Construction method for large-section tunnel to pass through goaf based on small pilot tunnel method

Abstract

The invention relates to the technical field of tunnel construction, and discloses a construction method for a large-section tunnel to penetrate through a goaf based on a small pilot tunnel method.The construction method comprises the steps that S1, the excavation position of an advanced small pilot tunnel is determined; s2, excavating a tunnel face of a part I of the advanced small pilot tunnel, permanently supporting one side, close to a tunnel outline, of a single side wall of the part I of the advanced small pilot tunnel, temporarily supporting other tunnel faces, drilling a goaf, discharging gas and water in the goaf, grouting around the advanced small pilot tunnel to form a grout stop wall, and grouting a construction area of the goaf; and S3, excavating tunnel faces of the second part, the third part and the fourth part of the advanced small pilot tunnel, and supporting the whole tunnel after the tunnel faces of the second part, the third part and the fourth part of the advanced small pilot tunnel are excavated and penetrate through the goaf. According to the method, the damage of the original stress of the goaf is relieved through the method of advanced small pilot tunnel excavation, gas release and expanding excavation, and the threat of gas and water seepage in the goaf is relieved.

Description

Technical Field

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

[0002] Small pilot tunnel method to cross goaf construction technology method In tunnel construction, goaf is a major difficulty in tunnel construction. The quality of its treatment technology and safety measures directly affects the safety of tunnel construction and operation. The spatial relationship between the goaf and the tunnel is the key factor in determining the goaf treatment measures.

[0003] When building roads in mountainous areas with rich underground resources, tunnel projects will inevitably cross existing goafs due to the constraints of design indicators such as specific geometric lines and route longitudinal slopes, as well as the conditions of mining areas in specific areas. With the development of science and technology, the construction technology of tunnels crossing goafs is becoming more and more advanced, but it still faces many problems, which affect the construction technology to a certain extent. The characteristics of goafs are the impact on the stability of the surrounding rock. When the tunnel passes through the goaf, the construction disturbance will affect the stability of the old goaf, the original stress balance of the rock mass in the coal mining area is broken, and the overlying rock mass in the goaf forms a caving zone, a crack zone and a bending zone, which reduces the bearing capacity of the goaf and cannot be stable for a long time. Gas in the goaf may cause explosions, fires, poisoning and other accidents, causing direct harm to the human body. When gas is mixed with air, it is very easy to cause fires. When the gas concentration exceeds a certain standard, as long as there is a little fire source, it may cause a fire, causing losses and injuries. Gas protrusion may also cause the tunnel to be destroyed and blocked, further affecting the safety during the construction process. Therefore, effective ventilation safety measures must be taken in the goaf to prevent gas from causing harm to the human body and the environment. The underground rock and soil will inevitably be disturbed during the tunnel excavation process, breaking the original equilibrium state and transitioning to a new equilibrium state. Therefore, a construction method for a large-section tunnel through the goaf based on the small pilot tunnel method is urgently needed. The small pilot tunnel method can be used to release pressure, minimize the instability of the old goaf, and further ensure the 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 caving zone caused by the collapse of the goaf roof makes the rock strata in the goaf extremely unstable and has many cracks, and the coal seam itself has a lot of gas, which can easily cause a great impact on the construction. The gas and water are discharged by drilling along the direction of the coal seam in the goaf and grouting is performed along the layer through drilling to block the penetration of gas and water outside the goaf construction area 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 face and the goaf is closest;

[0008] Step S2: excavation of the first section of the advanced small pilot tunnel;

[0009] Step S2.1, advance from the upper step of the tunnel to the goaf until the vertical distance between the tunnel and the goaf is 7m, and excavate the heading face of the first part of the advance small pilot tunnel;

[0010] Step S2.2, after the tunnel face of the first part of the advance small pilot tunnel is excavated, a permanent support is provided on the side of the single side wall of the first part of the advance small pilot tunnel close to the tunnel contour, and temporary support is provided on the remaining tunnel faces;

[0011] Step S2.3, drilling 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 construction area of ​​the goaf reaches below 0.5%;

[0012] Step S2.4, after the gas and water in the goaf construction area are discharged, grouting is performed around the advance small pilot hole to form a grout stop wall, and grouting is performed toward the goaf construction area;

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

[0014] Step S3.1, expanding the tunnel face of the advanced small pilot tunnel part II, and after the expansion, providing permanent support for the tunnel face of the advanced small pilot tunnel part II;

[0015] Step S3.2, control the distance between the headings of the advanced small pilot tunnel parts III and IV and the advanced small pilot tunnel parts I and II within 30m, and provide support during the forward advancement, wherein the headings of the advanced small pilot tunnel parts III and IV are the invert and middle step parts;

[0016] Step S3.3, after the heading faces of the advance small pilot tunnels II, III, and IV are excavated and pass through the goaf, the entire tunnel is supported.

[0017] In some embodiments of the present application, in the step S2.1, when excavating the heading 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 connected with the goaf to minimize the exposure of the heading of the advance small guide tunnel part II to the excavation space.

[0018] In some embodiments of the present application, in the step S2.2, when temporarily supporting the heading 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 the step S2.4, grouting is performed around the advance small guide tunnel to form a grouting stop wall, including: grouting around the advance small guide tunnel through drilling, and forming a grouting stop wall to prevent slurry from flowing back into the advance small guide tunnel when grouting is performed in the construction area of ​​the goaf, wherein the thickness of the grouting stop wall is 2-3m.

[0021] In some embodiments of the present application, in step S3.1, when the heading face of the advanced small pilot tunnel part II is permanently supported, 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 shotcrete construction method is used to support the entire tunnel, the shotcrete is constructed by wet spraying, an accelerator is added to the nozzle, and the secondary lining is cast-in-place lining, with cast-in-place concrete being used as the lining material for the inner 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 and middle steps 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 is that the present invention 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 under the premise of ensuring the construction space, and performs gas discharge by drilling holes along the coal seam in the small pilot tunnel to the goaf area. After the concentration of dangerous gas in the goaf area reaches the construction requirement, grouting is performed along the coal seam goaf area 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 alleviates the damage of the original stress in the goaf area, and reduces the threat of gas and water seepage in the goaf area. Because the collapse of the roof in the goaf area 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 diffuse more fully, so that the construction area is fully isolated from the external goaf area. The safety of the construction process is ensured, it is easy to promote and apply, the original tunnel section is fully adopted, the equipment is reasonably and effectively used, and the construction is more convenient and efficient.

[0026] The advance small pilot tunnel can be used as a transportation channel for earth and stone at the tunnel entrance and for construction materials and machinery at the tunnel entrance, greatly saving the cost of building a temporary road. The small cross-section of the advance small pilot tunnel is beneficial to the stability of the surrounding rock. At the same time, the geological conditions can be further explored by excavating the advance small pilot tunnel, and the advance small pilot tunnel can be used to solve the drainage and discharge of dangerous gases, which is beneficial to improve the ventilation in the tunnel, and can greatly reduce the disturbance of the surrounding rock during the excavation process, ensuring the safety of the 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0028] Figure 1 It is a schematic flow chart of a construction method of a large-section tunnel passing through a goaf area based on a small pilot tunnel method of 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 It is a 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 advance pilot tunnel for a tunnel passing through a goaf in an embodiment of the present invention;

[0033] Figure 6 is a top view of an advanced small pilot tunnel of a tunnel passing through a goaf in an embodiment of the present invention;

[0034] Figure 7 is a side view of an advanced small pilot tunnel of a tunnel passing through a goaf in an embodiment of the present invention;

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

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] When building roads in mountainous areas with rich underground resources, tunnel projects will inevitably cross existing goafs due to the constraints of design indicators such as specific geometric lines and route longitudinal slopes, as well as the conditions of mining areas in specific areas. With the development of science and technology, the construction technology of tunnels crossing goafs is becoming more and more advanced, but it still faces many problems, which affect the construction technology to a certain extent. The characteristics of goafs are the impact on the stability of the surrounding rock. When the tunnel passes through the goaf, the construction disturbance will affect the stability of the old goaf, the original stress balance of the rock mass in the coal mining area is broken, and the overlying rock mass in the goaf forms a caving zone, a crack zone and a bending zone, which reduces the bearing capacity of the goaf and cannot be stable for a long time. Gas in the goaf may cause explosions, fires, poisoning and other accidents, causing direct harm to the human body. When gas is mixed with air, it is very easy to cause fires. When the gas concentration exceeds a certain standard, as long as there is a little fire source, it may cause a fire, causing losses and injuries. Gas protrusion may also cause the tunnel to be destroyed and blocked, further affecting the safety during the construction process. Therefore, effective ventilation safety measures must be taken in the goaf to prevent gas from causing harm to the human body and the environment. The underground rock and soil will inevitably be disturbed during the tunnel excavation process, breaking the original equilibrium state and transitioning to a new equilibrium state. Therefore, a construction method for a large-section tunnel through the goaf based on the small pilot tunnel method is urgently needed. The small pilot tunnel method can be used to release pressure, minimize the instability of the old goaf, and further ensure the 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 area 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 upper step of the tunnel 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 first part of the advance small pilot tunnel.

[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 7m, and excavate the heading face of the first part of the advance small pilot tunnel.

[0043] In some embodiments of the present application, in step S2.1, when excavating the heading 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 connected with the goaf to reduce the exposure of the heading face of the advance small guide tunnel part II to the excavation space.

[0044] In this embodiment, the tunnel upper step is advanced to the goaf, and the advance small pilot tunnel method is used to excavate the advance small pilot tunnel part I face. The advance small pilot tunnel with a height greater than 1-2m and a width of 4-5m is excavated on the single side wall of the tunnel upper step and penetrates the entire goaf. The excavated advance small pilot tunnel can ensure that equipment and people can enter the cave to understand the situation. Strengthen the monitoring and measurement work inside and outside the cave, analyze the measurement data in time, suspend construction in time when problems are found, and take effective measures before construction.

[0045] Step S2.2, after the excavation of the heading face of the advance small pilot tunnel part I, the single side wall of the advance small pilot tunnel part I close to the tunnel contour is permanently supported, and the remaining heading faces are temporarily supported.

[0046] In some embodiments of the present application, in step S2.2, when temporarily supporting the heading 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, the single side wall of the first part of the advance small pilot tunnel is permanently supported on the side close to the tunnel contour, and the rest is temporarily supported. 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 time with 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 in a short time. I-shaped steel arch frames are used, with a longitudinal spacing of 80cm, 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 can be selected from polyethylene lightweight materials or marl fragments, which are filled between the arch frames. The purpose is to fill the space of the steel arch frames and fill the goaf to prevent deformation and collapse of the goaf.

[0048] Step S2.3, drilling 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 construction area of ​​the goaf 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 guide tunnel part I is excavated into the goaf and supported, holes are drilled in the advance small guide tunnel along the direction of the coal seam goaf to discharge gas and water in the goaf. In order to discharge gas and water in the goaf of the construction area 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 is relatively stable after grouting, so the hole can be drilled in one time. 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 deflection of the steel pipe drilling. If the deflected direction of the 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 the slag, ensure that the hole diameter and hole depth meet the requirements, and prevent hole blockage. The gas extraction in the goaf is usually done by the pressure ventilation method, where the local fan sucks fresh air outside the small guide hole and presses it into the small guide hole through the wind tube to dilute and discharge the toxic and harmful gases and dust in the goaf. The polluted air flows through the entire small guide hole and is discharged from the small guide hole. The pressure ventilation method is used to make the gas concentration in the construction area of ​​the goaf reach below 0.5% of the construction requirement.

[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 grout stop wall, and grouting is performed toward the goaf construction area.

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

[0053] In this embodiment, after the gas concentration in the construction area of ​​the goaf reaches the construction requirements, grouting is carried out along the direction of the goaf of the coal seam. First, grouting is carried out around the advance small pilot tunnel to form a grouting wall, and then grouting is carried out to the construction area of ​​the goaf. The thickness of the grouting wall is 2 to 3 meters. Its function is to prevent the slurry from flowing back to 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 opening diameter is generally 130 to 150 mm. ② Establish a grouting station. The grouting station should fully consider the change of the grouting hole position and be set up in the most appropriate position to ensure that it is close to the grouting hole, the grouting pipeline is short, there are few elbows and few diameter changes, which is easy to manage. The grouting system is put into trial operation and the grouting pipeline is subjected to a pressure test. ③ Borehole flushing and water pressure test. Before flushing, the water level of the grouting hole and the adjacent hole should be measured first. During the flushing process, the water level changes should be observed at all times to understand whether the holes are connected. Through the water pressure test, check whether the borehole or the rock formation cracks and pores are blocked and the degree of blockage to ensure that the grouting pipe is unobstructed. ④ Prepare slurry and grouting. Generally, the downward method of grouting has good quality and simple process, but the construction period is long and the economic benefits are low. The general diffusion distance is 5 to 50m, and the farthest can reach 100m. The grouting distance is 5 to 10m from the tunnel contour line. ⑤ Observation and recording. Before, during and after grouting, the water level of nearby holes, pump pressure, orifice pressure, slurry solution, etc. are regularly observed and recorded. This is an important part of grouting work and is also the basis for evaluating the quality of drilling grouting. ⑥ Grouting process. During the grouting process, always pay attention to the catheter and grouting hole to prevent the occurrence of pipe and hole blocking, ensure the smooth flow of the catheter and grouting hole, and ensure the quality of grouting. ⑦ Close the orifice valve, dismantle and wash the grouting pipeline and equipment outside the hole. During pressure grouting, air is compressed in the slurry, and elastic release will occur after the pump is stopped, and backflow and grouting often occur at the orifice. Therefore, after the grouting is completed, the water must be pressed and the orifice valve must be closed, and it will be opened after the pressure in the hole disappears. ⑧ Sealing the hole. After careful analysis, ensure that the grouting task is completed, and use mortar to seal the grouting hole to avoid air exposure. 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 method of grouting along the layer is adopted to grout the goaf.

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

[0055] Step S3.1, the heading face of the advanced small pilot tunnel part II is expanded and excavated, and after the expansion, the heading face of the advanced small pilot tunnel part II is permanently supported.

[0056] In some embodiments of the present application, in step S3.1, when the heading face of the advanced small pilot tunnel part II is permanently supported, 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 first part of the advanced small pilot tunnel, the second part of the advanced small pilot tunnel is expanded and permanently supported after the expansion; the use of steel arch support is to use the steel arch as the main load-bearing structure of the tunnel to support the top and sides of the tunnel. First, holes are drilled on the tunnel wall, steel pipes are installed as bones, connecting plates are installed between the arch bones, and then steel pipes are welded on the connecting plates as connectors, and finally a continuous steel arch is formed. The advantages of the steel arch are high strength and high rigidity, and it can withstand greater loads and deformations, which can greatly improve the safety and stability of the tunnel.

[0058] Step S3.2, control the distance between the heading faces of the advanced small pilot tunnel parts III and IV and the advanced small pilot tunnel parts I and II within 30m, and provide support when advancing forward, wherein the heading faces of the advanced small pilot tunnel parts III and IV are the invert and middle step parts.

[0059] Step S3.3, after the heading faces of the advance small pilot tunnels II, III, and IV are excavated and pass through the goaf, the entire tunnel is supported.

[0060] In some embodiments of the present application, in step S3.3, a wet shotcrete construction method is used to support the entire tunnel, the shotcrete is constructed by wet spraying, an accelerator is added to the nozzle, and the secondary lining is cast-in-place lining, with cast-in-place concrete being used as the lining material for the inner lining.

[0061] In this embodiment, after the excavation of the advanced small pilot tunnel II, III, and IV faces through the goaf, the tunnel is supported as a whole. The tunnel is constructed using the new Austrian tunneling method and a composite lining. The composite lining is completed by primary support and secondary lining. The primary support is a wet spraying concrete construction method. The order of spraying concrete should be wall first and arch later. When the rock surface is uneven, spray the concave first to level it. In the side wall part, it is from bottom to top, from left to right or from right to left, and pay attention to the rotation trajectory movement. One circle presses half a circle, and the longitudinal direction is carried out in sequence. The rotation radius is generally 15cm, and the serpentine length each time is 3 to 4m. From the arch foot to the arch waist of the arch, from bottom to top. The arch waist to the arch top is sprayed from the inside to the outside. Because the coal seam goaf is soft and easy to collapse, the spraying operation follows the working face closely, and the wall is sprayed first and the arch is sprayed later. When spraying concrete, the spraying speed is maintained throughout and adjusted in time. The maximum thickness of the one-time spraying concrete is not more than 10cm for the arch and not more than 15cm for the side wall. The second lining is cast-in-place lining, which uses cast-in-place concrete as the lining material for the inner lining. The sequential method is usually used, and the pouring is carried out in the order of bottom-up, first wall and then 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 and middle steps of the expanded excavation area.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

[0064] The system provided in the above embodiment is only illustrated by the division of the above functional modules. In practical 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 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 regarded as improper limitations of the present invention.

[0065] Those skilled in the art should be able to appreciate that the modules and method steps of each example described in conjunction with the embodiments disclosed herein can be implemented 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 technical field. In order to clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described in the above description according to the function. 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 face and the goaf is closest; Step S2: excavation of the first section of the advanced small pilot tunnel; Step S2.1, advance from the upper step of the tunnel to the goaf until the vertical distance between the tunnel and the goaf is 7m, and excavate the heading face of the first part of the advance small pilot tunnel; Step S2.2, after the tunnel face of the first part of the advance small pilot tunnel is excavated, a permanent support is provided on the side of the single side wall of the first part of the advance small pilot tunnel close to the tunnel contour, and temporary support is provided on the remaining tunnel faces; Step S2.3, drilling 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 construction area of ​​the goaf reaches below 0.5%; Step S2.4, after the gas and water in the goaf construction area are discharged, grouting is performed around the advance small pilot hole to form a grout stop wall, and grouting is performed toward the goaf construction area; Step S3: excavation of the heading faces of parts II, III and IV of the advance small pilot tunnel; Step S3.1, expanding the tunnel face of the advanced small pilot tunnel part II, and after the expansion, providing permanent support for the tunnel face of the advanced small pilot tunnel part II; Step S3.2, control the distance between the headings of the advanced small pilot tunnel parts III and IV and the advanced small pilot tunnel parts I and II within 30m, and provide support during the forward advancement, wherein the headings of the advanced small pilot tunnel parts III and IV are the invert and middle step parts; Step S3.3, after the heading faces of the advance small pilot tunnels II, III, and IV are excavated and pass through the goaf, the entire tunnel is supported.

2. The construction method of a large-section tunnel crossing a goaf area based on a small pilot tunnel method according to claim 1 is characterized in that: In step S2.1, when excavating the face of the advance small guide tunnel part I, the advance small guide tunnel with a 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.

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

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

5. The construction method of a large-section tunnel crossing a goaf area 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 guide tunnel to form a grouting stop wall, including: grouting around the advance small guide tunnel through drilling and forming a grouting stop wall to prevent slurry from flowing back into the advance small guide tunnel when grouting is performed in the goaf construction area, wherein the thickness of the grouting stop wall is 2-3m.

6. The construction method of a large-section tunnel crossing a goaf area based on a small pilot tunnel method according to claim 1, characterized in that: In the step S3.1, when the heading face of the advanced small pilot tunnel part II is permanently supported, a steel arch support method is adopted to support the top and sides of the tunnel.

7. The construction method of a large-section tunnel crossing a goaf area based on a small pilot tunnel method according to claim 1, characterized in that: In step S3.3, a wet shotcrete construction method is used to support the entire tunnel. The shotcrete is constructed by wet spraying, and an accelerator is added to the nozzle. The secondary lining is cast-in-place lining, and cast-in-place concrete is used as the lining material for the inner lining.

8. The construction method of a large-section tunnel passing through a goaf area based on a small pilot tunnel method according to claim 1, characterized in that: The advance small pilot tunnel section I is the excavation area of ​​the advance small pilot tunnel, the advance small pilot tunnel section II is the area on the upper step of the expanded excavation area excluding the advance small pilot tunnel, and the advance small pilot tunnel sections III and IV are the invert and middle steps of the expanded excavation area.

9. The construction method of a large-section tunnel passing through a goaf area based on a small pilot tunnel method according to claim 3, characterized in that: The anchor bolts are arranged in a plum blossom shape.

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