Tunnel hard rock advanced pilot hole expansion construction method

Abstract

The present application relates to the technical field of underground tunnel construction, in particular to a kind of construction method of tunnel hard rock. The upper bench excavation working face is sequentially divided into advance pilot hole milling face and expansion face from left to right, and parallel construction of advance pilot hole and expansion is adopted. Through zoning operation of excavation working face, parallel operation of advance pilot hole excavation and initial support can be realized, effectively avoiding the influence time of traditional upper bench support, ensuring the overall construction progress of the tunnel; the tunnel hard rock advance pilot hole expansion construction method of the present application uses drilling + breaking hammer excavation for expansion face, reduces the amount of upper bench milling, reduces the consumption of cutting teeth, has lower comprehensive cost, reduces dust generation, is beneficial to environmental protection, and has higher use value compared with the traditional bench method milling process.

Description

Technical Field

[0001] This invention relates to the field of underground tunnel construction technology, and in particular to a method for excavating a pilot tunnel in hard rock. Background Technology

[0002] Currently, both domestically and internationally, besides TBMs, the main excavation methods in non-blasting hard rock include: cantilever milling, drilling and splitting rigs, hydraulic fracturing, chemical expansion agents, and rock cutting. Based on preliminary research of ongoing domestic construction projects, cantilever milling is gradually becoming a core piece of equipment in non-blasting excavation, and its application is widespread across various construction fields.

[0003] However, when the rock strength reaches 80-120 MPa, the hard geological conditions increase the wear and tear on the equipment. As the tunneling progresses deeper, the equipment failure rate rises and the construction efficiency decreases. This not only results in high excavation costs but also increases the pressure on the construction schedule.

[0004] In view of this, it is necessary to design a new method for tunnel hard rock pilot tunnel expansion construction that is suitable for rock strength of 80~120Mpa, and give full play to the advantages of mechanical equipment to solve problems in terms of progress, cost, and construction period.

[0005] Furthermore, both domestically and internationally, dust removal in the milling process of cantilever tunneling machines currently employs jet fans to centrally extract dust to the outside of the tunnel, which is then filtered by dry / wet dust collectors before being discharged to the outside. This dust removal process causes significant disruption to construction and has poor dust removal efficiency, making it unsuitable for current pilot tunnel and enlargement excavation methods.

[0006] During the initial construction phase, the following problems were found with traditional dust removal processes:

[0007] 1. The jet fan has a long duct layout, resulting in high maintenance costs. It intersects with multiple construction work areas, leading to frequent damage and repairs. Furthermore, dust levels at these work areas exceed standards, impacting construction progress.

[0008] 2. Dry / wet dust collectors have poor filtration effects, resulting in polluted air that cannot meet emission standards and making mud discharge and treatment difficult, which affects civilized construction and environmental protection.

[0009] 3. The jet fan is fixed in position and cannot be moved, which cannot effectively solve the problem of dust on the work surface, resulting in a poor construction environment and harming the health of the workers.

[0010] In view of this, it is necessary to develop a dust removal method that matches the hard rock pilot tunnel excavation construction method, and to purify the polluted air in the tunnel through layer-by-layer dust removal, thereby solving problems related to progress, cost, and construction period. Summary of the Invention

[0011] The purpose of this invention is to provide a rapid construction method suitable for non-explosive tunnel hard rock excavation, which uses a combination of equipment such as cantilever tunneling machines, rock drilling rigs, and hydraulic breakers for excavation.

[0012] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for excavating and widening a pilot tunnel in hard rock, characterized in that the construction method is a non-explosive tunneling method applicable to large-section hard rock with a rock strength of 80~120Mpa. The upper bench excavation face is divided from left to right into a pilot tunnel milling face and an widening face, and the pilot tunnel and widening are constructed in parallel. Specifically, it includes the following steps:

[0013] S1, Advanced Geological Prediction and Surrounding Rock Monitoring Measurement

[0014] The pilot tunnel method was adopted for excavation. The cross-sectional parameters of the pilot tunnel included: a 1.52m radius arc connecting the arch to the excavation outline; an excavation height of 6.2m; an excavation width of 8.7m; and the pilot tunnel excavation surface occupying 49% of the upper bench cross-sectional area. The monitoring of the surrounding rock of the pilot tunnel included settlement observation points at the arch and horizontal convergence observation points at the arch waist, with a cross-section set every 5m. To ensure the safety and stability of the pilot tunnel, corresponding geological forecasting was conducted to determine whether adverse geological conditions existed within a certain range outside the pilot tunnel's surrounding rock outline. Ground-penetrating radar was used for the pilot tunnel's geological forecasting. The geological forecasting and surrounding rock monitoring were implemented in two stages based on the on-site construction conditions.

[0015] Phase 1: Set up circumferential ground-penetrating radar survey lines at the outline of the tunnel face, with a point measurement interval of no more than 20cm; the radar detection direction is 10° outward in a circle, and ground-penetrating radar advance prediction is carried out every 20m along the excavation direction to detect the surrounding rock conditions outside the outline of the tunnel arch; the detection is carried out through a work platform.

[0016] Phase 2: Every 4m of tunnel excavation, a radar survey line along the tunnel axis is set at the arch crown and arch waist of the tunnel. The detection direction is radial outward, and the point measurement interval is 20cm to detect the surrounding rock conditions behind the arch crown and arch waist of the tunnel. The detection personnel work on the tunneling machine platform and achieve the detection work throughout the entire process by slowly moving the equipment.

[0017] S2. Setting out the excavation outline

[0018] Before each shift begins excavation, a total station is used to measure the excavation outline, which is then marked with red paint, with the circumferential spacing between the points not exceeding 40cm.

[0019] S3, Advanced Pilot Tunnel Milling

[0020] The pre-drilling area is 35m².2 The slag is loaded and transported to the spoil disposal site using a combination of loaders and dump trucks; the advance of the pilot tunnel is determined based on the rock strength, with the advance range of a single cycle controlled between 1.2m and 2.0m, and the single cycle operation time controlled within 11 hours; the distance between the pilot tunnel and the enlarged excavation face is kept within 20m, and dust removal is carried out using onboard special dust removal equipment.

[0021] S4. Excavation of the widened face

[0022] The parameters for the enlarged excavation section include an excavation height of 6.2m, an excavation width of 8.06m, and the enlarged excavation section accounting for 51% of the area of ​​the upper bench section. The excavation face will be excavated using a drilling + hydraulic hammer excavation scheme. Drilling parameters for the enlarged excavation face include: a hole diameter of 110mm, a hole depth of 5m, and a horizontal and vertical hole spacing of no more than 40cm. The operation time will be controlled between 4 and 6 hours. For hydraulic hammer excavation, a single-cycle construction advance will be carried out with a spacing between two steel frames. The diameter of the hydraulic hammer drill rod must be larger than the hole diameter, and the average construction efficiency will be 5-6 cubic meters per hour. The enlarged excavation will be carried out in parallel with the milling of the pilot tunnel. After the enlarged excavation is completed, the tunneling machine needs to withdraw to trim the outline, ensuring a smooth excavation outline and improving excavation quality.

[0023] S5, Step support

[0024] After the excavation of the enlarged face is completed, the initial support of the upper bench is promptly constructed. The scaffolding operation adopts the construction of a modular and separate working platform, and the shotcreting operation adopts the construction of a wet shotcreting robotic arm. The single-cycle support advances at a spacing of 2 steel frames, and the shotcreting protection of the pilot tunnel is synchronized with the initial support shotcreting cycle.

[0025] S6. Excavation of the lower bench and invert arch

[0026] The lower steps and invert arch were excavated using hydraulic hammers, and the construction equipment used was a PC500 excavator and an SG4500 tower breaker.

[0027] The equipment used for dumping and loading is a PC360 excavator, and the excavated material is transported using 20-cubic-meter dump trucks.

[0028] The dust removal method used in the construction method specifically includes the following steps:

[0029] C1. Arrangement of ventilation ducts

[0030] A set of variable frequency axial flow fans is installed at the tunnel entrance, using forced air supply. The motor power is 2×110KW, the ventilation duct diameter is 2m, the duct is set near the side arch of the excavation face, and the air outlet is no more than 10m away from the excavation face.

[0031] C2. Dust removal arrangement for the pilot tunnel

[0032] The advanced pilot tunnel method is adopted for construction. Due to the small cross-section and deep depth of the pilot tunnel, it is not conducive to the arrangement of dust removal vehicles. Therefore, on-board dust removal equipment is used for dust reduction. The motor power of the on-board dust removal machine is 2×37KW. The on-board dust removal machine is installed on the top platform of the tunneling machine and the bottom is equipped with vibration damping rubber pads. The power supply voltage is the same as that of the tunneling machine, and 1140V high-voltage cable is used for connection.

[0033] C3. Dust removal arrangement at the excavation face

[0034] To further purify the residual dust in the air discharged from the pilot tunnel, an XCS1500 tunnel dust removal vehicle is installed on the left side wall of the step on the widened excavation face. The vehicle uses water atomization, filtration, and water film dust removal mechanism to draw dust-containing gas into the air duct and send it into the dust collector. The dust gas is fully mixed with the high-pressure water mist in the dust collector, and the gas and liquid are separated by multiple layers of metal filter screens. Finally, the clean air is discharged through the exhaust port, and the dust and water form mud, which is pumped into the temporary sedimentation tank in the tunnel.

[0035] The XCS1500 tunnel dust removal vehicle is arranged in parallel with the excavation face equipment, with a reserved muck discharge channel in the middle. The distance between the dust removal vehicle's air suction pipe opening and the pilot tunnel opening is no more than 2m.

[0036] C4. Sprinkler dust suppression system

[0037] In order to further purify the polluted air emitted by the XCS1500 tunnel dust removal vehicle and reduce the temperature inside the tunnel, a spray pipe was installed circumferentially on the initial support surface of the upper step, and a water tank and booster pump were configured. The distance between the spray arrangement section and the exhaust pipe outlet at the tail of the dust removal machine is 5m.

[0038] In step S3, the pilot tunnel is excavated using an XTR7 / 360 cantilever tunneling machine.

[0039] In step S4, the rock face is excavated using a ZYS113 three-arm rock drilling rig for assisted drilling, and the hydraulic hammer excavation equipment is a PC500 short-arm excavator + SG4500 tower breaker.

[0040] Compared with the prior art, the advantages of the present invention are as follows:

[0041] The tunnel hard rock pilot tunnel expansion construction method of the present invention enables parallel operation of pilot tunnel excavation and initial support by dividing the excavation face into zones, effectively avoiding the time impact of traditional bench support and ensuring the overall tunnel construction progress. The tunnel hard rock pilot tunnel expansion construction method of the present invention uses drilling + hydraulic breaker excavation for the expansion face, which can reduce the amount of upper bench milling by an average of 40%, reduce the consumption of cutting teeth by 50%, and reduce the overall cost by 30% to 40%. It also reduces dust generation, which is beneficial to environmental protection. Compared with the traditional bench milling process, it has higher application value.

[0042] The tunnel hard rock pilot tunnel expansion construction method of the present invention enables parallel operation of pilot tunnel excavation and initial support by dividing the excavation face into zones, effectively avoiding the time impact of traditional bench support and ensuring the overall tunnel construction progress. The expansion face of the tunnel hard rock pilot tunnel expansion construction method of the present invention adopts drilling + hydraulic breaker excavation, which can reduce the amount of bench milling by an average of 40%, reduce cutting tooth consumption by 50%, and reduce overall costs by 30%~40%. A three-stage dust removal system is adopted, taking advantage of the adjustable suction port position, strong dust removal capacity, and self-propelled design of the dust removal equipment. Together with the ventilation fans outside the tunnel, a circulating ventilation and dust suppression system was formed. According to the tunnel construction dust concentration tester, the concentration of 10% silica dust emitted by the locomotive dust collector in the pilot tunnel was 5~10mg / m³, the concentration of 10% silica dust emitted by the XCS1500 vehicle-mounted dust collector was 2~3mg / m³, and the concentration of 10% silica dust at the tunnel entrance was reduced to below 2mg / m³. This effectively improved the working environment inside the tunnel, met the specifications, and was beneficial to environmental protection. Compared with the traditional step-method milling and its dust removal process, it has higher application value. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings not only show some embodiments of the present invention, but should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a flowchart illustrating the construction process of the pilot tunnel widening method of the present invention.

[0045] Figure 2 This is a construction procedure diagram of the pilot tunnel widening method of the present invention.

[0046] Figure 3 This is a schematic diagram of the construction process of the pilot tunnel widening method of the present invention.

[0047] Figure 4 This is a diagram showing the location of the circular survey line layout on the arch of the pilot tunnel according to the present invention.

[0048] Figure 5 This is a cross-sectional view of the advanced tunneling ground-penetrating radar of the present invention.

[0049] Figure 6 This is a three-dimensional schematic diagram of the longitudinal detection of the advanced tunneling ground-penetrating radar of the present invention.

[0050] Figure 7 This is a three-dimensional schematic diagram of the advanced pilot tunnel monitoring and measurement densification layout of the present invention.

[0051] Figure 8 This is a design drawing for the borehole of the enlarged excavation section of the present invention.

[0052] Figure 9 This is a plan view of the ventilation and dust removal circulation system of the present invention.

[0053] Figure 10 This is a schematic diagram of the airflow path for ventilation and dust removal according to the present invention.

[0054] Figure 11 This is a cross-sectional view of the step on the dust removal equipment of the present invention.

[0055] Figure 12 This is a cross-sectional layout diagram of the water spray dust removal device of the present invention.

[0056] In the diagram: 1-Initial support of the upper step, 2-Initial support of the lower step, 3-Invert arch lining, 4-Invert arch filling, 5-Arch wall lining, 6-Air supply duct, 7-Dust removal fan on the milling machine, 8-XCS1500 vehicle-mounted dust removal fan, 9-Sprinkling device, 10-Excavation face operation machinery, 11-Water tank and booster pump system, 12-Circular water supply main pipeline, 13-Spray head. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the specific embodiments. Example

[0058] According to the construction sequence diagram ( Figure 2 , Figure 3 The entire tunnel excavation includes three working faces: the upper bench pilot tunnel (Ⅰ), the upper bench enlargement face (Ⅱ), and the lower bench and invert (Ⅲ). Section Ⅰ will be initially sealed with 5cm thick C25 shotcrete after excavation. The initial support for the upper bench will be constructed after the excavation of Section Ⅱ, and the initial support for the lower bench will be constructed after the excavation of Section Ⅲ. The invert lining will be constructed after the invert excavation.

[0059] like Figure 1 As shown, the method for excavating and widening a pilot tunnel in hard rock is a non-explosive, cut-and-cover tunnel construction method for large-section hard rock, applicable to rock strengths of 80-120 MPa. The upper bench excavation face is divided from left to right into a pilot tunnel milling face and an enlargement face. The pilot tunnel and enlargement are constructed in parallel, specifically including the following steps:

[0060] S1, Advanced Geological Prediction and Surrounding Rock Monitoring Measurement

[0061] The pilot tunnel method was adopted for excavation. The cross-sectional parameters of the pilot tunnel included: a 1.52m radius arc connecting the arch to the excavation outline; an excavation height of 6.2m; an excavation width of 8.7m; and the pilot tunnel excavation surface occupying 49% of the upper bench cross-sectional area. The monitoring of the surrounding rock of the pilot tunnel included settlement observation points at the arch and horizontal convergence observation points at the arch waist, with a cross-section set every 5m. To ensure the safety and stability of the pilot tunnel, corresponding geological forecasting was conducted to determine whether adverse geological conditions existed within a certain range outside the pilot tunnel's surrounding rock outline. Ground-penetrating radar was used for the pilot tunnel's geological forecasting. The geological forecasting and surrounding rock monitoring were implemented in two stages based on the on-site construction conditions.

[0062] Phase 1: As Figure 4 , Figure 5 A circumferential ground-penetrating radar survey line is set at the outline of the tunnel face, with a point measurement interval of no more than 20cm. The radar detection direction is 10° outward in a circumferential direction. A ground-penetrating radar advance prediction is carried out every 20m along the excavation direction to detect the surrounding rock conditions outside the outline of the tunnel arch. The detection is carried out through a work platform.

[0063] Phase Two: As Figure 6 Every 4 meters of tunnel excavation, a radar survey line along the tunnel axis is set at the arch top and arch waist of the tunnel. The detection direction is radial outward, and the point measurement interval is 20cm to detect the surrounding rock behind the arch top and arch waist of the tunnel. The detection personnel work on the tunneling machine platform and realize the detection work throughout the entire process by slowly moving the equipment.

[0064] S2. Setting out the excavation outline

[0065] Before each shift begins excavation, a total station is used to measure the excavation outline, which is then marked with red paint, with the circumferential spacing between the points not exceeding 40cm.

[0066] S3, Advanced Pilot Tunnel Milling

[0067] The pilot tunnel was excavated using an XTR7 / 360 cantilever tunneling machine, with a working area of ​​35m². 2 The slag is loaded and transported to the spoil disposal site using a combination of loaders and dump trucks; the advance of the pilot tunnel is determined based on the rock strength, with the advance range of a single cycle controlled between 1.2m and 2.0m, and the single cycle operation time controlled within 11 hours; the distance between the pilot tunnel and the enlarged face is kept within 20m, and dust is removed using a 75kw onboard dust removal fan;

[0068] S4. Excavation of the widened face

[0069] like Figure 8The parameters for the enlarged excavation section include an excavation height of 6.2m, an excavation width of 8.06m, and the enlarged excavation section accounting for 51% of the area of ​​the upper bench section. The excavation face will employ a drilling + hydraulic hammer excavation scheme. Drilling on the enlarged rock face will be assisted by a ZYS113 three-arm rock drilling rig. The hydraulic hammer excavation equipment will consist of a PC500 short-arm excavator and an SG4500 tower breaker. The drilling parameters for the enlarged excavation face are: hole diameter 110mm, hole depth 5m, and relatively small horizontal and vertical hole spacing. The depth should be 40cm, and the operation time should be controlled within 4-6 hours; the hydraulic hammer excavation should be carried out in a single cycle with a spacing of two steel frames, and the diameter of the hydraulic hammer drill rod must be larger than the borehole diameter, with an average construction efficiency of 5-6 cubic meters per hour; the enlargement excavation should be carried out in parallel with the milling of the pilot tunnel; after the enlargement excavation is completed, the tunneling machine needs to be withdrawn to trim the outline, ensuring a smooth excavation outline and improving the excavation quality; the enlargement excavation should be carried out with an XCS1500 vehicle-mounted dust removal fan for dust removal.

[0070] S5, Step support

[0071] After the excavation of the enlarged face is completed, the initial support of the upper bench is promptly constructed. The scaffolding operation adopts the construction of a modular and separate working platform, and the shotcreting operation adopts the construction of a wet shotcreting robotic arm. The single-cycle support advances at a spacing of 2 steel frames, and the shotcreting protection of the pilot tunnel is synchronized with the initial support shotcreting cycle.

[0072] S6. Excavation of the lower bench and invert arch

[0073] The lower steps and invert arch were excavated using hydraulic hammers, and the construction equipment used was a PC500 excavator and an SG4500 tower breaker.

[0074] The equipment used for dumping and loading is a PC360 excavator, and the excavated material is transported using 20-cubic-meter dump trucks.

[0075] The dust removal method used in the construction method specifically includes the following steps:

[0076] C1. Arrangement of ventilation ducts

[0077] A set of variable frequency axial flow fans is installed at the tunnel entrance, using forced air supply. The motor power is 2×110KW, the ventilation duct diameter is 2m, the duct is set near the side arch of the excavation face, and the air outlet is no more than 10m away from the excavation face.

[0078] C2. Dust removal arrangement for the pilot tunnel

[0079] The advanced pilot tunnel method is adopted for construction. Due to the small cross-section and deep depth of the pilot tunnel, it is not conducive to the arrangement of dust removal vehicles. Therefore, on-board dust removal equipment is used for dust reduction. The motor power of the on-board dust removal machine is 2×37KW. The on-board dust removal machine is installed on the top platform of the tunneling machine and the bottom is equipped with vibration damping rubber pads. The power supply voltage is the same as that of the tunneling machine, and 1140V high-voltage cable is used for connection.

[0080] C3. Dust removal arrangement at the excavation face

[0081] To further purify the residual dust in the air discharged from the pilot tunnel, an XCS1500 tunnel dust removal vehicle is installed on the left side wall of the step on the widened excavation face. The vehicle uses water atomization, filtration, and water film dust removal mechanism to draw dust-containing gas into the air duct and send it into the dust collector. The dust gas is fully mixed with the high-pressure water mist in the dust collector, and the gas and liquid are separated by multiple layers of metal filter screens. Finally, the clean air is discharged through the exhaust port, and the dust and water form mud, which is pumped into the temporary sedimentation tank in the tunnel.

[0082] The XCS1500 tunnel dust removal vehicle is arranged in parallel with the excavation face equipment, with a reserved muck discharge channel in the middle. The distance between the dust removal vehicle's air suction pipe opening and the pilot tunnel opening is no more than 2m.

[0083] C4. Sprinkler dust suppression system

[0084] In order to further purify the polluted air emitted by the XCS1500 tunnel dust removal vehicle and reduce the temperature inside the tunnel, a spray pipe was installed circumferentially on the initial support surface of the upper step, and a water tank and booster pump were configured. The distance between the spray arrangement section and the exhaust pipe outlet at the tail of the dust removal machine is 5m.

Claims

1. A method for widening and excavating a pilot tunnel in hard rock, characterized in that, The construction method described is a non-explosive cut-and-cover tunnel construction method applicable to large-section hard rock tunnels with rock strength of 80~120Mpa. The upper bench excavation face is divided from left to right into a pilot tunnel milling face and a widening face. The pilot tunnel and widening face are constructed in parallel, and the specific steps include: S1, Advanced Geological Prediction and Surrounding Rock Monitoring Measurement The pilot tunnel method was adopted for excavation. The cross-sectional parameters of the pilot tunnel included: a 1.52m radius arc connecting the arch to the excavation outline; an excavation height of 6.2m; an excavation width of 8.7m; and the pilot tunnel excavation face occupying 49% of the upper bench cross-sectional area. The monitoring of the surrounding rock of the pilot tunnel included settlement observation points at the arch and horizontal convergence observation points at the arch waist. A cross-section was set up every 5m for these settlement and horizontal convergence observation points. To ensure the safety and stability of the pilot tunnel, corresponding geological advance prediction was required to determine whether there were any adverse geological conditions within a certain range outside the pilot tunnel's surrounding rock outline. Ground-penetrating radar was used for the pilot tunnel's geological advance prediction. The geological advance prediction and surrounding rock monitoring were implemented in two stages based on the on-site construction conditions. Phase 1: Set up circumferential ground-penetrating radar survey lines at the outline of the tunnel face, with a point measurement interval of no more than 20cm; the radar detection direction is 10° outward in a circle, and ground-penetrating radar advance prediction is carried out every 20m along the excavation direction to detect the surrounding rock conditions outside the outline of the tunnel arch; the detection is carried out through a work platform. Phase 2: Every 4m of tunnel excavation, a radar survey line along the tunnel axis is set at the arch crown and arch waist of the tunnel. The detection direction is radial outward, and the point measurement interval is 20cm to detect the surrounding rock conditions behind the arch crown and arch waist of the tunnel. The detection personnel work on the tunneling machine platform and achieve the detection work throughout the entire process by slowly moving the equipment. S2. Setting out the excavation outline Before each shift begins excavation, a total station is used to measure the excavation outline, which is then marked with red paint, with the circumferential spacing between the points not exceeding 40cm. S3, Advanced Pilot Tunnel Milling The pre-drilling area is 35m². 2 The slag is loaded and transported to the spoil disposal site using a combination of loaders and dump trucks; the advance of the pilot tunnel is determined based on the rock strength, with the advance range of a single cycle controlled between 1.2m and 2.0m, and the single cycle operation time controlled within 11 hours; the distance between the pilot tunnel and the enlarged excavation face is kept within 20m, and dust removal is carried out using onboard special dust removal equipment. S4. Excavation of the widened face The parameters for the enlarged excavation section include an excavation height of 6.2m, an excavation width of 8.06m, and the enlarged excavation section accounting for 51% of the area of ​​the upper bench section. The excavation face will be excavated using a drilling + hydraulic hammer excavation scheme. Drilling parameters for the enlarged excavation face include: a hole diameter of 110mm, a hole depth of 5m, and a horizontal and vertical hole spacing of no more than 40cm. The operation time will be controlled between 4 and 6 hours. For hydraulic hammer excavation, a single-cycle construction advance will be carried out with a spacing between two steel frames. The diameter of the hydraulic hammer drill rod must be larger than the hole diameter, and the average construction efficiency will be 5-6 cubic meters per hour. The enlarged excavation will be carried out in parallel with the milling of the pilot tunnel. After the enlarged excavation is completed, the tunneling machine needs to withdraw to trim the outline, ensuring a smooth excavation outline and improving excavation quality. S5, Step support After the excavation of the enlarged face is completed, the initial support of the upper bench is promptly constructed. The scaffolding operation adopts the construction of a modular and separate working platform, and the shotcreting operation adopts the construction of a wet shotcreting robotic arm. The single-cycle support advances at a spacing of 2 steel frames, and the shotcreting protection of the pilot tunnel is synchronized with the initial support shotcreting cycle. S6. Excavation of the lower bench and invert arch The lower steps and invert arch were excavated using hydraulic hammers, and the construction equipment used was a PC500 excavator and an SG4500 tower breaker. The equipment used for dumping and loading is a PC360 excavator, and the excavated material is transported using 20-cubic-meter dump trucks.

2. The method for excavating a pilot tunnel in hard rock as described in claim 1, characterized in that, The dust removal method used in the construction method specifically includes the following steps: C1. Arrangement of ventilation ducts A set of variable frequency axial flow fans is installed at the tunnel entrance, using forced air supply. The motor power is 2×110KW, the ventilation duct diameter is 2m, the duct is set near the side arch of the excavation face, and the air outlet is no more than 10m away from the excavation face. C2. Dust removal arrangement for the pilot tunnel The advanced pilot tunnel method is adopted for construction, and on-board dust removal equipment is used for dust suppression. The motor power of the on-board dust removal machine is 2×37KW. The on-board dust removal machine is installed on the top platform of the tunneling machine, and vibration damping rubber pads are set at the bottom. The power supply voltage is the same as that of the tunneling machine, and 1140V high-voltage cable is used for connection. C3. Dust removal arrangement at the excavation face To further purify the residual dust in the air discharged from the pilot tunnel, an XCS1500 tunnel dust removal vehicle is installed on the left side wall of the step on the widened excavation face. The vehicle uses water atomization, filtration, and water film dust removal mechanism to draw dust-containing gas into the air duct and send it into the dust collector. The dust gas is fully mixed with the high-pressure water mist in the dust collector, and the gas and liquid are separated by multiple layers of metal filter screens. Finally, the clean air is discharged through the exhaust port, and the dust and water form mud, which is pumped into the temporary sedimentation tank in the tunnel. The XCS1500 tunnel dust removal vehicle is arranged in parallel with the excavation face equipment, with a reserved muck discharge channel in the middle. The distance between the dust removal vehicle's air suction pipe opening and the pilot tunnel opening is no more than 2m. C4. Sprinkler dust suppression system In order to further purify the polluted air emitted by the XCS1500 tunnel dust removal vehicle and reduce the temperature inside the tunnel, a spray pipe was installed circumferentially on the initial support surface of the upper step, and a water tank and booster pump were configured. The distance between the spray arrangement section and the exhaust pipe outlet at the tail of the dust removal machine is 5m.

3. The method for excavating a pilot tunnel in hard rock as described in claim 1, characterized in that, In step S3, the pilot tunnel is excavated using an XTR7 / 360 cantilever tunneling machine.

4. The method for excavating a pilot tunnel in hard rock as described in claim 1, characterized in that, In step S4, the rock face is excavated using a ZYS113 three-arm rock drilling rig for assisted drilling, and the hydraulic hammer excavation equipment is a PC500 short-arm excavator + SG4500 tower breaker.

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