Tunnel primary support process for railway engineering

Abstract

The invention provides a tunnel primary support process for railway engineering, and relates to the technical field of tunnel primary support. The tunnel primary support process of the railway engineering comprises the following steps: immediately carrying out danger elimination work after tunnel excavation, then carrying out primary concrete spraying operation, carrying out mortar anchor rod or hollow anchor rod construction, laying a reinforcing mesh, carrying out steel frame construction, advanced small pipe construction, anchor rod construction and advanced pipe shed construction, immediately carrying out danger elimination after tunnel excavation, and carrying out primary concrete spraying. The rock mass can be quickly closed, relaxation deformation of the rock mass is prevented, early deformation of surrounding rock is effectively controlled, stability of the surrounding rock is enhanced, safety guarantee is provided for follow-up construction, the reinforcing mesh is laid and firmly connected with the anchor rod and the steel frame, the integrity of the supporting structure is further enhanced, and the impact resistance of the supporting structure is improved. Through auxiliary construction measures such as advanced small guide pipes and advanced pipe sheds, surrounding rock is effectively reinforced, the strength and stability of the surrounding rock are improved, the construction risk is reduced, and it is ensured that tunnel construction smoothly passes through unfavorable geological sections.

Description

Technical Field

[0001] The present application relates to the technical field of initial tunnel support, and in particular to an initial tunnel support process for railway engineering. Background Art

[0002] In railway engineering, initial tunnel support is crucial to ensure tunnel construction safety and overall structural stability. The geological conditions of the tunnels in this section are complex, the surrounding rock is mainly grade VI and V, and most of them are micro-gas tunnels. Some sections have toxic and harmful gases and radioactive substances. At the same time, they face the situation of crossing fault zones, karst development areas, and underpasses existing structures. Traditional initial support technology is difficult to meet the support needs under complex geological conditions, such as inadequacies in support timeliness, effectiveness, and adaptability to special geological conditions.

[0003] Therefore, it is necessary to develop a more optimized, efficient and targeted initial tunnel support technology. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a tunnel initial support process for railway engineering, including carrying out risk elimination work immediately after tunnel excavation, followed by the implementation of initial concrete spraying operation, using a wet spraying process, centralized mixing outside the tunnel, transporting concrete to the tunnel by a concrete transport vehicle, and then spraying it using a wet spraying machine. The initial concrete spraying should seal the rock mass in time to prevent the rock mass from loosening; mortar anchor rods or hollow anchor rods are constructed, and a handheld pneumatic drill is used to make holes. After the holes are made, anchor rods and positioning rings are inserted, and then a grouting pump is used to inject early-strength cement sand into the holes. The cement mortar or mortar is used, and the hole pad is installed after the cement mortar is finally set; the steel mesh is laid, and it is processed and formed according to the design specifications at the steel component processing site, and is manually installed after the initial spraying of concrete. It is fixed to the anchor rod or steel frame by electric spot welding or binding. The steel mesh needs to rise and fall with the sprayed surface and maintain a certain distance. If any stone or concrete block is stuck by the steel mesh during the spraying process, it should be removed in time; steel frame construction ensures that the steel quality and joint position meet the specifications and design requirements. The steel frame adopts cold bending forming technology, and the grid steel frame adopts fetal membrane welding. The size is controlled by 1:1 large sample. After the temporary support is removed, a full-section measurement system is established, and the lining work is followed up in time. For the construction of small pipes in advance, a handheld air drill is used to drill holes. The layout range, length and spacing of the small pipes are arranged according to the design. Cement slurry is used as the grouting material. The grouting pressure is controlled within a reasonable range. The water-cement ratio meets the corresponding requirements. When the surrounding rock is broken and groundwater is developed, cement + water glass double liquid slurry can be partially used. The slurry strength grade is required to meet the specified standards. For anchor construction, mortar anchors or hollow anchors are used according to the design. Mortar anchors Use threaded steel for processing, and use anchor drilling rigs or rock drills to drill holes. When drilling, the designed position and the external insertion angle of the rod must be guaranteed, and the water volume must be controlled to prevent hole collapse. In the advanced pipe shed construction, the pipe shed is made of hot-rolled seamless steel pipes. The drilling process first and then inserting pipes or following the pipe drilling process is selected according to the actual situation of the stratum. The tunnel entrance pipe shed is positioned by a sleeve arch, and the pipe shed joints are connected by threaded connections. The thread length reaches the specified size, and the adjacent steel pipe joints are staggered a certain distance as required. During construction, the steel pipe is driven into the surrounding rock along the external insertion angle specified in the design around the tunnel, and then cement slurry is poured.

[0005] In addition, a railway engineering tunnel initial support process according to an embodiment of the present application also has the following additional technical features:

[0006] Preferably, during the initial spraying of concrete, the spraying equipment should maintain a good performance state to ensure that the concrete is sprayed evenly and continuously to avoid spraying interruptions or concrete accumulation.

[0007] Preferably, during the construction of mortar anchors or hollow anchors, the drilling operation should ensure that the hole wall is smooth and has no obvious collapse, the rod body and the positioning ring should not be damaged when inserting the anchor, and the grouting process should ensure that the slurry fully fills the space in the hole and there is no leakage.

[0008] Preferably, when the steel mesh is laid, the processing of the steel mesh should ensure accurate size and regular shape, and during the installation process, it should be ensured that it is firmly connected to the anchor rod or steel frame without looseness or displacement.

[0009] Preferably, during steel frame construction, the cold-bent steel frame should have good curvature consistency, the grating steel frame welded with the membrane should ensure reliable welding quality, and the components should be tightly connected. During the removal of temporary support and the establishment of the measurement system, damage to the completed support structure should be avoided.

[0010] Preferably, when grouting with a small advance tube, the grouting parameters should be adjusted in a timely manner according to the actual situation of the surrounding rock and the feedback of the grouting effect to ensure that the slurry is evenly diffused in the surrounding rock and achieves the expected reinforcement effect, while avoiding excessive disturbance of the surrounding rock due to excessive grouting pressure.

[0011] Preferably, during the anchor construction process, the hole-guiding operation should be precisely positioned to ensure that the anchor can be smoothly inserted into the hole and fit tightly against the hole wall. The anchoring length of the mortar anchor should ensure that the designed anchoring force requirements are met. The rod length of the hollow anchor should comply with the design requirements to ensure that its support function is effectively exerted.

[0012] Preferably, in the construction of the advanced pipe-roof, the process of drilling first and then inserting pipes should ensure that the drilling accuracy and the insertion depth meet the design requirements, the following pipe drilling process should ensure that the casing follows smoothly and cooperates well with the drill rod, and the grouting after the pipe-roof is installed should ensure that the slurry in the pipe-roof is densely filled and the pipe-roof structure is stable.

[0013] Preferably, during the entire initial support construction period, a complete surrounding rock deformation monitoring system should be established. The monitoring equipment should be stable and reliable, and the data collection should be accurate and timely. The support parameters should be adjusted in a timely and scientific manner according to the monitoring data to ensure the safety of tunnel construction.

[0014] Preferably, the raw materials used for shotcrete should be strictly screened to ensure qualified quality, and the mix ratio of concrete should be reasonably adjusted according to actual construction conditions and design requirements to ensure that the performance of concrete meets the initial support requirements.

[0015] According to an initial tunnel support process for railway engineering according to an embodiment of the present application, the beneficial effects are:

[0016] 1. Improve the timeliness and effectiveness of support

[0017] After tunnel excavation, immediate risk elimination and initial concrete spraying can quickly seal the rock mass, prevent it from loosening and deforming, effectively control the early deformation of the surrounding rock, enhance the stability of the surrounding rock, and provide safety guarantees for subsequent construction.

[0018] The wet spraying process is used to make the concrete fit better with the surrounding rock, improve the joint bearing capacity of the support structure and the surrounding rock, give full play to the support function, effectively reduce the risk of accidents such as surrounding rock collapse, and ensure construction safety;

[0019] 2. Enhance the stability of the support structure

[0020] The construction of anchor rods (mortar anchor rods or hollow anchor rods) increases the anchoring force of the surrounding rock through reasonable drilling, anchor rod insertion and grouting operations, so that the surrounding rock and the supporting structure form a whole, improve the self-bearing capacity of the surrounding rock, and effectively control the deformation and displacement of the surrounding rock.

[0021] The laying of the steel mesh and its firm connection with the anchor rods and steel frames further enhances the integrity of the support structure, prevents local rock from falling, evenly disperses the surrounding rock pressure, improves the impact resistance of the support structure, and better maintains the stability of the tunnel structure under complex geological conditions.

[0022] Steel frame construction strictly controls steel quality, processing technology and installation accuracy to ensure that the steel frame has sufficient strength and rigidity to effectively withstand the surrounding rock pressure, prevent excessive deformation of the support structure, and ensure safety and structural stability during tunnel construction, especially in areas with weak surrounding rocks.

[0023] 3. Adapt to complex geological conditions

[0024] According to different surrounding rock conditions, such as broken, weak, and water-rich, auxiliary construction measures such as advance small guide tubes and advance pipe racks are adopted, and appropriate construction processes and parameters are adopted, such as adjusting grouting materials and pressure. This can effectively reinforce the surrounding rock, improve the strength and stability of the surrounding rock, reduce construction risks, and ensure that the tunnel construction can pass smoothly through poor geological areas.

[0025] For tunnels that may contain toxic and harmful gases and radioactive substances, such as Youping Tunnel and Lijiacun Tunnel, strengthening ventilation and detection measures during construction, combined with effective initial support technology, can ensure the safety of construction workers, avoid safety accidents caused by special geological conditions, and ensure the durability of the support structure;

[0026] 4. Ensure construction quality and efficiency

[0027] Each construction process has clear technical requirements and quality control standards, such as raw material screening, equipment debugging, construction process parameter control, etc., to ensure the quality of each process, thereby ensuring the quality of the entire initial support structure, reducing rework and delays caused by quality problems, and improving construction efficiency.

[0028] A complete construction monitoring and adjustment mechanism can grasp the deformation of the surrounding rock in real time, discover problems in time and adjust support parameters to ensure that the support structure is always in a reasonable stress state, avoid excessive or insufficient support, ensure construction quality, optimize the construction process, improve the scientificity and rationality of construction, and effectively shorten the construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the implementation methods of the present application, the drawings required for use in the implementation methods will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 It is a flow chart of an initial tunnel support process for railway engineering according to an embodiment of the present application;

[0031] Figure 2 It is a cross-sectional view of the Class II surrounding rock composite lining according to an embodiment of the present application;

[0032] Figure 3 It is a cross-sectional view of a Class III surrounding rock composite lining according to an embodiment of the present application;

[0033] Figure 4 It is a cross-sectional view of a Class IV surrounding rock composite lining according to an embodiment of the present application;

[0034] Figure 5 It is a cross-sectional view of a Class V surrounding rock composite lining according to an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the implementation methods of this application clearer, the technical solutions in the implementation methods of this application will be clearly and completely described below in conjunction with the drawings in the implementation methods of this application. Obviously, the described implementation methods are part of the implementation methods of this application, not all of the implementation methods. Based on the implementation methods in this application, all other implementation methods obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0036] The following describes in detail a tunnel initial support process for a railway engineering project of the present invention through a specific implementation method, including a construction preparation stage, initial shotcrete construction, mortar anchor rod or hollow anchor rod construction, steel mesh laying, steel frame construction, advanced small guide tube construction, anchor rod construction, advanced pipe shed construction, construction monitoring and adjustment, and quality control and inspection.

[0037] 1. Construction preparation stage

[0038] A professional initial support construction team is formed, and comprehensive technical training is provided to construction personnel to familiarize them with the process, technical points, quality standards and safety precautions of the initial tunnel support technology. At the same time, detailed safety briefings are carried out to improve the safety awareness and operational standardization of construction personnel.

[0039] Prepare advanced and stable construction equipment, such as handheld pneumatic drills, wet spraying machines, grouting pumps, anchor drills, electric welders, etc. Before the equipment enters the site, conduct strict inspection and commissioning to ensure that the equipment is in good operating condition and that all performance indicators meet the construction requirements. Rationally plan the equipment parking and operation areas at the construction site to ensure that the equipment is easy to use and operates in an orderly manner during the construction process.

[0040] Strictly screen and inspect the raw materials. Steel must meet national standards, and its material, specifications and other parameters must meet the design requirements. The mechanical properties of steel should be sampled to ensure reliable quality. Cement should be selected from ordinary Portland cement with stable quality, and the strength grade should not be less than 42.5. The stability, setting time and strength of cement should be tested. Sand should be hard, clean and medium-coarse sand with a mud content of no more than 3%. The particle size of the sand should be determined by screening test to meet the requirements. The stone particle size should be no more than 15mm, the texture should be hard, the gradation should be good, the crushing index should not be greater than the specified value, and the needle-like particle content and mud content of the stone should be strictly controlled. Accelerators and other admixtures should be strictly screened and tested to ensure their stable performance and good compatibility with raw materials such as cement. The dosage should be determined according to the test results and design requirements, generally 3%-5% of the weight of cement. A special material storage site should be set up at the construction site to store raw materials of different types and specifications in a classified manner, and effective moisture-proof, rain-proof and rust-proof measures should be taken to ensure that the quality of raw materials is not affected during storage.

[0041] 2. Initial spraying of concrete

[0042] After the tunnel excavation is completed, experienced troubleshooters are quickly organized to enter the work site. The troubleshooters wear complete safety protection equipment and use appropriate tools such as crowbars and pneumatic picks to carefully remove loose rock blocks on the surface of the surrounding rock from the outside to the inside, first the top and then the sides. During the troubleshooting process, pay close attention to the changes in the surrounding rock. If abnormal sounds, rock falling and other dangerous signs are found, stop the work immediately and take corresponding safety protection measures to ensure the safety of the construction workers.

[0043] The initial spraying of concrete is carried out immediately after the risk elimination work. A special concrete mixing station is set up outside the tunnel, and a forced mixer is used for centralized mixing. According to the concrete mix ratio required by the design, the amount of raw materials such as cement, sand, gravel, water and accelerator is accurately measured to ensure that the workability, strength and durability of the concrete meet the initial support requirements. During the mixing process, the mixing time is strictly controlled to ensure that the raw materials are fully mixed and evenly mixed, and the concrete color is consistent and there is no segregation.

[0044] The concrete transport vehicle should be in good condition and have good tank sealing performance. The tank should be kept rotating at a constant speed during transportation to prevent the concrete from segregating and losing too much slump. After the concrete is transported to the construction site in the tunnel, the slump should be tested immediately. If the slump does not meet the requirements, it should be adjusted or handled in time. It is strictly forbidden to use unqualified concrete.

[0045] The wet spraying machine is fully inspected and debugged before spraying to ensure that the spraying pressure is stable and the spraying angle can be flexibly adjusted. During the spraying operation, the spraying pressure is reasonably adjusted according to the surface conditions of the surrounding rock and the spraying distance. It is generally controlled between 0.3-0.5MPa. The spraying angle is kept vertical or slightly inclined to the sprayed surface, and the nozzle is 0.8-1.2m away from the sprayed surface. The layered spraying is carried out in the order from bottom to top and from both sides to the middle. The spraying thickness of each layer is controlled at 3-5cm, and the interval time of each layer is 3-5 minutes. Ensure that the next layer of concrete is sprayed after the final setting of the previous layer of concrete to avoid hollowing and falling of concrete. During the spraying process, the operator closely observes the concrete spraying situation and adjusts the spraying parameters in time according to the spraying effect to ensure that the concrete is sprayed evenly and densely, without spraying interruption or concrete accumulation. The thickness of the initial sprayed concrete is not less than the design value, effectively sealing the rock mass to prevent it from loosening and deformation.

[0046] 3. Construction of mortar anchor or hollow anchor

[0047] Use a handheld pneumatic drill for drilling operations. The pneumatic drill operator must undergo professional training and be familiar with the operation methods and safety precautions of the pneumatic drill. Before drilling, accurately calibrate the drilling position on the surrounding rock surface according to the anchor position, angle and depth required by the design. During the drilling process, control the drilling speed and pressure of the pneumatic drill, and adjust them in time according to the hardness of the surrounding rock to ensure that the drilling process is smooth, the hole wall is smooth, and there is no obvious collapse. The drilling depth is 3-5cm larger than the designed length of the anchor to ensure that the anchor has sufficient anchoring length after installation.

[0048] After drilling is completed, use high-pressure air or water to thoroughly clean the hole, remove rock powder, debris and water in the hole, ensure that the hole is clean and dry, and create good conditions for anchor installation and grouting. Carefully insert the processed and qualified anchor and positioning ring into the hole, avoid damaging the rod and positioning ring during the insertion process, ensure that the rod is in the center of the hole, and the spacing of the positioning rings is uniform, generally 0.5-1m, to ensure the stability of the anchor position in the hole.

[0049] The grouting pump should be debugged and inspected before use to ensure that the grouting pressure is stable and the flow rate is adjustable. According to the design requirements, select appropriate grouting materials, such as early-strength cement mortar or mortar, and prepare them according to the specified mix ratio to ensure that the consistency, strength and other properties of the slurry meet the requirements. During the grouting process, insert the grouting pipe into the bottom of the hole, slowly inject the slurry, and pull out the grouting pipe at a uniform speed while grouting. At the same time, closely observe the hole opening to prevent the slurry from overflowing or leaking, and ensure that the slurry fully fills the space in the hole and is tightly combined with the anchor rod and the surrounding rock. After the cement mortar is finally set, install the hole opening pad. The pad should be installed flat and firmly, perpendicular to the anchor rod, and tighten the nut to make the pad fit tightly with the surrounding rock, so that the anchoring force of the anchor rod is evenly transferred to the surrounding rock.

[0050] 4. Laying of steel mesh

[0051] At the steel component processing site, the steel mesh is carefully processed using professional equipment such as steel bar cutting machines and bending machines according to the precise design specifications. The cutter of the steel bar cutting machine should be sharp to ensure that the steel bar cutting length is accurate and the error does not exceed ±5mm. The mold of the bending machine should be customized according to the shape and size of the steel mesh required by the design to ensure that the bending angle of the steel bar is accurate and the curvature is consistent. After the processing, the mesh size deviation of the steel mesh does not exceed ±5mm and the shape is regular.

[0052] After the initial spraying of concrete, the processed steel mesh is manually transported to the working surface. During the transportation process, pay attention to protecting the steel mesh to avoid its deformation or damage. When laying the steel mesh, according to the shape of the surrounding rock surface and the arrangement of anchor rods and steel frames, the steel mesh is laid flat on the surface of the initial spraying concrete, ensuring that the steel mesh is 3-5cm away from the sprayed surface, and the lap length between adjacent steel meshes is not less than the side length of one grid, generally 15-20cm, and the lap parts are connected by electric spot welding or firm binding. The spacing between spot welding or binding points is not more than 20cm to ensure that the overall connection of the steel mesh is firm without looseness or displacement. The steel mesh should rise and fall naturally with the sprayed surface, and must not be forcibly pulled or twisted to ensure that the steel mesh fits tightly with the surrounding rock and can bear force together during the spraying process. During the spraying process, arrange special personnel to observe the situation of the steel mesh at any time. Once it is found that stones or concrete blocks are stuck by the steel mesh, use tools to clean it immediately to ensure that the spraying operation proceeds smoothly and the steel mesh can fully play its role in reinforcing the surrounding rock.

[0053] 5. Steel frame construction

[0054] Steel procurement is strictly carried out in accordance with design requirements, and suppliers with good reputation and reliable quality are selected to ensure that the material and specifications of the steel meet national standards and design regulations. After the steel enters the site, it is strictly inspected by batch. The inspection content includes chemical composition analysis, mechanical property testing (yield strength, tensile strength, elongation, impact toughness, etc.) and appearance quality inspection (whether there are cracks, folds, rust and other defects on the surface). Steel that fails the random inspection will be resolutely withdrawn and is strictly prohibited from being used in construction.

[0055] The steel frame adopts cold bending forming technology, and a high-precision cold bending mold is made according to the tunnel design contour line. The curvature and size of the mold should be completely consistent with the design requirements to ensure that the curvature of the steel frame is consistent after cold bending, with a deviation of no more than ±1cm, and it fits closely with the tunnel design contour line. During the cold bending process, the operating parameters of the cold bending equipment, such as bending speed and pressure, are controlled to ensure that the steel frame is not damaged during the cold bending process, and the surface of the steel frame after cold bending is flat, without obvious wrinkles or deformation.

[0056] The grid steel frame adopts the membrane welding process. The membrane production should be carried out strictly according to the 1:1 sample to ensure the size and shape of the membrane are accurate. During the welding process, skilled and experienced welders are selected to operate, and the welding current, voltage, welding speed and other parameters are strictly controlled to ensure reliable welding quality, full and uniform welds, no defects such as pores, slag inclusions, cracks, etc., and each component is tightly connected, and the node welding strength meets the design requirements.

[0057] Before installing the steel frame, the tunnel excavation profile is accurately measured, and the installation position of the steel frame is determined based on the measurement results. During the installation process, the spacing between adjacent steel frames is strictly controlled, with an error of no more than ±5cm, to ensure that the steel frames are evenly arranged. Use total stations and other high-precision measuring instruments to measure the verticality of the steel frame. The verticality deviation of each steel frame after installation does not exceed ±1° to ensure that the steel frame is installed vertically and firmly. High-strength bolts are used to connect each section of the steel frame. The specifications and models of the bolts should meet the design requirements. During installation, ensure that the tightening torque of the bolts reaches the design value. Use a torque wrench to check to prevent the bolts from loosening and affecting the overall stability of the steel frame.

[0058] During the temporary support removal process, a detailed removal plan should be formulated, and a reasonable removal sequence and safety protection measures should be adopted to avoid damage to the completed support structure. After the removal, a full-section measurement system should be established in a timely manner. The arrangement of the measurement points should be representative, with a spacing of no more than 5m, and can accurately reflect the deformation of the surrounding rock. High-precision monitoring equipment such as total stations and convergence meters are used for data collection. The data collection frequency is determined according to the deformation of the surrounding rock. Generally, the collection frequency is appropriately increased when the surrounding rock deformation is large to ensure that the measurement data is accurate and timely. The collected data is analyzed and processed in a timely manner, and the stability of the surrounding rock and the effectiveness of the support structure are judged based on the analysis results, providing a reliable basis for subsequent construction, and adjusting the lining construction time in a timely manner to ensure the safety of tunnel construction.

[0059] 6. Advanced small duct construction

[0060] A handheld air drill is used for the advance small conduit drilling operation. The air drill operator should have skilled operation skills and rich experience. Before drilling, the drilling position is accurately calibrated on the tunnel face according to the design requirements of the small conduit layout range, length, spacing and external insertion angle. During the drilling process, the drilling direction and angle of the air drill are strictly controlled to ensure that the drilling angle is consistent with the designed external insertion angle, the error does not exceed ±1°, and the drilling depth meets the design requirements. The small conduit uses a hot-rolled seamless steel pipe with a diameter of 42-50mm and a length of 3-5m to ensure that the small conduit can be accurately driven into the predetermined position of the surrounding rock, providing a good channel for subsequent grouting reinforcement.

[0061] The processing and manufacturing of small pipes are strictly carried out in accordance with the design requirements to ensure that the diameter, wall thickness, length and other parameters of the steel pipe meet the requirements. The front end of the steel pipe is processed into a cone to facilitate insertion into the surrounding rock, and a grouting stop valve is welded at the tail to prevent slurry backflow during grouting. The layout range, length and spacing of the small pipes should be reasonably arranged according to the geological conditions of the surrounding rock and the design requirements of the tunnel to ensure uniform and effective grouting reinforcement effect.

[0062] The grouting material is selected from suitable cement slurry, and the water-cement ratio is adjusted according to the surrounding rock conditions and design requirements, generally 0.8:1-1:1. In special cases such as surrounding rock fragmentation and groundwater development, cement + water glass double slurry is partially used, and the volume ratio of cement slurry to water glass slurry is 1:0.8, and the slurry strength grade is not less than M10. Before grouting, the grouting equipment is fully inspected and debugged to ensure that the grouting pump has stable performance, adjustable pressure, and the grouting pipe is firmly connected and leak-free.

[0063] During the grouting process, the grouting pipe is tightly connected to the small guide tube to ensure that the grouting passage is unobstructed. When starting grouting, slowly apply pressure, gradually increase the grouting speed, and control the grouting pressure between 0.5-1.0MPa to avoid excessive disturbance of the surrounding rock caused by excessive grouting pressure, while ensuring that the slurry can be evenly diffused in the surrounding rock. Closely observe the grouting situation, and adjust the grouting parameters such as grouting pressure, grouting speed, slurry ratio, etc. in a timely manner according to the slurry diffusion situation and surrounding rock feedback. When the surrounding rock absorbs a large amount of grouting, intermittent grouting can be used, with an interval of 10-15 minutes between each grouting, so that the slurry has a certain diffusion time in the surrounding rock and improves the grouting reinforcement effect. After the grouting is completed, the grouting effect is checked by drilling and coring, and the filling of the slurry in the surrounding rock is observed to ensure that the slurry is fully filled and achieve the expected reinforcement effect.

[0064] 7. Anchor construction

[0065] Mortar anchors or hollow anchors are selected according to design requirements. Mortar anchors are made of high-quality threaded steel to ensure that the rod diameter is not less than 20mm and the length meets the design requirements. The material of threaded steel should meet national standards, and its mechanical properties such as yield strength and tensile strength should meet the design requirements. During the processing, the length, diameter and other dimensional accuracy of the anchor rod are strictly controlled to ensure the processing quality.

[0066] Use anchor drill or rock drill to drill holes. Before drilling, the operator should accurately mark the drilling position on the surrounding rock surface according to the anchor position, angle and depth required by the design. During the drilling process, control the drilling speed and pressure of the drill or rock drill to ensure that the drilling position and the external insertion angle of the rod meet the design requirements. At the same time, strictly control the water volume to prevent hole collapse. The drilling depth is 5-10cm larger than the design length of the anchor. After inserting the anchor, pour mortar of M30 or above to ensure that the anchoring length meets the design requirements. The rod length of the hollow anchor meets the design requirements. During installation, insert the anchor into the drill hole, connect the grouting pipe, and inject cement slurry to ensure that the rod fits tightly with the hole wall to play an effective support role.

[0067] 8. Advanced pipe shed construction

[0068] The pipe shed is made of hot-rolled seamless steel pipes that meet quality standards, and the pipe diameter is selected according to design requirements. When the formation conditions permit, the process of drilling first and then inserting pipes is adopted. Before drilling, according to the design parameters of the pipe shed, the drilling position, angle and depth are accurately determined, and professional drilling equipment is used for construction to ensure the drilling accuracy. The drilling diameter is 20-30mm larger than the pipe diameter of the pipe shed, and the drilling depth meets the design requirements. When inserting pipes, the steel pipes are accurately driven into the surrounding rock along the external insertion angle specified in the design around the tunnel. The pipe shed joints are connected by threaded connections, and the thread length reaches the specified size. Adjacent steel pipe joints are staggered a certain distance as required to ensure a firm connection.

[0069] When the geological conditions are complex, the following pipe drilling process is adopted. During construction, the casing and drill rod are drilled in at the same time, and the drilling speed and pressure are controlled to ensure that the casing follows smoothly and cooperates well with the drill rod. After the hole is formed, the drill rod is taken out, the pipe shed is pushed in, and the outer casing is pulled out. After the installation of the pipe shed is completed, pressure grouting is carried out. The grouting pressure and grouting volume are determined according to the design requirements to ensure that the slurry in the pipe shed is densely filled and the pipe shed structure is stable and reliable.

[0070] 9. Construction monitoring and adjustment

[0071] During the entire process of initial tunnel support construction, a complete surrounding rock deformation monitoring system should be established. Monitoring points should be reasonably arranged around the tunnel, and high-precision monitoring equipment such as total stations and convergence meters should be used to ensure the accuracy and timeliness of monitoring data. The arrangement of monitoring points should cover different geological conditions and support structure parts, and be able to fully reflect the surrounding rock deformation.

[0072] Monitor at the prescribed frequency. Generally, when the surrounding rock deformation is large, the acquisition frequency should be appropriately increased. Analyze and process the collected data in real time, use professional data analysis software to draw deformation curves, and analyze deformation trends. When the monitoring data shows abnormal deformation of the surrounding rock, such as when the displacement rate exceeds the reasonable range or when the deformation curve shows a sudden change, construction should be suspended immediately.

[0073] Organize professional and technical personnel to conduct in-depth analysis of the causes, which may include geological changes, unreasonable support parameters, construction process problems, etc. According to the analysis results, quickly and scientifically adjust the support parameters, such as increasing the number of anchors, adjusting the anchor spacing, strengthening the steel frame support strength, changing the grouting parameters, etc. The adjusted support plan must be implemented after expert demonstration or approval by relevant departments to ensure the safety of tunnel construction.

[0074] 10. Quality Control and Inspection

[0075] After each construction process is completed, a comprehensive quality inspection is carried out in strict accordance with relevant specifications and standards. The thickness and strength of the initial shotcrete are checked. The core drilling method is used to test the strength. The core samples are drilled from the concrete structure and sent to the laboratory for compression tests to ensure that the strength meets the design requirements. The thickness is checked using measuring equipment such as laser rangefinders to ensure that the thickness is not less than the design value.

[0076] Check the pull-out strength of anchor rods and conduct pull-out tests on the specified number of anchor rods. Install pulling equipment on the anchor rods, gradually apply tension, and record the pull-out strength of the anchor rods to ensure that the pull-out strength meets the design standard. Check the mesh spacing, distance from the sprayed surface, and connection firmness of the steel mesh. Use a steel ruler to measure the mesh spacing, observe the fit between the steel mesh and the sprayed surface, and check whether the welding points or binding points are firm.

[0077] Check the installation position, spacing, verticality, connection quality, etc. of the steel frame. Use a total station to measure the position and verticality of the steel frame, and a steel ruler to measure the spacing. Check whether the bolt connection is tight and whether the weld is full and defect-free. Check the length, angle, grouting effect, etc. of the small duct and pipe shed in advance. Observe the slurry filling by drilling and coring to ensure that the grouting is full, and the installation position and angle of the pipe shed and small duct meet the design requirements. For parts that do not meet the quality requirements, immediately formulate corrective measures and carry out thorough rectification. After the rectification is completed, re-inspect strictly to ensure that the initial support quality fully meets the design and specification requirements.

[0078] Among them, in the specific embodiment of the present application, the full tunnel door is divided into four styles: end wall type, double-line double-ear wall type A, single-line double-ear wall type, and single pressure type. The entrance of Bailang Tunnel is connected to the long-mileage bridge and tunnel of Hongshui River Super-Large Bridge, and the exit is connected to the short-mileage bridge and tunnel of Longna Bridge. The entrance of Bailang Tunnel is 17m long, and the exit is 23m long; the exit of Youping Tunnel and the entrance of Lijiacun Tunnel are respectively connected to the short-mileage and long-mileage bridge and tunnel of Masancun Bridge. The exit of Youping Tunnel is 11m long, and the entrance of Lijiacun Tunnel is 15m long.

[0079] The total length of the main tunnel is 32.926 km, of which the Class II surrounding rock accounts for 7.6%, the Class III surrounding rock accounts for 33%, the Class IV surrounding rock accounts for 55%, and the Class V surrounding rock accounts for 11.2%. The construction adopts the step method, step method + temporary invert, three-step method + temporary invert, micro-step method, and full-section method. The tunnel entrance section is shallowly buried, and two specifications of Φ89 and Φ108 pipe shed support are used respectively. The DK186+681~+688 section of Bailang Tunnel passes under the existing rural road, and the Φ89 medium pipe shed in the tunnel is used for support. The surface of the DK214+973 section of Shangli Tunnel is Changsha River, and the Φ89 medium pipe shed in the tunnel + surface channelization paving reinforcement support is adopted. The DK214+790~930 section of Shangli Tunnel passes under the Yinbai Expressway, and the Φ159 large pipe shed is used for advanced grouting reinforcement support in the tunnel.

[0080] The auxiliary caverns for tunnel construction in the project mainly include small car shelters, large car shelters and ladder car shelters, with dimensions of 2m wide, 1m deep, 2.2m high, 4m wide, 2.5m deep, 2.8m high, and 2.5m wide, 7.53m deep, to meet the needs of construction organization. The design of each auxiliary cavern adopts steel arch support and lining concrete structure. During the construction period, the caverns only complete the initial support part to meet the space requirements of construction organization.

[0081] The above embodiments are only used to illustrate the specific embodiments of the present invention and are not limited thereto. For those skilled in the art, various similar deformations and changes can be made according to the concept of the present invention, and these deformations and changes should be regarded as the protection scope of the present invention.

Claims

1. A tunnel initial support process for railway engineering, characterized in that: The following steps are involved: After tunnel excavation, the risk elimination work is carried out immediately, followed by the initial concrete spraying operation. The wet spraying process is adopted, and the concrete is mixed centrally outside the tunnel. The concrete is transported into the tunnel by a concrete transport truck and then sprayed by a wet spraying machine. The initial concrete spraying should seal the rock mass in time to prevent the rock mass from loosening; Carry out mortar anchor or hollow anchor construction, use a handheld pneumatic drill to make holes, insert anchors and positioning rings after the holes are made, and then use a grouting pump to inject early-strength cement mortar or mortar into the holes, and install the hole pad after the cement mortar is finally set; The steel mesh is laid and formed according to the design specifications at the steel component processing site. It is manually installed after the initial spraying of concrete and fixed to the anchor rod or steel frame by electric spot welding or binding. The steel mesh needs to rise and fall with the sprayed surface and maintain a certain distance. If there are stones or concrete blocks stuck by the steel mesh during the spraying process, they should be removed in time; Steel frame construction ensures that the steel quality and joint position meet the specifications and design requirements. The steel frame adopts cold bending forming technology, and the grid steel frame adopts membrane welding. The size is controlled by 1:1 large sample. After the temporary support is removed, a full-section measurement system is established, and the lining work is followed up in a timely manner; For the construction of advanced small pipes, a handheld pneumatic drill is used to drill holes. The layout range, length and spacing of the small pipes are based on the design layout. Cement slurry is used as the grouting material. The grouting pressure is controlled within a reasonable range and the water-cement ratio meets the corresponding requirements. When the surrounding rock is broken and groundwater is developed, cement + water glass double liquid slurry can be partially used. The slurry strength grade is required to meet the specified standards. Anchor construction: mortar anchor or hollow anchor is used according to the design. Mortar anchor is made of threaded steel and drilled with anchor drill or rock drill. When drilling, the designed position and the external insertion angle of the rod must be ensured, and the water volume must be controlled to prevent the hole from collapsing. In the advanced pipe shed construction, the pipe shed is made of hot-rolled seamless steel pipes. The drilling process first and then inserting pipes or following the pipe drilling process is selected according to the actual situation of the stratum. The tunnel entrance pipe shed is positioned by a sleeve arch. The pipe shed joints are connected by threaded connections. The thread length reaches the specified size. Adjacent steel pipe joints are staggered at a certain distance as required. During construction, the steel pipe is driven into the surrounding rock along the external insertion angle specified in the tunnel perimeter design, and then cement slurry is poured.

2. A tunnel initial support process for railway engineering as claimed in claim 1, characterized in that: During the initial spraying of concrete, the spraying equipment should be kept in good performance condition to ensure uniform and continuous concrete spraying and avoid spraying interruptions or concrete accumulation.

3. The tunnel initial support process for railway engineering as claimed in claim 1, characterized in that: During the construction of mortar anchors or hollow anchors, the drilling operation should ensure that the hole wall is smooth and there is no obvious collapse. The rod body and positioning ring must not be damaged when inserting the anchor. The grouting process should ensure that the slurry fully fills the space in the hole and there is no leakage.

4. The tunnel initial support process for railway engineering as claimed in claim 1, characterized in that: When laying the steel mesh, the processing of the steel mesh should ensure accurate size and regular shape. During the installation process, it should be ensured that it is firmly connected to the anchor rod or steel frame, and no looseness or displacement should occur.

5. The tunnel initial support process for railway engineering as claimed in claim 1, characterized in that: During steel frame construction, the cold-bent steel frame should have good curvature consistency, the grating steel frame welded with membrane should ensure reliable welding quality, and the components should be tightly connected. During the temporary support dismantling and measurement system establishment process, damage to the completed support structure should be avoided.

6. The railway engineering tunnel initial support process according to claim 1, characterized in that: When grouting with a small advance tube, the grouting parameters should be adjusted in a timely manner according to the actual situation of the surrounding rock and the feedback of the grouting effect to ensure that the slurry is evenly diffused in the surrounding rock and achieves the expected reinforcement effect, while avoiding excessive disturbance of the surrounding rock due to excessive grouting pressure.

7. The railway engineering tunnel initial support process according to claim 1, characterized in that: During the anchor construction process, the hole-guiding operation should be precisely positioned to ensure that the anchor can be smoothly inserted into the hole and fit tightly against the hole wall. The anchoring length of the mortar anchor should ensure that the designed anchoring force requirements are met. The rod length of the hollow anchor should comply with the design requirements to ensure that its support function is effectively exerted.

8. The railway engineering tunnel initial support process according to claim 1, characterized in that: During the construction of advanced pipe-roof, the process of drilling first and then inserting pipes should ensure that the drilling accuracy and pipe insertion depth meet the design requirements. The pipe-following drilling process should ensure that the casing follows smoothly and cooperates well with the drill rod. After the pipe-roof is installed, the grouting should ensure that the slurry in the pipe-roof is densely filled and the pipe-roof structure is stable.

9. The railway engineering tunnel initial support process according to claim 1, characterized in that: During the entire initial support construction period, a complete surrounding rock deformation monitoring system should be established. The monitoring equipment should be stable and reliable, and the data collection should be accurate and timely. The support parameters should be adjusted in a timely and scientific manner based on the monitoring data to ensure the safety of tunnel construction.

10. The railway engineering tunnel initial support process according to claim 1, characterized in that: The raw materials used for shotcrete should be strictly screened to ensure qualified quality. The mix ratio of concrete should be reasonably adjusted according to actual construction conditions and design requirements to ensure that the performance of concrete meets the initial support requirements.

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