPa. After completion, grouting is performed at any depth of 100m. 2 The waterproof area has ≤7 water films / wet stains, and each individual water film / wet stain is ≤0.3m in size.2 The single-point leakage rate is ≤2.5L / d, and the composite lining construction in step S6 can only be carried out after the radial grouting is completed.

[0013] In a further implementation, a three-level advanced geological forecasting system is established before construction, and a closed-loop feedback mechanism of forecasting, adjustment, construction, verification, and updating is implemented. The forecasting results are used to dynamically adjust the grouting range and support parameters.

[0014] In a further implementation, the construction sequence control is as follows: drainage is carried out first and throughout the entire construction process, surface grouting is performed and inspected for compliance, paving and backfilling are performed, pipe roof is installed inside the tunnel, three-stage excavation and initial support are performed, radial grouting is performed, composite lining is performed and full-ring waterproofing is completed, and surface construction and tunnel excavation are staggered in the longitudinal space.

[0015] The collaborative construction method for tunnels crossing fault fracture zones within the surface tunnel of this application addresses complex conditions where the surface of the tunnel crossing the fault fracture zone is a ditch and the burial depth is relatively shallow. It achieves collaborative construction within the surface tunnel through a series of procedures including surface interception and drainage with paving and counterpressure, surface sleeve valve grouting reinforcement, graded pipe roof advance support within the tunnel, three-stage temporary invert arch excavation, and composite lining with full-ring waterproofing. By spatially overlapping, transferring stress, and locking the procedures between the two sets of measures, a three-dimensional control system is formed for the shallow buried section of the fault fracture zone, ensuring tunnel safety during both the construction and operation periods.

[0016] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the collaborative construction method in this application; Figure 2 A structural schematic diagram of the water-retaining cofferdam, retaining wall, pile cap, and pile foundation; Figure 3 A structural diagram of the paving layer and backfill; Figure 4 This is a schematic diagram of the grouting area; Figure 5 A schematic diagram of surface grouting; Figure 6 A schematic diagram of the pipe roof caverns and pipe roof layout; Figure 7 This is a cross-sectional view of the VB composite lining. Figure 8 This is a cross-sectional view of the V-type expanded composite lining; Figure 9 This is a cross-sectional view of the VFS composite lining. Figure 10 This is a schematic diagram of the drainage and waterproofing arrangement for the inverted arch. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] In the description of this application, it should be noted that the terms "inner" and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0021] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "setup" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] See Figure 1 The collaborative construction method for tunnels crossing fault fracture zones within surface tunnels in this application is mainly for actual working conditions where the surface of the tunnel crossing the fault fracture zone is a ditch and the burial depth is relatively shallow. Specifically, it includes the following steps: S1. Surface water interception and drainage: A temporary water-blocking cofferdam is set up upstream of the surface ditch corresponding to the fault fracture zone. A drainage pipe is reserved at the bottom of the water-blocking cofferdam and laid down along the gully to the downstream to intercept and drain surface water, providing a dry working surface for surface reinforcement construction. S2. Surface sleeve valve grouting reinforcement: Sleeve valve grouting is carried out in the corresponding area of ​​the surface where the tunnel passes through the fault fracture zone. The segmented retreat grouting process is used for reinforcement. The reinforcement depth is not less than 2m from the surface to the bottom of the tunnel, forming a surface grouting reinforcement ring.

[0023] The reinforcement ring includes a reinforcement ring at the bottom of the ditch and a reinforcement ring around the tunnel. The reinforcement ring at the bottom of the ditch extends from 20m upstream of the tunnel to 15m downstream of the tunnel. The reinforcement width of the reinforcement ring around the tunnel is 7m outside the structures on both sides of the tunnel, and the reinforcement depth is not less than 2m from the ground surface to below the tunnel bottom.

[0024] S3. Surface paving and counter-pressure backfill: After clearing the silt and boulders at the bottom of the gully, anti-buoyancy anchors are installed. A reinforced concrete paving layer is laid above the tunnel culvert at the bottom of the gully as a sealed base. Concrete is then backfilled in layers above the paving layer up to the top of the tunnel culvert excavation outline. The concrete thickness is not less than 5m above the top of the tunnel, forming a surface counter-pressure backfill. At the same time, the initial support and secondary lining inside the tunnel on both sides of the gully, together with the paving layer and backfill, form a cohesive structural system. S4. Advanced pipe roof support in the tunnel: Advanced long pipe roofs are constructed at the tunnel face, including the first pipe roof in the transition section of the fault fracture zone and the second pipe roof in the core section of the fault. The overlap length of the two pipe roofs is not less than 3m, forming a pipe roof reinforcement ring in the tunnel. S5. Three-stage temporary invert arch excavation in the tunnel: After the pre-support is completed, the three-stage temporary invert arch method is used for tunnel excavation. Temporary invert arches are set at the bottom of the middle and upper steps and sealed with shotcrete. The tunnel is excavated step by step and the initial support of steel frame, anchor bolts and steel mesh is constructed. The invert arch is sealed into a ring in time and the distance from the tunnel face is no more than 35m. At the same time, radial grouting is carried out. S6. Construction of composite lining and drainage system inside the tunnel: Different types of composite linings are constructed according to the design sections, and drainage systems at the bottom of the invert arch and blind drainage pipes on the sidewalls are constructed. The tunnel is fully waterproofed in the crossing section, forming a waterproof system with a fully enclosed waterproof membrane and geotextile. The surface sleeve valve grouting reinforcement ring in step S2 and the tunnel pipe roof reinforcement ring in step S4 overlap radially along the tunnel within the influence range of the fault fracture zone, forming a three-dimensional reinforcement ring together; the surface counter-pressure backfill in step S3, the initial support in step S5, and the secondary lining in step S6 together form a stress-coordination system radially along the tunnel; the surface water interception and drainage in step S1 continues to operate during the construction of steps S2 and S3, and the tunnel construction in step S4 is carried out after the surface grouting in step S2 is completed. The surface grouting reinforcement and the tunnel excavation are staggered in space and connected in time.

[0025] See Figure 2 and combined Figure 3 Specifically, in step S1, the temporary water-retaining cofferdam adopts a composite gravity structure, which consists of a gravity retaining wall, a foundation, and pile foundations.

[0026] The gravity retaining wall is made of C35 concrete and is set vertically and horizontally along the gully. The two sides are stepped and embedded into the gully rock mass for no less than 50cm. The retaining wall has a top width of 0.5m, a bottom width of 2.6m, and a height of 3m. The slope of the water-facing side is 1:0.2 and the slope of the water-repellent side is 1:0.5.

[0027] The foundation is located below the retaining wall, made of C35 reinforced concrete, and is 6.77m long, 5.5m wide and 2m high, buried in the bottom of the gully.

[0028] The pile foundation is located at the bottom of the pile cap. It consists of C35 reinforced concrete piles with a diameter of 1.2m and a length of 1.5m. The net spacing between piles in the width direction of the pile cap is 1.3m, and the net spacing between piles in the length direction is 2.18m.

[0029] The drainage pipes consist of four corrugated pipes with a diameter of 1000mm. They are pre-installed at the bottom of the cofferdam and laid along the gentle slope on the right side of the gully to the downstream backfill area. The corrugated pipes are connected by socket joints and equipped with sealing rings. In some suspended sections, they are laid using steel pipe supports with fasteners. The diameter and number of drainage pipes can be calculated based on the actual water volume in the gully.

[0030] The reinforced concrete pavement layer mentioned in step S3 is 50cm thick, using C35 concrete, and two layers of Φ22mm@200×200 HRB400 steel mesh are set inside the pavement layer. The backfill concrete is C35 concrete. The top surface of the surface counter-pressure backfill adopts an asymmetrical slope to ensure that the thickness of the overburden directly above the tunnel is not less than 5m, gradually thinning towards the upstream and downstream. Specifically, the backfill slope is 1:50 in the upstream range of the gully, 1:5 in the range from the tunnel centerline to the excavation outline of the sidewall, and 1:2 in the range from the sidewall structure outline to the downstream range of the gully, forming an asymmetrical backfill cross-section.

[0031] Anti-buoyancy anchors were installed, and the paved layer, backfill, and reinforced concrete sidewalls on both sides of the gully were continuously configured with steel mesh to form a U-shaped wall structure. Specifically, the reinforced concrete sidewalls on both sides of the gully were 3m high and 50cm thick, made of C35 concrete, and had two layers of Φ22mm@200×200 HRB400 steel mesh inside.

[0032] Concrete backfilling is carried out in layers with continuous pouring, each layer being 1-2m high. Construction proceeds from bottom to top, with backfilling extending 5m above the top of the tunnel excavation outline. During the backfilling process, the top slope is checked in real time to ensure there is no reverse slope or water accumulation.

[0033] The stress synergy between the surface counter-pressure backfill and the tunnel support is as follows: the weight of the counter-pressure backfill is transferred to the gully base through the paving layer, forming an active ballast on the top of the shallow-buried tunnel to suppress the loosening of the surrounding rock and surface subsidence; at the same time, the counter-pressure backfill, together with the initial support and secondary lining inside the tunnel, jointly bear the pressure of the surrounding rock along the radial direction of the tunnel, improving the stress state of the tunnel in the fault zone.

[0034] Sleeve valve grouting is performed on the corresponding area of ​​the ground surface where the tunnel passes through the fault fracture zone. In step S2, the reinforcement range of the surface sleeve valve grouting is: the reinforcement width of the gully is 20m upstream and 15m downstream of the gully, and the excavation reinforcement width is 7m outside the structure edge.

[0035] Combination Figures 4-5 Before grouting, a 20cm thick C20 concrete grout stop plate is set on the ground surface within the grouting area, and a Φ8 steel mesh is installed inside the grout stop plate; the spacing between grouting holes is 2m×2m; the segment length of the sleeve valve pipe segmented retreating grouting is 2.0m, the grout is cement grout with a water-cement ratio of 1:1, and the grouting pressure is 0.5~2.0MPa; the final grouting condition for a single hole is that the grouting pressure reaches the design final pressure and grouting continues for more than 10 minutes, and the grouting volume is less than 5L / min.

[0036] The coordination of surface grouting in step S2 and the three-dimensional reinforcement ring of pipe roof in step S4 is as follows: the surface grouting reinforcement extends downward from the surface to 2m below the tunnel bottom, and the pipe roof radiates upward and outward from inside the tunnel. The two overlap radially above the tunnel arch and in the surrounding rock, so that the surface grouting reinforcement ring and the pipe roof reinforcement ring are spatially closed, forming a double-layer constraint on the surrounding rock of the fault fracture zone.

[0037] After grouting in step S2 is completed, the grouting effect is inspected. The inspection criteria are: (1) The PQt curve reaches the design final pressure during the grouting process, the Pt curve shows an upward trend, and the Qt curve shows a downward trend; (2) The grout filling coefficient is calculated back to 80% or more based on the total grouting volume; (3) 5% of the total number of grouting holes are extracted for inspection and re-drilling. The core sampling rate of the inspection holes reaches 80% or more, the grout filling coefficient reaches 80% or more, and the pressure rises rapidly and the grouting volume is very small when grouting the inspection holes. Only after the grouting effect inspection is qualified can the excavation construction inside the tunnel be carried out.

[0038] Combination Figure 6 In step S4, the first pipe roof is located in the transition section of the fault fracture zone. It adopts a long pipe roof with a diameter of 89mm, a wall thickness of 5mm, a circumferential spacing of 40cm, an external insertion angle of 1°~5°, and a pipe roof length of 10m per ring. The setting range is 140° of the arch. The pipe roof adopts hot-rolled seamless steel pipe and steel flower pipe. Grouting holes are drilled on the periphery of the odd-numbered steel pipes, and no holes are drilled on the even-numbered steel pipes.

[0039] The second pipe shed is located in the core section of the fault. It adopts a Φ108mm long pipe shed with a wall thickness of 6mm and a circumferential spacing of 40cm. The angle between the steel pipe axis and the outer edge of the lining is 0°~2°. The setting range is 120° of the arch. The length of each construction is 41m, crossing the valley. Before the construction of the second pipe shed, a pipe shed working chamber is set up. The initial support outline of the working chamber is 1m larger than the normal outline. The working chamber uses an outer ring initial support connected to the inner ring initial support through arch foot connecting steel. The two ends are sealed with 10cm thick C30 mesh sprayed concrete. After the pipe shed is completed and before the waterproofing liner is constructed, C35 molded concrete is used to backfill and expand the excavated space. The overlap length of the two pipe shed sections is not less than 3m.

[0040] In the three-stage temporary invert arch construction described in step S5, the excavation and support advance of the upper stage per cycle shall not exceed the spacing of one steel frame, and the sidewall shall not exceed the spacing of two steel frames per cycle. Before excavation of the invert arch, the steel frame anchor bolts shall be completed, and the excavation advance per cycle shall not exceed 3m. The distance between the closed position of the invert arch and the working face shall not exceed 35m. The bottom of the middle and upper stages shall be sealed with a temporary invert arch made of I18 steel and sprayed with 10cm thick C30 concrete. Specifically, the temporary support includes two types: one where only 10cm thick concrete is sprayed for sealing, and the other where a 10cm thick concrete is first used to seal the bottom before erecting the I18 steel.

[0041] Two Φ50mm anchor pipes, each 5m long, are installed at the arch feet on both sides of each step. The temporary invert arch serves two purposes: firstly, to promptly seal the bottom of the step to prevent the surrounding rock from loosening; and secondly, to act as lateral support for the initial support, thereby improving the overall stability of the structure.

[0042] During construction, temporary steel frame cross bracing may be added as needed to increase overall stability, based on monitoring and measurement data.

[0043] In the initial support, the transition section of the fault fracture zone uses I22a steel frames spaced 0.6m per frame; the pipe roof working chamber uses I22a steel frames with inner and outer rings for full enclosure, spaced 0.6m per frame; and the core section of the fault uses I22b steel frames spaced 0.6m per frame. The steel frames are connected by Φ22 longitudinal connecting bars, with the connecting bars forming a 30° angle with the horizontal direction.

[0044] In step S5, the initial support shotcrete is applied using a wet spraying process with an initial thickness of 4cm. After the initial spraying is completed, steel arches, anchor bolts, and steel mesh are installed, and the shotcrete is then applied to the designed thickness of 28cm. The shotcrete is applied in sections, segments, and layers sequentially, with the spraying sequence from bottom to top. The length of each section is no more than 6m, and the thickness of each shotcrete application on the sidewalls is no more than 15cm, and on the arches no more than 10cm. The working air pressure is 0.3~0.5MPa for the sidewalls and 0.4~0.65MPa for the arches. The distance between the nozzle and the sprayed surface is 0.6~1.8m, and the spraying angle is no less than 70°. The re-spraying is carried out after the previous layer of concrete has set. The next blasting operation can only be carried out 3 hours after the previous layer of concrete has set.

[0045] After excavation in step S5, radial grouting is carried out within the tunnel for 5m. The grouting holes are arranged in a quincunx pattern, with a diameter of 52mm, and 38 holes per ring. The spacing between the hole openings is 120cm towards the circumferential arch wall, 80cm towards the wall foot, and 150cm towards the invert arch. The circumferential spacing between the hole bottoms is 200cm, and the longitudinal spacing between the grouting holes is 200cm. The hole opening pipes are 1m long Φ50×3.5mm hot-rolled seamless steel pipes, firmly embedded and equipped with grout-stopping measures. Ordinary cement grout is used for grouting, with a grouting pressure of 1~1.5MPa. After grouting, any 100m... 2 There should be no more than 7 water films / wet stains on the waterproof area, and the area of ​​each water film / wet stain should not exceed 0.3 m². 2 The single-point leakage rate should not exceed 2.5L / d. The composite lining construction in step S6 can only be carried out after the radial grouting is completed.

[0046] See Figures 7-9 and combined Figure 10 In step S6, the composite lining is constructed in the following sections: The transition section of the fault fracture zone uses a Vb-type composite lining, with an arch wall thickness of 50cm and an invert arch thickness of 60cm, internally equipped with Φ22@200 circumferential main reinforcement, Φ14@250 longitudinal distribution reinforcement, and fully covered with Φ8 hook reinforcement; a V-shaped expanded composite lining is used as the pipe roof working chamber, with an arch wall thickness of 55cm and an invert arch thickness of 65cm, internally equipped with Φ25@200 circumferential main reinforcement, Φ14@250 longitudinal distribution reinforcement, and fully covered with Φ8 hook reinforcement; the fault core section uses a Vfs-type waterproof membrane and geotextile fully wrapped waterproof lining, with the arch wall... The tunnel is 55cm thick, and the invert is 65cm thick. It is equipped with Φ25@200 circumferential main reinforcement, Φ14@250 longitudinal distribution reinforcement, and Φ8 hook reinforcement throughout. The drainage system at the bottom of the invert is equipped with circumferential Φ100DG drainage blind pipes connected to vertical Φ100WG drainage blind pipes and leading to the central ditch. The longitudinal spacing of the circumferential blind pipes is generally 12m in general sections and 6m in sections with developed groundwater. Two Φ100DG drainage blind pipes are longitudinally connected at the bottom of the tunnel. Φ150DG drainage blind pipes are longitudinally installed at the bottom of the waterproof slab on the outer sidewall. Every 3m, a T-junction sidewall outlet pipe is installed to directly lead to the tunnel side ditch.

[0047] Before construction, a three-level advanced geological forecasting system was established: long-range control forecasting adopted advanced horizontal drilling, with one borehole drilled every 30-50m, and an overlap length of 5-8m. An additional borehole was added in abnormal areas; medium-range forecasting adopted ground-penetrating radar, with each detection length not exceeding 20m and an overlap length not less than 5m; short-range verification forecasting adopted geological sketching once per cycle, with three boreholes drilled in each cycle to deepen the blast holes, with a blast hole length of 5-6m and a depth of more than 3m compared to the blasting hole.

[0048] Establish a closed-loop feedback process for forecasting, adjustment, construction, verification, and updating: the forecast results are reviewed and reported, and the grouting range, pipe roof parameters, excavation methods, and other support parameters are dynamically adjusted based on the forecast results; during the excavation process, the actual geological conditions revealed are compared and verified with the forecast results, and the geological information system is updated as the basis for the next cycle of forecasting, so as to realize information-based construction.

[0049] The construction sequence control in this application is as follows: surface water interception and drainage (step S1) is implemented first and continues to operate throughout the construction process from step S2 to step S6; surface sleeve valve pipe grouting reinforcement (step S2) is implemented after step S1 is completed; surface paving and backfilling (step S3) is implemented after step S2 is completed, and step S4 can only proceed after the grouting effect is inspected and approved; tunnel pre-pipe roof support (step S4) is implemented after the grouting inspection in step S3 is approved; tunnel three-stage temporary invert arch excavation (step S5) is implemented after step S4 is completed, and step S6 can only proceed after the invert arch is closed into a ring; tunnel composite lining and drainage system construction (step S6) is implemented after step S5 is completed.

[0050] Surface construction and tunnel excavation are staggered in the longitudinal space to avoid mutual interference. This timing control ensures the coordination of surface and tunnel measures in time and space, enabling orderly connection of each process and controllable quality.

[0051] In existing shallow-buried tunnels, gully backfilling often uses plain concrete or soil and rock, serving only as weight and surface water drainage. Reinforcement is only used for the structural strength of the paving layer itself, and there is no stress connection design between the backfill and the tunnel support system. The backfill, paving layer, and lateral retaining walls are mostly constructed independently, lacking an overall connection.

[0052] In this application, the backfill, the initial support and the secondary lining inside the tunnel form a synergistic force along the radial direction of the tunnel. The weight of the backfill is transferred to the gully base through the paving layer to form active ballast, which inhibits the loosening of the surrounding rock and the surface subsidence. At the same time, the backfill and the tunnel support jointly bear the pressure of the surrounding rock.

[0053] The backfill material transforms from a simple weight carrier into a structural load-bearing component, participating in the rock-support collaborative load-bearing system and improving the mechanical state of tunnels in shallow fault zones. The asymmetric slope causes the backfill material to form the thickest section above the tunnel arch (a steep slope of 1:5 on the tunnel side, specifically the slope to ensure drainage of the arch, combined with the slope to avoid bias pressure), concentrating the weight on the top of the tunnel. At the same time, the gentle slopes upstream and downstream follow the original terrain, reducing the amount of backfilling work.

[0054] In existing fault fracture zone treatment, surface grouting and in-tunnel pipe roofing are usually designed and implemented independently. The design parameters for surface grouting are mainly determined based on the geological conditions and the reinforcement range, while the parameters for in-tunnel pipe roofing are determined based on the surrounding rock conditions and support standards. There are no clear requirements for the overlap between the grouting depth and the pipe roofing length.

[0055] In this application, the surface grouting reinforcement depth is required to be no less than 2m from the surface to the bottom of the tunnel, that is, it extends downward from the surface through the entire tunnel cross section and outwards. The pipe roof inside the tunnel radiates outwards from the tunnel, with an external insertion angle of 1°~3°, forming a reinforcement ring above the tunnel arch and in the surrounding rock. The two overlap radially above the tunnel arch and in the surrounding rock, so that the surface grouting reinforcement ring and the pipe roof reinforcement ring inside the tunnel are spatially closed, forming a three-dimensional reinforcement ring.

[0056] Surface grouting improves the overall mechanical properties of the fault fracture zone on a large scale from the outside and reduces the permeability of the surrounding rock. The pipe roof inside the tunnel provides direct support to the tunnel profile at the front of the excavation, controlling the deformation of the surrounding rock in front of the tunnel face. After the two overlap in space, the weak zone between surface reinforcement and tunnel reinforcement is eliminated, so that the surrounding rock reinforcement forms a continuous and complete closed loop in the radial direction of the tunnel, avoiding the problem of discontinuity in the reinforcement range of a single measure. Surface grouting can only enter the tunnel after the excavation inside the tunnel is completed and inspected and qualified. The water-stopping effect of surface reinforcement provides dry conditions for the construction and excavation of the pipe roof inside the tunnel, and the grouting slurry of the pipe roof is not affected by the erosion of groundwater.

[0057] Temporary cofferdams used in tunnel construction often employ earth-rock cofferdams, sandbag cofferdams, or sheet pile cofferdams. Earth-rock cofferdams have poor erosion resistance and limited water-stopping effect; sandbag cofferdams lack structural stability; and sheet pile cofferdams are difficult to drive into hard rock strata. While concrete gravity retaining walls are structurally stable, they are not economical as temporary works and require high foundation bearing capacity, and shallow foundations are insufficient to resist sliding in steep gully terrain.

[0058] This application adopts a three-stage composite structure of pile foundation, pile cap, and gravity retaining wall as a temporary water-retaining cofferdam. The pile foundation solves the problem of insufficient anti-sliding of shallow foundations on weakly weathered rock layers. The manual construction of the pile foundation overcomes the difficulty of large machinery not being able to operate in steep gullies. The pile cap is buried in the bottom of the gully to evenly transfer the load of the retaining wall to the pile foundation. Multiple corrugated pipes are reserved at the bottom of the retaining wall as temporary drainage channels, realizing the integration of water retention by the cofferdam and drainage by the culvert.

[0059] The pile foundation transfers horizontal and vertical loads to deep, stable rock strata, solving the problem of insufficient anti-sliding stability of shallow foundations for gravity retaining walls in steep gully terrain; the overall erosion resistance of the composite structure is far superior to that of earth-rock cofferdams, and it can withstand floods during the flood season; the pre-embedded corrugated pipes at the bottom of the retaining wall enable the cofferdam to have both water-blocking and drainage functions, eliminating the need for separate pumping stations or temporary drainage ditches.

[0060] Tunnel pre-construction pipe roofs are typically constructed using a single-specification, cyclical method, with each ring ranging from 10 to 30 meters in length, and multiple rings overlapping during construction. The pipe roof diameter is usually selected uniformly according to the design, lacking graded transitions between different sections. When the fault fracture zone is wide, the overlapping points of multiple ring pipe roofs are often weak points in the support, and the limited length of a single ring leads to frequent overlaps, increasing construction procedures and safety risks.

[0061] The transition section of this application uses Φ89mm pipe roofs, with 10m rings, an external insertion angle of 1°~5°, and an arch within a 140° range; the core section of the fault uses Φ108mm pipe roofs, constructed in one 41m phase, with an external insertion angle of 0°~2° and an arch within a 120° range; the overlap length between the two pipe roofs is ≥3m, and the pipe roof working chamber is expanded by 1m to provide space for the Φ108mm pipe roof construction; the 41m core section pipe roof is completed by drilling, segmented pipe connection, and grouting in one phase using a complete set of pipe roof machines.

[0062] Φ89mm pipe roofs are used in the transition section to meet basic advanced support requirements, with controllable cost and construction period; Φ108mm large-diameter pipe roofs are used in the fault core section to provide higher bending stiffness and bearing capacity, adapting to the large deformation requirements of the fault fracture zone; the 41m single-pass construction significantly reduces the number of pipe roof overlaps, eliminating weak links in the support caused by multiple ring overlaps; the 120° setting range of the arch is suitable for the fault core section (surrounding rock is extremely poor, mainly controlling the risk of arch collapse), and the 140° setting range is suitable for the transition section (while also taking into account the stability of the sidewalls). The graded and differentiated design makes the support more precise.

[0063] The three-tiered advanced geological forecasting system combines short-term and long-term spatial forecasts with continuous temporal coverage, improving the accuracy and reliability of forecasts. After review and approval, forecast results are directly used to adjust grouting ranges, pipe roof parameters, and excavation methods, realizing an information-based construction mode that guides construction through forecasts. Excavation verification and information updates continuously optimize forecast parameters, making subsequent forecasts more accurate and creating a virtuous cycle. The dedicated geological organization system ensures the professionalism and continuity of geological work.

[0064] It should be noted that, where there is no conflict, the features in the embodiments of this application can be combined with each other.

[0065] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A collaborative construction method for a tunnel passing through a surface tunnel within a fault fracture zone, wherein the surface of the fault fracture zone corresponds to a river ditch and is relatively shallow, characterized in that... The collaborative construction method includes the following steps: S1. Set up a temporary water-blocking cofferdam upstream of the surface river corresponding to the fault fracture zone, and lay drainage pipes to intercept and drain surface water. S2. Sleeve valve grouting is carried out in the corresponding area of ​​the ground surface where the tunnel passes through the fault fracture zone. The reinforcement depth is not less than 2m from the ground surface to the bottom of the tunnel, forming a surface grouting reinforcement ring. S3. Lay a reinforced concrete paving layer above the culvert at the bottom of the ditch, and backfill concrete above the paving layer to the top of the tunnel culvert excavation outline. The concrete thickness shall not be less than 5m above the top of the tunnel to form a surface counter-pressure backfill. At the same time, the initial support and secondary lining inside the tunnel on both sides of the gully shall form a stress-coordinated overall structure. S4. Construct advanced long pipe roofs at the tunnel face, including constructing the first pipe roof in the transition section of the fault fracture zone and the second pipe roof in the core section of the fault, to form a pipe roof reinforcement ring inside the tunnel. S5. After the pre-support is completed, the tunnel is excavated using the three-stage temporary invert arch method, and initial support and radial grouting are carried out. S6. Construct composite lining and a fully enclosed waterproof system; The surface grouting reinforcement ring and the tunnel pipe roof reinforcement ring are radially overlapped in the surrounding rock of the tunnel to form a closed three-dimensional reinforcement ring; the drainage of surface water runs continuously throughout the entire construction process; the tunnel construction is carried out after the surface grouting is completed and passes inspection.

2. The collaborative construction method according to claim 1, characterized in that, In step S2, the reinforcement ring includes a reinforcement ring at the bottom of the ditch and a reinforcement ring around the tunnel. The reinforcement ring at the bottom of the ditch extends from 20m upstream of the tunnel to 15m downstream of the tunnel. The reinforcement width of the reinforcement ring around the tunnel is 7m outside the structures on both sides of the tunnel, and the reinforcement depth is not less than 2m from the ground surface to below the tunnel bottom.

3. The collaborative construction method according to claim 1, characterized in that, In step S3, the top surface of the surface counter-pressure backfill adopts an asymmetric slope to ensure that the thickness of the overburden layer directly above the tunnel is not less than 5m, and gradually decreases towards the upstream and downstream. Anti-buoyancy anchors are installed, and the reinforced concrete side walls on both sides of the paving layer, backfill, and gully are continuously configured with steel mesh to form a U-shaped wall structure.

4. The collaborative construction method according to claim 1, characterized in that, The grouting effect inspection standard in step S2 is as follows: the Pt curve shows an upward trend and the Qt curve shows a downward trend, the back-calculated grout filling coefficient is ≥80%, and the core sampling rate of the inspection hole is ≥80%.

5. The collaborative construction method according to claim 1, characterized in that, The water-retaining cofferdam described in step S1 is a composite structure consisting of a gravity retaining wall, a foundation, and pile foundations. The retaining wall is embedded in the gully rock mass on both sides, the foundation is buried in the bottom of the gully, and the pile foundations are located at the bottom of the foundation.

6. The collaborative construction method according to claim 1, characterized in that, In step S4, the first pipe roof uses Φ89mm pipe roof with a 10m ring, and the second pipe roof uses Φ108mm pipe roof, which is constructed in one go across the valley, with an overlap length of ≥3m between the two sections; before the construction of the second pipe roof, a pipe roof working chamber with an enlarged excavation of 1m is set up.

7. The collaborative construction method according to claim 1, characterized in that, In step S5, the excavation advance of the upper step in each cycle shall not exceed the spacing of one steel frame, the excavation support of the sidewall shall not exceed two frames in each cycle, the excavation advance of the invert arch shall not exceed 3m in each cycle, and the closing position of the invert arch shall not exceed 35m from the working face. A temporary invert arch shall be set at the bottom of the middle and upper steps and sealed with shotcrete. According to the monitoring and measurement, temporary steel frame cross bracing shall be added as necessary to increase the overall stability.

8. The collaborative construction method according to claim 1, characterized in that, After step S5 is completed, radial grouting is performed within the tunnel for 5m, with a grouting pressure of 1-1.5MPa. After completion, grouting is performed at any depth of 100m. 2 The waterproof area has ≤7 water films / wet stains, and each individual water film / wet stain is ≤0.3m in size. 2 The single-point leakage rate is ≤2.5L / d, and the composite lining construction in step S6 can only be carried out after the radial grouting is completed.

9. The collaborative construction method according to claim 1, characterized in that, Before construction, a three-level advanced geological forecasting system is established and a closed-loop feedback mechanism of forecasting, adjustment, construction, verification, and updating is implemented. The forecast results are used to dynamically adjust the grouting range and support parameters.

10. The collaborative construction method according to claim 1, characterized in that, The construction sequence control is as follows: drainage is carried out first and throughout the entire construction process, surface grouting is performed and inspected and qualified, paving and backfilling are carried out, pipe roof is built inside the tunnel, three-stage excavation and initial support are carried out, radial grouting is carried out, composite lining is carried out and full-ring waterproofing is carried out. Surface construction and tunnel excavation are carried out separately in the longitudinal space.

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