Step type layered and regional construction method for bridge type pilot tunnel

Abstract

The invention discloses a step-type layered and regional construction method for a bridge pilot tunnel. The step-type layered and regional construction method comprises the following steps that the position of a chamber is planned; according to the planned position of the chamber, a slope ramp is firstly tunneled in the direction of the chamber at the construction roadway to serve as a measure roadway, and the measure roadway is lifted to the height of a top plate of a comprehensive machine overhaul room and then falls flat; the construction roadway is provided with a semicircular arch-shaped section, according to actual exposed rocks, when the rocks are broken, the construction roadway is supported by adopting a full-section anchor net shotcrete, and guniting sealing is carried out on the side part; after the top plate of the pilot tunnel reaches the height of the top plate of the comprehensive machine overhaul room, turning flat and continuing forward construction; constructing a first step; performing back expansion construction; constructing a second step; and third step construction. A multi-layer high-strength bolt grouting and deep hole grouting combined anchor cable combined supporting technology is adopted, the construction progress is accelerated, the labor intensity is greatly reduced, the integrality of the surrounding rock and the bearing capacity of the surrounding rock are effectively improved, common bearing of the supporting structure and the surrounding rock is achieved, and the good supporting effect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of chamber construction, and particularly to a construction method for a bridge-type pilot tunnel with stepped layered and zoned construction. Background Art

[0002] A chamber is a horizontal tunnel that does not directly lead to the surface exit, has a relatively large cross-section and a short length, and is used for installing various equipment, storing materials, etc. When constructing a super-large cross-section chamber in a coal mine underground, due to the large cross-section, many changes, and short length of the chamber, it is difficult for large construction machinery to enter the working face for construction. Moreover, the chamber is often connected to other chambers, roadways, and shafts, with a complex structure and a stress state that is not easy to accurately analyze, resulting in great construction difficulty.

[0003] The existing chamber construction methods mainly include the full-face one-time tunneling method, the bench working face construction method, and the pilot tunnel construction method. The full-face one-time tunneling method is commonly used for chambers with relatively stable surrounding rocks and not particularly large cross-sections. The bench working face construction method is generally used under the condition of stable or relatively stable rock formations. The pilot tunnel construction method is to first drive a small cross-section in advance and then expand it to the designed cross-section, but for the construction of super-large cross-section chambers, the construction efficiency is low, the labor intensity is high, and there are safety hazards such as excessive exposed area and long exposure time of the lower layer roof during the construction process, and roof fall and rib spalling. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a construction method for a bridge-type pilot tunnel with stepped layered and zoned construction, which has high construction efficiency and good support effect.

[0005] The technical solution of the present invention to solve the above technical problems is: a construction method for a bridge-type pilot tunnel with stepped layered and zoned construction, including the following steps:

[0006] Step P1: Plan the position of the chamber. The chamber includes a first bench, a second bench, and a third bench arranged in sequence from top to bottom. The top of the chamber is an arc-shaped arch roof, that is, the top of the first bench is an arc-shaped arch roof;

[0007] Step P2: According to the planned position of the chamber, drive a ramp as a measure roadway in the construction roadway towards the chamber. The measure roadway is inclined upward and levels off after being raised to the height of the roof of the comprehensive machine maintenance room;

[0008] The construction roadway has a semi-circular arched cross-section. When the actually exposed rock is broken, the construction roadway is supported by full-section bolt-net-shotcrete, and the sidewalls are sprayed for sealing;

[0009] After the roof of the pilot tunnel roadway reaches the height of the roof of the comprehensive machine maintenance room, start to level off and continue to drive forward;

[0010] Step P5: Construction of the first bench; divided into the first area and the second area, the bench sectional tunneling method is adopted, and the cyclic method is to advance forward in parallel in the way of "two excavations and one shotcrete" to the designed termination position. After each blasting, observe the mountain and search for loose rocks on the roof and both sides. After all the loose and dangerous rocks are removed, multiple single hydraulic props are used in cooperation with wooden boards to support the steel bar mesh as temporary support. The lower end of the roof prop is placed on the solid bottom, the steel bar mesh is propped against the controlled roof area, and the bolting with wire mesh support follows the working face closely for shotcreting and sealing; after the first bench is shotcreted into a roadway, the hollow grouting bolt support, the hollow grouting cable bolt support, the grouting combined cable bolt support, the cable beam support, and the ordinary steel strand cable bolt support are carried out in sequence. The secondary support is parallel to the working face construction. After all the supports in the first bench are completed and meet the roadway forming standard, the reaming construction is entered;

[0011] Step P6: Reaming construction: Blast and cut the bottom under the plug wall at the termination position of the roadway, then adjust the ventilation route, connect the air duct from the track transportation crossheading, the belt transportation crossheading through the breakthrough point to the heading face. During reaming, the reaming amount changes continuously with the tunneling position, divided into the left and right areas, and the cyclic method is "two excavations and one shotcrete". The left and right areas alternate for cyclic operation and advance forward in parallel to the designed termination position. After reaming is completed, all the supports in all areas are completed and meet the roadway forming standard, and then the construction of the next stage is entered;

[0012] Step P7: Construction of the second bench: The construction method of the second bench is the same as that of the first bench. After all the supports in the second bench are completed and meet the roadway forming standard, ensure that the track and rubber connection roadway is completely filled with ballast;

[0013] Step P8: Construction of the third bench: The construction method of the third bench is the same as that of the first bench. After all the supports in the third bench are completed and meet the roadway forming standard, remove all the accumulated ballast in the roadway.

[0014] In the above-mentioned bridge-type pilot drift bench-type layered sectional construction method, in step P2, the measure roadway adopts full-section bolting with wire mesh and shotcrete support, the cyclic footage is 1.6 m, the bolts are Φ22×2600 mm high-strength bolts, the spacing in rows is 800×800 mm, the wire mesh is Φ6 mm, the grid spacing is 80×80 mm, the lap length is 100 mm, the shotcrete thickness is 50 mm, and the shotcrete strength is C20.

[0015] In the above-mentioned bridge-type pilot drift bench-type layered sectional construction method, in step P5, smooth blasting technology is adopted for roadway blasting, and coal mine permitted grade III emulsion explosive is used. The cartridge specification is: Φ35×400 mm, 0.44 kg / roll, forward charging, detonated by coal mine permitted millisecond-delay electric detonator, and detonated once by an MBF-200 type mine explosion-proof detonator; during shotcreting, the initial shotcrete thickness is 30 - 50 mm, the re-shotcrete thickness is 50 - 70 mm, the shotcrete strength is C20, and the total thickness is T = 100 mm.

[0016] For the above-mentioned construction method of bridge-type pilot drift step-by-step layered and zoned construction, in step P5, when carrying out bolt-net-shotcrete support, the bolts used are KMG22-500 type left-handed non-longitudinal high-strength resin bolts with a diameter of Φ22×2800mm, the spacing in rows and columns is 800×800mm, 37 bolts per row, 3 resin cartridges per bolt. The first cartridge is MSK2635 quick-setting resin cartridge, and the latter 2 cartridges are MSZ2635 medium-setting resin cartridges. The anchoring force is not less than 280kN; the trays used are dish-shaped trays with a diameter of Φ150×10mm; the wire meshes are all made of Φ6 steel bar meshes with a mesh spacing of 80×80mm and a lap length of not less than 100mm; the thickness of the shotcrete is T = 100mm; the volume ratio of the concrete mixture is cement:sand:gravel = 1:2:2, and the dosage of the accelerator in the shotcrete is 2.5-4% of the weight of the cement.

[0017] For the above-mentioned construction method of bridge-type pilot drift step-by-step layered and zoned construction, in step P5, when carrying out hollow grouting bolt support, Φ25×3000mm hollow grouting bolts are used, the spacing in rows and columns is 1600×1600mm, 19 bolts are arranged in each row, the trays used are dish-shaped trays with a diameter of Φ150×10mm, the grouting uses single-component cement slurry, the water-cement ratio of the slurry is 1:1 to 1:1.2, and ACZ-I type cement additive is added in the proportion of 8% of the cement dosage, and the grouting pressure is controlled at 3.0-5.0 Mpa.

[0018] For the above-mentioned construction method of bridge-type pilot drift step-by-step layered and zoned construction, in step P5, when carrying out hollow grouting cable support, Φ21.8×10000mm cables are used, the spacing in rows and columns is 2400×3200mm, 12 cables are arranged in each row, and square trays with a size of 300×300×16mm are used. The grouting uses single-component cement slurry, the water-cement ratio of the slurry is 1:1 to 1:1.2, and ACZ-I type cement additive is added in the proportion of 8% of the cement dosage, and the grouting pressure is controlled at 4.0-6.0 Mpa.

[0019] For the above-mentioned construction method of bridge-type pilot drift step-by-step layered and zoned construction, in step P5, after the bolt-net-shotcrete support, hollow grouting bolt support and hollow grouting cable support are completed, secondary bolt-net support is carried out. The bolt parameters of the secondary bolt-net support are the same as those of the primary bolt selection; the steel bar mesh is made of steel wire woven mesh with a diameter of Φ4-40×40mm.

[0020] For the above-mentioned construction method of the bridge-type pilot drift stepwise layered and sectionalized, in step P5, regarding the cable anchor beam support, the top cable anchors are Φ21.8×7500mm 19-strand steel wire strand cable anchors, with a spacing of 2000×1400mm between rows and 7 anchors per row. Five resin cartridges are used per anchor. The first two cartridges are MSK2635 quick resin cartridges, and the last three cartridges are MSZ2635 medium-speed resin cartridges. The anchoring force is not less than 250KN. The side cable anchors are Φ21.8×5500mm 19-strand steel wire strand cable anchors, with a spacing of 2000×1400mm between rows and 8 anchors per row. The cable anchors need to be installed with bearing beams. The bearing beams are processed from U36 steel. The beam length is 1700mm. Two cable anchor holes are reserved on each bearing beam, with a spacing of 1400mm between the cable anchor holes. The installation direction of the bearing beam is the same as the driving direction of the roadway. Anchor fittings are installed outside the bearing beam.

[0021] For the above-mentioned construction method of the bridge-type pilot drift stepwise layered and sectionalized, in step P5, when carrying out grouting combined cable anchor support, each bundle of the grouting combined cable anchors is composed of multiple Φ22mm steel wire strands, with a length of 21m, a spacing of 2400×3200mm between rows, and 5 bundles per row.

[0022] For the above-mentioned construction method of the bridge-type pilot drift stepwise layered and sectionalized, the exposed length of the grouting combined cable anchors is allowed not to exceed 500mm. The grouting combined cable anchor plates are welded and processed from a Φ360×20mm thick steel plate and a Φ260×16mm thick steel plate. Drill holes on the cable anchor plate, and the hole spacing is processed according to the hole spacing of the grouting cable anchor fittings. The grouting combined cable anchor fittings adopt Φ22mm×3 high-strength cast iron combined lock fittings. A Φ25mm plastic pipe is sleeved on the 5m section at the end of the grouting combined cable anchor. A Φ8mm plastic pipe is inserted between the three steel wire strands of the grouting combined cable anchor as the exhaust pipe during grouting construction. The three steel wire strands are fixed by support frames, and one support frame is tied every 2m. The support frames are processed by welding three Φ6×100mm steel bars outside a Φ24mm nut. Before grouting the grouting combined cable anchor, a grouting pipe is installed at the hole mouth. The grouting pipe adopts a Φ25.4×1000mm galvanized pipe. The grouting pipe is processed into fish scale buckles, and the slurry inlet end is processed with threads, and a Φ25.4mm ball valve is installed to control the slurry in the hole. Grouting is carried out with P.O42.5 grade cement single liquid slurry, and ACZ-I type cement additive is added at a ratio of 8% of the cement dosage. The grouting pressure is controlled at 7.0Mpa. Ten days later, the combined grouting cable anchors are tensioned one by one. When installing the anchor plate before tensioning, first level the hole mouth, install the anchor fittings, and then put on the jack for tensioning. During tensioning, tension in groups and cycles strand by strand.

[0023] The beneficial effects of the present invention are as follows: The present invention proposes a construction method for a bridge-type pilot tunnel step-by-step layered and zoned construction. Based on the traditional bolt-net-cable-shotcrete support, a combined support technology of multi-layer high-strength bolt grouting and deep-hole grouting combined cable bolts is adopted, which not only speeds up the construction progress but also greatly reduces the labor intensity, effectively improves the integrity of the surrounding rock and the bearing capacity of the surrounding rock itself, realizes the common bearing of the support structure and the surrounding rock, and achieves good support effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a side view of the chamber of the present invention.

[0025] Figure 2 It is a side view of the cross-section of the measure roadway of the present invention.

[0026] Figure 3 It is a construction plan view of the measure roadway of the present invention.

[0027] Figure 4 It is a construction sectional view of the measure roadway of the present invention.

[0028] Figure 5 It is a construction plan view of the maintenance construction of the present invention.

[0029] Figure 6 It is a construction sectional view of the maintenance construction of the present invention.

[0030] Figure 7 It is a construction plan view of the reaming construction of the present invention.

[0031] Figure 8 It is a construction sectional view of the reaming construction of the present invention.

[0032] Figure 9 It is a construction plan view of the third step of the present invention.

[0033] Figure 10 It is a construction sectional view of the third step of the present invention.

[0034] Figure 11 It is a support diagram of the chamber cross-section of the present invention;

[0035] In the figure, 1 is the construction roadway; 2 is the measure roadway; 3 is the first step; 4 is the second step; 5 is the third step; 6 is the chamber; 7 is the shotcrete; 8 is the steel bar mesh; 9 is the reaming area; 10 is the high-strength bolt; 11a is the high-strength resin bolt 11a; 11b is the roof cable bolt; 11c is the side cable bolt; 12a is the hollow grouting bolt support; 12b is the hollow grouting cable bolt support. SPECIFIC EMBODIMENTS

[0036] The present invention will be further described below with reference to the drawings and embodiments.

[0037] A construction method for a bridge-type pilot tunnel step-by-step layered and zoned construction includes the following steps:

[0038] Step P1: Plan the location of chamber 6. Chamber 6 includes a first step 3, a second step 4, and a third step 5 arranged in sequence from top to bottom. The top of chamber 6 is an arc vault, that is, the top of the first step 3 is an arc vault. The height of the first step 3 is 3.8 meters, the height of the second step 4 is 4 meters, and the height of the third step 5 is 3.5 meters.

[0039] Step P2: According to the planned location of chamber 6, drive a ramp as the measure roadway 2 in the direction of chamber 6 at the construction roadway 1. The measure roadway 2 is inclined upward, and the inclination angle is controlled at about 20°, and it is leveled after being raised to the height of the roof of the fully-mechanized mining face maintenance room.

[0040] The measure roadway 2 is supported by full-section bolt-net-shotcrete, with a cycle footage of 1.6 meters. The bolts selected are Φ22×2600mm high-strength bolts 10, with a row spacing of 800×800mm. The steel mesh is Φ6mm, with a grid spacing of 80×80mm, a lap length of 100mm, a shotcrete thickness of 50mm, and a shotcrete strength of C20.

[0041] The construction roadway 1 has a semi-circular arch section. When the rock actually exposed is broken, the construction roadway 1 is supported by full-section bolt-net-shotcrete, and the sidewalls are sealed with shotcrete.

[0042] After the roof of the pilot roadway reaches the height of the roof of the fully-mechanized mining face maintenance room, it starts to turn flat and continue to be constructed forward. The pilot roadway has a semi-circular arch section, with a height of 3.8 meters and a width of 4.2 meters.

[0043] Step P5: Construction of the first step 3; it is divided into a first area 3a and a second area 3b. The step-by-step area driving method is adopted, and the cycle method is "two drivings and one shotcreting" to push forward in parallel to the designed termination position, with a cycle footage of 1.6 meters; after each blasting, a special person is set to observe the mountain and search for the top. After all the loose rocks and dangerous rocks on the roof and both sidewalls are removed, 3 single hydraulic props are used in cooperation with a wooden board to support the steel bar mesh 8 as temporary support. The lower end of the roof column is placed on the solid bottom, the steel bar mesh is pushed against the controlled roof area, and the bolt-net support follows the working face closely, and shotcrete sealing is carried out in a timely manner; after the first step 3 is shotcreted to 70% of the roadway formation, hollow grouting bolt support 12a, hollow grouting cable support 12b, grouting combined cable support, cable beam support, and ordinary steel strand cable support are carried out in sequence. The secondary support is parallel to the working face construction. After all the supports in the first step 3 are completed and reach the roadway formation standard, the reaming construction is carried out;

[0044] Smooth blasting technology is used for roadway blasting. Coal mine permitted grade III emulsion explosive is used, with a cartridge specification of Φ35×400mm, 0.44kg / roll, forward charging, detonated by coal mine permitted millisecond-delay electric detonator, and detonated once by an MBF-200 type mine explosion-proof detonator.

[0045] During shotcreting, the initial shotcrete thickness is 30 - 50 mm, the secondary shotcrete thickness is 50 - 70 mm, the shotcrete strength is C20, and the total thickness is T = 100 mm.

[0046] For bolt - mesh - shotcrete support, the bolt used is the KMG22 - 500 type left - hand non - longitudinal high - strength resin bolt with Φ22×2800 mm, the bolt spacing and row spacing are 800×800 mm, there are 37 bolts per row, 3 resin cartridges per bolt. The first cartridge is the MSK2635 quick - setting resin cartridge, and the latter 2 cartridges are the MSZ2635 medium - setting resin cartridges. The anchoring force is not less than 280 kN; the tray used is a Φ150×10 mm dish - shaped tray, and the steel tray and screw thread are matched with the bolt to reach the design strength; the metal mesh used is a Φ6 steel bar mesh with a mesh spacing of 80×80 mm and a lap length of not less than 100 mm; the shotcrete thickness is T = 100 mm, and the strength of the sprayed concrete is not less than C20; the volume ratio of the concrete mixture is cement:sand:gravel = 1:2:2, and the admixture amount of the quick - setting agent in shotcreting is 2.5 - 4% of the cement weight.

[0047] When carrying out hollow grouting bolt support 12a, Φ25×3000 mm hollow grouting bolts are used, the bolt spacing and row spacing are 1600×1600 mm, 19 bolts are arranged in each row, the tray used is a Φ150×10 mm dish - shaped tray, the grouting uses single - liquid cement slurry, the water - cement ratio of the slurry is 1:1 - 1:1.2, and an ACZ - I type cement additive is added at a ratio of 8% of the cement dosage. The grouting pressure is controlled at 3.0 - 5.0 Mpa.

[0048] When carrying out hollow grouting cable support 12b, Φ21.8×10000 mm cables are used, the cable spacing and row spacing are 2400×3200 mm, 12 cables are arranged in each row, and a 300×300×16 mm square tray is equipped. The grouting uses single - liquid cement slurry, the water - cement ratio of the slurry is 1:1 - 1:1.2, and an ACZ - I type cement additive is added at a ratio of 8% of the cement dosage. The grouting pressure is controlled at 4.0 - 6.0 Mpa.

[0049] After the bolt - mesh - shotcrete, hollow grouting bolt support 12a and hollow grouting cable support 12b are completed, secondary bolt - mesh support is carried out. The bolt parameters of the secondary bolt - mesh support are the same as those of the primary bolt selection; the steel bar mesh used is a steel wire woven mesh with Φ4 - 40×40 mm.

[0050] Regarding the cable-beam support, the top cable 11b is a 19-wire strand cable with a diameter of Φ21.8×7500mm. The row and column spacing is 2000×1400mm, with 7 cables per row. 5 resin cartridges are used per cable. The first 2 cartridges are MSK2635 quick resin cartridges, and the last 3 cartridges are MSZ2635 medium-speed resin cartridges. The anchoring force is not less than 250KN. The side cable 11c is a 19-wire strand cable with a diameter of Φ21.8×5500mm. The row and column spacing is 2000×1400mm, with 8 cables per row. The cable needs to be installed with a bearing beam, which is made of U36 steel. The beam length is 1700mm. Two cable holes are reserved on each bearing beam, and the spacing between the cable holes is 1400mm. The installation direction of the bearing beam is the same as the roadway driving direction, and an anchor fitting is installed outside the bearing beam.

[0051] When carrying out grouting combined cable support, each bundle of grouting combined cables is composed of 3 steel strands with a diameter of Φ22mm, with a length of 21m. The row and column spacing is 2400×3200mm, and there are 5 bundles per row. The whole bundle of cables is composed of steel strands, guide caps, plastic sleeves, support frames, and exhaust pipes. The exposed length of the grouting combined cable is allowed not to exceed 500mm. The grouting combined cable tray is welded and processed from a 360×20mm thick steel plate and a 260×16mm thick steel plate. There are 3 holes drilled on the cable tray, and the hole spacing is processed according to the hole spacing of the grouting cable lock. The grouting combined cable lock is a Φ22mm×3 high-strength cast iron combined lock. The 5m section at the end of the grouting combined cable is sleeved with a Φ25mm plastic pipe. A Φ8mm plastic pipe is inserted between the 3 steel strands of the grouting combined cable as the exhaust pipe during grouting construction. The guide cap is processed from a DN50mm×200mm steel pipe, and the end of the steel pipe is made into a cone to facilitate the cable to penetrate into the cable hole. The 3 steel strands are fixed by support frames, and one support frame is tied every 2m. The support frame is processed by welding 3 Φ6×100mm steel bars outside a Φ24mm nut. Before grouting the grouting combined cable, a grouting pipe is installed at the hole mouth. The grouting pipe is a Φ25.4×1000mm galvanized pipe, and the grouting pipe is processed into fish scale buckles. The slurry inlet end is processed with threads, and a Φ25.4mm ball valve is installed to control the slurry in the hole. The grouting uses P.O42.5 grade cement single-fluid slurry and adds ACZ-I type cement additive at a ratio of 8% of the cement dosage. The grouting pressure is controlled at 7.0Mpa. After 10 days, the combined grouting cables are tensioned one by one. Before tensioning, when installing the anchor plate, first level the hole mouth, install the anchor fitting, and then put on the jack for tensioning. During tensioning, tension in groups by strands in a cyclic manner. The tension strength of a single cable shall not be less than 100KN.

[0052] Step P6: Reaming construction: Blasting and bottom cutting are carried out under the plug wall at the end position of the roadway. The bottom cutting area for blasting and bottom cutting is 5 meters long and 4 meters wide. Then, adjust the ventilation route, connect the air duct from the track transportation crossheading, belt transportation crossheading through the breakthrough point to the heading face. During reaming, the reaming amount changes continuously with the driving position, and is divided into two areas, left and right. The cyclic method adopts "two drivings and one shotcreting". The left and right areas alternate for cyclic operation and advance parallelly to the designed end position. After reaming is completed, all support in all areas is completed to meet the roadway forming standard, and then the construction of the next stage is entered. During reaming, personnel walking and material transportation all take the side of the belt crossheading. A fence is set up at the opening of the track-belt connection roadway, and it is strictly prohibited for personnel to enter.

[0053] Step P7: Construction of the second bench 4: The construction method of the second bench 4 is the same as that of the first bench 3, and is divided into the first area 4a and the second area 4b. After all support in the second bench 4 is completed to meet the roadway forming standard, ensure that the track-belt connection roadway is completely filled with muck.

[0054] Step P8: Construction of the third bench 5: The construction method of the third bench 5 is the same as that of the first bench 3, and is divided into the first area 5a and the second area 5b. After all support in the third bench 5 is completed to meet the roadway forming standard, clean out all the accumulated muck in the roadway.

Claims

1. A bridge-type pilot tunnel step-by-step layered and regional construction method, characterized in that: The following steps are involved: Step P1: planning the position of the chamber, the chamber comprising a first step, a second step and a third step arranged in sequence from top to bottom, the top of the chamber being a circular arc dome, that is, the top of the first step being a circular arc dome; Step P2: According to the planned location of the chamber, a ramp is first excavated in the construction tunnel towards the chamber as a measure tunnel, and the measure tunnel is tilted upward and raised to the height of the roof of the comprehensive machine maintenance room and then leveled; Step P3: The construction tunnel has a semicircular arch section. According to the actual exposed rock, when the rock is broken, the construction tunnel adopts full-section anchor mesh spraying support, and the side is sealed by spraying; Step P4: After the top plate of the pilot tunnel reaches the height of the top plate of the comprehensive machine maintenance room, it starts to level and continue to move forward; Step P5: Construction of the first step; divided into the first area and the second area, the step-by-step regional excavation method is adopted, and the circulation method adopts "two excavations and one spraying" to advance forward in parallel to the designed end position. After each blasting, the mountain is observed to find the top. After the top plate and the two sides of active gangue and dangerous rocks are all found, multiple single hydraulic pillars are used in conjunction with wooden boards and steel fences as temporary support. The lower end of the top column is placed on the solid bottom, and the steel fence is placed on the top control area. The anchor net support follows the working face and is sprayed and closed; after the first step is sprayed into the lane, hollow grouting anchor rod support, hollow grouting anchor cable support, grouting combined anchor cable support, anchor cable beam support, and ordinary steel strand anchor cable support are carried out in turn. The secondary support is carried out in parallel with the working face construction. After all the supports in the first step are completed and meet the lane forming standards, the expansion construction begins; Step P6: Back-expansion construction: Blasting is carried out under the plugging wall at the end position of the tunnel, and then the ventilation route is adjusted. The air duct is connected from the circular parking lot of the track transport stone gate and the belt transport stone gate through the penetration point to the head. During the back-expansion, the expansion and brushing volume changes with the excavation position. It is divided into two areas, left and right. The circulation method adopts "two excavations and one spraying". The left and right areas are alternately cycled and pushed forward in parallel to the designed end position. After the back-expansion is completed, all supports in all areas are completed to meet the tunneling standards, and then enter the next stage of construction; Step P7: Construction of the second step: The construction method of the second step is the same as that of the first step. After all the supports in the second step are completed and meet the tunnel standard, ensure that the rail-joint tunnel is completely filled with ballast; Step P8: Construction of the third step: The construction method of the third step is the same as that of the first step. After all the supports in the third step are completed and meet the standards for tunneling, all the accumulated ballast in the tunnel will be cleared.

2. The step-by-step, layered and zoned construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In step P2, the measure tunnel adopts full-section anchor mesh spraying support, with a cycle advance of 1.6 meters, and the anchor rods are Φ22×2600mm high-strength anchor rods, the spacing between rows is 800×800mm, the steel mesh is Φ6mm, the grid spacing is 80×80mm, the overlap length is 100mm, the spraying thickness is 50mm, and the spraying strength is C20.

3. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In the step P5, the tunnel blasting adopts the smooth blasting technology, uses the third-level emulsion explosive permitted in coal mines, the specifications of the explosive roll are: Φ35×400mm, 0.44kg / roll, forward charging, and the millisecond delay electric detonator permitted in coal mines is detonated. The MBF-200 type mine flameproof detonator is used for one-time detonation; when spraying, the initial spraying thickness is 30-50mm, the re-spraying thickness is 50-70mm, the spraying strength is C20, and the total thickness is T=100mm.

4. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In the step P5, when the anchor net is sprayed for support, the anchor rods are Φ22×2800mm KMG22-500 left-handed high-strength resin anchor rods without longitudinal reinforcement, with a row spacing of 800×800mm, 37 rods / row, 3 rolls of resin medicine / root, the first roll is MSK2635 fast resin medicine roll, and the next two rolls are MSZ2635 medium-speed resin medicine rolls, with an anchoring force of not less than 280kN; the pallet is Φ150×10mm disc pallet; the metal mesh is Φ6 steel mesh, with a grid spacing of 80×80mm and a lap length of not less than 100mm; the sprayed concrete thickness is T=100mm; the volume ratio of the concrete material is cement: sand: gravel=1:2:2, and the amount of the accelerating agent added during spraying concrete is 2.5-4% of the weight of the cement.

5. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In step P5, when hollow grouting anchor support is performed, Φ25×3000mm hollow grouting anchors are used, the spacing between rows is 1600×1600mm, 19 anchors are arranged in each row, the tray is a Φ150×10mm disc tray, and cement single-liquid slurry is used for grouting. The slurry water-cement ratio is 1:1 to 1:1.2, and ACZ-I type cement additive is added at a ratio of 8% of the cement dosage. The grouting pressure is controlled at 3.0-5.0Mpa.

6. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In step P5, when hollow grouting anchor cable support is performed, Φ21.8×10000mm anchor cables are used, the spacing between rows is 2400×3200mm, 12 cables are arranged in each row, and a 300×300×16mm square tray is provided. Cement single-liquid slurry is used for grouting, and the slurry water-cement ratio is 1:1 to 1:1.

2. ACZ-I type cement additive is added at a ratio of 8% of the cement dosage, and the grouting pressure is controlled at 4.0-6.0Mpa.

7. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In step P5, after the anchor net spraying, hollow grouting anchor support and hollow grouting anchor cable support are completed, secondary anchor net support is carried out. The anchor rod parameters of the secondary anchor net support are consistent with the primary anchor rod selection; the steel fence mesh adopts a Φ4-40×40mm steel wire braided mesh.

8. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1 is characterized in that: In the step P5, regarding the anchor cable beam support, the top anchor cable is Φ21.8×7500mm19-wire steel hinged wire anchor cable, the row spacing is 2000×1400mm, 7 pieces / row, 5 rolls of resin medicine / root, the first 2 rolls are MSK2635 fast resin medicine rolls, and the last 3 rolls are MSZ2635 medium-speed resin medicine rolls, and the anchoring force is not less than 250KN; the auxiliary anchor cable is Φ21.8×5500mm19-wire steel hinged wire anchor cable, the row spacing is 2000×1400mm, 8 pieces / row; the anchor cable needs to be installed with a joist, the joist is made of U36 steel, the beam length is 1700mm, two anchor cable holes are reserved on each joist, the anchor cable hole spacing is 1400mm, the joist installation direction is consistent with the tunnel excavation direction, and the anchor is installed outside the joist.

9. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1, characterized in that: In step P5, when the grouting combined anchor cable support is performed, each bundle of the grouting combined anchor cable is composed of a plurality of Φ22mm steel strands, with a length of 21m, a row spacing of 2400×3200mm, and 5 bundles per row.

10. The step-by-step, stratified and regionalized construction method of a bridge-type pilot tunnel according to claim 1, characterized in that: The exposed length of the grouting combined anchor cable is allowed to be no more than 500mm. The grouting combined anchor cable disc is welded by Φ360×20mm thick steel plate and Φ260×16mm thick steel plate. Holes are drilled on the anchor cable disc, and the hole spacing is processed according to the hole spacing of the grouting anchor cable lock. The grouting combined anchor cable lock adopts Φ22mm×3 high-strength cast iron combined lock. The 5m section at the tail end of the grouting combined anchor cable is inserted into a Φ25mm plastic pipe. The grouting combined anchor cable inserts a Φ8mm plastic pipe in the middle of the three steel strands as an exhaust pipe during grouting construction. The three steel strands are fixed by a support frame, and a support frame is tied every 2m. The support frame is welded with 3 Φ24mm nuts. 6×100mm steel bars are processed; before grouting the grouting combined anchor cable, a grouting pipe is installed at the hole mouth. The grouting pipe adopts a Φ25.4×1000mm galvanized pipe. The grouting pipe is processed into a fish scale buckle, and the slurry inlet end is processed with a thread. A Φ25.4mm ball valve is installed to control the slurry in the hole; P.O42.5 grade cement single liquid slurry is used for grouting, and ACZ-I type cement additives are added at a ratio of 8% of the cement dosage. The grouting pressure is controlled at 7.0Mpa. After 10 days, the combined grouting anchor cables are expanded and pulled one by one. When installing the anchor plate before expansion and pulling, the hole mouth is leveled first, and the anchor is installed, and then the jack is put on for expansion and pulling. When expanding and pulling, each strand is expanded and pulled in a cycle.

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