Tunnel portal section edge and front slope miniature steel pipe pile-anchor rod support tunnel-entering construction method

Abstract

The invention discloses a tunnel portal section edge and front slope miniature steel pipe pile-anchor rod support tunnel entering construction method, relates to the technical field of tunnel construction, and aims to prevent and support the edge and front slope instability condition at a tunnel portal, a large number of anchoring type support structures are applied, and miniature steel pipe piles are convenient to construct, simple in structure and flexible in arrangement; however, the miniature steel pipe piles in engineering are prone to bending shear damage. The invention provides a tunnel portal section edge and front slope miniature steel pipe pile-anchor rod support tunnel entering construction method. The method comprises the steps that miniature steel pipe piles are constructed, and a top beam is poured; cutting the side slope; along with step-by-step excavation of the side slope, a waist beam and an anchor rod are constructed; advanced large pipe shed construction; and pile breaking and full-section excavation are carried out. The pre-stressed anchor rods and the miniature steel pipe piles are stressed together to resist landslide thrust, the slope reinforcing effect is enhanced, passive stress is changed into active stress, the structural stress is more reasonable, the engineering difficulty of pile breaking and hole entering is reduced, meanwhile, hole opening ground surface settlement and surrounding rock deformation are reduced, and the supporting and retaining slope does not collapse.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a tunnel portal section side upturn slope micro steel pipe pile-anchor support tunnel construction method. Background Art

[0002] In the current situation of rapid economic development, investment in the field of transportation construction is constantly expanding. Highway construction is carried out under complex terrain. Because the complexity of external terrain conditions will increase the technical difficulty of construction, especially the influence of height difference, a large number of tunnel construction is favored. The tunnel entrance, as the starting point of the tunnel, will form an air surface after excavation. The freely released surrounding rock force will cause the internal surrounding rock force to be redistributed. The slope surface will produce cracks because the surrounding rock force generated by the re-excavation is not enough to bear the previous surrounding rock force state. In severe cases, collapse engineering disasters will occur. Therefore, the stability of the slope is very important to the normal operation of the main project. Therefore, the preventive support of the instability of the side slope at the tunnel entrance is particularly important.

[0003] For the preventive support of the instability of the side slope at the tunnel entrance, surface drainage, groundwater interception, load reduction, retaining wall and other measures and large-diameter anti-slide pile reinforcement were adopted. However, surface drainage, groundwater interception, load reduction, retaining wall and other methods are temporary. When the external environment changes, the slope will be damaged again. Large-diameter anti-slide pile reinforcement requires heavy machinery and professional operation due to its large cross-section, and requires high design accuracy, which is not convenient in engineering. Nowadays, anchored support structures are widely used in engineering. The emergence of micro steel pipe piles makes construction more convenient, simple in structure, and flexible in layout, but it is prone to bending and shear failure. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention aims to provide a tunnel portal section side slope micro steel pipe pile-anchor support construction method, which can solve the problems of small excavation depth, poor geological conditions, poor stability of the side slope and the inability to naturally slope the slope due to terrain restrictions in the tunnel entrance section, as well as small construction site and difficulty in using large construction machinery; at the same time, in response to the actual situation that after the excavation of the tunnel portal, the redistribution of surrounding rock stress causes slope surface disturbance, and the slope is insufficient to bear the previous surrounding rock force state, this combined support system can effectively control the deformation of the slope, ensure the safety of tunnel excavation, and the use of micro steel pipe piles greatly reduces the construction difficulty when breaking piles to enter the hole.

[0005] The main idea of ​​the technical solution adopted by the present invention is as follows: the micro steel pipe pile-anchor support system is a pile-anchor structure system formed by a number of vertically or obliquely arranged micro steel pipe piles, pile top crown beams, oblique anchors and surrounding rock and soil; in the specific structure, one end of the prestressed anchor is anchored to the micro steel pipe pile structure, and the other end is anchored to the stable stratum, so that the two anti-slip structures of the micro steel pipe pile and the anchor are combined to bear force together to form a pile-anchor coordination system. Therefore, the prestressed anchor and the pile are jointly subjected to force to resist the thrust of the landslide, which enhances the slope reinforcement effect, changes the passive force into active force, and makes the structural force more reasonable. The selection of micro steel pipe piles in engineering reduces the difficulty of cutting piles and makes it feasible to break the pile body into the hole.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A tunnel portal side slope micro steel pipe pile-anchor support tunnel construction method, comprising: Step 1: First construct micro steel pipe piles and cast the crown beam; Step 2: Slope cutting; Step 3: As the slope is excavated step by step, the waist beam and anchor rods are constructed; After excavating the first layer of slope, a waist beam is constructed on the outside of the steel pipe pile. There is an inclined guide tube on the waist beam. The drill rod passes through the guide tube to drill an inclined anchor hole, and the prestressed anchor rod is put in. The anchor rod passes through the guide tube on the waist beam and the micro steel pipe pile and is anchored in the surrounding rock. The anchor section is placed deep in the surrounding rock, and concrete is poured. After the concrete solidifies, the anchor rod is tensioned to apply prestress, and the anchor rod at the other end is cast and fixed to the guide tube of the waist beam; and so on, the waist beam and prestressed anchor rod are constructed in time after each step of slope excavation; Step 4: Advance large pipe shed construction; Step 5: Break piles and excavate the entire section.

[0007] Through the above technical scheme, further: in the step one, drilling is performed to check the hole position, and micro steel pipe piles are installed after the inspection is qualified. After installation, grouting construction is carried out. After the construction of the micro steel pipe pile wall is completed, the top is connected with a crown beam; the length of the steel pipe is 10-28m, 120 Φ168 steel pipes are set, and the spacing between the steel pipes is 0.5m. The length of the micro steel pipe piles varies according to their location. On both sides, due to the small thrust of the supporting soil, the pile length is the shortest; the surrounding rock deformation of the entrance section is large, and the micro steel pipe piles here are arranged the longest.

[0008] Through the above technical scheme, further: in the step 2, the side and back slope excavation and the tunnel entrance excavation are carried out step by step from top to bottom.

[0009] Through the above technical scheme, further: in the step three, as the soil in front of the slope is excavated, a waist beam composed of double-shaped steel S355 of the HEA180 series is applied step by step, a guide tube with a preset inclination is screwed on the waist beam, a hole is drilled through the tube mouth, and a prestressed anchor rod is applied.

[0010] Through the above technical scheme, further: in the step three, a prestressed anchor rod with a prestress of 300kN is applied on the waist beam to form a micro steel pipe pile-anchor rod support system, so that they are jointly stressed, thereby protecting the rock and soil behind the slope.

[0011] Through the above technical solution, further: in the step 3, the anchor rod construction process includes: (1) Anchor hole measurement and placement; (2) Anchor hole drilling; (3) Cleaning holes; (4) Anchor hole inspection; (5) Anchor bolt installation; (6) Grouting; (7) Tensioning.

[0012] Through the above technical scheme, further: when the anchor rod is installed, the hole is cleaned with high-pressure air, and then the anchor rod is slowly inserted into the bottom of the hole, and the grouting pipe is installed together with the anchor rod, and the pipe mouth is kept 30 to 50 cm away from the bottom of the hole.

[0013] Through the above technical scheme, further: when drilling the anchor hole, the drill rig drills through the guide hole on the waist beam, the hole diameter coordinate error shall not be greater than 5cm, the hole slope error shall not be greater than 1%, the drilling hole diameter is 180mm, and after drilling to the designed depth, steady drilling is performed for 3 to 5 minutes to prevent the bottom of the hole from pinching out.

[0014] Through the above technical scheme, further: in the step four, a multifunctional drilling rig is used to drill holes from the guide pipe, the drilling diameter is 135mm, and the drilling sequence is from high hole position to low hole position; high-pressure air is used to clean the drill slag from the bottom of the hole to the hole mouth; the pipe-roof steel pipe is installed, and the pipe-roof steel pipe is pushed in by a machine. After the pipe-roof steel pipe is pushed into place, the gap between the pipe-roof steel pipe and the guide steel pipe is sealed with an anchor to prevent grouting during grouting; the grouting steel flower pipe is connected to the grouting plug.

[0015] Through the above technical scheme, further: in the step five, first use a three-dimensional laser scanner to determine the contour line of the broken pile, and then use a hydraulic wall saw to cut the micro steel pipe piles along the line to break the pile body at the tunnel entrance into the hole.

[0016] The beneficial effects of the present invention are: The micro steel pipe pile-anchor support system is a pile-anchor structure system composed of a number of vertically or obliquely arranged micro steel pipe piles, pile top beams, oblique anchors and surrounding rock and soil. One end of the prestressed anchor is anchored to the micro steel pipe pile structure, and the other end is anchored to the stable stratum, that is, the two anti-slip structures of micro steel pipe piles and anchors are combined to bear force together to form a pile-anchor coordination system. Therefore, the prestressed anchor and piles are jointly subjected to force to resist the thrust of the landslide, which enhances the slope reinforcement effect, changes passive force to active force, and makes the structural force more reasonable. The selection of micro steel pipe piles reduces the difficulty of breaking piles into holes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the construction flow chart of micro steel pipe pile-anchor bolt entering the hole; Figure 2 It is a schematic diagram of the micro steel pipe pile-anchor support reinforcement scheme; Figure 3 This is a schematic diagram of the elevation layout of the micro steel pipe pile-anchor support reinforcement solution; Figure 4 This is a schematic diagram of the elevation layout of the micro steel pipe pile-anchor support reinforcement solution; Figure 5 This is the construction flow chart of micro steel pipe piles; Figure 6 This is a detailed drawing of micro steel pipe piles; Figure 7 This is a schematic diagram of the pipe shed layout; Figure 8 This is the waist beam structure diagram; Among them: 1. Crown beam; 2. Micro steel pipe piles; 3. Waist beam; 4. Backfill soil; 5. Prestressed anchor rods; 6. Ground; 7. Waist beam; 8. Guide pipe. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0019] The inventors have found that the preventive support for the instability of the side slope at the tunnel entrance mainly adopts surface drainage, cross-cutting groundwater, reducing loads, retaining walls and other measures in the early slope management. The disadvantage is that this method is temporary, and when the external environment changes, the slope will be damaged again. Later, large-diameter anti-slide piles were used for reinforcement, but due to their large cross-section, heavy machinery and professional operation are required for construction, and high design accuracy is required. Nowadays, more and more anchored support structures are widely used in engineering. Micro steel pipe piles are used in engineering due to their advantages of convenient construction, simple structure and flexible layout, but micro steel pipe piles in actual engineering are prone to bending and shear failure.

[0020] Based on the above findings, this application proposes a tunnel portal section side slope micro steel pipe pile-anchor support construction method, constructs a micro steel pipe pile-anchor support system, and uses a number of vertically or obliquely arranged micro steel pipe piles, pile top crown beams, oblique anchors and surrounding rock and soil to form a pile-anchor structure system; in the specific structure, one end of the prestressed anchor is anchored to the micro steel pipe pile structure, and the other end is anchored to the stable stratum, that is, the two anti-slip structures of the micro steel pipe pile and the anchor are combined to bear force together to form a pile-anchor coordination system. Therefore, the prestressed anchor and the pile are jointly subjected to force to resist the thrust of the landslide, which enhances the slope reinforcement effect, changes the passive force to active force, and makes the structural force more reasonable. The selection of micro steel pipe piles reduces the engineering difficulty of breaking piles into the hole, and after excavation into the hole, it can reduce the surface settlement of the hole and the deformation of the surrounding rock, and the retaining slope does not slide and collapse.

[0021] Embodiment 1 See also Figure 1 The present application discloses a tunnel portal side slope micro steel pipe pile-anchor support tunnel construction method, comprising: Step 1: First construct micro steel pipe piles and cast the crown beam; Step 2: Slope cutting; Step 3: As the slope is excavated step by step, the waist beam and anchor rods are constructed; Step 4: Advance large pipe shed construction; Step 5: Break piles and excavate the entire section.

[0022] Embodiment 2 See also Figure 2-Figure 8 , step one includes the following steps: 1. Micro steel pipe pile protection In slope support, this design uses single-row piles for protection design according to the on-site conditions. The length of the micro steel pipe piles varies according to their location. On both sides, due to the small thrust of the supporting soil, 10 piles of 10m, 8 piles of 15m, and 5 piles of 17m are used; in the middle rock of the small clear distance tunnel, the stress release is large after the tunnel excavation, so 8 piles of 23m and 44 piles of 25m are set; at the tunnel entrance, after the piles are broken into the cave, the surrounding rock of the entrance section is greatly deformed. Here, the micro steel pipe piles are arranged the longest and must be deeply driven into the lower rock layer. 6 piles of 27m and 33 piles of 28m are arranged.

[0023] There are 120 piles in total, each with a diameter of 168.3mm, a thickness of 10mm, a hole of 240mm, and a steel pipe spacing of 0.5m. After the construction of the micro steel pipe piles is completed, pressure grouting is carried out, the grouting pressure is 1-3MPa, the water-cement ratio is controlled to be no more than 0.5, the strength grade is C30, and one-time grouting is used.

[0024] (1) Draw construction drawings: Draw a construction plan based on the topography of the construction site.

[0025] (2) Level and clean the site; use manual labor and excavators to level and clean the micro steel pipe pile construction platform, install a drilling rig to start drilling, and first use the C6 multi-functional drilling rig to drill holes according to the geological conditions. If hole collapse occurs, use the pipe following process; after the construction is completed, inspect and protect the piles.

[0026] (3) Grouting steel pipe production and welding: Cut the material according to the depth required by the design drawings, and control the deviation value within 10mm.

[0027] (4) Positioning of micro steel pipe piles: This process uses dry drilling method to drill holes. According to the positioning of micro steel pipe piles, the drilling rig is accurately positioned at the hole location.

[0028] (5) Drilling in place: Place the multifunctional drilling rig at the designated location, level it and prevent it from tilting; lift the drill rod to the side of the drilling rig, start the drilling rig, and slowly drill the hole with a diameter of 240 mm; the drill rod needs to be connected every 3 m until the designed effective depth is reached. When the steel pipe is extended, the upper and lower sections of the steel pipe are connected by casing.

[0029] (6) Grouting machine installation: The grouting machine is fixed at the designated location on site. The power supply is connected to the designated distribution box using a 6 square three-phase five-wire cable.

[0030] (7) Install the lowered steel pipe: promptly install the prefabricated steel pipe in the hole. The steel pipe has a diameter of 168.3 mm and a wall thickness of 10 mm. A 50 mm PVC pipe is placed on the steel pipe, 200 mm above the ground, to facilitate access to the grouting pipe.

[0031] (8) Install the grouting pipe: After the steel pipe is lowered, grouting should be carried out in a timely manner. The grouting pipe is connected to the bottom of the steel pipe in the hole by a grouting machine.

[0032] (9) Mixing cement mortar: Cement mortar is mixed by special machinery, and the water-cement ratio is controlled to be no more than 0.5. The strength grade is M25. The mixed cement mortar is placed in a steel 1m*1m*1m mortar trough and then grouting is performed by a grouting machine.

[0033] (10) Grouting: The grouting pressure is 0.3Mpa, the water-cement ratio is controlled not to exceed 0.5, and one-time grouting is adopted. After the grouting pipe is lowered to the bottom of the hole, it is lifted 300mm and open grouting is carried out until pure grout emerges from the hole mouth; grouting starts from the bottom of the hole, and the grouting is pulled out while it is being poured to ensure that the grout is dense. After the grout is initially solidified, the inside and outside of the pipe wall are promptly grouted to ensure that the pile hole is completely filled.

[0034] During the construction of micro steel pipe piles, the hole depth, steel pipe length and grouting pipe length should be carefully measured to avoid false piles and broken piles. The elevation of the pile top and bottom should be strictly controlled.

[0035] 2. Casting crown beam After the construction of the micro steel pipe pile wall is completed, the top is connected with a crown beam to form a whole and bear the force together.

[0036] In slope protection projects, micro steel pipe piles are used as an important retaining structure. They mainly use drilling, steel pipe and grouting technology. After drilling, steel pipes are placed for pressure grouting. The slurry diffuses through the gaps to the surrounding rock and soil, thereby reinforcing the sliding rock and soil and improving the physical and mechanical parameters of the rock and soil. The piles and the surrounding rock and soil form a composite structure to jointly resist the thrust of the rock and soil behind the piles. In the project, it is possible to arrange a crown beam on the top of the pile, which can limit the movement of the pile top and make the shear resistance of the micro steel pipe pile better. The pile row forms a spatial frame structure through the crown beam, which enhances the integrity and improves the rigidity. The micro steel pipe pile itself has high pile rigidity and strength. The interaction between the crown beam on the pile top and the pile soil forms a more stable spatial grid. The reasonable pile spacing can effectively transmit the thrust of the soil between the piles to the pile body, and finally transmit it to the stable stratum below the unstable sliding surface through the pile body. Under reasonable design parameters, the entire spatial grid structure is equivalent to an anti-sliding retaining wall, which plays a role in protecting the slope.

[0037] Embodiment 3 Step 2 includes the following steps: side and back slope excavation, tunnel portal excavation is carried out step by step from top to bottom, the excavated earth and stone are excavated and loaded by excavators, and transported to the waste soil pile by dump trucks.

[0038] Embodiment 4 Step 3 includes the following steps: 1. Construction of waist beam: With the excavation of the soil in front of the slope, waist beams composed of double-shaped steel S355 of the HEA180 series are applied step by step. The waist beams are screwed with guide tubes with preset inclinations, holes are drilled through the tube mouths, and prestressed anchor rods are installed.

[0039] Each excavation height is between 3 and 5m. For example, the first layer of slope is excavated with a height and width of about 4.5m. Then, a waist beam made of steel is constructed on the outside of the steel pipe pile. A prefabricated guide tube with a 10° inclination is screwed on the waist beam (the inclination angle is determined according to the needs of anchor bolt installation). The waist beam and the guide tube can be welded, which is easy to operate and does not require secondary connection. They can also be threaded for easy storage and space saving. At the same time, they can be disassembled after the anchor bolt connection is completed, and the guide tube can be reused to reduce costs.

[0040] The drill rod passes through the guide tube to make a hole, and then the T1 type prestressed anchor rod is put in. The anchor rod passes through the waist beam and the micro steel pipe pile and is anchored in the surrounding rock. The anchor section is placed at a certain depth of the surrounding rock, and concrete is poured. After the concrete reaches a certain strength, the anchor rod is tensioned to apply prestress, and the anchor rod at the other end is cast and fixed with the waist beam, which can achieve the effect of isolation and sealing to protect the anchor rod; and so on, the waist beam and prestressed anchor rod are timely applied after each step of slope excavation. The combined use of the waist beam and anchor rod of the present invention can greatly reduce the loss of prestress, and at the same time reduce the sinking of the pile body of the micro steel pipe pile, so that the support capacity of the micro steel pipe pile is improved, and the effect of reducing the pile diameter can be achieved. A group of waist beams are laid after the excavation of the first layer of slope; after the excavation of the second layer of slope, it is laid once just above the tunnel entrance; with the excavation of the third layer of slope, two groups of waist beams are laid obliquely above the tunnel, and the pressure of the left tunnel is relatively large due to the bias pressure of the tunnel; after the excavation of the fourth and fifth layers of slope, waist beams are laid in the rock between the two tunnels. The waist beam is on the outside of the micro steel pipe pile. According to calculations, a guide tube with a certain inclination is prefabricated on the waist beam. The drill rod is inserted into the guide tube to drill holes. The anchor rod is passed through the waist beam and the micro steel pipe pile to anchor it in the surrounding rock. The anchor section is placed at a certain depth in the surrounding rock and concrete is poured. After the concrete reaches a certain strength, the anchor rod is tensioned to apply prestress, and the other end of the anchor rod is cast and fixed to the guide tube of the waist beam.

[0041] 2. Anchor construction: Prestressed anchors with a prestress of 300kN are applied on the waist beam to form a micro steel pipe pile-anchor support system, so that they can bear the force together, thereby protecting the rock and soil behind the slope. The anchor construction process is as follows: (1) Anchor hole measurement and placement: Use a total station to accurately measure and place the anchor hole positions according to the hole layout diagram, and position the guide tubes on the waist beam in relation to the holes.

[0042] (2) Anchor hole drilling, the drilling rig drills in an inclined manner according to the guide tube of the waist beam. The coordinate error of the hole diameter shall not be greater than 5cm, and the error of the hole slope shall not be greater than 1%. The hole diameter is 180mm. After the drilling reaches the designed depth, the drilling cannot be stopped immediately. It is required to drill steadily for 3 to 5 minutes to prevent the bottom of the hole from being pinched out. It is forbidden to drill with water when drilling anchor holes to ensure that the construction does not deteriorate the engineering geological conditions of the slope. During the drilling process, the geological conditions of each hole (rock powder conditions), penetration speed (drilling speed, drilling pressure, etc.), humidity level and some special conditions should be recorded on site. In case of hole collapse, casing follow-up combined drilling tool operation or cement slurry treatment should be used.

[0043] (3) Before cleaning the hole, use a high-pressure blower to clean the hole repeatedly and use a polyethylene tube to check the hole depth. When the dust in the hole is blown away and the hole depth is not less than the designed length of the anchor, pull out the polyethylene tube and plug the hole for later use.

[0044] (4) Anchor hole inspection: After the anchor hole is drilled, the hole diameter and hole depth must be inspected by the on-site supervisor to ensure they are qualified. The hole position, inclination and orientation of the anchor hole must also be rechecked. Only after all the sub-items of the anchor hole construction are qualified can the next process be carried out.

[0045] (5) Anchor installation: There are three types of anchors for pile walls. The anchors are T-shaped anchors with the same diameter of 180 mm, an inclination of 10°, and three total lengths. After checking and confirming that the anchor and hole numbers are consistent, first use high-pressure air to clean the hole, then slowly insert the anchor into the bottom of the hole, and install the grouting pipe together with the anchor. The pipe mouth should be kept 30 to 50 cm away from the bottom of the hole. When installing, pay attention to the following: ① Keep the anchor straight, release the force evenly, and do not swing left and right; ② Before lowering the anchor, check the quality of each anchor to ensure that there is no rust or other undesirable phenomena, and check the hole number to avoid lowering the wrong anchor.

[0046] (6) Grouting: The grouting material in the anchor hole should be M20 cement mortar, and the cement should be a mixed material of silicate cement or slag cement, with a maximum water-cement ratio of 0.5. Grouting should be carried out from the bottom of the hole to the hole mouth, and the grouting pressure should not be less than 0.6-0.8MPa to ensure that the grout in the hole is full.

[0047] (7) Tensioning: Before prestressing, the expansion and contraction of the free section should be eliminated first, and the expansion and contraction should be distributed to each level of tensioning. After the elastic deformation is eliminated by a jack, the prestressing should be tensioned normally to each level of the designed load. The anchor rod should not be pulled or moved before the mortar is completely cured. The anchor rod can only be tensioned after the anchor body reaches 80% of the designed strength.

[0048] There are three types of anchor rods for pile walls in this project, namely T1, T2 and T3. T1 anchor rods are used for supporting the upper part of the tunnel entrance, while T2 and T3 anchor rods are used in the surrounding rock sandwiched between the left and right tunnels. The diameter of the T1 anchor rod is 180mm, the inclination is 10°, and the total length is 19m, of which the free section is 15m and the anchor section is 4m; the diameter of the T2 anchor rod is 180mm, the inclination is 10°, and the total length is 17m, of which the free section is 13m and the anchor section is 4m; the diameter of the T3 anchor rod is 180mm, the inclination is 10°, and the total length is 15m, of which the free section is 11m and the anchor section is 4m.

[0049] One end of the prestressed anchor rod that applies the main force is anchored in the stable stratum, and the other end is anchored through the guide tube of the waist beam. The two are combined to bear the force together to form a pile-anchor coordinated action system.

[0050] 3. Construction of shotcrete Before spraying, use a high-pressure air duct to blow away the loose soil and debris on the spraying surface, and bury the marking nails to control the thickness of the concrete spraying; before spraying, remove loose stones or objects that block the spraying of concrete in time. The spraying operation is carried out in sections and pieces from bottom to top, and the length of each section does not exceed 6 meters. The initial spraying thickness is 4-6cm. The spraying distance is less than 0.6 meters and meets the design requirements. During spraying, the nozzle should move horizontally and slowly in a circular manner, step by step. After the sprayed concrete has been finally set for 2 hours, start water spraying maintenance (cover and keep warm immediately after the spraying has been finally set in winter), and the maintenance time is not less than 7 days.

[0051] Embodiment 5 Step 4 includes the following steps 1. Arch construction The arch is made of C35 concrete, and double rows of IPN180 I-beam steel arch frames are set inside. Each unit of the steel frame is connected by steel plates + bolts. Seamless steel pipes are installed on the connected steel arch frames as guide steel pipes for the pipe shed. The guide pipes are welded and fixed to the arch I-beams with steel bar clamps.

[0052] 2. Guide wall construction After the temporary steel frame of the portal structure is installed and welded firmly, the formwork construction shall be carried out in time. Construction measurement shall be carried out during the formwork construction to ensure the concrete thickness and the lining thickness of the next lining construction. Concrete construction shall be carried out immediately after the formwork installation is completed. Manual pouring and compaction shall be carried out with the cooperation of machinery. The pouring sequence is symmetrical pouring from both sides of the arch foot to the arch top. After the concrete pouring is completed, it shall be maintained in time, and the maintenance period shall not be less than 7 days.

[0053] 3. Construction of advanced large pipe sheds. Considering that the surrounding rock of the inlet section is weak and broken, and the burial depth is shallow, in order to prevent excessive settlement and deformation after entering the cave and damage to the micro steel pipe piles, a large pipe shed is first used for advanced support. The principle of advanced support is to drive (drill, press) the pipe shed into the formation at a certain angle around the working face, and use a grouting pump to inject slurry into it. The slurry seeps through the pipe shed and diffuses into the pores or cracks in the formation, enhancing the physical and mechanical properties of the surrounding soil. It can not only stop water, but also form a bearing shell around the working face - a self-supporting arch of the formation. At the same time, the pipe body can also play the role of an advanced anchor rod, thereby improving the self-stabilizing ability of the formation and limiting the relaxation and deformation of the formation.

[0054] Embodiment 6 Step 5 includes the following steps: 1. Broken pile A 3D laser scanner is used to locate the broken pile section. During tunnel construction, a 3D laser scanner is used to determine the broken pile section.

[0055] ① Usage: On site, ensure that the tunnel construction area is safe and there are no obstacles interfering with the scanning. Select an appropriate scanning position to ensure that the scanner can cover the entire broken pile section; install and calibrate the 3D laser scanner to ensure that its horizontal and vertical angles are correct; start the scanner and perform a full-scale scan of the broken pile section. The scanner converts the collected reflected laser points into 3D coordinate data to form a point cloud. The point cloud data contains the precise size and shape information of the broken pile section. Use 3D modeling software to process the data and analyze the shape, size and any irregularities of the section to determine the cutting line and construction plan.

[0056] ② Design and planning: According to the analysis results, design the cutting scheme for pile breaking, including cutting depth, angle and sequence. According to the designed cutting scheme, use the corresponding mechanical equipment (hydraulic wall saw) to carry out pile breaking construction. During the construction process, continuously monitor the pile breaking effect to ensure that it is consistent with the design.

[0057] Using 3D laser scanners to determine the broken pile sections during tunnel construction can greatly improve the accuracy and efficiency of construction while reducing construction risks. With accurate 3D data, the construction team can better plan and execute pile breaking work to ensure the smooth progress of the tunnel project.

[0058] The application of the micro steel pipe piles of the present invention in the design can reduce the difficulty of pile breaking and cutting, because the diameter of the micro steel pipe piles is small, and the length of the micro steel pipe piles continuously cut by the hydraulic wall saw becomes smaller, which is more labor-saving than the construction of large piles.

[0059] When cutting, start cutting from the upper end of the micro steel pipe pile and cut along the marked line. Align the saw blade of the hydraulic wall saw with the marked cutting line. During the cutting process, keep the hydraulic wall saw stable and ensure that the saw blade moves along the predetermined cutting line. When the saw blade completely passes through the micro steel pipe pile, stop the hydraulic pump and slowly pull the saw blade out of the cutting port. After the cutting is completed, clean the cutting area and remove the metal fragments generated by the cutting. And check whether the cut surface is flat, and grind or trim it if necessary. And a lifting device is required to transport the pile body cut off in the middle of the cutting to ensure the safety of the site.

[0060] 2. Full-section excavation The project was designed and constructed based on the "New Idea Method", and the excavation of the entire tunnel was carried out using the full section method. The specific construction steps for the excavation of the tunnel portal section are as follows: (1) Depending on the groundwater conditions, if necessary, place a drainage pipe in front of the face; (2) Use mechanical excavation or blasting excavation to carry out full-section excavation with a maximum cycle advance of 2.4m; (3) Carry out initial support; (4) Repeat steps 2 and 3 to complete the pre-specified cycle; (5) Excavation and casting of side wall guides and tunnel inverts; (6) Carry out secondary lining construction.

[0061] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A tunnel portal side slope micro steel pipe pile-anchor support construction method, comprising: Step 1: First construct micro steel pipe piles and cast the crown beam; Step 2: Slope cutting; Step 3: As the slope is excavated step by step, the waist beam and anchor rods are constructed; After the first layer of slope is excavated, a waist beam is constructed on the outside of the steel pipe pile. An inclined guide tube is provided on the waist beam. The drill rod passes through the guide tube to drill an inclined anchor hole, and the prestressed anchor rod is put in. The anchor rod passes through the guide tube and the micro steel pipe pile on the waist beam and is anchored in the surrounding rock. The anchor section is placed deep in the surrounding rock, and concrete is poured. After the concrete solidifies, the anchor rod is tensioned to apply prestress, and the anchor rod at the other end is cast and fixed to the guide tube of the waist beam; and so on. After each step of slope excavation, the waist beam and prestressed anchor rod are constructed in time; Step 4: Advanced large pipe shed construction; Step 5: Break piles and excavate the entire section.

2. The tunnel portal section side slope micro steel pipe pile-anchor support construction method according to claim 1 is characterized by: In the step 1, the hole position is checked by drilling, and the micro steel pipe pile is installed after the inspection is qualified. After the installation, grouting construction is carried out. After the micro steel pipe pile wall is completed, the top is connected with a crown beam; The length of the steel pipe is 10-28m. 120 Φ168 steel pipes are set with a spacing of 0.5m. The length of the micro steel pipe piles varies according to their location. On both sides, the pile length is the shortest due to the smaller thrust of the supporting soil. The surrounding rock deformation in the tunnel entrance section is large, and the micro steel pipe piles here are the longest.

3. The tunnel portal section side slope micro steel pipe pile-anchor support construction method according to claim 1 is characterized by: In the step 2, the side and back slopes are excavated, and the tunnel entrance is excavated step by step from top to bottom.

4. The tunnel portal section side slope micro steel pipe pile-anchor support construction method according to claim 1, characterized in that: In the step three, as the soil in front of the slope is excavated, a waist beam composed of double-shaped steel S355 of the HEA180 series is applied step by step, a guide pipe with a preset inclination is screwed onto the waist beam, a hole is drilled through the pipe mouth, and a prestressed anchor rod is applied.

5. The tunnel portal side slope micro steel pipe pile-anchor support construction method according to claim 4 is characterized by: In the step three, a prestressed anchor rod with a prestress of 300 kN is applied on the waist beam to form a micro steel pipe pile-anchor rod support system, which is stressed together to protect the rock and soil behind the slope.

6. The tunnel portal section side slope micro steel pipe pile-anchor support construction method according to claim 5, characterized in that: In step 3, the anchor bolt construction process includes: (1) Anchor hole measurement and placement; (2) Anchor hole drilling; (3) Cleaning holes; (4) Anchor hole inspection; (5) Anchor bolt installation; (6) Grouting; (7) Tensioning.

7. The tunnel portal section side slope micro steel pipe pile-anchor support construction method according to claim 6, characterized in that: When installing the anchor rod, the hole is cleaned with high-pressure air, and then the anchor rod is slowly inserted into the bottom of the hole. The grouting pipe is installed together with the anchor rod, and the pipe mouth is kept at a distance of 30 to 50 cm from the bottom of the hole.

8. The tunnel portal side slope micro steel pipe pile-anchor support construction method according to claim 6, characterized in that: When drilling the anchor hole, the drill passes through the guide tube on the waist beam to keep the inclination and azimuth accurate. The borehole diameter is 180 mm. After reaching the designed depth, the drill is steady for 3 to 5 minutes to prevent the bottom of the hole from pinching out.

9. The tunnel portal side slope micro steel pipe pile-anchor support construction method according to claim 1, characterized in that: In the step 4, a multifunctional drilling rig is used to drill holes in the guide pipe, the diameter of the holes is 135 mm, and the drilling sequence is from high hole position to low hole position; high-pressure air is used to clean the drill slag from the bottom of the hole to the hole mouth; the pipe-roof steel pipe is installed, and the pipe-roof steel pipe is pushed in by a machine. After the pipe-roof steel pipe is pushed into place, the gap between the pipe-roof steel pipe and the guide steel pipe is sealed with an anchor to prevent grouting during grouting; the grouting steel flower pipe is connected to the grouting stopper.

10. The tunnel portal side slope micro steel pipe pile-anchor support construction method according to claim 1, characterized in that: In the step 5, a three-dimensional laser scanner is used to determine the contour line of the broken pile, and then a hydraulic wall saw is used to cut the micro steel pipe pile along the line.

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