Close-connection rapid construction method for urban large-section ultra-shallow-buried excavation tunnel

Abstract

The invention discloses an urban large-section ultra-shallow-buried underground excavation tunnel approaching rapid construction method. The method comprises the following steps that S1, construction preparation is conducted; s2, an advanced large pipe shed is constructed; s3, reinforcing and grouting the bridge pile; s4, when the distance L between the tunnel face and the bridge pile in the longitudinal direction of the tunnel is larger than 3 m, the soil body around the tunnel is reinforced through full-section curtain grouting, otherwise, the soil body around the tunnel is reinforced through ground surface grouting, and compensation grouting in the tunnel is conducted according to the excavation condition of the tunnel; s5, tunnel excavation; during tunnel excavation, the tunnel is divided into a left pilot tunnel, a middle pilot tunnel and a right pilot tunnel, and meanwhile, the pilot tunnels are further divided into multiple steps for cyclic excavation; primary supporting and temporary supporting are conducted immediately after excavation of all the pilot tunnels is completed; and when the deformation displacement degree of the tunnel is gradually reduced, the temporary support is removed, an inverted arch is constructed, and the secondary lining is tightly followed. Therefore, under various auxiliary construction methods for tunnel construction, the self-stabilization capability of the soil covering stratum of the tunnel can be effectively improved, and the construction safety and the construction efficiency are improved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, in particular to a close-joint rapid construction method for an urban large-section ultra-shallow buried dark-excavated tunnel. Background Art

[0002] With the continuous development of urban underground space construction in my country, the number of tunnel projects passing under urban roads and bridges is increasing. When tunnels pass under existing structures, it will have a great impact on the safety of the tunnel construction itself and the stability of the structures being passed through.

[0003] Especially when the tunnel section is large, the burial depth is very shallow, and the surrounding rock grade is poor, the double side wall pilot method is usually selected for excavation.

[0004] The double-side wall pilot tunnel method divides the tunnel into three pilot tunnel cycles: left, middle and right. The pilot tunnels on both sides are staggered and excavated in sequence. At the same time, the pilot tunnel is further divided into multiple steps for cyclic excavation. The principle of this method is to reduce the disturbance to the surrounding rock by dividing the large section into multiple small sections.

[0005] However, in the prior art, the simultaneous excavation of the pilot pits in this method usually requires that the pilot pits be staggered by at least 30m, and there is also a certain distance between the steps in each pilot pit. Therefore, the distance between the initial excavation chamber and the final excavation chamber of the tunnel is very far, and the length of the urban shallow buried tunnel section is usually short, so there is a situation where the upper steps of the left pilot pit have been penetrated, while the lower steps of the middle pilot pit are just excavated, which will lead to the initial support and closure time of the tunnel being prolonged, the construction efficiency is low, which greatly affects the overall stability of the tunnel and the surrounding rock, and is bound to affect the safety of the structure being traversed.

[0006] Therefore, the patent of the present invention proposes a method for close and rapid construction of large-section ultra-shallow buried dark-excavated tunnels in cities, which effectively solves the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a method for rapid close-proximity construction of large-section ultra-shallow buried dark-excavated tunnels in cities, which can effectively improve the self-stabilization capacity of the tunnel overlying stratum, ensure the safety of the tunnel under close-proximity construction, and effectively shorten the construction period.

[0008] In order to achieve the above object, the solution of the present invention is: A rapid construction method for a large-section ultra-shallow buried tunnel in an urban area, comprising the following steps: S1. Construction preparation; S2, advanced large pipe shed construction; S3, bridge pile reinforcement grouting: reinforcement grouting is carried out around the bridge pile cap within the influence range of tunnel excavation; S4, full-section curtain grouting or surface grouting + in-hole compensation grouting; When the distance L between the tunnel face and the bridge pile along the longitudinal direction of the tunnel is greater than 3m, full-section curtain grouting is used to reinforce the soil around the tunnel. Otherwise, surface grouting is used to reinforce the soil around the tunnel, and in-tunnel compensatory grouting is performed according to the tunnel excavation conditions. S5, tunnel excavation, and multiple cycles of step S4 and step S2 are performed according to the length of the tunnel; during the tunnel excavation, the tunnel is divided into three pilot pits, left, middle and right, and the pilot pits on the left and right sides are staggered and first excavated, and at the same time, the pilot pit is further divided into multiple steps for cyclic excavation; the tunnel excavation process is divided into first excavating the far-end pilot pit away from the bridge pile, then excavating the near-end pilot pit close to the bridge pile, and then excavating the middle pilot pit, and at the same time, after the steps of each pilot pit are excavated for 0.5-1m, initial support and temporary support are immediately carried out; when the deformation displacement degree of the tunnel gradually converges, the temporary support is removed, the initial support is retained, the invert is constructed, and the secondary lining is kept closely.

[0009] Furthermore, the construction sequence in step S5 is as follows: S51, excavate the far end pilot pit first, and then excavate the upper and middle steps together. Apply initial support and temporary support after every 0.5m of excavation, and stop after 3m of excavation. S52, excavate the lower step of the far pilot pit, with a circular advance of 1m. After each 1m of excavation, carry out initial support and temporary support. After 3m of excavation, the far pilot pit excavation section is closed into a ring, and the far pilot pit construction is suspended; S53, excavate the near-end pilot pit, and excavate the upper and middle steps together. Apply initial support and temporary support after every 0.5m of excavation, and stop after 3m of excavation; S54, excavate the lower step of the near-end pilot pit, with a circular advance of 1m. After each 1m of excavation, carry out initial support and temporary support. After 3m of excavation, the excavation section of the near-end pilot pit is closed into a ring, and the construction of the near-end pilot pit is suspended; S55, excavate the upper steps of the pilot pit, cycle the advance by 0.5m, apply initial support after every 0.5m of excavation, and stop after 3m of excavation; S56, excavate the middle step of the middle pilot pit, cycle advance 0.5m, and pause after excavating 3m; S57, excavate the lower step of the middle pilot pit, cycle advance 0.5m, apply initial support after every 0.5m of excavation, pause after 3m of excavation, and the 3m tunnel excavation section has been closed into a ring; Repeat the above steps and remove the temporary support when the initial support deformation converges to no more than 0.2mm / d; remove the temporary support every three times and observe the deformation and deformation rate of the tunnel at the same time. When the deformation and deformation rate of the tunnel do not exceed 0.2mm / d within 24 hours, remove the remaining temporary supports one by one; The longitudinal length of each temporary support removal is the length of the tunnel secondary lining formwork trolley. After the removal is completed, the invert arch, invert arch filling and secondary lining are carried out in a timely manner.

[0010] Furthermore, the step S3 includes the following steps: S31. Grouting test Before the construction of bridge pile reinforcement grouting, several holes are taken for grouting test to verify whether the grouting slurry diffusion radius, grouting final pressure, slurry setting time, slurry mix ratio, slurry single hole design quantity and solid soil radius are reasonable, and to determine the grouting construction process, technical parameters and inspection effect; only after the test verification is reasonable, the grouting control can be carried out according to the selected parameters; S32. Determine the grouting range First determine the number of viaduct piles within the tunnel underpass impact area; perform grouting reinforcement on the bridge pile foundations where the horizontal straight-line distance between the bridge piles and the tunnel excavation contour line is less than 1.5 times the tunnel diameter, which refers to the maximum width of the tunnel contour section; S33, drilling Two rows of grouting holes are arranged around each cap. The first row of grouting holes is 80-100 cm away from the edge of the cap. The second row of grouting holes is staggered with the first row of grouting holes, and the spacing between adjacent grouting holes is 50-100 cm. The opening diameter of the grouting holes is not less than 100 mm, and the final hole diameter is not less than 60 mm. Among them, the spacing between the grouting holes on the cap side close to the tunnel excavation contour line is arranged at 50-80 cm, and the spacing between the drilled holes on other cap sides is arranged at 80-100 cm. S34, Grouting In addition, backward grouting and integrated drilling and grouting are adopted. Cement slurry grouting is used to reinforce the 2m range around the viaduct pile cap. The grouting depth covers the height of the tunnel. The grouting is done first around the periphery and then in the middle, and the grouting is done symmetrically around the cap.

[0011] Furthermore, in step S4, when full-section curtain grouting is adopted, the grouting length of each cycle of the full-section curtain grouting is 15m, the excavation is 12m, the grouting overlap is 3m, the grouting diffusion radius is 0.7m, the grouting hole spacing is 0.8m, the number of grouting holes is determined according to the size of the tunnel section, the grouting hole opening diameter is not less than 108mm, the final hole diameter is not less than 90mm, the orifice pipe is a hot-rolled seamless steel pipe, the orifice pipe is firmly buried with the help of an anchor, and a slurry stop valve is welded on the orifice pipe; the grouting material within the tunnel excavation contour line is pure cement slurry, and cement-water glass double slurry is used outside the tunnel excavation contour line; the curtain grouting reinforcement range is 3m outside the tunnel excavation contour line to form a water-stop curtain.

[0012] Furthermore, when the first cycle of full-section curtain grouting is carried out after the construction of the first cycle of pipe shed is completed, ensure that the heading face is level before grouting, hang a mesh to spray and seal the heading face, and carry out full-section curtain grouting of the upper and lower steps. The number of grouting holes is determined according to the size of the tunnel section; the subsequent cycle of full-section curtain grouting construction is carried out after the corresponding pilot pit is excavated to the corresponding mileage section. After each pilot pit is excavated to the grouting mileage, the heading face is hung with shotcrete for the first time as a grouting stop wall.

[0013] Further, in step S4, when surface grouting + in-tunnel compensatory grouting is adopted, the surface grouting is carried out on the surface above the tunnel, the surface grouting width is 3m outward from the tunnel excavation contour line, the grouting depth is 2m below the bottom of the tunnel invert, the grouting holes are arranged in a plum blossom shape with a spacing of 1.5m, and the grouting diffusion radius is calculated as 0.8m; the grouting material is cement-water glass double liquid slurry; the in-tunnel compensatory grouting is carried out on the steps below the left and right guide pits of the tunnel, the grouting width of the in-tunnel compensatory grouting is 3m outward from the contour line, the grouting depth is 2m below the bottom of the invert, the hole spacing is 1.5m, and the grouting diffusion radius is calculated as 0.8m; wherein a temporary middle partition wall is formed between the left and right guide pits after excavation, and the holes close to the temporary middle partition wall are grouted obliquely downward toward the middle guide pit; the holes close to the heading face are grouted obliquely downward toward the heading face; the grouting material is cement-water glass double liquid slurry.

[0014] Furthermore, in the construction preparation of step S1, the following operations are performed: S11. Dig a foundation pit at the predetermined location, set up intercepting ditches around the top of the foundation pit to intercept surface water and prevent it from flowing into the foundation pit and scouring the slopes; set up drainage ditches in the foundation pit, set up water collection pits every 100m, and equip the water collection pits with water pumps to prevent water accumulation in the pit; S12. Pipeline relocation: If there are municipal pipelines in the construction area where the tunnel passes under the road in the city, the pipelines will be relocated outside the construction area; S13. Traffic organization: set up warning signs and fences on the surface of the construction area, restrict the passage of heavy-loaded vehicles, and turn off red lights at intersections.

[0015] Furthermore, the advanced large pipe shed construction in step S2 is performed by performing the following steps: S21. Construction of arch At the starting section of tunnel excavation, a sleeve arch is constructed as the guide wall of the first circulation pipe shed. Four I-beams are arranged in the sleeve arch, spaced longitudinally. The base is compacted and reinforced before erection. The bearing capacity of the sleeve arch base should be greater than 250kPa, otherwise concrete is added to expand the foundation. The I-beams are connected longitudinally with steel bars to form an arch frame, which is welded firmly. Several guide pipes are arranged along the arch frame. The guide pipes have an elevation angle of 2° and are parallel to the central axis of the tunnel excavation direction. The guide pipes and the arch frame are welded firmly with steel bars to prevent displacement when pouring the sleeve arch concrete. Thick wooden boards are used to build the sleeve arch formwork, and three I-beams are used to form a steel support under the bottom formwork. The sleeve arch concrete is poured symmetrically on both sides to avoid bias pressure that causes the cross-section center and elevation of the guide wall to be incorrect. The core soil in the middle of the tunnel is reserved at the sleeve arch, and the bottom formwork is supported by round logs on the core soil. In the second cycle, if the tunnel has been excavated for a certain distance, a pipe shed workshop will be formed in the tunnel to provide working space for the second cycle of advanced large pipe shed drilling; S22, drilling Before drilling, mark the hole numbers on the guide wall and pipe shed studio. Drill the odd-numbered holes first, install the steel pipe and grout the odd-numbered holes before drilling the even-numbered holes. Check the grouting quality of the odd-numbered holes when drilling the even-numbered holes. In order to prevent the hole from collapsing during the drilling operation, the drilling operation adopts the pipe-following drilling method. The external insertion angle of the first cycle pipe shed is 2°, and the external insertion angle of the second and third cycle pipe sheds is 6°. The diameter of the drill bit is larger than the guide pipe. After drilling, sweep the hole back and forth to remove the scum to the bottom of the hole to ensure that the hole diameter and hole depth meet the requirements and prevent blockage. S23, Grouting Grouting is carried out after the hole is drilled. A grouting field test should be carried out before grouting. The grouting parameters should be determined according to the actual situation through field tests. Grouting can be terminated only after ensuring that the rock mass around the borehole and the pores around the steel pipe are filled with slurry. After grouting, the slurry in the pipe should be removed in time and filled densely with cement mortar.

[0016] After adopting the above technical scheme, the grouting mode is adjusted according to different construction conditions through the dynamic grouting method to effectively ensure the safety of the tunnel under close construction. In the case that the urban large-section ultra-shallow buried dark-cut tunnel needs to pass under the urban bridge, the bridge piles are reinforced and grouted in advance to improve the stability of the soil layer within the construction range, and when the tunnel face is more than 3m away from the bridge piles along the longitudinal direction of the tunnel, the full-section curtain grouting is used to reinforce the soil around the tunnel to improve the construction safety. When the tunnel face is within 3m away from the bridge piles along the longitudinal direction of the tunnel, in order to prevent the full-section curtain grouting from producing a more significant horizontal squeezing effect on the surrounding bridge piles, resulting in greater additional stress on the bridge piles, surface grouting is used instead. Since the surface grouting has a poor reinforcement effect on the soil at a deeper level, when the tunnel is excavated, in-hole compensation grouting is carried out according to the excavation of the lower steps of the tunnel, so as to achieve a good reinforcement effect and improve construction safety.

[0017] In addition, during the tunnel excavation process in this scheme, the soil parameters in the tunnel excavation area are significantly improved through the dynamic grouting method, which reduces the influence between the excavation chambers of the double-sidewall pilot method, thereby greatly reducing the distance between the tunnel pilot and the steps in the pilot. This not only speeds up the construction progress and reduces the waiting time for the subsequent pilot excavation, but also effectively increases the mechanical construction space of the tunnel, further speeds up the tunnel construction efficiency, and effectively shortens the construction period. At the same time, the initial support of the tunnel can be ringed earlier, giving full play to the initial support bearing capacity, maintaining the safety and stability of the tunnel construction, and fully ensuring the uninterrupted surface traffic, which has significant social and economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a method flow chart of an embodiment of the present invention; Figure 2 A schematic diagram of a tunnel pilot pit according to an embodiment of the present invention; Figure 3 A schematic diagram of a cap reinforced by grouting of bridge pile reinforcement according to an embodiment of the present invention; Figure 4 A schematic diagram of grouting locations for grouting to reinforce bridge piles according to an embodiment of the present invention; Figure 5 A schematic diagram of the drilling positions on the periphery of the cap for the bridge pile reinforcement grouting according to an embodiment of the present invention; Figure 6 It is a front view schematic diagram of drilling grouting of full-section curtain grouting according to an embodiment of the present invention; Figure 7 It is a cross-sectional schematic diagram of drilling and grouting of full-section curtain grouting according to an embodiment of the present invention; Figure 8 A schematic diagram of the scope of surface grouting in an embodiment of the present invention; Fig. 9 Schematic diagram of hole positions for compensatory grouting in a hole according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] 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.

[0020] refer to Figure 1 As shown, a method for rapid construction of a large-section ultra-shallow buried tunnel in an urban area in this embodiment includes the following steps: S1. Construction preparation; S2, advanced large pipe shed construction; S3, bridge pile reinforcement grouting: reinforcement grouting is carried out around the bridge pile cap within the influence range of tunnel excavation; S4, full-section curtain grouting or surface grouting + in-hole compensation grouting; When the distance L between the tunnel face and the bridge pile along the longitudinal direction of the tunnel is greater than 3m, full-section curtain grouting is used to reinforce the soil around the tunnel. Otherwise, surface grouting is used to reinforce the soil around the tunnel, and in-tunnel compensatory grouting is performed according to the tunnel excavation conditions. S5, tunnel excavation, and multiple cycles of step S4 and step S2 are performed according to the length of the tunnel; during the tunnel excavation, the tunnel is divided into three pilot pits, left, middle and right, and the pilot pits on the left and right sides are staggered and first excavated, and at the same time, the pilot pit is further divided into multiple steps for cyclic excavation; the tunnel excavation process is divided into first excavating the far-end pilot pit away from the bridge pile, then excavating the near-end pilot pit close to the bridge pile, and then excavating the middle pilot pit, and at the same time, after the steps of each pilot pit are excavated for 0.5-1m, initial support and temporary support are immediately carried out; when the deformation displacement degree of the tunnel gradually converges, the temporary support is removed, the initial support is retained, the invert is constructed, and the secondary lining is kept closely.

[0021] Thus, this embodiment can adjust the grouting mode according to different construction conditions through the dynamic grouting method, and effectively ensure the safety of the tunnel under close construction. First, for the situation where the urban large-section ultra-shallow buried dark-cut tunnel needs to pass under the urban bridge, the bridge piles are reinforced and grouted in advance to improve the stability of the soil layer within the construction range, and when the tunnel face is more than 3m away from the bridge piles along the longitudinal direction of the tunnel, the full-section curtain grouting is used to reinforce the soil around the tunnel to improve the construction safety. When the tunnel face is within 3m away from the bridge piles along the longitudinal direction of the tunnel, the full-section curtain grouting has a more significant horizontal squeezing effect on the surrounding bridge piles, resulting in a large additional stress on the bridge piles, so it is necessary to change to surface grouting. Since the surface grouting has a poor reinforcement effect on the soil at a deeper layer, when the tunnel is excavated, the in-hole compensation grouting is carried out according to the excavation of the lower step of the tunnel, so as to achieve a good reinforcement effect and improve construction safety.

[0022] In summary, under various tunnel construction auxiliary methods, the rapid construction method of the present invention can effectively improve the self-stabilizing ability of the tunnel overburden layer, improve construction safety and efficiency, ensure the passage of small vehicles on surface roads, and has significant social and economic value.

[0023] The step S1 construction preparation includes the following steps: 1) Set up intercepting ditches around the top surface of the foundation pit to intercept surface water and prevent it from flowing into the foundation pit and scouring the slope. Set up drainage ditches in the foundation pit, set up water collection pits every 100m, and equip the water collection pits with water pumps to prevent water accumulation in the pit.

[0024] 2) Pipeline relocation. Since municipal pipelines usually exist in the construction area where tunnels pass under the road surface in the city, in order to avoid the impact of grouting on existing pipelines, the pipelines are relocated outside the affected area.

[0025] 3) Traffic organization: The thickness of the soil covering the top of the ultra-shallow tunnel is extremely small, and there are certain safety hazards caused by the heavy vehicles on the surface road. Therefore, warning signs and fences are set up on the surface to restrict the passage of heavy vehicles such as large trucks, and red lights at intersections are closed to avoid vehicle congestion and excessive surface load.

[0026] After the construction preparation is completed, a large advance pipe shed is constructed before excavation. The arch effect formed by the pipe shed is used to effectively resist the settlement of the overlying soil and part of the surface load during the tunnel excavation process.

[0027] Specifically, the step S2 of implementing the large pipe shed in advance includes the following steps: Construction of the arch: The arch is constructed at the starting section of the tunnel excavation as the guide wall of the first circulation pipe shed. The cross-sectional size of the arch is 0.8m×2m (thickness×length). There are 4 I22b I-beams in the arch. The longitudinal spacing of the steel frame is 50cm. Each arch frame consists of 7 units. The base is compacted and reinforced before the steel support is erected. The bearing capacity of the arch base should be greater than 250kPa, otherwise C15 rubble concrete is added to expand the foundation. Each I-beam is connected longitudinally with steel bars to form an arch frame and welded firmly. Several guide pipes are set along the arch frame. The guide pipes are Φ203mm×5mm, 2.0m long steel pipes, with a circumferential center spacing of 25cm, an elevation angle of 2°, and a direction parallel to the central axis of the tunnel excavation direction. Φ12 steel bars are used to weld the guide pipes and the arch frame firmly to prevent displacement when pouring the arch concrete. The arch formwork is constructed with 5cm thick wooden boards, and three 20a I-beams are used to form steel supports under the bottom formwork. The arch concrete is poured symmetrically on both sides to avoid bias pressure that may cause the cross-section center and elevation of the guide wall to be incorrect. In order to meet the requirements of bearing the deadweight of concrete and construction loads and ensure the stability of the bottom formwork support arch frame, the core soil in the middle of the tunnel is reserved at the arch, and 10cm diameter round wood (1m spacing) is used on the core soil to support the steel support of the bottom formwork.

[0028] In the second cycle, if the tunnel has been excavated for a certain distance, a pipe shed workshop will be formed in the tunnel to provide working space for the second cycle of advanced large pipe shed drilling; 2) Drilling Before drilling, mark the hole numbers on the same circulation guide wall and pipe shed studio. Drill the single-numbered holes first, install the steel flower pipe and grout the single-numbered holes, and then drill the double-numbered holes. The grouting quality of the single-numbered holes can be checked when drilling the double-numbered holes. In order to prevent the hole from collapsing during the drilling operation, the drilling operation adopts the pipe-following drilling. The external insertion angle of the first circulation pipe shed is 2°, and the external insertion angle of the second and third circulations is 6°. In order to facilitate the installation of steel pipes, the drill bit diameter is larger than the steel flower pipe of the guide pipe. When the drilling rig starts drilling, it can be low-speed and low-pressure. After the hole is 1.0m deep, the drilling speed and wind pressure can be gradually adjusted according to the geological conditions. Use drilling cuttings for geological judgment and description, as a geological pre-exploration forecast for the excavation of the cave body, and can be used as a basis for guiding the excavation of the cave body. After drilling, use the geological core drill rod and the drill bit to sweep the hole back and forth, remove the scum to the bottom of the hole, ensure that the hole diameter and hole depth meet the requirements, and prevent blockage. Use high-pressure gas to clean the drilling cuttings from the bottom of the hole to the hole mouth. Use total station, inclinometer, etc. to detect hole depth, inclination, and external insertion angle.

[0029] 3) Grouting Grouting can be carried out after the hole is drilled. Before grouting, a grouting field test should be carried out first. The grouting parameters should be determined according to the actual situation through field tests to facilitate construction. Grouting materials: cement slurry water-cement ratio 1:1~1:1.5. Use KB-50 / 70 hydraulic grouting machine for grouting, the grouting pressure is 0.7MPa~1.0MPa, the grouting pressure gradually increases, the final pressure is 1.0MPa, and the grouting is stopped after holding the pressure for 5 minutes. The grouting volume is generally 1.5 times the borehole cylinder. If the grouting volume exceeds the limit and does not meet the grouting pressure requirements, the slurry concentration should be adjusted to continue grouting until it meets the grouting quality standards, ensuring that the rock mass around the borehole and the pores around the steel pipe are filled with slurry before grouting can be stopped. After the grouting is completed, the slurry in the pipe should be removed in time, and filled with M30 cement mortar to enhance the rigidity and strength of the pipe shed.

[0030] See also Figure 3 , Figure 4 and Figure 5 The step S3 of bridge pile reinforcement grouting comprises the following steps: 1) Grouting test Before grouting construction, 2 to 3 holes are taken for grouting test to verify whether the grouting slurry diffusion radius, grouting final pressure, slurry setting time, slurry mix ratio, slurry single hole design quantity and soil solid radius are reasonable, and to determine the grouting construction process, technical parameters and inspection effect. Grouting control can only be carried out according to the selected parameters after the test verification is reasonable.

[0031] 2) Determine the grouting range Determine the number of viaduct pile foundations within the influence range of the tunnel underpass, and determine it within 1.5 times the tunnel diameter. Grouting reinforcement is performed on the bridge pile foundations within 1.5 times the tunnel diameter. The tunnel diameter refers to the maximum width of the contour section in the tunnel. Grouting reinforcement is performed with 1:1 cement slurry within 2m around the cap, and the grouting depth is 15m (7.5m above and below the tunnel centerline, covering the tunnel height). The cap reinforced by grouting is as follows Figure 3 and Figure 4 shown.

[0032] 3) Drilling The backward grouting is adopted, and the drilling and grouting are integrated. Two rows of grouting holes are arranged around each cap. The first row of grouting holes is about 80-100cm away from the edge of the cap. The second row of grouting holes is staggered with the first row of grouting holes. The diameter of the grouting holes is 100mm and the spacing is 50-100cm. The opening diameter of the grouting hole is not less than 100mm, and the final hole diameter is not less than 60mm. Through the grouting sleeve and high-pressure ball valve, start drilling. After drilling to the designed depth, increase the amount of water to flush the drill cuttings and mud and sand. Stop drilling after all the drill cuttings are flushed out. At the hole mouth, remove the drill rod, put the grouting plug and grouting pressure cap on the drill rod, and then push the grouting plug into the grouting sleeve with force, put on the pressure cap and connect the bolts to ensure that the inner and outer walls of the grouting plug are tightly combined with the outer wall of the drill rod and the inner wall of the grouting sleeve to play a grouting role. For surface grouting, the hole is swept up and down every 2-5m of drilling. After the hole is cleaned, insert the drill rod into the bottom of the hole and sweep the hole up and down once. See the diagram of the grouting hole sequence and grouting hole arrangement for details. Figure 5 .

[0033] 4) Grouting The 2m range around the viaduct cap is reinforced by 1:1 cement slurry grouting, with a grouting depth of 15m and a grouting pressure of 0.7-1.0MPa. The drilling spacing on the cap side close to the tunnel excavation contour line is 0.5-0.8m, and the drilling spacing on other cap sides is 0.8-1.0m. Grouting is first done around the periphery and then in the middle, and grouting is done symmetrically around the cap. Grouting end standard: When the grouting pressure of a single hole reaches 1.5 times the design final pressure and continues grouting for more than 10 minutes, the grouting of this hole can be ended. After the grouting is completed, an inspection hole is drilled within 2m around the cap to monitor the grouting effect.

[0034] See also Figure 6 and Figure 7In step S4, for bridge pile foundations with a distance between the bridge pile foundation and the tunnel greater than 3m, full-section curtain grouting can be used. The grouting length of each cycle of curtain grouting is 15m, the excavation is 12m, the grouting overlap is 3m, the grouting diffusion radius is 0.7m, the grouting hole spacing is 0.8m, and there are 204 grouting holes in total. The specific number of grouting holes can be determined according to the size of the tunnel section. The opening diameter of the grouting hole is not less than 108mm, and the final hole diameter is not less than 90mm. The orifice pipe adopts a Φ110×5mm hot-rolled seamless steel pipe with a pipe length of 3m. The orifice pipe is firmly buried with the help of an anchor, and a grout stop valve is welded on the orifice pipe. The grouting material within the tunnel excavation contour line is pure cement slurry, and cement-water glass double slurry is used outside the excavation contour line. The grouting pressure is the hydrostatic pressure plus 0.5~1.5MPa. Cement slurry ratio: cement: water = 1:1 (weight ratio); grouting slurry ratio: cement slurry: water glass = 1:1 (volume ratio), grouting pressure is 1.5 ~ 2.0MPa. The curtain grouting reinforcement range is 3m outside the tunnel excavation contour line, forming a water-stop curtain to achieve the purpose of blocking water and reinforcing the soil. Grouting construction is carried out through grouting tests and other measures, and the specific implementation can be reasonably adjusted according to the actual situation and design requirements.

[0035] After the first cycle of pipe-roof construction is completed, the first cycle of full-section curtain grouting is carried out. Before grouting, ensure that the face is level, hang a mesh to seal the face, and carry out curtain grouting of the upper and lower steps, with a total of 204 grouting holes; subsequent cycle curtain grouting construction is carried out according to the corresponding pilot pit excavation to the mileage section. After each pilot pit is excavated to the grouting mileage, the face is hung with shotcrete for the first time as a grouting stop wall. The left and right guide pits are set with 6 rings of 54 grouting holes, the upper and middle guide pits are set with 7 rings of 59 grouting holes, and the middle and lower guide pits are set with 6 rings of 37 grouting holes.

[0036] The grouting method adopts backward grouting, and drilling and grouting are integrated; forward grouting is used when the rock layer in front is relatively broken and easy to cause hole collapse. The overall idea of ​​drilling and grouting is to drill and grout from the outside to the inside, first from the bottom and then from the top, drill and grout every other hole in the same circle, grout while drilling, grouting in time, and reduce the exposure time of empty holes. When water gushing or drill stuck due to rock layer breaking during drilling, drilling should be stopped, and grouting and hole sweeping should be carried out before drilling.

[0037] See also Figure 8 and Fig. 9 In step S4, when the distance between the bridge pile foundation and the tunnel is less than 3m, in order to ensure that the pile foundation of the viaduct and the traffic on the road are not affected by the grouting operation, the scheme of "surface grouting as the main method and in-tunnel compensation grouting as the auxiliary method" is adopted, and the surface grouting absorption rate is controlled at 20%.

[0038] Surface grouting is carried out on the surface above the tunnel. The width of the grouting is 3m outward from the contour line, the grouting depth is 2m below the bottom of the invert, the hole spacing is 1.5m in a plum blossom shape, and the grouting diffusion radius is calculated as 0.8m; there are 125 grouting holes in the left tunnel and 126 grouting holes in the right tunnel. The specific hole locations are shown in Figure 8 Grouting drilling cross-section diagram. The grouting material is cement-water glass double liquid slurry, the volume ratio of cement: water glass is 1: (0.6-1), and the mass ratio of cement: water: water glass is 385:385:685.

[0039] When the grouting volume reaches more than 1.5 times the expected grouting volume of a single hole and the pressure still does not rise, intermittent grouting and other measures can be taken to make the pressure reach the designed final pressure and end the grouting of the hole. When the grouting pressure reaches the designed 2MPa~2.5MPa, stop grouting in the hole and change the hole for grouting.

[0040] Since the reinforcement effect of surface grouting on deeper strata will be weakened, compensatory grouting is carried out in the tunnel according to the actual excavation conditions of the tunnel. In this case, the grouting effect of the invert arch and temporary middle partition wall was not obvious, resulting in landslides and water seepage.

[0041] Therefore, the in-tunnel compensatory grouting is carried out at the lower steps of the left and right pilot pits of the tunnel. The grouting width is 3m outward from the contour line, the grouting depth is 2m below the bottom of the invert arch, the hole spacing is 1.5m, and the grouting diffusion radius is calculated as 0.8m. For specific hole positions, see Fig. 9 Grouting drilling plan, the construction sequence of the compensation grouting method in the tunnel is that the grouting of holes 1 to 5 is slanted downward toward the face, and the grouting holes 1 and 2 expand outward at the same time, covering the area 3m outside the tunnel and within 2m of the bottom. The grouting holes 6 and 7 are drilled after the excavation of the lower step of the tunnel, aiming at the temporary middle partition formed between the left and right guide pits after excavation, and the direction is slanted downward toward the middle guide pit, covering the soil within 2m of the bottom. The grouting material is cement-water glass double liquid slurry, the volume ratio of cement: water glass is 1: (0.6-1), and the mass ratio of cement: water: water glass is 385:385:685.

[0042] After the advanced large pipe shed, bridge pile reinforcement grouting, and full-section curtain grouting are completed, the main tunnel is excavated. The tunnel excavation method in step S5 can refer to the double-side wall pilot method and be improved, with mechanical excavation as the main method and manual pneumatic pick as the auxiliary method. Figure 2 After each excavation, the initial support is immediately applied. Assuming that the right side of the tunnel is closer to the bridge pile, the specific improved construction sequence is as follows: S51, excavate the far end pilot pit (left pilot pit) first, and then excavate the upper and middle steps together. Apply initial support and temporary support after every 0.5m of excavation, and stop after 3m of excavation. S52, excavate the lower step of the far pilot pit, with a circular advance of 1m. After each 1m of excavation, carry out initial support and temporary support. After 3m of excavation, the far pilot pit excavation section is closed into a ring, and the far pilot pit construction is suspended; S53, excavate the near-end pilot pit (right pilot pit), excavate the upper and middle steps together, apply initial support and temporary support after every 0.5m of excavation, and suspend after 3m of excavation; S54, excavate the lower step of the near-end pilot pit, with a circular advance of 1m. After each 1m of excavation, carry out initial support and temporary support. After 3m of excavation, the excavation section of the near-end pilot pit is closed into a ring, and the construction of the near-end pilot pit is suspended; S55, excavate the upper steps of the pilot pit, cycle the advance by 0.5m, apply initial support after every 0.5m of excavation, and stop after 3m of excavation; S56, excavate the middle step of the middle pilot pit, cycle advance 0.5m, and pause after excavating 3m; S57, excavate the lower step of the middle pilot pit, cycle advance 0.5m, apply initial support after every 0.5m of excavation, pause after 3m of excavation, and the 3m tunnel excavation section has been closed into a ring; Repeat the above steps and remove the temporary support when the initial support deformation converges to no more than 0.2mm / d; remove the temporary support every three times and observe the deformation and deformation rate of the tunnel at the same time. When the deformation and deformation rate of the tunnel are within the normal range within 24 hours, that is, no more than 0.2mm / d, remove the remaining temporary supports one by one; The longitudinal length of the temporary support dismantled is the length of the tunnel secondary lining formwork trolley. After the dismantling is completed, the invert, invert filling and secondary lining shall be constructed in time.

[0043] In this way, the longitudinal spacing between the pilot pits can be reduced during construction, which has the following advantages: 1) Facilitate the organization and coordination of excavation work in each branch; 2) It helps to quickly construct the initial support of the section and quickly play the role of initial support to improve the overall stability of the tunnel and surrounding rock.

[0044] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, equivalent changes and modifications without departing from the principle of the present invention should still belong to the protection scope of the present invention.

Claims

1. A rapid construction method for urban large-section ultra-shallow buried tunnels, characterized by: The steps include: S1. Construction preparation; S2, advanced large pipe shed construction; S3, bridge pile reinforcement grouting: reinforcement grouting is carried out around the bridge pile cap within the influence range of tunnel excavation; S4, full-section curtain grouting or surface grouting + in-hole compensation grouting; When the distance L between the tunnel face and the bridge pile along the longitudinal direction of the tunnel is greater than 3m, full-section curtain grouting is used to reinforce the soil around the tunnel. Otherwise, surface grouting is used to reinforce the soil around the tunnel, and in-tunnel compensatory grouting is performed according to the tunnel excavation conditions. S5, tunnel excavation, and multiple cycles of step S4 and step S2 are performed according to the length of the tunnel; during the tunnel excavation, the tunnel is divided into three pilot pits, left, middle and right, and the pilot pits on the left and right sides are staggered and first excavated, and at the same time, the pilot pit is further divided into multiple steps for cyclic excavation; the tunnel excavation process is divided into first excavating the far-end pilot pit away from the bridge pile, then excavating the near-end pilot pit close to the bridge pile, and then excavating the middle pilot pit, and at the same time, after the steps of each pilot pit are excavated for 0.5-1m, initial support and temporary support are immediately carried out; when the deformation displacement degree of the tunnel gradually converges, the temporary support is removed, the initial support is retained, the invert is constructed, and the secondary lining is kept closely.

2. According to claim 1, a rapid construction method for urban large-section ultra-shallow buried tunnels is characterized by: The construction sequence in step S5 is as follows: S51, excavate the far end pilot pit first, and then excavate the upper and middle steps together. Apply initial support and temporary support after every 0.5m of excavation, and stop after 3m of excavation. S52, excavate the lower step of the far pilot pit, with a circular advance of 1m. After every 1m of excavation, carry out initial support and temporary support. After 3m of excavation, the far pilot pit excavation section is closed into a ring, and the far pilot pit construction is suspended; S53, excavate the near-end pilot pit, and excavate the upper and middle steps together. Apply initial support and temporary support after every 0.5m of excavation, and stop after 3m of excavation; S54, excavate the lower step of the near-end pilot pit, with a circular advance of 1m. After each 1m of excavation, carry out initial support and temporary support. After 3m of excavation, the excavation section of the near-end pilot pit is closed into a ring, and the construction of the near-end pilot pit is suspended; S55, excavate the upper steps of the pilot pit, cycle the advance by 0.5m, apply initial support after every 0.5m of excavation, and stop after 3m of excavation; S56, excavate the middle step of the middle pilot pit, cycle advance 0.5m, and pause after excavating 3m; S57, excavate the lower step of the middle pilot pit, cycle advance 0.5m, apply initial support after every 0.5m of excavation, pause after 3m of excavation, and the 3m tunnel excavation section has been closed into a ring; Repeat the above steps and remove the temporary support when the initial support deformation converges to no more than 0.2mm / d; remove the temporary support every three times and observe the deformation and deformation rate of the tunnel at the same time. When the deformation and deformation rate of the tunnel do not exceed 0.2mm / d within 24 hours, remove the remaining temporary supports one by one; The longitudinal length of each temporary support removal is the length of the tunnel secondary lining formwork trolley. After the removal is completed, the invert arch, invert arch filling and secondary lining are carried out in a timely manner.

3. The method for rapid construction of a large-section ultra-shallow urban tunnel according to claim 1 is characterized by: The step S3 includes the following steps: S31. Grouting test Before the construction of bridge pile reinforcement grouting, several holes are taken for grouting test to verify whether the grouting slurry diffusion radius, grouting final pressure, slurry setting time, slurry mix ratio, slurry single hole design quantity and solid soil radius are reasonable, and to determine the grouting construction process, technical parameters and inspection effect; only after the test verification is reasonable, the grouting control can be carried out according to the selected parameters; S32. Determine the grouting range First determine the number of viaduct piles within the tunnel underpass impact area; perform grouting reinforcement on the bridge pile foundations where the horizontal straight-line distance between the bridge piles and the tunnel excavation contour line is less than 1.5 times the tunnel diameter, which refers to the maximum width of the tunnel contour section; S33, drilling Two rows of grouting holes are arranged around each cap. The first row of grouting holes is 80-100 cm away from the edge of the cap. The second row of grouting holes is staggered with the first row of grouting holes, and the spacing between adjacent grouting holes is 50-100 cm. The opening diameter of the grouting holes is not less than 100 mm, and the final hole diameter is not less than 60 mm. Among them, the spacing between the grouting holes on the cap side close to the tunnel excavation contour line is arranged at 50-80 cm, and the spacing between the drilled holes on other cap sides is arranged at 80-100 cm. S34, Grouting In addition, backward grouting and integrated drilling and grouting are adopted. Cement slurry grouting is used to reinforce the 2m range around the viaduct pile cap. The grouting depth covers the height of the tunnel. The grouting is done first around the periphery and then in the middle, and the grouting is done symmetrically around the cap.

4. The method for close proximity rapid construction of an urban large-section ultra-shallow buried dark-excavated tunnel according to claim 1 is characterized by: In the step S4, when full-section curtain grouting is adopted, the grouting length of each cycle of the full-section curtain grouting is 15m, the excavation is 12m, the grouting overlap is 3m, the grouting diffusion radius is 0.7m, the grouting hole spacing is 0.8m, the number of grouting holes is determined according to the size of the tunnel section, the grouting hole opening diameter is not less than 108mm, the final hole diameter is not less than 90mm, the orifice pipe is a hot-rolled seamless steel pipe, the orifice pipe is firmly buried with the help of an anchor, and a slurry stop valve is welded on the orifice pipe; the grouting material within the tunnel excavation contour line is pure cement slurry, and cement-water glass double slurry is used outside the tunnel excavation contour line; the curtain grouting reinforcement range is 3m outside the tunnel excavation contour line to form a water-stop curtain.

5. The method for rapid construction of a large-section ultra-shallow urban tunnel according to claim 4 is characterized by: After the first cycle of pipe shed construction is completed, the first cycle of full-section curtain grouting is carried out. Before grouting, ensure that the heading face is level, hang the mesh to seal the heading face, and carry out full-section curtain grouting of the upper and lower steps. The number of grouting holes is determined according to the size of the tunnel section; the subsequent cycle of full-section curtain grouting construction is carried out after the corresponding pilot pit is excavated to the corresponding mileage section. After each pilot pit is excavated to the grouting mileage, the heading face is hung with shotcrete for the first time as a grouting stop wall.

6. The method for rapid close-proximity construction of an urban large-section ultra-shallow buried tunnel according to claim 1 is characterized by: In step S4, when surface grouting + in-tunnel compensatory grouting is adopted, the surface grouting is carried out on the surface above the tunnel, the surface grouting width is 3m outward from the tunnel excavation contour line, the grouting depth is 2m below the tunnel invert arch, the grouting hole spacing is 1.5m plum blossom arrangement, and the grouting diffusion radius is calculated as 0.8m; the grouting material is cement-water glass double liquid slurry; the in-tunnel compensatory grouting is carried out on the steps below the left and right guide pits of the tunnel, the grouting width of the in-tunnel compensatory grouting is 3m outward from the contour line, the grouting depth is 2m below the invert arch, the hole spacing is 1.5m, and the grouting diffusion radius is calculated as 0.8m; wherein a temporary middle partition wall is formed between the left and right guide pits after excavation, and the holes close to the temporary middle partition wall are grouted obliquely downward toward the middle guide pit; the holes close to the heading face are grouted obliquely downward toward the heading face; the grouting material is cement-water glass double liquid slurry.

7. The method for rapid close-proximity construction of an urban large-section ultra-shallow buried tunnel according to claim 1 is characterized by: In the construction preparation of step S1, the following operations are performed: S11. Dig a foundation pit at the predetermined location, set up intercepting ditches around the top of the foundation pit to intercept surface water and prevent it from flowing into the foundation pit and scouring the slopes; set up drainage ditches in the foundation pit, set up water collection pits every 100m, and equip the water collection pits with water pumps to prevent water accumulation in the pit; S12. Pipeline relocation: If there are municipal pipelines in the construction area where the tunnel passes under the road in the city, the pipelines will be relocated outside the construction area; S13. Traffic organization: set up warning signs and fences on the surface of the construction area, restrict the passage of heavy-loaded vehicles, and turn off red lights at intersections.

8. The method for rapid close-proximity construction of an urban large-section ultra-shallow buried tunnel according to claim 1 is characterized by: The advanced large pipe shed construction in step S2 is performed by performing the following steps: S21. Construction of arch At the starting section of tunnel excavation, a sleeve arch is constructed as the guide wall of the first circulation pipe shed. Four I-beams are arranged in the sleeve arch, spaced longitudinally. The base is compacted and reinforced before erection. The bearing capacity of the sleeve arch base should be greater than 250kPa, otherwise concrete is added to expand the foundation. The I-beams are connected longitudinally with steel bars to form an arch frame, which is welded firmly. Several guide pipes are arranged along the arch frame. The guide pipes have an elevation angle of 2° and are parallel to the central axis of the tunnel excavation direction. The guide pipes and the arch frame are welded firmly with steel bars to prevent displacement when pouring the sleeve arch concrete. Thick wooden boards are used to build the sleeve arch formwork, and three I-beams are used to form a steel support under the bottom formwork. The sleeve arch concrete is poured symmetrically on both sides to avoid bias pressure that causes the cross-section center and elevation of the guide wall to be incorrect. The core soil in the middle of the tunnel is reserved at the sleeve arch, and the bottom formwork is supported by round logs on the core soil. In the second cycle, if the tunnel has been excavated for a certain distance, a pipe-roof studio will be formed in the tunnel to provide working space for the second cycle of advanced large pipe-roof drilling; S22, drilling Before drilling, mark the hole numbers on the guide wall and pipe shed studio. Drill the odd-numbered holes first, install the steel pipe and grout the odd-numbered holes before drilling the even-numbered holes. Check the grouting quality of the odd-numbered holes when drilling the even-numbered holes. In order to prevent the hole from collapsing during the drilling operation, the drilling operation adopts the pipe-following drilling method. The external insertion angle of the first cycle pipe shed is 2°, and the external insertion angle of the second and third cycle pipe sheds is 6°. The diameter of the drill bit is larger than the guide pipe. After drilling, sweep the hole back and forth to remove the scum to the bottom of the hole to ensure that the hole diameter and hole depth meet the requirements and prevent blockage. S23, Grouting Grouting is carried out after the hole is drilled. A grouting field test should be carried out before grouting. The grouting parameters should be determined according to the actual situation through field tests. Grouting can be terminated only after ensuring that the rock mass around the borehole and the pores around the steel pipe are filled with slurry. After grouting, the slurry in the pipe should be removed in time and filled densely with cement mortar.

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