Construction Method for Opposite Bracing of Radial Steel Pipes in Highway Tunnel Cavity Collapse

Abstract

The present invention relates to the technical field of radial steel pipe butt support for highway tunnel collapse cavities, and particularly to the construction method of radial steel pipe butt support for highway tunnel collapse cavities. For the severely collapsed section of the vault, double-layer steel arch supports are adopted. First, on the basis of the original tunnel section, the outline of the tunnel section is enlarged by 26 cm as a whole, and the initial support of the steel arch is carried out. The specific parameters and steps of the support are as follows: initial spraying of C25 shotcrete (thickness 5 - 15 cm) → φ6.5 double-layer steel mesh (spacing 0.2 m × 0.2 m) → I20a I-beam (spacing 0.5 m / frame) for the first layer of steel arch → φ60 mm steel pipe support frame → C25 shotcrete (thickness 26 cm) → φ6.5 double-layer steel mesh (spacing 0.2 m × 0.2 m) → I20a I-beam (spacing 0.5 m / frame) for the second layer of steel arch → C25 shotcrete (thickness 26 cm) → φ42 double-row locking feet steel pipes → monitoring and measurement. After the support is completed, the shotcrete is used for closing.

Description

Technical Field

[0001] The present invention relates to the technical field of radial steel pipe opposite support for highway tunnel collapse cavities, and particularly relates to a construction method for radial steel pipe opposite support for highway tunnel collapse cavities. Background Art

[0002] In recent years, with the development of the economy, the road engineering industry in China has been continuously progressing, and tunnel engineering is an important part of road engineering and has received increasing attention. During tunnel construction, if a karst cave collapse occurs, it will have a huge impact and danger on tunnel construction. The treatment of tunnel collapses must be based on a correct understanding of the collapses. The formulation of a collapse treatment plan is like the formulation of a battle plan. If the plan is inappropriate or fails, it will not only lead to greater economic losses but may also cause casualties. Therefore, the general treatment principle is to first consolidate the rear to prevent the collapse from expanding, and then, relying on or protected by the safe rear, proceed with the treatment forward. Usually, the support structures in the collapsed section are backfill, protective arch, and lining from top to bottom. Intuitively, it seems safe to construct the protective arch first and then construct the lining under the protection of the protective arch. However, in fact, constructing the protective arch itself is extremely difficult and extremely dangerous. Practice has proved that after a collapse occurs, it will tend to be stable within a certain period of time and form a natural arch. It is a safe and economical method to first construct the lining and then construct the protective arch and backfill. Summary of the Invention

[0003] The purpose of the present invention is to provide a construction method for radial steel pipe opposite support for highway tunnel collapse cavities in view of the deficiencies of the prior art. It is applicable to the relatively stable, thixotropic, and highly fluid rock sections of tunnel collapse cavities, especially when a core soil needs to be left at the heading face to prevent the collapse cavity from continuing to expand.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A construction method for radial steel pipe opposite support for highway tunnel collapse cavities, characterized by including the following steps:

[0006] Step 1. Preparation work

[0007] Judgment of collapse stability: Making a correct judgment on the stability after the collapse is the key to formulating a treatment plan. Otherwise, it is either taking risks or increasing investment. Generally, the collapse is basically stable 1 - 2 days after it occurs. Except for individual small pieces falling off, there is no large-scale collapse. After determining the collapse stability, the treatment can be started.

[0008] Step 2. Removal of dangerous rocks

[0009] Removal of individual dangerous rocks: After the landslide forms an arch and stabilizes, the newly formed free face will quickly weather and soften under the combined action of air and groundwater. The interlayer bonding force will rapidly weaken, resulting in phenomena such as continuous chipping of dangerous rocks and overhanging rocks, endangering construction safety. It is necessary to carefully observe and remove them;

[0010] Step 3: Shotcrete for sealing

[0011] Spray C25 concrete with a thickness of 5 - 15 cm on the free face after removing the dangerous rocks to reduce the oxidation effect of air on the surrounding rock;

[0012] Step 4: Mucking and cleaning the excavation face

[0013] The mucking range is determined according to the stability of the surrounding rock, the safety of the landslide body, and the lining length;

[0014] Set double-row φ42mm foot-locking anchor pipes at the arch feet, with a length of 3.5 m and a spacing of 0.5 m to ensure the stability of the side walls during the lower excavation;

[0015] Step 5: First-layer steel arch support and second-layer steel arch support

[0016] For the severely collapsed section of the arch crown, double-layer steel arch support is adopted. First, expand the overall outline of the tunnel section by 26 cm on the basis of the original tunnel section, and carry out initial support of the steel arch. The specific parameters and steps of the support are: initial spraying of C25 shotcrete (thickness 5 - 15 cm) → double-layer φ6.5 steel bar mesh (spacing 0.2 m × 0.2 m) → I20a steel I-beam (spacing 0.5 m / frame) for the first-layer steel arch → φ60mm steel pipe support frame → C25 shotcrete (thickness 26 cm) → double-layer φ6.5 steel bar mesh (spacing 0.2 m × 0.2 m) → I20a steel I-beam (spacing 0.5 m / frame) for the second-layer steel arch → C25 shotcrete (thickness 26 cm) → double-row φ42 foot-locking steel pipes → monitoring and measurement. After the support is completed, shotcrete is used for sealing;

[0017] To ensure the safety of the next-cycle support, after the construction of the first-layer steel arch is completed, set φ60*4mm steel pipes vertically in the abdomen of the steel arch, with a spacing (0.2 m horizontally × 0.5 m vertically) and a height of about 2 - 3 m, which can be lengthened according to the height of the collapse cavity, and then start the second-layer steel arch support;

[0018] When about 1 m³ of muck is cleared, a steel arch frame is erected. When more than two steel arch frames are installed, a transverse (0.2 m) * longitudinal (0.5 m) grid steel pipe support framework can be formed above the tunnel crown, initially forming an opposite support framework, which firmly supports the dangerous large boulders existing above the crown, preventing the plastic slip body from forming in the surrounding rock of the crown collapse cavity and causing shear failure of the support structure. Generally speaking, the steel pipe support framework plays a buffering role in the crown collapse cavity falling blocks, avoiding the impact force of the falling blocks on the steel arch frame support and causing the initial support to deform under force. The steel pipe support framework not only plays a role in temporary support during the collapse treatment process, but also has another function: jointly forming a C30 concrete protective arch framework structure system with the steel arch frame and concrete, enhancing the axial compression of the initial support. Using it in this special situation has achieved good results.

[0019] Step 6: Monitoring and measurement

[0020] During the whole process of collapse treatment, the inside of the tunnel is monitored and measured, and the measured data is timely analyzed and fed back to guide the construction. A total of two horizontal measurement lines, two inclined measurement lines, and one crown settlement line are arranged in the tunnel. The monitoring and measurement are carried out strictly in accordance with relevant specifications and designs. After the measurement is completed every day, the data is analyzed in time and the monitoring conclusions are fed back to the construction technicians and the on-site person in charge; when the horizontal convergence value in the tunnel is greater than 5 mm / d or abnormal conditions are found in the surface monitoring, the on-site personnel should be immediately notified to evacuate, and reported to the higher level in time; when the collapse section treatment is completed, the monitoring can be stopped only after the convergence in the tunnel is less than 0.2 mm / d;

[0021] Step 7: Next cycle of support

[0022] Step 8: C30 concrete protective arch

[0023] Construct a C30 concrete protective arch on the outer contour of the lining. The thickness of the protective arch is 1.0 - 1.5 m. After the initial support of the tunnel is closely attached to the surrounding rock of the heading face and the lining reaches a certain strength, grouting is carried out. First, backfill grouting is used to fill the gap between the lining and the rock, and then consolidation grouting is used to consolidate the rock around the tunnel. First, a grouting pipe is reserved at the crown. After the concrete at the crown of the lining has solidified, grouting is carried out. When the vent pipe starts to leak slurry, it means that the concrete injected at the crown has reached the expected quantity;

[0024] Step 9: 4% cement fly ash filling

[0025] To reduce the stress on the initial support, the void area above the protective arch is backfilled with 4% cement fly ash until it is full. The fly ash fills the upper collapse cavity until the filling thickness reaches about 4 m. After the slurry has solidified and stabilized, excavation operations can be carried out.

[0026] The lining thickness is increased to 80 cm, and 50 kg / m steel rails are added to the secondary lining concrete as arch supports for reinforcement, with a spacing of 1.0 m. The longitudinal connection of the arch supports is welded firmly with 18 kg / m steel rails, and the circumferential spacing is 1.0 m. The waterproof and drainage structure is the same as the original design and is densely bonded to the constructed section.

[0027] In Step 5, the steel arch support includes the following steps:

[0028] 1. Shotcrete support

[0029] The wet shotcrete technology is used for construction. The wet shotcrete process of concrete is carried out in two times. For the initial shotcrete, the exposed surface after removing the dangerous rocks is sprayed with 5 - 15 cm thick C25 concrete for closure to reduce the oxidation of the surrounding rock by air. The re - shotcrete is carried out after the installation of the first - layer steel arch support, steel mesh, and radial steel pipes, reaching the design thickness at one time. The wet shotcrete process is adopted, and the shotcrete is carried out by a manipulator. The shotcrete operation surface closely follows the excavation surface to minimize the exposure time of the excavation surface.

[0030] (1) Treatment of the surface to be shotcreted: Check whether the size and geometric shape of the surface to be shotcreted meet the design requirements, remove the obstacles on the surface to be shotcreted that affect the shotcrete operation, and cover and protect the remaining objects and embedded components.

[0031] (2) Shotcrete construction: Accelerators are added to the shotcrete according to the design quantity. The XBS - Ⅱ shotcrete machine is used for wet shotcrete of concrete. First, adjust the compressed air pressure to ensure that the shotcrete has good adhesiveness. The distance between the nozzle and the surface to be shotcreted is preferably 0.6 - 1.0 m and perpendicular to the surface to be shotcreted. When encountering steel bars or steel frame structures, it can be tilted at an appropriate angle. During shotcrete, it should be carried out in sections (not exceeding 6 m), parts (from bottom to top), and blocks (2 m×2 m), strictly in the order from bottom to top to reduce the sliding or falling of concrete caused by gravity. The shotcrete movement can be carried out in an S - shaped reciprocating movement or a spiral movement. The shotcrete should be carried out in multiple layers for re - shotcrete to prevent excessive rebound of concrete. Finally, spray until the design shotcrete thickness is reached. The shotcrete surface should be flat, smooth, without concavities or convexities, dry patches, or flowing problems. After being inspected and qualified by the supervising engineer, the operation ends. If it is unqualified, re - shotcrete is carried out. If the interval time exceeds 2 hours, the surface should be wetted with water before re - shotcrete.

[0032] 2. Steel mesh laying

[0033] The steel mesh is processed in pieces outside the tunnel and laid, hung, and welded inside the tunnel. The requirement for hanging the mesh is that the steel mesh follows the undulation of the surface to be shotcreted. The lap length of the φ6.5 steel mesh sheet is not less than 30d (d is the diameter of the steel bar), and it shall not be less than the length of one long side of a grid, and it is welded firmly to the steel arch support, which is beneficial to reducing the rebound during shotcrete.

[0034] 3. Steel arch support construction

[0035] (1) The steel frame is fabricated on a 1:1 mock-up platform set up in the processing workshop. It is fabricated by cold bending and in sections, and after unit welding and trial assembly, it is transported to the site for installation. During processing, ensure accurate dimensions and smooth arcs; the welding (or lapping) length of the steel bars meets the design requirements. When welding and forming, it is carried out symmetrically on both sides of the steel frame. The center of the steel frame coincides with the tunnel center line, and the plane of the steel frame is perpendicular to the tunnel center line. At the joint, the adjacent two connecting steel plates coincide, and the connection hole positions are accurate;

[0036] After processing, conduct a trial assembly first to check for any distortion. The joints of each frame can be interchanged, and the error along the tunnel perimeter must comply with the technical specification requirements; after the trial assembly after processing, the allowable error is: the deviation along the tunnel perimeter is ±3 cm, and the plane (warpage) deviation is ±2 cm. Those that do not meet the requirements are prohibited from use;

[0037] (2) After the initial shotcrete, install the steel frame strictly according to the design. The allowable deviation for the installation of the steel frame is ±5 cm both horizontally and in elevation, and the inclination shall not be greater than 2°. After the construction of the first layer of steel arch frame is completed, set up φ60*4 mm steel pipes vertically in the abdomen of the steel arch frame, with a spacing (0.2 m horizontally * 0.5 m vertically) and a height of about 2 - 3 m, which can be lengthened depending on the height of the collapse cavity, and then start the support of the second layer of steel arch frame;

[0038] (3) The foundations at both arch feet on both sides of the steel frame must be firm and solid. Before installing the arch feet or wall feet, remove the floating debris under the bearing plates, place the steel frame on the original surrounding rock, and pad the arch frame with steel plates under the arch feet. Do not use block stones, floating slag or crushed stones for padding;

[0039] During installation, first pre-assemble the steel frame segments into the installation section and tighten the connection bolts; after the steel frame is erected, the dimensions between the steel arch supports are strictly implemented according to the design; use the center line and arch foot line to control the installation support distance of the steel arch frame during installation, so that the two arch feet and the arch top are in the same vertical plane to avoid torsion. The steel support segments are connected by high-strength bolts, and then fixed with positioning bars. Longitudinally, use Φ22 connecting steel bars to connect it firmly with the adjacent steel frames, and arrange them staggeredly on the inner and outer edges of the steel frame support. All supports are welded on both sides, and the weld thickness shall not be less than 4 mm;

[0040] (4) Wedge the space between the steel arch frame and the rock wall with steel wedges or concrete pads. After the steel arch frame is installed in place, set up locking anchor pipes at the arch feet to fix the steel frame, and weld the tail of the anchor pipe to the steel frame.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1. Strong applicability. The processing and installation of the two-layer arch frame are basically the same as those of the conventional single-layer arch frame construction, without the need to add equipment or specially train personnel.

[0043] 2. Good safety performance. It adopts a concrete structure composed of two layers of steel arch frames, seamless steel pipes of φ60*4mm arranged radially along the tunnel, and C25 shotcrete. The operation of personnel and equipment in the tunnel is safer, and the safety factor of the primary support structure itself is improved.

[0044] 3. Reliable quality. The support composed of two layers of steel arch frames and seamless steel pipes of φ60*4mm arranged radially along the tunnel improves the strength of the initial support of the tunnel, eliminates quality hazards caused by insufficient support capacity of the steel arch frame, and improves the quality of the engineering entity.

[0045] 4. Shorten the construction period. The use of two layers of steel arch frame support in the soft rock tunnel of the highway avoids the occurrence of diseases in the initial support, ensures continuous and balanced construction of the tunnel, and shortens the construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the elevation view of the treatment of the tunnel collapse cavity in the present invention;

[0047] Figure 2 It is the model diagram of the treatment of the tunnel collapse cavity in the present invention;

[0048] Figure 3 It is the construction sequence diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, and are not used to limit the present invention.

[0050] Embodiment 1

[0051] The process principle of the construction method of the present invention: The framework composed of two layers of steel arch frames, seamless steel pipes of φ60*4mm arranged radially along the tunnel, and C30 protective arch is a secondary steel arch frame support on the basis of the traditional single-layer steel arch frame support. At the same time, the use of φ60*4mm radial seamless steel pipes, shotcrete, and steel arch frames forms a concrete steel support, thereby strengthening the quality of the initial support. The specific process is as follows:

[0052] (1) Due to the broken lithology and developed joints in the water-rich karst section, after the tunnel is excavated, a large amount of tunnel water inrush, mud outburst and other geological problems often occur on the tunnel face. Therefore, after the excavation is completed and the collapsed surrounding rock is stable, the framework composed of two layers of steel arch frames and seamless steel pipes of φ60*4mm arranged radially along the tunnel can quickly form a strong initial support, effectively support the surrounding rock pressure, inhibit deformation, and avoid large-area collapses;

[0053] (2) Pour C30 arch protection outside the initial support to make the arch protection the main stress point of the initial support, avoiding the direct contact between the steel arch and the surrounding rock, which may cause the compression deformation of the steel arch and thus affect the quality of the initial support;

[0054] (3) In response to the problem of large-area collapse cavities, to reduce the self-weight of concrete and other filling materials, the collapse cavity is backfilled with 4% cement fly ash bags until full. The fly ash and 4% cement form a filling material, making the cavity wall in direct contact with the cement fly ash to prevent the continuous expansion of the collapse cavity range.

[0055] Example 2

[0056] The construction method of the opposite top support of radial steel pipes for highway tunnel collapse cavities is characterized by including the following steps:

[0057] Step 1. Preparation work

[0058] Judgment of landslide stability: Making a correct judgment on the stability after the landslide is the key to formulating a treatment plan. Otherwise, it will either be risky or increase investment. Generally, the landslide will be basically stable 1 to 2 days after it occurs. Except for individual small pieces falling off, there will be no large-scale collapse. After determining the landslide stability, treatment can be started.

[0059] Step 2. Removal of dangerous rocks

[0060] Removal of individual dangerous rocks: After the landslide forms an arch and stabilizes, the newly formed free face will quickly weather and soften under the combined action of air and groundwater. The interlayer bonding force will quickly weaken, resulting in phenomena such as dangerous rocks and hanging rocks constantly falling off, endangering construction safety. It is necessary to carefully observe and remove them.

[0061] Step 3. Spraying concrete for sealing

[0062] Spray 5 - 15 cm thick C25 concrete on the free face after removing the dangerous rocks to reduce the oxidation effect of air on the surrounding rock.

[0063] Step 4. Mucking and cleaning the excavation face

[0064] The mucking range is determined according to the stability of the surrounding rock, the safety of the collapsed body, and the lining length.

[0065] Set double-row φ42mm foot-locking anchor pipes at the arch feet, with a length of 3.5 m and a spacing of 0.5 m to ensure the stability of the side wall during the lower excavation.

[0066] Step 5. First-layer steel arch support and second-layer steel arch support

[0067] For the severely collapsed section of the vault, double-layer steel arch supports are adopted. First, the outline of the tunnel section is enlarged by 26 cm as a whole on the basis of the original tunnel section, and the initial support of the steel arch is carried out. The specific parameters and steps of the support are as follows: initial spraying of C25 shotcrete (with a thickness of 5 - 15 cm) → double-layer φ6.5 steel bar mesh (spacing 0.2 m × 0.2 m) → first-layer I20a steel I-beam (spacing 0.5 m per bay) → φ60 mm steel pipe support framework → C25 shotcrete (with a thickness of 26 cm) → double-layer φ6.5 steel bar mesh (spacing 0.2 m × 0.2 m) → second-layer I20a steel I-beam (spacing 0.5 m per bay) → C25 shotcrete (with a thickness of 26 cm) → φ42 double-row lock-foot steel pipes → monitoring and measurement. After the support is completed, the shotcrete is used for sealing;

[0068] To ensure the safety of the next-cycle support, after the construction of the first-layer steel arch is completed, φ60 * 4 mm steel pipes are vertically installed in the abdomen of the steel arch, with a spacing (transverse 0.2 m * longitudinal 0.5 m) and a height of about 2 - 3 m, which can be extended depending on the height of the collapse cavity, and then the support of the second-layer steel arch is started;

[0069] When about 1 m of muck is cleared, one bay of steel arch is erected. When more than two bays of steel arches are installed, a transverse (0.2 m) * longitudinal (0.5 m) grid steel pipe support framework can be formed above the tunnel vault, initially forming an opposite support framework, which firmly supports the dangerous large boulders existing on the vault, preventing the plastic slip body from being formed in the surrounding rock of the vault collapse cavity and causing the shear failure of the support structure. Generally speaking, the steel pipe support framework plays a buffering role in the falling blocks of the vault collapse cavity, avoiding the impact force of the falling blocks on the steel arch support and causing the initial support to be deformed under force. The steel pipe support framework not only plays a role of temporary support in the process of dealing with the collapse, but also has another function: jointly with the steel arch and concrete, it forms a C30 concrete arch protection framework structure system, enhancing the axial compression of the initial support. Using it in this special situation has achieved good results.

[0070] Step Six: Monitoring and Measurement

[0071] During the whole process of collapse treatment, the inside of the tunnel is monitored and measured, and the measured data is timely fed back and analyzed to guide the construction. A total of two horizontal measurement lines, two inclined measurement lines and one vault settlement line are arranged in the tunnel. The monitoring and measurement are carried out strictly in accordance with relevant specifications and designs. After the measurement is completed every day, the data analysis is carried out in a timely manner, and the monitoring conclusions are fed back to the construction technicians and the on-site person in charge; when the horizontal convergence value in the tunnel is greater than 5 mm / d or abnormalities are found in the surface monitoring, the on-site personnel should be immediately notified to evacuate, and reported to the higher level in a timely manner; when the treatment of the collapsed section is completed and the convergence in the tunnel is less than 0.2 mm / d, the monitoring can be stopped;

[0072] Step Seven: Next-Cycle Support

[0073] Step Eight: C30 Concrete Arch Protection

[0074] Construct a C30 concrete protective arch on the outer contour of the lining. The thickness of the protective arch is 1.0 - 1.5m. After the initial support of the tunnel is closely attached to the surrounding rock of the heading face and the lining reaches a certain strength, grouting is carried out. First, use backfill grouting to fill the gap between the lining and the rock, and then use consolidation grouting to consolidate the rock around the tunnel. First, reserve grouting pipes at the crown. After the concrete at the crown of the lining has solidified, grouting is carried out. When the vent pipe starts to leak slurry, it indicates that the concrete injected at the crown has reached the expected quantity;

[0075] Step Nine: Filling with 4% Cement Fly Ash

[0076] To reduce the stress on the initial support, the void area above the protective arch is backfilled with 4% cement fly ash until it is full. The fly ash fills the upper cavity until the filling thickness reaches about 4m. Excavation operations can only be carried out after the slurry has solidified and stabilized.

[0077] The thickness of the lining is increased to 80cm, and 50kg / m steel rails are added to the secondary lining concrete as arch frames for reinforcement. The spacing is 1.0m. The longitudinal connection of the arch frames is welded firmly with 18kg / m steel rails, and the circumferential spacing is 1.0m. The waterproof and drainage structure is the same as the original design and is bonded tightly to the constructed section.

[0078] In Step Five, the steel arch frame support includes the following steps:

[0079] 1. Shotcrete Support

[0080] The wet shotcrete technology is used for construction. The wet shotcrete process of concrete is carried out in two times. For the initial shotcrete, a 5 - 15cm thick layer of C25 concrete is sprayed on the free face after the removal of dangerous rocks to reduce the oxidation of the surrounding rock by air. The re - shotcrete is carried out after the installation of the first - layer steel arch frame, steel mesh, and radial steel pipes, reaching the design thickness at one time. The wet shotcrete process is adopted, and the shotcrete is carried out by a manipulator. The shotcrete operation surface follows the excavation face closely to minimize the exposure time of the excavation face;

[0081] (1) Treatment of the surface to be shotcreted: Check whether the size and geometric shape of the surface to be shotcreted meet the design requirements, remove the obstacles on the surface to be shotcreted that affect the shotcrete operation, and cover and protect the remaining objects and embedded components;

[0082] (2) Shotcrete construction: Add accelerator into the shotcrete according to the designed dosage; Use the XBS-II shotcrete machine for wet shotcrete. First, adjust the compressed air pressure to ensure good adhesiveness of the shotcrete; The distance between the nozzle and the shot surface should be appropriately 0.6 - 1.0 m and perpendicular to the shot surface. When encountering steel bars or steel frames, it can be tilted at an appropriate angle. During spraying, it should be carried out in sections (not exceeding 6 m), in parts (from bottom to top first), and in blocks (2 m × 2 m), strictly following the sequence from bottom to top to reduce the occurrence of sliding or falling of the concrete due to gravity; The spraying movement can be carried out in an S-shaped reciprocating movement or a spiral movement; During spraying, it should be sprayed in multiple layers to prevent excessive rebound of the concrete. Finally, spray until the designed spraying thickness is reached; The sprayed concrete surface should be flat, smooth, without concavities or convexities, dry patches, flowing, etc. After being inspected and qualified by the supervision engineer, it ends. If it is unqualified, it should be re-sprayed. If the interval time exceeds 2 hours, the surface should be wetted with water before re-spraying;

[0083] 2. Installation of steel mesh

[0084] Process the steel mesh in pieces outside the tunnel and lay, hang, and weld it inside the tunnel. The requirement for hanging the mesh is that the steel mesh should be laid along the undulation of the shot surface. The lap length of the φ6.5 steel mesh sheet should not be less than 30d (d is the diameter of the steel bar), and should not be less than the length of one long side of a grid, and should be welded firmly to the steel arch frame, which is beneficial to reducing the rebound during shotcrete;

[0085] 3. Construction of steel arch frame

[0086] (1) The steel frame is fabricated on a 1:1 production template set up in the processing workshop. It is fabricated by cold bending and in sections. After unit assembly welding and trial assembly, it is transported to the site for installation. During processing, ensure accurate dimensions and smooth arcs; The welding (or lapping) length of the steel bars meets the design requirements. When welding and forming, it is carried out symmetrically along both sides of the steel frame. The center of the steel frame coincides with the tunnel center line, the plane of the steel frame is perpendicular to the tunnel center line, the adjacent connecting steel plates at the joints coincide, and the connection hole positions are accurate;

[0087] After processing, conduct a trial assembly first to check for any distortion. The joints of each frame can be interchanged. The error along the tunnel perimeter contour must meet the requirements of the technical specifications; After processing and trial assembly, the allowable error is: the deviation along the tunnel perimeter contour is ±3 cm, and the plane (warpage) deviation is ±2 cm. Those that do not meet the requirements are not allowed to be used;

[0088] (2) After the initial shotcrete, strictly install the steel frame according to the design. The allowable deviation for the installation of the steel frame is ±5 cm both horizontally and in elevation, and the inclination should not be greater than 2°; After the construction of the first layer of steel arch frame, vertically set φ60*4 mm steel pipes in the abdomen of the steel arch frame, with a spacing (0.2 m horizontally * 0.5 m vertically) and a height of about 2 - 3 m, which can be extended depending on the height of the collapse cavity, and then start the support of the second layer of steel arch frame;

[0089] (3) The foundations at the arch feet on both sides of the steel frame must be firm and solid. Before installing the arch feet or wall feet, remove the loose debris under the sole plates, place the steel frame on the original surrounding rock, and pad the arch frame with steel plates under the arch feet. Do not use block stones, floating slag, or crushed stones for padding.

[0090] During installation, first pre-assemble the steel frame segments into an installation section and tighten the connecting bolts. After the steel frame is erected, the dimensions between the steel arch supports shall be strictly in accordance with the design. Use the center line and arch foot line to control the installation spacing of the steel arch frame, so that the two arch feet and the arch crown are in the same vertical plane to avoid torsion. The steel support segments are connected by high-strength bolts, then fixed with positioning bars. Longitudinally, use Φ22 connecting steel bars to connect it firmly with the adjacent steel frames, and arrange them alternately at the inner and outer edges of the steel frame support. All supports are welded on both sides, and the weld thickness shall not be less than 4 mm.

[0091] (4) Wedge the steel arch frame and the rock wall tightly with steel wedges or concrete cushion blocks. After the steel arch frame is installed in place, set up locking foot anchor pipes at the arch feet to fix the steel frame, and weld the tails of the anchor pipes to the steel frame.

[0092] Example 3, Application Example 1

[0093] Project Name: Design and Construction General Contracting Department of Liangdang to Huixian Expressway on G316 Line

[0094] Project Location: Liulin Town, Huixian County, Longnan Area, Gansu Province

[0095] Project Cost: 1.861076 billion yuan

[0096] Construction Period: Commenced in July 2016 - Completed in July 2019

[0097] Project Overview: Xiakou Tunnel is located in Xiakou Village, Liulin Town, Shihui County, Longnan City, Gansu Province. It is a long four-lane highway tunnel with separated left and right lanes. The tunnel runs through Mogou and the mountain on the left side of Xiakou. The designed driving speed is 80km / h. The cross-section type is: the clear width of the construction limit is 10.25m (7.5m for the driving lane, 0.5m for the left side of the curb, 0.75m for the right side, and 0.75m for the inspection road), the clear height is 5.0m, the inner contour of the tunnel, the arch is a single-center semicircle, the side wall is a large-radius arc, and the invert and the side wall are connected by a small-radius arc. The right line mileage pile number is YK24+083~YK26+241, with a length of 2152 meters, a designed V-level surrounding rock of 1383 meters, a IV-level surrounding rock of 775 meters, and a 24-meter long open hole; the left line mileage pile number is ZK24+082~ZK26+245, with a length of 2157 meters, a designed V-level surrounding rock of 1390.5 meters, a IV-level surrounding rock of 772.5 meters, and a 24-meter long open hole. The two holes are 4321 meters in total. The tunnel door form is: the entrance adopts an end wall tunnel door, and the entrance adopts a bamboo-cut tunnel door. The longitudinal slope of the right line of the tunnel is -1.400% / 2137m, -0.5% / 21m, and the longitudinal slope of the left line is -1.399% / 2138m, -0.5% / 25m. The maximum burial depth of the tunnel is about 350 meters. There are six pedestrian tunnels and two vehicle tunnels in the tunnel, namely 1#, 2#, 3#, 4#, 5#, 6# pedestrian tunnels and 1#, 2# vehicle tunnels, and a 50-meter emergency parking strip is set at each end of the vehicle tunnel. The surrounding rock of the tunnel is mainly sandstone, conglomerate and a small amount of granodiorite. The rock strata are well folded, with large changes in occurrence and relatively broken rock mass. According to the drilling exposure, it is speculated that the conglomerates in the YK24+900~YK25+610 (ZK24+900~ZK25+610) section have different degrees of dissolution and developed caves; due to the dissolution of the conglomerates in the YK24+900~YK25+610 (ZK24+900~ZK25+610) section, there are dissolution cavities below the design elevation of the tunnel. In addition, within this section, mud burst problems often occur simultaneously with caves.

[0098] In order to complete the construction task of Xiakou Tunnel safely and efficiently, after communicating with the project company and the design unit, this section was changed to a construction method combining two-layer steel arch frames with φ60*4mm seamless steel pipes and C25 shotcrete arranged along the radial direction of the tunnel. This effectively solved the problems of the difficulty in construction of the water-rich karst section of Xiakou Tunnel and the difficulty in ensuring the quality of initial support. During the construction process, no safety and quality accidents occurred.

[0099] Embodiment 4, application example 2

[0100] Project name: Lanzhou to Haikou Expressway Lintao to Weiyuan Section 8 Contract Section

[0101] Project location: Qingyuan Town, Weiyuan County, Dingxi City, Gansu Province

[0102] Construction period: from August 2013 to December 2014.

[0103] Project cost: 233.69 million yuan.

[0104] Project overview: The starting and ending stake numbers of the route in this contract section are K132+200~K138+800, and the total line length is 6.6 km. The stake numbers of Weiyuan Tunnel (exit section) are K132+200~K133+178, and the total length of the tunnel is 978 m. The lithology of the strata penetrated by the tunnel is mainly mudstone and muddy sandstone, with low hardness and in a state of strong weathering. The engineering geological conditions in the tunnel area are poor, and the surrounding rock is of grade IV and V. When constructing in the water-rich karst section, a construction method combining two layers of steel arch frames with seamless steel pipes of φ60*4mm arranged radially along the tunnel and C25 shotcrete is adopted, which effectively guarantees the construction progress and quality, speeds up the construction progress, reduces the working hours of the construction personnel in the tunnel, and has remarkable quality and economic effects.

[0105] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Construction method for radial steel pipe opposite support of highway tunnel collapse cavity, characterized in that, It includes the following steps: Step 1. Preparation Judgment of landslide stability: Making a correct judgment on the stability after the landslide is the key to formulating a treatment plan; if the landslide becomes stable within 1 to 2 days after its occurrence, and there is no large-scale collapse except for individual small pieces falling off, after determining the landslide stability, treatment can be started; Step 2. Removal of dangerous rocks Removal of individual dangerous rocks: After the landslide forms an arch and becomes stable, under the combined action of air and groundwater, the newly formed free face will quickly weather and soften, the interlayer bonding force will rapidly weaken, and dangerous rocks and overhanging rocks will continuously fall off; Step 3. Sealing with shotcrete The free face after the removal of dangerous rocks is sprayed with C25 concrete with a thickness of 5 - 15 cm for sealing to reduce the oxidation effect of air on the surrounding rock; Step 4. Mucking and cleaning the excavation face The mucking range is determined according to the stability of the surrounding rock, the safety of the collapsed body, and the lining length; Double-row φ42mm foot-locking anchor pipes with a length of 3.5 m and a spacing of 0.5 m are set at the arch feet to ensure the stability of the side wall during the lower part excavation; Step 5. First-layer steel arch support and second-layer steel arch support For the severely collapsed section at the arch top, double-layer steel arch support is adopted. First, the cross-section contour line of the tunnel is enlarged by 26 cm as a whole on the basis of the original tunnel cross-section for the initial support of the steel arch. The specific parameters and steps of the support are: initially spray C25 concrete with a thickness of 5 - 15 cm → double-layer φ6.5 steel bar mesh with a spacing of 0.2 m×0.2 m → I20a steel I-beam with a spacing of 0.5 m per frame, the first-layer steel arch → φ60mm steel pipe support frame → C25 shotcrete with a thickness of 26 cm, → double-layer φ6.5 steel bar mesh with a spacing of 0.2 m×0.2 m → I20a steel I-beam with a spacing of 0.5 m per frame, the second-layer steel arch → C25 shotcrete with a thickness of 26 cm, → double-row φ42 foot-locking steel pipes → monitoring and measurement, and after the support is completed, it is sealed with shotcrete; To ensure the safety of the next-cycle support, after the construction of the first-layer steel arch is completed, φ60*4mm steel pipes are vertically set in the abdomen of the steel arch with a spacing of: 0.2 m horizontally×0.5 m vertically and a height of 2 - 3 m, which can be lengthened according to the height of the collapsed cavity, and then the second-layer steel arch support is started; Step 6. Monitoring and measurement During the whole process of landslide treatment, the tunnel is monitored and measured, and the measured data is timely feedback and analyzed to guide the construction. A total of two horizontal measuring lines, two inclined measuring lines, and one crown settlement line are arranged in the tunnel. The monitoring and measurement are carried out strictly in accordance with relevant specifications and designs. After the measurement is completed every day, the data is analyzed in time and the monitoring conclusions are fed back to the construction technicians and the on-site person in charge; when the horizontal convergence value in the tunnel is greater than 5 mm / d or abnormal is found in the surface monitoring, the on-site personnel should be immediately notified to evacuate, and it should be reported to the higher level in time; when the treatment of the landslide section is completed and the convergence in the tunnel is less than 0.2 mm / d, the monitoring can be stopped; Step 7. Next-cycle support Step 8. C30 concrete arch protection Construct a C30 concrete protective arch on the outer contour of the lining. The thickness of the protective arch is 1.0 - 1.5m. After the initial support of the tunnel is closely attached to the surrounding rock of the heading face and the lining reaches a certain strength, grouting is carried out. First, use backfill grouting to fill the gap between the lining and the rock, and then use consolidation grouting to consolidate the rock around the tunnel. First, reserve grouting pipes at the crown. After the concrete at the crown of the lining has solidified, grouting is carried out. When the vent pipe starts to leak slurry, it indicates that the concrete injected at the crown has reached the expected quantity. Step Nine: Filling with 4% Cement Fly Ash To reduce the stress on the initial support, the void area above the protective arch is backfilled with 4% cement fly ash until it is full. The fly ash fills the upper cavity until the filling thickness reaches 4m. Excavation operations can only be carried out after the slurry has solidified and stabilized.

2. The radial steel pipe opposite support construction method for the cavity collapse of highway tunnels according to claim 1, characterized in that, It includes the following steps: In Step Five, the steel arch support includes the following steps:

1. Shotcrete Support The wet shotcrete technology is used for construction, and the wet shotcrete process of concrete is carried out in two times. For the initial shotcrete, C25 concrete with a thickness of 5 - 15cm is sprayed on the free face after removing the dangerous rocks to reduce the oxidation of the surrounding rock by air. The re-shotcrete is carried out after the installation of the first layer of steel arch, steel mesh, and radial steel pipes, and reaches the design thickness at one time. Adopt the wet shotcrete process and use a shotcreting robot for spraying; the spraying operation surface closely follows the excavation face. (1) Treatment of the surface to be sprayed: Check whether the size and geometric shape of the surface to be sprayed meet the design requirements, remove the obstacles on the surface to be sprayed that affect the spraying operation, and cover and protect the remaining objects and embedded components. (2) Construction of shotcrete: Add accelerator to the shotcrete according to the designed quantity. Use an XBS-II shotcreting machine to wet-spray concrete. First, adjust the compressed air pressure to ensure that the sprayed concrete has good adhesion. The distance between the nozzle and the sprayed surface is preferably 0.6 - 1.0m and perpendicular to the sprayed surface. When encountering steel bars or steel frame structures, it can be tilted at an appropriate angle. Spraying should be carried out in sections, with each spraying not exceeding 6m. It should be sprayed in a bottom-up and sectional manner, with a spraying area of 2m × 2m. It should be carried out strictly in the bottom-up order to reduce the sliding or falling of concrete due to gravity. The spraying movement can be carried out in an S-shaped reciprocating movement or a spiral movement. Spraying should be carried out in multiple layers for re-spraying to prevent excessive rebound of concrete. Finally, spray until the design spraying thickness is reached. The sprayed concrete surface should be flat, smooth, without concavity or convexity, dry spots, or flowing problems. After passing the inspection by the supervision engineer, it ends. If it is unqualified, it is re-sprayed. If the interval time exceeds 2 hours, the surface should be wetted with water before re-spraying.

2. Steel Mesh Laying The steel mesh is processed in pieces outside the tunnel and laid, hung, and welded inside the tunnel. The requirement for hanging the mesh is that the steel mesh is laid along the undulation of the sprayed surface. The lap length of the φ6.5 steel mesh sheet is not less than 30d (d is the diameter of the steel bar) and not less than the long side dimension of one grid, and it is welded firmly to the steel arch, which is beneficial to reducing the rebound during shotcrete.

3. Steel Arch Construction (1)The steel frame is fabricated on a 1:1 mock-up platform set up in the processing workshop. It is cold-bent and fabricated in sections. After unit-by-unit welding and trial assembly, it is transported to the site for installation. During processing, ensure accurate dimensions and smooth arcs. The welding or lap length of the steel bars meets the design requirements. When welding, it is carried out symmetrically on both sides of the steel frame. The center of the steel frame coincides with the tunnel center line, and the plane of the steel frame is perpendicular to the tunnel center line. At the joint, the adjacent connecting steel plates coincide, and the connection hole positions are accurate. After processing, conduct a trial assembly first to check for any distortion. The joints of each frame can be interchanged. The error along the tunnel perimeter must comply with the technical specification requirements. After the trial assembly during processing, the allowable errors are: the deviation along the tunnel perimeter is ±3 cm, and the plane deviation is ±2 cm. Those that do not meet the requirements are not allowed to be used. (2)After the initial shotcrete, erect the steel frame strictly according to the design. The allowable deviation for the installation of the steel frame is ±5 cm both horizontally and in elevation, and the inclination shall not be greater than 2°. After the construction of the first layer of steel arch, vertically install φ60*4 mm steel pipes in the abdomen of the steel arch. Spacing: 0.2 m horizontally * 0.5 m vertically, with a height of 2 - 3 m, which can be extended depending on the height of the collapse cavity. Then start the support of the second layer of steel arch. (3)The foundations at the arch feet on both sides of the steel frame must be firm. Before installing the arch feet or wall feet, remove the loose debris under the bearing plates, place the steel frame on the original surrounding rock, and pad the arch frame with steel plates under the arch feet. Do not use block stones, floating slag, or crushed stones for padding. During installation, first pre-assemble the steel frame segments into the installation section and tighten the connecting bolts. After the steel frame is erected, the dimensions between the steel arch supports are strictly implemented according to the design. The installation uses the center line and arch foot line to control the installation support distance of the steel arch frame, so that the two arch feet and the arch top are in the same vertical plane to avoid torsion. The steel support segments are connected by high-strength bolts, and then fixed with positioning bars. Longitudinally, use Φ22 connecting steel bars to firmly connect it with the adjacent steel frames, and arrange them alternately at the inner and outer edges of the steel frame support. All supports are welded on both sides, and the weld thickness shall not be less than 4 mm. (4)Wedges or concrete pads are used to wedge tightly between the steel arch frame and the rock wall. After the steel arch frame is installed in place, set up lock-foot anchor pipes at the arch feet to fix the steel frame, and weld the tails of the anchor pipes to the steel frame.

Images