Rapid treatment method for large-scale collapse cavities at the vault of tunnels in soft and fractured surrounding rocks

Abstract

The present invention discloses a rapid treatment method for large-scale collapse cavities at the vault of a tunnel in soft and fractured surrounding rock, comprising the following steps: (1) spraying concrete to seal the surface of the collapse cavity; (2) erecting a steel arch frame; (3) embedding perforated steel pipes in the cavity; (4) backfilling with counterpressure until the last steel arch frame; (5) arranging monitoring and measurement sections; (6) carrying out layered rapid backfilling; (7) carrying out excavation and support; (8) using a handheld pneumatic drill to drill advanced small conduits; (9) excavating and appropriately expanding the excavation in the pipe shed area at the vault to leave sufficient space for the pipe shed construction by a multi-functional drill; (10) driving medium pipe sheds; (11) erecting arch frames; (12) using a handheld pneumatic drill to drive advanced grouting small conduits between the pipe shed gaps, and spraying concrete to seal the steel arch frame; (13) carrying out normal excavation and support. The present invention improves the operation efficiency of dealing with collapse accidents in soft and fractured surrounding rock, reduces the construction and management costs, and increases the construction safety.

Description

Technical Field

[0001] This invention patent relates to the technical field of tunnel engineering construction. Specifically, it relates to a rapid treatment method for large-scale collapse cavities at the vault of tunnels in soft and fractured surrounding rocks. Background Art

[0002] In tunnel engineering under the condition of soft and fractured surrounding rocks, the geological structure is complex, the surrounding rock stability is poor, and the construction risk is high. The tunnel face often shows the phenomenon of collapse cavity at the vault of the tunnel face due to reasons such as developed fissures in the surrounding rocks, poor bonding force between fissure layers, unfavorable tectonic attitude for the stability of the tunnel face, and gushing of groundwater. At present, the treatment plan for the collapsed cavity section is to backfill with counter-pressure and use the method of shotcrete or pumped mortar to backfill the collapsed cavity body. At the same time, the combination of pipe shed and advanced small ducts is used to cross the collapsed cavity section and the subsequent soft and fractured section. After the collapse cavity occurs, the main purpose of cavity backfilling is to quickly seal the surrounding rocks, prevent the further increase of the collapse cavity range, and at the same time restore the contact between the surrounding rocks and the initial support to ensure that the surrounding rocks and the support structure form a common load-bearing system. The main purpose of installing pipe shed and advanced small ducts is to share the surrounding rock pressure in front of the collapsed cavity section to ensure the stability of the surrounding rocks in front of the collapsed cavity body. In the actual construction process, the above methods have certain limitations: (1) After the collapse cavity occurs, the amount of counter-pressure backfilling at the tunnel face is large, and it is not easy for the tunnel face to be adjacent to the stable initial support after backfilling; (2) When a large-scale collapse cavity occurs at the vault of the tunnel, using the method of shotcrete or pumped mortar to fill the collapsed cavity body is not easy to ensure the compactness of the backfilled body of the collapse cavity. At the same time, the self-weight of the backfilled body is too large, which is not conducive to the stability of the support structure; (3) The requirements for grouting of advanced small ducts are high, the time consumption is long, and the grouting effect is not easy to control; (4) It is not easy to ensure the installation angle of the pipe shed when installing the arch frame first and then the pipe shed. It is not easy to form an effective arch shed structure in front of the tunnel face to share the surrounding rock pressure in front of the tunnel face. After continuous excavation, the loose rock mass between the pipe shed and the tunnel has no support, and it is extremely easy to continue to have a collapse cavity accident; (5) The treatment time of the collapse cavity is too long, which is not conducive to the rapid sealing and ring formation of the tunnel support in soft and fractured surrounding rocks, and may cause secondary collapse cavities while affecting the construction progress. Therefore, for the collapse cavity phenomenon in soft and fractured surrounding rocks, adopting a rapid and effective collapse cavity backfilling method and ensuring the effectiveness of advanced support are the most effective methods for treating the collapse cavity at the vault and crossing the collapsed cavity section.

[0003] Regarding the problems in the related technology, no effective solution has been proposed yet. Summary of the Invention

[0004] Therefore, in order to solve the above-mentioned deficiencies, the present invention provides a rapid treatment method for large-scale collapse of the arch of a tunnel in a weak and broken surrounding rock, which overcomes the above-mentioned deficiencies in existing products and methods, can reduce the amount of backfill under back pressure, and ensure the stability of the primary support structure adjacent to the collapsed cavity; can control the safety of the arch frame erection after the collapse occurs; can ensure the rapid closure of the collapsed cavity surface and the effective filling of the cavity after the collapse occurs, and reduce the deadweight of the collapsed cavity backfill body; under difficult grouting conditions, can control the speed of the advanced small conduit to ensure the strength and rigidity of the small conduit; can control the angle of the pipe shed to ensure that the arch shed structure is stressed. The present invention improves the operational efficiency of the collapse cavity accident treatment in the weak and broken surrounding rock, reduces the construction and management costs, and increases the construction safety.

[0005] The present invention is implemented by constructing a rapid treatment method for large-scale collapse of the vault of a tunnel with weak and broken surrounding rock, which is characterized by comprising the following steps:

[0006] 1) After the collapse cavity occurs, C25 shotcrete is used to spray and seal the surface of the collapse cavity to form a shell protection structure. The spraying thickness is adjusted according to the self-stability of the surrounding rock, generally 25-45cm. On the one hand, the shell is formed to prevent the soft and broken surrounding rock from further weathering and the scope of the loose circle of the vault from further expanding; on the other hand, the water flow channel on the surface of the collapse cavity is closed to prevent the surrounding rock from further deteriorating due to groundwater loss;

[0007] 2) Under the protection of the self-made rockfall prevention trolley, erect steel arch frames as close to the tunnel face behind the collapsed cavity as possible, and strengthen the connections between the steel arch frames to ensure overall stability. The model of the newly erected steel arch frames should be stronger than the original design;

[0008] 3) Pre-buried a row of large-diameter perforated steel pipes in the collapsed cavity as a subsequent layered backfilling and pouring channel;

[0009] 4) The tunnel face is backfilled to the position of the last steel arch frame, and a slope is formed near the tunnel face to ensure the stability of the tunnel face. Concrete is sprayed to seal the tunnel face, slope and the surface of the newly erected arch frame;

[0010] 5) Set up monitoring and measurement sections in the newly erected arch frame section to focus on recording and monitoring the arch crown sinking;

[0011] 6) Use a variety of materials to backfill the large-volume cavities of the collapsed cavity in layers to ensure the compactness of the collapsed cavity, control the self-load generated by the large-volume backfill of the collapsed cavity, and reduce the impact of falling rocks or collapsed bodies on the tunnel lining. First, pour cement mortar through the pre-buried steel pipe, and after the cement mortar has solidified the collapsed debris, pump C20 concrete to form a "protective arch", and finally blow sand backfill to form a buffer layer;

[0012] 7) After the backfill material consolidates and the settlement data of the vault is slightly stable, the three - step method is used for excavation to reduce excavation disturbance. Excavate 1 - 2 m and set up 3 - 4 steel arch frames.

[0013] 8) After each steel arch frame is set up, an advanced small - diameter pipe is drilled using a handheld pneumatic rock drill. According to the filling state of the surrounding rock joints and fissures, pre - grouted mortar small - diameter pipes or small - diameter pipe grouting reinforcement methods are used in different cases to form a double - layer advanced support with a certain stiffness and strength above the area to be excavated.

[0014] 9) Under the protection of the double - layer advanced support, excavate 1 - 2 m and appropriately expand the excavation area (at least 40 cm) in the area where the pipe shed is installed at the vault to leave enough space for the down - the - hole drill to install the pipe shed. Immediately spray concrete to seal the exposed surrounding rock after excavation.

[0015] 10) Use a down - the - hole drill to install the pipe shed at the face position and grout to reinforce the surrounding rock.

[0016] 11) After the pipe shed is installed, adjust the spacing of the arch frames according to the angle and position of the pipe shed, and then set up the steel arch frames so that the outer side of the arch frames is closely attached to the pipe shed, and weld the connection between the pipe shed and the arch frames.

[0017] 12) Install advanced small - diameter pipes between the pipe sheds to make the advanced small - diameter pipes fill the void area between the pipe sheds as much as possible. According to the filling state of the surrounding rock joints and fissures, use pre - grouted mortar small - diameter pipes or small - diameter pipe grouting methods to form an advanced support.

[0018] 13) Carry out excavation and support according to the normal process, and install pipe sheds and advanced small - diameter pipes according to the surrounding rock conditions during subsequent construction.

[0019] According to a rapid treatment method for large - scale collapse cavities at the vault of tunnels in soft and fractured surrounding rock described in the present invention, it is characterized in that: the sprayed concrete used in step 1 is C25 sprayed concrete, and the thickness of the sprayed concrete is controlled within 15 - 20 cm, ensuring at least 15 cm thick.

[0020] According to a rapid treatment method for large - scale collapse cavities at the vault of tunnels in soft and fractured surrounding rock described in the present invention, it is characterized in that: for the collapse cavity section of soft and fractured surrounding rock in step 2, steel arch frames strengthened compared with the original design should be used. At the same time, the spacing of the arch frames should be appropriately reduced, and the spacing of the arch frames does not exceed 60 cm. Under the protection of a self - made rock - fall prevention trolley, the steel arch frames are set up as close as possible to the face formed after the collapse cavity.

[0021] In step 2, I - shaped steel should be used to strengthen the connection between the arch frames to ensure the overall stability of the arch frames.

[0022] The self-made anti-rockfall trolley used in the step 2 is composed of longitudinal beams, cross beams, diagonal braces and columns. The material used is I18 or I20b I-beams. The size of the self-made anti-rockfall trolley can be flexibly adjusted according to the size of the collapsed cavity and the shape of the face formed after the collapsed cavity.

[0023] According to the method for rapidly treating large-scale collapse of soft and broken surrounding rock tunnel vaults of the present invention, it is characterized in that: in the step 3, a row of perforated steel pipes are pre-buried in the collapsed cavity at a spacing of 2m, and large-diameter steel pipes of Ø108 or more should be used to meet the needs of subsequent multi-material layered backfilling construction;

[0024] The perforated steel pipe in step 3 extends into the collapsed cavity at least 5m beyond the excavation contour line or the collapsed debris surface, and the other end extends more than 1m, and is covered with geotextile at the hole mouth. It is removed after the steel arch frame is sealed by spraying concrete in step 4.

[0025] According to the method for rapid treatment of large-scale collapse of the arch of a tunnel with soft and broken surrounding rock described in the present invention, it is characterized in that: in the step 4, the back pressure is backfilled from the tunnel face to the last steel arch frame, and a slope is backfilled near the tunnel face. The backfill slope material can be cave slag, and the slope surface is sealed with C20 sprayed concrete to form a stable step. The thickness of the sprayed concrete is controlled to be about 10 cm. The height and length of the step should meet the angle and length of the pipe shed and the advance small guide tube of the multi-functional drilling rig (or down-the-hole drill), which varies according to the size of the tunnel section. The height is generally 4m from the arch, and the length is generally 8-10m.

[0026] According to the method for rapid treatment of large-scale collapse of the vault of a tunnel with soft and broken surrounding rock described in the present invention, it is characterized in that: in the step 5, a monitoring and measuring section is arranged on the newly erected arch section of the collapsed cavity section, and the monitoring and measuring frequency is increased to observe the deformation of the support system during the subsequent layered backfilling process, and adjust the layered backfilling plan according to the deformation conditions.

[0027] According to the method for rapidly treating large-scale collapse of soft and broken surrounding rock tunnel vaults of the present invention, the characteristic is that: in step 6, a plurality of materials are used to backfill the collapsed cavity in layers, which can ensure the compactness of the backfill of the collapsed cavity on the one hand, and control the impact of the self-load, rockfall or slag on the tunnel lining caused by the large-volume backfill of the collapsed cavity on the other hand;

[0028] In Step 6, a variety of materials including cement mortar, pumped concrete and sand are used. During backfilling, cement mortar is first poured. During the pouring process, attention should be paid to the mix ratio of the cement mortar. The initial mix ratio is controlled at a water-cement ratio of 1:1 for diffusion, and the later mix ratio is controlled at a water-cement ratio of 1:1.5 - 1:2 for filling and consolidation. After the slurry has slightly solidified, pumped concrete is used for backfilling. The pumping volume is adjusted according to the estimated volume of the collapse cavity to form a concrete arch protection layer with a thickness of 3 - 4m. The concrete in the collapse cavity is poured in two layers with an interval of about 8h, and finally sand blowing backfilling is carried out.

[0029] According to a rapid treatment method for large-scale collapse cavities at the vault of a tunnel with soft and broken surrounding rock according to the present invention, it is characterized in that: after the backfill material has slightly solidified (12h) in Step 7, the three-step method is used for excavation and support. Excavate at least the distance of two steel arch frames. Immediately after excavation, a steel arch frame is constructed, and the overall stability of the arch frame is strengthened by using enhanced foot locking and enhanced arch frame connection methods;

[0030] In Step 8, immediately after each arch frame is excavated, an advanced small duct is driven. In the subsequent excavation and expansion process, an advanced support with strong stiffness and strength is formed above the excavation and expansion area. When the surrounding rock has a thin-layered structure (such as shale, schist) or there is clay filling between structural planes and the filling is relatively thick, the requirements for grouting of the advanced small duct are high, the time is long, and the effect is not good. A pre-grouted mortar small duct is used for advanced support. The spacing of the small ducts is not greater than 20cm, the length is not less than 3m, and the longitudinal lap length is not greater than 1m; when the opening degree of the structural plane of the surrounding rock is relatively large and the clay filling is relatively small, a grouted small duct is used for advanced support.

[0031] According to a rapid treatment method for large-scale collapse cavities at the vault of a tunnel with soft and broken surrounding rock according to the present invention, it is characterized in that: in Step 9, the three-step method is used for excavation and expansion. The longitudinal length of the excavation and expansion is 2 - 3m, and the reserved deformation amount is increased by 40 - 50cm compared with the designed amount to meet the requirements for driving the pipe shed in subsequent construction;

[0032] In Step 9, blasting excavation should be avoided to reduce the disturbance of the surrounding rock excavation.

[0033] According to a rapid treatment method for large-scale collapse cavities at the vault of a tunnel with soft and broken surrounding rock according to the present invention, it is characterized in that: in Step 10, a down-the-hole drill is used to drive the pipe shed. For soft and broken surrounding rock, the length of the pipe shed should not be too long. The rock-entering end should extend into the rock for 9 - 12m, and the other end should extend out of the free face by 1 - 2m. On the one hand, the probability of hole collapse is reduced, and on the other hand, it is ensured that the subsequent construction pipe shed can be effectively connected to the arch frame. The spacing of the pipe shed is controlled at 30 - 50cm according to the stability of the surrounding rock;

[0034] In the said step 11, after the pipe-roof is installed, adjust the spacing of the arch frames according to the installation angle and position of the pipe-roof, and install the arch frames closely against the pipe-roof, which can ensure the stable force at the end of the pipe-roof while controlling the installation angle of the pipe-roof in the tunnel, and reduce the volume of the loosened rock mass under the pipe-roof entering the rock;

[0035] In the said step 12, driven pilot pipes are installed between the voids of the pipe-roof. When the surrounding rock has a laminated structure (such as shale, schist) or there is cohesive soil filling between the structural planes and the filling is relatively thick, the requirements for grouting of the driven pilot pipes are high, the time is long, and the effect is not good. In this case, pre-grouted mortar pilot pipes are used for advanced support; when the opening degree of the structural plane of the surrounding rock is relatively large and the cohesive soil filling is less, grouted pilot pipes are used for advanced support.

[0036] The present invention has the following advantages: To sum up, by means of the above technical method of the present invention, the amount of backfill can be reduced, the stability of the primary support structure adjacent to the collapse cavity section can be ensured; the safety of installing the arch frames after the collapse cavity occurs can be controlled; the rapid closure of the surface of the collapse cavity, the effective filling of the cavity, and the reduction of the self-weight of the backfill body of the collapse cavity after the collapse cavity occurs can be ensured; under difficult grouting conditions, the construction speed of the driven pilot pipes can be controlled, and the strength and stiffness of the pilot pipes can be ensured; the installation angle of the pipe-roof can be controlled, and the force of the arch shed structure can be ensured. It solves the problem of rapid disposal and crossing when a collapse cavity occurs at the crown of a tunnel in soft and broken surrounding rock, improves the operation efficiency, reduces the construction and management costs, increases the construction safety, and has certain reference and guiding functions for the construction of similar surrounding rock. Brief Description of the Drawings

[0037] Figure 1 is the longitudinal sectional view of a method for rapid disposal and crossing of a loose body collapse cavity at the crown of a tunnel according to the present invention;

[0038] Figures 2 - 3 is the schematic diagram of a self-made rockfall prevention trolley for a method for rapid disposal and crossing of a loose body collapse cavity at the crown of a tunnel according to the present invention;

[0039] Figure 4 is the schematic diagram of steps 1-2 of a method for rapid disposal and crossing of a loose body collapse cavity at the crown of a tunnel according to the present invention;

[0040] Figure 5 is the schematic diagram of steps 3-5 of a method for rapid disposal and crossing of a loose body collapse cavity at the crown of a tunnel according to the present invention;

[0041] Figure 6 is the schematic diagram of step 6 of a method for rapid disposal and crossing of a loose body collapse cavity at the crown of a tunnel according to the present invention;

[0042] Figure 7 is the schematic diagram of steps 7-8 of a method for rapid disposal and crossing of a loose body collapse cavity at the crown of a tunnel according to the present invention;

[0043] Figure 8It is a schematic diagram of steps 9-10 of a method for quickly handling and overcoming a tunnel vault loose body collapse cavity of the present invention;

[0044] Figure 9 It is a schematic diagram of steps 11-12 of a method for quickly handling and overcoming a tunnel vault loose body collapse cavity according to the present invention;

[0045] Figure 10 It is a schematic diagram of step 13 of a method for quickly handling and overcoming a tunnel vault loose body collapse cavity according to the present invention.

[0046] Among them: 1. Sand blowing backfill buffer layer; 2. Pumped concrete "arch protection" layer; 3. Collapse cavity consolidation layer; 4. Collapse cavity surface; 5. Pre-buried perforated steel pipe; 6. Backfill steps around the heading face; 7. Pipe shed; 8. Advance small guide tube; 9. Heading face; 10. Lower step; 11. Upper step; 12. Steel arch frame; 13. Excavation area; 21. I-beam longitudinal beam; 22. I-beam horizontal beam; 23. Column; 24. Longitudinal diagonal brace; 25. Horizontal diagonal brace. DETAILED DESCRIPTION

[0047] The following will be combined with the attached Figures 1 - 10 The present invention is described in detail, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present invention provides a method for rapidly treating large-scale collapse of a tunnel vault with weak and broken surrounding rock through improvement, which can be implemented in the following manner; comprising the following steps:

[0049] 1) After the collapse cavity occurs, C25 shotcrete is used to spray and seal the surface of the collapse cavity to form a shell protection structure. The spraying thickness is adjusted according to the self-stability of the surrounding rock, generally 25-45cm. On the one hand, the shell is formed to prevent the soft and broken surrounding rock from further weathering and the scope of the loose circle of the vault from further expanding; on the other hand, the water flow channel on the surface of the collapse cavity is closed to prevent the surrounding rock from further deteriorating due to groundwater loss;

[0050] 2) Under the protection of the self-made rockfall prevention trolley, erect steel arch frames as close to the tunnel face behind the collapsed cavity as possible, and strengthen the connections between the steel arch frames to ensure overall stability. The model of the newly erected steel arch frames should be stronger than the original design;

[0051] 3) Pre-buried a row of large-diameter perforated steel pipes in the collapsed cavity as a subsequent layered backfilling and pouring channel;

[0052] 4) Backfill the face in reverse pressure up to the position of the last steel arch, and backfill near the face to form a slope to ensure the stability of the face. Spray concrete to seal the face, the slope and the surface of the newly erected arch;

[0053] 5) Arrange monitoring and measurement sections in the section of the newly erected arch, and focus on recording and monitoring the settlement of the arch crown;

[0054] 6) Use a variety of materials to backfill the large-volume cavity of the collapse cavity in layers to ensure the compaction degree of the collapse cavity backfill, control the self-load generated by the large-volume backfill of the collapse cavity, and reduce the impact of falling stones or collapsed bodies on the tunnel lining. First, pour cement mortar through pre-buried steel pipes. After the cement mortar consolidates the collapsed slag body, pump C20 concrete to form a "protective arch", and finally blow sand to backfill to form a buffer layer;

[0055] 7) After the backfill material consolidates and the arch crown settlement data is slightly stable, use the three-step method for excavation to reduce the excavation disturbance. Excavate 1-2 m and erect 3-4 steel arches;

[0056] 8) After each arch is erected, use a handheld pneumatic rock drill to drill the advanced small pipe holes. According to the filling state of the surrounding rock joints and fissures, in different cases, use the pre-grouted mortar small pipe or the small pipe grouting reinforcement method to form a double-layer advanced support with a certain stiffness and strength above the area to be excavated;

[0057] 9) Under the protection of the double-layer advanced support, excavate 1-2 m, and appropriately expand the excavation area (at least 40 cm) in the area where the pipe shed is drilled at the arch crown to leave enough space for the down-the-hole drill to install the pipe shed. Immediately spray concrete to seal the exposed surrounding rock after excavation;

[0058] 10) Use a down-the-hole drill to install the pipe shed at the face position and grout to reinforce the surrounding rock;

[0059] 11) After the pipe shed is erected, adjust the arch spacing according to the angle and position of the pipe shed, and then erect the steel arch so that the outside of the arch is close to the pipe shed, and weld the connection between the pipe shed and the arch;

[0060] 12) Drive advanced small pipes between the pipe sheds to make the advanced small pipes fill the gap area between the pipe sheds as much as possible. Depending on the filling state of the surrounding rock joints and fissures, use the pre-grouted mortar small pipe or the small pipe grouting method to form an advanced support;

[0061] 13) Carry out excavation and support according to the normal process, and install pipe sheds and advanced small pipes according to the surrounding rock conditions during subsequent construction.

[0062] When implementing this method: the sprayed concrete used in step 1 is C25 sprayed concrete, and the thickness of the sprayed concrete is controlled at 15-20 cm, ensuring at least 15 cm thick.

[0063] When implementing this method: for the cavity section of soft and broken surrounding rock in step 2, it is advisable to use a steel arch frame strengthened compared with the original design. At the same time, the spacing of the arch frames should be appropriately reduced, and the arch frame spacing should not exceed 60 cm. Under the protection of a self-made rockfall protection trolley, the steel arch frame should be erected as close as possible to the tunnel face formed after the cavity.

[0064] In step 2, I-beams should be used to strengthen the connection between the arch frames to ensure the overall stability of the arch frames.

[0065] The self-made rockfall protection trolley used in step 2 is composed of longitudinal beams, cross beams, diagonal braces and columns. The materials used are I18 or I20b I-beams. The size of the self-made rockfall protection trolley can be flexibly adjusted according to the size of the cavity and the shape of the tunnel face formed after the cavity.

[0066] When implementing this method: in step 3, a row of perforated steel pipes should be embedded in the cavity of the cavity at a spacing of 2 m. Large-diameter steel pipes with a diameter of more than Ø108 should be used to meet the requirements of subsequent multi-material layered backfilling construction.

[0067] For the perforated steel pipes in step 3, the end extending into the cavity body should extend at least 5 m beyond the excavation outline or the surface of the collapsed slag body, and the other end should extend more than 1 m. The orifice should be covered with geotextile and removed after spraying concrete to close the steel arch frame in step 4.

[0068] When implementing this method: in step 4, the tunnel face should be backfilled by counterpressure to the last steel arch frame, and a slope should be backfilled near the tunnel face. The backfill slope material can be tunnel muck. The slope surface should be closed with C20 shotcrete to form a stable step. The thickness of the shotcrete should be controlled at about 10 cm. The height and length of the step should meet the angles and lengths of the pipe shed and advanced small pipes drilled by a multi-functional drill (or down-the-hole drill). They vary according to the size of the tunnel section. Generally, the height is 4 m from the crown, and the length is generally 8 - 10 m.

[0069] When implementing this method: in step 5, monitoring and measurement sections should be arranged for the newly erected arch frame section in the cavity section, and the monitoring and measurement frequency should be strengthened to observe the deformation of the support system during the subsequent layered backfilling process, and adjust the layered backfilling plan according to the deformation situation.

[0070] When implementing this method: in step 6, the cavity body should be backfilled in layers with multiple materials. On the one hand, it can ensure the compaction degree of the cavity backfill, and on the other hand, it can control the self-load generated by the large-volume backfill of the cavity body and the impact of falling rocks or collapsed slag bodies on the tunnel lining.

[0071] In step 6, a variety of materials including cement mortar, pumped concrete, and sand are used. During the backfilling process, cement mortar is first poured. During the pouring process, attention should be paid to the mix ratio of the cement mortar. The initial mix ratio is controlled at a water-cement ratio of 1:1 for diffusion, and the later mix ratio is controlled at a water-cement ratio of 1:1.5 - 1:2 for filling and consolidation. After the slurry has slightly solidified, pumped concrete is used for backfilling. The pumping volume is adjusted according to the estimated volume of the collapse cavity to form a concrete arch with a thickness of 3 - 4m. The concrete in the collapse cavity is poured in two layers with an interval of about 8h, and finally, sand is blown for backfilling.

[0072] When this method is implemented: In step 7, after the backfilling material has slightly solidified (12h), the three-step method is used for excavation and support. Excavate at least the distance of two steel arch frames. Immediately after excavation, install the steel arch frame, and strengthen the overall stability of the arch frame by using enhanced foot locking and enhanced arch frame connection methods;

[0073] In step 8, immediately after each arch frame is excavated, advanced small pipes are driven. In the subsequent excavation and expansion process, an advanced support with strong stiffness and strength is formed above the excavation area. When the surrounding rock has a laminated structure (such as shale, schist) or there is clay filling between structural planes and the filling is relatively thick, the requirements for grouting of the advanced small pipes are high, the time is long, and the effect is not good. Pre-grouted mortar small pipes are used for advanced support. The spacing of the small pipes is not greater than 20cm, the length is not less than 3m, and the longitudinal lap length is not greater than 1m; when the opening degree of the structural plane of the surrounding rock is relatively large and the clay filling is less, grouted small pipes are used for advanced support.

[0074] When this method is implemented: In step 9, the three-step method is used for excavation and expansion. The longitudinal length of the excavation and expansion is 2 - 3m, and the reserved deformation amount is increased by 40 - 50cm compared with the designed amount to meet the requirements for driving the pipe shed in the subsequent construction;

[0075] In step 9, blasting excavation should be avoided to reduce the disturbance of the surrounding rock excavation.

[0076] When this method is implemented: In step 10, a down-the-hole drill is used to drive the pipe shed. For soft and broken surrounding rock, the length of the pipe shed should not be too long. The rock-entering end should extend into the rock by 9 - 12m, and the other end should extend out of the free face by 1 - 2m. On the one hand, it reduces the probability of hole collapse, and on the other hand, it ensures that the subsequent construction pipe shed can be effectively connected to the arch frame. The spacing of the pipe shed is controlled at 30 - 50cm according to the stability of the surrounding rock;

[0077] In step 11, after the pipe shed is driven, adjust the spacing of the arch frame according to the driving angle and position of the pipe shed, and set up the arch frame closely against the pipe shed, which can control the driving angle of the pipe shed in the tunnel while ensuring the stable force at the end of the pipe shed and reducing the volume of the loosened rock mass under the rock-entering pipe shed;

[0078] In step 12, advanced small pipes are driven between the gaps of the pipe shed. When the surrounding rock has a laminated structure (such as shale or schist), or there is clay filling between structural planes and the filling is thick, the requirements for grouting of advanced small pipes are high, the time is long, and the effect is not good. In this case, pre-grouted mortar small pipes are used for advanced support; when the opening degree of the structural plane of the surrounding rock is large and the clay filling is less, grouting small pipes are used for advanced support.

[0079] In summary, the present invention discloses a rapid treatment method for large-scale collapse cavities at the vault of a tunnel in soft and broken surrounding rock, including the following steps: (1) spraying concrete to seal the surface of the collapse cavity; (2) erecting a steel arch frame under the protection of a self-made rockfall protection trolley, making the steel arch frame as close as possible to the heading face; (3) embedding perforated steel pipes in the cavity formed by the collapse cavity; (4) backfilling the heading face in reverse pressure to the last steel arch frame, and backfilling near the heading face to form a slope, and spraying concrete to seal the heading face, slope and the surface of the newly erected arch frame; (5) arranging a monitoring and measurement section in the newly erected arch frame section; (6) using a perforated steel pipe embedded beforehand to carry out layered rapid backfilling with three materials: cement mortar, pumped concrete and sand. First, pour cement mortar to consolidate the collapsed slag, then pump concrete, and finally blow sand for backfilling; (7) after the slurry solidifies and the monitored and measured crown settlement data is slightly stable, adopt the three-step method for excavation and support, and erect a steel arch frame; (8) after the arch frame is erected, use a handheld pneumatic drill to drill holes for advanced small pipes. According to the filling situation of joints and fissures, adopt the method of pre-grouted mortar small pipes or small pipe grouting reinforcement to form a double-layer advanced support with a certain stiffness and strength above the subsequent excavation area; (9) under the action of the double-layer advanced support, excavate and appropriately expand the pipe shed area at the vault to leave enough space for the pipe shed construction of a multi-functional drill; (10) use a down-the-hole drill to first drive medium pipe sheds at the heading face position and grout to reinforce the surrounding rock; (11) after the pipe shed grouting is stable, adjust the spacing of the arch frames according to the pipe shed angle and distance, erect the arch frames, ensure that the outside of the arch frames is closely attached to the pipe shed, and weld the connection between the pipe shed and the arch frames; (12) use a handheld pneumatic drill to drive advanced grouting small pipes between the gaps of the pipe shed, and spray concrete to seal the steel arch frame; (13) carry out normal excavation and support according to the design data and construction plan.

[0080] The beneficial effects of the present invention are as follows: It can effectively and quickly handle the support and backfilling after a large-scale cavity collapse accident occurs at the vault of a tunnel with soft and broken surrounding rock, and prevent secondary cavity collapses caused by cavity collapse disturbance and long-term exposure without support of this type of surrounding rock. In addition, under the protection of a self-made rockfall prevention trolley, the steel arch is erected as close as possible to the collapsed slag body. On the one hand, it can ensure the safety of the erected arch after the cavity collapse, and on the other hand, it can reduce the backfilling volume and save the backfilling time; the cavity is backfilled with mortar, concrete, and sand in layers to form a collapsed slag consolidation body, an arch protection, and a buffer layer respectively. On the one hand, it ensures the filling degree and stability of the collapsed slag body, and on the other hand, it reduces the self-weight of the backfill body; according to the filling state of the joint fissures in the surrounding rock, a double-layer advanced support with a certain stiffness and strength is formed above the subsequent excavation area by using small pipes pre-filled with mortar or small pipe grouting reinforcement in different cases. This can accelerate the construction speed while ensuring the strength and stiffness of the small pipes; the construction method of three-step excavation and first driving the pipe shed and then erecting the arch can effectively control the driving angle of the pipe shed and solve the problems of excessive pipe shed angle and greatly weakened support effect of the pipe shed on the surrounding rock ahead caused by the small arch frame spacing in soft and broken surrounding rock.

[0081] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rapid treatment method for large-scale collapse of the vault of a tunnel with weak and broken surrounding rock. Features: The method comprises the following steps: 1) After the collapse cavity occurs, C25 shotcrete is used to spray and seal the surface of the collapse cavity to form a shell protection structure. The spraying thickness is adjusted according to the self-stability of the surrounding rock, and the thickness is 25-45cm. On the one hand, the shell is formed to prevent the soft and broken surrounding rock from further weathering and the scope of the loose circle of the vault from further expanding; on the other hand, the water flow channel on the surface of the collapse cavity is closed to prevent the surrounding rock from further deteriorating due to groundwater loss; 2) Under the protection of the self-made rockfall prevention trolley, erect steel arch frames as close to the tunnel face behind the collapsed cavity as possible, and strengthen the connections between the steel arch frames to ensure overall stability. The model of the newly erected steel arch frames should be stronger than the original design; 3) Pre-buried a row of large-diameter perforated steel pipes in the collapsed cavity as a subsequent layered backfilling and pouring channel; 4) The tunnel face is backfilled to the position of the last steel arch frame, and a slope is formed near the tunnel face to ensure the stability of the tunnel face. Concrete is sprayed to seal the tunnel face, slope and the surface of the newly erected arch frame; 5) Set up monitoring and measurement sections in the newly erected arch frame section to focus on recording and monitoring the arch crown sinking; 6) Use a variety of materials to backfill the large-volume cavities of the collapsed cavity in layers to ensure the compactness of the collapsed cavity, control the self-load generated by the large-volume backfill of the collapsed cavity, and reduce the impact of falling rocks or collapsed bodies on the tunnel lining. First, pour cement mortar through the pre-buried steel pipe, and after the cement mortar has solidified the collapsed debris, pump C20 concrete to form a "protective arch", and finally blow sand backfill to form a buffer layer; 7) After the backfill material is consolidated and the arch settlement data is slightly stable, the three-step method is used to excavate to reduce excavation disturbance. After excavating 1-2m, 3-4 steel arch frames are erected; 8) After each arch frame is erected, a handheld pneumatic rock drill is used to drill a small advance pipe hole. According to the filling state of the surrounding rock joints and fissures, a pre-cast mortar small pipe or a small pipe grouting reinforcement method is used to form a double-layer advance support with a certain rigidity and strength above the area to be excavated; 9) Under the protection of double-layer advance support, dig 1-2m further, and appropriately expand the excavation in the area where the pipe shed is set up on the arch, by at least 40cm, to leave enough space for the down-the-hole drill to operate the pipe shed. After excavation, spray concrete immediately to seal the exposed surrounding rock; 10) Use a down-the-hole drill to set up a pipe shed at the tunnel face and inject grout to reinforce the surrounding rock; 11) After the pipe shed is erected, adjust the distance between the arch frames according to the angle and position of the pipe shed, erect the steel arch frames, make the outer side of the arch frames close to the pipe shed, and weld the connection between the pipe shed and the arch frames; 12) Small advance pipes are set between pipe sheds to fill the gaps between pipe sheds as much as possible. Depending on the filling status of the joints and fissures in the surrounding rock, small pipes filled with mortar in advance or small pipe grouting are used to form advance support; 13) Carry out excavation and support according to normal procedures. In subsequent construction, set up pipe racks and advance small guide tubes according to the surrounding rock conditions.

2. A rapid treatment method for large-scale collapse of a tunnel vault in soft and broken surrounding rock according to claim 1, Features: In the step 1, the thickness of the shotcrete is controlled to be 15-20 cm.

3. A rapid treatment method for large-scale cavity collapse at the crown of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: For the cavity collapse section of the soft and fractured surrounding rock in step 2, a steel arch frame strengthened compared with the original design should be adopted. At the same time, the spacing of the arch frames should be appropriately reduced, and the spacing of the arch frames does not exceed 60 cm. Under the protection of a self-made rockfall prevention trolley, the steel arch frame should be erected as close as possible to the tunnel face formed after the cavity collapse; In step 2, I-beams should be used to strengthen the connection between the arch frames to ensure the overall stability of the arch frames; The self-made rockfall prevention trolley adopted in step 2 is composed of longitudinal beams, cross beams, diagonal braces and columns, and the materials used are I18 or I20b I-beams. The size of the self-made rockfall prevention trolley is flexibly adjusted according to the size of the cavity collapse and the shape of the tunnel face formed after the cavity collapse.

4. A rapid treatment method for large-scale cavity collapse at the crown of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: In step 3, a row of perforated steel pipes should be embedded in the cavity of the cavity collapse at a spacing of 2 m. Large-diameter steel pipes with a diameter of more than Ø108 should be used to meet the requirements of subsequent multi-material layered backfilling construction; For the perforated steel pipes in step 3, the end extending into the cavity collapse body extends at least 5 m beyond the excavation outline or the surface of the collapsed slag body, and the other end extends more than 1 m, and the orifice is covered with geotextile and removed after spraying concrete to seal the steel arch frame in step 4.

5. A rapid treatment method for large-scale cavity collapse at the crown of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: In the above-mentioned step 4, the backfill slope material is the tunnel muck, and the slope surface is sealed with C20 shotcrete to form a stable step. The thickness of the shotcrete is controlled at about 10 cm. The height and length of the step should meet the angles and lengths of the pipe shed and the advanced small ducts drilled by the multi-functional drill rig, which vary according to the size of the tunnel section. The height For is 4 m from the crown of the arch, and the length is 8 - 10 m.

6. A rapid treatment method for large-scale cavity collapse at the crown of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: In step 5, monitoring and measurement sections should be arranged on the cross section of the newly erected arch frame in the cavity collapse section, and the monitoring and measurement frequency should be strengthened. Observe the deformation of the support system during the subsequent layered backfilling process, and adjust the layered backfilling plan according to the deformation situation.

7. A rapid treatment method for large-scale cavity collapse at the crown of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: In step 6, multiple materials are used to backfill the cavity collapse body. On the one hand, it can ensure the compaction degree of the cavity collapse backfilling, and on the other hand, it can control the self-load generated by the large-volume backfilling of the cavity collapse body, the impact of falling rocks or collapsed slag bodies on the tunnel lining; The multiple materials adopted in step 6 include cement mortar, pumped concrete and sand. During the backfilling process, cement mortar is first poured. Pay attention to the mix ratio of the cement mortar during the pouring process. The initial mix ratio is controlled at a water-cement ratio of 1:1 for diffusion, and the later mix ratio is controlled at a water-cement ratio of 1:1.5 - 1:2 for filling and consolidation. After the slurry has slightly solidified, pumped concrete is used for backfilling, and the pumping volume is adjusted according to the estimated volume of the cavity collapse body to form a concrete protective arch with a thickness of 3 - 4 m. The concrete in the cavity collapse is poured in 2 layers, with an interval of about 8 h, and finally sand blowing backfilling is carried out.

8. A rapid treatment method for large-scale cavity collapse at the crown of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: After the backfill material in step 7 has slightly solidified for 12 hours, the three - bench method is used for excavation support. Excavate a distance of at least two sets of steel arch frames. Immediately after excavation, install the steel arch frames, and strengthen the overall stability of the arch frames by using enhanced foot - locking and enhanced arch - frame connection methods. In step 8, immediately after the excavation of each set of arch frames, advanced small pipes are driven. In the subsequent excavation and expansion process, an advanced support with strong stiffness and strength is formed above the excavation area. When the surrounding rock has a laminated structure or there is clay filling between structural planes and the filling is thick, the requirements for grouting of the advanced small pipes are high, the time is long, and the effect is not good. Pre - grouted mortar small pipes are used for advanced support. The spacing of the small pipes is not greater than 20 cm, the length is not less than 3 m, and the longitudinal lap length is not greater than 1 m. When the opening degree of the structural plane of the surrounding rock is large and the clay filling is less, grouted small pipes are used for advanced support.

9. A rapid treatment method for large - scale cavity collapse at the vault of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: In step 9, the three - bench method is used for excavation and expansion. The longitudinal length of the excavation and expansion is 2 - 3 m, and the reserved deformation amount is increased by 40 - 50 cm compared with the designed amount to meet the requirements for driving the pipe shed in subsequent construction. In step 9, blasting excavation should be avoided to reduce the disturbance of the surrounding rock excavation.

10. A rapid treatment method for large - scale cavity collapse at the vault of a tunnel in soft and fractured surrounding rock according to claim 1, characterized in that: In step 10, a down - the - hole drill is used to drive the pipe shed. For soft and fractured surrounding rock, the length of the pipe shed should not be too long. The rock - entering end should extend 9 - 12 m, and the other end should extend 1 - 2 m out of the free face. On the one hand, it reduces the probability of hole - collapse phenomenon, and on the other hand, it ensures that the subsequent construction pipe shed can be effectively connected with the arch frame. The spacing of the pipe shed is controlled at 30 - 50 cm according to the stability of the surrounding rock. In step 11, after the pipe shed is driven, adjust the spacing of the arch frames according to the driving angle and position of the pipe shed, and set up the arch frames closely against the pipe shed, which can control the driving angle of the pipe shed in the tunnel while ensuring the stable force at the end of the pipe shed, and reduce the volume of the loosened rock mass under the rock - entering pipe shed. In step 12, advanced small pipes are driven between the voids of the pipe shed. When the surrounding rock has a laminated structure or there is clay filling between structural planes and the filling is thick, the requirements for grouting of the advanced small pipes are high, the time is long, and the effect is not good. Pre - grouted mortar small pipes are used for advanced support. When the opening degree of the structural plane of the surrounding rock is large and the clay filling is less, grouted small pipes are used for advanced support.

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