Open cut tunnel main structure suitable for water-rich stratum and construction method thereof

Abstract

The application discloses a kind of open cut tunnel main body structure suitable for water-rich stratum and construction method thereof, relate to tunnel construction technical field, the main body structure includes prefabricated box structure, the side wall outer surface of prefabricated box structure, bottom plate outer surface reserved recess, recess is filled with foam concrete to form drainage passage by reserved grouting pipe;Two side walls of prefabricated box structure reserved operation hole, and water diversion pipe is reserved to drilling pile through wall reserved operation hole and drilling pile and is punched to spin jet water stop pile and drains karst water;Two sides of the passage bottom of prefabricated box structure are provided with support column, prefabricated pressure plate is laid on support column, prefabricated road surface plate, drainage ditch and cable trench are laid on prefabricated pressure plate, form sandwich with bottom plate, bottom plate reserved drainage pipe intercommunication sandwich and install triple pressure relief system, the right side wall bottom of prefabricated box structure is equipped with one-way drain valve.Utilize the present application, can simultaneously solve karst water runoff protection, structure safety under high water pressure, anti-permeation leakproof, construction efficient, operation and maintenance convenient and so on.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a main structure for an open-cut tunnel and its construction method. Background Technology

[0002] Cut-and-cover tunnels have become a common structural form for traversing shallow strata in urban transportation infrastructure and inter-regional road network projects due to their mature construction technology, high construction efficiency, and controllable space utilization. They are widely used in the construction of transportation corridors in limestone distribution areas. Limestone areas have complex hydrogeological conditions, with widespread development of karst fissures and caves, forming interconnected karst aquifers and groundwater runoff channels. These areas have high groundwater levels and large fluctuations in water pressure. Furthermore, the groundwater forms a symbiotic hydrological ecological chain with regional springs and surface water bodies, making them highly sensitive and high-risk strata for engineering construction.

[0003] The existing open-cut tunnel main structure design has significant shortcomings in adaptability to water-rich karst strata. Conventional designs often follow technical solutions for ordinary strata, with the core structure being a single reinforced concrete lining. Waterproofing relies on external waterproof membranes and coatings, and drainage systems consist only of conventional facilities such as internal tunnel ditches and blind drains. The overall design does not fully consider the hydrogeological characteristics of water-rich karst strata, resulting in a series of technical defects and ecological problems in engineering applications, specifically manifested in the following aspects: 1. Karst water flow channels are cut off, and regional hydrological ecology is damaged: The existing tunnel lining structure is an integral closed form, which directly blocks the natural flow channels of groundwater when passing through karst aquifers, resulting in the interruption of karst water replenishment, causing ecological problems such as the interruption of regional springs, the drop in groundwater level, and the withering of surface vegetation. Some projects have even caused shortages of irrigation water for surrounding farmland and domestic water for residents.

[0004] 2. The lining structure has insufficient impermeability and deformation resistance, resulting in prominent water leakage problems: Ordinary reinforced concrete lining has low compressive strength and poor crack resistance, and is prone to structural cracks under long-term high water pressure in water-rich karst strata; External waterproof membranes are easily damaged during construction excavation and structural assembly, and the interface between the membrane and the lining structure is prone to forming water seepage channels. The permeability coefficient is difficult to meet the long-term waterproof requirements of water-rich strata, resulting in a high leakage rate during tunnel operation. This not only affects the use of internal facilities but also accelerates steel corrosion and reduces the service life of the structure.

[0005] 3. Lack of targeted water pressure control mechanism threatens structural stability: The existing structure is not equipped with special pressure relief and control facilities. Water pressure concentration is likely to occur in the water-rich karst strata floor. When the water pressure exceeds the structural bearing limit, it can easily cause the tunnel floor to float, the sidewalls to crack, and the overall structure to shift. In severe cases, it can affect the safety of tunnel operation. Conventional reinforcement measures are difficult to implement, costly and have limited effect.

[0006] 4. Inadequate design of karst water diversion and drainage, leading to high maintenance difficulty: Existing projects often use simple drilling and pipe laying methods for karst water diversion and drainage, without anti-siltation and maintenance design. The mud and rock debris in the karst water can easily cause pipe blockage, resulting in the failure of the diversion and drainage function.

[0007] 5. Precast assembly joints pose a significant risk of leakage: When precast assembly lining is used in some open-cut tunnels, the joints of the box lining are designed with simple flat openings, resulting in poor sealing of the joint surfaces; moreover, the joint waterproofing only uses ordinary waterstop strips, without grouting reinforcement or water-swelling strengthening designs, which become the main weak link for structural water leakage.

[0008] 6. Low construction and operation efficiency and high total cost: The existing structure mostly adopts the cast-in-place construction process. In water-rich strata, the dewatering and support cycle of the foundation pit is long, which has a great impact on the surrounding traffic and residents' lives. Moreover, the structure does not have a special maintenance mezzanine or maintenance port design. During the operation period, the inspection and maintenance of waterproofing, drainage and drainage facilities require the demolition of the structure, which is difficult to construct, has high operation and maintenance costs, and will cause the tunnel operation to be interrupted.

[0009] In summary, existing open-cut tunnel main structures, when applied to water-rich karst strata, cannot simultaneously address core issues such as karst water runoff protection, structural safety under high water pressure, seepage prevention, efficient construction, and convenient operation and maintenance. In engineering practice, there is an urgent need for an open-cut tunnel main structure design scheme that takes into account ecological protection, structural safety, and engineering economy, in order to make up for the deficiencies of existing technologies and meet the engineering construction needs of water-rich karst strata. Summary of the Invention

[0010] The technical problem to be solved by this invention is to provide a main structure and construction method for open-cut tunnels in water-rich strata that can simultaneously solve core problems such as karst water runoff protection, structural safety under high water pressure, seepage prevention and leakage prevention, high construction efficiency, and convenient operation and maintenance, while taking into account ecological protection, structural safety and engineering economy.

[0011] The technical solution adopted by the present invention to solve its technical problem is: a main structure of an open-cut tunnel suitable for water-rich strata, including a tunnel lining structure in the section intersecting with karst water. The tunnel lining structure is a precast box structure. Grooves are reserved on the outer surface of the side wall and the outer surface of the bottom plate of the precast box structure. Foamed concrete is filled in the grooves through reserved grouting pipes to form drainage channels, which can directionally discharge karst water from the upper head of the tunnel to the lower head. The prefabricated box structure has pre-reserved operation holes on both sides of the wall. Karst water is drained through the pre-reserved operation holes in the wall and the pre-reserved water pipes in the drilled pile to the jet grouting water stop pile. The holes are filled with permeable geotextile and prefabricated hole plugs are installed in the pre-reserved operation holes in the wall. The prefabricated box structure has support columns on both sides of the bottom of the channel. Prefabricated pressure plates are laid on the support columns. Prefabricated road panels, drainage ditches and cable trenches are laid on the prefabricated pressure plates, forming a sandwich with the bottom plate of the prefabricated box structure. The bottom plate has a reserved drainage pipe to connect the sandwich and a triple pressure relief system is installed. A one-way drainage valve is provided on the bottom right wall of the prefabricated box structure.

[0012] Furthermore, the precast box structure adopts a double-layer precast box structure with a UHPC outer layer and an ECC tough concrete inner layer.

[0013] Furthermore, the grooves are arranged in a crisscross pattern to form a grid structure.

[0014] Furthermore, the foamed concrete is low-density foamed concrete with a dry density of 500-800 kg / m³ and a compressive strength of 0.8-1.5 MPa. The foamed concrete is pumped and filled through a pre-reserved grouting pipe. After filling, the pipe opening is sealed with micro-expansion mortar, and the pipe body is retained as a channel for later operation, maintenance, grouting, and monitoring.

[0015] Furthermore, the precast pressure plate is provided with an inspection port.

[0016] Furthermore, when the prefabricated box structure has two or more sections, a dovetail groove is provided at the circumferential joint of the prefabricated box structure, and a grouting pipe is pre-embedded in the circumferential joint and water-swellable sealing tape is pasted on it. Finally, epoxy resin mortar is injected into the dovetail groove through the pre-embedded grouting pipe to form a seal.

[0017] Furthermore, end-sealing walls are provided on both sides of the interlayer of the prefabricated box structure to achieve interlayer closure.

[0018] Furthermore, the precast box structure is connected to the cast-in-place sections on both sides, wherein the precast road panels, drainage ditches, and cable trenches are aligned, dovetail grooves are provided at the circumferential joints, and grouting pipes are pre-embedded and water-swellable sealing tape is pasted at the circumferential joints. Finally, epoxy resin mortar is injected into the dovetail grooves through the pre-embedded grouting pipes to form a seal.

[0019] Furthermore, the triple pressure relief system includes a first pressure relief system, a second pressure relief system, and a third pressure relief system. The first pressure relief system employs an electro-hydraulic valve and a pressure sensor linkage system. When the water pressure is >0.3MPa, the electro-hydraulic valve in the bottom plate drain pipe automatically opens to relieve pressure, allowing water below the bottom plate to enter the interlayer and be discharged through the one-way drain valve at the bottom. After pressure relief, the electro-hydraulic valve automatically closes. The second pressure relief system employs a rupture diaphragm. When the water pressure is >0.32MPa, the rupture diaphragm in the bottom plate drain pipe ruptures to relieve pressure, allowing water below the bottom plate to enter the interlayer and be discharged through the one-way drain valve at the bottom. The third pressure relief system employs a mechanical safety valve. When the water pressure is ≥0.35MPa, the mechanical safety valve in the bottom plate drain pipe automatically opens to relieve pressure, allowing water below the bottom plate to enter the interlayer and be discharged through the one-way drain valve at the bottom. After pressure relief, the mechanical safety valve automatically closes.

[0020] The present invention also provides a construction method for the main structure of the open-cut tunnel suitable for water-rich strata, specifically including the following steps: (1) Advanced geological exploration 3D geological scanning: Detection sections are set up for exploration, geological BIM models are generated, and sensitive sections are delineated; Dewatering system layout: Dewatering wells are arranged in a ring around the outer edge of the foundation pit, and automatic monitoring instruments are installed to monitor water level and flow in real time; (2) Construction of retaining structure Drilled pile installation: A stainless steel pipe is pre-embedded in the drilled pile as a water inlet pipe, with a positioning error of ≤10mm. The pipe opening is sealed with a sealing plug or foam plug during the pre-embedding process. Jet grouting water-stop pile construction; (3) Excavation and foundation treatment of the foundation pit Layered excavation: Excavation is carried out in stages according to topsoil, igneous rock layer and limestone layer, and the depth of water runoff is strictly controlled; Foundation reinforcement: Inject micro-expansion cement grout into the karst area and lay a graded crushed stone cushion layer; (4) Installation of the box structure Planar positioning accuracy ≤3mm, elevation positioning accuracy ≤2mm; (5) Installation of triple pressure relief system Foamed concrete is injected into the wall recesses, and a triple pressure relief system is installed by pre-installing drainage pipes in the base slab. (6) Karst water diversion and drainage Karst water is drained through pre-reserved operating holes in the side wall and pre-reserved water pipes in the bored piles, and permeable geotextile is inserted into the holes. Pre-fabricated plugs are installed in the pre-reserved operating holes in the wall to control the water diversion volume to ≤ 30% of the natural runoff. (7) Backfilling and monitoring Layered backfilling; quarterly inspections of water pipe blockage during operation, and real-time comparison of spring water flow.

[0021] Compared with the prior art, the present invention has the following beneficial effects: By setting the tunnel lining structure in the section intersecting with karst water as a precast box structure, the main construction period can be shortened and the impact on surrounding traffic and residents' lives can be reduced. By pre-reserving grooves on the outer surface of the side walls and the outer surface of the bottom plate of the precast box structure, and filling the grooves with foamed concrete through pre-reserved grouting pipes to form drainage channels, the karst water from the upper head of the tunnel can be directionally discharged to the lower head. In particular, the pre-reserved operating holes on both sides of the precast box structure allow karst water to be discharged through the pre-reserved operating holes in the walls and the pre-reserved water pipes in the drilled piles to drill holes in the jet grouting water-stop piles. This can solve the problem that the existing tunnel lining structure directly blocks the natural flow channels of groundwater when passing through karst aquifers, resulting in the interruption of karst water recharge, causing ecological problems such as the interruption of regional springs, the drop in groundwater level, and the withering of surface vegetation. In some projects, it can even cause shortages of irrigation water for surrounding farmland and domestic water for residents. By setting a mezzanine at the bottom of the precast box structure, and reserving a drainage pipe in the bottom slab to connect the mezzanine and install a triple pressure relief system, and by setting a one-way drainage valve on the bottom right wall of the precast box structure, targeted water pressure control can be achieved, effectively avoiding threats to structural stability; at the same time, the design of the mezzanine and the inspection port facilitates the inspection and maintenance of waterproofing, drainage and drainage facilities during operation, which can reduce construction difficulty and operation and maintenance costs. The precast box structure adopts a double-layer precast box structure with an outer layer of UHPC and an inner layer of ECC tough concrete. The circumferential joints of the precast box structure are equipped with dovetail grooves, and grouting pipes are pre-embedded in the circumferential joints and water-swellable sealing tape is pasted. Finally, epoxy resin mortar is injected into the dovetail grooves through the pre-embedded grouting pipes to form a seal. This can solve the problems of insufficient anti-seepage and anti-deformation capacity of existing lining structures, as well as the large potential for leakage at the precast assembly joints.

[0022] In summary, the open-cut tunnel structure of this invention takes into account ecological protection, structural safety, and engineering economy, and is suitable for engineering construction needs in water-rich karst strata. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of the main structure of an existing open-cut tunnel; Figure 2 This is a cross-sectional view of the main structure of an open-cut tunnel suitable for water-rich strata, according to an embodiment of the present invention. Figure 3 for Figure 2 Cross-sectional view of the prefabricated box structure of the embodiment shown; Figure 4 For along Figure 3 Cross-sectional view of line I-I; Figure 5 For along Figure 3 Cross-sectional view of line II-II; Figure 6 Elevation view of the circumferential joint of the precast box structure; Figure 7 For along Figure 6 Cross-sectional view of line III-III; Explanation of the reference numerals in the figure: 1. Precast box structure; 2. Groove; 3. Grouting pipe; 4. Foamed concrete; 5. Operating hole; 6. Drilled pile; 7. Support column; 8. Precast bearing plate; 9. Precast pavement panel; 10. Base plate; 11. Drainage pipe; 12. Drainage hole; 13. One-way drain valve; 14. Cast-in-place section; 15. Circumferential joint; 16. End cap wall; 17. Electro-hydraulic valve; 18. Bursting diaphragm; 19. Mechanical safety valve; 20. Water-swellable sealing tape; 21. Drilling. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see Figures 2 to 7 As shown, this embodiment provides a main structure for an open-cut tunnel suitable for water-rich strata, including a tunnel lining structure for the section intersecting with karst water. The tunnel lining structure is a precast box structure 1. The outer surface of the side wall and the outer surface of the bottom plate of the precast box structure 1 are reserved with grooves 2. The grooves 2 are filled with foamed concrete 4 through reserved grouting pipes 3 to form a drainage channel, which can directionally discharge the karst water from the upper head of the tunnel to the lower head. The prefabricated box structure 1 has pre-reserved operation holes 5 on both sides of the wall. After the lining construction is completed, the karst water is drained through the pre-reserved operation holes 5 and the pre-reserved water pipes of the drilled pile 6 to the jet grouting water stop pile. The holes are filled with permeable geotextile to prevent the grooves 2 from being blocked. Prefabricated hole plugs are installed in the pre-reserved operation holes 5 of the wall. During the operation period, they can be inspected and cleaned regularly. The prefabricated box structure 1 has support columns 7 on both sides of the bottom of the passage. A prefabricated pressure plate 8 is laid on the support columns 7. A prefabricated road panel 9, drainage ditch and cable trench are laid on the prefabricated pressure plate 8, forming a sandwich with the bottom plate 10 of the prefabricated box structure 1. The bottom plate 10 has a reserved drainage pipe 11 to connect the sandwich and install a triple pressure relief system. A one-way drainage valve 13 is provided on the bottom of the right wall of the prefabricated box structure 1.

[0026] In this embodiment, the prefabricated box structure 1 is a left-right dual-channel structure, and a drainage hole 12 is reserved at the bottom of the middle wall of the prefabricated box structure 1. Of course, the prefabricated box structure 1 can also be designed as a single-channel structure.

[0027] In this embodiment, the precast box structure 1 adopts a double-layer precast box structure with an outer layer of UHPC (ultra-high performance concrete) and an inner layer of ECC (elastomer concrete). Outer layer: 30cm thick UHPC (compressive strength ≥150MPa, permeability coefficient ≤10) －12 m / s); Inner layer: 30cm thick fiber-reinforced ECC (ultimate strain ≥3%, crack width self-healing ≤0.1mm).

[0028] In this embodiment, the groove 2 is 30cm wide and 15cm deep, and is arranged in a crisscross pattern to form a grid structure. This ensures sufficient drainage space without compromising the structural strength. The crisscross grid allows the foamed concrete to fit more tightly into the box after filling, forming an overall load-bearing layer and improving structural stability.

[0029] In this embodiment, the foamed concrete 4 is low-density foamed concrete with a dry density of 500-800 kg / m³ and a compressive strength of 0.8-1.5 MPa. It is lightweight, self-leveling, slightly permeable, and has low shrinkage characteristics. Its function is to form a continuous karst water guiding channel in the grooves of the side walls and bottom slab, reducing the structural load, accommodating the deformation of the box, and ensuring a dense, void-free filling. The foamed concrete 4 is pumped and filled through the reserved grouting pipe 3. After filling, the pipe opening is sealed with micro-expansion mortar, and the pipe body is retained as a channel for later maintenance, grouting, and monitoring.

[0030] In this embodiment, the bottom of the prefabricated box structure 1 is provided with two rows of Φ500mm support columns with a spacing of 2m on both sides, and a 2.5m wide and 30cm thick prefabricated pressure plate is laid on it, and an inspection port is provided on the prefabricated pressure plate.

[0031] In this embodiment, the prefabricated box structure 1 is a single section. When the prefabricated box structure 1 has two or more sections, a dovetail groove is provided at the circumferential joint 15 of the prefabricated box structure 1. A grouting pipe (not shown in the figure) is pre-embedded in the circumferential joint 15, and water-swellable sealing tape 20 is pasted on it. Finally, epoxy resin mortar is injected into the dovetail groove through the pre-embedded grouting pipe to form a seal. The dovetail treatment can improve the bonding stability between the epoxy resin mortar and the UHPC box and reduce the risk of water leakage.

[0032] In this embodiment, end-sealing walls 16 are provided on both sides of the interlayer of the prefabricated box structure 1 to achieve interlayer closure.

[0033] In this embodiment, the precast box structure 1 is connected to the cast-in-place sections 14 on both sides. The precast road panel, drainage ditch and cable trench are aligned. The circumferential joint 15 is provided with a dovetail groove. A grouting pipe is pre-embedded in the circumferential joint 15 and a water-swellable sealing tape 20 is pasted on it. Finally, epoxy resin mortar is injected into the dovetail groove through the pre-embedded grouting pipe to form a seal.

[0034] In this embodiment, the triple pressure relief system includes a first pressure relief system (main pressure relief), a second pressure relief system (emergency pressure relief), and a third pressure relief system (forced bottom protection). The first pressure relief system uses an electro-hydraulic valve 17 and a pressure sensor linkage system. When the water pressure is >0.3MPa (adjustable), the electro-hydraulic valve in the bottom plate drain pipe automatically opens to relieve pressure. Water below the bottom plate enters the interlayer and is discharged through the one-way drain valve at the drain head, expanding the drainage surface and reducing the water pressure. After pressure relief, the electro-hydraulic valve automatically closes. The second pressure relief system... The pressure relief system uses a rupture diaphragm 18. When the water pressure is greater than 0.32 MPa, the rupture diaphragm in the bottom plate drain pipe ruptures to release pressure. Water below the bottom plate enters the interlayer and is discharged through the one-way drain valve at the drain head. The rupture diaphragm is detachable and can be quickly replaced during operation and maintenance. The third pressure relief system uses a mechanical safety valve 19. When the water pressure is greater than or equal to 0.35 MPa, the mechanical safety valve in the bottom plate drain pipe automatically opens to release pressure. Water below the bottom plate enters the interlayer and is discharged through the one-way drain valve at the drain head. After the pressure is released, the mechanical safety valve automatically closes.

[0035] The general design rules for triple pressure relief systems are as follows: Step 1: Measure the conventional stable water pressure of the target formation → set it as the pressure relief threshold of the first electro-hydraulic valve; Step 2: Increase by 0.02-0.05 MPa → Set as the emergency threshold for the second rupture diaphragm; Step 3: Rise to the extreme peak water pressure of the formation → set as the third mechanical safety valve bottom threshold.

[0036] This embodiment also provides a construction method for the main structure of the open-cut tunnel suitable for water-rich strata, specifically including the following steps: (1) Advanced geological exploration (preparation before construction) 3D geological scanning: Detection sections are set up every 5m, and detection is carried out using TSP303 (Geological Advanced Prediction System) or 400MHz geological radar system to generate geological BIM model and delineate sensitive sections. Dewatering system layout: Dewatering wells are laid out in a ring 10m around the outer edge of the foundation pit, and automatic monitoring instruments are installed to monitor water level and flow in real time; (2) Construction of retaining structure (key water barrier) Drilled pile installation: A Φ100mm stainless steel pipe is pre-embedded in the drilled pile as a water inlet pipe with a positioning error of ≤10mm. When the water inlet pipe is pre-embedded, the pipe opening is sealed with a sealing plug or foam plug to prevent cement slurry and sand from entering the pipe and solidifying to block it when the drilled pile is poured with concrete. Jet grouting water-stop pile construction: diameter 800mm, interlocking 300mm, water-cement ratio 1:1, admixture ≥25%, verticality deviation ≤1 / 200; (3) Excavation and foundation treatment of the foundation pit (layered water control excavation) Layered excavation: Excavation is carried out in stages according to topsoil, igneous rock layer and limestone layer, and the depth of water runoff is strictly controlled; Foundation reinforcement: Inject micro-expansion cement grout into the karst area and lay a 300mm thick graded crushed stone cushion layer; (4) Installation of the box structure The plane positioning accuracy is ≤3mm, and the elevation positioning accuracy is ≤2mm. When the precast box structure 1 has two or more sections, the circumferential joint 15 of the precast box structure 1 is treated with dovetail, and grouting pipes are pre-embedded in the circumferential joint 15 and water-swellable sealing tape 20 is pasted. Finally, epoxy resin mortar is injected into the dovetail groove through the pre-embedded grouting pipe to form a seal. The prefabricated box structure has end-sealing walls 16 on both sides of the interlayer to achieve interlayer closure; The precast box structure 1 is connected to the cast-in-place sections 14 on both sides. The precast road panels, drainage ditches, and cable trenches are aligned. The circumferential joint 15 is treated with dovetails. A grouting pipe is pre-embedded in the circumferential joint 15 and water-swellable sealing tape 20 is pasted on it. Finally, epoxy resin mortar is injected through the pre-embedded grouting pipe to form a seal. (5) Installation of triple pressure relief system After foamed concrete is injected into the wall recesses, a triple pressure relief system is installed. (6) Karst water diversion and drainage Karst water is drained through pre-reserved operating holes in the side wall and pre-reserved water pipes in the bored piles, and permeable geotextile is inserted into the holes to prevent siltation. Pre-made plugs are installed in the pre-reserved operating holes in the wall to control the water diversion volume to ≤ 30% of the natural runoff. (7) Backfilling and monitoring Layered backfilling with a compaction degree of ≥95%; quarterly inspections of water pipe blockage during operation, and real-time comparison of spring water flow.

[0037] Social impact of this invention: (1) Ecological protection and the sustainability of spring groups Double-layer lining and directional drainage achieve zero interruption of spring water flow, and triple pressure relief maintains the "three-layer hydrogeological" ecological chain, increasing pressure relief efficiency by more than 90% during the high-water season; (2) Coordinated improvement of urban infrastructure and people's livelihood Prefabrication and assembly technology shortens the main construction period by 30-40%, reduces the enclosure time from 18 months to 11 months, and reduces the impact on travel. (3) Economic benefits and efficient use of resources UHPC / ECC materials have a lifespan of ≥100 years, reducing total lifecycle costs by 20-25%; the interlayer inspection port improves drainage and cleaning efficiency by over 70%, and reduces operation and maintenance costs by over 40%.

[0038] Although embodiments of the present invention have been shown and described above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A main structure for an open-cut tunnel suitable for water-rich strata, comprising a tunnel lining structure in the section intersecting with karst water, characterized in that: The tunnel lining structure is a precast box structure. The outer surface of the side wall and the outer surface of the bottom plate of the precast box structure are reserved with grooves. Foamed concrete is filled into the grooves through reserved grouting pipes to form drainage channels, which can directionally discharge karst water from the upper head of the tunnel to the lower head. The prefabricated box structure has pre-reserved operation holes on both sides of the wall. Karst water is drained through the pre-reserved operation holes in the wall and the pre-reserved water pipes in the drilled pile to the jet grouting water stop pile. The holes are filled with permeable geotextile and prefabricated hole plugs are installed in the pre-reserved operation holes in the wall. The prefabricated box structure has support columns on both sides of the bottom of the channel. Prefabricated pressure plates are laid on the support columns. Prefabricated road panels, drainage ditches and cable trenches are laid on the prefabricated pressure plates, forming a sandwich with the bottom plate of the prefabricated box structure. The bottom plate has a reserved drainage pipe to connect the sandwich and a triple pressure relief system is installed. A one-way drainage valve is provided on the bottom right wall of the prefabricated box structure.

2. The main structure of an open-cut tunnel suitable for water-rich strata according to claim 1, characterized in that: The precast box structure adopts a double-layer precast box structure with an outer layer of UHPC and an inner layer of ECC tough concrete.

3. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: The grooves are arranged in a crisscross pattern to form a grid structure.

4. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: The foamed concrete is low-density foamed concrete with a dry density of 500-800 kg / m³ and a compressive strength of 0.8-1.5 MPa. The foamed concrete is pumped and filled through a pre-reserved grouting pipe. After filling, the pipe opening is sealed with micro-expansion mortar, and the pipe body is retained as a channel for later operation, maintenance, grouting and monitoring.

5. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: The precast pressure plate is equipped with an inspection port.

6. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: When the prefabricated box structure has two or more sections, a dovetail groove is provided at the circumferential joint of the prefabricated box structure, and a grouting pipe is pre-embedded in the circumferential joint and water-swellable sealing tape is pasted on it. Finally, epoxy resin mortar is injected into the dovetail groove through the pre-embedded grouting pipe to form a seal.

7. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: The prefabricated box structure has end-sealing walls on both sides of the interlayer to achieve interlayer closure.

8. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: The precast box structure is connected to the cast-in-place sections on both sides. The precast road panels, drainage ditches, and cable trenches are aligned. Dovetail grooves are set in the circumferential joints. Grouting pipes are pre-embedded in the circumferential joints and water-swellable sealing tape is pasted on them. Finally, epoxy resin mortar is injected into the dovetail grooves through the pre-embedded grouting pipes to form a seal.

9. A main structure for an open-cut tunnel suitable for water-rich strata according to claim 1 or 2, characterized in that: The triple pressure relief system includes a first pressure relief system, a second pressure relief system, and a third pressure relief system. The first pressure relief system uses an electro-hydraulic valve and a pressure sensor linkage system. When the water pressure is >0.3MPa, the electro-hydraulic valve in the bottom plate drain pipe automatically opens to relieve pressure, and the water below the bottom plate enters the interlayer and is discharged through the one-way drain valve at the bottom. After pressure relief, the electro-hydraulic valve automatically closes. The second pressure relief system uses a rupture diaphragm. When the water pressure is >0.32MPa, the rupture diaphragm in the bottom plate drain pipe ruptures to relieve pressure, and the water below the bottom plate enters the interlayer and is discharged through the one-way drain valve at the bottom. The third pressure relief system uses a mechanical safety valve. When the water pressure is ≥0.35MPa, the mechanical safety valve in the bottom plate drain pipe automatically opens to relieve pressure, and the water below the bottom plate enters the interlayer and is discharged through the one-way drain valve at the bottom. After pressure relief, the mechanical safety valve automatically closes.

10. A construction method for the main structure of an open-cut tunnel suitable for water-rich strata, as described in claim 1, characterized in that, Specifically, the following steps are included: (1) Advanced geological exploration 3D geological scanning: Detection sections are set up for exploration, geological BIM models are generated, and sensitive sections are delineated; Dewatering system layout: Dewatering wells are arranged in a ring around the outer edge of the foundation pit, and automatic monitoring instruments are installed to monitor water level and flow in real time; (2) Construction of retaining structure Drilled pile installation: A stainless steel pipe is pre-embedded in the drilled pile as a water inlet pipe, with a positioning error of ≤10mm. The pipe opening is sealed with a sealing plug or foam plug during the pre-embedding process. Jet grouting water-stop pile construction; (3) Excavation and foundation treatment of the foundation pit Layered excavation: Excavation is carried out in stages according to topsoil, igneous rock layer and limestone layer, and the depth of water runoff is strictly controlled; Foundation reinforcement: Inject micro-expansion cement grout into the karst area and lay a graded crushed stone cushion layer; (4) Installation of the box structure Planar positioning accuracy ≤3mm, elevation positioning accuracy ≤2mm; (5) Installation of triple pressure relief system Foamed concrete is injected into the wall recesses, and a triple pressure relief system is installed by pre-installing drainage pipes in the base slab. (6) Karst water diversion and drainage Karst water is drained through pre-reserved operating holes in the side wall and pre-reserved water pipes in the bored piles, and permeable geotextile is inserted into the holes. Pre-fabricated plugs are installed in the pre-reserved operating holes in the wall to control the water diversion volume to ≤ 30% of the natural runoff. (7) Backfilling and monitoring Layered backfilling; quarterly inspections of water pipe blockage during operation, and real-time comparison of spring water flow.

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