A permanent wet-sprayed concrete support structure for hard rock highway tunnels

Abstract

This invention discloses a permanent wet-sprayed concrete support structure for hard rock highway tunnels, comprising a system of anchor bolts, a high-toughness rapid support layer, a cross-type close-fitting drainage layer, a body-toughened waterproof layer, and a surface finishing layer. The system anchor bolts are radially arranged across the entire cross-section. The high-toughness rapid support layer is tightly attached to the surrounding rock, and the cross-type close-fitting drainage layer connects to the high-toughness rapid support layer, forming a multi-channel, full-section longitudinal and transverse drainage system. The body-toughened waterproof layer covers the cross-type close-fitting drainage layer, forming the main structural component and providing multiple functions including load-bearing, toughening, and waterproofing. The surface finishing layer, on the surface of the body-toughened waterproof layer, seals coarse fibers and improves smoothness, serving as a surface sealing and finishing layer. This wet-sprayed concrete permanent support structure eliminates the need for steel mesh, waterproofing membrane, and secondary lining, adapts to irregular cross-sections, and features a thin, tough, and durable high-toughness rapid support layer, enabling rapid, efficient, and safe construction.

Description

Technical Field

[0001] This invention relates to a wet-sprayed concrete permanent support structure for hard rock highway tunnels, belonging to the field of highway tunnel support technology. Background Technology

[0002] Transportation is a fundamental, leading, and strategic industry in the national economy. The 14th Five-Year Plan for Transportation Development emphasizes the high-quality development of highway transportation to achieve the goal of building a strong transportation nation. In recent years, to promote the interconnection of national highways and optimize navigation capacity, the southwest region has gradually strengthened highway planning and construction. With its mountainous terrain and hilly landscape, the high proportion of tunnels has made them one of the key control projects and major structures.

[0003] Currently, tunnel support structure design is still dominated by the New Austrian Tunneling Method (NATM), employing composite lining consisting of initial support shotcrete, waterproofing membrane, and secondary lining. However, the rock mass quality distribution in Southwest China varies greatly, with many tunnels surrounded by Class IV, III, or even II rock, exhibiting high self-stability and relatively scarce groundwater, with only dampness or dripping water. Under these geological conditions, using composite lining is overly conservative, with secondary lining primarily serving waterproofing, finishing, and safety reserve functions, or even being dispensable. This not only wastes resources but also prolongs construction time. Domestically and internationally, there is a widespread search for alternative methods, leading to the concepts of "single-layer lining" or "permanent support." The Norwegian method is now a recognized guiding approach, recommending the use of shotcrete lining directly as permanent support, replacing composite lining, which offers significant economic, social, and time-saving benefits.

[0004] According to statistics from the International Tunneling and Underground Space Association (ITA), the design concept of wet-sprayed concrete permanent support has been widely accepted as a relatively economical structural type. However, its application is still limited, mostly used in non-main tunnel sections such as inclined shafts and pilot tunnels, or in tunnel sections with small spans such as mines, roadways, railways, and subways, or in non-passage structures such as hydraulic tunnels. Especially since the individual collapse accidents in 1994, the application of this technology has become increasingly cautious, and the review of plans has become increasingly strict, with many problems still not being well resolved.

[0005] If anchor-sprayed lining is to be transformed from temporary support (initial support) to permanent support, simply removing the waterproof membrane and secondary lining is not advisable, and the structural form must be changed. Compared with the composite lining commonly used in highway tunnels, wet-sprayed concrete permanent support has four problems that need to be solved: (1) The strength of anchor-sprayed lining concrete is lower than that of secondary lining concrete, and the bearing capacity is low; (2) The anchor-sprayed lining has a low reinforcement ratio and poor bearing toughness. When displacement (deflection) occurs, the concrete is easy to fall off in chunks, which is not conducive to the safety of pedestrians and vehicles; (3) The anchor-sprayed lining has poor compactness, low waterproof performance, and no drainage system; (4) In areas with high ground stress, broken rock mass, and high risk of collapse, the timeliness and safety of the existing anchor-sprayed lining support are not enough.

[0006] Chinese Patent Publication No. CN110359915A discloses a waterproof single-layer lining structure and its manufacturing method suitable for double-track tracks in Class IV surrounding rock. The Class IV surrounding rock surface is sequentially subjected to washing, spraying a first layer of coarse fiber concrete and curing, spraying mortar and curing, spraying waterproofing and curing, and then spraying a second layer of fine fiber concrete and curing. This invention comprehensively improves the structure's waterproofing and drainage capabilities by spraying a waterproof membrane between the two layers of sprayed concrete and installing Ω-shaped spring drainage half-pipes closely attached to the surrounding rock. However, there are still several shortcomings: ① The two-layer fiber-reinforced shotcrete only requires fiber strength and does not mention other indicators such as impermeability, crack resistance, and strength, thus ignoring the self-waterproofing value of wet-sprayed concrete lining as the main structural component; ② In the construction method, before spraying the first layer of coarse fiber concrete, it goes through many processes such as grouting reinforcement, laying Ω-shaped spring drainage half-pipes, installing anti-corrosion hollow grouting anchors, high-pressure water cleaning, and installing the grid steel frame. The support work lacks timeliness, and the surrounding rock is not sealed as early as possible and its stability is not restored in time, resulting in a high risk of collapse and a great safety threat; ③ Spraying coarse fiber concrete on the inside of the grid steel frame can easily create voids in the shaded area on the outside of the steel frame, increasing the area of ​​loose material, which is detrimental to the waterproofing of the structure itself.

[0007] Chinese patent CN112554887A discloses a construction method and structure for a waterproof single-layer lining. The construction method and lining structure of this invention are quite similar to those in CN110359915A, also employing small-pipe grouting for water blocking, Ω-shaped spring drainage for half-pipe drainage, and spraying a waterproof membrane for waterproofing, forming an integrated waterproof system of blocking-prevention-drainage. The problems are similar: ① High-strength fiber reinforced concrete covering the steel mesh does not mention any technical indicators such as impermeability, crack prevention, or strength, ignoring the technical value of self-waterproofing in wet-sprayed concrete lining structures; ② In the construction method, before spraying the first layer of coarse fiber concrete, there are many procedures including grouting reinforcement, laying Ω-shaped spring drainage half-pipes, laying hollow anchors, and installing grid mesh. If the support is not timely, there is a risk of collapse or even rock burst; ③ The outer side of the grid mesh is directly and tightly attached to the surrounding rock, while the inner side is covered with sprayed high-strength fiber reinforced concrete. The uneven surface of the surrounding rock, coupled with the obstruction of the steel mesh reinforcement, easily creates voids and loose areas on the outer side of the mesh, which is detrimental to the waterproofing of the structure itself.

[0008] Chinese patent CN215486082U discloses a waterproof structure for tunnels with single-layer lining. This utility model includes a waterproof partition wall, an Ω-shaped water guide pipe, a drainage pipe, an installation groove, a waterstop strip, a sealing gasket, a concrete pad, a first waterproof layer, a second waterproof layer, a third waterproof layer, and a concrete reinforcement layer. It can divert and drain seepage water from the surrounding rock surface. A waterproof membrane is sprayed between the concrete layers, acting as a "middle-barrier" against water, similar in function to waterproof membranes. However, it fails to specify requirements for waterproof materials and concrete quality, does not recognize the functional design points of the load-bearing layer and waterproof layer, simply lists the waterproof layers, lacks understanding of the concept of timely support, and has insufficient safety considerations, posing significant safety hazards to drainage operations.

[0009] Chinese patent CN107352893A discloses a PVA-ECC single-layer lining. This invention includes a PVA-ECC sprayed layer, a PVA-ECC lining, and a steel frame. Combined with the ultra-high toughness of ECC material, it can adapt to high ground stress and large deformation of surrounding rock, which is beneficial to the safety of the support structure. However, the PVA fiber content is 3–20 kg / m². 3 Without appropriate technical measures, it is difficult to ensure smooth spraying. PVA fiber is expensive, and using it for the entire lining would be too costly and impractical. The lining structure lacks waterproofing and drainage design, and the simultaneous use of fiber-reinforced concrete and steel frame can easily leave loose areas, making it difficult to meet the durability requirements of permanent support.

[0010] Chinese patent CN109458196A discloses an environmentally friendly and durable single-layer lining structure suitable for tunnels in weak surrounding rock. The inner wall of the excavated tunnel in weak surrounding rock is sequentially lined with basalt fiber shotcrete, a single-layer lining composed of basalt corrugated plates, several anchor bolts driven into the rock layer from the outside, a steel mesh, and an outer layer of concrete mixed with basalt fiber sprayed onto the steel mesh. The basalt fiber concrete adheres closely to the surrounding rock, ensuring timely and effective structural support; the basalt corrugated plates are equipped with drainage pipes, ensuring drainage capacity. However, this invention has several problems. The basalt corrugated plates are laid across the entire cross-section, resulting in high rigidity. The outer layer of non-woven fabric results in a large proportion of lining thickness. There is no adhesion between the non-woven fabric and the corrugated plates, or between the corrugated plates and the initial shotcrete, easily forming a "layer" within the single-layer lining, thus reverting to the stress characteristics of composite linings. Furthermore, the shear force between the inner and outer layers of basalt fiber shotcrete cannot be effectively transferred.

[0011] Chinese patent CN110284901A discloses a waterproof single-layer lining structure and its construction process. The lining structure includes, sequentially arranged from the arched structure near the tunnel body towards the ground surface, a base concrete layer, a supporting concrete layer, a waterproof isolation layer, a reinforcing concrete layer, a waterproof concrete layer, and a waterproof coating layer. This invention eliminates the need for a waterproofing membrane and uses a waterproof coating, solving the problem of ineffective shear stress transfer in conventional composite linings, thus conforming to the basic concept of single-layer lining. The waterproof isolation layer, waterproof concrete layer, and waterproof coating layer aim to improve the structure's waterproofing capability. However, all layers use cast-in-place concrete, without the use of shotcrete, making timely support difficult to guarantee and resulting in structural insecurity. The formwork assembly and disassembly process is complex, and it has poor adaptability to irregular cross-sections, lacking flexibility.

[0012] Chinese patent CN109626914A discloses a material and preparation method for a waterproof single-layer lining for hard rock tunnels. The single-layer lining material is composed of the following raw materials in parts by weight: 980-1020 parts cement, 1804-1916 parts medium sand, 1203-1277 parts crushed stone, 16.8-17.2 parts polycarboxylate superplasticizer, 9.9-10.1 parts silica fume, 11.9-12.1 parts polyolefin fiber, 396-404 parts water, and 79.2-80.8 parts alkali-free quick-setting agent. The product has a 56-day electrical flux of 1450C and a low density. While the use of coarse polyolefin fiber provides toughening and crack resistance, it lacks sufficient resistance to drying shrinkage and autogenous volume shrinkage, resulting in a high risk of cracking and making it difficult to guarantee the "permanence" of the lining.

[0013] Chinese patent CN114776338A discloses a single-layer lining structure and its construction method for tunnels in Class IV surrounding rock. It includes a steel fiber shotcrete layer formed on the surface of the tunnel chamber in the surrounding rock and multiple anchor bolts inserted radially along the tunnel chamber. The steel fiber shotcrete layer comprises a first steel fiber shotcrete layer and a second steel fiber shotcrete layer. This eliminates the need for a steel frame and reinforcing mesh for initial support, optimizing the construction process. The steel fiber concrete achieves an 8-hour strength of no less than 10 MPa and a 24-hour strength of no less than 15 MPa, ensuring timely early support and significantly improving safety. While this invention eliminates the reinforcing mesh, improving the overall density, it lacks a systematic drainage and crack-resistant design. It is suitable for early-stage stabilization of surrounding rock, but its long-term service durability is questionable.

[0014] Chinese patent publication number CN 207960676 U discloses a drainage system for a single-layer shotcrete lining. It includes drainage branch pipes, arc-shaped drainage pipes, longitudinal drainage pipes, and transverse drainage pipes. Two longitudinal drainage pipes are arranged side-by-side, with a transverse drainage pipe located inside each longitudinal drainage pipe. An arc-shaped drainage pipe is positioned above the longitudinal drainage pipes, and a drainage branch pipe is located on one side of each arc-shaped drainage pipe. The drainage branch pipe is fixed to the inside of the tunnel using fiber adhesive tape, with nails on both sides of the tape. Both the drainage branch pipe and the arc-shaped drainage pipe have suction holes on their inner tunnel-facing sides. While the drainage system design is relatively complete, the pipes are made of PVC or HDPE corrugated pipe, which are brittle materials. During shotcrete construction, the high-speed, high-pressure impact of the concrete jet causes the pipes to undergo almost no elastic deformation, making them prone to impact damage and failure. Furthermore, the pipe surface is very smooth, making it difficult for the shotcrete to adhere, resulting in poor operability.

[0015] Chinese Patent Publication No. CN 109723475 A discloses a construction process and application of a single-layer waterproof lining spraying method for hard rock tunnels. The process includes: Step 1. Base surface pretreatment; cleaning the base surface; Step 2. Equipment preparation; Step 3. Slurry preparation: mixing the main materials of the spraying material and water on-site to prepare the slurry; Step 4. Spraying the first layer of waterproof coating, using an orange waterproof coating; Step 5. Curing the first layer of waterproof coating; Step 6. Spraying the second layer of waterproof coating, using a gray waterproof coating; Step 7. Curing the second layer of waterproof coating; Step 8. Spraying concrete. This invention designs multiple spray layers and specifically designs waterproof materials, but does not change the drainage and the main concrete structure of the support structure.

[0016] Chinese patents CN 110030016 A and CN 210509196 U disclose a single-layer lining structure for a large-section subway parking line excavated in hard rock strata. The structure includes: a permanent tunnel support structure consisting of shotcrete and anchor lining for the arch and sidewalls; a waterproof concrete base slab at the tunnel bottom; arch foot longitudinal beams at the junction of the arch and sidewalls; multiple longitudinal drainage blind pipes, multiple transverse drainage blind pipes, and a longitudinal drainage ditch below the waterproof concrete base slab; an arc-shaped ventilation duct slab fixedly connected at both ends to the arch foot longitudinal beams, with a block partition wall at the top and a middle partition wall at the bottom; longitudinal drainage ditches fixedly installed on the inner side of the junction between the sidewalls and the waterproof concrete base slab; and pre-embedded drainage pipes embedded in the arch foot longitudinal beams, which are then connected to the longitudinal drainage ditches within the sidewalls. This invention involves spraying two layers of concrete: a 150mm thick first layer and a 100mm thick second layer, with a waterproof membrane between the two layers. Four 100mm diameter longitudinal drainage pipes are installed along the tunnel's longitudinal direction, and a 75mm diameter transverse drainage pipe is installed every 10m. This improves the drainage and waterproofing capabilities of wet-sprayed concrete permanent support. However, the invention lacks specific requirements for the 25cm thick sprayed concrete's impermeability, crack resistance, and strength, neglecting the importance of waterproofing the concrete itself and compromising structural safety. The conventional "plain concrete + steel mesh" type is unsuitable for permanent support due to insufficient reinforcement; in the event of displacement, the concrete is prone to detachment in chunks. Furthermore, the material of the drainage pipes lacks specific requirements; if conventional PVC is used, its smooth surface makes it difficult for concrete to adhere, resulting in insufficient flexibility and susceptibility to high-speed concrete jet impact damage. Summary of the Invention

[0017] To address the aforementioned problems, this invention proposes a permanent wet-shot concrete support structure for hard rock highway tunnels, replacing composite lining. It eliminates the need for steel mesh, waterproofing membrane, and secondary lining, offering a simple construction process, adaptability to various complex cross-sections, and high flexibility. Compared to existing wet-shot concrete permanent support or single-layer lining structures, this invention introduces a thin-layer rapid support concept and a structural waterproofing concept, and features specially designed strip-shaped drainage strips suitable for wet-shot concrete construction and adhesion. This improves structural and operational safety while enhancing overall drainage capabilities.

[0018] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0019] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels, comprising a system of anchor bolts, a high-toughness rapid support layer, a cross-type close-fitting drainage layer, a body-toughened waterproof layer, and a surface finishing layer. The system of anchor bolts is radially distributed and is always perpendicular to the surrounding rock base. The high-toughness rapid support layer is in close contact with the surrounding rock. The cross-type close-fitting drainage layer is connected to the high-toughness rapid support layer. The body-toughened waterproof layer covers the cross-type close-fitting drainage layer. The surface finishing layer is on the surface of the body-toughened waterproof layer. Most of the system of anchor bolts penetrates into the surrounding rock, with the portion exposed on the surrounding rock base being 5cm to 10cm less than the thickness of the entire permanent support structure.

[0020] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels, which is suitable for hard rock tunnels with surrounding rock of Class III (III1, III2) and Class IV (IV1, IV2) and groundwater conditions with dampness or dripping water.

[0021] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels. The system anchors are mortar anchors with a full-section design and radial distribution. The system anchors are always perpendicular to the surrounding rock base. The system anchors are made of ribbed steel bars with a diameter of 22mm and a length of 3m to 5m. They are arranged in both directions with a spacing of 1.0m to 1.5m. Most of the length of the anchor penetrates into the surrounding rock, and the part exposed on the surrounding rock base is 5cm to 10cm less than the thickness of the entire permanent support structure. That is, the support structure covering the end of the anchor away from the surrounding rock base is 5cm to 10cm thick.

[0022] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels, wherein the high-toughness rapid support layer has a thickness of 2cm to 3cm.

[0023] The material composition of the high-toughness rapid support layer is as follows: 57-70 parts cement, 5-8 parts silica fume, 25-35 parts microspheres, 30-35 parts aggregate, 34-38 parts water, 1-1.5 parts water-reducing agent, 0.1-0.5 parts air-entraining agent, and 0.15-1.0 parts fiber.

[0024] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength greater than 46 MPa; the silica content in the microsilica powder is higher than 90%, and the volume average particle size D (4,3) 100nm~120nm; Volume average particle size D of microspheres (4,3) 10μm~15μm; aggregate is river sand, maximum particle size 1.18mm; water-reducing agent is polycarboxylate high-performance water-reducing agent, water reduction rate greater than 25%; air-entraining agent is sodium alkyl sulfonate; fiber is one of polyvinyl alcohol fiber, polyethylene fiber or polyester fiber, elastic modulus greater than 35GPa, diameter 25μm~40μm, length 9mm~15mm;

[0025] First, put cement, silica fume, microspheres, and aggregate into the mixer and dry mix for 30 seconds. Then, while the mixer is running, add the fiber evenly. After the fiber is added, stop mixing. Dissolve the water-reducing agent and air-entraining agent in the mixing water, pour them into the mixer together, and continue mixing for 3 minutes. Then it is ready to be served.

[0026] The properties of the high-toughness rapid support layer material are as follows: slump 100mm~150mm; air content 20%~30%; 28-day compressive strength 30MPa~40MPa; bending test energy absorption value T 8.0 Greater than 2500 N·mm; tensile strain greater than 2.0%.

[0027] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels. The cross-type close-fitting drainage layer consists of longitudinal and transverse strip-shaped drainage strips arranged in both directions and intersecting each other. The longitudinal strips are arranged on both sides of the arch waist, both sides of the arch shoulder and the arch top, a total of 5 strips, with a distance of not less than 50cm from the system anchor bolts. The transverse strips are evenly distributed with a longitudinal spacing of 3m to 5m and a distance of not less than 50cm from the system anchor bolts. The tail of the drainage strip is connected to the longitudinal blind pipe at the arch foot.

[0028] The drainage strip is strip-shaped, 1.0cm to 1.5cm high, 8cm to 10cm wide, and has a rectangular cross-section. It consists of an outer elastic permeable cover and an inner high-modulus water conveying plate. The water conveying plate and the permeable cover are not connected to each other, and the width is slightly smaller than the width of the rectangular cross-section.

[0029] The external elastic permeable cover is made of basalt fiber by needle punching or weaving, with a thickness of 1.5mm to 2.0mm and a permeability coefficient greater than 0.1cm / s; multiple steel wires with a diameter of 0.5mm to 0.8mm are embedded in the middle of the permeable cover fiber fabric, arranged in a serpentine pattern along the length direction, with a lateral distance of 8mm to 10mm between the steel wires.

[0030] The height of the internal high-modulus water conveying plate is slightly less than the height of the rectangular cross section. It consists of multiple vertical strip baffles with a spacing of 0.5cm to 1.0cm, forming a fence-like structure. The height is divided into two parts with a horizontal partition in the middle, allowing for drainage in both upper and lower layers. The material is polytetrafluoroethylene with a thickness of 1.0mm to 1.5mm and an elastic modulus greater than or equal to 3.0GPa.

[0031] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels, wherein the thickness of the toughened waterproof layer is 20cm to 30cm.

[0032] The materials used in the toughened waterproof layer are as follows: 62-75 parts cement, 10 parts silica fume, 10-20 parts microspheres, 5-8 parts expansion component, 170-200 parts fine aggregate, 145-170 parts coarse aggregate, 34-38 parts water, 1.0-1.5 parts water-reducing agent, 0.03-0.1 parts air-entraining agent, and 1.5-4 parts fiber.

[0033] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength greater than 46 MPa; the silica content of the microsilica powder is higher than 90%, and the volume average particle size D (4,3) 100nm~120nm; Volume average particle size D of microspheres (4,3) 10μm~15μm; the expanding component contains two expansion sources: calcium oxide and calcium sulfate, with a volume average particle size D (4,3) The aggregate consists of 25μm to 30μm particles with a 7-day water-restricted expansion rate of 0.12% to 0.15%; the fine aggregate is manufactured sand with a fineness modulus of 2.8; the coarse aggregate is artificial crushed stone with a particle size of 5mm to 10mm; the water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water reduction rate greater than 25%; the air-entraining agent is sodium alkyl sulfonate; and the fiber is polypropylene fiber with an equivalent diameter of 0.7mm to 1.0mm and a length of 45mm to 50mm.

[0034] First, dissolve the water-reducing agent and air-entraining agent in the mixing water, and then add them to the mixer along with cement, silica fume, microspheres, expansion components, fine aggregate, and coarse aggregate. Mix for 60 seconds, and then add the fiber evenly while mixing for another 60 seconds. After the fiber addition is complete, mix for another 60 seconds, for a total of 180 seconds. Then the mixture is ready to be discharged from the machine.

[0035] The properties of the toughened waterproof layer material are as follows: slump 160mm~200mm; air content 5%~8%; 28d compressive strength 55MPa~70MPa; impermeability grade greater than P25; frost resistance grade greater than F300; low tendency for ring cracking; flexural toughness index I5 greater than 3.5.

[0036] The present invention discloses a wet-sprayed concrete permanent support structure for hard rock highway tunnels, wherein the surface finishing layer has a thickness of 2cm to 3cm;

[0037] The material composition of the surface modification layer is as follows: 75-85 parts cement, 10-15 parts fly ash, 5-10 parts microspheres, 50-70 parts aggregate, 40-45 parts water, 1-1.5 parts water-reducing agent, 0.1-0.5 parts air-entraining agent, and 0.08-0.15 parts fiber.

[0038] First, dissolve the water-reducing agent and air-entraining agent in the mixing water, and then add them to the mixer along with cement, fly ash, microspheres, and aggregates. Mix for 60 seconds, and then add the fiber evenly while mixing for another 60 seconds. After the fiber addition is complete, mix for another 60 seconds, for a total of 180 seconds. Then the mixture can be discharged from the machine.

[0039] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength greater than 46 MPa; the fly ash is Grade I fly ash with a volume average particle size D. (4,3) 15μm~25μm; Volume average particle size D of microspheres (4,3)10μm~15μm; aggregate is manufactured sand with a fineness modulus of 2.8 and a maximum particle size of 5mm; water-reducing agent is polycarboxylate high-performance water-reducing agent with a water reduction rate of more than 25%; air-entraining agent is sodium alkyl sulfonate; fiber is either polypropylene fiber or polyacrylonitrile fiber with a diameter of 20μm~30μm and a length of 15mm~18mm.

[0040] The surface modification layer material has the following properties: slump 120mm~160mm; air content 20%~30%; 28d compressive strength 20MPa~30MPa.

[0041] The system features radially arranged anchor bolts across the entire cross-section; a thin, high-toughness rapid support layer closely adheres to the surrounding rock, capable of absorbing significant energy and rapidly restoring rock stability; a cross-laid, tightly fitted drainage layer connects to the high-toughness rapid support layer, forming a multi-channel, full-section longitudinal and transverse drainage system; a body-toughened waterproof layer covers the cross-laid, tightly fitted drainage layer, serving as the main structural element with multiple functions including load-bearing, toughening, and waterproofing; a surface finishing layer seals coarse fibers and improves smoothness on the surface of the body-toughened waterproof layer, providing surface sealing and finishing. This invention relates to a wet-sprayed concrete permanent support structure that eliminates the need for steel mesh, waterproofing membrane, and secondary lining, adapting to irregular cross-sections. The thin, tough, high-toughness rapid support layer allows for quick, efficient, and safe construction.

[0042] The beneficial technical effects of this invention are:

[0043] (1) The concept of thin-layer rapid support is proposed. After the surrounding rock is excavated, high-toughness cement-based materials are sprayed to construct a high-toughness rapid support layer. Only 2cm to 3cm of construction is needed to restore the stability of the surrounding rock and ensure construction safety. This avoids the disadvantages of slow progress and insufficient toughness of conventional "steel mesh + plain concrete" support.

[0044] (2) The concept of waterproofing of the main structure was proposed, a toughened waterproof layer was designed, and corresponding wet sprayed concrete was prepared. The impermeability grade is greater than P25; the frost resistance grade is greater than F300; and the tendency of circular cracking is "low".

[0045] (3) Special strip drainage strip is thin and can work together with the entire support structure to bear the force; it has strong deformation capacity and appropriate surrounding rock deformation will not affect its function; it has a rough surface, which facilitates concrete adhesion and has a low rebound rate; it has a high modulus and good elasticity, and the impact of concrete jet will not cause the drainage function to fail. Attached Figure Description

[0046] Figure 1 This is a schematic cross-sectional view of the wet-sprayed concrete permanent support structure for hard rock highway tunnels involved in this invention.

[0047] Figure 2 This is a cross-sectional view of the permanent support structure involved in this invention;

[0048] Figure 3 This is a schematic diagram of the laying of longitudinal and transverse strip drainage belts involved in this invention;

[0049] Figure 4 This is a schematic diagram of the cross-section of the strip-shaped drainage belt involved in this invention;

[0050] Among them: 1-surrounding rock, 2-high toughness rapid support layer, 3-cross-type close-fitting drainage layer, 4-body toughening waterproof layer, 5-surface decoration layer, 6-system anchor bolt, 7-strip drainage strip, 8-arch foot, 9-arch waist, 10-arch shoulder, 11-arch top, 12-external elastic permeable cover, 13-internal high modulus water conveyance plate.

[0051] Figure 5 Bending test procedure;

[0052] Figure 6 Dimensions of the specimen used for tensile testing;

[0053] Figure 7 Bending load-deflection curve;

[0054] Figure 8 Tensile stress-strain curve;

[0055] Figure 9 Flexural toughness curve

[0056] Figure 10 Diagram of the test equipment. Detailed Implementation

[0057] The following is in conjunction with the appendix Figures 1-10 Tables 1 and 2 describe specific embodiments and provide a detailed description of the present invention. It is important to note that the following embodiments are for further illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0058] The present invention describes a wet-sprayed concrete permanent support structure for hard rock highway tunnels, such as... Figure 1 , Figure 2As shown, the system consists of system anchor bolts 6, a high-toughness rapid support layer 2, a cross-type close-fitting drainage layer 3, a body-toughened waterproof layer 4, and a surface finishing layer 5. The system anchor bolts 6 are radially distributed and always perpendicular to the surrounding rock base. After tunnel excavation, the base of the surrounding rock 1 is exposed, and most of the length of the system anchor bolts 6 penetrates into the surrounding rock. The exposed ends of the anchor bolts 6 are covered by a 5cm-10cm thick support structure for protection. The permanent support structure is implemented layer by layer from the outer side (closer to the surrounding rock base) to the inner side (away from the surrounding rock base). The high-toughness rapid support layer 2 is closely fitted to the surrounding rock. The cross-type close-fitting drainage layer 3 connects to the high-toughness rapid support layer 2. The body-toughened waterproof layer 4 is implemented across the entire cross section, covering the cross-type close-fitting drainage layer 3. The surface finishing layer 5 covers the surface of the body-toughened waterproof layer 4 and is also implemented across the entire cross section.

[0059] The system anchor 6 is a mortar anchor with a full-section design and radial distribution. The system anchor 6 is always perpendicular to the surrounding rock base. The system anchor 6 is made of ribbed steel bars with a diameter of 22mm and a length of 3m to 5m. The system anchor 6 is arranged in both directions with a spacing of 1.0m to 1.5m. The end of the system anchor 6 away from the surrounding rock base is covered by a support structure with a thickness of 5cm to 10cm.

[0060] The high-toughness rapid support layer 2 is 2cm to 3cm thick, the cross-type close-fitting drainage layer 3 is 1.0cm to 1.5cm thick, the body toughening waterproof layer 4 is 20cm to 30cm thick, and the surface finishing layer 5 is 2cm to 3cm thick.

[0061] The typical material composition of the high-toughness rapid support layer is as follows: 65 parts cement, 8 parts silica fume, 27 parts microspheres, 32 parts aggregate, 36 parts water, 1.2 parts water-reducing agent, 0.3 parts air-entraining agent, and 0.25 parts polyvinyl alcohol fiber. In the material preparation process, first, the cement, silica fume, microspheres, and aggregate are added to a mixer and dry-mixed for 30 seconds. Then, while the mixer is running, the fiber is added evenly. After the fiber addition is complete, the mixing is stopped. The water-reducing agent and air-entraining agent are dissolved in the mixing water and poured into the mixer. The mixture is then stirred for another 3 minutes before being removed from the heat.

[0062] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength of 47.8 MPa; the silica content of the microsilica is 92%, and the volume average particle size D (4,3) 106 nm; Volume average particle size D of microspheres (4,3) 12μm; aggregate is river sand with a maximum particle size of 1.18mm; water-reducing agent is polycarboxylate high-performance water-reducing agent with a water reduction rate of 28%; air-entraining agent is sodium alkyl sulfonate; fiber is polyvinyl alcohol fiber with an elastic modulus of 36GPa, a diameter of 38μm, and a length of 12mm.

[0063] Compressive strength tests were performed using 350mm×450mm×120mm wet-sprayed slab specimens, cut into 100mm×100mm×100mm cubes, sprayed, and cured under standard conditions (temperature (20±2)℃, relative humidity >95%) until the specified age. Bending and tensile tests were conducted using concrete with 4% accelerator, rapidly mixed and vibrated. Bending specimens were 300mm×75mm×15mm in size, with a loading rate of 0.5mm / min. The bending test procedure was as follows: Figure 5 As shown; the dimensions of the specimens used for the tensile test are shown in the figure. Figure 6 The loading speed is 0.3 mm / min.

[0064] The properties of the high-toughness rapid support layer material are as follows: slump 130mm; air content 23.5%; 28-day compressive strength 35.3MPa; bending load-deflection curve as shown in the figure. Figure 7 Energy absorption value T 8.0 The stress-strain ratio is 3170 N·mm; the tensile stress-strain curve is shown below. Figure 8 The tensile strain is 2.5%. The gas content of this material exceeds 20%, which is different from conventional high-toughness cement-based composite materials. It uses high content of microbubbles to reduce viscosity and improve transportability. At the same time, it uses the "impact-collapse" characteristics of bubbles in the spraying process to maintain the hardening performance without significant decline. Under the premise of reducing the probability of pipe blockage during transportation and spraying, it can appropriately increase the fiber volume content and improve bending toughness and tensile elongation characteristics.

[0065] The longitudinal and transverse strip drainage bands arrangement and cross-sectional composition of the cross-sectional drainage bands of the intersecting closely fitted drainage layer 3 are shown in the figure. Figure 3 and Figure 4 The cross-type close-fitting drainage layer 3 consists of longitudinal and transverse strip drainage strips, arranged in both directions and intersecting each other; longitudinally, it is arranged on both sides of the arch waist 8, both sides of the arch shoulder 9 and the arch top 10, a total of 5 strips, and the distance from the system anchor rod 6 is not less than 50cm; transversely, it is evenly distributed, with a longitudinal spacing of 3m to 5m, and the distance from the system anchor rod 6 is not less than 50cm, and the strip tail is connected to the longitudinal blind pipe of the arch foot 11.

[0066] The strip-shaped drainage strip is strip-shaped, 1.0cm to 1.5cm high, 8cm to 10cm wide, and has a rectangular cross-section. It consists of an outer elastic permeable cover 12 and an inner high-modulus water conveying plate 13. The inner high-modulus water conveying plate 13 is not connected to the outer elastic permeable cover 12, and its width is slightly smaller than the width of the rectangular cross-section.

[0067] The external elastic permeable cover 12 is made of basalt fiber by needle punching or weaving, with a thickness of 1.5mm to 2.0mm and a permeability coefficient greater than 0.1cm / s; multiple steel wires with a diameter of 0.5mm to 0.8mm are embedded in the middle of the permeable cover fiber fabric, arranged in a serpentine pattern along the length direction, with a lateral distance of 8mm to 10mm between the steel wires.

[0068] The internal high-modulus water conveying plate 13 is slightly less than the height of the rectangular cross section. It is composed of multiple vertical strip baffles with a spacing of 0.5cm to 1.0cm, forming a fence-like structure. The height is divided into two parts with a horizontal partition in the middle, allowing for drainage in both upper and lower layers. The material is polytetrafluoroethylene with a thickness of 1.0mm to 1.5mm and an elastic modulus greater than or equal to 3.0GPa.

[0069] Table 1 shows a comparison of the concrete rebound rates of the cross-shaped, tightly bonded drainage layer composed of the strip-shaped drainage strips and different drainage pipes during the spraying process. It can be seen that the waterproof membrane does not adhere to the concrete, resulting in a 100% rebound rate; the PVC drainage half-pipe has a smooth surface and high hardness, leading to strong concrete rebound, with a 50% rebound rate; the Ω-shaped spring drainage half-pipe has a relatively large diameter and does not adhere tightly to the wall, easily causing rebound, with a 30% rebound rate, which is still better than the waterproof membrane and PVC drainage half-pipe. The strip-shaped drainage strips proposed in this technology correspond to a concrete rebound rate of only 9%, slightly higher than the 8% for pure concrete substrates, significantly reducing the rebound rate and benefiting both construction efficiency and material savings.

[0070] Table 1 Rebound rate of wet-mixed shotcrete under different substrate conditions

[0071] concrete Strip drainage belt Ω-type spring drain half-pipe Waterproof board PVC drainage half pipe 8％ 9％ 30％ 100％ 50％

[0072] Wet-mixed concrete jet spraying has an impact on the drainage system, which can easily cause drainage failure. After the concrete is applied, water is passed through the pipes to determine whether the drainage function has failed. Drainage materials can be calculated based on their length, but pipes without water flow are considered to be ineffective. The percentage of the failed pipe length to the total length used for testing is the drainage failure rate. The comparison results of different drainage pipes are shown in Table 2. The failure rate of the strip drainage strip proposed in this technology is 1%, while the failure rate of common PVC drainage half-pipes and Ω-type spring drainage half-pipes is 10% to 17%. The failure rate is significantly reduced, and the drainage function can be better maintained.

[0073] Table 2 Failure rate of drainage function after concrete jet impact

[0074] Strip drainage belt PVC drainage half pipe Ω-type spring drain half-pipe 1％ 17％ 10％

[0075] The materials used in the toughened waterproof layer are as follows: 69 parts cement, 10 parts silica fume, 15 parts microspheres, 6 parts expansion component, 190 parts fine aggregate, 160 parts coarse aggregate, 35 parts water, 1.2 parts water-reducing agent, 0.07 parts air-entraining agent, and 2 parts fiber.

[0076] In the material preparation process, the water-reducing agent and air-entraining agent are first dissolved in the mixing water, and then simultaneously added to the mixer along with cement, silica fume, microspheres, expansion components, fine aggregate, and coarse aggregate. The mixture is stirred for 60 seconds, and then the fiber is added evenly while stirring for another 60 seconds. After the fiber addition is completed, the mixture is stirred for another 60 seconds, for a total of 180 seconds. After that, the mixture is ready to be discharged from the machine.

[0077] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength of 47.8 MPa; the silica content of the microsilica is 92%, and the volume average particle size D (4,3) 106 nm; Volume average particle size D of microspheres (4,3) 12μm; the expanded component contains two expansion sources: calcium oxide and calcium sulfate, with a volume average particle size D. (4,3) 26.5μm, 7-day water-limited expansion rate of 0.136%; fine aggregate is manufactured sand with a fineness modulus of 2.8; coarse aggregate is artificial crushed stone with a particle size of 5mm to 10mm; water-reducing agent is polycarboxylate high-performance water-reducing agent with a water reduction rate of 28%; air-entraining agent is sodium alkyl sulfonate; fiber is polypropylene fiber with an equivalent diameter of 0.8mm and a length of 45mm.

[0078] The performance tests were mainly conducted using a wet-sprayed concrete machine to form specimens. The permeability test specimens were frustum-shaped, with an upper base of 175mm, a lower base of 185mm, and a height of 150mm. Before testing, the surface was leveled with high-strength mortar. For compressive strength, freeze-thaw resistance, and flexural toughness tests, large 350mm×450mm×120mm slab specimens were prepared and then cut into 100mm×100mm×100mm, 100mm×100mm×400mm, and 100mm×100mm×400mm specimens, respectively. The compressive strength test was conducted according to GB / T 50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete," while the permeability and freeze-thaw resistance tests were conducted according to GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete." The flexural toughness test was conducted according to CECS 13:2009 "Standard for Test Methods of Fiber Reinforced Concrete," using a four-point bending loading mode at a rate of 1.0mm / min.

[0079] Based on the above test methods and material composition, the properties of the toughened waterproof layer material are as follows: slump 185mm; air content 7.8%; 28-day compressive strength 63.6MPa; impermeability test: no water seepage after 8 hours under 2.5MPa pressure, impermeability grade greater than P25; freeze-thaw resistance test: relative dynamic modulus of elasticity 86% after 300 freeze-thaw cycles, higher than 60%, mass loss 1.9%, less than 5%, freeze-thaw resistance grade greater than F300; flexural toughness curve is shown in [reference needed]. Figure 9 The bending toughness index I5 is 3.56.

[0080] The test was conducted according to ASTM C1581-2009, "Standard test method for determining age atcracking and induced tensile stress characteristics of mortar and concrete under restrained shrinkage," using equipment such as... Figure 10 As shown. The specimen had an inner diameter of 330 mm, an outer diameter of 406 mm, and a height of 150 mm. The concrete contained 4% quick-setting agent, was rapidly mixed and vibrated to form the concrete, and was demolded after 24 hours. The specimen was then placed in a constant temperature and humidity environment with a relative humidity of 60% ± 5% and a temperature of 20℃ ± 2℃ to observe cracks and record the cracking time. It was found that the concrete did not crack after 56 days, and the trend of circular cracking was "low".

[0081] The material composition of the surface modification layer is as follows: 80 parts cement, 10 parts fly ash, 10 parts microspheres, 60 parts aggregate, 41 parts water, 1.1 parts water-reducing agent, 0.3 parts air-entraining agent, and 0.1 parts fiber.

[0082] In the material preparation process, the water-reducing agent and air-entraining agent are first dissolved in the mixing water, and then simultaneously added to the mixer along with cement, fly ash, microspheres, and aggregates. The mixture is stirred for 60 seconds. Then, the fiber is added evenly while stirring for another 60 seconds. After the fiber addition is completed, the mixture is stirred for another 60 seconds. The total stirring time is 180 seconds, after which the mixture is ready to be discharged from the machine.

[0083] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength of 47.8 MPa; the fly ash is Grade I fly ash with a volume average particle size D. (4,3) 18μm; Volume average particle size D of microspheres (4,3) 12μm; aggregate is manufactured sand with a fineness modulus of 2.8 and a maximum particle size of 5mm; water-reducing agent is polycarboxylate high-performance water-reducing agent with a water reduction rate of 28%; air-entraining agent is sodium alkyl sulfonate; fiber is polyacrylonitrile fiber with a diameter of 29μm and a length of 18mm;

[0084] The compressive strength test was conducted using 350mm×450mm×120mm wet-sprayed large plate specimens, cut into 100mm×100mm×100mm cubes, sprayed and molded, and cured under standard conditions (temperature (20±2)℃, relative humidity>95%) until the specified age.

[0085] The surface modification layer material has the following properties: slump 145 mm; air content 24.7%; 28-day compressive strength 25.6 MPa.

[0086] like Figures 1-4 As shown, the wet-sprayed concrete permanent support structure for hard rock highway tunnels of the present invention is constructed according to the following steps:

[0087] Step 1: For hard rock highway tunnels, in the case of dampness or dripping water, after the tunnel is excavated, first clean the debris, then spray a 2cm to 3cm high-toughness rapid support layer, spraying to the specified thickness in one go;

[0088] Step 2: After the high-toughness rapid support layer material has set for 8 hours and most of the stress has been released and the rock mass has basically returned to stability, boreholes are drilled and anchors are installed according to the system anchor design scheme. The system anchors are radially distributed, always perpendicular to the surrounding rock base, arranged in both directions, and maintaining the set spacing. Full-length bonded grouting is used. The exposed length of the anchors outside the rock body is 5cm to 10cm less than the thickness of the entire wet-sprayed concrete permanent support structure, that is, the end of the anchor on the side away from the surrounding rock base covers the thickness of the support structure by 5cm to 10cm.

[0089] Step 3: After grouting for 24 hours, once the grout has solidified and formed sufficient strength, arrange a cross-type close-fitting drainage layer, fix the strip drainage strip with nails, pass through the high-toughness rapid support layer, and connect the strip drainage strip, the high-toughness rapid support layer, and the surrounding rock into one.

[0090] Step 4: Apply the toughened waterproof layer with a total thickness of 20cm to 30cm. Apply it in 4 to 5 sprayed concrete layers, each layer being 5cm to 7cm thick. The time interval between spraying two layers of concrete should not be less than 2 hours. Spray curing should begin 2 hours after the concrete has set and should last for at least 14 days. When spraying each layer, the longitudinal length of a single layer should not be less than 20m.

[0091] Step 5: Apply a 2cm to 3cm thick surface finishing layer by spraying, spraying to the specified thickness in one go. Start spray curing 2 hours after the concrete has set, and continue for at least 14 days.

Claims

1. A permanent support structure for a hard rock highway tunnel by wet spray concrete, characterized by: The system anchor rod, high toughness rapid support layer, cross type close drainage layer, body toughening waterproof layer and surface modification layer are composed; the system anchor rod is distributed radially, the system anchor rod is always perpendicular to the surrounding rock base surface, the high toughness rapid support layer is close to the surrounding rock, the cross type close drainage layer is connected with the high toughness rapid support layer, the body toughening waterproof layer covers the cross type close drainage layer, the surface modification layer is on the surface of the body toughening waterproof layer, most of the system anchor rod penetrates into the surrounding rock, and the exposed part of the surrounding rock base surface is 5cm-10cm less than the thickness of the whole permanent support structure; The material used in the body toughening waterproof layer is as follows: cement 62-75 parts, microsilica powder 10 parts, microbead 10-20 parts, expansion component 5-8 parts, fine aggregate 170-200 parts, coarse aggregate 145-170 parts, water 34-38 parts, water reducing agent 1.0-1.5 parts, air entraining agent 0.03-0.1 part and fiber 1.5-4 parts; The material used in the surface modification layer is as follows: cement 75-85 parts, fly ash 10-15 parts, microbead 5-10 parts, aggregate 50-70 parts, water 40-45 parts, water reducing agent 1-1.5 parts, air entraining agent 0.1-0.5 parts and fiber 0.08-0.15 parts.

2. A permanent support structure for a hard rock highway tunnel by wet shotcreting according to claim 1, characterized in that: The system anchor rod is a mortar anchor rod, and the full-face design is adopted; the material used in the system anchor rod is ribbed steel, the length is 3m-5m, the bidirectional arrangement is adopted, the spacing is 1.0m-1.5m, and the support structure covering thickness of the end of the anchor rod away from the surrounding rock base surface is 5cm-10cm.

3. A permanent support structure for a hard rock highway tunnel by wet shotcreting according to claim 1, characterized in that: The thickness of the high toughness rapid support layer is 2cm-3cm. The material used in the high toughness rapid support layer is as follows: cement 57-70 parts, microsilica powder 5-8 parts, microbead 25-35 parts, aggregate 30-35 parts, water 34-38 parts, water reducing agent 1-1.5 parts, air entraining agent 0.1-0.5 parts and fiber 0.15-1.0 parts.

4. A permanent support structure for a hard rock highway tunnel by wet shotcreting according to claim 1, characterized in that: The thickness of the cross type close drainage layer is 1.0cm-1.5cm, and the cross type close drainage layer is composed of longitudinal and transverse strip-shaped drainage belts, the bidirectional arrangement is adopted, the longitudinal arrangement is arranged on the two side spandrels, two side haunches and the vault top, and the distance from the system anchor rod is not less than 50cm; the transverse arrangement is uniformly arranged, the longitudinal spacing is 3m-5m, and the distance from the system anchor rod is not less than 50cm; and the tail of the strip-shaped drainage belt is connected with the longitudinal blind pipe of the springing.

5. A permanent support structure for a hard rock highway tunnel by wet gunite concrete according to claim 1, characterized in that: The thickness of the body toughening waterproof layer is 20cm-30cm, and the thickness of the surface modification layer is 2cm-3cm.

6. A permanent support structure for a hard rock highway tunnel by wet gunite concrete according to claim 4, characterized in that: The strip-shaped drainage belt has a strip-shaped appearance and a rectangular cross section, and is composed of an external elastic water permeable cover and an internal high modulus water conveying plate; the internal high modulus water conveying plate and the external elastic water permeable cover are not connected with each other, and the width is slightly smaller than the width of the rectangular cross section.

7. A permanent support structure for a hard rock highway tunnel by wet gunite concrete according to claim 6, characterized in that: The external elastic water permeable cover is formed by needling or weaving basalt fibers, and has a thickness of 1.5mm-2.0mm; a plurality of steel wires are implanted in the middle of the water permeable cover fiber fabric and are arranged in a serpentine shape along the length direction, and the transverse distance between the steel wires is 8mm-10mm.

8. A permanent support structure for a hard rock highway tunnel by wet gunite concrete according to claim 6, characterized in that: The internal high modulus water conveying plate has a height slightly smaller than the height of the rectangular cross section, is composed of a plurality of vertical strip-shaped baffles, has a spacing of 0.5cm-1.0cm, has a fence shape, is divided into two parts in height, has a transverse partition plate in the middle, and has upper and lower two layers of drainage.

9. The use of the hard rock highway tunnel wet shotcrete permanent support structure according to any one of claims 1 to 8 in a hard rock tunnel, under the conditions of surrounding rock grade III, grade IV, and damp or trickling groundwater.

Images