A treatment method suitable for a shallow-buried portal of a tunnel in poor geological conditions

Abstract

This invention discloses a treatment method for shallow-buried tunnel entrances in geologically challenging conditions involving silt deposits, relating to the field of highway tunnel construction technology. The method includes the following steps: S1, initial support of the silt deposits at the tunnel entrance section of a mountainous highway; S2, tunnel exit construction of the shallow-buried section based on guide walls, large pipe roofs, and the CD method; S3, real-time monitoring of the entire construction process of the shallow-buried section. This invention enables the treatment of silt deposits and tunnel exit construction while maintaining existing traffic flow, improving the efficiency of silt deposit treatment and tunnel exit construction, shortening the overall tunnel construction period, increasing the reliability of the tunnel exit section structure, reducing construction safety risks, and minimizing environmental damage.

Description

Technical Field

[0001] This invention relates to the field of highway tunnel construction technology, and more specifically, to a treatment method for shallow-buried tunnel entrances in geologically unfavorable geology involving silt deposits. Background Technology

[0002] Currently, the CD method (tunnel exit construction method) and CRD method, commonly used both domestically and internationally for tunnel portal sections in silt-filled areas, suffer from drawbacks such as large-scale temporary support removal, inconvenience for large construction machinery, and low construction efficiency. With advancements in construction technology, the rapid excavation, rapid support, and rapid ring formation micro-step excavation method, centered on micro-step excavation, wet-spraying robotic support, and rapid invert arch closure, is gaining popularity among engineering professionals. However, these methods are not yet widely adopted, and their implementation requires adaptation to varying geological conditions; the construction techniques still need further refinement.

[0003] For example, a method and structure for supporting a deep sedimentary slope, patent number CN105648982A, uses two rows of staggered circular cross-section reinforced concrete piles as the main supporting structure for the deep sedimentary slope. The clear distance between the pile edges is controlled at approximately 10cm, primarily to prevent water flow erosion and scouring of the deep sedimentary slope. The tops of the circular cross-section reinforced concrete piles are connected as a single unit by a concrete connecting beam, which is integrated with the concrete slope above it to ensure that the circular cross-section reinforced concrete piles and the concrete slope bear the load as a whole. By using circular cross-section reinforced concrete piles as the main supporting structure for the deep sedimentary slope, and employing mechanical drilling as the primary construction method, construction efficiency can be significantly improved. It effectively reduces construction difficulty and safety risks during construction, resulting in a high construction schedule guarantee rate. Through reasonable pile spacing design, the problem of water flow erosion of the sedimentary slope between piles can be effectively solved.

[0004] However, the above-mentioned methods for supporting slopes of deep deposits are too simplistic and cannot guarantee the overall stability of the deposits. They are not suitable for situations where there are buildings or roads above the deposits.

[0005] For example, a method for excavating railway tunnels with large cross-sections in Class IV and V surrounding rock, patent number CN101105131A, employs advanced support, excavating an arc-shaped pilot tunnel and reserving core soil; staggered excavation of the left and right sidewalls of the middle step and reserving core soil; staggered excavation of the left and right sidewalls of the lower step and reserving core soil; sequential excavation of the upper, middle, and lower steps and reserving core soil; excavation of the invert arch and implementation of initial support, etc. This method offers a large construction space, allows for parallel operation on multiple work faces, and has high efficiency. It also facilitates flexible and timely conversion to other construction methods when geological conditions change. The reserved core soil maintains the staggered excavation on the left and right sides, which is beneficial to the stability of the excavation face. When the surrounding rock deformation is large, the closure time can be adjusted as quickly as possible while ensuring safety and meeting the clearance requirements.

[0006] However, the excavation methods described above, which are applicable to railway tunnels with large cross-sections in Class IV and V surrounding rock, are not applicable to the area above the tunnel, as they have poor stability and can have a significant impact on structures around the tunnel entrances and exits.

[0007] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] To address the shortcomings of existing technologies, this invention provides a treatment method for shallow-buried tunnel entrances in geologically challenging conditions involving silt deposits. This method offers the advantages of treating the silt deposits while maintaining existing traffic flow, reducing construction safety risks, and minimizing damage to the natural environment. It also solves the problems of existing treatment methods being too simplistic, failing to guarantee the overall stability of the silt deposits, and having a significant impact on structures around the tunnel entrances and exits.

[0010] (II) Technical Solution

[0011] To achieve the advantages of maintaining existing traffic flow, treating the accumulated debris, reducing construction safety risks, and minimizing damage to the natural environment, the specific technical solution adopted by this invention is as follows:

[0012] A treatment method for shallow-buried tunnel entrances in geologically unfavorable sedimentary formations includes the following steps:

[0013] S1. Initial support for the accumulation material at the tunnel entrance section of a mountain expressway;

[0014] S2. Construction of shallow buried tunnel sections based on guide walls, large pipe sheds and CD method;

[0015] S3. Real-time monitoring of the entire construction process of the shallow buried section of the tunnel.

[0016] Furthermore, the initial support for the accumulation mass at the tunnel entrance section of a mountain highway includes the following steps:

[0017] S11. Circular anti-slide piles are installed on both the left and right sides of the tunnel body;

[0018] S12. Steel pipe piles are installed within the tunnel body, and a capping beam is installed on top of the steel pipe piles;

[0019] S13. Surface grouting is used to reinforce the slope of the section from the circular anti-slide piles and steel pipe piles to the tunnel entrance.

[0020] S14. Based on the relative position of the sliding surface and the slope, an anti-slip retaining wall shall be installed on the upper part of the first-level slope.

[0021] S15. Mechanical construction methods are adopted, and slope brushing and load reduction are carried out according to the preset slope ratio.

[0022] Furthermore, the circular anti-slide piles are located at a distance of 4m or more from the tunnel excavation outline, and the pile holes for the circular anti-slide piles are formed using a rotary drilling rig.

[0023] Furthermore, the steel pipe piles are arranged in a quincunx pattern, and the pile holes are drilled using a crawler-mounted geological drilling rig.

[0024] Furthermore, both the circular anti-slide piles and the steel pipe piles are constructed using C30 concrete.

[0025] Furthermore, the surface grouting uses steel pipes with a diameter of 89mm arranged in a quincunx pattern.

[0026] Furthermore, the foundation and wall body of the anti-slide retaining wall are reinforced gabion stones. The toe of the anti-slide retaining wall is buried at a depth greater than or equal to 1m. Permeable geotextile is installed on the mountain-facing side of the anti-slide retaining wall, and impermeable geotextile is installed at the bottom of the anti-slide retaining wall. The back of the anti-slide retaining wall is backfilled and compacted with crushed stone soil.

[0027] Furthermore, mechanical construction methods are employed, and slope trimming and load reduction are carried out according to a preset slope ratio, including the following steps:

[0028] S151. Mark the slope boundary and construct a combined permanent and temporary drainage system according to the preset requirements;

[0029] S152. Excavators are used to excavate and load earth according to the preset slope, and dump trucks are used to transport the earth to the spoil disposal site.

[0030] Furthermore, the construction of the shallow-buried section of the tunnel based on the guide wall, large pipe roof, and CD method includes the following steps:

[0031] S21. Construction of guide walls is carried out in the shallow buried section of the tunnel exit.

[0032] S22. Construction of large pipe sheds will be carried out in the shallow buried section of the tunnel exit.

[0033] S23. The CD method is used for excavation and support of large-section shallow-buried tunnels.

[0034] S24. Dynamically adjust the support parameters based on the monitoring data of the tunnel arch settlement, arch waist convergence and tunnel arch bottom.

[0035] Furthermore, real-time monitoring of the entire construction process of the shallow-buried section of the tunnel includes the following steps:

[0036] S31. Before the permanent support construction of the sump is completed, set up several monitoring points and equip them with GNSS stations to monitor the support construction.

[0037] S31. After the permanent support construction of the accumulator is completed, several monitoring points are added and equipped with GNSS stations to monitor the displacement of the permanent support structure of the accumulator.

[0038] (III) Beneficial Effects

[0039] Compared with the prior art, the present invention provides a treatment method for shallow-buried tunnel entrances in geologically unfavorable geology of silt deposits, which has the following beneficial effects:

[0040] (1) The present invention can treat the accumulator and carry out tunnel exit construction while maintaining existing traffic, thereby improving the efficiency of accumulator treatment and tunnel exit construction, shortening the overall tunnel construction period, increasing the reliability of the tunnel exit section engineering structure, reducing construction safety risks, and reducing damage to the natural environment.

[0041] (2) This invention treats the landslide outside the tunnel body by using anti-slide piles. By combining multiple support methods, it increases the reliability of the support of the landslide and improves the permanent stability of the landslide. It also focuses on prevention and comprehensive treatment to avoid future problems. It can effectively prevent geological disasters such as landslide and surface deformation, reduce the disturbance of the natural environment to the site construction, and protect the surrounding structures. It uses micro steel pipe piles + cap beams to treat the landslide directly above the tunnel body, solves the potential risks of landslides during the construction stage, and ensures the safety of the construction process.

[0042] (3) The present invention uses surface drainage, surface grouting reinforcement, deformation monitoring and other technical measures to pre-reinforce and monitor the shallow buried section of the tunnel, so as to ensure the quality and safety of the tunnel body construction process.

[0043] (4) The present invention uses the CD method to excavate and support large-section shallow buried tunnels, which can protect existing roads and buildings above the tunnel, reduce the amount of excavated soil during tunnel construction, thereby reducing the occupation of natural farmland, improving the efficiency of tunnel exit construction, shortening the overall tunnel construction period, ensuring the safety of tunnel construction, and dynamically adjusting the support parameters based on the monitoring data of tunnel top settlement, arch waist convergence and tunnel arch bottom, which can ensure the safe exit of the tunnel and guarantee the quality of subsequent tunnel construction. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a flowchart of a treatment method for shallow-buried tunnel entrances in poor geological conditions of accumulated land, according to an embodiment of the present invention.

[0046] Figure 2 This is one of the schematic diagrams of CD method excavation in the treatment method for shallow buried tunnel entrances in poor geological conditions of accumulated bodies according to an embodiment of the present invention;

[0047] Figure 3 This is the second schematic diagram of the CD method excavation in the treatment method for shallow buried tunnel entrances in poor geological conditions of accumulated bodies according to an embodiment of the present invention;

[0048] Figure 4 This is a construction process flow diagram of the CD method in the treatment method for shallow buried tunnel entrances in poor geological conditions of accumulated bodies according to an embodiment of the present invention. Detailed Implementation

[0049] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0050] According to an embodiment of the present invention, a treatment method is provided for shallow-buried tunnel entrances in geologically unfavorable geology of silt deposits.

[0051] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figure 1As shown, the present invention provides a method for treating shallowly buried tunnel entrances in geologically unfavorable geology, comprising the following steps:

[0052] S1. Initial support for the accumulation material at the tunnel entrance section of a mountain expressway;

[0053] In addition, the following steps are included before the initial support is provided for the accumulation material at the entrance section of a mountain highway tunnel:

[0054] Provide timely technical and safety briefings to the construction team;

[0055] Before construction, inspect and repair the relevant machinery and equipment to ensure that the equipment is in good working order;

[0056] Check whether the materials are prepared in place and meet the specifications.

[0057] Implement temporary drainage and waterproofing measures at the tunnel entrance to ensure the drainage system remains unobstructed;

[0058] Once the arch excavation is completed, its foundation bearing capacity shall not be less than 300 kPa.

[0059] Preferably, the initial support for the accumulator at the entrance section of a mountain highway tunnel includes the following steps:

[0060] S11. Circular anti-slide piles are installed on both the left and right sides of the tunnel body;

[0061] Specifically, the circular anti-slide piles are located at a distance of 4m or more from the tunnel excavation outline, and the pile holes for the circular anti-slide piles are formed using a rotary drilling rig.

[0062] It should be noted that a row of nine circular anti-slide piles, each 2.2m in diameter, with a center-to-center spacing of 5m and a length of 22-28m, are installed on both sides of the right tunnel. A row of six circular anti-slide piles, each 2.0m in diameter, with a center-to-center spacing of 5m and a length of 20-25m, are installed on both sides of the left tunnel. The reinforcing cages for the circular anti-slide piles are fabricated outside the borehole and hoisted in by crane, with internal installation performed if necessary.

[0063] S12. Steel pipe piles are installed within the tunnel body, and a capping beam is installed on top of the steel pipe piles;

[0064] Specifically, the steel pipe piles are arranged in a quincunx pattern, and the pile holes are drilled using a crawler-mounted geological drilling rig.

[0065] It should be noted that, given the shallow tunnel depth and insufficient embedment depth of the anti-slide piles within the tunnel body, miniature steel pipe piles were used to reinforce the tunnel section. Specifically, one row of miniature steel pipe piles was installed within the right tunnel section, and another row was installed within the left tunnel section. The miniature steel pipe piles were arranged in a quincunx pattern, with a lateral spacing of 1.5m and a longitudinal spacing of 1.2m. The borehole diameter was 150mm, and the hole depth was 12-18m.

[0066] Miniature steel pipe piles adopt Seamless steel pipe with no holes for 0.5m below the top. Holes with a diameter of 4mm are drilled every 30cm along the axis at 45° intervals below 0.5m, with only one hole per section. The bottom of the pipe is sealed and perforated, and the top is fixed with U-shaped steel bars. Three 28mm diameter threaded steel bars are placed in the holes and tied with stirrups. The diameter of the micro steel pipe pile hole is 150mm, and the top of the micro steel pipe pile extends 30cm into the capping beam. The main reinforcement of the capping beam is connected to the micro pile steel pipe by welding.

[0067] Specifically, both the circular anti-slide piles and the steel pipe piles are constructed using C30 concrete, which is poured and vibrated simultaneously.

[0068] Specifically, the grouting requirements for the steel pipes are as follows: pure cement grout with a water-to-cement mass ratio of 1:1; grouting is performed in two stages. The first grouting pressure is controlled at 0.3-0.5 MPa; the second grouting uses a splitting grouting method with a pressure controlled at 0.8-1.0 MPa, with an interval of 10-12 hours between the two stages. The cement dosage is controlled at 100-200 kg / m. If the final grouting pressure remains above 10 minutes or cement grout seeps out locally from the slope, the process should be paused until initial setting. Before construction, a grouting test should be conducted to determine the optimal hole depth, hole spacing, grout mix ratio, grouting pressure, and grouting volume.

[0069] S13. Surface grouting is used to reinforce the slope of the section from the circular anti-slide piles and steel pipe piles to the tunnel entrance.

[0070] It should be noted that the slope from the anti-slide piles and micro steel pipe piles to the tunnel entrance is potentially unstable. The design adopts surface grouting reinforcement to improve the stability of the tunnel slope and ensure the long-term effectiveness of the anti-slide retaining structure.

[0071] The surface grouting uses 89mm diameter steel pipes arranged in a quincunx pattern with a longitudinal and transverse spacing of 1.5m.

[0072] S14. Based on the relative position of the sliding surface and the slope, an anti-slip retaining wall shall be installed on the upper part of the first-level slope.

[0073] Specifically, the foundation and wall body of the anti-slide retaining wall are reinforced gabion stones. The toe of the anti-slide retaining wall is buried at a depth of 1m or more. Permeable geotextile is installed on the mountain-facing side of the anti-slide retaining wall, and impermeable geotextile is installed at the bottom of the anti-slide retaining wall. The back of the anti-slide retaining wall is backfilled and compacted with crushed stone soil.

[0074] It should be noted that reinforced gabions are engineering components made from double-twisted hexagonal wire mesh woven from thick galvanized and plastic-coated low-carbon steel wire. When using them, test reports on the tensile strength and edge strength of the mesh surface must be provided. The gabion baskets are filled with rubble or pebbles, with 10-25cm particles accounting for more than 80%, and the remainder filled with smaller-diameter stones to fill the gaps. Based on the opening and construction schedule, the advantages of reinforced gabion retaining walls—fast construction speed, good permeability, flexibility, integrity, environmental friendliness, and economy—should be fully utilized. During installation, gabions should be staggered and connected vertically, and continuous joints are strictly prohibited.

[0075] S15. Mechanical construction methods are adopted, and slope brushing and load reduction are carried out according to the preset slope ratio.

[0076] Specifically, the mechanical construction method, and the slope reduction and load reduction according to the preset slope ratio, includes the following steps:

[0077] S151. Mark the slope boundary and construct a combined permanent and temporary drainage system according to the preset requirements.

[0078] It should be noted that the combined permanent and temporary interception and drainage system includes permanent slope top interception ditches and drainage ditches, as well as drainage ditches temporarily excavated due to construction needs, which can prevent surface water from flowing into the tunnel construction area.

[0079] S152. Excavators are used to excavate and load earth according to the preset slope, and dump trucks are used to transport the earth to the spoil disposal site.

[0080] It should be noted that after the anti-slide retaining wall backfilling is completed, slope brushing and load reduction at the top of the slope are required.

[0081] S2. Construction of shallow buried tunnel sections based on guide walls, large pipe sheds and CD method;

[0082] Preferably, the tunnel exit construction based on guide walls, large pipe sheds, and the CD method includes the following steps:

[0083] S21. Construction of guide walls is carried out in the shallow buried section of the tunnel exit.

[0084] Specifically, the construction of the guide wall in the shallow buried section of the tunnel includes the installation of steel frames, guide pipes, formwork, and concrete construction of the arch.

[0085] It should be noted that the steel frame installation includes the following steps:

[0086] Core soil should be reserved during the excavation of arches and open tunnels. The core soil should be 5-8m long and 3-4m high. The core soil should serve as the working platform for arch construction and should be 1.5-2m away from the arch.

[0087] The arch foundation pit is excavated according to the survey and layout. The slope is set according to the design slope. The bottom of the pit is widened by 50cm on both sides. The foundation should be placed on the bedrock layer. When it is placed on the soil layer, M10 mortar-grouted rubble masonry should be used for replacement. The arch foundation base is not allowed to have any under-excavation.

[0088] Four 22 guide arch frames were fabricated according to the design drawings. The arch frames were processed by the steel bar processing plant and then installed on site. During installation, the arch frames were accurately positioned according to the elevation determined by the surveyors and the arch frame installation control line. The bolt connections were required to be firm and the verticality of the arch frames was strictly checked to ensure that the arch frames were controlled on the same plane.

[0089] The installation of the guide tube includes the following steps:

[0090] The guide pipes are made of Φ133*4mm seamless steel pipes, with a circumferential spacing of 40cm, a length of 2.0m, and an external insertion angle of 1-3° (excluding the longitudinal slope of the route), totaling 49 pipes. The guide pipes are welded to the steel arch frame, and the pipe openings are sealed to prevent concrete from entering the pipe openings. The positioning of the orifice pipes is precisely determined by the surveying team. The elevation and direction must be accurate, and small steel plates or reinforcing bars can be used for adjustment.

[0091] The guide pipe is welded to the orifice pipe and 22 I-beams on both sides using Φ16 fixed steel bars. The weld length is no more than 8cm. The steel arch frame without orifice pipe is connected by Φ25 longitudinal connecting steel bars with a circumferential spacing of 1m.

[0092] Template installation includes the following steps:

[0093] The arch formwork uses two inner I22a steel arch frames + 12-type steel connecting beams. The steel arch frame support beams are supported by 42 steel pipes at 60*60mm intervals, and the steel pipes are horizontally connected. Top and bottom supports are designed, and the formwork is connected to the arch frame with tie rods. The I22a steel arch frames and the arch frame are placed on the same concrete foundation.

[0094] Wooden formwork is used for arch construction. The formwork is tightened with wooden wedges and reinforced with tie rods on the sides. The formwork must be firm, flat, and the joints must be tight to ensure no grout leakage during pouring.

[0095] The template has sufficient strength, rigidity, and stability.

[0096] The concrete construction of the arch section includes the following steps:

[0097] Before pouring concrete, strictly check the reinforcement of the steel support and re-measure the position of the guide pipe. If there is any deviation, make adjustments in time.

[0098] The arch is made of C30 concrete with a radial thickness of 60cm and a longitudinal length of 2.0m. To ensure uniform and dense concrete compaction, the radial thickness of the arch formwork is precisely controlled, and the pouring process is continuous without interruption. The concrete is compacted using a vibrator, and each part must be compacted. Generally, it is advisable to vibrate until the concrete no longer settles, no obvious air bubbles rise, a thin layer of cement paste appears on the concrete surface, and the surface is smooth. In addition, during concrete pouring, the vibrator should not touch the guide tube to prevent the guide tube from shifting.

[0099] Two hours after the concrete has set, cover it for curing.

[0100] S22. Construction of large pipe sheds will be carried out in the shallow buried section of the tunnel exit.

[0101] Specifically, the construction of large pipe roofs in the shallow buried section of the tunnel includes design parameters, drilling, processing and installation of pipe roof steel pipes, installation of small steel cages and grouting.

[0102] It should be noted that the design parameters include a 32m long pre-construction pipe shed, including a 2m arch section; Φ108*6mm hot-rolled seamless steel pipes, 49 pipes in total at each location, spaced 40cm apart; no more than 50% of the joints in the same longitudinal section of the tunnel; joints of adjacent steel pipes must be staggered by at least 1m, with an external insertion angle of 1°; and M30 cement grout as the grouting material.

[0103] Drilling includes the following steps:

[0104] Stone chips were used for backfilling and compaction, and the backfill height was determined and adjusted according to the height of the tracked pipe roof drilling rig.

[0105] Place the drilling rig on the drilling platform, adjust the height and drill rod inclination angle, then firmly fix the drilling rig on the drilling platform and check that all pipelines and connections are correct.

[0106] Pass the drill bit and drill rod through the guide tube, align them with the marked hole position and center, and slowly start the drilling machine. Make sure the hole is straight and the bottom deviation distance is less than the radius of the hole.

[0107] Using a spiral drill rod and a three-wing drill bit, dry drilling is used to form holes. The pipe roof construction adopts a segmented and intermittent construction method. The odd-numbered holes are drilled first to construct the pipe roof, and the even-numbered holes are constructed after grouting is completed, so as to check the grouting effect of the odd-numbered holes.

[0108] The borehole diameter is Φ120mm; the borehole plane error is no more than 50mm; the borehole inclination control measure is to use an inclination measuring instrument to measure the drilling inclination, and if the inclination exceeds the design requirements, it should be corrected in time.

[0109] In order to ensure the smooth installation of pipes, the holes are cleaned after drilling to ensure the smooth flow of the pipes; after the large pipe shed is completed, it will be arranged in an umbrella-shaped radial pattern.

[0110] The processing and installation of steel pipes for pipe sheds includes the following steps:

[0111] The steel pipe material is Φ108×6mm hot-rolled seamless steel pipe.

[0112] The steel pipes are processed into two types: 4m and 6m in length.

[0113] To facilitate grouting, the steel pipes for the pipe roof are perforated perforated pipes with Φ15mm holes spaced 20cm apart in a quincunx pattern. To facilitate pipe laying, the frontmost steel pipe is made into a conical shape.

[0114] When installing the large pipe shed, a drilling rig is used to push it in. The steel pipes are connected by threads and tightened by rotating with free pliers. The thread is 15cm long. The joints should be staggered on the tunnel cross section. The first pipe section of odd-numbered holes is 4m long, the first pipe section of even-numbered holes is 6m long, and each subsequent section is 6m long.

[0115] When pushing in the steel pipe, ensure that the inclination angle of the guide pipe is consistent with the inclination angle of the drill rod. It is best not to move the drilling machine after drilling a hole, but immediately push the guide pipe of that hole into the hole. After installing the guide pipe, move the drilling machine away to drill the next hole.

[0116] The process of installing a small steel cage includes the following steps:

[0117] The reinforcing cage is made of HRB400 steel bars with a diameter of Φ20mm.

[0118] The reinforcing cage is centrally and uniformly manufactured in sections by the steel plant, and the reinforcing bars are welded to the Φ50×4mm fixing rings.

[0119] When connecting the reinforcing cage on site, the joints shall be double-sided lap welded, with a weld length of not less than 5d (d represents the diameter of the reinforcing bar), and staggered. The number of joints in the same section shall not exceed 1 / 2 of the total number of reinforcing bars.

[0120] After the steel pipes for the pipe shed are installed, the reinforcing cage should be inserted in a timely manner and grouting should be carried out.

[0121] Grouting includes the following steps:

[0122] M30 cement grout was used for pipe roof grouting. The grouting was uniformly mixed by the mixing plant. Reasonable grouting parameters were determined by on-site tests, and samples were taken for testing.

[0123] The grouting pipes are made of rigid plastic and are arranged along the entire length of the pipe roof; the venting holes are also made of rigid plastic and are located above the holes in the pipe roof.

[0124] After the steel pipe is installed, the gap between the steel pipe and the hole wall is sealed with hemp fiber and anchoring agent at the pipe opening. The steel pipe itself uses the end cap installed at the hole opening to press the sealing ring tightly. A tee joint is installed on the grouting pipe opening.

[0125] The grout must be thoroughly mixed. Water and cement must be weighed using weighing equipment to ensure a water-cement ratio of 1:1. Water glass as required by the design must be added. The grout is then placed into a storage tank through a filter screen and injected into the steel pipe of the pipe roof by a grouting pump through pipeline.

[0126] The grout is mixed using a ZJ-400 high-speed grout mixer. After the grout is thoroughly mixed, it is placed in a storage tank and then injected into the steel pipe via a grouting pump. During grouting, a designated person must operate the grouting pump and the steel pipe head to control the grouting pressure and speed. The grouting valve must be closed promptly after each tank is filled.

[0127] Grouting is completed when the final pressure is reached and grouting continues for more than 15 minutes. After grouting, the cementitious grout in the pipe is swept out and tightly filled with cement mortar.

[0128] S23. The CD method is used for excavation and support of large-section shallow-buried tunnels.

[0129] S24. Dynamically adjust the support parameters based on the monitoring data of the tunnel arch settlement, arch waist convergence and tunnel arch bottom.

[0130] It should be noted that, for example, there is an existing village road directly above the stockpile at the exit section of the Zhangjiawan Tunnel, which is the only access road for the local village. Interruption of construction is prohibited, therefore the cut-and-cover method should be selected for tunnel excavation to maintain existing traffic. However, the cut-and-cover method involves a large volume of earthwork excavation. Since the project site is mostly mountainous forest and farmland with no available spoil disposal sites, this option was abandoned, and the "guide wall + large pipe shed + CD method" was chosen for the shallow-buried section of the tunnel exit construction.

[0131] Due to the shallow burial depth of Zhangjiawan Tunnel, 70.6% of the surrounding rock is of Class V quality, and the entire 200m range from the exit section is Class V, indicating a poor rock quality. Therefore, the CD method was adopted for excavation and support of the large-section shallow-buried tunnel section (which can provide temporary support for the tunnel surrounding rock, increasing the safety of tunnel construction). The support parameters were dynamically adjusted based on the monitoring data of the tunnel arch settlement, arch waist convergence, and tunnel arch bottom to ensure safe tunnel exit and guarantee the quality of subsequent construction inside the tunnel.

[0132] Specifically, the key control points for the CD method construction are as follows: The excavation cycle advance of the pilot tunnels (I: upper step of the pilot tunnel) and (II: lower step of the pilot tunnel) is controlled at one steel frame spacing (0.65-0.7m). The excavation of the subsequent pilot tunnels (III: upper step of the subsequent pilot tunnel) and (IV: lower step of the subsequent pilot tunnel) can be appropriately increased according to geological conditions, as detailed below. Figure 2 As shown.

[0133] During the construction of the tunnels on both sides, the longitudinal spacing should be greater than or equal to 2D (D being the maximum span of a single tunnel excavation); the distance between the upper and lower steps of the same pilot tunnel should be controlled at 3-5m. The excavation diameter and step height of the pilot tunnel can be adjusted appropriately according to the arrangement of construction machinery and personnel. The longitudinal connecting steel bars between steel frames should be installed in a timely manner and firmly connected. Before pouring the secondary lining, the temporary support of the central partition wall should be removed section by section. During removal, measurements should be strengthened, and the length removed at one time should generally not exceed 15m.

[0134] like Figure 2-4 As shown, the construction sequence of the CD method is as follows:

[0135] ① Excavation of the upper bench of the pilot tunnel on the side of the interlocking rock;

[0136] ② Initial (temporary) support for the upper bench of the pilot tunnel on the side of the interlocking rock, installation of steel frame;

[0137] ③ Excavation of the lower bench of the pilot tunnel in the middle interbedded rock;

[0138] ④ Initial (temporary) support for the lower bench of the pilot tunnel in the middle interlocking rock, extending the steel frame;

[0139] ⑤ Initial support of the invert arch of the pilot tunnel on the side of the interlocking rock, and the steel frame of the pilot tunnel forms a closed loop;

[0140] ⑥ Constructing the invert arch of the guide tunnel on the side of the interlocking rock;

[0141] ⑦ Excavation of the upper step of the pilot tunnel on the other side;

[0142] ⑧ Initial (temporary) support for the upper step of the other side of the pilot tunnel, installation of steel frame;

[0143] ⑨ Excavation of the lower step of the pilot tunnel on the other side;

[0144] ⑩ Initial (temporary) support for the lower step of the other side of the guide tunnel, extending the steel frame;

[0145] On the other side, the initial support of the pilot tunnel invert arch is completed, and the steel frame around the tunnel forms a closed loop.

[0146] The invert arch of the other pilot tunnel was poured;

[0147] The arch wall was poured with concrete around its entire circumference.

[0148] Compared to other tunnel excavation methods, the CD method significantly reduces crown settlement and horizontal convergence deformation, which helps control large deformations of the surrounding rock and prevents collapse accidents. While the CD method involves additional vertical temporary supports, resulting in significant fluctuations in the internal forces and deformations of the support structures in each section, the fluctuations are relatively smaller compared to the three-step, seven-stage excavation method, thus ensuring the stability of the tunnel's surrounding rock support system. From the perspective of support structure safety, using the CD method, supplemented by necessary pre-reinforcement measures, is beneficial for safe tunnel construction.

[0149] S3. Real-time monitoring of the entire construction process of the shallow buried section of the tunnel.

[0150] Preferably, real-time monitoring of the entire construction process of shallow-buried tunnel sections includes the following steps:

[0151] S31. Before the permanent support construction of the sump is completed, set up several monitoring points and equip them with GNSS stations to monitor the support construction.

[0152] It should be noted that before the permanent support construction of the stockpile was completed, four monitoring points were set up at the top of the stockpile, and the data of the GNSS fully automatic monitoring system was exported in a 20-day cycle. The monitoring data is shown in Table 1.

[0153] Table 1. Coordinates of monitoring points at the exit of Zhangjiawan Tunnel (before treatment)

[0154]

[0155] S31. After the permanent support construction of the accumulator is completed, several monitoring points are added and equipped with GNSS stations to monitor the displacement of the permanent support structure of the accumulator.

[0156] It should be noted that nine monitoring points were set up after the permanent support construction of the slab was completed, and the data from the GNSS fully automatic monitoring system was exported in a 20-day cycle. The monitoring data is shown in Table 2.

[0157] Table 2 Monitoring Points and Displacement at the Exit of Zhangjiawan Tunnel

[0158]

[0159]

[0160] In summary, by utilizing the above-mentioned technical solutions of this invention, the invention can treat the landslide debris and carry out tunnel exit construction while maintaining existing traffic flow. This improves the efficiency of landslide debris treatment and tunnel exit construction, shortens the overall tunnel construction period, increases the reliability of the tunnel exit section's engineering structure, reduces construction safety risks, and minimizes damage to the natural environment. This invention treats the landslide debris around the tunnel body using anti-slide piles, combines multiple support methods to increase the reliability of the landslide debris support, improve the permanent stability of the landslide debris, and adopts a comprehensive prevention-oriented approach to avoid future problems. It effectively prevents geological disasters such as landslide debris collapse and surface deformation, reduces the disturbance to the natural environment during on-site construction, protects surrounding structures, and uses micro-steel pipe piles + capping beams for the tunnel body. The above-ground accumulation is treated to address potential landslide risks during construction and ensure safety. This invention employs surface drainage, surface grouting reinforcement, and deformation monitoring to pre-reinforce and monitor the shallow-buried section of the tunnel, ensuring quality and safety during construction. The CD method is used for excavation and support of large-section shallow-buried tunnels, protecting existing roads and buildings above the tunnel, reducing excavated soil, minimizing land occupation, improving tunnel exit efficiency, shortening overall construction time, and ensuring construction safety. Dynamic adjustments to support parameters based on data from tunnel roof settlement, arch waist convergence, and tunnel arch bottom monitoring ensure safe tunnel exit and guarantee subsequent construction quality within the tunnel.

[0161] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A treatment method suitable for a poor geological tunnel shallow-buried portal, characterized in that, The treatment method applicable to shallow-buried tunnel entrances in geologically unfavorable geology includes the following steps: S1. Initial support for the accumulation material at the tunnel entrance section of a mountain expressway; S2. Construction of shallow buried tunnel sections based on guide walls, large pipe sheds and CD method; S3. Real-time monitoring of the entire construction process of the shallow buried section of the tunnel; The initial support for the accumulation at the entrance section of a mountain highway tunnel includes the following steps: S11. Circular anti-slide piles are installed on both the left and right sides of the tunnel body; S12. Steel pipe piles are installed within the tunnel body, and a capping beam is installed on top of the steel pipe piles; S13. Surface grouting is used to reinforce the slope of the section from the circular anti-slide piles and steel pipe piles to the tunnel entrance. S14. Based on the relative position of the sliding surface and the slope, an anti-slip retaining wall shall be installed on the upper part of the first-level slope. S15. Mechanical construction methods are adopted, and slope brushing and load reduction are carried out according to the preset slope ratio; The circular anti-slide pile is located at a distance of 4m or more from the tunnel excavation outline, and the pile hole of the circular anti-slide pile is formed by rotary drilling rig. The steel pipe piles are arranged in a quincunx pattern, and the pile holes of the steel pipe piles are formed using a crawler-type geological drilling rig. Both the circular anti-slide pile and the steel pipe pile are constructed using C30 concrete. The surface grouting uses steel pipes with a diameter of 89mm arranged in a quincunx pattern; The foundation and wall body of the anti-slide retaining wall are both made of reinforced gabion stone cages. The toe of the anti-slide retaining wall is buried at a depth greater than or equal to 1m. The mountain-facing side of the anti-slide retaining wall is equipped with permeable geotextile. The bottom of the anti-slide retaining wall is equipped with impermeable geotextile. The back of the anti-slide retaining wall is backfilled and compacted with crushed stone soil. The method of using mechanical construction and reducing the load by brushing the slope according to a preset slope ratio includes the following steps: S151. Mark the slope boundary and construct a combined permanent and temporary drainage system according to the preset requirements; S152. Excavators are used to excavate and load earth according to the preset slope, and dump trucks are used to transport the earth to the spoil disposal site.

2. The treatment method for shallow-buried tunnel entrances in adverse geological conditions of silt deposits according to claim 1, characterized in that, The tunnel exit construction based on guide walls, large pipe sheds, and CD method includes the following steps: S21. Construction of guide walls is carried out in the shallow buried section of the tunnel exit. S22. Construction of large pipe sheds will be carried out in the shallow buried section of the tunnel exit. S23. The CD method is used for excavation and support of large-section shallow-buried tunnels. S24. Dynamically adjust the support parameters based on the monitoring data of the tunnel arch settlement, arch waist convergence and tunnel arch bottom.

3. The method according to claim 1, wherein the method is characterized in that, The real-time monitoring of the entire construction process of the shallow-buried section of the tunnel includes the following steps: S31. Before the permanent support construction of the sump is completed, set up several monitoring points and equip them with GNSS stations to monitor the support construction. S31. After the permanent support construction of the accumulator is completed, several monitoring points are added and equipped with GNSS stations to monitor the displacement of the permanent support structure of the accumulator.

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