Reinforcing method for large-diameter shield tunnel with soft soil layer and jointed segments

Abstract

The application discloses a reinforcing method suitable for a large-diameter shield tunnel of a CT joint segment in a soft soil layer, which comprises the following steps: firstly, according to the stratum properties, anchoring and anti-floating needs, the setting range of a reserved grouting hole on a segment, the length of a grouting pipe and the expansion position of a grouting bag are planned; secondly, a high-performance engineering plastic pipe is pre-buried in the grouting hole, and a plain concrete protective layer is reserved between the outer end of the engineering plastic pipe and the segment outer skin; thirdly, a buried steel pipe with a grouting bag is chiseled and installed in the engineering plastic pipe, a grouting pipe is installed in the buried steel pipe, and the buried steel pipe and the grouting pipe are respectively sleeved with annular neoprene rubber plates as a mud-proof water-stopping device at the grouting hole; fourthly, the grouting pipe is used for "retreating type" grouting, and the grouting bag is filled from outside to inside; when the grouting slurry reaches the initial strength, the grouting pipe is pulled out and the port of the buried steel pipe is blocked; and finally, after the shield segment is assembled and the shield tail is moved out by a distance of at least the outer diameter of the shield tunnel, the stratum surrounding the shield tunnel is reinforced within 24 hours.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, specifically relating to a reinforcement method for large-diameter shield tunnels with CT joint segments in soft soil strata. Background Technology

[0002] With the increasing demands of coastal economic development, and to minimize the impact on maritime shipping and marine ecology, cross-sea tunnels have become an excellent solution. Large-diameter shield tunnels offer advantages such as high construction efficiency, easy quality control, and low carbon footprint, and are increasingly being adopted by construction companies. However, large-diameter shield tunnels inevitably traverse soft soil layers. In some areas, the unconfined compressive strength of soft soil is only 40-50 kPa. Reinforcing the sea surface presents drawbacks such as high cost and significant impact on the marine ecosystem. Simultaneous shield tunneling and secondary grouting have unsatisfactory reinforcement effects over a large area around the tunnel perimeter. Meanwhile, to effectively improve the tunnel's deformation resistance, enhance the annular stress performance, and reduce the pressure of later tunnel operation and maintenance, CT joints are mostly used for tunnel segments in soft soil layers. Compared to traditional bolt-type segments, socket-type segments have significant advantages in prefabrication accuracy, assembly accuracy, and control of leakage in the formed tunnel. This technology provides important reference and basis for future construction of similar municipal and highway tunnel projects.

[0003] The publicly available technologies for reinforcing the surrounding strata of tunnel boring machines also have significant limitations:

[0004] For example, application number CN118959022A discloses a radial cement-soil pile structure system and construction method for shield tunnels. Inside the shield tunnel, radial cement-soil piles are formed using the TJS or MJS method to reinforce the surrounding strata. This method only improves the surrounding strata. However, because the reinforced material is unreinforced and the pile sides are relatively smooth, it is not conducive to anchoring and pull-out resistance; this method lacks measures for sealing the grouting holes of the tunnel segments; and the piles formed by this method are prone to material waste due to grout leakage.

[0005] Patent No. CN220081439U discloses a radial reinforcement system for shield tunnels crossing waterways. The system uses threaded connections for steel pipes, anchors for grouting pipes inside the tunnel segments, and sealing gaskets and water-swellable sheets to prevent water seepage between the anchors and the inner sides of the segments. The grouting material is single-component cement grout (grouting diffusion radius 2m), and the sealing material for the grouting pipes is a combination of cement-water glass grout and fine aggregate concrete. This method uses multiple materials, including single-component cement grout, double-component grout, fine aggregate concrete, sealing gaskets, and water-swellable sheets, resulting in complex construction processes and high material costs. Furthermore, the radially reinforced body formed by this method is prone to material waste due to grout leakage.

[0006] In view of this, and in view of the shortcomings and limitations of existing technologies, a multifunctional reinforcement method for large-diameter shield tunnels with CT joint segments in soft soil strata is provided. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a reinforcement method for large-diameter shield tunnels with CT joint segments in soft soil strata.

[0008] This invention is achieved through the following technical solution:

[0009] A reinforcement method for large-diameter shield tunnels with CT joint segments in soft soil strata includes the following steps:

[0010] Step 1: Based on the geological properties, anchoring and anti-buoyancy requirements, plan the setting range of reserved grouting holes and grouting pipes on the shield tunnel segments, the length of the grouting pipes, and the expansion range of the grouting bladders cast by a single grouting pipe;

[0011] Step 2: Pre-embed high-performance engineering plastic pipes in the reserved holes on the shield tunnel segments, and leave a plain concrete protective layer between the outer wall of the high-performance engineering plastic pipe and the outer skin of the segment.

[0012] Step 3: Insert the buried steel pipe containing the grouting bladder into the stratum outside the shield tunnel segment inside the high-performance engineering plastic pipe. The length of the buried steel pipe outside the segment shall not be less than that of the grouting pipe. The end and side wall of the buried steel pipe shall be provided with openings. The end of the buried steel pipe located at the reserved grouting hole position of the shield tunnel segment shall be fitted with an annular neoprene rubber sheet as a mud-proof and water-stopping device. Weld a steel plate at the end of the buried steel pipe located inside the segment as an anchor or pull-out anchor head.

[0013] Step 4: Insert a grouting pipe into the buried steel pipe. The end of the grouting pipe is open. A ring-shaped neoprene rubber sheet is fitted at the end of the grouting pipe as a mud-proof and water-stopping device.

[0014] Step 5: The grouting pipe is grouted in the buried steel pipe using a "reverse" grouting method. The grouting bag cast on the buried steel pipe is filled from the outside to the inside, causing it to expand and expand outward through the end opening and side wall opening. When the grout reaches the initial setting strength, the grouting pipe is pulled out completely and the end of the buried steel pipe is sealed.

[0015] Step 6: After the shield tunnel segments are assembled and have propelled out of the shield tail by at least the outer diameter of the shield tunnel, the surrounding soil reinforcement of the shield tunnel shall be completed within 24 hours.

[0016] Furthermore, the planning of the grouting pipe installation range and length in step 1 is as follows:

[0017] When the shield tunnel is located in a pure soft soil layer, grouting pipes are installed in the entire cross-section with a 360-degree range, and the length of the grouting pipes is 2.5 to 3.0m.

[0018] When the shield tunnel is located in a layer of soft soil above and gravel or muddy sandstone below, grouting pipes are installed in the upper half of the cross section within a 180-degree range, and the length of the grouting pipes is 2.0 to 2.5m.

[0019] When the shield tunnel is located in the layer where the upper layer is sand and gravel or muddy sandstone and the lower layer is soft soil, grouting pipes are installed in the lower half of the cross section within a 180-degree range, and the length of the grouting pipes is 1.5 to 2.0m.

[0020] When the shield tunnel is located in a layer where soft soil and gravel or muddy sandstone meet on one side, grouting pipes are installed within a 180-degree range on the soft soil side half of the cross section, with a length of 2.0m.

[0021] Furthermore, compressive strength calculations are performed based on the selected grouting pipe installation range and length, and adjustments are made to settings where the compressive strength calculation results do not meet the requirements.

[0022] If the reinforced area is considered as a composite foundation with bond strength enhancement, then the characteristic value of the bearing capacity of the reinforced foundation is... The calculation formula is as follows:

[0023] ;

[0024] In the formula: For area replacement rate, , For the calculated area of ​​a solidified body within a finite area, for The calculated area of ​​the corresponding reinforced zone; The characteristic value of the axial compressive bearing capacity of a single pile (KN); The effective cross-sectional area of ​​the pile (m²) 2 ); The characteristic value of the bearing capacity of soft soil natural foundation (kPa) ranges from 40 kPa to 100 kPa. Let be the angle between the axis of a certain solidified body and the direction of gravity;

[0025] Characteristic value of axial compressive bearing capacity of reinforced single pile Calculate using the following formula:

[0026] ;

[0027] In the formula: The perimeter of the pile is (m). The characteristic value of the lateral resistance of the soft soil layer (KPa) ranges from 7 to 15 KPa. The effective pile length (m) of the reinforced body; The characteristic value of the pile end resistance (kPa) ranges from 28 to 60 kPa.

[0028] Characteristic value of bearing capacity of reinforced foundation after deep correction Calculate using the following formula:

[0029] ;

[0030] In the formula: Weighted average unit weight of soil above the foundation bottom surface (KN / m²) 3 ), the buoyancy unit weight of soil layers located below the groundwater level; The depth of the foundation bottom (m);

[0031] The bearing capacity of the foundation soil is checked using the following formula:

[0032] ;

[0033] In the formula: The average pressure (kPa) at the bottom of the foundation when corresponding to the standard combination of actions.

[0034] The pressure on the foundation bottom surface is determined according to the following formula:

[0035] ;

[0036] In the formula: For the standard combination of actions, the longitudinal single-ring tunnel live load (KN). The weight of the longitudinal single-ring tunnel structure and the weight of the soil above the tunnel (KN) is taken as the buoyancy unit of the soil layer below the groundwater level. The base area is the tunnel outer diameter multiplied by the ring width (m). 2 ).

[0037] Furthermore, pull-out resistance calculations are performed based on the selected grouting pipe installation range and length, and adjustments are made to settings where the pull-out resistance calculation results do not meet the requirements.

[0038] When the tunnel is shallow, some tunnel sections cannot meet the requirements for uplift stability. Uplift resistance is provided by the reinforcement at the bottom of the tunnel to ensure uplift stability. When the pile foundation fails as a whole, the uplift bearing capacity of the piles is calculated using the following formula:

[0039] ;

[0040] In the formula: The sum of the pull-out forces (KN) of the longitudinal single-ring tunnel piles is calculated based on the standard combination of load effects calculated according to the anti-buoyancy safety requirements. The standard value (kN) of the ultimate tensile bearing capacity of the piles when the pile group fails in a non-integral manner. The weight of the foundation pile is taken as its own weight (KN), and the buoyancy unit weight is taken below the groundwater level. Let be the angle between the axis of a certain solidified body and the direction of gravity;

[0041] The sum of the pull-out forces of the longitudinal single-ring tunnel piles, calculated using the standard combination of load effects, is calculated according to the following formula:

[0042] ;

[0043] In the formula: The standard value of buoyancy force (KN) for a longitudinal single-ring tunnel. The sum of the tunnel's self-weight and the soil compressive weight within the longitudinal single ring (KN) is used. The tunnel's self-weight and the strata above the groundwater level are taken as the total unit weight, and the strata below the groundwater level are taken as the buoyant unit weight.

[0044] Furthermore, deformation calculations are performed based on the selected grouting pipe installation range and length, and adjustments are made to settings where the deformation calculation results do not meet the requirements.

[0045] Compression modulus of composite reinforced strata Calculated by the following formula:

[0046] ;

[0047] In the formula: The value is the compression modulus (MPa) of natural soft soil layers, ranging from 1.2 to 7.0 MPa. The characteristic value of the bearing capacity of soft soil natural foundation (kPa) ranges from 40 kPa to 100 kPa. This represents the characteristic value of the bearing capacity of the reinforced foundation.

[0048] Foundation deformation calculation depth Calculate using the following formula:

[0049] ;

[0050] In the formula: The outer diameter of the shield tunnel (m);

[0051] Final vertical deformation of the foundation Calculate using the following formula (mm):

[0052] ;

[0053] In the formula: Empirical coefficients are used to calculate vertical deformation. This refers to the number of soil layers within the depth range used for calculating foundation deformation. The additional pressure (kPa) at the bottom of the foundation when the quasi-permanent combination of forces is applied. ; The quasi-permanent combined pressure at the base location (KPa); This represents the self-weight pressure of the soil at the base location (kPa). For the first i The compressibility modulus of composite reinforced strata; From the foundation bottom to the first i layer of soil, No. i-1 Distance between the bottom surfaces of soil layers (m); The calculation points from the foundation bottom surface to the first i layer of soil, No. i-1 The average additional stress coefficient within the bottom surface area of ​​the soil layer shall be adopted in accordance with Appendix K of the Code for Design of Building Foundations (GB 50007-2011);

[0054] when s If positive, it indicates base subsidence; when... s If the value is negative, it indicates a basal elevation.

[0055] The empirical coefficients for calculating vertical deformation are taken from the following table:

[0056] .

[0057] Furthermore, the grouting grout used in the grouting pipe is a single-component cement grout, and the final grouting pressure is controlled at 0.1~0.2MPa.

[0058] Furthermore, a pre-embedded steel plate is installed on the inner wall of the shield tunnel segment around the high-performance engineering plastic pipe. The pre-embedded steel plate is connected to the anchoring steel bars in the shield tunnel segment. The steel plate welded to the end of the buried steel pipe in step 3 is fixedly connected to the pre-embedded steel plate.

[0059] Furthermore, the inner end of the buried steel pipe is provided with an internal thread, and after the grouting pipe is pulled out, a rubber cap with an external spiral is used to suspend and screw onto the end of the buried steel pipe for sealing.

[0060] Furthermore, the high-performance engineering plastic pipe uses an inner diameter of 54mm, the buried steel pipe uses a welded steel pipe with an inner diameter of 42mm and a wall thickness of 3.5mm, and the grouting pipe uses a welded steel pipe or a water / gas pipe with an inner diameter of 32mm and a wall thickness of 3.5mm.

[0061] Furthermore, the end of the buried steel pipe located in the reserved grouting hole is equipped with 2 to 3 layers of annular neoprene rubber sheets with an inner diameter of 40 mm, an outer diameter of 58 mm, and a thickness of 15 mm; the grouting pipe located at the end of the buried steel pipe is equipped with 2 layers of annular neoprene rubber sheets with an inner diameter of 34 mm, an outer diameter of 39 mm, and a thickness of 15 mm.

[0062] Compared with the prior art, the beneficial effects of this invention are as follows:

[0063] This invention is applicable to the reinforcement of shield tunnels in soft soil strata. It features a simple structure, convenient construction, and low material costs. The reinforced body simultaneously possesses multiple functions including compressive strength, tensile strength, and deformation resistance. The connection between the embedded steel pipe and the reinforced concrete segments, along with water prevention devices, the connection between the grouting pipe and the embedded steel pipe, and grout-stopping devices, ensure construction safety. Principles regarding the circumferential installation range of the grouting pipe and the timing of reinforcement provide convenience for the design and construction of grouting reinforcement. The calculations of the compressive strength, deformation resistance, and tensile strength of the reinforced strata provide a theoretical method for the design of shield tunnel reinforcement. Attached Figure Description

[0064] Figure 1 This is a flowchart illustrating the implementation steps of the present invention;

[0065] Figure 2 This is a schematic diagram of the overall reinforcement structure of the present invention;

[0066] Figure 3 This is a schematic diagram of the reinforcement structure of the present invention located at the reserved hole in the segment.

[0067] The attached figures are labeled as follows: 1-Shield tunnel segment, 2-Buried steel pipe, 3-Grouting bag, 4-Plain concrete, 5-Anchoring steel bar, 6-Embedded steel plate, 7-End steel plate, 8-Annular neoprene rubber sheet, 9-Grouting pipe, 10-Steel pipe opening, 11-High-performance engineering plastic pipe. Detailed Implementation

[0068] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0069] This invention discloses a reinforcement method for large-diameter shield tunnels with CT joint segments in soft soil strata. During the construction of large-diameter shield tunnels in soft soil strata, after the shield tunnel segments are assembled and positioned for a certain period of time, a buried steel pipe containing a grouting bag and partially perforated on the sidewall is wedged into the stratum outside the shield tunnel segment through pre-reserved grouting holes. Multiple layers of outer circumferential rubber strips are used at the junction of the buried steel pipe and the grouting hole to prevent water and mud inflow. A grouting pipe is installed inside the buried steel pipe, and single-liquid grouting is applied to the grouting pipe inside the tunnel. Cement grouting employs a backward grouting method. The grouting bladder inside the embedded steel pipe is filled with grout from the outside in, forming a shape resembling a "candied hawthorn skewer," enhancing compaction and pull-out resistance. A circumferential rubber strip is installed on the inner side of the embedded steel pipe at the inner edge of the shield segment to prevent grout leakage. Grouting is stopped when the grouting pipe is pulled back to near the inner edge of the shield segment. The final grouting pressure is controlled at 0.1~0.2 MPa. Once the grout reaches its initial setting strength, the grouting pipe is pulled out, and the end of the embedded steel pipe is sealed with a rubber cap, completing the single-hole reinforcement. The range of reserved grouting holes and the length of the grouting pipe are adjusted according to the geological properties, anchoring requirements, and anti-buoyancy needs.

[0070] See Figures 1 to 3 The technical solution of the present invention will be further described below with reference to specific embodiments. The construction process is as follows: Figure 1 As shown, the specific steps are as follows:

[0071] Step 1: Based on the geological properties, anchoring, and anti-buoyancy requirements, plan the setting range of pre-reserved grouting holes on shield tunnel segment 1, the length of grouting pipe 9, and the expansion range of the grouting bag 3 cast by a single grouting pipe 9; the specific selection of the circumferential setting range and length of grouting pipe 9 is as follows:

[0072] ① When the shield tunnel is located in a pure soft soil layer, grouting pipes 9 are installed in the entire cross-section 360 degrees, and the length of the grouting pipes 9 is 2.5 to 3.0m;

[0073] ② When the shield tunnel is located in the layer where the upper soft soil and the lower sand and gravel layer (or muddy sandstone) meet, grouting pipe 9 is installed in the upper half section within a 180-degree range, and the length of grouting pipe 9 is 2.0 to 2.5m.

[0074] ③ When the shield tunnel is located in the layer where the upper gravel layer (or muddy sandstone) meets the lower soft soil layer, grouting pipe 9 is installed in the lower half section within a 180-degree range, and the length of grouting pipe 9 is 1.5 to 2.0m.

[0075] ④ When the shield tunnel is located in the layer where soft soil on one side and gravel layer (or muddy sandstone) on the other side meet, grouting pipe 9 is installed in the 180-degree range of the side half section, and the length of grouting pipe 9 is 2.0m.

[0076] Step 2: A high-performance engineering plastic pipe 11 with an inner diameter of 54mm is pre-embedded in the reserved grouting holes on the shield segment 1. A 50mm plain concrete 4 protective layer is reserved between the outer wall of the high-performance engineering plastic pipe 11 and the outer skin of the segment. The high-performance engineering plastic pipe 11 can be made of polyamide, semi-aromatic polyamide, polyetheretherketone, or polyimide. A pre-embedded steel plate 6 is installed on the inner wall of the shield segment 1 around the high-performance engineering plastic pipe 11, and the pre-embedded steel plate 6 is connected to the anchoring steel bars 5 inside the shield segment 1.

[0077] Step 3: Insert the buried steel pipe 2, containing the grouting bag 3, into the stratum outside the shield tunnel segment within the high-performance engineering plastic pipe 11. The length of the buried steel pipe 2 should not be less than that of the grouting pipe 9. The buried steel pipe 2 is a DN42×3.5mm (nominal diameter×wall thickness) welded steel pipe. Openings are provided at the ends of the buried steel pipe 2 and on the sidewalls corresponding to the grouting bag 3 positions. The longitudinal spacing of the openings 10 on the sidewalls of the buried steel pipe 2 can be 0.3m~0.5m to facilitate the filling of the grouting bag 3 with grout. Two to three layers of annular neoprene rubber sheets 8, with an inner diameter of 40mm, an outer diameter of 58mm, and a thickness of 15mm, are fitted over the inner end of the buried steel pipe 2 located within the pre-reserved grouting hole as a mud-proof and water-stopping device. An end steel plate 7 is welded to the end of the buried steel pipe 2 located inside the shield segment 1 as an anchor or pull-out anchor. The welded end steel plate 7 is a square steel plate with a circular hole of the same inner diameter as the buried steel pipe 2 in the center. The end of the buried steel pipe 2 is welded to the square steel plate at the circular hole, and then the end steel plate 7 is fixed on the pre-embedded steel plate 6.

[0078] Step 4: Install the grouting pipe 9 inside the buried steel pipe 2, forming a sleeve between the buried steel pipe 2 and the grouting pipe 9. The grouting pipe 9 is a DN32×3.5mm (nominal diameter×wall thickness) welded steel pipe (or water / gas pipe), with only the end open. Two layers of annular neoprene rubber sheets 8, with an inner diameter of 34mm, an outer diameter of 39mm, and a thickness of 15mm, are fitted over the inner end of the grouting pipe 9 located at the end of the buried steel pipe 2, serving as a grout-stopping device.

[0079] Step 5: After the steel pipe 2 is in place, the grouting pipe 9 is inserted into the steel pipe 2 and grouting is performed in a reverse manner from the outside to the inside. The grouting slurry type is single-component cement slurry, and the final grouting pressure is controlled at 0.1~0.2MPa. The grouting bag 3, which is cast and poured onto the steel pipe 2, is filled from the outside to the inside. When the grouting pipe 9 is pulled to the vicinity of the inner wall of the shield segment 1, grouting is stopped. After the grouting slurry reaches its initial setting strength, the grouting pipe 9 is completely pulled out and the port of the steel pipe 2 is sealed. The grouting pipe 9 is inserted into the steel pipe 2 and grouting is performed in a "reverse" manner. After the grouting slurry reaches its initial setting strength, the grouting pipe 9 is completely pulled out and a rubber cap with an external spiral is used to suspend and tighten the inner end of the steel pipe 2, which has a pre-reserved internal spiral, to seal the port of the steel pipe 2, thus completing the single-hole reinforcement.

[0080] Step 6: After the shield segment 1 is assembled and extends beyond the shield tail by at least the outer diameter of the shield tunnel, the surrounding strata reinforcement of the shield tunnel shall be completed within 24 hours. Single-component cement grout is injected into the grouting bag 3 inside the buried steel pipe 2. The grouting bag 3 forms several protrusions along with the pre-reserved holes at the port and side wall of the buried steel pipe 2, ultimately forming a reinforced body resembling a "candied hawthorn".

[0081] The selected grouting pipe location, length, and reinforcement effect are verified. If the verification results do not meet the requirements, the grouting pipe location, length, and grout type are adjusted, and the verification is performed again until the reinforcement effect of the planned scheme meets the requirements. The specific verification content is as follows:

[0082] 1) Compression resistance calculation

[0083] Analogous to composite foundations with bond strength reinforcement, the characteristic value of the bearing capacity of the foundation reinforced using the method of this patent is... It can be estimated using the following formula:

[0084] ;

[0085] In the formula: For area replacement rate, , For the calculated area of ​​a solidified body within a finite area, for The calculated area of ​​the corresponding reinforced zone; The characteristic value of the axial compressive bearing capacity of a single pile (KN); The effective cross-sectional area of ​​the pile (m²) 2 ); The characteristic value (kPa) of the bearing capacity of soft soil natural foundation can be taken as 40 kPa to 100 kPa; Let be the angle between the axial direction of a solid object and the direction of gravity.

[0086] Characteristic value of axial compressive bearing capacity of reinforced single pile It can be estimated using the following formula:

[0087] ;

[0088] In the formula: The perimeter of the pile is (m). The characteristic value of the lateral resistance of soft soil strata (KPa) can be taken as 7~15KPa; The effective pile length (m) of the reinforced body; The characteristic value of the pile end resistance (kPa) can be taken as 28~60 kPa.

[0089] Characteristic value of bearing capacity of reinforced foundation after deep correction It can be calculated using the following formula:

[0090] ;

[0091] In the formula: Weighted average unit weight of soil above the foundation bottom surface (KN / m²) 3 ), the buoyancy unit weight of soil layers located below the groundwater level; The depth of the foundation bottom (m).

[0092] The bearing capacity of the foundation soil is checked using the following formula:

[0093] ;

[0094] In the formula: The average pressure (kPa) at the bottom of the foundation when corresponding to the standard combination of actions.

[0095] The pressure on the foundation bottom surface can be determined using the following formula:

[0096] ;

[0097] In the formula: For the standard combination of actions, the longitudinal single-ring tunnel live load (KN). The weight of the longitudinal single-ring tunnel structure and the weight of the soil above the tunnel (KN) is taken as the buoyancy unit of the soil layer below the groundwater level. The base area is the tunnel outer diameter multiplied by the ring width (m). 2 ).

[0098] 2) Pull-out resistance verification

[0099] When the tunnel is shallow, some tunnel sections cannot meet the requirements for anti-buoyancy stability. In such cases, the reinforcement at the bottom of the tunnel can be used to provide pull-out resistance and ensure anti-buoyancy stability.

[0100] The tensile bearing capacity of the piles when the pile group foundation fails in a non-integral manner is verified using the following formula:

[0101] ;

[0102] In the formula: The sum of the pull-out forces (KN) of the longitudinal single-ring tunnel piles is calculated based on the standard combination of load effects calculated according to the anti-buoyancy safety requirements. The standard value (KN) of the ultimate tensile bearing capacity of the piles when the pile group fails in a non-integral manner. The weight of the foundation pile is the self-weight (KN), and the buoyancy unit weight is taken below the groundwater level. Let be the angle between the axial direction of a solid object and the direction of gravity.

[0103] The sum of the pull-out forces of the longitudinal single-ring tunnel piles, calculated using the standard combination of load effects, is calculated according to the following formula:

[0104] ;

[0105] In the formula: The standard value of buoyancy force (KN) for a longitudinal single-ring tunnel. The sum of the tunnel's self-weight and the soil compressive weight within the longitudinal single ring (KN) is used. The tunnel's self-weight and the strata above the groundwater level are taken as the total unit weight, and the strata below the groundwater level are taken as the buoyant unit weight.

[0106] 3) Deformation verification

[0107] The compressibility modulus of the composite reinforced strata is calculated using the following formula. :

[0108] ;

[0109] In the formula: It is the compression modulus (MPa) of natural soft soil layers, which can be taken as 1.2~7.0MPa.

[0110] Foundation deformation calculation depth The following simplified formula can be used for calculation:

[0111] ;

[0112] In the formula: The outer diameter of the shield tunnel (m).

[0113] Final vertical deformation of the foundation Calculate using the following formula (mm):

[0114] ;

[0115] In the formula: Empirical coefficients are used to calculate vertical deformation. This refers to the number of soil layers within the depth range used for calculating foundation deformation. The additional pressure (kPa) at the bottom of the foundation when the quasi-permanent combination of forces is applied. ; The quasi-permanent combined pressure at the base location (KPa); This represents the self-weight pressure of the soil at the base location (kPa). For the first i The compressibility modulus of composite reinforced strata; From the foundation bottom to the first i layer of soil, No. i-1 Distance between the bottom surfaces of soil layers (m); The calculation points from the foundation bottom surface to the first ilayer of soil, No. i-1 The average additional stress coefficient within the bottom surface of the soil layer shall be adopted in accordance with Appendix K of the Code for Design of Building Foundations (GB 50007-2011).

[0116] When s is positive, it indicates basement subsidence; when s is negative, it indicates basement uplift.

[0117] The empirical coefficients for calculating vertical deformation can be obtained from the following table:

[0118] .

[0119] This invention employs a bag-type radial grouting method in soft soil strata to form a grout body resembling a "candied hawthorn skewer" shape to reinforce the strata surrounding a shield tunnel. Simultaneously, a steel pipe is embedded within this grout body, providing anchorage for the tunnel roof and anti-buoyancy support for the tunnel floor. This radial reinforcement method, using a bag-type grouting technique, overcomes the shortcomings of traditional grouting pipes, such as grout leakage and wasted material costs. This invention systematically elucidates key construction points including the shape of the reinforcement body, reinforcement materials, embedded pipe materials, grouting pipe materials, connections, water sealing, grout sealing, reinforcement timing, final grouting pressure, and the principles for the circumferential installation range of the grouting pipe. The method also details calculation formulas for the compressive strength of the reinforced strata, the pull-out strength of the reinforcement body, and deformation verification.

[0120] The present invention has been described in detail above through embodiments, but the content described is only an exemplary embodiment of the present invention and should not be considered as limiting the scope of the present invention. The scope of protection of the present invention is defined by the claims. Any technical solutions designed by those skilled in the art using the technical solutions described in the present invention, or similar technical solutions designed by those skilled in the art under the inspiration of the technical solutions of the present invention, within the substance and scope of protection of the present invention, to achieve the above-mentioned technical effects, or equivalent changes and improvements made to the scope of the application, should still fall within the patent protection scope of the present invention. It should be noted that, for clarity, descriptions of some components and processes that are not directly and obviously related to the scope of protection of the present invention but are known to those skilled in the art have been omitted in the description of the present invention.

Claims

1. A reinforcing method suitable for a large-diameter shield tunnel of a CT joint segment in a soft soil layer, characterized in that, Includes the following steps: Step 1: Based on the geological properties, anchoring, and anti-buoyancy requirements, plan the placement range of grouting holes and grouting pipes on the shield tunnel segments, the length of the grouting pipes, and the expansion range of the grouting bag cast by a single grouting pipe. Specifically: when the shield tunnel is located in pure soft soil, grouting pipes are installed across the entire cross-section (360 degrees), with a pipe length of 2.5–3.0 m; when the shield tunnel is located in a layer where soft soil lies above and gravel or argillaceous sandstone intersects, the upper half of the cross-section is used. Grouting pipes are installed within a 180-degree range, with a length of 2.0–2.5 m. When the shield tunnel is located in a layer where the upper sand and gravel layer or argillaceous sandstone layer meets the lower soft soil layer, grouting pipes are installed within a 180-degree range on the lower half of the cross-section, with a length of 1.5–2.0 m. When the shield tunnel is located in a layer where soft soil meets sand and gravel layer or argillaceous sandstone layer on one side and soft soil meets the other side, grouting pipes are installed within a 180-degree range on the soft soil side of the cross-section, with a length of 2.0 m. Step 2: Pre-embed high-performance engineering plastic pipes in the reserved grouting holes on the shield tunnel segments, and reserve a plain concrete protective layer between the outer wall of the high-performance engineering plastic pipe and the outer skin of the segment. Step 3: Insert the buried steel pipe containing the grouting bladder into the stratum outside the shield tunnel segment inside the high-performance engineering plastic pipe. The length of the buried steel pipe outside the segment shall not be less than that of the grouting pipe. The end and side wall of the buried steel pipe shall be provided with openings. The end of the buried steel pipe located at the reserved grouting hole position of the shield tunnel segment shall be fitted with an annular neoprene rubber sheet as a mud-proof and water-stopping device. Weld a steel plate at the end of the buried steel pipe located inside the segment as an anchor or pull-out anchor head. Step 4: Insert a grouting pipe into the buried steel pipe. The end of the grouting pipe is open. A ring-shaped neoprene rubber sheet is fitted at the end of the grouting pipe as a mud-proof and water-stopping device. Step 5: The grouting pipe is grouted in the buried steel pipe using a "reverse" grouting method. The grouting bag cast on the buried steel pipe is filled from the outside to the inside, causing it to expand and expand outward through the end opening and side wall opening. When the grout reaches the initial setting strength, the grouting pipe is pulled out completely and the end of the buried steel pipe is sealed. Step 6: After the shield tunnel segments are assembled and have propelled out of the shield tail by at least the outer diameter of the shield tunnel, the surrounding soil reinforcement of the shield tunnel shall be completed within 24 hours.

2. The method of claim 1, wherein, Perform compressive strength calculations based on the selected grouting pipe installation range and length, and adjust settings where the compressive strength calculation results do not meet the requirements: The reinforced area is regarded as a composite foundation with bond strength reinforcement, and the characteristic value of the bearing capacity of the reinforced foundation is The calculation formula is as follows: ； In the formula: is the area replacement rate, , is the calculated area of a certain reinforcing body within a limited range, is the calculated area of the corresponding reinforcing area; is the characteristic value of the axial compressive bearing capacity of a single pile, with units of KN; is the effective cross-sectional area of the pile, with units of m 2 ; is the characteristic value of the natural foundation bearing capacity of soft soil, with units of kPa, and the value range is 40Kpa~100Kpa; is the angle between the axial direction of a certain reinforcing body and the direction of gravity; Reinforced single pile axial compressive bearing capacity characteristic value The following formula is used: ； In the formula: is the circumference of the pile, in meters; is the side resistance characteristic value of the soft soil layer, in KPa, and the value range is 7~15 KPa; is the effective pile length of the reinforcement, in meters; is the tip resistance characteristic value of the pile, in kPa, and the value range is 28~60 KPa; characteristic value of bearing capacity of a ground improved by deep correction is calculated by the following equation: ； In the formula: is the weighted average unit weight of the soil above the base bottom, in KN / m 3 The soil layer below the groundwater level takes the buoyant unit weight. is the depth of the base bottom, in m; The bearing capacity of the foundation soil is checked using the following formula: ； wherein: Pbaseis the average pressure value at the base surface, in KPa, corresponding to the standard combination of actions. The pressure on the foundation bottom surface is determined according to the following formula: ； In the formula: is the longitudinal single-ring tunnel live load, unit: KN, corresponding to the standard combination in action; is the longitudinal single-ring tunnel self-weight and soil weight above the tunnel, unit: KN, the soil layer below the groundwater level takes the buoyant weight; is the base bottom area, which is the outer diameter of the tunnel multiplied by the ring width, unit: m 2 .

3. The method of claim 1, wherein, Based on the selected grouting pipe installation range and length, pull-out resistance calculations were performed, and adjustments were made to settings where the pull-out resistance calculation results did not meet the requirements. When the tunnel is shallow, some tunnel sections cannot meet the requirements for uplift stability. Uplift resistance is provided by the reinforcement at the bottom of the tunnel to ensure uplift stability. When the pile foundation fails as a whole, the uplift bearing capacity of the piles is calculated using the following formula: ； In the formula: is the sum of the longitudinal single-ring tunnel pile uplift force calculated by the load effect standard combination according to the anti-floating safety requirement, with units of KN; is the standard value of the uplift ultimate bearing capacity of the foundation pile when the group pile is in non-integral failure, with units of KN; is the self-weight of the foundation pile, with units of KN, and the buoyant weight is taken below the groundwater level; is the angle between the axial direction of a certain reinforcing body and the direction of gravity; The sum of the pull-out forces of the longitudinal single-ring tunnel piles, calculated using the standard combination of load effects, is calculated according to the following formula: ； In the formula: is the standard value of the longitudinal single-ring tunnel buoyancy effect, with units of KN; is the sum of the tunnel self-weight and the soil pressure within the longitudinal single-ring range, with units of KN. The tunnel self-weight and the strata above the groundwater level take the full specific weight, and the strata below the groundwater level take the buoyant specific weight.

4. The method of claim 1, wherein, Deformation calculations were performed based on the selected grouting pipe installation range and length, and adjustments were made to settings where the deformation calculation results did not meet the requirements. Compression modulus of composite reinforced ground is calculated from the formula: ； In the formula: is the compression modulus of the natural soft soil layer, with a unit of MPa, and a value range of 1.2-7.0 MPa; is the characteristic value of the bearing capacity of the natural soft soil foundation, with a unit of KPa, and a value range of 40 KPa-100 KPa; is the characteristic value of the bearing capacity of the reinforced foundation; Depth of calculation of ground deformation is calculated by the following equation: ； In the formula: is the outer diameter of the shield tunnel, in meters; The final vertical deformation of the foundation is calculated according to the number of soil layers divided in the depth range of the foundation deformation calculation , in mm, and the calculation formula is as follows: ； In the formula: is the vertical deformation calculation empirical coefficient; is the additional pressure at the base surface corresponding to the action of the quasi-permanent combination, with units of KPa, ; is the quasi-permanent combination pressure at the base position, with units of KPa; is the self-weight pressure value of the soil at the base position, with units of KPa; is the compression modulus of the composite reinforced stratum of the first i layer; are the distances from the base surface to the bottom surfaces of the first i layer soil and the second i-1 layer soil, respectively, with units of m; are the average additional stress coefficients within the ranges from the calculation points of the base surface to the bottom surfaces of the first i layer soil and the second i-1 layer soil, respectively, according to Appendix K of the "GB 50007-2011 Code for Design of Building Foundation". when s If positive, it indicates base subsidence; when... s If the value is negative, it indicates a basal elevation. Esp For pressures of 2.5, 4.0, 7.0, 15.0, and 20.0 MPa respectively, the empirical coefficients for calculating vertical deformation are taken according to the following standards: additional pressure at the foundation bottom. P 0 <0 When the time is right, the value is always 1.0; 0≤P 0 ≤0.75f spk When, the values ​​are 1.4, 1.3, 1.0, 0.4, and 0.2 respectively; P 0 ≥f spk When, the values ​​are 1.1, 1.0, 0.7, 0.4, and 0.2 respectively.

5. The method according to claim 1, characterized in that, The grouting grout used in the grouting pipe is a single-component cement grout, and the final grouting pressure is controlled at 0.1~0.2MPa.

6. The method according to claim 1, characterized in that, An embedded steel plate is installed on the inner wall of the shield tunnel segment around the high-performance engineering plastic pipe. The embedded steel plate is connected to the anchoring steel bar in the shield tunnel segment. The steel plate welded to the end of the buried steel pipe in step 3 is fixedly connected to the embedded steel plate.

7. The method according to claim 1, characterized in that, The buried steel pipe has an internal thread at its inner end. After the grouting pipe is pulled out, a rubber cap with an external spiral is used to suspend and screw onto the end of the buried steel pipe for sealing.

8. The method according to claim 1, characterized in that, The high-performance engineering plastic pipes use an inner diameter of 54mm, the buried steel pipes use welded steel pipes with an inner diameter of 42mm and a wall thickness of 3.5mm, and the grouting pipes use welded steel pipes with an inner diameter of 32mm and a wall thickness of 3.5mm or water / gas pipes.

9. The method according to claim 8, characterized in that, The end of the buried steel pipe located in the reserved grouting hole is equipped with 2 to 3 layers of annular neoprene rubber sheets with an inner diameter of 40 mm, an outer diameter of 58 mm, and a thickness of 15 mm; the grouting pipe located at the end of the buried steel pipe is equipped with 2 layers of annular neoprene rubber sheets with an inner diameter of 34 mm, an outer diameter of 39 mm, and a thickness of 15 mm.

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