Tunnel portal construction method

Abstract

The invention relates to the technical field of tunnel construction, and provides a tunnel portal construction method. The tunnel portal construction method comprises the following steps: S1, comprehensive treatment of dangerous rocks at the portal: removing the dangerous rocks on the slope surface of the portal, and carrying out inlaying reinforcement on the slope surface of the portal; s2, water interception gutter construction, wherein a water interception gutter is formed in the edge and front slope, and an expansion joint and a water stop strip are arranged; s3, carrying out layered excavation and dynamic support on the edge and front slope: excavating the edge and front slope step by step, and carrying out combined support on the edge and front slope; s4, construction of hole reinforcing piles: excavating pile holes at intervals, dynamically adjusting the sectional height of the retaining wall, and pouring concrete into the pile holes; the upper half section of the open cut tunnel is excavated to the light and shade boundary, then a large pipe shed of the blind hole is constructed, then the lower half section of the open cut tunnel is excavated, and finally the blind hole is tunneled. The tunnel portal construction method solves the problems that in the prior art, a tunnel portal construction method is low in construction efficiency and large in potential safety hazard, and the tunnel portal construction method integrating dangerous rock treatment, structure stabilization and process optimization is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel construction, in particular to a tunnel portal construction method. BACKGROUND

[0002] Traditional tunnel portal construction often faces problems such as dangerous rock falling, surface runoff scouring, and slope instability, especially in the rainy season or adjacent to existing roads and bridges, the construction risk increases significantly. In the prior art, the portal reinforcement, drainage system and excavation support are mostly adopted by single process, lacking of collaborative control of multiple risk factors, resulting in low construction efficiency and great safety hazards. SUMMARY

[0003] The present application provides a tunnel portal construction method to solve the defects of low construction efficiency and great safety hazards of the prior art tunnel portal construction method, and realizes a tunnel portal construction method integrating dangerous rock treatment, ecological protection, structural stability and process optimization.

[0004] The tunnel portal construction method provided by the present application comprises: Comprehensive treatment of dangerous rock at the portal: removing dangerous rock on the portal slope surface, and embedding and reinforcing the portal slope surface; Construction of water interception gutter: setting a water interception ditch on the side slope, and setting expansion joints and water stop strips inside the water interception ditch; Layered excavation and dynamic support of side slope: excavating the side slope in steps, and jointly supporting the side slope with anchor rods, steel mesh and sprayed concrete; Construction of portal reinforcement pile: excavating pile holes at intervals, and dynamically adjusting the sectional height of the retaining wall, after the pile holes are completed, pouring concrete into the pile holes; Cooperative construction of open and dark tunnels: excavating the upper half of the open tunnel to the open-dark boundary, then constructing a dark tunnel large pipe shed, then excavating the lower half of the open tunnel, and finally excavating the dark tunnel.

[0005] According to the tunnel portal construction method provided by the present application, the embedding and reinforcing of the portal slope surface comprises applying a protective component to the portal slope surface; The protective component comprises a protective net and a plurality of anchor cables, and the protective net is fixed to the portal slope surface by the anchor cables; Wherein, the concrete strength of the base of the anchor cable is ≥C30, and the embedding depth of the anchor cable is ≥3m.

[0006] According to the tunnel portal construction method provided by the present application, each water interception ditch is provided with a plurality of expansion joints inside; The plurality of expansion joints are arranged at intervals along the length direction of the water interception ditch; Each expansion joint is arranged along the cross section of the water interception ditch.

[0007] The tunnel portal construction method provided by the application has the advantages that the interval of the expansion joint is 10-20 m, the width of the expansion joint is 1.5-2.5 cm, and the waterstop is arranged in the expansion joint.

[0008] The tunnel portal construction method provided by the application has the advantages that the waterstop is filled with asphalt reinforcement outside.

[0009] The tunnel portal construction method provided by the application has the advantages that in the layered excavation of the side slope, the earthwork section is excavated by a excavator in cooperation with manual excavation, and the stone section is drilled by a air drill and weakly blasted, and the excavation is supported in time.

[0010] The tunnel portal construction method provided by the application has the advantages that the layered excavation of the side slope includes: The type of the rock and soil of the side slope, the weathering degree and the position of the potential sliding surface are determined according to a geological survey report, and the side slope is excavated layer by layer from top to bottom; When the type of the rock and soil of the side slope is loose soil or strongly weathered rock, the height of each layer is ≤2 m; when the type of the rock and soil of the side slope is moderately weathered rock, the height of each layer is 2-3 m; and when the type of the rock and soil of the side slope is intact bedrock, the height of each layer is ≤4 m.

[0011] The tunnel portal construction method provided by the application has the advantages that the layered excavation of the side slope includes: The excavation boundary line is marked by lime or paint spraying; The side slope is mechanically excavated to the designed elevation of the current layer, and a 20 cm manual slope finishing allowance is reserved; The slope surface is manually finished, and the error range of overexcavation is within 5 cm; The slope surface is cleaned of loose stones, and the integrity of the rock mass is checked.

[0012] The tunnel portal construction method provided by the application has the advantages that the upper half section of the open cut tunnel includes: the open cut tunnel is excavated in steps along the design contour line of the open cut tunnel by mechanical excavation combined with a weak blasting process, the step height is ≤3 m, the core soil width is ≥2 m, the open cut tunnel is excavated to the junction of the open cut tunnel and the buried tunnel, and a stable transition surface is formed; The construction of the buried tunnel large pipe shed includes: the buried tunnel section at the open-buried cut-off point is provided with steel pipes arranged in a ring shape along the tunnel vault, the ring spacing of the steel pipes is 30-50 cm, the outer insertion angle of the steel pipes is 2-5°, the front end of the steel pipe is tapered, and the tail part is welded with a Φ16 reinforcing hoop; The lower half section of the open cut tunnel includes: after the construction of the buried tunnel large pipe shed is completed, the lower half section of the open cut tunnel is excavated in two layers, the upper layer is mechanically excavated to a position 1 m above the base, and the lower layer is manually finished and provided with temporary inverted arch support; The tunneling dark hole comprises: the dark hole is excavated in three parts of upper, middle and lower by using bench method, initial support is simultaneously constructed every 1.2m of cycle footage, and a ring is closed in time.

[0013] According to the tunnel portal construction method provided by the application, the hole position deviation of the steel pipe is less than or equal to 5 cm, the external insertion angle deviation of the steel pipe is less than or equal to 0.5 degrees, and the joint deviation of the steel pipe is less than or equal to 2 mm.

[0014] The tunnel portal construction method provided by the application directly improves the stability of the portal area and reduces potential risk factors by comprehensively treating the dangerous rock of the portal slope surface and embedding and reinforcing the portal slope surface. Next, the water interception gutter construction sets a water interception ditch on the side slope and sets expansion joints and water stop strips inside the water interception ditch, effectively preventing surface runoff from eroding the side slope and further enhancing the stability of the side slope. The side slope is excavated in layers and dynamically supported by excavating the side slope in steps and jointly supporting the side slope with anchor rods, steel mesh and sprayed concrete. This method can adapt to different geological conditions and ensure the stability of the side slope during excavation. The portal reinforcement pile construction excavates the pile holes at intervals and dynamically adjusts the segment height of the retaining wall according to the actual situation, pours concrete into the pile holes after the pile holes are completed, thereby improving the foundation bearing capacity of the entire structure.

[0015] The application not only ensures the continuity of tunnel construction, but also ensures the smooth transition between each part of the tunnel. The above steps are closely connected to form a systematic construction process, effectively solving the problems of dangerous rock falling, surface runoff erosion and slope instability in the traditional tunnel portal construction process, thereby improving the overall construction efficiency and safety. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0017] Figure 1 It is a flowchart of the tunnel portal construction method provided by the application; DETAILED DESCRIPTION

[0018] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0019] With reference to Figure 1 The tunnel portal construction method provided by the present application comprises the following steps (it should be noted that the labels of the following steps are only for description, and do not limit the sequence) : S1, comprehensive treatment of dangerous rocks at the portal: removing the dangerous rocks on the portal slope surface and embedding and reinforcing the portal slope surface; S2, construction of water interception gutter: setting a water interception ditch on the side slope and setting expansion joints and water stop strips inside the water interception ditch; S3, layered excavation and dynamic support of the side slope: excavating the side slope in steps and jointly supporting the side slope by using anchor rods, steel mesh and sprayed concrete; S4, construction of portal reinforcing piles: excavating pile holes at intervals and dynamically adjusting the sectional height of the retaining wall, after the pile holes are completed, pouring concrete into the pile holes; S5, coordinated construction of open and dark tunnels: excavating the upper half of the open tunnel to the open-dark boundary, then constructing a large pipe shed for the dark tunnel, then excavating the lower half of the open tunnel, and finally excavating the dark tunnel.

[0020] In the present application, first, the comprehensive treatment of dangerous rocks at the portal involves removing the dangerous rocks on the portal slope surface and embedding and reinforcing the portal slope surface, which directly improves the stability of the portal area and reduces potential risk factors. Next, the construction of the water interception gutter sets a water interception ditch on the side slope and sets expansion joints and water stop strips inside the water interception ditch, effectively preventing surface runoff from eroding the side slope and further enhancing the stability of the side slope. The layered excavation and dynamic support of the side slope excavates the side slope in steps and jointly supports the side slope by using anchor rods, steel mesh and sprayed concrete, which can adapt to different geological conditions and ensure the stability of the side slope during excavation. The construction of portal reinforcing piles excavates pile holes at intervals and dynamically adjusts the sectional height of the retaining wall according to the actual situation, and after the pile holes are completed, pours concrete into the pile holes, thereby improving the foundation bearing capacity of the entire structure.

[0021] This method not only ensures the continuity of tunnel construction, but also ensures the smooth transition between each part of the tunnel. The above steps are closely connected to form a systematic construction process, effectively solving the problems of dangerous rockfall, surface runoff erosion and side slope instability in the traditional tunnel portal construction process, thereby improving the overall construction efficiency and safety.

[0022] In step S1, the dangerous rock on the slope surface of the tunnel portal is removed, which specifically includes the following steps: S1.1 Safety assessment and geological survey: A professional technician uses advanced equipment such as geological radar and three-dimensional laser scanning to conduct a comprehensive detection on the slope surface of the tunnel portal to determine the location, size and stability of the dangerous rock. If necessary, manual inspection and recording are also required.

[0023] S1.2 Formulate a dangerous rock removal plan: Based on the above detection results, combined with the actual engineering situation, a detailed dangerous rock removal plan is developed. The plan should include but not limited to the removal sequence of the dangerous rock, the tools and methods used (such as manual prying, static breaking agent breaking or light blasting), and the corresponding safety measures.

[0024] S1.3 Perform dangerous rock removal operations: For small and isolated dangerous rocks, manual prying can be directly used. If the dangerous rock is large or located in a difficult-to-access location, static breaking agent can be used for breaking treatment. Static breaking agent is a non-explosive material that generates expansion force to break rocks through chemical reaction, with the characteristics of simple operation and high safety. In some cases, if the conditions allow and after strict safety assessment, light blasting can also be used for dangerous rock removal, but the impact on the surrounding environment must be minimized.

[0025] S1.4 Safety monitoring and protection measures: During the entire dangerous rock removal process, a dedicated person is responsible for on-site safety monitoring to ensure that all operations are carried out according to the predetermined plan. At the same time, necessary safety warning signs and protective facilities are set up around the operation area to prevent unrelated personnel from entering the danger zone.

[0026] S1.5 Cleaning and inspection: After completing the removal of dangerous rocks, the construction site should be cleaned up in a timely manner to remove all loose stones and other debris. Finally, a detailed inspection of the cleaned slope surface is conducted to confirm whether there are any missed dangerous rocks or other safety hazards.

[0027] In some embodiments of the present application, after the dangerous rock on the slope surface of the tunnel portal is removed, the next step is to reinforce the slope surface of the tunnel portal, which includes applying protective components to the slope surface of the tunnel portal; the protective components include a protective net and a plurality of anchor cables, the protective net is fixed to the slope surface of the tunnel portal through the anchor cables; wherein the concrete strength of the base of the anchor cable is ≥ C30, and the embedding depth of the anchor cable is ≥ 3m. Specifically, reinforcing the slope surface of the tunnel portal includes the following steps: S1.6 Preparation of materials and equipment: First, prepare the required protective nets, anchor cables and related construction equipment. The protective net should be made of materials with sufficient strength and corrosion resistance to ensure its stability during long-term use. The base concrete strength of the anchor cable should reach C30 or above to provide sufficient bearing capacity. The embedding depth of the anchor cable should not be less than 3m to ensure that it can be firmly fixed in the rock.

[0028] S1.7 Marking anchor cable position: According to the design drawings, mark the specific installation position of each anchor cable on the slope surface of the opening. The selection of these positions needs to consider the actual geological conditions of the slope surface and potential risk points to ensure that each anchor cable can effectively share the pressure of the slope surface.

[0029] S1.8 Drilling operation: Use professional drilling equipment to drill holes at the marked positions. The diameter and depth of the hole should strictly follow the design requirements, and in general, the hole diameter is slightly larger than the anchor cable diameter to facilitate subsequent grouting operations. After drilling, check whether the hole depth meets the requirements and clean the hole of debris.

[0030] S1.9 Installation of anchor cable: Insert the anchor cable into the pre-drilled hole, ensuring that the anchor cable fully enters the hole bottom. Then, inject cement mortar or other suitable filling materials into the hole to make the anchor cable tightly combined with the surrounding rock. The filling material should be evenly distributed to avoid voids, thereby ensuring the stability of the anchor cable.

[0031] S1.10 Fixing protective net: After all anchor cables are installed and reach a certain strength, start laying the protective net. The protective net is fixed on the anchor cable through steel wire or special connecting pieces to ensure that it tightly fits the slope surface. The joints between the protective nets should overlap at least 10mm and be tightly bound with steel wire to prevent local damage leading to overall failure.

[0032] S1.11 Quality inspection and acceptance: After completing the laying of the protective net, conduct a comprehensive quality inspection of the entire embedded reinforcement system. The inspection includes whether the installation position, angle and embedding depth of the anchor cable meet the design requirements, whether the protective net is flat and has no obvious defects, and whether the connecting parts are firm and reliable. If necessary, a pull-out test can be conducted to verify the actual bearing capacity of the anchor cable.

[0033] Through the above steps, the slope surface of the opening is effectively embedded and reinforced, significantly improving the overall stability and safety of the slope surface, providing a solid foundation for subsequent tunnel construction. This systematic reinforcement method is not only suitable for various complex geological conditions, but also can effectively meet the needs of different scale engineering projects.

[0034] Step S2 includes the following steps: S2.1 Preparation: First, determine the location, size, and orientation of the cutoff trench according to the design drawings. Prepare the required materials, including concrete, steel reinforcement, expansion joint materials (such as rubber sheets or steel plates), sealing strips, and asphalt felt for filling materials.

[0035] S2.2 Excavate the trench: According to the design requirements, excavate the trench on the side slope. The depth and width of the trench should meet the design standards to ensure that enough concrete can be accommodated to form a solid cutoff trench. The bottom of the trench should be kept level, and a layer of crushed stone cushion should be laid if necessary to enhance drainage.

[0036] S2.3 Install the steel reinforcement cage: Install the steel reinforcement cage in the trench, ensuring its accurate position and firm fixation. The design of the steel reinforcement cage should meet the structural strength requirements, capable of bearing the pressure from external water flow and potential ground settlement.

[0037] S2.4 Pour concrete: Use concrete that meets the design requirements for pouring. The concrete should be evenly distributed to avoid voids and honeycomb phenomena. During the pouring process, a vibrating rod can be used to ensure that the concrete density meets the standard. After the initial setting of the concrete, perform surface smoothing treatment to ensure that the cutoff trench surface is smooth and defect-free.

[0038] S2.5 Set expansion joints: Place multiple expansion joints along the length of the cutoff trench, each set along the cross-section of the cutoff trench. The spacing of the expansion joints is 10m~20m, and the joint width is 1.5cm to 2.5cm. The purpose of the expansion joints is to allow the cutoff trench to have a certain amount of expansion space when the temperature changes and the ground settles, preventing the occurrence of cracks.

[0039] S2.6 Install sealing strips: Install sealing strips inside each expansion joint. The sealing strips should tightly adhere to the concrete surface on both sides of the expansion joint and ensure good sealing performance. The material of the sealing strips can be selected from rubber or other synthetic materials with good elasticity and durability to adapt to different environmental conditions.

[0040] S2.7 Fill asphalt felt: After the sealing strips are installed, fill the outside of the sealing strips with asphalt felt. Asphalt felt not only enhances the adhesion between the sealing strips and the surrounding concrete, but also absorbs a certain amount of deformation, further improving the sealing effect of the expansion joint. When filling, pay attention to uniform compaction to avoid voids.

[0041] S2.8 Quality inspection and acceptance: After completing the above steps, conduct a comprehensive quality inspection of the entire cutoff trench system. The inspection content includes but is not limited to the dimensional accuracy of the cutoff trench, the density of the concrete, whether the arrangement of the expansion joints meets the design requirements, the installation of the sealing strips, and the compaction degree of the filling materials. Only when all inspection items meet the standard requirements can it be considered qualified.

[0042] By the above steps, the water interception ditch is arranged on the side slope, and the expansion joint and the water stop strip are arranged, so that not only the erosion of surface runoff to the side slope can be effectively prevented, but also the stability and durability of the water interception ditch itself can be ensured. The method is suitable for tunnel portal construction under various geological conditions, and significantly improves the overall quality and safety of the project.

[0043] Specifically, a plurality of expansion joints are arranged inside each water interception ditch; the expansion joints are arranged at intervals along the length direction of the water interception ditch; and each expansion joint is arranged along the cross section of the water interception ditch. The interval of the expansion joints is 10m-20m, and the joint width of the expansion joints is 1.5cm-2.5cm. Specifically, the joint width of the expansion joints is 2cm. The water stop strip is arranged inside the expansion joint. The outside of the water stop strip is filled with asphalt reinforcement. This design not only effectively solves the deformation problem of the water interception ditch caused by temperature change and foundation settlement, but also significantly improves the reliability and durability of the entire drainage system.

[0044] When the external temperature changes, the concrete structure will expand and contract due to heat and cold. Without the presence of expansion joints, this stress may cause the water interception ditch to crack or even break, thereby affecting its normal use function. The present application can make each section of the water interception ditch independently expand and contract by arranging expansion joints, thereby avoiding damage to the overall structure due to stress concentration. In addition, the interval between the expansion joints is 10m-20m, which can not only ensure sufficient flexibility to cope with the influence of temperature change, but also not weaken the overall strength of the water interception ditch.

[0045] The water stop strip arranged inside the expansion joint can effectively prevent water from penetrating into the expansion joint, further protecting the structural integrity of the water interception ditch. The asphalt reinforcement filled outside the water stop strip plays a dual role: on the one hand, it can enhance the adhesion between the water stop strip and the surrounding concrete, ensuring that the water stop strip will not be displaced due to water flow erosion or long-term use; on the other hand, the asphalt reinforcement has good flexibility and elasticity, and can absorb and buffer small deformations caused by uneven foundation settlement to a certain extent, thereby maintaining the sealing performance of the expansion joint.

[0046] Therefore, by reasonably arranging the expansion joints and the water stop strips inside them, and filling the outside with asphalt reinforcement, the present application not only solves the structural deformation problem caused by temperature change and foundation settlement, but also ensures the waterproof performance and overall stability of the water interception ditch. This method not only improves the service life of the water interception ditch, but also reduces the maintenance cost, making the entire tunnel portal construction scheme more scientific, reasonable and efficient.

[0047] In some embodiments of the present application, step S3 comprises the following steps: S3.1 Geological Survey and Scheme Development: Determine the slope rock-soil type, weathering degree, and potential sliding surface location based on detailed geological survey reports. According to the slope rock-soil type, the height of each layer is set as follows: When the slope rock-soil type is loose soil or strongly weathered rock, the height of each layer does not exceed 2m; When the slope rock-soil type is moderately weathered rock, the height of each layer is 2m to 3m; When the slope rock-soil type is intact bedrock, the height of each layer does not exceed 4m.

[0048] S3.2 Marking Excavation Boundary Line: Use lime or paint to mark the excavation boundary line of each layer on the slope. These markings should be clear and explicit to facilitate accurate adherence to design requirements during subsequent mechanical excavation operations. During the marking process, attention should be paid to ensuring the accuracy of the boundary line position to avoid deviations.

[0049] S3.3 Mechanical Excavation to Current Layer Design Elevation: Use excavators and other mechanical equipment to preliminarily excavate according to the marked boundary line until the current layer design elevation is reached. A 20mm manual slope finishing allowance is reserved to ensure the final slope surface is smooth, with an over-excavation amount controlled within ±5mm. The excavation depth and width need to be strictly controlled during the process to ensure the structural stability of the next layer is not damaged. It should be noted that during the layered excavation of the slope, excavators are used for earthwork sections in combination with manual excavation, and wind drills are used for stone sections with weak blasting and supporting as excavation progresses.

[0050] S3.4 Manual Slope Surface Finishing: After mechanical excavation is completed, workers are arranged to finely finish the slope surface. Remove floating stones from the slope surface, check the integrity of the rock mass, and ensure that the slope surface has no obvious defects or safety hazards. Special attention should be paid to the flatness and perpendicularity of the slope surface during manual finishing to ensure the installation quality of the subsequent support structure.

[0051] S3.5 Installation of Anchor Rods: According to the design drawings, drill holes in the slope and insert anchor rods. The hole diameter is slightly larger than the anchor rod diameter to ensure smooth insertion of the anchor rod. The drilling depth needs to meet the design requirements, and in general, the embedded depth of the anchor rod is not less than 3m.

[0052] Inject cement mortar or other suitable filling materials into the drilled hole to firmly fix the anchor rod in the rock. Ensure uniform distribution of the filling material to avoid voids. During grouting, attention should be paid to controlling the grouting pressure and speed to ensure the grouting effect.

[0053] S3.5 Laying Steel Mesh: After all anchor rods are installed, start laying steel mesh. Steel mesh is fixed on anchor rods by steel wire or special connectors, ensuring it closely fits the slope surface. The joints between steel meshes should overlap at least 10mm and be tightly bound with steel wire to prevent partial damage leading to overall failure. Pay attention to the flatness and tightness of steel mesh during laying to ensure it can effectively transfer stress.

[0054] S3.6 Spraying Concrete: Finally, use spraying concrete equipment to cover steel mesh, forming a solid protective layer. Spraying concrete should be evenly distributed, with thickness meeting design requirements, ensuring it has sufficient strength and durability. Pay attention to controlling water-cement ratio during spraying to ensure the quality of concrete. Spraying concrete not only enhances the overall stability of the slope, but also effectively prevents rainwater erosion and other external factors.

[0055] S3.7 Quality Inspection and Acceptance: After completing each layer of excavation and support, conduct a comprehensive quality inspection. Inspection content includes but is not limited to the flatness of the slope, the installation position and angle of anchor rods, the laying of steel mesh, and the compactness of sprayed concrete, etc. Only when all inspection items meet the standard requirements can the next layer of excavation work continue. Detailed records of various data should be kept during quality inspection to ensure traceability of construction quality.

[0056] Through the above steps, the stepped excavation of the slope and the combined support of anchor rods, steel mesh and sprayed concrete not only improve the construction efficiency, but also significantly enhance the stability and safety of the slope. This method can flexibly adjust the excavation and support strategy according to different geological conditions, ensuring the safe and smooth progress of the entire tunnel portal construction. This method effectively solves the problems of slope instability, landslide and other problems in traditional construction methods, improves the overall quality and reliability of the project, reduces maintenance costs, and ensures the safety of construction personnel.

[0057] In some embodiments of the present application, step S4 includes the following steps: S4.1 Geological Survey and Scheme Development: First, conduct detailed geological survey to determine the specific location, depth and diameter of the pile hole and other parameters. According to the geological conditions and design requirements, develop a reasonable construction plan. The plan should include pile hole layout, excavation sequence, retaining structure design and concrete pouring plan, etc.

[0058] S4.2 Marking Pile Hole Position: According to the design scheme, use surveying instruments (such as total station or theodolite) to accurately mark the position of each pile hole on the construction site. Marking should be clear and explicit, and ensure that the distance between each pile hole meets the design requirements to avoid mutual interference.

[0059] S4.3 Intervals of Pile Hole Excavation: According to the design scheme, use rotary drilling rigs or other suitable drilling equipment for pile hole excavation. To reduce the impact on adjacent pile holes, usually adopt the way of interval excavation, that is, excavate a part of the pile hole first, and then excavate the rest of the pile hole after it is preliminarily stable.

[0060] During the excavation process, real-time monitoring of the changes in geological conditions, and dynamic adjustment of the height of the segmented wall according to the actual situation. The height of the wall should be adjusted flexibly according to the stability of the soil layer, groundwater level and other factors, to ensure the stability and safety of the pile hole wall surface.

[0061] S4.4 Installation of Wall Structure: After each section of the pile hole is excavated, immediately install the wall structure. The wall can be made of steel casing, reinforcement cage or other suitable materials, the specific selection should be determined according to the geological conditions and design requirements.

[0062] When installing the wall, ensure its verticality and tightness to prevent the pile hole wall from collapsing or deforming. For unstable strata, support structures can be added inside the wall to further enhance its stability.

[0063] S4.5 Dynamic Adjustment of Wall Segmentation Height: During the excavation process, dynamically adjust the segmentation height of the wall according to the changes in geological conditions and the actual stability of the pile hole. For example, when encountering soft soil layers or areas with abundant groundwater, appropriately shorten the segmentation height of the wall, increase the number of wall layers, to improve the stability of the pile hole wall surface.

[0064] After each adjustment of the wall height, quality inspection is required to ensure that the wall is installed firmly and has no obvious defects.

[0065] S4.6 Pile Hole Bottom Cleaning and Inspection: After the pile hole is excavated to the designed depth, use a bottom cleaning tool to thoroughly clean the sludge and debris at the bottom of the pile hole, ensuring that the bottom is smooth and clean. Then, conduct a detailed inspection of the pile hole to confirm that its size, verticality and bottom condition meet the design requirements.

[0066] S4.7 Pouring Concrete into the Pile Hole: After confirming that the pile hole meets the design requirements, begin pouring concrete into the pile hole. Concrete should be poured using pumping or conduit method to ensure continuous and uniform pouring, avoiding the occurrence of faults or voids. During the pouring process, pay attention to controlling the slump of the concrete to ensure its good fluidity and compactness. At the same time, regularly vibrate the concrete to remove air bubbles, ensuring the density and strength of the concrete. When the concrete is poured to the design elevation of the pile top, perform surface smoothing treatment to ensure the smoothness of the pile top.

[0067] S4.8 Quality Inspection and Acceptance: After the completion of concrete pouring for all pile holes, a comprehensive quality inspection is conducted. The inspection includes but is not limited to the verticality of the pile holes, the compactness of the concrete, the stability of the retaining wall, and the overall bearing capacity, etc. Only when all inspection items meet the standard requirements, it can be considered as qualified.

[0068] Through the above steps, the pile holes are excavated and the sectional height of the retaining wall is dynamically adjusted, and then the concrete is poured into the pile holes. This not only improves the construction efficiency of the pile foundation, but also significantly enhances its stability and bearing capacity. This method can flexibly adjust the construction strategy according to different geological conditions, ensuring the safe and smooth progress of the entire tunnel portal construction. This method effectively solves the problems of pile hole collapse and non-compact concrete in traditional construction methods, improves the overall quality and reliability of the project, reduces maintenance costs, and ensures the safety of construction personnel.

[0069] In the present application, step S5 includes the following steps: S5.1 Preparation: According to the design drawings and geological survey report, the specific location, size and excavation sequence of the open and hidden tunnels are determined. The required mechanical equipment (such as excavators, air drills, etc.), materials (such as steel pipes, concrete, etc.) and safety protection facilities are prepared.

[0070] S5.2 Excavate the upper half of the open tunnel to the open-hidden boundary: Use mechanical excavation combined with weak blasting technology to excavate along the design contour line of the open tunnel in steps. The height of each step does not exceed 3m, and the core soil width is not less than 2m to ensure the stability during excavation. During the excavation process, gradually advance downward until reaching the junction mileage of the open and hidden tunnels, forming a stable transition surface. During the excavation process, clean the floatstone and debris in time to ensure a clean construction environment, and check the stability of the slope to prevent landslides or collapses.

[0071] S5.3 Construction of hidden tunnel large pipe shed: In the hidden tunnel section at the open-hidden boundary, Φ108×6mm hot-rolled seamless steel pipes (i.e. large pipe shed) are arranged along the tunnel vault in a ring shape. The ring spacing of the steel pipes is 30mm to 50mm, the external insertion angle is 2° to 5°, the front end is tapered, and the tail is welded with Φ16 reinforcing stirrups. The hole position deviation of the steel pipe should be controlled within 5mm, the external insertion angle deviation should not exceed 0.5°, and the joint misalignment should not exceed 2mm to ensure the installation accuracy of the steel pipe. After the steel pipe installation is completed, grouting operation is carried out using cement mortar or other suitable filling materials to ensure that the steel pipe is tightly combined with the surrounding rock and enhances its bearing capacity.

[0072] S5.4 Excavating the lower half of the open tunnel: After the completion of the large pipe shed support for the hidden tunnel, the excavation of the lower half of the open tunnel is started in two layers. First, mechanical excavation is used to a height of 1 m above the upper half of the tunnel base level to ensure the stability of the upper layer structure. Then, manual finishing and temporary inverted arch support are applied to ensure the stability and safety of the lower layer structure. The temporary inverted arch can be made of sprayed concrete or other suitable support materials to ensure sufficient strength and durability. Throughout the excavation process, monitoring of the side slope and top is maintained to promptly identify and address potential safety hazards.

[0073] S5.5 Excavating the hidden tunnel: The hidden tunnel is excavated in three parts using the bench method, with each cycle of 1.2 m in length and simultaneous application of primary support, including anchor rods, steel mesh, and sprayed concrete, to ensure timely and effective support of the excavated rock mass. After each excavation section is completed, it is immediately closed to prevent deformation or instability of the surrounding rock. The primary support should be closely coordinated with the subsequent secondary lining to ensure the stability and safety of the overall structure. During the excavation process, real-time monitoring of changes in geological conditions is conducted to adjust the construction plan as needed to ensure construction quality and safety.

[0074] S5.6 Quality inspection and acceptance: After each step is completed, a comprehensive quality inspection is conducted. The inspection content includes but is not limited to the dimensional accuracy of the excavation section, the integrity of the support structure, the installation accuracy of the steel pipe, and the compactness of the concrete, etc. Only when all inspection items meet the standard requirements can the next stage of construction continue. Detailed records of various data should be kept during the quality inspection process to ensure traceability of construction quality.

[0075] Through the above steps, from excavating the upper half of the open tunnel to the open-hidden boundary, then applying the large pipe shed for the hidden tunnel, and then excavating the lower half of the open tunnel, and finally excavating the hidden tunnel, not only improves the construction efficiency, but also significantly enhances the overall stability and safety of the tunnel. This method can flexibly adjust the construction strategy according to different geological conditions to ensure the safe and smooth progress of the entire tunnel construction. This method effectively solves the instability factors in traditional construction methods, improves the overall quality and reliability of the project, reduces maintenance costs, and ensures the safety of construction personnel.

[0076] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for constructing a tunnel entrance, characterized in that, include: Comprehensive treatment of dangerous rocks at the tunnel entrance: Remove dangerous rocks from the slope of the tunnel entrance and reinforce the slope by patching; Construction of intercepting gutter: An intercepting ditch is set up on the side slope, and expansion joints and waterstop strips are installed inside the intercepting ditch; Layered excavation and dynamic support of the slope: The slope is excavated in stages and supported by a combination of anchor bolts, steel mesh and shotcrete. Construction of reinforcement piles at the tunnel entrance: Piles are excavated at intervals, and the height of the retaining wall is dynamically adjusted. After the pile holes are completed, concrete is poured into the pile holes. Coordinated construction of open and closed tunnels: excavate the upper half of the open tunnel to the boundary between open and closed sections, then construct the large pipe shed for the closed tunnel, excavate the lower half of the open tunnel, and finally excavate the closed tunnel.

2. The tunnel portal construction method according to claim 1, characterized in that, The reinforcement of the slope of the opening includes installing protective components on the slope of the opening; The protective component includes a protective net and multiple anchor cables, and the protective net is fixed to the slope of the opening by the anchor cables; The concrete strength of the anchor cable base is ≥C30, and the embedment depth of the anchor cable is ≥3m.

3. The tunnel portal construction method according to claim 1, characterized in that, Each of the intercepting ditches is provided with multiple expansion joints inside; The expansion joints are arranged at intervals along the length of the intercepting ditch; Each of the expansion joints is provided along the cross-section of the intercepting ditch.

4. The tunnel portal construction method according to claim 3, characterized in that, The expansion joints are spaced 10m to 20m apart, and the joint width is 1.5cm to 2.5cm. The waterstop strip is installed inside the expansion joint.

5. The tunnel portal construction method according to claim 4, characterized in that, The exterior of the waterstop strip is filled with asphalt-impregnated hemp fiber.

6. The tunnel portal construction method according to claim 1, characterized in that, In the layered excavation of the slope, the earthwork section is excavated by excavators in combination with manual labor, while the rock section is excavated by pneumatic drills and weak blasting, and support is provided as excavation progresses.

7. The tunnel portal construction method according to claim 6, characterized in that, The stepped excavation side slope includes: Based on the geological survey report, the slope soil and rock type, weathering degree and potential sliding surface location are determined, and excavation is carried out layer by layer from top to bottom; Specifically, when the slope soil and rock type is loose soil or strongly weathered rock, the height of each layer is ≤2m; when the slope soil and rock type is moderately weathered rock, the height of each layer is 2m~3m; and when the slope soil and rock type is intact bedrock, the height of each layer is ≤4m.

8. The tunnel portal construction method according to claim 7, characterized in that, The stepped excavation side slope also includes: Mark the excavation boundary lines using lime or spray paint; Mechanical excavation will proceed to the current layer's design elevation, with a 20cm margin reserved for manual slope trimming. The slope surface is manually trimmed, and the error range for over-excavation is within 5cm. Remove loose rocks from the slope and check the integrity of the rock mass.

9. The tunnel portal construction method according to claim 1, characterized in that, The excavation of the upper half section of the open tunnel to the boundary between the open and dark sections includes: using mechanical excavation combined with weak blasting technology, excavating in steps along the designed outline of the open tunnel, with a step height ≤3m, a reserved core soil width ≥2m, and excavating to the boundary between the open and dark tunnels to form a stable transition surface. The construction of the large pipe shed in the dark tunnel includes: in the dark tunnel section at the boundary between light and dark, steel pipes are arranged circumferentially along the tunnel arch, the circumferential spacing of the steel pipes is 30cm~50cm, the external insertion angle of the steel pipes is 2°~5°, the front end of the steel pipes is processed into a cone shape, and the tail end is welded with Φ16 stiffening stirrups; The lower half of the excavated open tunnel section includes: after the support of the pipe shed in the dark tunnel is completed, the lower half of the open tunnel section is excavated in two layers. The upper layer is mechanically excavated to the base elevation of 1m, and the lower layer is manually trimmed and temporary invert arch support is constructed. The excavation of the tunnel includes: using the step method to excavate the tunnel in three parts: upper, middle and lower, with an advance of 1.2m per cycle, simultaneous initial support, and timely closure to form a ring.

10. The tunnel portal construction method according to claim 9, characterized in that, The hole position deviation of the steel pipe is ≤5cm; the external insertion angle deviation of the steel pipe is ≤0.5°; and the joint misalignment of the steel pipe is ≤2mm.

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