A buoyancy-resistant reinforcement system for the shallow overburden starting zone of a shield tunnel

Abstract

This utility model relates to the field of tunnel and underground engineering technology, specifically to the field of large-diameter shield tunnel construction, and more specifically to an anti-buoyancy reinforcement system for the shallow overburden starting zone of a shield tunnel. It overcomes the problems of complex construction, high cost, low anti-buoyancy efficiency, or potential damage to the tunnel structure itself in existing technologies. The system includes enlarged-base anti-uplift piles located within the ground reinforcement zone and on both sides of the shield tunnel. Each enlarged-base anti-uplift pile includes a normal diameter section, with an enlarged-base section at the lower end of the normal diameter section. The outer diameter of the enlarged-base section is larger than that of the normal diameter section. Laterally distributed anti-buoyancy pressure plates are connected to the tops of the enlarged-base anti-uplift piles on both sides of the shield tunnel.

Description

Technical Field

[0001] This utility model relates to the field of tunnel and underground engineering technology, specifically to the field of large-diameter shield tunnel construction, and specifically to an anti-buoyancy reinforcement system for the shallow overburden starting zone of a shield tunnel. Background Technology

[0002] With the rapid development of urban underground space, the application of shallow tunnels in subway tunnels, integrated utility tunnels, and underground passages is becoming increasingly widespread. Shallow tunnels are often located in the launching area of ​​shield tunnels, and these tunnels are often situated in soft soil strata with high groundwater levels. Due to the relatively light weight of the tunnel structure, when the overburden thickness is insufficient or the groundwater level rises sharply, the tunnel will experience enormous buoyancy. When the buoyancy exceeds the sum of the tunnel's own weight and the effective weight of the overburden, the tunnel will experience uneven uplift, leading to segment joint opening, lining cracking, water leakage, and even serious engineering problems such as track irregularities, threatening operational safety.

[0003] Existing tunnel anti-buoyancy measures mainly include: counterweight method, anti-uplift pile method, and anchor bolt anti-buoyancy method. The counterweight method primarily involves increasing the thickness of the overburden and applying weight at the top or inside of the tunnel, such as the counterweight concrete segments invented in Chinese patent application CN201420857897.5. This method involves a large amount of earthwork, increases vertical load, and places high demands on the tunnel structure and foundation bearing capacity, resulting in poor economic efficiency. The anti-uplift pile method mainly involves installing anti-uplift piles on both sides or directly below the bottom of the tunnel, such as the underpass anti-uplift piles in Chinese patent application CN202411065740.3. Traditional anti-uplift piles only provide vertical uplift resistance, offering limited effectiveness in improving the overall anti-buoyancy stability of the tunnel and controlling uneven deformation. Furthermore, pile foundation construction causes significant disturbance to the surrounding soil. The anchor bolt method, which involves drilling holes into the bottom soil from inside the tunnel and inserting anchor bolts, such as the anti-buoyancy anchor bolt described in Chinese patent application number CN202210728448.X, suffers from limited construction space, is prone to damaging the tunnel's waterproofing layer, and has significant long-term corrosion issues with the anchor bolts. Therefore, existing technologies suffer from problems such as complex construction, high cost, low anti-buoyancy efficiency, and potential damage to the tunnel structure itself. There is an urgent need for a highly efficient, reliable, easy-to-construct, and minimally disruptive anti-buoyancy reinforcement composite structure. Utility Model Content

[0004] This utility model provides an anti-buoyancy reinforcement system for the shallow overburden starting zone of a shield tunnel, overcoming the problems of complex construction, high cost, low anti-buoyancy efficiency, or potential damage to the tunnel structure itself in the existing technology. The structure forms a rigid portal frame by "expanded bottom anti-uplift piles" and "anti-buoyancy pressure plates", which efficiently transfers local buoyancy to the deep foundation. The structure is not only simple and easy to construct, but the expanded bottom design is also more economical than traditional anti-uplift piles.

[0005] This utility model is achieved through the following technical solution:

[0006] A shallow overburden initiation zone anti-buoyancy reinforcement system for shield tunnels includes enlarged-base anti-tension piles set within the stratum reinforcement range and located on the left and right sides of the shield tunnel. The enlarged-base anti-tension piles include a normal diameter section of the anti-tension pile, and an enlarged-base section of the anti-tension pile is provided at the lower end of the normal diameter section of the anti-tension pile. The outer diameter of the enlarged-base section of the anti-tension pile is larger than that of the normal diameter section of the anti-tension pile.

[0007] The tops of the expanded bottom anti-uplift piles located on the left and right sides of the shield tunnel are connected to horizontally distributed anti-buoyancy pressure plates.

[0008] Furthermore, an enlarged diameter inclined section is provided between the normal diameter section of the tension pile and the enlarged base section of the tension pile. The enlarged diameter inclined section is a frustum-shaped structure with a diameter that gradually increases from top to bottom.

[0009] Furthermore, capping beams are provided at the top of the expanded bottom anti-uplift piles located on both sides of the shield tunnel, and the sides of the capping beams are integrated with the anti-buoyancy pressure plate.

[0010] Furthermore, the expanded-base anti-uplift pile is manufactured using the expanded-base pile construction process, and the capping beam and anti-buoyancy pressure plate are both made of reinforced concrete.

[0011] Furthermore, the pile head of the expanded-base anti-tension pile is connected to the capping beam by first binding the reinforcing steel and then pouring concrete; the side of the capping beam is connected to the anti-buoyancy pressure plate by first binding the reinforcing steel and then pouring concrete.

[0012] Furthermore, the top surface of the anti-buoyancy pressure plate is flush with the ground surface located in the ground reinforcement area.

[0013] Furthermore, the vertical slope of the widened inclined section is 10°-15°;

[0014] The outer diameter of the normal diameter section of the tension pile is 800-1100mm, and the outer diameter of the enlarged bottom section of the tension pile is 1400-1700mm.

[0015] Furthermore, multiple grouting pipes are pre-embedded on the anti-buoyancy pressure plate.

[0016] The working principle of the anti-buoyancy reinforcement system for the shallow overburden starting zone of the shield tunnel described in this utility model is as follows:

[0017] First, the anti-buoyancy reinforcement system for the shallow overburden starting zone of the shield tunnel, as described in this invention, is established within the soil reinforcement area of ​​the shallow overburden section before shield tunnel construction. After the tunnel is formed, due to the large volume of water discharged, according to Archimedes' principle, the large-diameter shield tunnel experiences significant buoyancy. Simultaneously, the pressure from synchronous grouting also generates buoyancy in the tunnel. As the grout solidifies, this buoyancy gradually dissipates and is therefore not considered in the anti-buoyancy calculation. In the shallow overburden section, the weight of the shield tunnel segments and the weight of the overburden layer are insufficient to balance the buoyancy. Under shallow overburden conditions, the soil fails along the shear zone. In this condition, the soil resistance of the shear zone can play a role in anti-buoyancy. Due to the large tunnel diameter and shallow overburden, additional anti-buoyancy force is required. The portal structure composed of the expanded-base anti-uplift piles and anti-buoyancy pressure plate described in this invention efficiently transfers local buoyancy to the deep foundation, thus playing an anti-buoyancy role. The pile side friction of the expanded-base anti-uplift piles can fully exert the anti-buoyancy effect.

[0018] The beneficial effects achieved by this utility model compared with the prior art are as follows:

[0019] (1) This utility model forms a rigid portal frame by using "expanded base anti-tension piles" and "anti-buoyancy pressure plate" to efficiently transfer local buoyancy to the deep foundation through the anti-buoyancy pressure plate and expanded base anti-tension piles. It fully utilizes the advantage of high anti-tension bearing capacity of expanded base piles and achieves group pile synergy through pressure plate. It has good anti-buoyancy performance and high bearing capacity. The overall anti-buoyancy performance far exceeds that of traditional equal cross section anti-tension pile scheme.

[0020] (2) The rigid portal frame structure provides great vertical and lateral stiffness, which can effectively suppress the overall uplift and differential deformation of the tunnel, which is extremely beneficial for controlling the internal force and deformation of the tunnel structure, making it strong in integrity and outstanding in deformation control.

[0021] (3) The force transmission path is clear and the reliability is high. The local buoyancy is efficiently transmitted to the deep foundation through the anti-buoyancy pressure plate and the expanded bottom anti-uplift pile. The buoyancy transmission path is clear and direct, the structural stress is clear, and the safety and reliability are high.

[0022] (4) Convenient construction and no interference: All anti-buoyancy components (piles and slabs) can be completed before the construction of the main tunnel structure. It belongs to the pre-protection mode of "support first, excavation later". The construction sequence of the main tunnel structure is clear and does not interfere with each other. It does not damage the tunnel segments or the structure itself and does not cause any disturbance.

[0023] (5) Good economic efficiency and obvious advantages: Under the premise of achieving the same anti-buoyancy safety factor, the number of piles can be reduced by 10% to 15% compared with the traditional equal cross-section pile scheme, or the cost can be reduced by 8% compared with the large-scale stratum reinforcement scheme, which has significant economic benefits.

[0024] (6) Good durability and low maintenance cost: The entire reinforcement system is made of reinforced concrete, which has excellent material durability. Unlike prestressed anchor rods and other systems, there is no need to worry about prestress relaxation or corrosion. The maintenance requirements throughout the entire life cycle are low and the cost is low. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the anti-buoyancy reinforcement system for the shallow overburden starting zone of the shield tunnel according to this utility model;

[0026] Figure 2 This is a schematic diagram of the enlarged base section of the expanded base anti-uplift pile in this utility model;

[0027] Figure 3 This is a construction flowchart of the expanded-base anti-uplift pile and anti-buoyancy pressure plate in this utility model.

[0028] In the diagram: 1. Crown beam, 2. Grouting pipe, 3. Anti-buoyancy pressure plate, 4. Shield tunnel, 5. Ground reinforcement zone, 6. Expanded bottom anti-tension pile, 7. Expanded bottom section of anti-tension pile, 8. Normal diameter section of anti-tension pile, 9. Expanded diameter inclined section. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0030] In the description of the utility model, it should be understood that the terms "front", "rear", "up", "down", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the utility model.

[0031] This embodiment takes the shallow overburden (approximately 1.39 m from the ground to the top of the shield tunnel) starting section of a large-diameter shield tunnel (outer diameter 14.3 m) as the application background, and discloses an anti-buoyancy reinforcement system for the shallow overburden starting area of ​​a shield tunnel. This reinforcement system needs to be completed before the shield tunnel construction.

[0032] Combined with appendix Figure 1As shown, before constructing the anti-buoyancy reinforcement system for the shallow overburden starting area of ​​the shield tunnel as described in this embodiment, a soil reinforcement zone 5 is first selected in the shallow overburden starting section. In this embodiment, the soil reinforcement zone 5 is the soil area extending from the left and right sides of the proposed shield tunnel, 5.0m below the bottom, to the ground surface. Then, the soil within this zone is initially reinforced by injecting cement grout using conventional triaxial mixing pile construction technology. Finally, the anti-buoyancy reinforcement system for the shallow overburden starting area of ​​the shield tunnel is constructed within the soil reinforcement zone 5. The anti-buoyancy reinforcement system for the shallow overburden starting area of ​​the shield tunnel mainly includes expanded-base anti-tension piles 6 located on the left and right sides of the shield tunnel 4. Multiple expanded-base anti-tension piles 6 are evenly distributed along the length of the shield tunnel 4 on each side.

[0033] like Figure 2 As shown, the enlarged-base tension pile 6 is a reinforced concrete structure constructed using C40 underwater concrete through an enlarged-base pile construction process. The enlarged-base tension pile 6 includes a normal diameter section 8, with an enlarged-base inclined section 9 and an enlarged-base section 7 sequentially located at the lower end of the normal diameter section 8. The enlarged-base section 7 provides greater lateral friction resistance to the structure. The normal diameter section 8 has a pile diameter of 1000 mm, and the enlarged-base section 7 has a pile diameter of 1600 mm and a vertical height of 750 mm. The enlarged-base inclined section 9 is a frustum-shaped structure with a gradually increasing diameter from top to bottom, and a height of 1500 mm, forming an angle of 11.3° with the vertical direction. Considering the impact of shield tunneling on the enlarged-base tension pile, the structural clearance between the enlarged-base tension pile and the shield tunnel 4 is 1.2 m.

[0034] The tops of the expanded-base anti-tension piles 6 located on both sides of the shield tunnel 4 are each equipped with a capping beam 1. The capping beam 1 is made of reinforced concrete and connects the expanded-base anti-tension piles 6 on the same side into a single unit. Anti-buoyancy pressure plates 3 are laterally distributed above the shield tunnel 4. The top surface of the anti-buoyancy pressure plates 3 is flush with the ground surface in the ground reinforcement zone 5. The plates are 1.0 m thick and are cast using C40 reinforced concrete. Multiple grouting pipes 2 are pre-embedded in the anti-buoyancy pressure plates 3 for later grouting. The width of the anti-buoyancy pressure plates 3 is the distance between the two expanded-base anti-tension piles 6. The anti-buoyancy pressure plates 3 and the expanded-base anti-tension piles 6 are connected as a single unit by the capping beams 1.

[0035] The construction process of the enlarged-base tension pile 6 is as follows: Figure 3 As shown, the specific construction method is as follows:

[0036] Step S1: Measurement and layout. Before installing the casing, at least four protective piles must be drawn from the center of the pile location. By pulling lines from the four protective piles, the center of the pile foundation can be determined more accurately, so as to be checked during the drilling process and when the reinforcement cage is positioned.

[0037] Step S2, Drill Rig Positioning: First, use a leveling device to adjust the drill rig to be horizontal, ensuring the drill rod is vertical. After the pile position is determined, pull out a crosshair to align the center of the drill rod with the pile center, controlling the deviation within 20 mm. Before installing the casing, first adjust the verticality of the drill rod using the drill rig's verticality instrument, then verify it with a theodolite to ensure the verticality is less than 1 / 200. After adjustment, the operator locks the horizontal, vertical, and center positions in the control room to bring the piling machine to its optimal state, thereby ensuring the quality of the hole formation.

[0038] Step S3: Steel casing installation. After the drilling rig is in place, drill a hole slightly larger in diameter than the casing and about 50 cm shallower than the designed casing depth. Hoist the casing and use a rotary drilling rig for static pressure insertion. Strictly control the center position of the casing according to the crosshair positioning lines. The casing is made of 20 mm thick steel plate, with 1-2 overflow holes at the top. The installation depth is generally 2-3 m to effectively stabilize the soil at the borehole opening. The top of the casing must be 200 mm above the ground to prevent surface debris and grout from flowing into the hole. After installation, check the center of the casing against the crosshair guide piles. The deviation between the casing and the pile center should not exceed 50 mm. The casing should be installed vertically, and the surrounding area should be filled with compacted clay in layers.

[0039] Step S4: After drilling to the same diameter and installing the casing, stabilizing fluid is injected into the hole using a mud pump. The drilling rig is driven by a diesel engine and hydraulic system, which rotates and presses down the drill rod and the cylindrical drill bit, using its own weight and hydraulic pressure for excavation. After the bucket is full, the drill is lifted and the soil is unloaded to the designated area. The bucket door is closed and the drilling rig is locked. The drill bit is then lowered again for cyclical operation to the design depth, with continuous replenishment of stabilizing fluid during the process. The drilling speed needs to be adjusted according to the strata, not exceeding 10 m / h, and controlled at 3 m / h for loose strata. The stabilizing fluid level is maintained at 0.5–1 m below the ground surface, and its density, viscosity, and other indicators, as well as the verticality of the hole, are monitored in real time. Appropriate drilling tools are selected based on the geological conditions. After reaching the design elevation at the same diameter, a reaming bit is used for reaming operations.

[0040] Step S5: Underreaming operation. The underreaming rotary drilling rig is replaced with an underreaming drill bit to carry out underreaming operation. During the underreaming construction, the rotary underreaming drill bit rotates, and the inverted titanium alloy inlay of the drill bit is divided into four parts to cut and excavate the sand and soil, and to carry out horizontal underreaming and propulsion operation. The original soil generated by the underreaming operation is contained by the drill bit, and the drill bit is retracted to bring the original soil out of the ground.

[0041] Step S6: Management of the artificial stabilizing fluid for borehole formation. For rotary drilling rigs, a high-quality bentonite-based artificial stabilizing fluid is used for wall protection, with a specific gravity controlled between 1.05 and 1.30. The main materials are bentonite, water, and CMC. This fluid slows down debris settling, facilitates borehole cleaning, and maintains long-term borehole stability. The stabilizing fluid is compatible with concrete and can be displaced during the grouting process. After injection into the borehole, it penetrates the soil layer, enhancing borehole wall strength and preventing groundwater inflow. The rotary drilling rig uses original soil for cutting and excavation. After borehole formation, a static mud-like stabilizing fluid is injected, which is ultimately displaced by pouring concrete. The fluid is then purified by a cyclone desanding device for reuse.

[0042] Step S7: Hole cleaning. During hole cleaning, lower the underreaming drill bit or rotary drilling bucket to the bottom of the hole and remove the slag by rotating and cutting. After cleaning, the sediment at the bottom of the hole needs to be measured to ensure that the sediment thickness is less than 200 mm before grouting after lowering the steel cage.

[0043] Step S8: Fabrication and installation of the reinforcing cage. The reinforcing cage shall be hoisted in sections. Collisions shall be strictly prevented during hoisting, and deformation shall not be allowed.

[0044] Step S9: Install the guide pipe. After the reinforcing cage is installed, the guide pipe should be lowered in a timely manner, and the sediment at the bottom of the hole should be strictly controlled. Before use, the guide pipe must undergo a water pressure test of 0.9-1.3 MPa. The threaded joint should be equipped with an O-ring and tightened to prevent leakage. After use, clean and maintain it in a timely manner. The guide pipe should be lowered slowly and in the center to avoid snagging on the reinforcing cage. The bottom end should be 300-500 mm away from the bottom of the hole. If the sediment exceeds 200 mm after lowering, the hole should be cleaned.

[0045] Step S10: Secondary hole cleaning. If the sediment exceeds the design and construction specifications, pump suction reverse circulation should be used to clean the hole. The next process can only be carried out after the control indicators of the specific gravity, viscosity, sand content and sediment thickness of the stabilizing liquid are met.

[0046] Step S11: Concrete pouring. Concrete pouring should begin within 30 minutes after hole cleaning is completed; otherwise, the hole should be cleaned again. The initial setting time of the concrete should be controlled within 3-4 hours, and the pouring time for a single pile should not exceed 2 hours. During pouring, first place a water-tight ball in the tremie pipe and a water-tight plate in the hopper. After the hopper is full, quickly open the water-tight plate to allow the concrete to fall along the water-tight ball. The initial pouring volume must meet the calculated value. Pouring should be continuous, and the tremie pipe should be buried at a depth of 2-6 m.

[0047] Step S12: Backfill the pile hole and pour the concrete to 1 m above the top of the engineering pile. Fill the upper empty hole with sand to the design elevation and continue to construct the anti-buoyancy pressure plate. Reinforcing bars are reserved on the left and right sides of the anti-buoyancy pressure plate.

[0048] After the expansion-base anti-uplift pile is completed, the pile head at the top is chiseled off to expose the reinforcing steel. Then the reinforcing steel is tied and concrete is poured to make the capping beam 1. The side of the capping beam 1 is reserved with reinforcing steel. The side of the capping beam 1 is connected to the anti-buoyancy pressure plate 3 by first tying the reinforcing steel and then pouring concrete.

[0049] Through the implementation of this combined structure, the shallow-buried tunnel section has formed a complete force transmission system consisting of "shield tunnel - overlying soil - anti-buoyancy pressure plate - enlarged-base anti-tension piles - foundation soil". Calculations and verifications show that its anti-buoyancy safety factor meets the specifications. The rigid portal frame formed by the "enlarged-base anti-tension piles" and "anti-buoyancy pressure plate" efficiently transmits local buoyancy to the deep foundation through the anti-buoyancy pressure plate and enlarged-base anti-tension piles, fully leveraging the high uplift bearing capacity of the enlarged-base piles. Furthermore, the pressure plate enables the collaborative work of the pile group, resulting in excellent anti-buoyancy performance, high bearing capacity, and overall anti-buoyancy performance far exceeding that of traditional uniform-section anti-tension pile schemes.

Claims

1. A anti-floating reinforcement system for shield tunneling shallow cover starting area, characterized in that, The structure includes expanded bottom anti-tension piles (6) set within the ground reinforcement zone (5) and located on the left and right sides of the shield tunnel (4). The expanded bottom anti-tension piles (6) include a normal diameter section (8) of the anti-tension piles. The lower end of the normal diameter section (8) of the anti-tension piles is provided with an expanded bottom section (7) of the anti-tension piles. The outer diameter of the expanded bottom section (7) of the anti-tension piles is larger than that of the normal diameter section (8) of the anti-tension piles. An expansion slope section (9) is provided between the normal diameter section (8) of the tension pile and the expansion base section (7) of the tension pile. The expansion slope section (9) is a frustum-shaped structure with a diameter that gradually increases from top to bottom. The tops of the expanded bottom anti-uplift piles (6) located on the left and right sides of the shield tunnel (4) are connected to the horizontally distributed anti-buoyancy pressure plates (3).

2. The anti-floating reinforcement system for a shield tunneling shallow cover starting area according to claim 1, wherein, The top of the expanded bottom anti-uplift piles (6) located on the left and right sides of the shield tunnel (4) are all equipped with cap beams (1), and the side of the cap beams (1) is connected to the anti-buoyancy pressure plate (3) as a whole.

3. The anti-float reinforcing system for a shallow-trench launching area of a shield tunnel according to claim 2, wherein, The expanded-base anti-uplift pile (6) is made using the expanded-base pile construction process, and the cap beam (1) and the anti-buoyancy pressure plate (3) are both made of reinforced concrete.

4. The anti-float reinforcing system for a shallow-trench launching area of a shield tunnel according to claim 3, characterized in that, The pile head of the expanded-base anti-uplift pile (6) is connected to the capping beam (1) by first binding the reinforcing steel and then pouring concrete; the side of the capping beam (1) is connected to the anti-buoyancy pressure plate (3) by first binding the reinforcing steel and then pouring concrete.

5. The anti-float reinforcement system for a shallow-trench launching area of a shield tunnel according to claim 1, wherein, The top surface of the anti-buoyancy pressure plate (3) is flush with the ground surface located in the ground reinforcement area (5).

6. The anti-floatation reinforcement system for a shallow cover initiation area of a tunneling machine according to any one of claims 1-5, wherein, The slope of the widened inclined section (9) in the vertical direction is 10°-15°; The outer diameter of the normal diameter section (8) of the tension pile is 800-1100mm, and the outer diameter of the expanded bottom section (7) of the tension pile is 1400-1700mm.

7. The anti-buoyancy reinforcement system for the shallow overburden starting zone of a shield tunnel according to any one of claims 1-5, characterized in that, Multiple grouting pipes (2) are pre-embedded on the anti-buoyancy pressure plate (3).

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