A method for dealing with collapse of a large-span tunnel excavated by step method

Abstract

The present application discloses a method for handling collapse of a large-span tunnel excavated by a step method. The method comprises the following steps: S1, reinforcing the surface of the collapse section and the collapse disturbance section; S2, closing the face and the collapse cavity surface; S3, excavating and supporting the upper, middle and lower steps and inverts of the collapse disturbance section; S4, reinforcing the surrounding rock in front of the face; S5, reinforcing the inside of the collapse cavity; S6, excavating and supporting the upper step of the collapse section; S7, excavating and supporting the middle and lower steps and inverts of the collapse section; S8, excavating and supporting the upper, middle and lower steps and inverts of the unexcavated disturbance section; S9, excavating and supporting the upper, middle and lower steps and inverts of the unexcavated and undisturbed section; S10, subsequent construction operations. The present invention improves the construction operability, reduces the risk of safe operation, speeds up the construction progress, saves construction time and economic costs by adopting a series of reinforcement measures and reasonably arranging the construction procedures. It has strong practicality and wide applicability in the construction of collapse handling of large-span tunnels excavated by the step method.

Description

Technical Field

[0001] The present application relates to the technical field of tunnel construction, and in particular to a method for handling collapse of a large-span tunnel excavated by a step method. Background Art

[0002] With the rapid development of my country's economy, tunnels, as an important part of transportation routes, are being built on a larger scale, and the problem of surrounding rock stability during tunnel construction has become more prominent. Due to my country's vast territory, complex geological conditions, and the influence of various factors during construction, landslide accidents are the most common engineering disasters in the process of tunnel construction. Reasonable landslide treatment plans are directly related to tunnel construction safety, construction schedule, and economic benefits. At present, the commonly used methods for handling landslide accidents in domestic tunnel projects include pipe-roof grouting, advanced anchor or advanced double-layer duct grouting, and lining support reinforcement. However, for large-span tunnels excavated by the step method, conventional treatment methods have certain limitations and are difficult to meet the requirements of surrounding rock stability and construction schedule. Summary of the invention

[0003] In view of this, the present application provides a method for handling collapse of a large-span tunnel excavated by the step method, which can avoid the problems of great safety hazards, long construction period and high construction cost in handling collapse of a large-span tunnel excavated by the step method.

[0004] A method for handling collapse of a large-span tunnel excavated by a step method comprises the following steps:

[0005] S1. Reinforce the surface of the collapsed section and the disturbed section by landslide: backfill and seal the collapsed section by back pressure, and fill and level the collapsed section and the disturbed section by landslide to form a construction platform;

[0006] S2, sealing the tunnel face and collapsed cavity surface: spraying plain concrete on the tunnel face and collapsed cavity surface for multiple times to perform sealing treatment;

[0007] S3. Excavation and support of upper, middle and lower steps and inverted arches in the landslide disturbance section: Mechanical excavation and enhanced support are adopted for the upper, middle and lower steps and inverted arches in the landslide disturbance section, and the excavation method adopts the three-step reserved core soil method;

[0008] S4, reinforcing the surrounding rock in front of the tunnel face: injecting a cement-water glass double liquid slurry with a predetermined ratio into the surrounding rock in front of the tunnel face to fill it densely;

[0009] S5, reinforcing the interior of the collapsed cavity: a grouting steel pipe is arranged in the collapsed cavity, and cement mortar and lightweight materials are injected into the collapsed cavity to fill it densely;

[0010] S6. Excavation and support of steps on the collapsed section: artificial excavation and strengthening of support of the steps on the collapsed section;

[0011] S7, excavation and support of the lower steps and inverted arch in the collapsed section: mechanical excavation and enhanced support are adopted for the lower steps and inverted arch in the collapsed section;

[0012] S8. Excavation and support of upper, middle and lower steps and inverted arches in the unexcavated disturbed section: the upper, middle and lower steps and inverted arches in the unexcavated disturbed section are excavated and strengthened with support by using micro-vibration smooth blasting technology;

[0013] S9. Excavation and support of upper, middle and lower steps and inverted arches in the unexcavated and undisturbed sections: The upper, middle and lower steps and inverted arches in the unexcavated and undisturbed sections are excavated using micro-seismic smooth blasting technology and supported according to the original design;

[0014] S10. Subsequent construction work: Construct tunnel drainage ditches, waterproof layers and secondary linings according to the original design to form a normal operating procedure.

[0015] Preferably, in step S1, the collapsed section is backfilled to the arch portion with sandbags and slag, so that the collapsed slag in the collapsed cavity falls again and scatters on the portion above the arch top, and the collapsed section and the collapsed disturbance section are compacted, repaired and leveled with an excavator hammer to form a dense and flat construction work platform.

[0016] Preferably, in step S2, the tunnel face and the collapsed cavity surface are sprayed with plain concrete of a first predetermined thickness to seal the surrounding rock. After the concrete reaches a predetermined strength, the plain concrete of the first predetermined thickness is sprayed again to seal the surrounding rock until the concrete layer reaches 3 to 5 layers, wherein structural positions such as cracks, joints, faults and structural surfaces in the tunnel face and the collapsed cavity surface are emphatically sealed.

[0017] Preferably, in steps S3, S4 and S6, an advanced double-layer conduit is constructed along the tunnel excavation contour line and used in conjunction with a steel frame. The steel pipe external insertion angles of the advanced double-layer conduit are staggered at 40 to 45° and 10 to 15°, respectively. The advanced double-layer conduit passes through the steel frame and the end is welded to the steel frame. The insertion length is not less than 90% of the steel pipe length, and the horizontal projection overlap length of two adjacent rows in the longitudinal direction meets the requirements of the specification.

[0018] Preferably, in steps S3, S6 and S7, the landslide section and the landslide disturbance section adopt the principle of "manual pneumatic pick excavation as the main method, mechanical excavation as the auxiliary method, and local weak blasting". After excavation, the steel frames are installed one by one along the tunnel excavation contour line immediately. I-beams are arranged longitudinally between the steel frames, and they are reinforced by locking anchor rods and concrete foundations are added at the arch waist joints. Plain concrete is sprayed to fill the space between the steel frames and the tunnel excavation contour line.

[0019] Preferably, in step S5, the grouting steel pipe is pre-poured with concrete outside the hole and then moved to the installation position. The grouting steel pipe is arranged in a plum blossom shape, one end of the pipe mouth is welded to the steel frame and the other end is supported on a stable collapsed cavity surface. The insertion length and the inclination angle are determined according to the collapsed cavity thickness and the flatness of the collapsed cavity surface. A waterproof board is placed and fixed above the steel frame. A plurality of grouting holes are reserved on the waterproof board. The cement mortar is injected at least twice, and cement mortar is injected into the collapsed cavity through the reserved grouting holes. After the cement mortar reaches a predetermined strength, a second grouting is performed. The lightweight material is a foam cement grouting material. When the slurry thickness reaches a second predetermined thickness, the foam cement grouting material is injected to densely fill the remaining cavity.

[0020] Preferably, in the steps S3 and S7, the landslide section and the landslide disturbance section are initially supported and then reinforced by radial grouting along the tunnel, and the grouting material is pure cement slurry with a mix ratio of 0.5:1 to 5:1.

[0021] Preferably, in step S8, the face of the unexcavated disturbed section is repeatedly layered with steel mesh and sprayed with concrete for support, and sandbags are used for back pressure at the toe of the slope, and micro-vibration smooth blasting technology is used for excavation, I-beams are arranged between the steel frames for longitudinal connection, and the steel frames are reinforced by locking anchor rods and a concrete foundation is added at the arch waist joint, and the space between the steel frames and the tunnel excavation contour line is compacted by spraying with plain concrete;

[0022] More preferably, the I-beam is spot-welded to several sections of steel frames, one end of which is connected to the steel frame and the other end is cantilevered to the unsupported section, and the ratio of the cantilever length to the total length is not greater than 1:2, the locking foot anchor rod adopts the end hook form and the hook is spot-welded to the steel frame, and the concrete foundation is connected to the arch waist joint of the steel frame in the excavated undisturbed section;

[0023] More preferably, when the multi-layer mesh spraying support is performed on the tunnel face of the unexcavated disturbed section, a layer of steel mesh is laid on the tunnel face and concrete of a third predetermined thickness is sprayed to seal the surrounding rock. After the concrete reaches a predetermined strength, the steel mesh is laid again and concrete of a third predetermined thickness is sprayed to seal the surrounding rock until the steel mesh and concrete layers reach 3-5 layers.

[0024] More preferably, the first predetermined thickness is 50 mm to 150 mm, the second predetermined thickness is 100 cm to 200 cm, and the third predetermined thickness is 50 mm to 100 mm;

[0025] Preferably, in step S9, the unexcavated and undisturbed section is excavated by micro-vibration smooth blasting technology, longitudinal connecting bars are arranged between the steel frames, and they are reinforced by locking anchor rods, and advanced double-layer conduits are used in conjunction with the steel frames, and plain concrete spraying is used to compact the space between the steel frames and the tunnel excavation contour line.

[0026] The beneficial effects of the present application are as follows: a method for handling landslides in a large-span tunnel excavated by a step method improves construction operability, reduces safety operation risks, speeds up construction schedule, saves construction time and economic costs through reasonable arrangements of processes such as reinforcing the surface of the landslide body, closing the heading face and the collapse cavity surface, excavating and supporting the disturbed section of the landslide, reinforcing the surrounding rock in front of the heading face, reinforcing the inside of the collapse cavity, excavating and supporting the landslide section, excavating and supporting the unexcavated disturbed section, excavating and supporting the unexcavated and undisturbed section, and subsequent construction operations. The method has strong practicality and wide applicability in the construction of landslide handling in large-span tunnels excavated by a step method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0028] Figure 1 It is a schematic diagram of the longitudinal section of the tunnel in the embodiment of the present application.

[0029] Figure 2 It is a cross-sectional schematic diagram of a tunnel collapse section in an embodiment of the present application.

[0030] Figure 3 It is a schematic diagram of the structure of the advanced double-layer catheter in the embodiment of the present application.

[0031] Figure 4 It is a structural schematic diagram of the connection between the I-beam and the steel arch frame in the embodiment of the present application.

[0032] The components in the figure are marked as follows:

[0033] 1-landslide section; 2-landslide disturbance section; 3-unduged disturbance section; 4-unduged undisturbed section; 5-excavated undisturbed section; 6-construction work platform; 7-head face; 8-collapse cavity face; 9-collapse cavity; 10-grouting steel pipe; 11-drainage ditch; 12-waterproof layer; 13-secondary lining; 14-advanced double-layer duct; 15-steel frame; 16-I-beam. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0035] As used herein, the term "landslide body" refers to the rock blocks that fall due to landslide. The landslide body forms landslide debris, and tunnel debris is the rock blocks after tunnel excavation.

[0036] As used in this article, the term "collapse cavity" refers to the cavity left after the landslide body falls, the collapse cavity surface is the surface of the collapse cavity, and the collapse section is the tunnel mileage section corresponding to the collapse cavity.

[0037] As used herein, the term "landslide disturbance section" refers to the mileage section corresponding to the collapse debris and cave debris after the landslide section is removed.

[0038] As used herein, the term "excavated undisturbed section" refers to a mileage section that has been excavated and supported and has not been disturbed by debris collapse.

[0039] As used herein, the term "unexcavated disturbed section" refers to a mileage section that is not excavated and supported and is disturbed by blasting, which is generally 5 times the diameter of the collapsed cavity.

[0040] As used herein, the term "unexcavated and undisturbed section" refers to a mileage section that has no excavation support and where blasting disturbance is negligible.

[0041] See also Figure 1-4 As shown, the embodiment of the present application provides a method for handling collapse of a large-span tunnel excavated by a step method, comprising the following steps:

[0042] S1, reinforce the surface of landslide section 1 and landslide disturbance section 2.

[0043] After the accident, the technical personnel immediately observed the surrounding rock properties, landslide volume, landslide block size and other information, and determined the landslide treatment plan based on the hydrogeological survey data. Specifically, sandbags and cave slag were first used to backfill the landslide slag to the arch part of the landslide section 1, so that the landslide slag in the collapse cavity 9 would fall again and scatter above the arch top. After the surrounding rock of the landslide section 1 was stable, an excavator was used to hammer and compact, repair and level the landslide slag and cave slag in the landslide section 1 and the landslide disturbance section 2 to form a dense and flat construction platform 6, which was convenient for the subsequent step S2 construction. The longitudinal slope ratio of the construction platform 6 was generally not greater than 1:1, which was determined based on comprehensive factors such as the size of the landslide slag, the strength of the surrounding rock and the construction machinery.

[0044] S2. Close the tunnel face 7 and the collapsed cavity face 8.

[0045] In order to prevent the further expansion of the collapse, the face 7 and the collapse cavity surface 8 were sealed by spraying plain concrete multiple times in time. The specific construction process is to use a wet spraying machine to spray 50-150mm C25 plain concrete on the face 7 and the collapse cavity surface 8 to seal the surrounding rock. After the concrete reaches a certain strength, 50-150mm C25 plain concrete is sprayed again to seal the surrounding rock until the concrete layer reaches 3-5 layers; among them, the cracks, joints, faults and structural surfaces in the face 7 and the collapse cavity surface 8 are sealed. In order to prevent the face 7 and the collapse cavity surface 8 from becoming unstable and collapsing, sand and cave slag in artificial woven bags are placed at the foot of the face 7 slope for back-pressure, with a stacking height of 3m and a thickness of 5m.

[0046] S3. Excavation and support of the upper, middle and lower steps and invert arch of landslide disturbance section 2.

[0047] The three-step reserved core soil method is adopted to mechanically excavate and strengthen the support of the upper, middle and lower steps and the invert arch of the landslide disturbance section 2. The core soil is kept at a distance of about 3 to 5m from the heading face 7. The core soil ensures its length and width. The excavation depth each time depends on the surrounding rock conditions.

[0048] Specifically, the collapsed slag and cave slag of the landslide disturbance section 2 are excavated by the excavator's own breaker hammer, transported to the slag dump by the side unloading loader and the dump truck for stacking, and the installation position of the steel frame 15 is cleared by the slag scraper, and the steel frame 15 is installed one by one along the tunnel excavation contour line; see Figure 3 As shown, an advanced double-layer conduit 14 and a steel frame 15 are then constructed for use together. The longitudinal arrangement distance of the advanced double-layer conduit 14 is 3m to ensure that the overlap length meets the requirements of the specification. C25 plain concrete is sprayed and filled densely between the steel frame 15 and the tunnel excavation contour line; wherein, an I-beam 16 is arranged longitudinally between the steel frames 15, which are reinforced by locking anchor rods and a concrete foundation is added at the arch waist joint to connect the arch waist position of the steel frame 15 of the landslide disturbance section 2 and the excavation undisturbed section 5.

[0049] S4. Strengthen the surrounding rock in front of the tunnel face 7.

[0050] Continue to see Figure 3 As shown, in order to prevent the surrounding rock in front of the face from collapsing and improve the self-bearing capacity of the surrounding rock, an advanced double-layer conduit 14 is constructed along the tunnel excavation contour line for advanced grouting reinforcement. The advanced double-layer conduit 14 passes through the steel frame 15 and the end is welded to the steel frame 15. The insertion length is not less than 90% of the steel pipe length. The steel pipe length is 5.0m. A hot-rolled seamless steel pipe with an outer diameter of 50mm and a thickness of 5mm is used. The circumferential spacing is 30cm, and the horizontal projection overlap length of two adjacent rows in the longitudinal direction is not less than 15 0cm, the external insertion angles of the steel pipes are staggered at 40-45° and 10-15° respectively; after installation by drilling method, the face 7 is filled densely with cement-water glass double slurry, the cement slurry mix ratio is 0.8:1-1.5:1, the water glass concentration is 25-40°Be, the volume ratio of cement slurry to water glass is 1:1-1:0.3, and the grouting pressure is 0.5-2.0MPa. During the construction process, attention should be paid to strengthening monitoring and measurement, and the landslide section 1 shall be excavated after the slurry strength is reached.

[0051] S5, reinforcing the interior of the collapsed cavity 9.

[0052] See also Figure 2As shown, a grouting steel pipe 10 is arranged in the collapse cavity 9. The grouting steel pipe 10 is pre-poured with concrete outside the hole and vibrated to be dense before being moved to the installation position. The grouting steel pipe 10 adopts a seamless steel pipe, and the front end is made into a pointed cone. One end of the pipe mouth is welded to the steel frame 15 and the other end is supported on the stable collapse cavity surface 8. It is arranged in a plum blossom shape with a spacing of no more than 50 cm to ensure the grouting quality. The insertion length and inclination angle of the steel pipe are determined according to the thickness of the collapse cavity 9 and the flatness of the collapse cavity surface 8. The grouting steel pipe 10 is cut according to the insertion length of the steel pipe; after the steel frame 15 is installed, a 1.5 mm thick EVA waterproof board is laid on it, and a number of grouting holes are reserved on the EVA waterproof board. Cement mortar and lightweight materials are injected into the collapse cavity 9 through the grouting holes to fill it densely.

[0053] As a demonstration method, cement mortar is injected at least twice. Cement mortar is injected into the collapsed cavity 9 through the reserved grouting holes. The second grouting is carried out after the cement mortar reaches a certain strength. The cement mortar mix ratio is 1:2.5, the injection pressure is 0.5~2MPa, and the lightweight material is foam cement grouting material. When the slurry thickness reaches 100cm~200cm, the foam cement grouting material is injected again to densely fill the remaining cavity.

[0054] S6. Excavation and support of the upper steps of landslide section 1.

[0055] The excavation method for the upper steps of the collapsed section 1 is mainly manual pneumatic picks, supplemented by mechanical excavation, to minimize the excavation of the tunnel edge by the excavator, and to use manual pneumatic picks to trim the tunnel periphery to reduce the disturbance to the surrounding rock; after excavation, the initial concrete spraying is carried out in time to seal the heading face 7 to avoid the phenomenon of block falling from the vault.

[0056] Continue to see Figure 3 As shown, an advanced double-layer conduit 14 of the arch is constructed along the tunnel excavation contour line. The advanced double-layer conduit 14 and the steel frame 15 are used in conjunction with each other. The longitudinal arrangement distance of the advanced double-layer conduit 14 is 2.5m to enhance the support effect. The arch foot of the steel frame 15 is close to the surrounding rock side and additional I-beam longitudinal connections, additional concrete foundations, additional locking anchor rods, and additional support channel steel pads are used to enhance the arch foot bearing capacity and reduce the sinking of the arch crown. C25 plain concrete is sprayed to fill the space between the steel frame 15 and the tunnel excavation contour line. At the same time, in order to improve the temporary drainage system in the tunnel, a transverse ditch is excavated near the heading face 7 to divert water to the tunnel drainage ditch 11 to discharge it out of the tunnel to avoid soaking the arch foot.

[0057] S7, excavation and support of the lower steps and invert arch in landslide section 1.

[0058] Mechanical excavation is adopted for the lower steps and invert arch of collapse section 1, and 30cm is reserved for manual excavation at the arch foot and wall corner. It is strictly forbidden to produce over-excavation. When encountering boulders, loosening blasting is adopted to avoid disturbing the surrounding rock as much as possible. The left and right section steps are staggered for excavation, with an excavation height of 2m. The excavation advance per cycle does not exceed 0.6-0.9m, and the excavation length of each step should be between 8-10m. Immediately after excavation, 50-150mm thick C25 concrete is sprayed to seal the heading face, and steel frames 15 are installed one by one along the tunnel excavation contour line. C25 plain concrete is sprayed to fill the space between the steel frames 15 and the tunnel excavation contour line. I-beams 16 are arranged between the steel frames 15 for longitudinal connection, and they are reinforced by locking anchor rods and concrete foundations are added at the arch waist joints to strengthen the support, so as to prevent the arch foot from sinking and moving inwards, causing excessive deformation, and leading to the collapse of the arch rock layer. Preferably, by shortening the step length and constructing the inverted arch in time, the initial support full-ring steel arch frame 15 is closed into a ring in time.

[0059] Here, in the steps S3 and S7, the landslide section 1 and the landslide disturbance section 2 are initially supported and then radially grouted along the tunnel for reinforcement. In this embodiment, the grouting material is pure cement slurry with a mix ratio of 0.5:1 to 5:1, and the grouting pressure is 0.5 to 1 MPa.

[0060] S8, excavation and support of the upper, middle and lower steps and invert arch of the unexcavated disturbed section 3.

[0061] The micro-vibration smooth blasting technology is used to excavate the upper, middle and lower steps and invert arches of the unexcavated disturbed section 3 and strengthen the support. The excavation volume is controlled during construction to reduce the disturbance of the surrounding rock, strengthen the advanced support, improve the integrity of the support structure, and improve the bearing capacity of the base through the foot treatment of the support structure. In this embodiment, first, the steel mesh is laid and sprayed on the face 7 for multiple times.

[0062] The specific implementation process is as follows: a layer of steel mesh is laid on the face 7 and 50mm-100mm of concrete is sprayed to seal the surrounding rock. After the concrete reaches a certain strength, the steel mesh is laid again and 50mm-100mm of concrete is sprayed to seal the surrounding rock until the steel mesh and concrete layers reach 3-5 layers; then, sandbags are used for counter-pressure at the foot of the slope, and micro-vibration smooth blasting technology is used for excavation. During the construction process, attention is paid to the stability of the primary support structure and the core soil. I-beams 16 are arranged between the steel frames 15 for longitudinal connection, and they are reinforced by locking anchor rods and a concrete foundation is added at the arch waist joint. The locking anchor rod adopts a hook at the end and the hook is spot-welded to the steel frame 15. Plain concrete is sprayed to fill the space between the steel frame 15 and the tunnel excavation contour line.

[0063] See also Figure 4As shown, in the steps S3 and S6-S8, the I-beam 16 is spot-welded to a plurality of steel frames 15, one end of which is connected to the steel frame 15 and the other end is cantilevered to the unsupported section, and the ratio of the cantilever length to the total length is not greater than 1:2. A steel mesh is laid on the I-beam and welded firmly to prevent large pieces of surrounding rock from falling and injuring workers, thereby ensuring the safety of construction operations.

[0064] S9, excavation and support of the upper, middle and lower steps and invert arch of the undisturbed section 4.

[0065] The micro-seismic smooth blasting technology is used to excavate the unexcavated and undisturbed section 4 and support it according to the original design. The blasting design adheres to the principle of "weak blasting, short advance, strong support, early closure, and frequent measurement", and should be comprehensively considered based on factors such as engineering geological conditions, excavation cycle advance, blasting materials, and slag discharge capacity. Specifically, first, the face 7 is paved with steel mesh and sprayed with concrete support. The initial support adopts support measures such as Φ8mm steel mesh, steel frame, C25 sprayed concrete, Φ22 mortar anchor rod, Φ25 hollow anchor rod, etc. After excavation and initial support, the arch and filling are closely followed; along the tunnel excavation contour line, the advanced double-layer guide tube 14 and the steel frame 15 are used in combination. The steel frame 15 and the tunnel excavation contour line are compacted with plain concrete spraying. The steel frames 15 are arranged with longitudinal connecting bars and connected firmly. The arch foot is reinforced by the locking foot anchor rod, and the locking foot anchor rod must be grouted to ensure the stability of the steel frame 15 foundation. It should be noted that during the construction process, monitoring and measurement should be strengthened, timely analysis and feedback should be given based on the monitoring and measurement results, and support parameters should be adjusted in a timely manner to ensure safe and smooth construction.

[0066] S10. Subsequent construction work.

[0067] After the initial support becomes stable, the tunnel drainage ditch 11, waterproof layer 12 and secondary lining 13 are constructed according to the original design to form a normal operation process; specifically, the tunnel is equipped with curb drainage ditches 11 and central drainage ditches 11 on the left and right sides of the driving lane, and the waterproof layer 12 is equipped with EVA waterproof membrane and non-woven waterproof board between the initial support and the secondary lining. The secondary lining 13 adopts a composite lining, which is pumped by a full-section steel mold integral hydraulic lining trolley and a concrete delivery pump or a car pump. The deformation joints and construction joints of the secondary lining 13 are weak links in tunnel construction and should be highly valued during construction; the distance between each process during construction is shortened as much as possible, the lining is closely followed by excavation and the full-section is closed as soon as possible to reduce the exposure and loosening of the rock formation and the increase in ground pressure.

[0068] Specifically, the advantages of this application are as follows:

[0069] First, the collapsed section 1 of the tunnel is backfilled and sealed by using artificial sandbags, cave slag, and collapsed slag, thus preventing the collapse from further expanding and forming a construction platform 6, which is convenient for the wet spraying machine to seal the tunnel face 7 and collapsed cavity surface 8, thereby restraining the deformation of the surrounding rock;

[0070] Second, this method significantly reduces the risk of surrounding rock deformation and collapse expansion through a series of measures, such as constructing an advanced double-layer conduit 14 and grouting reinforcement, connecting the steel arch frames with I-beams 16 and cantilevering the front end of the I-beams 16 to the unsupported part, adding grouting steel pipes 10 in the collapsed cavity 9 to support the surrounding rock, manual pneumatic picks in conjunction with mechanical excavation, radial grouting filling of the tunnel, adding transverse drainage ditches 11 to the face 7, laying steel mesh in layers for multiple times and spraying concrete, and micro-vibration smooth blasting technology, thereby ensuring the safety of construction workers to the greatest extent;

[0071] Third, this method adopts such treatment measures as using plain concrete to seal the tunnel face 7 and the collapsed cavity face 8, cement-water glass double liquid slurry to reinforce the surrounding rock in front of the tunnel face 7, cement mortar and foam cement grouting materials to fill the collapsed cavity 9, and pure cement slurry to perform radial reinforcement of the tunnel. According to the construction schedule and surrounding rock reinforcement requirements, the grouting materials and their mix ratios are comprehensively determined in combination with factors such as construction quality, construction schedule, safety and economy, thereby ensuring that the construction progress is accelerated, the construction quality is improved, the economic cost is reduced, and the collapsed section 1 of the tunnel is passed quickly and efficiently under the premise of construction safety.

[0072] Fourth, this method strengthens the support by setting a grouting steel pipe 10 in the collapsed cavity 9. The grouting steel pipe 10 is moved into the tunnel after being poured with concrete outside the tunnel in advance. One end of the pipe mouth is welded to the steel frame 15, and the other end is supported on the stable collapsed cavity surface 8. The grouting liquid is injected into the collapsed cavity 9 in layers through the reserved grouting holes. Compared with the traditional treatment method of only backfilling and grouting in the collapsed cavity 9 once, the loose surrounding rock in the collapsed cavity 9 is strengthened by grouting the collapsed cavity surface 8 after the grouting steel pipe 10 is densely set to support the collapsed cavity surface 8. The grouting steel pipe 10 is tightly pressed against the rock surface, avoiding the risk of landslides occurring again and significantly improving the rock reinforcement effect. In addition, due to the reinforcement effect of the grouting steel pipe 10, after the grouting steel pipe 10 is installed, only 100mm to 300mm slurry needs to be poured as the steel pipe foundation before the subsequent procedures can be constructed. The grouting process of the collapsed cavity 9 and the subsequent excavation and support process of the collapsed section 1 are constructed simultaneously, which greatly shortens the landslide treatment period, avoids tunnel door closing collapse accidents, and ensures construction safety.

[0073] The above is only a preferred specific implementation method, but the protection scope of this application is not limited to this. Any changes or substitutions that can be easily conceived by any technician familiar with this technical field within the technical scope of this disclosure should be included in the protection scope of this application.

Claims

1. A method for handling collapse of a large-span tunnel excavated by a step method, characterized in that: The following steps are involved: S1, reinforcing the surface of the collapsed section (1) and the collapsed disturbed section (2): backfilling and sealing the collapsed section (1) by counter pressure, and filling and leveling the collapsed section (1) and the collapsed disturbed section (2) to form a construction platform (6); S2, sealing the tunnel face (7) and the collapsed cavity surface (8): spraying plain concrete on the tunnel face (7) and the collapsed cavity surface (8) for multiple times to perform sealing treatment; S3, excavation and support of the upper, middle and lower steps and inverted arch of the landslide disturbance section (2): mechanical excavation and enhanced support are adopted for the upper, middle and lower steps and inverted arch of the landslide disturbance section (2), and the excavation method adopts the three-step reserved core soil method; S4, reinforcing the surrounding rock in front of the tunnel face (7): injecting a cement-water glass double liquid slurry with a predetermined ratio into the surrounding rock in front of the tunnel face (7) to fill it densely; S5, reinforcing the interior of the collapsed cavity (9): a grouting steel pipe (10) is arranged in the collapsed cavity (9), and cement mortar and lightweight materials are injected into the collapsed cavity (9) to fill it densely; S6. Excavation and support of the upper step of the collapsed section (1): artificial excavation and strengthening of support are performed on the upper step of the collapsed section (1); S7, excavation and support of the middle and lower steps and inverted arch of the collapsed section (1): mechanical excavation and strengthening of support are adopted for the middle and lower steps and inverted arch of the collapsed section (1); S8. Excavation and support of the upper, middle and lower steps and inverted arch of the unexcavated disturbed section (3): the upper, middle and lower steps and inverted arch of the unexcavated disturbed section (3) are excavated and strengthened with support by using micro-vibration smooth blasting technology; S9, excavation and support of the upper, middle and lower steps and invert of the unexcavated and undisturbed section (4): the upper, middle and lower steps and invert of the unexcavated and undisturbed section (4) are excavated by using micro-seismic smooth blasting technology and supported according to the original design; S10, subsequent construction work: construct the tunnel drainage ditch (11), waterproof layer (12), and secondary lining (13) according to the original design to form a normal operation process; In the step S5, the grouting steel pipe (10) is pre-cast with concrete outside the hole and then moved to the installation position. The grouting steel pipe (10) is arranged in a plum blossom shape, one end of the pipe mouth is welded to the steel frame (15) and the other end is supported on a stable collapsed cavity surface (8). The insertion length and the inclination angle are determined according to the thickness of the collapsed cavity (9) and the flatness of the collapsed cavity surface (8). A waterproof board is placed and fixed above the steel frame (15). A plurality of grouting holes are reserved on the waterproof board. The cement mortar is injected at least twice, and the cement mortar is injected into the collapsed cavity (9) through the reserved grouting holes. After the cement mortar reaches a predetermined strength, a second grouting is performed. The lightweight material is a foam cement grouting material. When the slurry thickness reaches a second predetermined thickness, the foam cement grouting material is injected to densely fill the remaining cavity part.

2. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 1, characterized in that: In the step S1, the collapsed section (1) is backfilled to the arch portion with sandbags and slag, so that the collapsed slag in the collapsed cavity (9) falls again and scatters on the part above the arch top. The collapsed section (1) and the collapsed disturbance section (2) are compacted, repaired and leveled with an excavator hammer to form a dense and flat construction platform (6).

3. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 1 is characterized in that: In the step S2, the tunnel face (7) and the collapsed cavity surface (8) are sprayed with a first predetermined thickness of plain concrete to seal the surrounding rock, and after the concrete reaches a predetermined strength, the first predetermined thickness of plain concrete is sprayed again to seal the surrounding rock until the concrete layer reaches 3 to 5 layers, wherein the cracks, joints, faults and structural surfaces in the tunnel face (7) and the collapsed cavity surface (8) are emphatically sealed.

4. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 1, characterized in that: In the steps S3, S4 and S6, an advanced double-layer conduit (14) and a steel frame (15) are constructed along the tunnel excavation contour line for use in combination. The steel pipe external insertion angles of the advanced double-layer conduit (14) are staggered at 40-45° and 10-15° respectively. The advanced double-layer conduit (14) passes through the steel frame (15) and its end is welded to the steel frame (15). Its insertion length is not less than 90% of the length of the steel pipe, and the horizontal projection overlap length of two adjacent rows in the longitudinal direction meets the requirements of the specification.

5. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 1, characterized in that: In the steps S3, S6 and S7, the collapse section (1) and the collapse disturbance section (2) adopt the principle of "manual pneumatic pick excavation as the main method, mechanical excavation as the auxiliary method, and local weak blasting". After excavation, the steel frames (15) are installed one by one along the tunnel excavation contour line in a timely manner. I-beams (16) are arranged between the steel frames (15) for longitudinal connection. The steel frames (15) are reinforced by locking anchor rods and a concrete foundation is added at the arch waist joint. The space between the steel frames (15) and the tunnel excavation contour line is filled with plain concrete.

6. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 1, characterized in that: In the steps S3 and S7, the landslide section (1) and the landslide disturbance section (2) are initially supported and then reinforced by grouting in the radial direction of the tunnel, and the grouting material is pure cement slurry with a mix ratio of 0.5:1 to 5:

1.

7. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 3 is characterized in that: In the step S8, the face (7) of the unexcavated disturbed section (3) is repeatedly layered with steel mesh and sprayed with concrete for support, and sandbags are used at the toe of the slope for counter pressure, and micro-vibration smooth blasting technology is used for excavation. I-beams (16) are arranged between the steel frames (15) for longitudinal connection, and are reinforced by locking anchor rods and a concrete foundation is added at the arch waist joint. Plain concrete is sprayed to fill the space between the steel frames (15) and the tunnel excavation contour line.

8. The method for handling collapse of a large-span tunnel excavated by the step method according to claim 5 or 7, characterized in that: The I-beam (16) is spot-welded to a plurality of shaped steel frames (15), one end of which is connected to the shaped steel frame (15) and the other end of which is cantilevered to the unsupported section, and the ratio of the cantilevered length to the total length is not greater than 1:

2. The locking foot anchor rod adopts a hook form at the end and the hook is spot-welded to the shaped steel frame (15), and the concrete foundation is connected to the arch waist joint of the shaped steel frame (15) of the excavated undisturbed section (5).

9. According to the method for handling collapse of a large-span tunnel excavated by the step method of claim 7, when the tunnel face (7) of the unexcavated disturbed section (3) is subjected to multi-layer mesh spraying support, a layer of steel mesh is laid on the tunnel face (7) and concrete of a third predetermined thickness is sprayed to seal the surrounding rock. After the concrete reaches a predetermined strength, the steel mesh is laid again and concrete of a third predetermined thickness is sprayed to seal the surrounding rock, until the steel mesh and concrete layers reach 3-5 layers; The first predetermined thickness is 50 mm to 150 mm, the second predetermined thickness is 100 cm to 200 cm, and the third predetermined thickness is 50 mm to 100 mm; In the step S9, the unexcavated and undisturbed section (4) is excavated by using micro-vibration smooth blasting technology, longitudinal connecting bars are arranged between the steel frames (15), and they are reinforced by locking anchor rods, and an advanced double-layer guide tube (14) and the steel frames (15) are used in conjunction with each other, and plain concrete is sprayed to fill the space between the steel frames (15) and the tunnel excavation contour line.

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