Precise settlement control construction method for ultra-shallow-earthing ultra-large-diameter shield tunnel

Abstract

The invention discloses a precise settlement control construction method for an ultra-shallow-earthing ultra-large-diameter shield tunnel, and relates to the technical field of tunnel engineering construction.The method comprises the steps that waterproof curtains are constructed along the two sides of a tunnel design axis, and pedestal piles are constructed in the waterproof curtains on the two sides; the pedestal piles are arranged at intervals in the length direction of the waterproof curtain; in the tunnel center area defined by the waterproof curtain, the soil body is integrally reinforced on the basis of the three-axis stirring piles; after construction of the expanded bore piles is completed, the longitudinal beams and the anti-floating plates are constructed to form a gate-type anti-floating structure, and under the condition of construction of the anti-floating plates, ground grouting pipelines are pre-buried on the anti-floating plates synchronously; grout is injected into the periphery of the tunnel segment in the process that the shield advances towards the target construction section along the tunnel design axis; and under the condition that the shield passes through the target construction section, grouting liquid is injected into a gap between the anti-floating plate and the tunnel segment through a ground grouting pipeline, so that tunnel construction is completed. According to the method, cooperative control of anti-floating and settlement of the tunnel structure can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel engineering construction, in particular to a construction method for precise control of settlement of an ultra-shallow covering super-large diameter shield tunnel. BACKGROUND

[0002] In recent years, with the continuous expansion of urban underground space development and the continuous densification of traffic network system, shield tunnel engineering is rapidly developing towards the direction of super-large section, super-long distance and ultra-shallow covering. The use of ultra-shallow covering scheme can effectively shorten the length of the tunnel, reduce the engineering cost and optimize the longitudinal slope of the line, which has advantages in improving the efficiency of tunnel operation and driving comfort. However, under the condition of ultra-shallow covering (usually referring to the covering thickness less than 0.5 times the diameter of the tunnel), the tunnel structure is close to the ground surface, and the problems of ground disturbance, excavation face stability, underground water control and tunnel anti-floating during construction are increasingly prominent.

[0003] At present, for the construction control of ultra-shallow covering shield tunnel, several typical technical measures have been formed in the industry. In terms of anti-floating, passive anti-floating means such as counterweight method, anti-floating pile and weight plate are often used; in terms of ground settlement control, methods such as synchronous grouting, secondary grouting and surface pre-reinforcement are mainly relied on. However, these typical technical measures have not yet formed a systematic collaborative control system.

[0004] Therefore, there is an urgent need for a construction method that can realize the collaborative control of tunnel anti-floating and settlement. SUMMARY

[0005] The present application provides a construction method for precise control of settlement of an ultra-shallow covering super-large diameter shield tunnel, which can realize the collaborative control of tunnel anti-floating and settlement.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The present application provides a construction method for precise control of settlement of an ultra-shallow covering super-large diameter shield tunnel, which comprises: A waterproof curtain is constructed along both sides of the design axis of the tunnel, and a spread footing pile is constructed in each side of the waterproof curtain; the spread footing piles are arranged at intervals along the length direction of the waterproof curtain; The soil body is overall reinforced based on triaxial mixing piles in the tunnel center area enclosed by the waterproof curtain; After the construction of the spread footing pile is completed, a longitudinal beam and an anti-floating plate are constructed to form a portal anti-floating structure, and a ground grouting pipeline is pre-buried on the anti-floating plate simultaneously under the condition of anti-floating plate construction; wherein the longitudinal beam is arranged along the length direction of the tunnel; Slurry is injected to the periphery of the tunnel segment during the process of pushing the shield along the design axis of the tunnel to the target construction section; In the case that the shield passes through the target construction section, grout is injected into the gap between the anti-floating plate and the tunnel segment through the ground grouting pipeline to complete the tunnel construction.

[0007] In some possible implementations, the waterproof curtain is constructed by using the triaxial mixing pile process, the pile body of the waterproof curtain extends to the target stratum below the tunnel bottom plate, and the horizontal spacing of the waterproof curtains on both sides is greater than the horizontal width of the tunnel design contour.

[0008] In some possible implementations, the reinforced range of the triaxial mixing pile on the soil body in the central area of the tunnel is: in the horizontal direction, the preset area extending to the left and right sides of the tunnel design contour line, and in the vertical direction, from the bottom surface of the anti-floating plate to a preset depth below the tunnel bottom plate, and the reinforced soil body forms an integral structure with the waterproof curtains on both sides.

[0009] In some possible implementations, the bottom of the longitudinal beam is fixedly connected with the pile top of the expanded pile through the embedded steel bars, and the top of the longitudinal beam is integrally poured with the bottom surface of the anti-floating plate.

[0010] In some possible implementations, the ground grouting pipeline penetrates the anti-floating plate in a direction perpendicular to the anti-floating plate, the opening of the first port of the ground grouting pipeline faces the top of the tunnel segment, and the opening of the second port of the ground grouting pipeline forms a grouting hole in the top of the anti-floating plate.

[0011] In some possible implementations, before the grout is injected into the gap between the anti-floating plate and the tunnel segment through the ground grouting pipeline, the method further comprises: Based on the position and volume of the gap between the anti-floating plate and the tunnel segment, the injection sequence and single injection amount of the grout are determined.

[0012] In some possible implementations, after the grout is injected into the gap between the anti-floating plate and the tunnel segment through the ground grouting pipeline, the method further comprises: The filling effect of the gap is verified, and in the case that there is an unfilled full area, secondary grouting is performed through the ground grouting pipeline.

[0013] In some possible implementations, the method comprises: In the case that the pile spacing between adjacent expanded piles is less than a preset spacing threshold, a skip pile construction method is used.

[0014] In some possible implementations, the grout is a double-liquid grout, which is mixed by cement grout and water glass based on a preset ratio.

[0015] In some possible implementations, a preset reinforcing steel mesh is arranged around the grouting hole of the ground grouting pipeline.

[0016] From the above technical solutions, the present application has at least the following beneficial effects: In the present application, an effective groundwater blocking system and reliable anti-floating foundation are established by constructing a waterproof curtain along both sides of the tunnel design axis and constructing the expansion piles arranged at intervals in the waterproof curtain on each side; in the tunnel center area enclosed by the waterproof curtain, the soil is overall reinforced based on the triaxial mixing pile, thereby improving the stratum stability and uniformity in the shield tunneling process; after the expansion pile construction is completed, the construction longitudinal beam and anti-floating plate are constructed to form a portal anti-floating structure, and in the case of anti-floating plate construction, the ground grouting pipeline is pre-buried on the anti-floating plate to form a synergistic permanent anti-floating system and realize the innovative technology of ground pre-burial and ground grouting; in the process of shield advancing along the tunnel design axis to the target construction section, the slurry is injected to the outside of the tunnel segment, which timely fills the shield tail gap and inhibits the tunnel floating and stratum settlement; in the case of shield passing through the target construction section, the slurry is injected to the gap between the anti-floating plate and the tunnel segment through the ground grouting pipeline to complete the tunnel construction, which completely eliminates the structural gap hidden danger and ensures the long-term stability of the tunnel structure. The entire construction method forms a systematic settlement control system and realizes the synergistic control of the tunnel structure anti-floating and settlement.

[0017] It should be understood that the description of technical features, technical solutions, beneficial effects or similar language in the present application does not imply that all features and advantages can be achieved in any single embodiment. On the contrary, it can be understood that the description of a feature or beneficial effect means that the specific technical feature, technical solution or beneficial effect is included in at least one embodiment. Therefore, the description of technical features, technical solutions or beneficial effects in the specification does not necessarily refer to the same embodiment. Further, the technical features, technical solutions and beneficial effects described in the embodiments can be combined in any appropriate manner. Those skilled in the art will understand that the embodiments can be implemented without one or more specific technical features, technical solutions or beneficial effects of a particular embodiment. In other embodiments, additional technical features and beneficial effects can be identified in specific embodiments that do not embody all embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 An application environment diagram of a precise control construction method for an ultra-shallow covering super-large diameter shield tunnel settlement provided by the embodiments of the present application; Figure 2 A flowchart of a precise control construction method for an ultra-shallow covering super-large diameter shield tunnel settlement provided by the embodiments of the present application. DETAILED DESCRIPTION

[0019] The terms "first", "second" and "third" and the like in the present application specification and the drawings are used to distinguish different objects, and are not used to limit a specific order.

[0020] In the embodiments of the present application, the word "exemplary" or "for example" is used to mean serving as an example, instance, or illustration. Any embodiment or design described in the embodiments of the present application as "exemplary" or "for example" should not be construed as preferred or advantageous over other embodiments or designs. Rather, the word "exemplary" or "for example" is used in the sense of "as an example". The embodiments described in the present application are intended to be illustrative rather than restrictive.

[0021] Therefore, the present application provides a construction method for precise control of settlement of an ultra-shallow covering super-large diameter shield tunnel. In order to make the technical solution of the present application clearer and easier to understand, the application scenario of the technical solution of the present application is introduced below in combination with the drawings. As shown in Figure 1 The present application provides a construction method for precise control of settlement of an ultra-shallow covering super-large diameter shield tunnel. In order to make the technical solution of the present application clearer and easier to understand, the application scenario of the technical solution of the present application is introduced below in combination with the drawings. As shown in

[0022] In the application scenario, a water-stop curtain is first constructed along the two sides of the design axis of the tunnel. The water-stop curtain is a continuous anti-seepage structure, which blocks the seepage of external groundwater to the tunnel area, so as to avoid excessive groundwater buoyancy or stratum seepage affecting construction. In the range of the water-stop curtain on each side, expansion piles are arranged at intervals. The expansion piles are expanded at the bottom, which can enhance the uplift resistance of the pile body and provide stable vertical support for the subsequent anti-floating structure. At the same time, the soil body in the tunnel center area enclosed by the water-stop curtain is reinforced as a whole by using triaxial mixing piles, so as to improve the compactness and bearing capacity of the soil body around the tunnel and reduce stratum settlement during shield propulsion. After the expansion piles are completed, longitudinal beams and anti-floating plates are constructed on the pile top. The longitudinal beams are arranged along the length direction of the tunnel and connected to the expansion piles on the same side. The anti-floating plates cross above the tunnel and are fixed to the expansion piles on both sides through the longitudinal beams, so that the whole tunnel area is covered like a "door frame". During construction of the anti-floating plate, the ground grouting pipeline is pre-buried, which prepares for subsequent filling of the gap. When the shield advances along the tunnel axis, grouting is performed to the periphery of the tunnel segment, that is, the gap between the segment and the stratum is filled, so as to preliminarily control the upward floating of the segment and the stratum settlement. After the shield passes through the target section, grout is injected into the gap between the anti-floating plate and the tunnel segment through the ground grouting pipeline pre-buried on the anti-floating plate. After the grout solidifies, the tunnel segment and the door-type anti-floating structure are connected as a whole, and the upward floating of the tunnel is limited by the weight of the anti-floating structure and the uplift resistance of the expansion piles. At the same time, grouting can further fill the stratum gap to avoid later settlement.

[0023] In order to make the technical solution of the present application clearer and easier to understand, the application scenario is introduced below in combination with the above-mentioned application scenario. As shown in Figure 2 The present application provides a construction method for precise control of settlement of an ultra-shallow covering super-large diameter shield tunnel. In order to make the technical solution of the present application clearer and easier to understand, the application scenario of the technical solution of the present application is introduced below in combination with the drawings. As shown in S201. Construct water-stop curtains on both sides of the tunnel design axis, and construct enlarged-base piles within the water-stop curtains on each side; the enlarged-base piles are arranged at intervals along the length of the water-stop curtains.

[0024] Optionally, the cutoff wall is constructed using a three-axis mixing pile process, with the bottom of the piles extending to the target stratum beneath the tunnel floor, and the horizontal spacing between the two cutoff walls being greater than the horizontal width of the tunnel's designed profile. If the spacing between adjacent enlarged-base piles is less than a preset spacing threshold, a skip-pile construction method is adopted.

[0025] Among them, the tunnel design axis refers to the centerline path of the tunnel in the horizontal and vertical directions, which is the theoretical position line of the tunnel design and is the main reference for determining the tunnel's direction and location.

[0026] A water-stop curtain is a type of continuous underground wall formed by methods such as cement-soil mixing piles. Its main function is to block the flow path of groundwater and prevent groundwater from seeping into the excavated area.

[0027] An enlarged-base pile is a type of pile foundation where the diameter of the base is larger than the diameter of the pile body (similar to an enlarged head), which can improve the pile's bearing capacity and pull-out resistance.

[0028] The length direction is the direction of extension along the tunnel axis, that is, longitudinal.

[0029] Intermittent arrangement means that the expanded base piles are not continuous, but arranged at certain intervals.

[0030] Triaxial mixing pile technology is a foundation treatment method that uses three drill rods to rotate and spray grout simultaneously, mixing with the soil to form a continuous cylindrical cement-soil pile. It is often used to form a water-stop curtain or foundation reinforcement.

[0031] The bottom of the pile extends to the target stratum below the tunnel floor. The pile body of the water-stop curtain not only needs to penetrate the depth of the tunnel floor, but also needs to continue to go deeper to reach a certain stable stratum or the depth required by the design, such as going into the soil 3 meters below the tunnel floor.

[0032] The tunnel design profile refers to the external dimensions of the tunnel cross-section (such as a circular cross-section), which is the theoretical boundary for determining the size of the tunnel cross-section.

[0033] The horizontal spacing refers to the lateral distance between the center lines of the two water-stop curtains, which is usually greater than the width of the tunnel outline to ensure the overall protection of the tunnel.

[0034] The pile spacing refers to the distance between the center points of the expanded-base piles on the same side.

[0035] The preset spacing threshold is the minimum allowable pile spacing set in advance in the engineering design to prevent piles from being too close, which could cause construction interference or soil damage.

[0036] When the distance between piles is small, the pile jump construction method is used, that is, every other pile is constructed first, and then the middle piles are constructed after the previous piles are solidified, so as to avoid the problem of extrusion or hole collapse caused by simultaneous construction of adjacent pile holes.

[0037] For example, before the construction of a very shallow overburden super-large diameter shield tunnel settlement precision control, first construct a waterproof curtain along the design axis of the tunnel on both sides to block the seepage of groundwater outside the tunnel section; then construct a spread footing pile at a certain interval inside the waterproof curtain on each side as the key vertical load-bearing component of the portal anti-floating structure. The waterproof curtain is usually constructed using the triaxial mixing pile process, and the pile bottom depth must extend to the stable stratum below the tunnel bottom plate. The horizontal distance between the two curtains should be greater than the width of the tunnel design contour to form an effective range of groundwater isolation and soil protection. If the distance between adjacent spread footings is too small, the pile jump construction method is used to avoid mutual interference and soil disturbance during construction, thereby ensuring the quality of the pile and the safety and stability of the overall structure.

[0038] S202, based on the triaxial mixing pile, the soil in the tunnel center area enclosed by the waterproof curtain is reinforced as a whole.

[0039] Optionally, the reinforcement range of the triaxial mixing pile on the soil in the tunnel center area is: in the horizontal direction, covering the preset area extending to the left and right of the tunnel design contour line; in the vertical direction, from the bottom surface of the anti-floating plate to a preset depth below the tunnel bottom plate, and the reinforced soil forms an integral structure with the two side waterproof curtains.

[0040] The tunnel center area enclosed by the waterproof curtain refers to the internal area enclosed by the waterproof curtains on both sides of the tunnel, which is the construction range of the tunnel main body.

[0041] The triaxial mixing pile is a ground treatment method that simultaneously rotates and sprays a solidifying agent (usually cement slurry) through three coaxial drill rods to fully mix with the foundation soil, forming a cylindrical continuous reinforcement body.

[0042] Overall reinforcement refers to the use of continuous, full or staggered piles to uniformly and omnidirectionally improve the strength and stability of the soil.

[0043] The reinforcement range refers to the spatial area of soil treatment using mixing piles.

[0044] The preset area is the reinforcement width determined according to the engineering design requirements, such as 5 meters on each side of the hole contour line.

[0045] The anti-floating plate is a reinforced concrete plate set above the tunnel covering the tunnel section, which resists the lifting effect of groundwater buoyancy on the tunnel through its own weight and connection with the lower structure.

[0046] Anti-floating plate bottom surface refers to the bottom elevation of the upper horizontal anti-floating plate in the portal anti-floating structure.

[0047] Tunnel bottom plate is the bottom of the tunnel structure, usually refers to the bottom end of the segment or lining.

[0048] Pre-set depth is the lower limit of the specified reinforcement depth in the design, such as 3 meters below the tunnel bottom plate.

[0049] Integrated structure refers to the close combination of the reinforced soil and the two side waterproof curtains in mechanics and space, forming a continuous and collaborative whole.

[0050] For example, after the construction of the two side waterproof curtains of the tunnel is completed, the soil in the tunnel center area enclosed by the curtains needs to be treated by overall reinforcement. The reinforcement uses the triaxial mixing pile technology, and the reinforcement range covers a certain width (for example, 5 meters each) extending to the left and right sides of the tunnel design contour line in the horizontal direction, and extends from the bottom surface elevation of the upper anti-floating plate to a certain depth (for example, 3 meters) below the tunnel bottom plate in the vertical direction. Through this reinforcement treatment, the bearing capacity and uniformity of the soil in the shield crossing area are significantly improved, and the reinforced soil and the two side waterproof curtains form a continuous and collaborative whole structure, providing reliable foundation support for subsequent shield tunneling and long-term stability of the tunnel structure.

[0051] S203, after the construction of the under-reamed pile is completed, the longitudinal beam and the anti-floating plate are constructed to form a portal anti-floating structure, and in the case of anti-floating plate construction, the ground grouting pipeline is pre-buried on the anti-floating plate.

[0052] Optionally, the longitudinal beam is arranged along the length direction of the tunnel. The grouting hole of the ground grouting pipeline is surrounded by a pre-set reinforcing mesh.

[0053] The bottom of the longitudinal beam is fixedly connected with the top of the under-reamed pile through the pre-buried reinforcing steel bars, and the top of the longitudinal beam is integrally poured with the bottom surface of the anti-floating plate.

[0054] The ground grouting pipeline penetrates the anti-floating plate along the direction perpendicular to the anti-floating plate, the opening of the first port of the ground grouting pipeline faces the top of the tunnel segment, and the opening of the second port of the ground grouting pipeline forms a grouting hole on the top of the anti-floating plate.

[0055] The longitudinal beam is a reinforced concrete beam arranged along the length direction of the tunnel, which plays a role in horizontal connection and load transfer in the portal anti-floating structure, connects the tops of the under-reamed piles and forms an integral frame with the upper anti-floating plate.

[0056] The portal anti-floating structure is an integral force system composed of the anti-floating plate, the longitudinal beam and the under-reamed pile, which looks like a "door" structure and can effectively resist the upward force of the tunnel for a long time.

[0057] The bottom of the longitudinal beam is fixedly connected with the pile top of the expanded pile, and the top of the longitudinal beam is fixedly connected with the bottom surface of the anti-floating plate, so that the expanded pile, the longitudinal beam and the anti-floating plate form a door-shaped frame which is in stress integration; the ground grouting pipeline penetrates the anti-floating plate, and a plurality of rows of grouting holes are pre-set on the top of the anti-floating plate.

[0058] The anti-floating plate is horizontally covered on the top of the reinforced soil body and the expanded pile, and the horizontal projection range of the anti-floating plate exceeds the left and right sides of the tunnel design contour line; the plurality of rows of grouting holes are arranged in the length direction of the tunnel, and the horizontal distribution range of each row of grouting holes covers the top projection area of the tunnel segment.

[0059] The pre-buried ground grouting pipeline refers to a grouting pipeline system which is pre-installed and fixed in the anti-floating plate before pouring the anti-floating plate concrete, and is used for later grouting operation through the ground.

[0060] The grouting hole is the opening of the grouting pipeline, which is divided into two categories: one is the injection hole located on the top of the anti-floating plate; and the other is the slurry outlet hole located on the bottom of the anti-floating plate and facing the tunnel segment.

[0061] The reinforced steel mesh is a reinforced steel mesh arranged around the grouting hole, which is used to enhance the local compressive strength of the concrete and prevent cracking.

[0062] The pre-buried steel bar is a steel bar which is pre-stretched from the top of the expanded pile, and is used to connect with the steel bar at the bottom of the longitudinal beam to ensure reliable force transmission between the pile and the beam.

[0063] The pouring as a whole refers to the construction method of integrally and continuously pouring the longitudinal beam and the anti-floating plate, so that the two form a seamless connection of reinforced concrete as a whole.

[0064] The top of the tunnel segment is the upper half of the outer surface of the prefabricated segment ring of the shield tunnel, and is the target area which needs to be filled by grouting.

[0065] The direction perpendicular to the anti-floating plate is the arrangement of the grouting pipeline which penetrates the thickness direction of the anti-floating plate, that is, the pipeline and the anti-floating plate plane are at a 90-degree angle.

[0066] For example, after the construction of the expanded pile is completed, the upper construction stage of the door-shaped anti-floating structure is entered. First, the longitudinal beam is constructed along the length direction of the tunnel, the bottom of the longitudinal beam is firmly connected with the top of the expanded pile through the pre-buried steel bar to form a reliable vertical force transmission node; then, the anti-floating plate is integrally poured on the top of the longitudinal beam, so that the longitudinal beam and the anti-floating plate become a seamless connection of reinforced concrete as a whole, thereby forming a complete door-shaped anti-floating structure system.

[0067] Simultaneously, during the construction of the anti-buoyancy slab, ground grouting pipelines were pre-embedded. These pipelines consist of multiple vertically penetrating the anti-buoyancy slab. The first port (open at the bottom) of each pipeline faces the grouting space reserved at the top of the tunnel segment, while the second port (open at the top) forms the grouting hole at the top of the anti-buoyancy slab. To enhance the local bearing capacity of the concrete around the grouting hole, reinforcing steel mesh was installed around the hole opening. The pre-embedded ground grouting pipelines provide a direct channel for subsequent ground grouting after the tunnel boring machine passes through, allowing for the filling and reinforcement of the tunnel top voids without needing to access the tunnel from within, thus achieving precise control of "ground pre-embedding and ground grouting."

[0068] S204. During the process of the shield tunnel advancing along the tunnel design axis towards the target construction section, grout is injected into the outer perimeter of the tunnel segments.

[0069] The grout is a two-component grout, which is made by mixing cement grout and water glass in a preset ratio.

[0070] The tunnel segment is a ring-shaped support structure assembled inside the tunnel excavation outline during the shield tunneling process. The outer ring surface of the tunnel segment is in contact with the soil reinforced by the three-axis mixing piles, and a pre-set gap is reserved between the top of the tunnel segment and the bottom surface of the anti-buoyancy plate.

[0071] Optionally, before injecting grout into the gap between the anti-buoyancy plate and the tunnel segments through the ground grouting pipeline, the following steps are also included: Based on the gap location and volume between the anti-buoyancy plate and the tunnel segment, the grouting sequence and single grouting volume of the pressure grouting fluid are determined.

[0072] After injecting grout into the gap between the anti-buoyancy plate and the tunnel segments through ground grouting pipelines, the process also includes: The gap filling effect was verified. In the case of unfilled areas, secondary grouting was carried out through ground grouting pipelines.

[0073] Among them, a shield tunneling machine is a large machine used for tunnel construction. It cuts the soil with a cutterhead at the front end and assembles precast segments at the rear to form the tunnel lining.

[0074] The target construction section refers to a specific tunnel section in which shield tunneling is underway, usually corresponding to a section where the portal anti-buoyancy structure construction and ground pretreatment have been completed.

[0075] The outer perimeter of a tunnel segment refers to the annular gap formed between the outer surface of the precast reinforced concrete segment ring and the surrounding soil after the segment ring is installed.

[0076] Two-component grout is a grouting material made by mixing two different liquids (usually cement grout and water glass) in a certain proportion. Its characteristic is that it can solidify quickly after mixing, so as to play a role in timely filling and reinforcement.

[0077] Cement grout is a slurry formed by mixing cement and water in a certain proportion, and it is a basic component of grouting materials.

[0078] Water glass is an aqueous solution of sodium silicate. As a setting accelerator for two-component grouts, it can significantly accelerate the setting time when mixed with cement grout.

[0079] The preset ratio is the mixing ratio of cement slurry and water glass that is pre-set according to engineering requirements and geological conditions, and can be determined through experiments.

[0080] The gap between the anti-buoyancy plate and the tunnel segment is the space that may exist between the top of the tunnel segment and the bottom surface of the anti-buoyancy plate after the tunnel segment is assembled. It is the main filling area for ground grouting.

[0081] Grouting sequence refers to the order in which multiple grouting holes are grouted, usually proceeding from one end to the other or from the middle to both ends.

[0082] The single grouting volume is the volume of grout injected through a single grouting hole each time, and it needs to be reasonably controlled according to the gap volume and grouting pressure.

[0083] The gap filling effect verification is to check whether the gap is completely filled by grout after the grouting is completed by geophysical exploration (such as ground-penetrating radar) or borehole sampling.

[0084] Unfilled areas are voids or loose areas that still exist after grouting, and usually require additional grouting.

[0085] Secondary grouting is a supplementary grouting operation carried out after the initial grouting to fill areas that have not been fully filled, in order to ensure that the gaps are completely compacted.

[0086] For example, during the tunnel boring machine's advance along the tunnel's designed axis, a dual-liquid grout is simultaneously injected into the annular gaps around the tunnel segments. This grout is made of cement grout and water glass mixed in a preset ratio, which can solidify quickly, stabilize the soil around the tunnel in a timely manner, and inhibit tunnel uplift and subsequent settlement.

[0087] After the tunnel boring machine passes through, before top grouting is carried out using the pre-embedded ground grouting pipeline, a reasonable grouting sequence (such as grouting from one end to the other or skipping holes at intervals) must be formulated based on the location distribution and total volume of the gap between the anti-buoyancy plate and the tunnel segments, and the single grouting volume of each grouting hole must be determined to achieve uniform and efficient filling.

[0088] After the initial grouting is completed, the gap filling effect needs to be verified (e.g., by using ground-penetrating radar scanning). If areas that are not fully filled are found, secondary grouting is carried out through ground grouting pipelines until the gaps are completely filled and compacted by the grout, thus completely eliminating the hidden dangers of soil loosening and voids and ensuring the long-term stability of the tunnel structure.

[0089] S205. When the tunnel boring machine passes through the target construction section, grout is injected into the gap between the anti-buoyancy plate and the tunnel segment through the ground grouting pipeline to complete the tunnel construction.

[0090] Among them, "shield tunneling passing through the target construction section" means that the shield tunneling machine has completed the advancement construction in a specific tunnel section, the segment assembly has also been completed, and the section is ready for subsequent processing.

[0091] Pressure grouting involves using grouting equipment to inject grout into the target voids through grouting pipes at a certain pressure, so that it can fully fill and penetrate into the soil cracks.

[0092] Tunnel construction refers to the entire process of tunnel engineering from excavation and support to the final structure formation, including shield tunneling, segment assembly, grouting reinforcement, and anti-buoyancy structure construction.

[0093] For example, once the tunnel boring machine has completed its excavation in the target construction section and the tunnel segments have been assembled and positioned, a grout with a specific ratio (such as ultrafine cement grout) is injected into the gap between the anti-buoyancy plate and the top of the tunnel segments using ground grouting pipelines pre-embedded in the anti-buoyancy plate. The grout is then pressurized to fully fill the gap and penetrate into the surrounding soil. This grouting process not only eliminates the potential for voids between structures but also effectively compacts the soil, enhances the overall structural stability, and ensures the long-term safe use of the tunnel under ultra-shallow overburden conditions, marking the final completion of the tunnel construction in that section.

[0094] Based on the above, the construction method for precise settlement control of ultra-shallow overburden, ultra-large diameter shield tunnels establishes an effective groundwater barrier system and a reliable anti-buoyancy foundation by constructing water-stop curtains on both sides of the tunnel's design axis and installing spaced-apart enlarged-base piles within each water-stop curtain. In the tunnel's central area enclosed by the water-stop curtain, the soil is reinforced as a whole using triaxial mixing piles, improving the stability and uniformity of the strata during shield tunneling. After the enlarged-base piles are constructed, longitudinal beams and anti-buoyancy plates are installed to form a portal anti-buoyancy structure. Furthermore, the construction of the anti-buoyancy plates is followed by... Simultaneously, ground grouting pipelines were pre-embedded on the anti-buoyancy plate, forming a synergistic permanent anti-buoyancy system and realizing the innovative process of ground pre-embedding and ground grouting. During the tunnel boring machine's (TBM) advancement along the tunnel's design axis towards the target construction section, grout was injected around the tunnel segments to promptly fill the shield tail gaps, suppressing tunnel uplift and ground settlement. After the TBM passed the target construction section, grout was injected into the gap between the anti-buoyancy plate and the tunnel segments through the ground grouting pipelines to complete tunnel construction, completely eliminating structural void hazards and ensuring the long-term stability of the tunnel structure. The entire construction method formed a systematic settlement control system, achieving synergistic control of tunnel structure anti-buoyancy and settlement.

[0095] The descriptions of the processes or structures corresponding to the above figures each have their own emphasis. For parts of a process or structure that are not described in detail, please refer to the relevant descriptions of other processes or structures.

[0096] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be covered within the scope of protection of this application.

Claims

1. A construction method for precise settlement control of ultra-shallow overburden, ultra-large diameter shield tunnels, characterized in that, The method includes: Water-stop curtains are constructed on both sides of the tunnel design axis, and enlarged-base piles are constructed within the water-stop curtains on each side; the enlarged-base piles are arranged at intervals along the length of the water-stop curtains. In the central area of ​​the tunnel enclosed by the water-stop curtain, the soil is reinforced as a whole based on the triaxial mixing piles; After the expansion piles are completed, longitudinal beams and anti-buoyancy plates are constructed to form a portal anti-buoyancy structure. During the construction of the anti-buoyancy plates, ground grouting pipelines are pre-embedded on the anti-buoyancy plates simultaneously. The longitudinal beams are set along the length of the tunnel. During the process of the shield tunnel advancing along the tunnel design axis toward the target construction section, grout is injected around the tunnel segments. When the tunnel boring machine passes through the target construction section, grout is injected into the gap between the anti-buoyancy plate and the tunnel segments through the ground grouting pipeline to complete the tunnel construction.

2. The method according to claim 1, characterized in that, The water-stop curtain is constructed using a three-axis mixing pile process. The bottom of the piles of the water-stop curtain extends to the target stratum under the tunnel floor, and the horizontal distance between the two water-stop curtains is greater than the horizontal width of the tunnel design outline.

3. The method according to claim 1, characterized in that, The reinforcement range of the soil in the central area of ​​the tunnel by the three-axis mixing pile is: in the horizontal direction, it covers the preset area extending to the left and right sides of the tunnel design outline; in the vertical direction, it extends from the bottom surface of the anti-buoyancy plate to a preset depth below the tunnel floor slab, and the reinforced soil and the water-stop curtains on both sides form an integrated structure.

4. The method according to claim 1, characterized in that, The bottom of the longitudinal beam is fixedly connected to the top of the expanded-base pile by pre-embedded steel bars, and the top of the longitudinal beam is cast as one piece with the bottom surface of the anti-buoyancy plate.

5. The method according to claim 1, characterized in that, The ground grouting pipeline penetrates the anti-buoyancy plate in a direction perpendicular to the anti-buoyancy plate. The opening of the first port of the ground grouting pipeline faces the top of the tunnel segment, and the opening of the second port of the ground grouting pipeline forms the grouting hole at the top of the anti-buoyancy plate.

6. The method according to claim 1, characterized in that, Before injecting grout into the gap between the anti-buoyancy plate and the tunnel segments through the ground grouting pipeline, the process also includes: Based on the gap location and volume between the anti-buoyancy plate and the tunnel segment, the grouting sequence and single grouting volume of the pressure grouting fluid are determined.

7. The method according to claim 1, characterized in that, After injecting grout into the gap between the anti-buoyancy plate and the tunnel segments through ground grouting pipelines, the process also includes: The gap filling effect was verified. In the case of unfilled areas, secondary grouting was carried out through ground grouting pipelines.

8. The method according to claim 1, characterized in that, The method further includes: When the distance between adjacent expanded-base piles is less than the preset distance threshold, a skip-pile construction method is adopted.

9. The method according to claim 1, characterized in that, The slurry is a two-component slurry, which is made by mixing cement slurry and water glass in a preset ratio.

10. The method according to claim 1, characterized in that, The ground grouting pipeline has a pre-set reinforcing steel mesh around the grouting hole.

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