A construction method for large-section tunnels passing through goaf based on small pilot tunnel method

Abstract

The present invention relates to the technical field of tunnel construction and discloses a construction method for a large-section tunnel crossing a goaf based on a small pilot tunnel method. The construction method comprises: step S1: determining the excavation position of an advance small pilot tunnel; step S2: excavating the tunnel face of part I of the advance small pilot tunnel, providing permanent support on the side of the single side wall of part I of the advance small pilot tunnel close to the tunnel contour, providing temporary support on the remaining tunnel faces, drilling holes in the goaf to discharge gas and water in the goaf, grouting around the advance small pilot tunnel to form a grouting wall, and grouting into the goaf construction area; step S3: excavating the tunnel faces of parts II, III, and IV of the advance small pilot tunnel, and supporting the entire tunnel after the tunnel faces of parts II, III, and IV of the advance small pilot tunnel have been excavated and passed through the goaf. The present invention alleviates the damage to the original stress of the goaf and reduces the threat of gas and water seepage in the goaf by excavating the advance small pilot tunnel, releasing gas, and expanding the excavation to achieve penetration.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, in particular to a construction method for a large-section tunnel passing through a goaf based on a small pilot tunnel method. Background Art

[0002] Small pilot tunnel construction techniques for crossing goafs. Goafs are a major challenge in tunnel construction. The effectiveness of treatment techniques and safety measures directly impacts tunnel construction and operational safety. The spatial relationship between the goaf and the tunnel is a key factor in determining goaf treatment measures.

[0003] When constructing highways in mountainous areas rich in underground resources, tunneling projects inevitably involve crossing existing goafs, constrained by specific design parameters such as geometry and longitudinal slope, as well as specific mining conditions. While technological advancements have advanced tunneling techniques through goafs, they still face numerous challenges that impact construction techniques. Goaf characteristics, specifically their impact on surrounding rock stability, can disrupt the stability of existing goafs, disrupting the original stress balance in the coal mining area and creating caving zones, fractures, and deflection zones in the overlying rock mass. This reduces the goaf's bearing capacity and makes it unstable over the long term. Gas within goafs can cause explosions, fires, and poisoning, posing direct risks to health. Gas mixed with air can easily cause fires. When gas concentrations exceed certain limits, even a small ignition source can spark a major fire, causing damage and injury. Gas outbursts can also destroy and block tunnels, further compromising construction safety. Therefore, effective ventilation safety measures must be implemented within goafs to prevent gas hazards to humans and the environment. Tunnel excavation inevitably disturbs the underground rock and soil, disrupting the original equilibrium and transitioning to a new one. Therefore, a construction method for large-section tunnels through goafs based on a small pilot tunnel method is urgently needed. This method can relieve pressure, minimize instability in old goafs, and further ensure construction progress and safety. Summary of the Invention

[0004] The purpose of the present invention is to provide a construction method for a large-section tunnel crossing a goaf based on a small pilot tunnel method, so as to solve the instability of the goaf. The rock strata in the goaf are extremely unstable and have many cracks due to the collapse of the goaf roof, and the coal seam itself contains a lot of gas, which can greatly affect the construction. By drilling along the direction of the coal seam in the goaf to discharge gas and water and grouting along the layer through drilling, the gas and water outside the goaf construction area can be blocked from penetrating into the goaf construction area.

[0005] The present invention provides a construction method for a large-section tunnel passing through a goaf based on a small pilot tunnel method, the construction method comprising:

[0006] Step S1: Determine the excavation position of the advance small pilot tunnel;

[0007] The excavation position of the advance small pilot tunnel is the single side wall of the tunnel upper step on the side where the vertical distance between the tunnel face and the goaf is closest;

[0008] Step S2: Excavation of the tunnel face of the first part of the advance small pilot tunnel;

[0009] Step S2.1: Advance from the upper step of the tunnel toward the goaf until the vertical distance between the tunnel and the goaf is 7m, and excavate the first section of the advanced small pilot tunnel face;

[0010] Step S2.2: After excavating the tunnel face of the first part of the advance small pilot tunnel, permanently support the side of the single side wall of the first part of the advance small pilot tunnel close to the tunnel contour, and temporarily support the remaining tunnel faces;

[0011] Step S2.3: Drill holes in the advance small pilot tunnel along the direction of the goaf to drain the gas and water in the goaf until the gas concentration in the goaf construction area reaches below 0.5%;

[0012] Step S2.4: After the gas and water in the goaf construction area are drained, grouting is performed around the advance small pilot tunnel to form a grouting wall, and grouting is performed toward the goaf construction area;

[0013] Step S3: Excavation of the tunnel faces of parts II, III, and IV of the advance small pilot tunnel;

[0014] Step S3.1: Expand the tunnel face of the advanced small pilot tunnel section II, and after expansion, provide permanent support for the tunnel face of the advanced small pilot tunnel section II;

[0015] Step S3.2: Control the distance between the working faces of Sections III and IV of the advance small pilot tunnel and Sections I and II of the advance small pilot tunnel to within 30m, and provide support during forward advancement. The working faces of Sections III and IV of the advance small pilot tunnel are the invert arch and the middle step.

[0016] In step S3.3, after the excavation of the heading faces of sections II, III, and IV of the advance small pilot tunnel passes through the goaf, the entire tunnel is supported.

[0017] In some embodiments of the present application, in the step S2.1, when excavating the part I face of the advance small guide tunnel, an advance small guide tunnel with an excavation height of 1-2m and a width of 4-5m is excavated, and the advance small guide tunnel is connected with the goaf so that the part II face of the advance small guide tunnel is less exposed in the excavation space.

[0018] In some embodiments of the present application, in step S2.2, when temporarily supporting the tunnel face of the advance small pilot tunnel part I, anchor bolts, steel mesh, I-beams and shotcrete are used for temporary support.

[0019] In some embodiments of the present application, in step S2.3, drilling along the direction of the goaf is drilling along the direction of the goaf toward the goaf construction area, so as to discharge gas and water in the goaf construction area.

[0020] In some embodiments of the present application, in step S2.4, grouting is performed around the advance small pilot tunnel to form a grouting wall, including: grouting around the advance small pilot tunnel through drilling, and forming a grouting wall to prevent slurry from flowing back into the advance small pilot tunnel when grouting is performed in the goaf construction area, wherein the thickness of the grouting wall is 2-3m.

[0021] In some embodiments of the present application, in step S3.1, when permanently supporting the tunnel face of the advanced small pilot tunnel part II, a steel arch support method is used to support the top and sides of the tunnel.

[0022] In some embodiments of the present application, in step S3.3, a wet spraying concrete construction method is adopted when supporting the entire tunnel, the sprayed concrete is constructed by wet spraying, a quick-setting agent is added to the nozzle, and the secondary lining adopts cast-in-place lining, with cast-in-place concrete being used as the lining material for the inner layer lining.

[0023] In some embodiments of the present application, part I of the advance small pilot tunnel is the excavation area of ​​the advance small pilot tunnel, part II of the advance small pilot tunnel is the area on the upper step of the expanded excavation area excluding the advance small pilot tunnel, and parts III and IV of the advance small pilot tunnel are the invert arch and middle step of the expanded excavation area.

[0024] In some embodiments of the present application, the anchor rods are arranged in a plum blossom shape.

[0025] Compared with the prior art, the beneficial effect of the present invention lies in that it utilizes the original design section of the tunnel, excavates a small pilot tunnel in advance on the upper step of the tunnel, performs advance support of the small pilot tunnel in advance while ensuring construction space, and drills holes in the small pilot tunnel toward the goaf along the direction of the coal seam to discharge gas. After the concentration of hazardous gas in the goaf reaches the construction requirement, grouting is carried out along the direction of the goaf through drilling, and then the face outside the small pilot tunnel is expanded. The method of excavating the small pilot tunnel in advance, releasing gas, and expanding the excavation to penetrate the goaf alleviates the damage to the original stress in the goaf and reduces the threat of gas and water seepage in the goaf. Because the collapse of the roof in the goaf of the coal seam causes the rock stratum to be unstable and contains many cracks, the method of grouting along the layer can make the slurry spread more fully, so that the construction area is fully isolated from the external goaf. The safety of the construction process is ensured, it is easy to promote and apply, fully utilizes the original tunnel section, and reasonably and effectively uses equipment, making the implementation of construction more convenient and efficient.

[0026] The small pilot tunnel can serve as a transportation channel for earthwork, construction materials, and equipment at the tunnel entrance, significantly reducing the cost of building a temporary access road. The small cross-section of the small pilot tunnel contributes to the stability of the surrounding rock. Excavating the small pilot tunnel also allows for further geological exploration. It can also address drainage and the emission of hazardous gases, improve ventilation within the tunnel, and significantly reduce disturbance to the surrounding rock during excavation, ensuring safe tunnel construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0028] Figure 1 This is a schematic flow chart of a construction method for a large-section tunnel passing through a goaf based on a small pilot tunnel method according to the present invention;

[0029] Figure 2 is a schematic flow chart of step S2 in an embodiment of the present invention;

[0030] Figure 3 is a schematic flow chart of step S3 in an embodiment of the present invention;

[0031] Figure 4 Schematic diagram of the position of the advance small pilot tunnel determined when the tunnel passes through the goaf in an embodiment of the present invention;

[0032] Figure 5 This is a front view of a small pilot tunnel for a tunnel passing through a goaf according to an embodiment of the present invention;

[0033] Figure 6 3. A top view of a small pilot tunnel for a tunnel passing through a goaf according to an embodiment of the present invention;

[0034] Figure 7 3. This is a side view of a small pilot tunnel for a tunnel passing through a goaf according to an embodiment of the present invention;

[0035] Among them, 1. The heading face; 2. Parts III and IV of the advance small pilot tunnel; 3. Part II of the advance small pilot tunnel; 4. Part I of the advance small pilot tunnel; 5. The slurry stop wall; 6. Drilling. DETAILED DESCRIPTION

[0036] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0037] When constructing highways in mountainous areas rich in underground resources, tunneling projects inevitably involve crossing existing goafs, constrained by specific design parameters such as geometry and longitudinal slope, as well as specific mining conditions. While technological advancements have advanced tunneling techniques through goafs, they still face numerous challenges that impact construction techniques. Goaf characteristics, specifically their impact on surrounding rock stability, can disrupt the stability of existing goafs, disrupting the original stress balance in the coal mining area and creating caving zones, fractures, and deflection zones in the overlying rock mass. This reduces the goaf's bearing capacity and makes it unstable over the long term. Gas within goafs can cause explosions, fires, and poisoning, posing direct risks to health. Gas mixed with air can easily cause fires. When gas concentrations exceed certain limits, even a small ignition source can spark a major fire, causing damage and injury. Gas outbursts can also destroy and block tunnels, further compromising construction safety. Therefore, effective ventilation safety measures must be implemented within goafs to prevent gas hazards to humans and the environment. Tunnel excavation inevitably disturbs the underground rock and soil, disrupting the original equilibrium and transitioning to a new one. Therefore, a construction method for large-section tunnels through goafs based on a small pilot tunnel method is urgently needed. This method can relieve pressure, minimize instability in old goafs, and further ensure construction progress and safety.

[0038] like Figure 1-Figure 7 As shown, the present invention provides a construction method for a large-section tunnel crossing a goaf based on a small pilot tunnel method, the construction method comprising:

[0039] Step S1: Determine the excavation position of the advance small pilot tunnel.

[0040] The excavation position of the advance small pilot tunnel is the single side wall of the tunnel upper step on the side where the vertical distance between the heading face and the goaf is closest.

[0041] Step S2: Excavation of the heading face of the advance small pilot tunnel part I.

[0042] Step S2.1: Advance from the upper step of the tunnel toward the goaf until the vertical distance between the tunnel and the goaf is 7 m, and excavate the face of the advanced small pilot tunnel part I.

[0043] In some embodiments of the present application, in step S2.1, when excavating the face of the advance small guide tunnel part I, the advance small guide tunnel with an excavation height of 1-2m and a width of 4-5m is excavated, and the advance small guide tunnel is connected with the goaf so that the face of the advance small guide tunnel part II is less exposed in the excavation space.

[0044] In this embodiment, the tunnel's upper step is advanced toward the goaf, and a small advance pilot tunnel is used to excavate the first section of the tunnel face. A small advance pilot tunnel with a height of greater than 1-2 meters and a width of 4-5 meters is excavated on the single side wall of the tunnel's upper step, penetrating the entire goaf. This small advance pilot tunnel ensures that equipment and personnel can enter the tunnel to understand the situation. Strengthen monitoring and measurement work inside and outside the tunnel, analyze measurement data in a timely manner, and suspend construction immediately if any problems are discovered, and resume construction after effective measures are taken.

[0045] In step S2.2, after the tunnel face of the advanced small pilot tunnel section I is excavated, permanent support is provided on the side of the single side wall of the advanced small pilot tunnel section I close to the tunnel contour, and temporary support is provided on the remaining tunnel faces.

[0046] In some embodiments of the present application, in step S2.2, when temporarily supporting the face of the advance small pilot tunnel part I, anchor bolts, steel mesh, I-beams and shotcrete are used for temporary support; wherein the anchor bolts are arranged in a plum blossom shape.

[0047] In this embodiment, after excavation, permanent support is applied to the side of the single side wall of the advance small pilot tunnel I close to the tunnel contour, and temporary support is applied to the remaining parts. The advance small pilot tunnel is initially supported by anchor bolts, steel mesh, I-beams and shotcrete, and the anchor bolts are arranged in a plum blossom shape. The shotcrete support is constructed in a timely manner following the excavation surface to reduce the exposure time of the surrounding rock, inhibit the deformation of the surrounding rock, and prevent the surrounding rock from loosening and peeling off in a short period of time. I-shaped steel arch frames are used, with a longitudinal spacing of 80 cm, and are connected with steel bars in the longitudinal and transverse directions to increase the strength and stability between the steel arch frames. Lightweight materials such as polyethylene lightweight materials or marl fragments can be selected and filled between the arch frames. The purpose is to fill the space between the steel arch frames and fill the goaf to prevent deformation and collapse of the goaf.

[0048] Step S2.3: Drill holes along the direction of the goaf in the advance small pilot tunnel to discharge gas and water in the goaf until the gas concentration in the goaf construction area reaches below 0.5%.

[0049] In some embodiments of the present application, in step S2.3, drilling along the direction of the goaf is drilling along the direction of the goaf toward the goaf construction area, so as to discharge gas and water in the goaf construction area.

[0050] In this embodiment, after the advance small pilot tunnel I is excavated into the goaf and supported, holes are drilled in the advance small pilot tunnel along the direction of the coal seam goaf to discharge gas and water in the goaf. In order to allow the gas and water in the goaf of the construction area to be discharged smoothly, holes are drilled along the direction of the coal seam goaf. Since the rock properties in the goaf are unstable, after grouting, there will be no hole collapse or drill jam during drilling, and the rock properties are relatively stable after grouting, so the hole can be drilled in one go. When the drilling rig starts drilling, the speed is low and the pressure is low. During the drilling process, an inclinometer is often used to measure the deviation of the steel pipe drilling. If the direction of the deviated coal seam goaf is found, it is corrected in time. Hole cleaning and hole inspection: Use a drilling rig to repeatedly sweep the hole to remove slag, ensure that the hole diameter and hole depth meet the requirements, and prevent hole blockage. Gas extraction within the goaf is typically achieved through forced-in ventilation. A local fan draws fresh air from the small pilot tunnel opening and forces it into the small pilot tunnel through a duct to dilute and expel toxic and harmful gases and dust from the goaf. The polluted air then flows through the entire small pilot tunnel and is discharged through the opening. This forced-in ventilation method ensures that the gas concentration within the construction area of ​​the goaf is below the required 0.5%.

[0051] Step S2.4, after completing the discharge of gas and water in the goaf construction area, grouting is performed around the advance small pilot tunnel to form a grouting wall, and grouting is performed toward the goaf construction area.

[0052] In some embodiments of the present application, in step S2.4, grouting is performed around the advance small pilot tunnel to form a grouting wall, including: grouting around the advance small pilot tunnel through drilling, and forming a grouting wall to prevent slurry from flowing back into the advance small pilot tunnel when grouting is performed in the goaf construction area, wherein the thickness of the grouting wall is 2-3m.

[0053] In this embodiment, after the gas concentration in the goaf construction area reaches the construction requirements, grouting is carried out along the direction of the coal seam goaf. First, grouting is performed around the advance small pilot tunnel to form a grouting wall, and then grouting is performed toward the goaf construction area. The thickness of the grouting wall is 2 to 3 meters. Its function is to prevent the slurry from flowing back into the advance small pilot tunnel during the grouting process in the goaf of the construction area. Grouting makes the surrounding rock of the goaf in the construction area more stable, prevents the surrounding rock from collapsing when the advance small pilot tunnel is advanced, and further ensures the safety of the construction process. Grouting is divided into the following steps: ① Construction of grouting holes. The location of the grouting holes should be designed according to the properties and thickness of the rock formations in the goaf, the degree of development of pores and cracks, the direction, and the connectivity and permeability characteristics in all directions. The diameter of the opening is generally 130 to 150 mm. ② Establish a grouting station. Grouting stations should fully consider the variability of grouting hole locations and be located in the most appropriate location, ensuring proximity to the grouting holes. Grouting pipelines should be short, with few elbows and diameter changes for ease of management. The grouting system should be commissioned and the grouting pipelines should be pressure-tested. ③ Borehole flushing and water pressure testing. Before flushing, measure the water level in the grouting hole and adjacent holes. During the flushing process, constantly monitor water level changes to determine if there is any communication between the holes. A water pressure test should be performed to check for blockage and the extent of blockage in the borehole or rock formation fissures and pores to ensure unobstructed grouting pipes. ④ Slurry preparation and grouting. The downward grouting method generally offers good quality and a simple process, but it also requires a long construction period and low economic efficiency. The typical diffusion distance is 5 to 50 meters, with a maximum of 100 meters. The grouting distance is 5 to 10 meters from the tunnel contour. ⑤ Observation and recording. Before, during, and after grouting, regular observation and recording of nearby hole water levels, pump pressure, orifice pressure, and slurry solution are essential steps in grouting and serve as a basis for evaluating the quality of borehole grouting. ⑥ Grouting process. During the grouting process, constant attention should be paid to the conduit and grouting holes to prevent pipe and hole blockages, ensure the smooth flow of the conduit and grouting holes, and guarantee the quality of grouting. ⑦ Close the orifice valve, dismantle and clean the grouting pipelines and equipment outside the hole. During pressure grouting, air is compressed in the slurry, which will release elastically after the pump is stopped, often resulting in backflow and grouting at the orifice. Therefore, after grouting is completed, the orifice valve must be closed and opened only after the pressure in the hole disappears. ⑧ Sealing the hole. After careful analysis, ensure that the grouting task is completed and seal the grouting hole with mortar to avoid air leakage. The extent of collapse in the coal seam goaf is unclear and the surrounding rock pressure is uncertain. The rock strata in the goaf are not compact and have many cracks compared to other rock strata. Due to the existence of these cracks, it is easier to grout the goaf, so the goaf is grouted by grouting along the layer.

[0054] Step S3: Excavation of the heading faces of parts II, III, and IV of the advance small pilot tunnel.

[0055] Step S3.1: Expand the tunnel face of the advanced small pilot tunnel section II, and after expansion, provide permanent support for the tunnel face of the advanced small pilot tunnel section II.

[0056] In some embodiments of the present application, in step S3.1, when permanently supporting the tunnel face of the advanced small pilot tunnel part II, a steel arch support method is used to support the top and sides of the tunnel.

[0057] In this embodiment, after the excavation of the tunnel face of Section I of the advance small pilot tunnel, the tunnel face of Section II of the advance small pilot tunnel is expanded and permanently supported. The steel arch support utilizes the steel arch as the tunnel's primary load-bearing structure, supporting the tunnel's roof and sides. First, holes are drilled in the tunnel wall, steel pipes are installed as support ribs, and connecting plates are installed between the arch ribs. Steel pipes are then welded to the connecting plates as connectors, ultimately forming a continuous steel arch. The advantages of a steel arch include high strength and rigidity, allowing it to withstand greater loads and deformation, significantly improving tunnel safety and stability.

[0058] In step S3.2, the distance between the working faces of sections III and IV of the advance small pilot tunnel and sections I and II of the advance small pilot tunnel is controlled within 30 m, and support is provided during forward advancement. The working faces of sections III and IV of the advance small pilot tunnel are the invert arch and the middle step.

[0059] In step S3.3, after the excavation of the heading faces of sections II, III, and IV of the advance small pilot tunnel passes through the goaf, the entire tunnel is supported.

[0060] In some embodiments of the present application, in step S3.3, a wet spraying concrete construction method is adopted when supporting the entire tunnel, the sprayed concrete is constructed by wet spraying, a quick-setting agent is added to the nozzle, and the secondary lining adopts cast-in-place lining, with cast-in-place concrete being used as the lining material for the inner layer lining.

[0061] In this embodiment, after the faces of Sections II, III, and IV of the advance pilot tunnels were excavated through the goaf, the entire tunnel was supported. The tunnel was constructed using the New Austrian Tunneling Method (NATM), employing a composite lining. The composite lining is completed through primary support and secondary lining. Primary support is achieved using wet shotcrete. The order of shotcrete spraying is wall-to-arch. If the rock surface is uneven, the concave surface is sprayed first to create a leveling effect. For the side walls, the spraying is done from bottom to top, left to right or right to left, with a rotational trajectory, one circle per half a circle, in a longitudinal sequence. The rotation radius is generally 15 cm, and each serpentine length is 3-4 m. For the arch, the spraying is done from bottom to top from the arch foot to the arch waist. From the arch waist to the arch crown, the spraying is done from the inside out. Because the goaf of the coal seam is soft and prone to collapse, the spraying operation closely follows the working face, with the initial spraying starting with the wall and ending with the arch. During the spraying process, the spraying speed is maintained consistently and adjusted appropriately. The maximum thickness of the shotcrete should not exceed 10 cm for the arch and 15 cm for the side walls. The secondary lining is cast-in-place lining, where cast-in-place concrete is used as the inner lining material. The lining is usually poured in a sequential manner, starting from the bottom up, first the wall and then the arch.

[0062] In some embodiments of the present application, part I of the advance small pilot tunnel is the excavation area of ​​the advance small pilot tunnel, part II of the advance small pilot tunnel is the area on the upper step of the expanded excavation area excluding the advance small pilot tunnel, and parts III and IV of the advance small pilot tunnel are the invert arch and middle step of the expanded excavation area.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

[0064] The system provided in the above embodiment is only illustrated by the division of the above functional modules. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiment can be combined into one module or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing the modules or steps and are not to be regarded as improper limitations of the present invention.

[0065] Those skilled in the art should be able to appreciate that, in conjunction with the modules and method steps of each example described in the embodiments disclosed herein, it is possible to implement them with electronic hardware, computer software, or a combination of the two, and the programs corresponding to the software modules and method steps can be placed in random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the art. In order to clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

Claims

1. A construction method for a large-section tunnel crossing a goaf based on a small pilot tunnel method, characterized in that: The construction method comprises: Step S1: Determine the excavation position of the advance small pilot tunnel; The excavation position of the advance small pilot tunnel is the single side wall of the tunnel upper step on the side where the vertical distance between the tunnel face and the goaf is closest; Step S2: Excavation of the tunnel face of the first part of the advance small pilot tunnel; Step S2.1: Advance from the upper step of the tunnel toward the goaf until the vertical distance between the tunnel and the goaf is 7m, and excavate the first section of the advanced small pilot tunnel face; Step S2.2: After excavating the tunnel face of the first part of the advance small pilot tunnel, permanently support the side of the single side wall of the first part of the advance small pilot tunnel close to the tunnel contour, and temporarily support the remaining tunnel faces; Step S2.3: Drill holes in the advance small pilot tunnel along the direction of the goaf to drain the gas and water in the goaf until the gas concentration in the goaf construction area reaches below 0.5%; Step S2.4: After the gas and water in the goaf construction area are drained, grouting is performed around the advance small pilot tunnel to form a grouting wall, and grouting is performed toward the goaf construction area; Step S3: Excavation of the tunnel faces of parts II, III, and IV of the advance small pilot tunnel; Step S3.1: Expand the tunnel face of the advanced small pilot tunnel section II, and after expansion, provide permanent support for the tunnel face of the advanced small pilot tunnel section II; Step S3.2: Control the distance between the working faces of Sections III and IV of the advance small pilot tunnel and Sections I and II of the advance small pilot tunnel to within 30m, and provide support during forward advancement. The working faces of Sections III and IV of the advance small pilot tunnel are the invert arch and the middle step. Step S3.3: After the excavation of the advanced small pilot tunnel sections II, III, and IV passes through the goaf, the entire tunnel is supported; In step S2.1, when excavating the tunnel face of the advanced small pilot tunnel part I, an advanced small pilot tunnel with a height of 1-2m and a width of 4-5m is excavated, and the advanced small pilot tunnel is connected with the goaf so that the tunnel face of the advanced small pilot tunnel part II is less exposed in the excavation space; In step S3.3, a wet shotcrete construction method is used for supporting the entire tunnel. The shotcrete is constructed by wet spraying, and an accelerating agent is added to the nozzle. The secondary lining is cast-in-place lining, and the cast-in-place concrete is used as the lining material for the inner layer lining. Part I of the advance small pilot tunnel is the excavation area of ​​the advance small pilot tunnel, Part II of the advance small pilot tunnel is the area on the upper step of the expanded excavation area excluding the advance small pilot tunnel, and Parts III and IV of the advance small pilot tunnel are the invert arch and middle step of the expanded excavation area.

2. The construction method of a large-section tunnel crossing a goaf based on a small pilot tunnel method according to claim 1 is characterized in that: In step S2.2, when temporarily supporting the tunnel face of the advance small pilot tunnel part I, anchor bolts, steel mesh, I-beams and shotcrete are used for temporary support.

3. The construction method of a large-section tunnel crossing a goaf based on a small pilot tunnel method according to claim 1, characterized in that: In the step S2.3, drilling along the direction of the goaf is drilling along the direction of the goaf toward the goaf construction area, so as to discharge gas and water in the goaf construction area.

4. The construction method of a large-section tunnel passing through a goaf based on a small pilot tunnel method according to claim 1, characterized in that: In the step S2.4, grouting is performed around the advance small pilot tunnel to form a grouting wall, including: grouting around the advance small pilot tunnel through drilling, and forming a grouting wall to prevent slurry from flowing back into the advance small pilot tunnel when grouting is performed in the goaf construction area, wherein the thickness of the grouting wall is 2-3m.

5. The construction method of a large-section tunnel passing through a goaf based on a small pilot tunnel method according to claim 1, characterized in that: In step S3.1, when permanently supporting the tunnel face of the advanced small pilot tunnel section II, a steel arch support method is used to support the top and sides of the tunnel.

6. The construction method of a large-section tunnel passing through a goaf based on a small pilot tunnel method according to claim 2, characterized in that: The anchor rods are arranged in a plum blossom shape.

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