Reinforcing structure for shield receiving end of existing subway station and construction method

Abstract

The invention discloses a reinforcing structure for a shield receiving end of an existing subway station and a construction method, and the reinforcing structure comprises a station enclosure structure underground diaphragm wall, a three-axis mixing pile, an MJS pile caulking, an MJS pile wrap angle, a right line center line, a left line center line, a TRD cement soil mixing wall bin water stop, a left line tunnel and a right line tunnel. The left and right line reinforcing structure comprises a three-axis stirring pile weak reinforcement part, a three-axis stirring pile strong reinforcement part, an MJS pile caulking reinforcement part, a station structure bottom plate, a station structure top plate, gravel filling soil and sandy silty soil with silt silty clay, the construction method of the reinforcing structure comprises the steps of triaxial mixing pile manufacturability test pile construction, TRD waterproof curtain construction, triaxial mixing pile reinforcing construction and MJS pile caulking construction. According to the reinforcing structure for the shield receiving end of the existing subway station and the construction method, the problem of water and sand burst caused by water stop failure easily occurring in a water-rich sand layer is solved, and the problem of operation track settlement caused by strong disturbance construction is also avoided.

Description

Technical Field

[0001] This invention belongs to the field of tunnel boring machine (TBM) construction technology, and more specifically, relates to a reinforcement structure and construction method for the receiving end of a TBM in an existing subway station. Background Technology

[0002] The shield tunneling receiving stage at existing subway stations is a critical juncture in shield tunneling construction, facing the dual core contradictions of ground reinforcement and operational protection. Under complex geological conditions such as water-rich sand layers, the soil stability around existing stations is poor, and risks such as water and sand inrush are very likely to occur during shield tunneling. At the same time, the disturbance generated during construction may cause settlement of the operating track, posing a serious threat to the safe operation of existing stations and the surrounding environment. Therefore, reliable end reinforcement structures and construction methods are urgently needed to ensure construction safety and operational stability.

[0003] Currently, there are various technical solutions in the industry for reinforcing the shield tunnel receiving end of existing subway stations. All of these technologies attempt to solve the safety hazards in construction through different reinforcement methods. Some technologies use grouting reinforcement to enhance soil stability, while others focus on improving the reinforcement effect through specific structural arrangements. However, none of these technologies have formed a complete solution in practical applications and have failed to fully address key requirements such as water-stopping effect, structural connection sealing, and construction disturbance control.

[0004] The existing technology has the following problems: (1) It lacks targeted water-stopping structure design, and the reliability of water-stopping in complex geological environments such as water-rich sand layers is insufficient, making it difficult to effectively avoid the risk of water and sand inrush; (2) It has not achieved the synergistic optimization of stratum reinforcement and operation protection, and some strong disturbance construction processes are prone to causing deformation of the surrounding soil, which in turn leads to track settlement during operation and cannot meet the safety protection requirements during the operation of existing stations. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a reinforcement structure and construction method for the shield receiving end of the existing subway station. By using TRD cement-soil mixing walls located on the outer front end of the reinforced structure and TRD cement-soil mixing walls set in the middle of the TRD cement-soil mixing walls for compartmentalized water sealing, the compartments formed by the TRD cement-soil mixing walls are divided into independent compartments at certain intervals, thereby limiting the leakage range, preventing groundwater from spreading along the entire wall, and improving the reliability of water sealing. By using MJS piles for joint sealing and MJS pile corner sealing at the connection between the TRD cement-soil mixing walls and the underground continuous wall of the station retaining structure, the gaps at the connection can be filled, the leakage channels can be eliminated, and they can also be used to enhance the structural cohesive force and compensate for the impact of construction deviations. By using multiple emergency dewatering wells set on the outer side of the reinforced structure and multiple dewatering wells set inside the TRD cement-soil mixing walls, the risk of uneven settlement of the strata caused by construction disturbance under water-rich sandy geological conditions can be reduced. It can also avoid problems such as wall cracking and pile displacement during subsequent triaxial mixing pile process test pile construction, TRD water-stop curtain construction, triaxial mixing pile reinforcement construction, and MJS pile joint sealing construction.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a reinforcement structure for the receiving end of a tunnel boring machine in an existing subway station is provided, comprising: The reinforcement structure includes a TRD cement-soil mixing wall located on the outer front end of the reinforcement structure and connected to the underground continuous wall of the station retaining structure; a three-axis mixing pile located on the TRD cement-soil mixing wall and close to one corner of the TRD cement-soil mixing wall; an MJS pile joint sealant located at the connection between the TRD cement-soil mixing wall and the underground continuous wall of the station retaining structure; an MJS pile corner sealant located at the connection between the TRD cement-soil mixing wall and the underground continuous wall of the station retaining structure for filling the gap at the connection; and a TRD cement-soil mixing wall compartmentalized waterstop connected to the middle of the TRD cement-soil mixing wall. The TRD cement-soil mixing wall compartmentalized waterstop serves as the outer protection of the reinforcement structure and can divide independent compartments to limit the leakage range. The left and right line reinforcement structures located at the bottom of the original ground include MJS pile joint reinforcement on the outer side of the underground continuous wall of the station retaining structure, weak reinforcement of triaxial mixing piles located at the top of the outer side of the MJS pile joint reinforcement, and strong reinforcement of triaxial mixing piles located at the bottom of the outer side of the MJS pile joint reinforcement.

[0007] Furthermore, the sinking speed of the triaxial mixing pile is 0.8~1m / min, the lifting speed is 0.8~1m / min, the mixing speed is 16r / min, the grouting pressure is 0.4~0.6 MPa, the grout flow rate is 80~120L / min, and the water-cement ratio is 1:1~1.5:1.

[0008] Furthermore, the cement content of the triaxial mixing pile weak reinforcement mixing pile is 8%, the unconfined compressive strength is not less than 0.5MPa, and the permeability coefficient should be less than 10-6cm / s.

[0009] Furthermore, the cement content of the triaxial mixing pile reinforced mixing pile is 20%, the unconfined compressive strength is not less than 1.0 MPa, and the permeability coefficient should be less than 10-6 cm / s.

[0010] Furthermore, in the MJS pile caulking reinforcement, the MJS pile diameter is 1200mm, the overlap is 250mm, the high-pressure water pressure control value of MJS jet grouting is 10~30 MPa, the grout flow rate is 85~100L / min, and the grout jet drill rod lifting speed is 1.85cm / min.

[0011] Furthermore, the reinforcement structure also includes an emergency dewatering well located on the outside of the reinforcement structure and a dewatering well located inside the TRD cement-soil mixing wall. The emergency dewatering well and the dewatering well are used in conjunction to reduce the risk of uneven settlement of the strata caused by construction disturbance under water-rich sandy geological conditions.

[0012] According to a second aspect of the present invention, a construction method for a reinforcement structure for the shield tunnel receiving end of an existing subway station is provided, which is implemented using a reinforcement structure for the shield tunnel receiving end of an existing subway station, comprising: S100: Use ground-penetrating radar to detect defects in existing pipelines and underground diaphragm joints around the station, and combine this with borehole sampling to determine the soil moisture content and bearing capacity. S200: Select two piles on the outer side of the end for triaxial mixing pile test piles to determine the optimal cement content and mixing speed in the reinforced zone. Verify the continuity of the wall by constructing a wall using TRD test piles. Select two piles on the outer side of the end for MJS pile test piles to determine the ground pressure control threshold. S300: Excavate a 1.2m×1.0m guide trench, embed guide steel plates, hoist the cutting box to the pre-embedded hole, and control the verticality deviation to ≤1 / 250 using an inclinometer; S400: The wall is constructed using a three-step method. The first step involves horizontal cutting at a speed of 0.5-1.0 m / h and injecting bentonite grout. The second step involves retracting and re-stirring at a speed of 5-8 m / h. The third step involves advancing at a speed of 1.0-2.0 m / h and injecting cement grout to form a closed water-stop curtain and complete the TRD water-stop curtain construction. S500: Triaxial mixing pile reinforcement construction is carried out in accordance with the steps of positioning the mixing machinery, pre-mixing and sinking, spraying and mixing and lifting, repeated mixing and sinking, and repeated mixing and lifting to the borehole opening. S600: MJS pile caulking construction is carried out according to the following steps: pile location layout, positioning of pilot drilling rig, pilot drilling, control of pilot hole verticality, lowering of drill rod, jetting, rotary jetting lifting, relocation of drilling rig, and waste slurry treatment.

[0013] Furthermore, the technical requirements for the triaxial mixing pile include: S201: Before foundation reinforcement, the direction of pipelines and the location of obstacles should be investigated by excavating sample trenches or other exploratory measures. S202: The weak reinforcement and strong reinforcement of the triaxial mixing piles adopt PO-42.5R grade ordinary Portland cement; S203: Test piles must be carried out before construction, and the construction process and various construction parameters should be adjusted according to the reinforcement effect. The reinforced soil should ensure good homogeneity and integrity. After the reinforcement is completed, core drilling tests must be carried out to check the reinforcement effect. S204: Before reinforcement construction, process test piles should be carried out according to the design, and the number should not be less than 2. During construction, the chassis of the mixing pile machine should be kept horizontal and the guide frame should be kept vertical. The vertical deviation of the mixing pile should not exceed 1 / 250, the deviation of the pile position should not be greater than 50mm, and the pile diameter and pile length should not be less than the design value. S205: The three-axis mixing pile reinforcement construction is carried out in accordance with the steps of positioning the mixing machinery, pre-mixing and sinking, spraying and mixing and lifting, repeated mixing and sinking, and repeated mixing and lifting to the orifice. S206: 28 days after the completion of pile construction, core samples should be taken to determine whether the unconfined compressive strength meets the design requirements. The core drilling and sampling requirements are 1% of the total number of piles at each end well, and not less than 3 piles. There should be no less than 5 sets of core samples for each pile, and no less than 3 test blocks in each set. A 110mm drill bit should be used to drill the pile core. The core should be drilled continuously within the pile body. In addition to vertical core sampling, horizontal core sampling should also be carried out within the tunnel area.

[0014] Furthermore, the technical requirements for the construction design of the TRD waterstop curtain include: S401: Cement-soil mixing wall thickness 800mm, wall verticality allowable deviation is 1 / 300, wall position deviation not greater than +20mm~-50mm, wall depth deviation not greater than 50mm, wall thickness should not be less than design wall thickness, deviation controlled within 0~-20mm; S402: Cement-soil mixing walls shall be constructed using standard continuous methods, with a curing time of not less than 28 days, an unconfined compressive strength qu≥1.0MPa, and a permeability coefficient of less than 10-7cm / sec; S403: Cement-soil mixing walls shall use ordinary Portland cement of not less than P42.5, with a cement admixture of ≥25%, a cement dosage of ≥450kg / m3, and a water-cement ratio of 1.2~1.5. Specific construction parameters shall be determined based on the results of on-site test piles. S404: The cement-soil mixing wall of uniform thickness adopts a three-stage construction process (i.e., excavation, retreat excavation, and wall mixing). After the stratum is excavated and loosened, the grout is sprayed, mixed and solidified to form the wall. S405: After the cement-soil mixing wall of equal thickness is completed, spray grouting and mixing are carried out in the area of ​​the cutting box during the lifting process of the cutting box to ensure that the space occupied by the cutting box is densely filled and effectively reinforced to prevent adverse effects on the wall. S406: Before tunnel boring machine (TBM) construction, the quality of the completed cement-soil mixing wall should be inspected. Inspection content includes core sampling, permeability coefficient testing, etc., with one sampling point on each side, and testing should be conducted in conjunction with dewatering. The specific sampling locations will be jointly determined by all relevant parties based on the actual construction conditions. S407: Cement-soil mixing walls of equal thickness should be constructed continuously, with a step distance not exceeding 50mm. Walls formed on the same day should overlap with existing walls by no less than 500mm. The excavation speed in the overlapping area should be strictly controlled to ensure that the curing liquid and the mixing mud are fully mixed. The mixing speed must be slowed down during the overlapping construction to ensure the quality of the overlap. S408: For adverse geological conditions and underground obstacles that affect the quality of cement-soil mixing walls of equal thickness, they should be treated in advance before the construction of cement-soil mixing walls of equal thickness is carried out. At the same time, the cement content should be appropriately increased.

[0015] Furthermore, the technical requirements for the MJS reinforcement design include: S601: Before construction, on-site test piles should be conducted, with no fewer than two piles. The pile diameter of the test piles must be monitored. Based on the test pile results, preliminary construction parameters such as water-cement ratio, pressure, rotation speed, and cement content should be determined. The quality of the completed piles must meet the water-stopping requirements of this project. During construction, close monitoring of the surrounding environment is essential. Pile formation should be uniform, continuous, and free from necking and discontinuity. Grouting interruption during the lifting and spraying process is strictly prohibited. In special circumstances where grouting interruption occurs, the piles must be re-formed. Pile position deviation should be less than 1cm, and vertical deviation should not exceed 0.2%. S602: The reinforced soil should have good homogeneity and integrity. After the tunnel entrance is removed, the stratum should be self-stabilizing and have good water-blocking and seepage prevention functions. After the reinforcement is completed, a core drilling test must be carried out to check the reinforcement effect. The 28-day unconfined compressive strength is 1.2 MPa, and the permeability coefficient should be less than 10-6 cm / s. S603: MJS pile caulking construction is carried out according to the following steps: pile location layout, positioning of pilot drilling rig, pilot drilling, control of pilot hole verticality, lowering of drill rod, jetting, rotary jetting lifting, relocation of drilling rig, and waste slurry treatment.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1. The reinforcement structure of this invention, through the TRD cement-soil mixing wall located on the outer front end of the reinforcement structure and the TRD cement-soil mixing wall compartmentalized in the middle of the TRD cement-soil mixing wall, divides the compartments formed by the TRD cement-soil mixing wall into independent compartments at a certain interval, thereby limiting the leakage range, preventing groundwater from spreading along the entire wall, and improving the reliability of water stop. The MJS pile joint filling and MJS pile corner setting at the connection between the TRD cement-soil mixing wall and the underground continuous wall of the station retaining structure can fill the gaps at the connection, eliminate leakage channels, and can also be used to enhance the structural cohesive force and compensate for the impact of construction deviations. Through the multiple emergency dewatering wells set on the outer side of the reinforcement structure and the multiple dewatering wells set inside the TRD cement-soil mixing wall, the risk of uneven settlement of the strata caused by construction disturbance under water-rich sandy geological conditions can be reduced. It can also avoid problems such as wall cracking and pile displacement during subsequent triaxial mixing pile process test pile construction, TRD water stop curtain construction, triaxial mixing pile reinforcement construction, and MJS pile joint filling construction.

[0017] 2. The left and right line reinforcement structure of the present invention, through the MJS pile joint reinforcement located on the outer side of the underground continuous wall of the station retaining structure, can fill the gap between the triaxial mixing pile and the underground continuous wall of the station retaining structure, eliminating leakage channels. The weak reinforcement of the surface soil by the triaxial mixing pile set at the top of the outer side of the MJS pile joint reinforcement enhances the integrity of the surface soil, avoids shallow settlement caused by construction disturbance, and also plays an excessive buffering role, avoiding stress concentration damage. The reinforcement of the outer side of the MJS pile joint reinforcement... The triple-axis mixing pile reinforcement can resist disturbances and deformations during shield tunneling. The original surface stratum consists of four parts: crushed stone fill, sandy silt mixed with silty clay, silt, and sandy clay. Through the interaction of triple-axis mixing pile process test pile construction, TRD water-stop curtain construction, triple-axis mixing pile reinforcement construction, and MJS pile caulking construction, the problem of water-stop failure leading to water and sand inrush in water-rich sand layers is solved, and the problem of track settlement caused by strong disturbance construction is also avoided. Attached Figure Description

[0018] Figure 1 This is a plan view of the reinforcement structure for the shield tunnel receiving end of an existing subway station according to an embodiment of the present invention; Figure 2 This is a cross-sectional view of the right-line reinforcement structure of the reinforcement structure used for the shield tunnel receiving end of an existing subway station according to an embodiment of the present invention; Figure 3 This is a cross-sectional view of the left-line reinforcement structure of the reinforcement structure for the shield receiving end of an existing subway station, according to an embodiment of the present invention. Figure 4 This is a flowchart illustrating the process of a reinforcement structure for the shield tunnel receiving end of an existing subway station, as described in an embodiment of the present invention.

[0019] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 101-Diaphragm wall for station retaining structure, 102-Station side wall, 103-TRD cement-soil mixing wall, 104-Triaxial mixing pile, 105-MJS pile caulking, 106-MJS pile corner wrapping, 107-Right track centerline, 108-Left track centerline, 109-TRD cement-soil mixing wall compartmentalized water-stopping, 110-Left track tunnel, 111-Right track tunnel, 11 2-Emergency dewatering well, 113-Drainage dewatering well, 201-Weak reinforcement of three-axis mixing piles, 202-Strong reinforcement of three-axis mixing piles, 203-MJS pile caulking reinforcement, 204-Site structural side wall, 205-Site structural frame column, 206-Site structural bottom slab, 207-Site structural top slab, 208-Original ground surface, 209-Tunnel, 210-Gravel fill, 211-Silty sand with silty clay, 212-Silty sand, 213-Silty clay containing sand. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0021] In the description of the embodiments of the present invention, it should be noted that if terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention 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, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first," "second," and "third" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] Furthermore, the use of terms such as "horizontal," "vertical," and "sag" does not imply that the component must be absolutely horizontal or suspended, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of the embodiments of the present invention, "multiple" means at least two.

[0024] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0025] This invention provides a reinforcement structure for the shield tunnel receiving end of an existing subway station, such as... Figure 1As shown, the structure includes a station retaining structure diaphragm wall 101, station side walls 102, TRD cement-soil mixing wall 103, triaxial mixing piles 104, MJS pile joint caulking 105, MJS pile corner caulking 106, right track centerline 107, left track centerline 108, TRD cement-soil mixing wall compartmentalized water-stopping 109, left track tunnel 110, right track tunnel 111, emergency dewatering well 112, and drainage dewatering well 113. The station retaining structure diaphragm wall 101 is evenly distributed on the outer side of the end of the reinforced structure, and the station side walls 102 are tightly attached to the inner side of the station retaining structure diaphragm wall 101. The station retaining structure diaphragm wall 101 and station side walls 102 are used to maintain the structural stability of the existing station and resist the pressure of the surrounding soil. To prevent deformation and structural cracking of the station sidewalls due to ground disturbance during tunnel boring machine (TBM) reception, thus ensuring the operational safety of the existing station, the TRD cement-soil mixing wall 103 is located on the outer front end of the reinforcement structure. The TRD cement-soil mixing wall 103 is connected to the underground diaphragm wall 101 of the station's retaining structure. The MJS pile caulking 105 and MJS pile corner 106 are located at the connection between the TRD cement-soil mixing wall 103 and the underground diaphragm wall 101. The MJS pile caulking 105 and MJS pile corner 106 can be used to fill gaps at the connection, eliminate leakage channels, enhance structural cohesion, compensate for construction deviations, and resolve loose connections between the TRD cement-soil mixing wall 103 and the underground diaphragm wall 101. The problem is that the three-axis mixing pile 104 is set inside the TRD cement-soil mixing wall 103 and close to one corner of the TRD cement-soil mixing wall 103. The TRD cement-soil mixing wall compartment waterstop 109 is set in the middle of the TRD cement-soil mixing wall 103. As the outer protection of the reinforcement structure, the TRD cement-soil mixing wall compartment waterstop 109 can form the first water-stop barrier through its closed wall design. It is divided into independent compartments at certain intervals to avoid the spread of local leakage caused by construction deviations and uneven geology of the whole wall. It also limits the leakage range through multiple independent compartments, prevents groundwater from spreading along the wall as a whole, and greatly improves the reliability of waterstop. The left tunnel 110 and the right tunnel 111 are distributed in the TRD cement-soil mixing wall compartment waterstop. In different compartments of water 109, left-line tunnel 110 and right-line tunnel 111 pass through three-axis mixing piles 104 and connect to the station side wall 102. The center line 107 of the right line and the center line 108 of the left line are respectively set at the center of the left-line tunnel 110 and the right-line tunnel 111. Multiple emergency dewatering wells 112 are set on the outside of the reinforced structure (four are set at the front end of the reinforced structure in this embodiment, and one is set on each of the left and right sides of the reinforced structure). Under the geological conditions of water-rich sandy layer, local groundwater can be quickly discharged by pumping water to reduce the impact of water pressure on the reinforced structure and prevent leakage from expanding into water and sand inrush accidents. Multiple dewatering wells 113 are set inside the TRD cement-soil mixing wall 103 (three are set in each independent compartment in this embodiment).It can stabilize the granular structure of the stratum and effectively dissipate the pore water pressure of the stratum, providing safe stratum conditions for subsequent construction disturbances and shield tunneling reception. The emergency dewatering well 112 and the dewatering well 113 can be used together to reduce the risk of uneven settlement of the stratum caused by construction disturbances under water-rich sandy geological conditions. It can also avoid problems such as wall cracking and pile displacement in subsequent triaxial mixing pile process test pile construction, TRD water-stop curtain construction, triaxial mixing pile reinforcement construction and MJS pile caulking construction. The reinforcement structure of this invention utilizes a TRD cement-soil mixing wall located on the outer front end of the reinforcement structure and a TRD cement-soil mixing wall section within the middle of the TRD cement-soil mixing wall for compartmentalized water sealing. This divides the compartments formed by the TRD cement-soil mixing wall into independent compartments at certain intervals, thereby limiting the leakage range, preventing groundwater from spreading along the entire wall, and improving the reliability of water sealing. The MJS pile joint filling and MJS pile corner protection at the connection between the TRD cement-soil mixing wall and the underground continuous wall of the station retaining structure can fill the gaps at the connection, eliminate leakage channels, and also enhance the structural cohesion and compensate for construction deviations. Multiple emergency dewatering wells located on the outer side of the reinforcement structure and multiple drainage wells located inside the TRD cement-soil mixing wall can reduce the risk of uneven ground settlement caused by construction disturbance in water-rich sandy geological conditions. It can also avoid problems such as wall cracking and pile displacement during subsequent triaxial mixing pile trial construction, TRD water-stop curtain construction, triaxial mixing pile reinforcement construction, and MJS pile joint filling construction.

[0026] Specifically, such as Figure 2 , Figure 3As shown, the reinforcement structure for the left and right lines includes three-axis mixing pile weak reinforcement 201, three-axis mixing pile strong reinforcement 202, MJS pile joint caulking reinforcement 203, station structure side wall 204, station structure frame column 205, station structure bottom slab 206, station structure top slab 207, original ground 208, tunnel 209, crushed stone fill 210, sandy silt mixed with silty clay 211, silt 212, and sandy silty clay 213. The MJS pile joint caulking reinforcement 203 is located on the outer side of the underground continuous wall 101 of the station retaining structure. The three-axis mixing pile weak reinforcement 201 is located at the top outer side of the MJS pile joint caulking reinforcement 203, and the three-axis mixing pile strong reinforcement 202 is located at the bottom outer side of the MJS pile joint caulking reinforcement 203. The joint reinforcement 203 can fill the gap between the triaxial mixing piles and the underground continuous wall 101 of the station retaining structure, eliminating leakage channels. It can also solve the problems of loose connection and stress discontinuity between the triaxial mixing piles and the underground continuous wall 101 of the station retaining structure. The weak reinforcement 201 and the strong reinforcement 202 of the triaxial mixing piles together constitute the triaxial mixing pile reinforcement. The weak reinforcement 201 can enhance the integrity of the surface soil, avoid shallow settlement caused by construction disturbance, and also play an excessive buffering role to avoid stress concentration damage. The strong reinforcement 202 of the triaxial mixing piles can resist disturbance and deformation during shield tunneling. The station structure bottom plate 206 is located at the bottom of the reinforcement structure. The station structure side wall 204 is perpendicularly connected to the outer side of the station structure bottom plate 206. Structural frame column 205 is connected to the middle of the station structure floor slab 206. The station structure roof slab 207 is located at the top of the reinforced structure. The left and right line reinforced structures are set at the bottom of the original ground 208. Tunnel 209 passes through the three-axis mixing pile reinforcement 202, inserts into the underground continuous wall 101 of the station retaining structure, and connects to the side wall 204 of the station structure. The surface strata of the original ground 208 consist of four parts: crushed stone fill 210, sandy silt mixed with silty clay 211, silt 212, and sandy silty clay 213. The crushed stone fill 210 is located below the original ground 208. The crushed stone fill 210 is the existing surface strata of the reinforced area. Under the treatment of the three-axis mixing pile weak reinforcement 201, it can become the surface connection part of the reinforcement system, improving the overall quality. The continuity and bearing capacity of the strata are ensured. Sandy silt mixed with silty clay 211 is distributed below crushed stone fill 210. Sandy silt mixed with silty clay 211 is the middle transition stratum of the reinforcement area, which enhances the bonding and overlapping effect of the triaxial mixing pile reinforcement and MJS pile joint caulking reinforcement 203, and improves the continuity and anti-seepage capacity of the overall reinforcement structure. Silt 212 is distributed below sandy silt mixed with silty clay 211. Silt 212 is the main object of triaxial mixing pile reinforcement 202, which ensures the stability of the strata and the anti-settlement requirements when the shield is received, and can block the deep seepage channel. It can also solve the risk of water and sand inrush in the water-rich sand layer in conjunction with the TRD water-stop curtain construction. Sandy silty clay 213 is distributed below silt 212.The left and right line reinforcement structure of this invention, through the MJS pile caulking reinforcement on the outer side of the underground continuous wall of the station retaining structure, can fill the gap between the triaxial mixing pile and the underground continuous wall of the station retaining structure, eliminating the leakage channel. The weak reinforcement of the triaxial mixing pile set at the top of the outer side of the MJS pile caulking reinforcement enhances the integrity of the surface soil, avoids shallow settlement caused by construction disturbance, and also plays an excessive buffering role to avoid stress concentration damage. The strong reinforcement of the triaxial mixing pile set at the bottom of the outer side of the MJS pile caulking reinforcement can resist the disturbance and deformation during shield tunneling. The surface stratum of the original ground consists of four parts: crushed stone fill, sandy silt mixed with silty clay, silt, and sandy clay. Through the interaction of triaxial mixing pile process test pile construction, TRD water-stop curtain construction, triaxial mixing pile reinforcement construction, and MJS pile caulking construction, the problem of water stop failure leading to water and sand inrush in water-rich sand layers is solved, and the problem of track settlement caused by strong disturbance construction is also avoided.

[0027] Preferably, in one embodiment of the present invention, a technical requirement for a triaxial mixing pile is provided, including the following: Before foundation reinforcement, the direction of pipelines and the location of obstacles (such as original pile foundations) should be investigated by excavating sample trenches or other exploratory measures. If pipelines or pile foundations are found, they should be relocated or protected before reinforcement. If unidentified obstacles or other factors are encountered during the reinforcement process and the original pile position is changed, a written record must be made and reported in a timely manner, and effective measures should be taken to ensure the quality of reinforcement.

[0028] The cement content of the weak reinforcement 201 mixing pile of the three-axis mixing pile is 8%, and the cement content of the strong reinforcement 202 mixing pile of the three-axis mixing pile is 20%, using PO-42.5R grade ordinary Portland cement.

[0029] Before construction, test piles must be carried out, and the construction process and various construction parameters should be adjusted according to the reinforcement effect. The reinforced soil should have good homogeneity and integrity, be able to stabilize itself after the tunnel entrance is removed, and have good water blocking and seepage prevention functions. After the reinforcement is completed, core drilling tests must be carried out to check the reinforcement effect. The unconfined compressive strength of the triaxial mixing pile weak reinforcement 201 should not be less than 0.5MPa, and the permeability coefficient should be less than 10-6cm / s. The unconfined compressive strength of the triaxial mixing pile strong reinforcement 202 should not be less than 1.0MPa, and the permeability coefficient should be less than 10-6cm / s.

[0030] The main construction parameters for the three-axis mixing pile 104 are as follows: sinking speed: 0.8~1m / min, lifting speed: 0.8~1m / min, mixing speed: 16r / min, grouting pressure: 0.4~0.6 MPa, grout flow rate: 80~120L / min, water-cement ratio: 1:1~1.5:1.

[0031] Before reinforcement construction, process test piles should be carried out according to the design, with no less than 2 piles. During construction, the chassis of the mixing pile machine and the guide frame should be kept horizontal and vertical. The vertical deviation of the mixing pile should not exceed 1 / 250, the deviation of the pile position should not be greater than 50mm, and the pile diameter and pile length should not be less than the design value.

[0032] The three-axis mixing pile reinforcement construction is carried out in accordance with the steps of positioning the mixing machinery, pre-mixing and sinking, spraying and mixing and lifting, repeated mixing and sinking, and repeated mixing and lifting to the orifice.

[0033] 28 days after the completion of pile construction, core samples should be taken to determine whether the unconfined compressive strength meets the design requirements. The core drilling and sampling requirements are 1% of the total number of piles at each end well, and no less than 3 piles. There should be no less than 5 sets of core samples for each pile, and no less than 3 test blocks in each set. A 110mm drill bit should be used to drill the pile core. The core should be drilled continuously within the pile body. In addition to vertical core sampling, horizontal core sampling should also be carried out within the tunnel area.

[0034] Preferably, in one embodiment of the present invention, an MJS reinforcement design technical requirement is provided, including the following: MJS piles have a diameter of 1200mm and an overlap of 250mm. The recommended construction parameters are as follows: cement content should not be less than 700kg / m³, water-cement ratio 0.8~1.3, 28-day unconfined compressive strength 1.5MPa, grouting pressure 40MPa (±2MPa), main air pressure 0.75~0.85MPa, high-pressure water pressure control value for MJS jet grouting 10~30 MPa; grout flow rate 85~100L / min; grout jet drill rod lifting speed 1.85cm / min.

[0035] Before construction, on-site test piles should be conducted, with no fewer than two piles. The pile diameter should be monitored during test pile formation. Based on the test pile results, preliminary construction parameters such as water-cement ratio, pressure, rotation speed, and cement content should be determined. The quality of the formed piles must meet the water-stopping requirements of this project. During construction, close monitoring of the surrounding environment is essential. Pile formation should be uniform, continuous, and free of necking and breaks. Grouting interruptions during the lifting and spraying process are strictly prohibited. In special circumstances where grouting is interrupted, the piles must be re-formed. Pile position deviation should be less than 1 cm, and vertical deviation should not exceed 0.2%.

[0036] The reinforced soil should have good homogeneity and integrity. After the tunnel entrance is removed, the stratum should be self-stabilizing and have good water-blocking and seepage prevention functions. After the reinforcement is completed, a core drilling test must be carried out to check the reinforcement effect. The 28-day unconfined compressive strength should be 1.2 MPa, and the permeability coefficient should be less than 10-6 cm / s.

[0037] The MJS pile caulking construction is carried out according to the following steps: pile location layout, positioning of pilot drilling rig, pilot drilling, control of pilot hole verticality, lowering of drill rod, jet grouting, rotary jet lifting, relocation of drilling rig, and waste slurry treatment.

[0038] Preferably, in one embodiment of the present invention, a design technical requirement for a TRD waterstop curtain is provided, including the following: The cement-soil mixing wall is 800mm thick, the allowable deviation of the wall verticality is 1 / 300, the deviation of the wall position is no greater than +20mm to -50mm (the deviation into the pit is positive), the deviation of the wall depth is no greater than 50mm, the wall thickness should not be less than the design wall thickness, and the deviation should be controlled within 0 to -20mm (controlling the size deviation of the cutting box blade).

[0039] The cement-soil mixing wall is constructed using a standard continuous method, with a curing time of no less than 28 days, an unconfined compressive strength qu≥1.0MPa, and a permeability coefficient of less than 10-7cm / sec.

[0040] The cement-soil mixing wall uses ordinary Portland cement of not less than P42.5, with a cement admixture of ≥25%, a cement dosage of ≥450kg / m3, and a water-cement ratio of 1.2~1.5. The specific construction parameters are determined based on the results of on-site test piles.

[0041] The cement-soil mixing wall of uniform thickness adopts a three-stage construction process (i.e., excavation, retreat excavation, and wall mixing). After the stratum is excavated and loosened, the grout is sprayed, mixed, and solidified to form the wall.

[0042] After the cement-soil mixing wall of equal thickness is completed, spray grouting is carried out on the area of ​​the cutting box during the lifting process of the cutting box to ensure that the space occupied by the cutting box is densely filled and effectively reinforced, so as to prevent adverse effects on the wall.

[0043] Before tunnel boring machine (TBM) construction, the quality of the cement-soil mixing wall formed by channel cutting should be inspected. The inspection includes core sampling, permeability coefficient testing, etc., with one borehole on each side, and testing should be conducted in conjunction with dewatering. The specific sampling locations will be jointly determined by all relevant parties based on the actual construction conditions.

[0044] Cement-soil mixing walls of uniform thickness should be constructed continuously, with a step distance not exceeding 50mm. Walls formed on the same day should overlap with existing walls by no less than 500mm. The excavation speed in the overlapping area should be strictly controlled to ensure that the curing liquid and the mixing mud are fully mixed. The mixing speed must be slowed down during the overlapping construction to ensure the quality of the overlap.

[0045] For adverse geological conditions and underground obstacles that affect the quality of cement-soil mixing walls of uniform thickness, they should be treated in advance before the construction of cement-soil mixing walls of uniform thickness is carried out. At the same time, the cement content should be appropriately increased.

[0046] like Figure 4As shown, in another embodiment of the present invention, a construction method for a reinforcement structure for the shield tunnel receiving end of an existing subway station is provided, comprising the following steps: Ground-penetrating radar was used to detect defects in pipelines and underground diaphragm joints around the existing station, and borehole sampling was used to determine the soil moisture content and bearing capacity.

[0047] Two piles on the outer side of the end were selected for three-axis mixing pile test pile 104 to determine the optimal cement admixture and mixing speed in the reinforced zone. The continuity of the wall was verified by TRD trial wall construction. Two piles on the outer side of the end were selected for MJS pile test pile to determine the ground pressure control threshold.

[0048] Excavate a 1.2m×1.0m guide trench, embed guide steel plates, hoist the cutting box to the pre-embedded hole, and control the verticality deviation to ≤1 / 250 using an inclinometer.

[0049] The wall is constructed using a three-step method. The first step involves horizontal cutting at a speed of 0.5-1.0 m / h and injecting bentonite grout. The second step involves retracting and re-stirring at a speed of 5-8 m / h. The third step involves advancing at a speed of 1.0-2.0 m / h and injecting cement grout (with an admixture of 25%) to form a closed water-stop curtain and complete the TRD water-stop curtain construction.

[0050] The three-axis mixing pile reinforcement construction is carried out in accordance with the steps of positioning the mixing machinery, pre-mixing and sinking, spraying and mixing and lifting, repeated mixing and sinking, and repeated mixing and lifting to the orifice.

[0051] The MJS pile caulking construction is carried out according to the following steps: pile location layout, positioning of pilot drilling rig, pilot drilling, control of pilot hole verticality, lowering of drill rod, jet grouting, rotary jet lifting, relocation of drilling rig, and waste slurry treatment.

[0052] In summary, the reinforcement structure and construction method for the shield receiving end of existing subway stations solves the problem of water and sand inrush caused by water-rich sand layer failure, and also avoids the problem of track settlement caused by strong disturbance construction.

[0053] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A reinforcement structure for the receiving end of a tunnel boring machine in an existing subway station, characterized in that, include: The reinforcement structure includes a TRD cement-soil mixing wall (103) located on the outer front end of the reinforcement structure and connected to the underground continuous wall (101) of the station retaining structure; a triaxial mixing pile (104) located on the TRD cement-soil mixing wall (103) and close to one corner of the TRD cement-soil mixing wall (103); an MJS pile caulking joint (105) located at the connection between the TRD cement-soil mixing wall (103) and the underground continuous wall (101) of the station retaining structure; an MJS pile corner protector (106) located at the connection between the TRD cement-soil mixing wall (103) and the underground continuous wall (101) of the station retaining structure for filling the gap at the connection; and a TRD cement-soil mixing wall compartmentalized waterstop (109) connected to the middle of the TRD cement-soil mixing wall (103). The TRD cement-soil mixing wall compartmentalized waterstop (109) serves as the outer protection of the reinforcement structure and can divide independent compartments to limit the leakage range. The left and right line reinforcement structures located at the bottom of the original ground (208) include MJS pile joint reinforcement (203) located on the outer side of the underground continuous wall (101) of the station enclosure structure, a triaxial mixing pile weak reinforcement (201) located on the top of the outer side of the MJS pile joint reinforcement (203), and a triaxial mixing pile strong reinforcement (202) located on the bottom of the outer side of the MJS pile joint reinforcement (203).

2. The reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 1, characterized in that, The sinking speed of the triaxial mixing pile (104) is 0.8~1m / min, the lifting speed is 0.8~1m / min, the mixing speed is 16r / min, the grouting pressure is 0.4~0.6 MPa, the grout flow rate is 80~120L / min, and the water-cement ratio is 1:1~1.5:

1.

3. A reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 2, characterized in that, The cement content of the weak reinforcement of the triaxial mixing pile (201) is 8%, the unconfined compressive strength is not less than 0.5MPa, and the permeability coefficient should be less than 10-6cm / s.

4. A reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 3, characterized in that, The cement content of the three-axis mixing pile reinforcement (202) is 20%, the unconfined compressive strength is not less than 1.0MPa, and the permeability coefficient should be less than 10-6cm / s.

5. A reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 4, characterized in that, In the MJS pile caulking reinforcement (203), the MJS pile diameter is 1200mm, the overlap is 250mm, the high pressure water pressure control value of MJS jet grouting is 10~30 MPa, the grout flow rate is 85~100L / min, and the grout jet drill rod lifting speed is 1.85cm / min.

6. A reinforcement structure for the shield tunnel receiving end of an existing subway station according to any one of claims 1-5, characterized in that, The reinforcement structure also includes an emergency dewatering well (112) located on the outside of the reinforcement structure and a dewatering well (113) located inside the TRD cement-soil mixing wall (103). The emergency dewatering well (112) and the dewatering well (113) are used together to reduce the risk of uneven settlement of the strata caused by construction disturbance under water-rich sandy geological conditions.

7. A construction method for a reinforcement structure at the shield tunnel receiving end of an existing subway station, characterized in that, The reinforcement structure for the shield tunnel receiving end of an existing subway station, as described in any one of claims 1-6, is implemented by means of: S100: Use ground-penetrating radar to detect defects in existing pipelines and underground diaphragm joints around the station, and combine this with borehole sampling to determine the soil moisture content and bearing capacity. S200: Select two piles on the outer side of the end for three-axis mixing pile (104) test piles to determine the optimal cement content and mixing speed in the reinforced area. Verify the continuity of the wall by forming a wall using TRD test wall. Select two piles on the outer side of the end for MJS pile test piles to determine the ground pressure control threshold. S300: Excavate a 1.2m×1.0m guide trench, embed guide steel plates, hoist the cutting box to the pre-embedded hole, and control the verticality deviation to ≤1 / 250 using an inclinometer; S400: The wall is constructed using a three-step method. The first step involves horizontal cutting at a speed of 0.5-1.0 m / h and injecting bentonite grout. The second step involves retracting and re-stirring at a speed of 5-8 m / h. The third step involves advancing at a speed of 1.0-2.0 m / h and injecting cement grout to form a closed water-stop curtain and complete the TRD water-stop curtain construction. S500: Triaxial mixing pile reinforcement construction is carried out in accordance with the steps of positioning the mixing machinery, pre-mixing and sinking, spraying and mixing and lifting, repeated mixing and sinking, and repeated mixing and lifting to the borehole opening. S600: MJS pile caulking construction is carried out according to the following steps: pile location layout, positioning of pilot drilling rig, pilot drilling, control of pilot hole verticality, lowering of drill rod, jetting, rotary jetting lifting, relocation of drilling rig, and waste slurry treatment.

8. A construction method for a reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 7, characterized in that, The technical requirements for the triaxial mixing pile (104) include: S201: Before foundation reinforcement, the direction of pipelines and the location of obstacles should be investigated by excavating sample trenches or other exploratory measures. S202: The weak reinforcement (201) and strong reinforcement (202) of the triaxial mixing piles adopt PO-42.5R grade ordinary Portland cement; S203: Test piles must be carried out before construction, and the construction process and various construction parameters should be adjusted according to the reinforcement effect. The reinforced soil should ensure good homogeneity and integrity. After the reinforcement is completed, core drilling tests must be carried out to check the reinforcement effect. S204: Before reinforcement construction, process test piles should be carried out according to the design, and the number should not be less than 2. During construction, the chassis of the mixing pile machine should be kept horizontal and the guide frame should be kept vertical. The vertical deviation of the mixing pile should not exceed 1 / 250, the deviation of the pile position should not be greater than 50mm, and the pile diameter and pile length should not be less than the design value. S205: The three-axis mixing pile reinforcement construction is carried out in accordance with the steps of positioning the mixing machinery, pre-mixing and sinking, spraying and mixing and lifting, repeated mixing and sinking, and repeated mixing and lifting to the orifice. S206: 28 days after the completion of pile construction, core samples should be taken to determine whether the unconfined compressive strength meets the design requirements. The core drilling and sampling requirements are 1% of the total number of piles at each end well, and not less than 3 piles. There should be no less than 5 sets of core samples for each pile, and no less than 3 test blocks in each set. A 110mm drill bit should be used to drill the pile core. The core should be drilled continuously within the pile body. In addition to vertical core sampling, horizontal core sampling should also be carried out within the tunnel area.

9. A construction method for a reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 8, characterized in that, The technical requirements for the construction design of the TRD water-stop curtain include: S401: Cement-soil mixing wall thickness 800mm, wall verticality allowable deviation is 1 / 300, wall position deviation not greater than +20mm~-50mm, wall depth deviation not greater than 50mm, wall thickness should not be less than design wall thickness, deviation controlled within 0~-20mm; S402: Cement-soil mixing walls shall be constructed using standard continuous methods, with a curing time of not less than 28 days, an unconfined compressive strength qu≥1.0MPa, and a permeability coefficient of less than 10-7cm / sec; S403: Cement-soil mixing walls shall use ordinary Portland cement of not less than P42.5, with a cement admixture of ≥25%, a cement dosage of ≥450kg / m3, and a water-cement ratio of 1.2~1.

5. Specific construction parameters shall be determined based on the results of on-site test piles. S404: The cement-soil mixing wall of uniform thickness adopts a three-stage construction process (i.e., excavation, retreat excavation, and wall mixing). After the stratum is excavated and loosened, the grout is sprayed, mixed and solidified to form the wall. S405: After the cement-soil mixing wall of equal thickness is completed, spray grouting and mixing are carried out in the area of ​​the cutting box during the lifting process of the cutting box to ensure that the space occupied by the cutting box is densely filled and effectively reinforced to prevent adverse effects on the wall. S406: Before shield tunneling, the quality of the cement-soil mixing wall cut by the channel should be inspected. The inspection includes core sampling, permeability coefficient testing, etc. One hole is used on each side. The test should be carried out in conjunction with the precipitation. The specific sampling location shall be jointly determined by the relevant parties based on the actual construction situation. S407: Cement-soil mixing walls of equal thickness should be constructed continuously, with a step distance not exceeding 50mm. Walls formed on the same day should overlap with existing walls by no less than 500mm. The excavation speed in the overlapping area should be strictly controlled to ensure that the curing liquid and the mixing mud are fully mixed. The mixing speed must be slowed down during the overlapping construction to ensure the quality of the overlap. S408: For adverse geological conditions and underground obstacles that affect the quality of cement-soil mixing walls of equal thickness, they should be treated in advance before the construction of cement-soil mixing walls of equal thickness is carried out. At the same time, the cement content should be appropriately increased.

10. A construction method for a reinforcement structure for the shield tunnel receiving end of an existing subway station according to claim 9, characterized in that, The technical requirements for the MJS reinforcement design include: S601: On-site test piles should be conducted before construction, with no fewer than two test piles. The diameter of the test piles should be monitored. Based on the test pile results, preliminary construction parameters such as water-cement ratio, pressure, rotation speed, and cement content should be determined. It is also necessary to ensure that the quality of the piles meets the water-stopping requirements of this project. During construction, the surrounding environment should be closely monitored. The piles should be formed evenly, continuously, and without necking or faults. Grouting interruption is strictly prohibited during the lifting and spraying process. If grouting interruption occurs due to special circumstances, the piles should be re-constructed. The pile position deviation is less than 1cm, and the vertical deviation is no more than 0.2%; S602: The reinforced soil should have good homogeneity and integrity. After the tunnel entrance is removed, the stratum should be self-stabilizing and have good water-blocking and seepage prevention functions. After the reinforcement is completed, a core drilling test must be carried out to check the reinforcement effect. The 28-day unconfined compressive strength is 1.2 MPa, and the permeability coefficient should be less than 10-6 cm / s. S603: MJS pile caulking construction is carried out according to the following steps: pile location layout, positioning of pilot drilling rig, pilot drilling, control of pilot hole verticality, lowering of drill rod, jetting, rotary jetting lifting, relocation of drilling rig, and waste slurry treatment.

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