Ultra-shallow-buried under-crossing highway tunnel pipe shed supporting structure and method

Abstract

The invention provides an ultra-shallow-buried under-crossing highway tunnel pipe shed supporting structure which comprises a large steel pipe and a small steel pipe arranged in the large steel pipe, and the inner diameter of the large steel pipe is larger than the outer diameter of the small steel pipe so that the small steel pipe can be arranged in the large steel pipe; the large steel pipes and the small steel pipes are filled with concrete to form cement mortar, and the whole pipe shed supporting structure is formed to improve the flexural rigidity. Pipe shed structural forms with different flexural rigidities can be reasonably selected based on actual conditions, material waste of high-specification pipe sheds in low-stress areas is avoided, engineering cost and resource consumption are effectively reduced, the method conforms to the green and environment-friendly concept, tunnel vault sinking and ground surface settlement can be greatly reduced, and the construction efficiency is improved. And the tunnel construction safety and the surrounding environment stability are practically guaranteed. The invention further provides an ultra-shallow-buried under-crossing highway tunnel pipe shed supporting method.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a pipe-roof support structure and method for an ultra-shallow buried underpass highway tunnel. Background Art

[0002] In ultra-shallow underground highway tunnel projects, pipe-roof support is a crucial measure to ensure tunnel construction safety and surrounding rock stability. Traditional pipe-roof support structures typically utilize a single steel pipe or other simple structures, which have limited flexural stiffness and load-bearing capacity. In the complex engineering environment of ultra-shallow underground highway tunnels, where surface settlement requirements are high and surrounding rock stress distribution is complex, traditional pipe-roof support systems struggle to effectively resist surrounding rock deformation and external loads. This can lead to pipe-roof bending and fracture, compromising tunnel construction safety and the operational safety of the upper road.

[0003] In the related art, a method for advanced support of a pipe shed with built-in steel sections and its application are disclosed, and the steps are as follows: transport the processed seamless steel pipes and I-beams to the site; use drilling equipment to drill holes and deliver pipes; insert the I-beams that match the seamless steel pipes into the seamless steel pipes; weld the I-beam flanges to the inner wall of the seamless steel pipes at the exposed end parts; use grouting equipment to grout the I-beams, seamless steel pipes and cement slurry to form a pipe shed; when the strength of the grouting body reaches the design requirements, construct the underground structure from top to bottom. This scheme uses a shallow buried and dark excavated pipe shed, which is a combination of I-beams, seamless steel pipes and cement slurry. It can improve the rigidity of the pipe shed, is beneficial to the protection of existing buildings and structures above, and also improves the safety of dark excavation construction. Although the seamless steel pipes, I-beams and grouting bodies form a beam with relatively high rigidity, this is only a fixed form. For complex engineering environments such as ultra-shallow buried underpasses in highway tunnels, it is necessary to consider both support strength and construction costs.

[0004] In the existing technology, the research on the mechanical properties of pipe-roof support structures mostly remains at the empirical level, lacking a systematic bending stiffness calculation method and comparative analysis of multiple cross-section forms. Therefore, there is an urgent need to develop a new type of pipe-roof support structure with scientific calculation theory support and high bending stiffness characteristics. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies in the above-mentioned background technology and provide a pipe-roof support structure and corresponding method for ultra-shallow buried underpass highway tunnels or similar engineering environments, which can improve the bending stiffness, bearing capacity and integrity of the pipe-roof, effectively control the deformation of the surrounding rock and reduce the impact on road operations. The structure and corresponding method can be adapted to different actual conditions to ensure the long-term stability of tunnel construction and operation.

[0006] To achieve the above-mentioned object, the present invention provides a pipe-roof support structure for an ultra-shallow buried underpass highway tunnel, comprising a large steel pipe and a small steel pipe disposed inside the large steel pipe. The inner diameter of the large steel pipe is larger than the outer diameter of the small steel pipe, so that the small steel pipe can be disposed inside the large steel pipe. Concrete is filled between the large steel pipe and the small steel pipe to form cement mortar, forming an overall pipe-roof support structure to improve bending stiffness.

[0007] The small steel pipe has a preset cross-sectional shape;

[0008] The large steel pipe and the small steel pipe are both prefabricated into standard lengths, and the standard length of the large steel pipe is equal to the standard length of the small steel pipe.

[0009] Furthermore, the cross-section of the small steel tube is circular or rectangular.

[0010] Furthermore, the centroids of the large steel pipe and the small steel pipe coincide with the centroid of the slurry formed by the concrete, and the small steel pipe includes a small round steel pipe and a rectangular steel pipe.

[0011] In this case, the moment of inertia of the pipe-roof support structure as a whole is:

[0012]

[0013] Among them, D1 is the diameter of the large steel pipe, d1 is the inner diameter of the large steel pipe, D2 is the diameter of the small round steel pipe, d2 is the inner diameter of the small round steel pipe, h is the length of the rectangular steel pipe section, b is the width of the rectangular steel pipe section, and d is the thickness of the rectangular steel pipe;

[0014] The moment of inertia of the cement mortar formed by grouting is:

[0015]

[0016] The bending stiffness of the entire pipe roof is:

[0017] EI=E s I s +E c I c

[0018] Among them, E is the elastic modulus of the pipe roof, E s is the elastic modulus of steel, E c is the elastic modulus of cement mortar.

[0019] Alternatively, the centroids of the large steel pipe and the small steel pipe do not coincide with the centroid of the slurry formed by the concrete, and the small steel pipe includes a small round steel pipe and a rectangular steel pipe.

[0020] In this case, the moment of inertia of the pipe-roof support structure as a whole is:

[0021]

[0022] Wherein, D1 is the diameter of the large steel pipe, d1 is the inner diameter of the large steel pipe, D2 is the diameter of the small round steel pipe, d2 is the inner diameter of the small round steel pipe, h is the length of the rectangular steel pipe section, b is the width of the rectangular steel pipe section, d is the thickness of the rectangular steel pipe, and a is the vertical distance from the centroid of the large steel pipe to the centroid of the small steel pipe;

[0023] The moment of inertia of cement mortar is:

[0024]

[0025] Therefore, the bending stiffness of the entire pipe roof is:

[0026] EI=E s I s +E c I c

[0027] Among them, E is the elastic modulus of the pipe roof, E s is the elastic modulus of steel, E c is the elastic modulus of cement mortar.

[0028] The present invention also provides a pipe-roof support method for an ultra-shallow buried underpass highway tunnel, which adopts the above-mentioned pipe-roof support structure for an ultra-shallow buried underpass highway tunnel, and comprises the following steps:

[0029] S1: Based on the overburden load and vehicle load, and taking into account the actual engineering parameters, the bending stiffness of the pipe shed that meets the bearing capacity requirements is calculated. Combined with geological radar scanning data and numerical simulation analysis, the pipe shed layout area is accurately divided;

[0030] S2: Based on the general formula for calculating the bending stiffness of the pipe roof section, determine the pipe roof structure that matches the numerical simulation results of step S1. Based on the stress distribution characteristics of different areas, accurately select the pipe roof structure from a variety of designed forms.

[0031] S3, construction of arch foundation;

[0032] S4, installation of arch steel frame and guide tube;

[0033] S5, arch concrete construction;

[0034] S6, adopts factory prefabrication, produces large and small steel pipes according to preset lengths, and the structural form is based on S2;

[0035] S7, drilling construction;

[0036] S8, first align the first section of the large steel pipe of the pipe rack with the guide hole, and use the drilling rig to advance it at a low speed. When the first section of the large steel pipe is pushed into the hole and the preset length remains outside the hole, the jacking coupling sleeve is separated from the first section of the large steel pipe; then, the second section of the small steel pipe is hoisted to the same height as the first section of the large steel pipe, and the drilling rig is slowly advanced at a low speed to align it with the end of the first section of the large steel pipe. The second section of the small steel pipe is connected to the first section of the large steel pipe manually or with equipment; the second section of the large steel pipe is connected to the first section of the large steel pipe in the same way; each section is extended and jacked into the pipe rack, and each section has a preset length remaining outside the hole to facilitate the connection of the next section;

[0037] S9. A grouting pipe and a return grouting pipe are set at the end of the pipe rack. Grouting is carried out through the grouting pipe, and excess grout is recovered through the return grouting pipe to assist in judging the grouting effect.

[0038] Furthermore, grouting holes are set on the pipe walls of the large steel pipe and the small steel pipe in S6 according to preset longitudinal and transverse spacings, and at the same time, a grouting stop section without drilling holes is retained at the tail of the large steel pipe, and a grouting stop section without drilling holes is also retained at the tail of the small steel pipe.

[0039] Furthermore, in S8, the small steel pipe is firmly connected to the corresponding large steel pipe by welding, so as to prevent the small steel pipe from floating up and causing deviation during grouting.

[0040] Furthermore, in S9, the grouting pipe is arranged in the small steel pipe, and the slurry return pipe is arranged in the large steel pipe.

[0041] The above solution of the present invention has the following beneficial effects:

[0042] The pipe-roof support structure and method for ultra-shallow buried underpass highway tunnels provided by the present invention can, based on a scientific pipe-roof zoning selection strategy, reasonably select pipe-roof structural forms with different bending stiffnesses while ensuring project safety, thereby avoiding material waste of high-specification pipe-roofs in low-stress areas, effectively reducing project costs and resource consumption, and conforming to the concept of green environmental protection; the steel pipe-concrete-steel pipe combined pipe-roof structure provided by the present invention utilizes increased cross-sectional bending stiffness and material synergistic working characteristics to significantly improve the pipe-roof's ability to resist surrounding rock deformation and external loads, greatly reducing tunnel vault subsidence and surface settlement, and effectively ensuring tunnel construction safety and surrounding environmental stability; the supporting method provided by the present invention has reasonable procedures and high efficiency, has little impact on the upper road, can effectively reduce construction risks, shorten construction period, and has both good economic and social benefits;

[0043] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the cross section of the pipe-roof support structure of the present invention (the centroid of the steel pipe and the slurry coincide);

[0045] Figure 2 Schematic diagram of the cross section of the pipe-roof support structure of the present invention (the centroid of the steel pipe and the slurry do not coincide);

[0046] Figure 3 A flowchart of the method of the present invention;

[0047] Figure 4 This is a schematic diagram of the pipe rack layout area division of the present invention.

[0048] [Description of Reference Numerals]

[0049] 1-Large steel pipe; 2-Small round steel pipe; 3-Rectangular steel pipe; 4-Cement mortar. DETAILED DESCRIPTION

[0050] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to a locking connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0053] like Figure 1 、 Figure 2As shown, an embodiment of the present invention provides a pipe-roof support structure for an ultra-shallow buried highway tunnel, comprising a large steel pipe 1 and a small steel pipe disposed within the large steel pipe 1. The inner diameter of the large steel pipe 1 is larger than the outer diameter of the small steel pipe, allowing the small steel pipe to be arranged within the large steel pipe 1. The space between the large steel pipe 1 and the small steel pipe is filled with concrete, forming an integrated support structure.

[0054] It should be noted that the large steel pipe 1 itself is consistent with the size specifications commonly used in pipe sheds in the prior art, and therefore adopts the form of a round pipe, including specifications such as 108*6mm and 159*6mm. The large steel pipe 1 is of standard length when prefabricated in the factory, for example, 4m. When assembled into a pipe shed at the construction site, multiple sections of large steel pipes 1 of standard length are spliced together. The cross-sectional shapes of small steel pipes include commonly used forms such as circular and rectangular, and may also include other forms. Similarly, the small steel pipe 1 maintains a standard length consistent with the large steel pipe 1 when prefabricated in the factory, which facilitates the corresponding splicing of multiple sections at the construction site.

[0055] For this steel pipe-concrete-steel pipe combination, its bending strength is significantly improved compared to the single large steel pipe 1. Therefore, it is necessary to calculate the bending stiffness of this steel pipe-concrete-steel pipe combination. The bending stiffness calculation of the pipe-roof section is divided into two cases: centroid coincidence and centroid non-coincidence. For the case of centroid coincidence (the centroid of the steel pipe and the slurry coincide), consider using two common pipes, small round steel pipe 2 or rectangular steel pipe 3, to reinforce the large steel pipe 1. The overall moment of inertia of the steel pipe is:

[0056]

[0057] Among them, D1 is the diameter of the large steel pipe 1, d1 is the inner diameter of the large steel pipe 1, D2 is the diameter of the reinforced small round steel pipe 2, d2 is the inner diameter of the reinforced small round steel pipe 2, h is the cross-sectional length of the reinforced rectangular steel pipe 3, b is the cross-sectional width of the reinforced rectangular steel pipe 3, and d is the thickness of the reinforced rectangular steel pipe 3.

[0058] The moment of inertia of the cement mortar 4 (or cement paste) formed by grouting is:

[0059]

[0060] Therefore, the bending stiffness of the entire pipe roof is:

[0061] EI=E s I s +E c I c

[0062] Among them, E is the elastic modulus of the pipe roof, E s is the elastic modulus of steel, E c is the elastic modulus of cement mortar 4 (or cement paste).

[0063] For the case where the centroids do not coincide (the centroids of the steel pipe and the slurry do not coincide), the two common pipe materials, small round steel pipe 2 or rectangular steel pipe 3, are also considered to reinforce the large steel pipe 1. The moment of inertia of the entire steel pipe is:

[0064]

[0065] Among them, D1 is the diameter of the large steel pipe 1, d1 is the inner diameter of the large steel pipe 1, D2 is the diameter of the reinforced small round steel pipe 2, d2 is the inner diameter of the reinforced small round steel pipe 2, h is the cross-sectional length of the reinforced rectangular steel pipe 3, b is the cross-sectional width of the reinforced rectangular steel pipe 3, d is the thickness of the reinforced rectangular steel pipe 3, and a is the vertical distance from the centroid of the large steel pipe 1 to the centroid of the small steel pipe.

[0066] The moment of inertia of cement mortar 4 (or cement paste) is:

[0067]

[0068] Therefore, the bending stiffness of the entire pipe roof is:

[0069] EI=E s I s +E c I c

[0070] Among them, E is the elastic modulus of the pipe roof, E s is the elastic modulus of steel, E c is the elastic modulus of cement mortar 4 (or cement paste).

[0071] Based on the above, the flexural stiffness of various reinforced pipe-roof structures can be calculated, and the comparison results are summarized in Table 1. This result can provide reliable data support for the subsequent design and selection of pipe-roof structures.

[0072] Table 1 Results of improvement in bending stiffness of pipe sheds with different structural forms and specifications

[0073]

[0074]

[0075] It can be seen from Table 1 that the use of curved cross-section steel pipes to reinforce the interior of the large steel pipe 1 has a more obvious effect on improving the bending stiffness of the pipe roof.

[0076] The embodiment of the present invention also provides a method for an ultra-shallow buried tunnel under a highway tunnel, based on the above-mentioned tunnel support structure, and at the same time, Figure 3 As shown, it specifically includes the following sub-steps:

[0077] S1, pipe shed area division. The pipe shed is simplified into a simply supported beam, which bears the load of the overburden and the vehicle load. Combining geological radar scanning data and numerical simulation analysis, the actual engineering parameters are comprehensively considered to calculate the bending stiffness of the pipe shed that meets the load-bearing requirements, and the pipe shed layout area is divided accordingly. If the upper part is covered with uniform thickness of soil, the pipe shed layout area can be divided into three areas, such as Figure 4 The stress of the pipe shed in the middle area I is relatively large, and it needs to be matched with a pipe shed with greater bending stiffness. The stress of the pipe shed in areas II and III is relatively small, and the same type of pipe shed can be arranged symmetrically, and the bending stiffness is smaller than that in area I.

[0078] S2: Select the pipe roof structure. Based on the general formula for calculating the bending stiffness of a pipe roof section, determine the pipe roof structure that matches the numerical simulation results of step S1. Optimize the pipe roof structure design and accurately select the pipe roof structure from a variety of designs based on the stress distribution characteristics of different areas.

[0079] In this embodiment, pipe roofs with corresponding bending stiffness can be arranged in a targeted manner according to the stress requirements of different areas to achieve precise matching of the pipe roof structure and the engineering stress. This design method of arranging pipe roofs according to stress zones reasonably distributes material strength and avoids material waste while ensuring the overall safety and reliability of the pipe roof structure, thereby achieving the effect of saving resources and realizing green and environmentally friendly construction goals.

[0080] S3: Construction of the sleeve arch foundation. It should be noted that the bearing capacity of the sleeve arch foundation must be tested before construction. If it is less than 0.3 MPa, replacement backfill with appropriate materials such as graded sand and gravel, lime soil, etc. is required. The depth and extent of the replacement backfill will be determined based on the actual geological conditions on site. Furthermore, the waterproofing and drainage system at the tunnel entrance should be strengthened. An intercepting ditch should be installed above the tunnel entrance to intercept surface water. Drainage ditches should be constructed on both sides of the tunnel entrance. The tunnel entrance drainage outlet should be integrated with the external road drainage network to form a drainage system, diverting accumulated water away from the construction area, preventing rainwater from eroding the road, slopes, and sleeve arch foundation, and ensuring safe and stable foundation construction. The intercepting ditch collects water through the drainage channel at the top of the end wall and directs it into the roadbed drainage network. The intercepting ditch should be located 5 meters outside the excavation line on the side slope, with a slope of no less than 3%. Slope treatment must ensure slope flatness and structural stability, and installation should not be placed close to the slope. The longitudinal slope of the drainage ditch should be constructed strictly according to the drawings, with a flat bottom, unobstructed drainage, and no water obstruction.

[0081] S4, installation of the arch steel frame and the guide tube. After the foundation concrete reaches the strength standard, the arch steel frame is installed. In one of the specific implementation methods, 8 double-layer I18b I-beam steel frames are installed in sequence at a spacing of 0.6m. After the three units of each steel frame are processed on the ground, they are transported to the site for splicing. When splicing, ensure that the curvature and size of each section of the steel frame meet the design, and each unit is welded and firmly connected with bolts through the connecting plate, and the connecting plate fits tightly. After the processing is completed, a trial splicing inspection is carried out, and a certain margin is reserved considering the settlement of the steel section. Between the two steel frames, Φ25 steel bars are arranged longitudinally at a circumferential spacing of 1m, and are firmly welded to the steel frame to enhance the overall stability.

[0082] For guide pipe installation, select seamless steel pipes with pre-set specifications, such as 127mm diameter, 4mm wall thickness, and 2.0m length, and bury them at circumferential intervals of 0.4m. While the pipe shed sleeve is typically 2.0m long, this can be extended based on the surrounding rock conditions and construction requirements to ensure a tight connection between the guide pipe and the underground excavation. During guide pipe installation, the external insertion angle must align with the designed pipe shed angle, and the pipe shed sleeve must fit snugly against the surrounding rock surface to prevent grouting during injection.

[0083] S5, arch concrete construction. Use custom steel formwork. Before installation, evenly apply release agent to the contact surface between the formwork and the concrete to facilitate demolding. The formwork should be installed securely and stably, with precise dimensions. After installation, perform a rigorous inspection to ensure the correct placement of embedded components. The formwork's centerline, levelness, and overall dimensions must meet design standards.

[0084] When pouring the arch concrete, a preset concrete model, such as C30 concrete, is used. It is centrally mixed at a mixing station and transported to the site by concrete tankers. When pouring, the process is carried out symmetrically on both sides of the arch foot, and manual and mechanical vibration are used to ensure that the concrete is dense and to avoid defects such as honeycombs and rough surfaces. When pouring to the top of the arch, pay attention to ensuring that the concrete is full. After the concrete is poured, it must be maintained in a timely manner. The maintenance method can be covering with watering or spraying curing agents, and the curing age must be no less than 7 days. When the concrete strength reaches 70% of the design strength, the outer formwork and end formwork are removed; when it reaches 100%, the inner formwork and support are removed. The excavation surface is sealed by spraying C20 concrete to form a slurry stop wall to prevent the slurry from flowing back and affecting the grouting effect.

[0085] S6, pipe shed production. Factory prefabrication is used to produce large steel pipes 1 and small steel pipes (reinforced steel pipes inside the large steel pipe 1) of preset length, for example, 4m. The structural form is customized according to S2. The front end of the first section of the large steel pipe 1 is welded into a cone shape to facilitate jacking and prevent the pipe head from bending or splitting. Φ15mm grouting holes are drilled in a plum blossom shape on the pipe walls of the large steel pipe 1 and the small steel pipe at preset longitudinal spacing, for example, 30cm, and transverse spacing, for example, 15cm. A 450cm non-drilled grouting stop section is set at the tail of the large steel pipe 1. No grouting holes are set within the 1 / 3 pipe shed length at the tail of the small steel pipe.

[0086] S7, drilling construction. Use a pipe-roof drilling rig equipped with a Φ120mm drill bit. Determine the height of the drilling rig platform based on the drilling sequence and the adjustable range of the drilling rig. The drilling rig platform must be constructed to withstand the load of machinery, materials, and personnel, and must be firmly and stably connected. When the drilling rig is in place, use a combination of a total station, hanging lines, and drill rod guides to repeatedly adjust the drill rod axis and the guide axis to coincide. When drilling, first drill at a low speed and low pressure for a preset distance, such as 10m, and then gradually adjust the drilling speed and air pressure according to the geological conditions. During the drilling process, use an inclinometer to measure the drilling deviation in real time to ensure that the power unit, stabilizer, and alloy drill bit drill in concentric circles. The construction sequence is to construct odd-numbered holes first, followed by even-numbered holes; and to construct high-position holes first, followed by low-position holes.

[0087] In addition, after the drilling is completed, it is necessary to conduct a hole excavation inspection to ensure that there is no hole collapse and the rock debris is cleaned up. Then report the inspection and wait for the installation of the pipe shed.

[0088] S8, pipe jacking construction. First, align the first section of the large steel pipe 1 of the pipe shed with the guide hole, and use a drill to push it forward at a low speed. When the first section of the large steel pipe 1 is pushed into the hole and there is 30 to 40 cm left outside the hole, start the drill to reverse and separate the jacking coupling sleeve from the first section of the large steel pipe 1. Then use an excavator to lift the second section of the small steel pipe to the same height as the first section of the large steel pipe 1. The drill moves forward slowly and at a low speed to align it with the end of the first section of the large steel pipe 1. Use a manual chain clamp to connect it so that the second section of the small steel pipe is connected to the first section of the large steel pipe 1 as a whole. Connect the second section of the large steel pipe 1 to the first section of the large steel pipe 1 in the same way. In this way, lengthen each section one by one and push it into the pipe shed. Each section has the above distance left outside the hole to facilitate the connection of the next section, and the installation of the entire pipe shed is completed.

[0089] Among them, the small steel pipe can be firmly connected to the corresponding large steel pipe 1 by direct welding to prevent the small steel pipe from floating during grouting, and avoid deviation between the actual bending stiffness and the calculated value during the installation of the overall pipe rack and subsequent grouting.

[0090] S9, pipe roof grouting. Following the principle of "low first, high later, both sides first, middle later, and from thin to thick", PO42.5 ordinary Portland cement is selected in this embodiment, and a cement slurry with a water-cement ratio of 1:1 is prepared, and water glass with a volume of 5% of the cement slurry is added. Use 2 to 3 grouting pumps for grouting, and set a grouting pipe and a return grouting pipe at the end of the pipe roof. The return grouting pipe is used to recover excess slurry and assist in judging the grouting effect. During the grouting process, pay close attention to the changes in grouting pressure and grouting volume. When the pressure reaches the designed grouting final pressure and stabilizes for 10 to 15 minutes, and the grouting volume reaches more than 80% of the designed grouting volume, the grouting of the hole is terminated.

[0091] Typically, a grouting pipe is disposed in a small steel pipe, and a slurry return pipe is disposed in a large steel pipe, so that the slurry can fully fill the gap between the large steel pipe and the small steel pipe.

[0092] It should be noted that if slurry seepage occurs, multiple grouting pumps can be used to inject grout simultaneously or block the slurry from seeping through the holes; if the grouting volume is large and the pressure does not increase for a long time, the slurry concentration and mix ratio should be adjusted to shorten the gelation time, and small amounts of low-pressure grouting or intermittent grouting should be performed to allow the slurry to have a relative residence time in the cracks to facilitate gelation, but the residence time cannot exceed the gelation time of the mixed slurry to avoid incomplete grouting.

[0093] As described above, the pipe-roof support structure and method for the ultra-shallow buried underpass highway tunnel provided in this embodiment can, based on a scientific pipe-roof zoning selection strategy, reasonably select pipe-roof structures with different bending stiffnesses while ensuring project safety, thereby avoiding material waste of high-specification pipe-roofs in low-stress areas, effectively reducing project costs and resource consumption, and conforming to the concept of green environmental protection; this steel pipe-concrete-steel pipe combined pipe-roof structure utilizes increased cross-sectional bending stiffness and material synergistic working characteristics to significantly improve the ability of the pipe-roof to resist surrounding rock deformation and external loads, greatly reducing tunnel vault subsidence and surface settlement, and effectively ensuring tunnel construction safety and surrounding environmental stability; the supporting method and process are reasonable and efficient, with little impact on the upper road, which can effectively reduce construction risks, shorten construction period, and have both good economic and social benefits.

[0094] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A pipe-roof support structure for an ultra-shallow buried underpass highway tunnel, characterized in that: The invention comprises a large steel pipe (1) and a small steel pipe arranged inside the large steel pipe (1); the inner diameter of the large steel pipe (1) is larger than the outer diameter of the small steel pipe, so that the small steel pipe can be arranged inside the large steel pipe (1); the space between the large steel pipe (1) and the small steel pipe is filled with concrete to form cement mortar (4), thereby forming an integral pipe shed support structure to improve bending stiffness; The small steel pipe has a preset cross-sectional shape; The large steel pipe (1) and the small steel pipe are both prefabricated into standard lengths, and the standard length of the large steel pipe (1) is equal to the standard length of the small steel pipe.

2. The pipe-roof support structure for an ultra-shallow buried underpass highway tunnel according to claim 1 is characterized in that: The cross-section of the small steel pipe is circular or rectangular.

3. The pipe-roof support structure for an ultra-shallow buried underpass highway tunnel according to claim 1 is characterized in that: The centroids of the large steel pipe (1) and the small steel pipe coincide with the centroid of the slurry formed by the concrete, and the small steel pipe comprises a small round steel pipe (2) and a rectangular steel pipe (3).

4. The pipe-roof support structure for an ultra-shallow buried underpass highway tunnel according to claim 3 is characterized in that: The overall moment of inertia of the pipe-roof support structure is: Wherein, D1 is the diameter of the large steel pipe (1), d1 is the inner diameter of the large steel pipe (1), D2 is the diameter of the small round steel pipe (2), d2 is the inner diameter of the small round steel pipe (2), h is the cross-sectional length of the rectangular steel pipe (3), b is the cross-sectional width of the rectangular steel pipe (3), and d is the thickness of the rectangular steel pipe (3); The moment of inertia of the cement mortar (4) formed by grouting is: The bending stiffness of the entire pipe roof is: EI=E s ESSENTIAL s +E c ESSENTIAL c Among them, E is the elastic modulus of the pipe roof, E s is the elastic modulus of steel, E c is the elastic modulus of cement mortar (4).

5. The pipe-roof support structure for an ultra-shallow buried underpass highway tunnel according to claim 1 is characterized in that: The centroids of the large steel pipe (1) and the small steel pipe do not coincide with the centroid of the slurry formed by the concrete, and the small steel pipe comprises a small round steel pipe (2) and a rectangular steel pipe (3).

6. The pipe-roof support structure for an ultra-shallow buried underpass highway tunnel according to claim 5 is characterized in that: The overall moment of inertia of the pipe-roof support structure is: Wherein, D1 is the diameter of the large steel pipe (1), d1 is the inner diameter of the large steel pipe (1), D2 is the diameter of the small round steel pipe (2), d2 is the inner diameter of the small round steel pipe (2), h is the cross-sectional length of the rectangular steel pipe (3), b is the cross-sectional width of the rectangular steel pipe (3), d is the thickness of the rectangular steel pipe (3), and a is the vertical distance from the centroid of the large steel pipe (1) to the centroid of the small steel pipe; The moment of inertia of cement mortar (4) is: Therefore, the bending stiffness of the entire pipe roof is: EI=E s ESSENTIAL s +E c ESSENTIAL c Among them, E is the elastic modulus of the pipe roof, E s is the elastic modulus of steel, E c is the elastic modulus of cement mortar (4).

7. A pipe-roof support method for an ultra-shallow buried underpass highway tunnel, using the pipe-roof support structure for an ultra-shallow buried underpass highway tunnel according to any one of claims 1 to 6, characterized in that: The steps include: S1: Based on the overburden load and vehicle load, and taking into account the actual engineering parameters, the bending stiffness of the pipe shed that meets the bearing capacity requirements is calculated. Combined with geological radar scanning data and numerical simulation analysis, the pipe shed layout area is accurately divided; S2: Based on the general formula for calculating the bending stiffness of the pipe roof section, determine the pipe roof structure that matches the numerical simulation results of step S1. Based on the stress distribution characteristics of different areas, accurately select the pipe roof structure from a variety of designed forms. S3, construction of arch foundation; S4, installation of arch steel frame and guide tube; S5, arch concrete construction; S6, adopts factory prefabrication, produces large steel pipe (1) and small steel pipe according to preset length, and the structure is carried out according to S2; S7, drilling construction; S8, first align the first section of the large steel pipe (1) of the pipe shed with the guide hole, and use a drilling rig to push it forward at a low speed. When the first section of the large steel pipe (1) is pushed into the hole and the remaining preset length outside the hole, the jacking coupling sleeve is separated from the first section of the large steel pipe (1); then the second section of the small steel pipe is lifted up to the same height as the first section of the large steel pipe (1), and the drilling rig is slowly advanced at a low speed to align it with the end of the first section of the large steel pipe (1), and the second section of the small steel pipe is connected to the first section of the large steel pipe (1) manually or by equipment; the second section of the large steel pipe (1) is connected to the first section of the large steel pipe (1) in the same way; each section is lengthened and pushed into the pipe shed, and each section has a preset length remaining outside the hole to facilitate the connection of the next section; S9. A grouting pipe and a return grouting pipe are set at the end of the pipe rack. Grouting is carried out through the grouting pipe, and excess grout is recovered through the return grouting pipe to assist in judging the grouting effect.

8. The pipe-roof support method for an ultra-shallow buried underpass highway tunnel according to claim 7 is characterized in that: Grouting holes are set on the pipe walls of the large steel pipe (1) and the small steel pipe in S6 according to preset longitudinal and transverse spacings, and at the same time, a grouting stop section without drilling holes is retained at the tail of the large steel pipe (1), and a grouting stop section without drilling holes is also retained at the tail of the small steel pipe.

9. The pipe-roof support method for an ultra-shallow buried underpass highway tunnel according to claim 7, characterized in that: In S8, the small steel pipe is firmly connected to the corresponding large steel pipe (1) by welding, so as to prevent the small steel pipe from floating up and causing deviation during grouting.

10. The pipe-roof support method for an ultra-shallow buried underpass highway tunnel according to claim 7, characterized in that: In S9, the grouting pipe is arranged in the small steel pipe, and the grouting pipe is arranged in the large steel pipe (1).

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