Anti-floating stabilizing device and method for ultra-shallow soil covering and ultra-large diameter shield tunnel

Abstract

The invention belongs to the technical field of shield tunnel construction, and particularly relates to an anti-floating stabilizing device and method for an ultra-shallow-earthing and ultra-large-diameter shield tunnel, and the anti-floating stabilizing device comprises an anti-floating pressing plate, a first expanded-base uplift pile, a second expanded-base uplift pile, a top beam and the like; the first expanded-base uplift pile is arranged above a tunnel, the second expanded-base uplift piles are vertically arranged on the two sides of a tunnel segment, the axes of the first expanded-base uplift pile and the second expanded-base uplift piles are vertically downward, the anti-floating pressing plate is connected with the first expanded-base uplift pile and a top beam, and vertical one-way grouting pipes are arranged in the anti-floating pressing plate and the first expanded-base uplift pile. The bottom of the one-way grouting pipe is flush with the bottom of the first expanded-base uplift pile. According to the scheme, the expanded-base uplift piles are adopted to improve the anti-floating bearing capacity, the anti-floating effect can be achieved as soon as possible, the functions of preventing slurry return of the grouting holes and maintaining stability of soil around the pipe piece are achieved, construction is convenient, stability is good, the high anti-floating stabilizing effect can be achieved, and the wide actual popularization and application value is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of shield tunnel construction, and in particular relates to an anti-floating stabilization device and method for an ultra-shallow covered ultra-large diameter shield tunnel. Background Art

[0002] As tunnel projects rapidly develop towards super-large diameters, the problems encountered in tunnel construction are increasing. Among them, the problem of pipe segment floating during shield construction has become a major challenge. At the same time, the complexity of shield tunnel projects is gradually increasing. Many super-large diameter shield tunnel projects are frequently encountering poor working conditions of super-shallow soil cover. Under super-shallow soil cover conditions, due to the small soil cover load and weak strata, pipe segments are more likely to float during super-large shield construction. If not handled properly, it is very easy to cause pipe segment dislocation, damage and leakage, and even cause stratum instability disasters.

[0003] In order to solve the problem of pipe segment floating, some solutions have been proposed in the prior art. The invention patent of [CN108301842A] discloses a fixing device and construction method for controlling the floating of shield tunnel segments, including a plurality of anti-floating piles arranged in sequence along the route direction of the shield tunnel. After the shield tunnel passes through the anti-floating piles, the distance between the segments and the anti-floating piles is only the distance between the outer diameter of the shield machine and the outer diameter of the segments, and the friction between the anti-floating piles and the mudstone formation is used to control the floating of the segments. However, the difference between the excavation section diameter and the outer diameter of the segments of super-large diameter shield tunnels is generally 300 mm or more, which results in the floating space of the segments after they are separated from the shield tail being at least 150 mm. When the above scheme is applied, the floating space of the segments is large. When the anti-floating piles contact the segments and play an anti-floating role, the floating amount of the segments has exceeded the limit, posing a great safety hazard. In addition, the invention patent with the publication number [CN118815503A] discloses a shield tunnel anti-floating structure and its construction method, including pre-placed steel plates, cement soil piles and anti-floating components, using the high-pressure rotary jet pile machine's rotary jet drill rod to construct cement soil piles in the soil layer outside the shield segment through the reserved grouting holes, and grouting the outer side of the shield segment to form a circumferential cushion layer to achieve the purpose of anti-floating of the segment. During the shield construction process, only after the segment is separated from the shield tail, can the on-site conditions for applying cement soil piles to the soil through the reserved grouting holes of the segment be met. However, during the construction period of the super-large diameter shield tunnel, due to the existence of the supporting trolley behind the shield, the working space inside the segment is narrow, and the application of this method is limited. In addition, compared with the segment floating period of 10 h to 20 h, the construction period of cement soil piles is longer. Before the anti-floating effect is fully exerted, the segment floating has already stagnated, resulting in poor anti-floating effect of the combined device. Summary of the invention

[0004] In order to solve the problems of poor safety and unsatisfactory anti-floating effect of existing anti-floating designs, an anti-floating stabilization device and method for ultra-shallow overburden ultra-large diameter shield tunnels are proposed. An anti-floating pressure plate and a crown beam are arranged above the shield tunnel, a first bottom-enlarged anti-pullout pile is arranged above the axis of the shield tunnel, and a second bottom-enlarged anti-pullout pile is arranged on both sides of the shield tunnel. This combined structure forms a three-sided enclosure structure, thereby constraining the soil displacement within the three-sided enclosure range, effectively reducing the instability risk of ultra-large diameter shields during construction in ultra-shallow overburden strata, and realizing safe construction of shield tunnels.

[0005] The present invention is implemented by adopting the following technical scheme: an anti-floating stabilization device for an ultra-shallow covered ultra-large diameter shield tunnel, comprising an anti-floating pressure plate, a first bottom-enlarged anti-pullout pile, a second bottom-enlarged anti-pullout pile and a crown beam, wherein the anti-floating pressure plate is connected to the first bottom-enlarged anti-pullout pile and the crown beam, and the anti-floating pressure plate and the crown beam are located above the first bottom-enlarged anti-pullout pile and the second bottom-enlarged anti-pullout pile and abut against the ground surface; The first expanded bottom anti-pullout pile is vertically arranged above the pipe segment, and the second expanded bottom anti-pullout pile is vertically arranged on both sides of the pipe segment. The first expanded bottom anti-pullout pile and the second expanded bottom anti-pullout pile extend downward from the ground surface, and the bottom of the first expanded bottom anti-pullout pile abuts against the excavation section, so that the pipe segment is constrained under the first expanded bottom anti-pullout pile, and the bottom of the second expanded bottom anti-pullout pile extends to below the pipe segment.

[0006] In addition, a one-way grouting pipe is provided through the anti-floating pressure plate and the first bottom-enlarged anti-pullout pile. The one-way grouting pipe is installed vertically, and its bottom is flush with the bottom of the first bottom-enlarged anti-pullout pile.

[0007] Furthermore, the anti-floating plate, the first expanded bottom anti-pullout pile, the second expanded bottom anti-pullout pile and the crown beam are all reinforced concrete structures, and embedded steel bars are provided between the anti-floating plate and the crown beam, between the anti-floating plate and the first expanded bottom anti-pullout pile, and between the crown beam and the second expanded bottom anti-pullout pile.

[0008] Furthermore, the one-way grouting pipe includes, from top to bottom, a first straight-through one-way valve, a grouting pipe, and a second straight-through one-way valve. The upper port of the first straight-through one-way valve is provided with a thread for external grouting equipment. The grouting slurry can only flow vertically downward through the first straight-through one-way valve, the grouting pipe, and the second straight-through one-way valve in sequence.

[0009] Furthermore, the first expanded bottom anti-pullout pile and the second expanded bottom anti-pullout pile adopt a variable cross-section design, including a pile of uniform cross-section and an expanded bottom end located at the bottom of the pile of uniform cross-section.

[0010] The present invention further proposes a method for preventing floating of an ultra-shallow covered ultra-large diameter shield tunnel, comprising the following steps: Step S1: Calculate the buoyancy of the segment per unit length along the tunnel axis. F and cover load W , determine the deadweight of the segment per unit length Gs ; F =γ g π R 2 W =γ s (2 Rd +(2-π / 2) R 2 ) In the formula, γ g It is a serous heavy grade; R is the outer radius of the segment; s is the average floating weight of the soil covering the upper part of the segment; d It is the thickness of soil cover on the upper part of the segment.

[0011] Step S2, setting initial values ​​of various dimensions of the first expanded bottom anti-pullout pile, the length of the first expanded bottom anti-pullout pile is the thickness of the covering soil, so that its bottom abuts against the top of the excavated section, setting initial values ​​of various dimensions of the second expanded bottom anti-pullout pile, and in the horizontal plane, the center distance between adjacent piles is not less than twice the expanded bottom end diameter; Step S3: Calculate the ultimate pull-out bearing capacity of the first bottom-enlarged pull-out pile Q k,1 And the ultimate pull-out bearing capacity of the pile foundation on one side of the second expanded bottom pull-out pile Q k,2 , the ultimate pull-out bearing capacity is calculated as follows: ; In the formula, i Depends on the number of different soil layer types; G k is the pile weight; q sik The pile side surface i Standard value of ultimate lateral resistance of layer soil; u i For the pile around i Perimeter of the damaged section of the soil layer; l i For the pile around i Thickness of soil layer; length measured from the bottom of the pile l i ≤4 d hour, u i Take π D , D is the bottom diameter of the expanded bottom end, d is the pile diameter; when the length is measured from the bottom of the pile l> 4 d , u Take π d ; λi For the i The pull-out coefficient of the pile in the soil layer is 0.5-0.7 for sandy soil and 0.7-0.8 for clay and silt.

[0012] Step S4, calculating the ultimate anti-buoyancy forces provided by the first bottom-enlarged anti-pullout pile and the second bottom-enlarged anti-pullout pile respectively within a unit length along the tunnel axis direction; ; In the formula, Q a,1 The ultimate buoyancy resistance provided by the first expanded bottom anti-pullout pile per unit length; Q k,1 is the ultimate pull-out bearing capacity of the first bottom-enlarged pull-out pile; m 1 is the spacing between the first expanded bottom anti-pullout piles; ; In the formula, Q a,2 It is the ultimate anti-buoyancy force provided by the second expanded bottom anti-pullout pile per unit length under the condition of vertical arrangement side by side on both sides of the segment; Q k,2 is the ultimate pull-out bearing capacity of the second bottom-enlarged pull-out pile; m 2 is the spacing of the second expanded bottom anti-pullout piles; Step S5: Determine the anti-floating stability and define the anti-floating coefficient η , ; And the anti-floating safety factor η s Compare( η s Take 1.1~1.2), if η<η s , then the anti-floating requirements are not met, the pile spacing can be reduced, and the size of the first expanded bottom anti-pullout pile and the second expanded bottom anti-pullout pile can be adjusted until η≥η s ; Step S6, constructing and installing the crown beam, the second bottom-enlarged anti-pullout pile, the first bottom-enlarged anti-pullout pile, and the one-way grouting pipe in the order of first the periphery and then the interior, and finally constructing the anti-floating pressure plate; Step S7, after the segment is separated from the shield tail of the shield machine by a certain distance, generally 1 m to 2 m, quick-setting slurry is injected into the grouting pipe through the upper port of the first straight-through one-way valve. The quick-setting slurry is a polyurethane slurry or a cement-water glass double liquid slurry with a setting time between 1 min and 30 min.

[0013] Compared with the prior art, the advantages and positive effects of the present invention are: This scheme forms an anti-floating stabilization device by setting a first bottom-enlarged anti-pullout pile above the axis of the shield tunnel, setting a second bottom-enlarged anti-pullout pile on both sides of the shield tunnel, and connecting them with the anti-floating pressure plate and the crown beam. During use, part of the uplift load on the segment is borne by the lateral friction resistance around the first bottom-enlarged anti-pullout pile, and the other part is transmitted to the second bottom-enlarged anti-pullout pile on both sides of the tunnel by the anti-floating pressure plate and the crown beam. This not only significantly improves the friction between the anti-pullout pile above the segment and the surrounding strata, thereby significantly increasing the uplift bearing capacity, but also can give full play to the restraining ability of the entire anti-floating stabilization device on the segment, thereby having better anti-floating performance. In addition, a one-way grouting pipe is arranged through the anti-floating pressure plate and the first bottom-enlarged anti-pullout pile, and quick-setting grouting liquid can be injected into the space above the pipe segment after the pipe segment is separated from the shield tail, so as to quickly fill the building gap between the pipe segment and the first bottom-enlarged anti-pullout pile, that is, the floating space of the pipe segment is reduced and the buoyancy force of the pipe segment is timely transmitted to the first bottom-enlarged anti-pullout pile, thereby effectively solving the floating problem of the pipe segment, and the risk of the synchronous grouting slurry around the pipe segment overflowing from the one-way grouting pipe is avoided by the design of the one-way valve; This design scheme can effectively reduce the risk of instability of ultra-large diameter shield during construction in ultra-shallow overburden strata, and realize safe construction of shield tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of the anti-floating stabilization device according to the first embodiment of the present invention; Figure 2 This is a schematic diagram of the transverse cross-sectional structure of the anti-floating stabilization device according to the first embodiment of the present invention; Figure 3 It is a side view of the first bottom-enlarged anti-pullout pile in the overall structure in the first embodiment of the present invention; Figure 4 It is a side view of the second bottom-enlarged anti-pullout pile in the overall structure in the first embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of a one-way grouting pipe in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the construction method flow chart of the second embodiment of the present invention. DETAILED DESCRIPTION

[0015] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0016] Embodiment 1: An anti-floating stabilization device for an ultra-shallow covered ultra-large diameter shield tunnel, combined with Figure 1-2As shown, it includes an anti-floating pressure plate 1, a first expanded bottom anti-pullout pile 2, a second expanded bottom anti-pullout pile 4 and a crown beam 5. The anti-floating pressure plate 1 and the crown beam 5 are located above the first expanded bottom anti-pullout pile 2 and the second expanded bottom anti-pullout pile 4 and abut against the ground surface. The cross-sectional shape of the anti-floating pressure plate 1 is rectangular, and it is connected to the first expanded bottom anti-pullout pile 2 and the crown beam 5. The first expanded bottom anti-pullout pile 2 is vertically arranged above the pipe segment 6, and the second expanded bottom anti-pullout pile 4 is vertically arranged on both sides of the pipe segment 6. The first expanded bottom anti-pullout pile 2 and the second expanded bottom anti-pullout pile 4 extend downward from the ground surface, and the bottom of the first expanded bottom anti-pullout pile 2 abuts against the excavation section 7, so that the pipe segment 6 is constrained below the first expanded bottom anti-pullout pile 2, and the bottom of the second expanded bottom anti-pullout pile 4 extends to below the pipe segment 6.

[0017] The axes of the first bottom-enlarged anti-pullout pile 2 and the second bottom-enlarged anti-pullout pile 4 are vertically downward. Figure 1 and Figure 4 As shown, it includes equal-section piles (first equal-section pile 21 and second equal-section pile 41) and expanded bottom ends (first expanded bottom end 22 and second expanded bottom end 42). In this embodiment, by setting a first expanded bottom pull-out pile above the axis of the shield tunnel, compared with the equal-section pile, there is one more expanded bottom end, which can significantly improve the friction between the pull-out pile and the surrounding strata, thereby significantly increasing the pull-out bearing capacity, thereby having better anti-floating performance; and, in combination with the second expanded bottom pull-out piles set on both sides of the shield tunnel, in use, part of the floating load on the segment is borne by the lateral friction resistance around the first expanded bottom pull-out pile, and the other part is transmitted to the second expanded bottom pull-out piles on both sides of the tunnel by the anti-floating pressure plate and the crown beam, and the second expanded bottom pull-out pile is also a variable diameter pile body, which can give full play to the lateral friction resistance of the stratum on the pile body.

[0018] Continue to refer Figure 1 and Figure 3 A one-way grouting pipe 3 is provided through the anti-floating pressure plate 1 and the first bottom-enlarged anti-pulling pile 2. The one-way grouting pipe 3 is installed vertically, and its bottom is flush with the bottom of the first bottom-enlarged anti-pulling pile 2. Figure 5 As shown, the one-way grouting pipe 3 includes a first straight one-way valve 31, a grouting pipe 32 and a second straight one-way valve 33 from top to bottom. The grouting slurry can only flow vertically downward through the first straight one-way valve 31, the grouting pipe 32 and the second straight one-way valve 33 in sequence, thereby avoiding the risk of the synchronous grouting slurry around the pipe segment overflowing from the one-way grouting pipe. In addition, a thread is provided at the upper port of the first straight one-way valve 31 for external grouting equipment. By setting a one-way grouting pipe, quick-setting slurry can be injected into the space above the pipe segment after the pipe segment is separated from the shield tail, so as to quickly fill the construction gap between the pipe segment and the first bottom-enlarged anti-pullout pile, that is, the floating space of the pipe segment is reduced and the buoyancy of the pipe segment is timely transmitted to the first bottom-enlarged anti-pullout pile, thereby effectively solving the problem of pipe segment floating.

[0019] In this embodiment, the anti-floating pressure plate 1, the first expanded bottom anti-pullout pile 2, the second expanded bottom anti-pullout pile 4 and the crown beam 5 are all reinforced concrete structures. Pre-embedded steel bars are provided between the anti-floating pressure plate 1 and the crown beam 5, and between the anti-floating pressure plate 1 and the first expanded bottom anti-pullout pile 2. Pre-embedded steel bars are also provided between the crown beam 5 and the second expanded bottom anti-pullout pile 4. When constructing the above structure, the anti-floating pressure plate 1, the first expanded bottom anti-pullout pile 2, the second expanded bottom anti-pullout pile 4 and the crown beam 5 are formed into an integral structure by pouring concrete, which can better prevent the pipe segment 6 from floating up and maintain the stability of the soil 8.

[0020] Embodiment 2: A method for the anti-floating stabilization device for an ultra-shallow covered ultra-large diameter shield tunnel based on the embodiment 1, comprising the following steps: Step S1: Calculate the buoyancy of the segment 6 per unit length along the tunnel axis. F and cover load W , determine the self-weight per unit length of segment 6 G s ; In this embodiment, the outer radius of the tube segment 6 is R The thickness is 7.15 m and the slurry density is 20 kN / m 3 , the cover thickness is 5 m, the deadweight of segment 6 G s Take 557.5 kN / m, γ s 10 kN / m 3 ; F =20π×7.15 2 =3212.1 kN / m W =10×(2×7.15×5+(2-π / 2)×7.15 2 )=934.4 kN / m Step S2, setting initial values ​​of the dimensions of the first expanded bottom anti-pullout pile 2, the length of the first expanded bottom anti-pullout pile 2 is the thickness of the covering soil, so that its bottom abuts against the top of the excavation section 7, setting initial values ​​of the dimensions of the second expanded bottom anti-pullout pile 4, and in the horizontal plane, the center distance between adjacent piles is not less than twice the expanded bottom end diameter, that is, the distance between the center of the two types of expanded bottom anti-pullout piles and the center of their corresponding adjacent expanded bottom anti-pullout piles is not less than twice the expanded bottom end diameter; In this embodiment, the length of the first expanded bottom anti-pullout pile 2 is 5 m, the length of the uniform cross-section pile 21 is 3 m, the diameter is 0.75 m, the diameter of the expanded bottom end 22 is 1.5 m, and the distance between the piles is 3 m. The length of the second expanded bottom anti-pullout pile 4 is 24 m, the length of the uniform cross-section pile 41 is 20 m, the diameter is 0.75 m, the diameter of the expanded bottom end 42 is 1.5 m, and the distance between the piles is 3 m; Step S3: Calculate the ultimate pull-out bearing capacity of the first bottom-enlarged pull-out pile 2 Q k,1, the ultimate pull-out bearing capacity of the pile foundation on one side of the second bottom-enlarged pull-out pile 4 Q k,2 ; In this embodiment, the first bottom-enlarged anti-pullout pile 2 λ 1 takes 0.7, q sik Take 50 kPa, G 1 Take 156.5 kN, the second expanded bottom anti-pulling pile 4 λ 2 takes 0.8, q sik Take 50 kPa, G 2 Taking 412.9 kN, we have: ; ; Step S4, calculating the ultimate anti-buoyancy forces respectively provided by the first bottom-enlarged anti-pullout pile 2 and the second bottom-enlarged anti-pullout pile 4 within a unit length range along the tunnel axis direction; ; ; Step S5, judging the anti-floating stability. In this embodiment, the anti-floating safety factor is set η s is 1.1; ; It can be seen that the anti-floating requirements are met.

[0021] Step S6, constructing and installing the crown beam 5, the second bottom-enlarged anti-pullout pile 4, the first bottom-enlarged anti-pullout pile 2, and the one-way grouting pipe 3 in the order of first the periphery and then the interior, and finally constructing the anti-floating pressure plate 1; Step S7, after the segment 6 is separated from the shield tail of the shield machine by a certain distance, quick-setting slurry 9 is injected into the grouting pipe 32 through the upper port of the first straight-through one-way valve 31, because the timing of quick-setting slurry grouting cannot be too early, otherwise the shield tail and the segment will stick together. If it is too late, the synchronous grouting slurry will coagulate and the floating will end. Generally, the distance should be greater than 1m, and 1m~2m is preferred in this embodiment; wherein, the quick-setting slurry 9 is selected from polyurethane slurry or cement-water glass double liquid slurry with a coagulation time between 1 min~30 min.

[0022] It can be seen that this scheme forms a three-sided enclosure structure by setting an anti-floating pressure plate, a crown beam and a first expanded bottom anti-pullout pile above the shield tunnel, and combining them with the second expanded bottom anti-pullout piles set on both sides of the shield tunnel to constrain the soil displacement within the three-sided enclosure range, effectively reducing the instability risk of the super-large diameter shield during construction in the ultra-shallow overburden layer, and realizing the safe construction of the shield tunnel.

[0023] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An anti-floating stabilization device for an ultra-shallow covered ultra-large diameter shield tunnel, characterized in that: It includes an anti-floating pressure plate, a first anti-pullout pile with an expanded bottom, a second anti-pullout pile with an expanded bottom, and a crown beam. The anti-floating pressure plate is connected with the first anti-pullout pile with an expanded bottom and the crown beam. The anti-floating pressure plate and the crown beam are located above the first anti-pullout pile with an expanded bottom and the second anti-pullout pile, and abut against the ground surface. The first expanded bottom anti-pullout pile is vertically arranged above the pipe segment, and the second expanded bottom anti-pullout pile is vertically arranged on both sides of the pipe segment. The first expanded bottom anti-pullout pile and the second expanded bottom anti-pullout pile extend downward from the ground surface, and the bottom of the first expanded bottom anti-pullout pile abuts against the excavation section, so that the pipe segment is constrained under the first expanded bottom anti-pullout pile, and the bottom of the second expanded bottom anti-pullout pile extends to below the pipe segment.

2. The anti-floating stabilization device for ultra-shallow covered ultra-large diameter shield tunnels according to claim 1 is characterized by: A one-way grouting pipe is provided through the anti-floating pressure plate and the first bottom-enlarged anti-pullout pile. The one-way grouting pipe is installed vertically, and its bottom is flush with the bottom of the first bottom-enlarged anti-pullout pile.

3. The anti-floating and stabilizing device for ultra-shallow covered ultra-large diameter shield tunnels according to claim 1 is characterized in that: The anti-floating plate, the first expanded bottom anti-pullout pile, the second expanded bottom anti-pullout pile and the crown beam are all reinforced concrete structures, and embedded steel bars are provided between the anti-floating plate and the crown beam, between the anti-floating plate and the first expanded bottom anti-pullout pile, and between the crown beam and the second expanded bottom anti-pullout pile.

4. The anti-floating stabilization device for ultra-shallow covered ultra-large diameter shield tunnels according to claim 2 is characterized by: The one-way grouting pipe includes, from top to bottom, a first straight-through one-way valve, a grouting pipe, and a second straight-through one-way valve. The upper port of the first straight-through one-way valve is provided with a thread for external grouting equipment. The grouting slurry can only flow vertically downward through the first straight-through one-way valve, the grouting pipe, and the second straight-through one-way valve in sequence.

5. The anti-floating stabilization device for ultra-shallow covered ultra-large diameter shield tunnels according to claim 1 is characterized by: The first expanded bottom anti-pullout pile and the second expanded bottom anti-pullout pile adopt a variable cross-section design, including a pile of uniform cross-section and an expanded bottom end located at the bottom of the pile of uniform cross-section.

6. The method for the anti-floating stabilization device of the ultra-shallow covered ultra-large diameter shield tunnel according to claim 2 is characterized in that: The following steps are involved: Step S1: Calculate the buoyancy of the segment per unit length along the tunnel axis F and cover load W , determine the deadweight of the segment per unit length G s ,in: F =c g p R 2 W =c s (2 Rd +(2-π / 2) R 2 ) In the formula, γ g It is a serous heavy grade; R is the outer radius of the segment; s is the average floating weight of the soil covering the upper part of the segment; d is the thickness of soil covering the upper part of the segment; Step S2, setting the initial values ​​of the sizes of the first expanded bottom anti-pullout pile and the second expanded bottom anti-pullout pile, the length of the first expanded bottom anti-pullout pile is the thickness of the covering soil, so that its bottom abuts against the top of the excavated section, and in the horizontal plane, the center distance between adjacent piles is not less than twice the expanded bottom end diameter; Step S3, respectively calculating the ultimate pull-out bearing capacity of the first bottom-enlarged pull-out pile and the ultimate pull-out bearing capacity of the pile foundation on one side of the second bottom-enlarged pull-out pile; Step S4, calculating the ultimate anti-buoyancy forces provided by the first bottom-enlarged anti-pullout pile and the second bottom-enlarged anti-pullout pile within a unit length range along the tunnel axis direction; Step S5: Determine the anti-floating stability and define the anti-floating coefficient η , ; And the anti-floating safety factor η s Compare, if η<η s , the anti-floating requirement is not met. By reducing the pile spacing, the sizes of the first and second expanded bottom anti-pullout piles are adjusted until η≥η s ;in, η s Take 1.1~1.2; Step S6: before the shield machine arrives at the anti-floating stabilization device installation area, the crown beam, the second bottom-enlarged anti-pullout pile, the first bottom-enlarged anti-pullout pile, and the one-way grouting pipe are constructed and installed in the order of the periphery first and the interior later, and finally the anti-floating pressure plate is constructed; Step S7: After the segment is separated from the shield tail of the shield machine by a certain distance, quick-setting slurry is injected into the one-way grouting pipe to complete the construction.

7. The method for anti-floating stabilization device of ultra-shallow soil-covered ultra-large diameter shield tunnel according to claim 6 is characterized in that: In step S3, the ultimate pull-out bearing capacity Q k Calculated by: ； In the formula, i is the number of soil layer types; G k is the pile weight; λ i For the first i Pull-out coefficient of piles in layer soil; q sik The pile side surface i Standard value of ultimate lateral resistance of layer soil; u i For the pile around i Perimeter of the damaged section of the soil layer; l i For the pile around i Thickness of soil layer.

8. The method for anti-floating stabilization device of ultra-shallow soil-covered ultra-large diameter shield tunnel according to claim 6 is characterized in that: In step S4, the ultimate anti-buoyancy force is calculated in the following manner: ； In the formula, Q a,1 The ultimate buoyancy resistance provided by the first expanded bottom anti-pullout pile per unit length; Q k,1 is the ultimate pull-out bearing capacity of the first bottom-enlarged pull-out pile; m 1 is the pile spacing of the first expanded bottom anti-pulling piles; ； In the formula, Q a,2 It is the ultimate anti-buoyancy force provided by the second expanded bottom anti-pullout pile per unit length under the condition of parallel arrangement on both sides of the segment; Q k,2 is the ultimate pull-out bearing capacity of the second bottom-enlarged pull-out pile; m 2 is the pile spacing of the second expanded bottom anti-pullout piles.

9. The method for anti-floating stabilization device of ultra-shallow soil-covered ultra-large diameter shield tunnel according to claim 6 is characterized in that: In step 7, the quick-setting slurry is a polyurethane slurry or a cement-water-glass double-liquid slurry with a setting time between 1 min and 30 min.

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