A construction method for treating the roof caving at the reverse exit of a tunnel

Abstract

The present invention relates to a construction method for treating the roof caving at the reverse exit of a tunnel. By using the collapsed slag body at the roof caving, a slope is built from the tunnel to the ground surface at the roof caving, and the slope is used for personnel and mechanical equipment to pass through. The present invention completely changes the traditional treatment method and creatively uses the slope built with the collapsed slag body, enabling personnel and mechanical equipment to quickly reach the ground surface from the slope, canceling the small pilot tunnel located in the collapsed slag body and relying entirely on manual construction, and the entire construction process can be carried out using large-scale machinery, with good construction safety; canceling the grouting of the collapsed slag body and the surrounding rock of the tunnel in the traditional treatment method, canceling the strong advance support, canceling the support of the small pilot tunnel, side walls, etc., greatly reducing the project cost; taking a 20m roof caving as an example, the traditional treatment method requires at least 3 months for reinforcement and the small pilot tunnel to exit, while the present invention only takes 3 days to reach the ground surface; this method has simple steps, high safety, saves project cost, has a fast construction period, and good effects.

Description

Technical Field

[0001] The present invention relates to the field of tunnel construction, and in particular to a construction method for treating the roof caving at the reverse exit of a tunnel. Background Art

[0002] In recent years, China's infrastructure construction has been booming. Many high-grade highways and railways have been built into mountainous areas. For example, in recent years, the Chengdu-Kunming Railway, the Sichuan-Tibet Railway, the Jinsha River Expressway, etc. The proportion of tunnel routes in these projects all exceeds 50%. Bridges are built over water and tunnels are drilled through mountains. More and more tunnels are being constructed. The auxiliary topographical and geological conditions make the construction of many tunnels extremely difficult. It is often necessary to set up construction adits to enter the main tunnel for auxiliary construction and then exit the tunnel in the reverse direction. Along with complex geological conditions, especially under the conditions of terrain bias pressure and geological bias pressure at the tunnel entrance, roof caving is extremely likely to occur during reverse tunnel exit. According to incomplete statistics, the roof caving rate of reverse-exiting tunnels due to improper treatment is as high as over 20%, which is extremely likely to lead to safety problems and quality problems, and is a very important safety hazard point in tunnel construction. Improper treatment after roof caving is likely to cause secondary disasters, which not only takes a lot of labor and time, but also involves huge safety risks.

[0003] After roof caving occurs due to terrain and geological bias pressure during reverse tunnel exit, generally, methods such as backfilling the caved slag in the tunnel with counter-pressure, setting up temporary support, backfilling and sealing the roof caving area, and grouting and consolidating the collapsed slag body in front of the tunnel face are adopted. Then, methods such as the three-step method, the side drift method, and the small adit method are used to continue tunneling forward along the main tunnel.

[0004] The existing construction methods for treating roof caving at the reverse exit of a tunnel with terrain and geological bias pressure have the following problems:

[0005] 1. The project scale is extremely large: The existing scheme grouts and consolidates the collapsed slag body, and uses very strong support parameters to excavate the collapsed slag body, resulting in an extremely large amount of engineering work. Generally, such a treatment scheme costs several million yuan.

[0006] 2. The construction period is very long: Whether it is grouting consolidation, or the three-step method, the side drift method, and the small adit method, the purpose is actually to reduce the disturbance to the surrounding rock, and excavation is carried out using a very small cross-section, which makes it impossible to use large-scale machinery and all construction must be carried out manually. The current methods generally take at least 2 to 3 months to complete the treatment.

[0007] 3. The safety hazard is very large: After roof caving, the caved slag in the filled tunnel section and the surrounding rock are also disturbed and loosened. This section is near the tunnel entrance, mostly covered with overburden or strongly weathered rock mass. Coupled with terrain and geological bias pressure, the construction risk is very high. The excavation methods are all small-section manual excavation and manual support, and large-scale construction machinery cannot be used. Moreover, tunneling is carried out in the naturally accumulated collapsed caved slag, and the construction risk is extremely large, and it is very easy to cause secondary collapse and roof caving. Summary of the Invention

[0008] The object of the present invention is to provide a construction method for treating the roof fall at the reverse exit of a tunnel, aiming at the problems existing in the prior art that in the existing construction method for treating the roof fall at the reverse exit of a tunnel with terrain and geological bias pressure, the project scale is large, the cost is high, the manual operation takes a long time, it is easy to cause secondary collapse and roof fall, and there are great potential safety hazards.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A construction method for treating the roof fall at the reverse exit of a tunnel, which utilizes the collapsed slag body at the roof fall to build a slope from the tunnel to the ground surface at the roof fall, and the slope is used for the passage of personnel and mechanical equipment.

[0011] Adopting the construction method for treating the roof fall at the reverse exit of a tunnel described in the present invention completely changes the traditional treatment method. By creatively using the slope built with the collapsed slag body, personnel and mechanical equipment can quickly reach the ground surface from the slope, eliminating the small pilot tunnel located in the collapsed slag body and relying entirely on manual construction. The entire construction process can be carried out using large machinery, and the construction safety is good; the grouting of the collapsed slag body and the surrounding rock of the tunnel in the traditional treatment method is cancelled, the strong advance is cancelled, and the supports such as the small pilot tunnel and the side wall are cancelled, greatly reducing the project cost; taking a 20m collapse and roof fall as an example, the traditional treatment method requires at least 3 months for reinforcement and the exit of the small pilot tunnel, while the present invention only needs 3 days to reach the ground surface; the steps of this construction method are simple, the construction safety is high, the project cost is saved, the construction period is fast, and the effect is good.

[0012] As a preferred technical solution of the present invention, the slope gradient is based on the maximum gradient that a crawler vehicle can climb through to minimize excavation or overexcavation.

[0013] As a preferred technical solution of the present invention, a number of portal steel frames are arranged on the slope to form a portal passage on the slope, and the portal passage is used for the passage of personnel and mechanical equipment.

[0014] By adopting this method, support is formed through the portal steel frames to prevent falling stones at the roof fall from invading the portal passage and protect the safety of the personnel and mechanical equipment passing through the portal passage.

[0015] As a further preferred technical solution of the present invention, the portal steel frame is welded into an Ω shape with I-beams, and adjacent portal steel frames are connected by cross braces.

[0016] As a further preferred technical solution of the present invention, the portal steel frame is welded from 118 I-beams.

[0017] As a further preferred technical solution of the present invention, the steel frame feet of the portal steel frame are back-pressed by the first backfill body.

[0018] By adopting this method, after the portal steel frame is installed in place, the stability of the portal steel frame is ensured by the first backfill body.

[0019] As a further preferred technical solution of the present invention, the first backfill body is a backfilled soil body.

[0020] As a further preferred technical solution of the present invention, the tunnel area near the roof fall is supported by a number of steel grid structures, and the steel grid structures are arranged in close contact with the existing initial support.

[0021] By adopting this method, the steel grid structures are arranged in the adjacent area of the roof fall, and the structure is supported jointly with the existing initial support, so as to strengthen the support and effectively avoid the secondary collapse of the roof fall.

[0022] As a further preferred technical solution of the present invention, the tunnel area within a range of 30 m near the roof fall is supported by the steel grid structures.

[0023] As a further preferred technical solution of the present invention, the circumferential steel bars of the grid are connected by bolts, and the longitudinal grids are welded.

[0024] As a further preferred technical solution of the present invention, the vertical and horizontal spacing of the steel grid structures is 40 cm to 80 cm.

[0025] As a further preferred technical solution of the present invention, the first backfill body is used to backfill the arch feet of the steel grid structures.

[0026] By adopting this method, the stability of the steel grid structures is ensured by the first backfill body, and at the same time, the arch feet are prevented from being soaked by construction water.

[0027] As a further preferred technical solution of the present invention, the surface of the first backfill body is sealed by spraying concrete.

[0028] As a further preferred technical solution of the present invention, the surface of the first backfill body is sealed by spraying C20 concrete with a thickness of 10 cm.

[0029] As a further preferred technical solution of the present invention, the spacing between adjacent portal steel frames is equal to the spacing between adjacent steel grid structures.

[0030] As a further preferred technical solution of the present invention, the top of the portal steel frames in the tunnel area is supported on the steel grid structures.

[0031] By adopting this method, the support capacity is enhanced, and the secondary collapse of the roof fall is effectively avoided.

[0032] As a further preferred technical solution of the present invention, for a tunnel excavated by the bench method, the excavated part of the lower bench behind the heading face is backfilled with muck, and the backfill height is flush with the bottom of the upper bench;

[0033] For a tunnel excavated by the full-face method, the excavated section behind the heading face is leveled, and the leveling height is based on the designed elevation.

[0034] As a further preferred technical solution of the present invention, for a tunnel excavated by the bench method, the steel grid is arranged on the unexcavated part of the lower bench and / or the excavated part of the lower bench that has been backfilled with muck;

[0035] For a tunnel excavated by the full-face method, the steel grid is arranged on the reference line at the designed elevation.

[0036] As a further preferred technical solution of the present invention, for a tunnel excavated by the bench method, the end of the lower bench is backfilled with muck to form a second backfill body with a conical slope-shaped working surface, and the slope of the second backfill body is not steeper than 45°;

[0037] For a tunnel excavated by the full-face method, the muck is backfilled below the designed elevation to form a second backfill body with a conical slope-shaped working surface, and the slope of the second backfill body is not steeper than 45°.

[0038] As a further preferred technical solution of the present invention, the opening at the crown fall is enlarged by a pneumatic pick from inside the tunnel, and the size of the enlarged section is the same as the size of the portal steel frame section.

[0039] As a further preferred technical solution of the present invention, the portal steel frame is erected while excavating. One rail is laid on each side of the ground in the portal chamber. Slide rails are installed at the arch feet of the circumferential main steel frames of the portal steel frame, and the slide rails are fitted on the rails. When the portal chamber is enlarged forward, the rails are successively lengthened forward, and then the base jacks are adjusted to push the portal steel frame forward.

[0040] By using this method, the rails are set on the slope, and then the portal steel frame is pushed forward along the slope by a jack to complete the formation of the entire portal passage. In this way, continuous excavation is carried out in the front, and the portal steel frame is quickly assembled and formed in the rear, and is installed by pushing with the rails, which can improve the construction efficiency.

[0041] As a further preferred technical solution of the present invention, the circumferential main steel frames of the portal steel frame are welded and formed outside the tunnel and assembled inside the tunnel. The circumferential main steel frames are connected in an X shape by using the same type of steel.

[0042] As a further preferred technical solution of the present invention, the wall surface is sealed with shotcrete after enlargement.

[0043] As a further preferred technical solution of the present invention, the thickness of the shotcrete for closing the wall surface after excavation is 24 cm.

[0044] As a preferred technical solution of the present invention, a drone is used for safety monitoring above the roof fall area.

[0045] The slopes with roof falls and collapses are in a critically stable state. Under external interference conditions such as vibration, rain, strong wind, etc., rockfalls or further collapses may occur at any time. To ensure safety, a drone is used for monitoring outside the tunnel. The drone operator observes the collapsed situation outside the tunnel, especially the rockfall situation, through the camera carried by the drone, and transmits it to the safety monitoring personnel inside the tunnel in real time through a walkie-talkie. When collapses, rockfalls, etc. occur outside the tunnel, the personnel inside the tunnel can be aware of it immediately and evacuate in time.

[0046] As a preferred technical solution of the present invention, the nozzle of the wet shotcreting machine is extended from inside the tunnel to the roof fall area, and the concrete is sprayed in a 360-degree rotation to seal the ground surface around the roof fall area with concrete.

[0047] By using this method, it is ensured that there are no loose blocks within a range of 2 m to 3 m around the ground surface of the roof fall area, and the nearby rock mass is stable, protecting the safety of personnel and mechanical equipment to exit the ground from the roof fall area.

[0048] As a further preferred technical solution of the present invention, the thickness of the concrete sprayed by the wet shotcreting machine is greater than 10 cm.

[0049] As a preferred technical solution of the present invention, the slope is hardened.

[0050] As a further preferred technical solution of the present invention, a layer of concrete or anchor plates is laid on the surface of the slope.

[0051] As a further preferred technical solution of the present invention, a layer of 10-cm-thick C20 concrete is laid on the surface of the slope.

[0052] As a preferred technical solution of the present invention, after personnel and mechanical equipment reach the ground from the slope, the collapsed slope surface is sealed with shotcrete with wire mesh.

[0053] As a further preferred technical solution of the present invention, the thickness of the shotcrete with wire mesh sealing is 10 cm.

[0054] As a further preferred technical solution of the present invention, after the shotcrete with wire mesh sealing is completed, the construction platform is excavated, and the terrain and slope protection after supplementary measurement and correction are carried out.

[0055] The present invention also provides a construction method for a tunnel portal. By using the tunnel reverse exit roof caving treatment construction method described in any of the above, it further includes the step of adjusting the tunnel section where the roof caving occurs from underground excavation to open cut construction.

[0056] By adopting the construction method for a tunnel portal of the present invention, on the basis of the tunnel reverse exit roof caving treatment construction method, the traditional underground excavation of the tunnel at the roof caving location can be adjusted to open cut of the tunnel, and the construction period can be saved by at least 1 month, and the labor cost can be saved.

[0057] As a preferred technical solution of the present invention, the step of adjusting the tunnel section where the roof caving occurs from underground excavation to open cut construction includes:

[0058] 1. Remove the dangerous rocks on the slope after exiting the tunnel.

[0059] 2. Use a drone to measure the current topographic data to facilitate the preparation of the treatment plan and the measurement of slag cleaning.

[0060] 3. While excavating the collapsed slag body from top to bottom, carry out slope protection at the same time. Protect the slope once for every certain distance of excavation of the collapsed slag body. The protection measures adopt cushion piers with bolts or cable bolts. The length of the cushion piers with bolts or cable bolts is 8m - 12m, and the set spacing is 3m - 4m. The specific length and spacing can be calculated and determined according to geological and topographic conditions. Keep excavating until 10cm outside the outer contour of the secondary lining of the tunnel.

[0061] 4. Construct side walls on the outside of the tunnel. The height of the side walls is greater than or equal to 1.5m higher than the arch crown.

[0062] 5. Construct the primary support of the tunnel at 10cm outside the outer contour of the secondary lining. The outside of the primary support is supported on the side walls, and the inside is supported on the rock mass. Use small ducts to fix the primary support on the rock mass.

[0063] 6. After the primary support reaches the strength, pour C20 concrete with a higher inside and a lower outside above it. The outside of the concrete is supported on the side walls, with a slope of 1:0.5, and the inside is supported on the rock mass. In this way, a rigid support is formed at the top of the tunnel to ensure that there is no more roof caving or collapse during tunnel excavation, and it is also beneficial to the stability of the slope.

[0064] 7. Excavate the tunnel according to the full section.

[0065] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0066] 1. A construction method for treating the roof fall at the reverse exit of a tunnel according to the present invention completely changes the traditional treatment method. By creatively using the slope built with the collapsed slag body, personnel and mechanical equipment can quickly reach the ground surface from the slope. The small pilot tunnel located inside the collapsed slag body and relying solely on manual construction is cancelled, and large machinery can be used for the entire construction process, ensuring good construction safety. The grouting of the collapsed slag body and the surrounding rock of the tunnel in the traditional treatment method is cancelled, the strong advance support is cancelled, and the supports such as the small pilot tunnel and the side wall are cancelled, greatly reducing the project cost. Taking a 20m roof fall as an example, the traditional treatment method requires at least 3 months for reinforcement and the exit of the small pilot tunnel, while the present invention only takes 3 days to reach the ground surface. The steps of this construction method are simple, with high construction safety, saving project cost, fast construction period, and good effect.

[0067] 2. A preferred construction method for treating the roof fall at the reverse exit of a tunnel according to the present invention involves erecting the portal steel frame while excavating. A steel rail is laid on each side of the ground at both sides of the portal chamber. The sliding rails are installed at the arch feet of the circumferential main steel frame of the portal steel frame, and the sliding rails cooperate with the steel rails. After the portal chamber is excavated forward, the steel rails are successively lengthened forward, and then the base jacks are adjusted to push the portal steel frame forward. By using this method, the steel rails are set on the slope, and then the portal steel frame is pushed forward along the slope by the jacks to complete the formation of the entire portal passage. In this way, continuous excavation is carried out in the front, and the portal steel frame is quickly assembled and formed in the rear, and is installed by pushing with the steel rails, which can improve the construction efficiency.

[0068] 3. A construction method for the tunnel entrance according to the present invention can adjust the traditional underground excavation of the roof fall tunnel to open cut on the basis of the construction method for treating the roof fall at the reverse exit of the tunnel, saving at least 1 month of construction period and reducing the labor cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is a plan view of the construction method for treating the roof fall at the reverse exit of the tunnel;

[0070] Figure 2 It is a cross-sectional view of the construction method for treating the roof fall at the reverse exit of the tunnel;

[0071] Figure 3 It is a longitudinal-sectional view of the construction method for treating the roof fall at the reverse exit of the tunnel.

[0072] Markings in the figure: 1 - roof fall area, 2 - collapsed slag body, 3 - unexcavated part of the lower bench, 31 - excavated part of the lower bench, 4 - second backfill body, 5 - steel grid lattice, 6 - portal steel frame, 7 - portal passage, 8 - existing initial support, 9 - first backfill body, 10 - trestle. DETAILED DESCRIPTION OF THE INVENTION

[0073] The present invention will be described in detail below with reference to the accompanying drawings.

[0074] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0075] Embodiment 1

[0076] As Figures 1 to 3 shown, a construction method for treating the roof fall at the reverse exit of a tunnel according to the present invention. The tunnel is constructed by the bench method and includes the following steps:

[0077] Step 1: Set a warning line and remove irrelevant mechanical equipment and personnel.

[0078] Step 2: Set peripheral convergence and crown settlement observation points at intervals of 2 m to 5 m within 30 m of the tunnel near the roof fall 1 for observation. When abnormalities are found, the data shall be promptly fed back to facilitate timely adjustment of the treatment plan.

[0079] Step 3: Backfill the excavated part 31 of the lower bench that has been trenched and excavated 10 m behind the tunnel face with muck. The backfill material is obtained locally, and the muck from another chamber or outside the tunnel can be used for backfilling. Compact the backfilled soil body, and the backfill height is flush with the bottom of the upper bench.

[0080] Step 4: Support the surface of the initial support of the chamber within 30 m of the roof fall 1 with a steel grid 5. The steel grid 5 is arranged on the unexcavated part 3 of the lower bench and / or the excavated part 31 of the lower bench that has been backfilled with muck. The steel grid 5 makes full use of the existing steel in the field. The circumferential steel of the grid is connected by bolts, and the longitudinal grid is connected by welding. The vertical and horizontal spacing varies from 40 to 80 cm, which is determined according to the size of the steel. After the steel grid 5 is erected, a first backfill body 9 with a height 1 m higher than the platform is backfilled near the arch foot. The first backfill body 9 is backfilled soil, which can ensure the stability of the steel grid 5 and avoid soaking the arch foot with construction water at the same time.

[0081] Step 5: Utilize the collapsed slag body 2 at the roof fall area 1 to build a slope from the tunnel to the ground surface of the roof fall area 1. The slope gradient shall be based on the maximum gradient that can be crawled through by a crawler vehicle to minimize excavation. In this embodiment, the slope gradient of the slope is 30%. After excavation, the slope is hardened. A 10-cm-thick C20 concrete layer can be laid on the surface of the slope, or anchor plates can be laid. While excavating, the portal steel frame 6 is erected. After the excavation is enlarged, the wall surface is sealed with shotcrete, with a thickness of 24 cm. A portal steel frame 6 is set in front of the collapsed slag body 2. The size of the portal of the portal steel frame 6 shall ensure the minimum space for mechanical equipment to pass through. The opening of the roof fall area 1 is enlarged from inside the tunnel using a pneumatic pick. The size of the enlarged section is the same as the section size of the portal steel frame 6. The portal steel frame 6 is made of I18 I-beams. The I18 I-beams are welded into an Ω shape. The steel frames are longitudinally connected by cross braces. The middle of the portal steel frame 6 is the construction vehicle passage. While excavating with the pneumatic pick, the portal steel frame 6 is erected. After the excavation is enlarged, the wall surface is sealed with shotcrete, with a thickness of 24 cm. The main steel frame of the portal steel frame 6 can use the existing steel frames on the construction site. First, a steel rail is laid on each side of the ground in the portal chamber. The arch feet of the circumferential main steel frame of the portal steel frame 6 are provided with slide rails, and the slide rails are fitted on the steel rails. When the portal chamber is excavated by 50 cm each time, the steel rails are successively extended forward, and then the base jacks are adjusted to push the portal steel frame 6 forward. The circumferential main steel frame of the portal steel frame 6 is welded and formed outside the tunnel and assembled inside the tunnel. The circumferential main steel frames are connected in an X shape using the same type of steel. The two sides of the portal steel frame 6 are backfilled with the first backfill body 9 to counter-pressure the steel frame feet. The top of the Ω-shaped steel frame is supported on the steel lattice 5, and the circumferential spacing is the same as that of the temporary steel frame. After the first backfill body 9 is backfilled, the surface of the first backfill body 9 is sealed with sprayed C20 concrete, with a thickness of 10 cm. Using this method, steel rails are set on the slope, and then the portal steel frame 6 is pushed forward along the slope using a jack to complete the formation of the entire portal passage 7. In this way, continuous excavation is carried out in the front, and the portal steel frame 6 is quickly assembled and formed in the rear, and is installed by pushing with the steel rails, which can improve the construction efficiency.

[0082] Step 6: After the construction of the steel lattice 5 and the portal steel frame 6 is completed, the end of the lower bench continues to pull slag and backfill to form a second backfill body 4 with a conical slope-shaped working surface. The slope of the second backfill body 4 is not steeper than 45°. A trestle 10 can be set in the gully behind the second backfill body 4.

[0083] Step 7: Use a drone for safety monitoring above the roof fall area 1. Extend the nozzle of the wet shotcreting machine from inside the tunnel to the roof fall area 1 and rotate it 360 degrees to spray concrete, so as to seal the ground surface around the roof fall area 1 with concrete. The thickness of the concrete sprayed by the wet shotcreting machine is greater than 10 cm to ensure that there are no loose blocks within a range of 2 m to 3 m around the ground surface of the roof fall area.

[0084] The slopes with roof falls and collapses are in a critically stable state. Under external interference conditions such as vibration, rain, strong wind, etc., rockfalls or secondary collapses may occur at any time. To ensure safety, use a drone for monitoring above the outside of the tunnel. The drone operator observes the collapse situation outside the tunnel, especially the rockfall situation, through the camera carried by the drone and transmits it to the safety monitoring personnel inside the tunnel in real time via a walkie-talkie. When collapses, rockfalls, etc. occur outside the tunnel, the personnel inside the tunnel can be aware of it immediately and evacuate in time. When there is no abnormality outside the tunnel, extend the nozzle of the wet shotcreting machine from inside the tunnel to the roof fall opening and rotate it 360 degrees to spray, ensuring the stability of the rock mass near the roof fall opening.

[0085] Step 8: After the personnel and mechanical equipment reach the ground surface, promptly seal the collapsed slope with shotcrete with wire mesh, with a thickness of 10 cm.

[0086] Step 9: After the sealing is completed, excavate the construction platform and re-survey and correct the terrain and slope protection.

[0087] The construction method for treating the roof fall at the reverse exit of the tunnel described in this embodiment completely changes the traditional treatment method. Creatively, the slope built with the collapsed slag body 2 enables personnel and mechanical equipment to quickly reach the ground surface from the slope, eliminating the small pilot tunnel located inside the collapsed slag body 2 that can only be constructed manually. The entire construction process can use large machinery for construction, with good construction safety. The grouting of the collapsed slag body 2 and the surrounding rock of the tunnel in the traditional treatment method is eliminated, the strong advance is eliminated, and the supports such as the small pilot tunnel and side walls are eliminated, greatly reducing the project cost. Taking a 20 m roof fall as an example, the traditional treatment method requires at least 3 months for reinforcement and exiting through the small pilot tunnel, while the present invention only takes 3 days to reach the ground surface. The steps of this construction method are simple, with high construction safety, saving project cost, fast construction period, and good effect.

[0088] Embodiment 2

[0089] The construction method for treating the roof fall at the reverse exit of the tunnel described in the present invention is different from that in Embodiment 1 in that in this embodiment, the tunnel is constructed by the full face method (not shown), where:

[0090] The step 3 described in Embodiment 1 is replaced with: Level the excavated section behind the heading face, with the leveling height based on the design elevation, and fill and compact the part below the design elevation.

[0091] Step 4 in Example 1 is replaced with: In the range of 30 m adjacent to the roof fall area 1, the surface of the initial support of the chamber is supported by a steel grid 5. The steel grid 5 is set on the reference line at the designed elevation. The steel grid 5 makes full use of the existing steel on site. The circumferential steel of the grid is connected by bolts, and the longitudinal grid is connected by welding. The vertical and horizontal spacing varies from 40 to 80 cm, which is determined according to the size of the steel. After the steel grid 5 is erected, a first backfill body 9 with a height 1 m higher than the platform is backfilled near the arch foot. The first backfill body 9 is a backfilled soil body, which can ensure the stability of the steel grid 5 and avoid the arch foot being soaked by construction water at the same time.

[0092] Step 6 in Example 1 is replaced with: After the construction of the steel grid 5 and the portal steel frame 6 is completed, the slag is backfilled below the designed elevation to form a second backfill body 4 with a conical slope-shaped working surface. The slope of the second backfill body 4 is not steeper than 45°.

[0093] Example 3

[0094] A construction method for a tunnel portal of the present invention uses the tunnel reverse exit roof fall treatment construction method as described in Example 1 or Example 2, and further includes the step of adjusting the tunnel section where the roof fall area 1 is located from the mined excavation to the open cut construction.

[0095] 1. Remove the dangerous rocks on the slope after exiting the tunnel.

[0096] 2. Use a drone to measure the current topographic data to facilitate the issuance of treatment plans and slag removal measurement.

[0097] 3. While excavating the collapse slag body 2 from top to bottom, slope protection is carried out on the slope. The slope is protected once every 3 m of excavation of the collapse slag body 2. The protection measures are cushion pier bolts or anchor cables. The length of the cushion pier bolts or anchor cables is generally 9 m, and the set spacing is 3 m. The specific length and spacing can be calculated and determined according to the geological and topographic conditions. Excavation is carried out until 10 cm outside the outer contour of the secondary lining of the tunnel.

[0098] 4. Construct a side wall on the outside of the tunnel. The height of the side wall is 1.5 m higher than the arch crown.

[0099] 5. Construct the initial support of the tunnel at 10 cm outside the outer contour of the secondary lining. The outside of the initial support is supported on the side wall, and the inside is supported on the rock mass. 42 small ducts are used to fix the initial support on the rock mass.

[0100] 6. After the initial support reaches the strength, pour C20 concrete with a higher inside and a lower outside above it. The outside of the concrete is supported on the side wall, with a slope of 1:0.5, and the inside is supported on the rock mass. In this way, a rigid support is formed at the top of the tunnel to ensure that the tunnel does not collapse or cave in during excavation and is also beneficial to the stability of the slope.

[0101] 7. Excavate the tunnel according to the full cross-section.

[0102] The working process of the present invention: monitoring and measurement - back pressure - support of the steel lattice 5 - backfilling - support of the portal steel frame 6 - excavate the slope leading to the ground - surface slope protection and measurement - excavate the construction platform at the tunnel entrance - construct the tunnel in the collapse section.

[0103] Through the practice in a certain highway tunnel, the tunnel had a collapse and roof fall of 20 m. The traditional method would take at least 3 months to carry out reinforcement and the small pilot tunnel to break through the exit. However, the present invention only takes 3 days to reach the ground surface. Moreover, it adjusts the traditional underground excavation of the tunnel to open cut excavation, which can save at least 1 month of the construction period, save labor costs, reduce the advanced large pipe shed, initial support, grouting consolidation, and temporary side support in the portal section. It saves about 50,000 yuan of direct engineering cost per meter, and saves 26,000 yuan of indirect cost per day. The total savings for this roof fall using the method of the present invention is 4.04 million yuan.

[0104] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A construction method for treating the roof caving at the reverse exit of a tunnel, characterized in that, Utilize the collapse debris (2) at the roof fall area (1) to build a slope from the tunnel to the ground surface of the roof fall area (1). The slope is used for the passage of personnel and mechanical equipment. A number of portal steel frames (6) are arranged on the slope to form a portal passage (7). The steel frame feet of the portal steel frames (6) are counterweighted with the first backfill body (9). The tunnel area near the roof fall area (1) is supported by a number of steel grid structures (5). The steel grid structures (5) are arranged in contact with the existing primary support (8). The top of the portal steel frames (6) within the tunnel area is supported on the steel grid structures (5). For a tunnel excavated by the bench method, the excavated part (31) of the lower bench behind the heading face is backfilled with muck, and the backfill height is flush with the bottom of the upper bench. The steel grid structures (5) are arranged on the unexcavated part (3) of the lower bench and / or the excavated part (31) of the lower bench that has been backfilled with muck. For a tunnel excavated by the full-face method, the excavated section behind the heading face is leveled, and the leveling height is based on the design elevation. The steel grid structures (5) are arranged on the reference line at the design elevation. While excavating, the portal steel frames (6) are erected. A steel rail is laid on each side of the ground in the portal chamber. Slide rails are installed at the arch feet of the circumferential main steel frames of the portal steel frames (6). The slide rails cooperate with the steel rails. After the portal chamber is excavated forward, the steel rails are successively extended forward, and then the base jacks are adjusted to push the portal steel frames (6) forward.

2. The construction method for treating the roof fall at the exit of the tunnel in the reverse direction according to claim 1, characterized in that, The portal steel frames (6) are welded with I-beams into an Ω shape, and adjacent portal steel frames (6) are connected by cross braces.

3. The construction method for treating the roof caving at the exit of the tunnel in the reverse direction according to claim 1 is characterized in that, The tunnel area within a range of 30 m near the roof fall area (1) is supported by the steel grid structures (5).

4. The construction method for treating the roof caving at the reverse exit of the tunnel according to claim 1 is characterized in that, The circumferential lattice steel sections are connected by bolts, and the longitudinal lattice is welded.

5. The construction method for treating the roof caving at the reverse exit of the tunnel according to claim 1, characterized in that, The vertical and horizontal spacings of the steel grid structures (5) are 40 cm to 80 cm.

6. The construction method for treating the roof caving at the exit of a tunnel in the reverse direction according to claim 1 is characterized in that, The arch feet of the steel grid structures (5) are backfilled with the first backfill body (9).

7. The construction method for treating the roof caving at the reverse exit of the tunnel according to claim 6, characterized in that, The surface of the first backfill body (9) is sealed by shotcrete.

8. The construction method for treating the roof caving at the reverse exit of the tunnel according to claim 1 is characterized in that, The spacing between adjacent portal steel frames (6) is equal to the spacing between adjacent steel grid structures (5).

9. The construction method for treating the roof caving at the exit of the tunnel in the reverse direction according to claim 1 is characterized in that, For a tunnel excavated by the bench method, the muck at the end of the lower bench is backfilled to form a second backfill body (4) with a conical slope-shaped working face, and the slope of the second backfill body (4) is not steeper than 45°. For a tunnel excavated by the full-face method, the muck is backfilled below the design elevation to form a second backfill body (4) with a conical slope-shaped working face, and the slope of the second backfill body (4) is not steeper than 45°.

10. The construction method for treating the roof caving at the exit of the tunnel in the reverse direction according to claim 1, characterized in that, The opening of the roof fall area (1) is enlarged from inside the tunnel using a pneumatic pick, and the enlarged section size is the same as the section size of the portal steel frames (6).

11. The construction method for treating the roof caving at the outlet of the tunnel in the reverse direction according to claim 10, characterized in that, After enlargement, the wall surface is sealed with shotcrete.

12. The tunnel reverse exit roof caving treatment construction method according to claim 1, characterized in that, An unmanned aerial vehicle is used for safety monitoring above the roof fall area (1).

13. The construction method for treating the roof caving at the exit of a tunnel in the reverse direction according to claim 1, characterized in that, The nozzle of a wet shotcreting machine is extended from inside the tunnel to the roof fall area (1), and shotcrete is sprayed in a 360-degree rotation to seal the ground surface around the roof fall area (1) with concrete.

14. The construction method for treating the roof caving at the exit of the tunnel in the reverse direction according to claim 1, characterized in that, The slope is hardened.

15. The construction method for treating the roof fall at the outlet of the tunnel in the reverse direction according to claim 14, characterized in that, A layer of concrete or anchor plates is laid on the surface of the slope.

16. The tunnel reverse exit roof caving treatment construction method according to any one of claims 1-15, characterized in that, After the personnel and mechanical equipment reach the ground surface by means of the slope, the collapsed slope surface is sealed by shotcrete with wire mesh.

17. The construction method for treating the roof caving at the exit of a tunnel in the reverse direction according to claim 16, characterized in that, After the shotcrete with wire mesh sealing is completed, a construction platform is excavated, and the terrain and slope protection after supplementary measurement and correction are carried out.

18. A construction method for a tunnel entrance, characterized in that, Using the construction method for treating the roof caving at the exit of the tunnel in the reverse direction as described in any one of claims 1-17, it further includes the step of adjusting the tunnel section where the roof caving (1) is located from the subsurface excavation to the open cut construction.

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