A construction method for cutting piles of a shield underground station

Abstract

A construction method for shield underground station pile cutting, the steps include: evaluating the health status of the existing station and the spatial position relationship between the station and the shield tunnel to determine the risk level of shield pile cutting; preliminarily selecting the adaptability of the shield machine and conducting numerical tests on the shield pile cutting; optimizing the shield pile cutting excavation parameters and the width of the reinforcement ring; fully reinforcing the MJS soil layer at the bottom of the existing station; determining the shield machine selection and modifying the shield machine; and executing the shield pile cutting before, during and after the pile cutting control. The construction method proposed in the present disclosure is particularly suitable for the pile cutting of stations where the vertical distance between the top of the shield tunnel and the existing station floor is less than or equal to 2.0m, simplifies the construction reinforcement process, has a simple overall construction method, low construction cost, high deformation control accuracy, short construction period and high construction efficiency, and can effectively remove the existing pile foundation and ensure safe, efficient, and ultra-close underpass of the existing station.

Description

Technical Field

[0001] The present invention relates to the field of construction, and particularly to a construction method for cutting piles of a shield underground station. Background Art

[0002] In recent years, with the rapid development of the urbanization process, the phenomenon of urban subway construction has become more and more common and the scale has become larger and larger. Most of the tunneling construction of urban subways is carried out by the shield method with a high degree of mechanization. However, due to the reasons of urban subway line planning, during the tunneling of the subway shield, it is often necessary to remove / cut the bearing piles under the existing station or the retaining piles around the station in order to ensure the smooth passage of the shield machine. However, the construction of such projects has extremely high risks, long construction periods, high costs, and it is very difficult to control the disturbance of the surrounding soil layer and the deformation of the existing station. The shield end is the key part of the shield machine's starting and receiving into and out of the tunnel, and it is also the area that needs to be key reinforced in shield construction. However, the construction at this position has the characteristics of great construction difficulty, high risk coefficient, and difficult reinforcement. If it is not handled properly, accidents such as water inrush and sand gushing are likely to occur, resulting in the failure of shield starting and receiving. When encountering the situation where the shield passes under the existing operating station with an ultra-small clear distance and needs to cut / remove its existing piles in the shield starting / receiving area, the construction difficulty increases sharply. Using the traditional construction method may be difficult to solve the above problems, and if there is a slight control problem during the construction, it is very easy to cause large deformation of the existing operating station or even damage its structure, which undoubtedly poses higher requirements and challenges for controlling construction disturbance.

[0003] So far, there are mainly two solutions to the problem that the shield needs to pass under the pile foundation within the shield contour: 1) Clear obstacles in advance and then advance the shield, that is, before the shield construction, some reasonable methods are used to remove / chisel away the existing pile foundation, and after the shield advancement requirements are met, the shield machine is directly advanced. For example, CN112647956A (a construction method for a shield in a water-rich composite stratum to pass under a subway station at a close distance) first uses horizontal and vertical freezing methods to reinforce the bottom soil layer of the existing station. After the strength of the reinforced body reaches the design requirements, the step method is used for excavation, and the ground connection walls on the sides of the foundation pit near and far from the existing station and the new station are gradually chiseled out to complete the obstacle clearance and remove the existing pile foundation, and then foam concrete is used for backfilling in time. After the filling is completed, the shield machine advances forward and passes under the existing station. This method can avoid the shield from directly removing the pile foundation, but a series of obstacle clearance operations must be completed. 2) The shield machine directly cuts the piles without clearing obstacles in advance, that is, after completing a series of preparatory work in the early stage (for example, shield machine cutterhead modification, etc.), the shield machine slowly advances and directly cuts off the existing pile foundation. For example, CN112523767A (a construction method for shield pile grinding in bentonite strata) directly cuts off the existing pile foundation after the shield machine has carried out measures such as early cutterhead modification, anti-settlement measures on the pile body, and excavation control before pile grinding. This method can reduce the early obstacle clearance link and construction procedures, but it has extremely high requirements on the adaptability of the shield machine and the shield cutterhead. The above two treatment ideas have their own advantages and disadvantages, and each has its own merits. Generally, the construction treatment idea to be adopted is comprehensively considered based on the actual situation faced in the construction.

[0004] However, there is almost no research on the ultra-close underpass of the existing station and cutting piles in the starting area of ​​the shield end, and there are very few related engineering cases, but they are nothing more than the above two construction treatment ideas. Nevertheless, due to the complex conditions of such construction, the difficulty of construction disturbance control and high control accuracy, and the extremely high requirements for the construction environment, it is difficult to better control the deformation of the existing station and its ancillary structures using the existing traditional construction technology methods.

[0005] Therefore, how to provide a construction method for grinding piles of an existing station at an ultra-close distance starting from the end of a shield machine and capable of strictly controlling the deformation of the existing station is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0006] In order to solve at least one technical problem in the prior art, the present disclosure provides a construction method for cutting piles in a shield underground station. The method has simple construction process, low construction cost, high deformation control accuracy, and short construction period. It can effectively cut off the existing pile foundation and ensure safe, efficient, and ultra-close passage through the existing station.

[0007] Among them, the "ultra-close distance" mentioned in the present invention means that the vertical distance between the top of the shield tunnel and the existing station floor is less than or equal to 2.0m.

[0008] In order to solve at least one of the above technical problems, the technical solution adopted by the present disclosure is:

[0009] A construction method for cutting piles in a shield underground station, comprising the following steps:

[0010] Evaluate the health status of the existing station and its spatial relationship with the shield tunnel to determine the risk level of shield pile cutting;

[0011] Based on the risk level, preliminary selection of shield machine adaptability is carried out and numerical tests of shield pile cutting are conducted;

[0012] Based on the shield pile cutting numerical test, the shield pile cutting excavation parameters and the width of the reinforcement ring are optimized;

[0013] Based on the optimized width of the reinforcement ring, the existing station bottom soil layer is fully reinforced with MJS;

[0014] Based on the shield pile cutting numerical test, the shield machine type is determined and the shield machine is modified;

[0015] Based on the optimized pile cutting excavation parameters, shield tunneling control is performed before, during and after pile cutting.

[0016] Furthermore, the health status of the existing station and the spatial position relationship between the station and the shield tunnel are evaluated to determine the risk level of shield pile cutting, and the steps include:

[0017] Detect the deformation status of the existing station structure and conduct non-destructive detection of the soil layer at the bottom and surrounding of the existing station to determine the health status of the existing station;

[0018] Based on the minimum vertical distance between the outer edge of the shield and the existing station floor, the relative clearance between the existing station and the shield tunnel is determined;

[0019] Based on the relative clearance between the existing station and the shield tunnel, the level of the spatial position between the existing station and the shield tunnel is determined;

[0020] The risk level of shield pile cutting is determined based on the level of health status of the existing station and the level of spatial location between the existing station and the shield tunnel.

[0021] Furthermore, the risk levels are divided into Level I, Level II, Level III and Level IV, and the higher the level, the higher the security risk; among them,

[0022] When the risk level of shield pile cutting is level I and II, the deformation standard of the existing station is consistent with the design requirements;

[0023] When the risk level of shield pile cutting is level III, the deformation standard of existing stations is 80% of the original standard design;

[0024] When the risk level of shield pile cutting is Level IV, the deformation standard of existing stations is 60% of the original standard design.

[0025] Furthermore, based on the risk level, the shield machine adaptability is preliminarily selected and a shield pile cutting numerical test is conducted, wherein:

[0026] When the risk level of shield pile cutting is level III or IV, the pile cutting condition is simulated numerically to determine the unstable area that may occur during pile cutting;

[0027] When the risk level of shield pile cutting is Level I or Level II, there is no need to perform numerical simulation of the pile cutting condition.

[0028] Furthermore, the optimization of shield pile cutting excavation parameters and the width of the reinforcement ring includes:

[0029] Optimizing shield pile cutting excavation parameters, wherein the shield pile cutting excavation parameters at least include soil bin pressure, grouting pressure and grouting filling rate parameters;

[0030] Finite element or finite difference numerical simulation is used to simulate the working conditions of different MJS reinforcement ring widths to determine the optimized reinforcement ring width.

[0031] Furthermore, the MJS full-floor reinforcement of the existing station bottom soil layer includes:

[0032] Based on the optimized width of the MJS reinforcement ring, the existing station bottom soil layer is horizontally reinforced with MJS full-floor reinforcement;

[0033] Among them, the reinforcement material is PO 42.5 ordinary silicate cement, the dosage is 45-50%, the water-binder ratio of cement slurry is 1.0-1.3, the unconfined compressive strength of the solidified body after 28 days of reinforcement is ≥3.0MPa, and the permeability coefficient of the reinforcement is ≤1×10 -7 cm / s, the verticality deviation of horizontal reinforcement pile depth is ≤1 / 150.

[0034] Furthermore, the shield machine selection and determination includes:

[0035] Based on the simulation results of the shield pile cutting numerical test, the selection of the shield machine is finally determined;

[0036] The transformation of the shield machine includes:

[0037] Cutterhead modification: a six-spoke composite cutterhead is used, with a combination of hobs and shell cutters on the cutterhead;

[0038] Screw machine transformation: Use a shaft-type screw machine with 6-8 inspection ports designed separately on the screw machine;

[0039] Propulsion system modification: During the pile cutting process, the propulsion speed of the cutter disc is controlled at 1-2mm / min.

[0040] Furthermore, after the step of selecting and modifying the shield machine, the step of applying additional anti-floating compensation measures to the existing station is also included, wherein:

[0041] The steps of implementing additional anti-floating compensation measures for existing stations are specifically as follows:

[0042] On the side of the existing station away from the newly built foundation pit, a row of bored piles with a diameter of Φ900mm and a horizontal center spacing of 1000mm are laid out. The pile bottom elevation of the bored piles is the same as the retaining structure of the existing station;

[0043] A top beam with a length and width of 800mm×800mm is laid on the top plate of the existing station;

[0044] On the side of the existing station close to the newly built foundation pit, the underground continuous wall of the new station foundation pit is used to add corbels and connect the corbels to the existing station.

[0045] Furthermore, after implementing additional anti-floating compensation measures for the existing station, the steps of constructing the shield tool changing area and auxiliary structures are also included, including:

[0046] After the shield machine passes under the existing station, the shield cutter changing area is set according to the environmental conditions around the shield construction;

[0047] The periphery of the tool changing area uses three-axis mixing piles with a diameter of Φ850mm and a horizontal center spacing of 600mm, and a circle of water-stop curtain is applied from the ground;

[0048] The cutterhead position in the cutter changing area is also reinforced from the ground with three-axis mixing piles with a diameter of Φ850mm and a horizontal center spacing of 600mm. The reinforcement length is 5-6m and the width is 2-2.5m outside the shield contour line;

[0049] And 6-8 emergency drainage wells are set up inside the water-stop curtain at a horizontal distance of 2-3m from the water-stop curtain.

[0050] Furthermore, the control before, during and after the shield pile cutting is to adopt different excavation speeds based on different stages during the shield excavation process;

[0051] Specifically:

[0052] When the distance between the cutter head of the shield machine and the existing pile foundation to be cut is only the width of one ring of shield segments, the shield tunneling speed is controlled at 6 - 8 mm / min;

[0053] When the distance between the cutter head of the shield machine and the existing pile foundation to be cut is 20 - 30 cm, the shield tunneling speed is controlled at 3 - 5 mm / min;

[0054] When the cutter head of the shield machine is exactly cutting the existing pile foundation to be cut, the shield tunneling speed is controlled at 1 - 2 mm / min, and the cutter head rotation speed is controlled at 0.8 - 1.0 rpm;

[0055] After the cutter head of the shield machine passes through the existing pile foundation to be cut, it still advances forward at a tunneling speed of 1 - 2 mm / min for 25 - 30 cm to completely cut and grind the remaining piles and residual steel bars of the existing pile foundation to be cut.

[0056] Furthermore, during the control process before, during, and after the shield pile cutting, it also includes the step of arranging the internal automated monitoring system of the existing station, specifically:

[0057] An automated monitoring system is used to monitor the pile grinding process of the shield starting from the end and passing under the existing station at multiple points. The monitoring system mainly includes: monitoring stations, control rooms, reference points, and deformation points; among them, the reference points are arranged 80 - 120 m away from the deformation area.

[0058] Using a construction method for shield cutting piles in an underground station designed by the present disclosure, a risk assessment framework that comprehensively considers two factors, namely the health status (vulnerability) of the existing station and the spatial position relationship (hazard) between the existing station and the shield tunnel, is proposed in the present invention. The safety risk level of shield tunneling under the existing station and cutting piles is quantitatively evaluated in advance, reducing the influence of human subjective factors and improving the accuracy of the risk level assessment of pile cutting, laying a foundation for subsequent construction design and control.

[0059] At the same time, before the shield pile cutting, numerical simulation is also proposed to simulate the shield pile cutting process. According to the mechanical effects of pile cutting construction, it guides the key reinforcement areas for subsequent construction, optimizes the range of shield tunneling construction parameters and the width of the reinforcement ring, avoids the blindness of setting tunneling parameters during the construction process, improves the construction quality of shield tunneling and cutting piles, reduces the influence of shield pile cutting on the existing station, reduces resource waste, and reduces the construction cost.

[0060] Furthermore, by reconstructing the shield machine, implementing anti-floating compensation measures for existing stations, and constructing a shield cutter head tool-changing area, it is only necessary to use horizontal MJS to fully reinforce the soil layer at the bottom of the existing station. By strictly controlling the tunneling construction parameters and strengthening the automated monitoring during construction, not only can the end reinforcement for shield launching be achieved to ensure the smooth launching of the shield, but also during the process of the shield tunneling under the station at a very close distance and cutting the piles, the disturbance and impact on the existing station can be minimized to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The drawings illustrate exemplary embodiments of the present disclosure and, together with the description thereof, are used to explain the principles of the present disclosure. The drawings are included to provide a further understanding of the present disclosure and are incorporated in this specification and form a part of this specification.

[0062] Figure 1 It is a flow chart of the shield tunneling method for cutting piles under an existing station of the present invention;

[0063] Figure 2 It is a safety risk assessment framework diagram of the shield tunneling under an existing station of the present invention;

[0064] Figure 3 It is a plan view of the shield launching and closely tunneling under an existing station to cut piles in the engineering example of the present invention;

[0065] Figure 4 In the engineering example of the present invention Figure 3 A - A sectional view;

[0066] Figure 5 In the engineering example of the present invention Figure 3 B - B sectional view;

[0067] Figure 6 It is a three-dimensional numerical model of the shield cutting the uplift resistance piles at the bottom of the existing Pinghe Road Station on Line 2 of the present invention in the engineering example;

[0068] Figure 7 It is the numerical test result of the shield tunneling under the station to cut piles before the soil layer at the bottom of the existing Line 2 station of the present invention in the engineering example is reinforced;

[0069] Figure 8 It is a schematic diagram of the reconstructed shield cutter head in the engineering example of the present invention;

[0070] Figure 9 It is a detailed schematic diagram of implementing the corbel anti-floating compensation measure for the existing Line 2 Pinghe Road Station in the engineering example of the present invention;

[0071] Figure 10 It is a schematic diagram of the shield cutter head tool-changing area set after the shield of the newly built Subway Line 6 tunnels under the existing Line 2 Pinghe Road Station and cuts the piles in the engineering example of the present invention;

[0072] Figure 11 This is the automated monitoring result of the vertical displacement of the existing station structure after the piles of the Pinghe Road Station on Line 2 of the existing station are cut by the newly built subway Line 6 in the engineering example of the present invention.

[0073] In the figure:

[0074] Specific implementation manners

[0075] The following will describe the present disclosure in detail with reference to the accompanying drawings and specific embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant content and do not limit the present disclosure. Additionally, it should be noted that for the sake of convenience of description, only parts related to the present disclosure are shown in the drawings.

[0076] It should be noted that, without conflict, the embodiments in the present disclosure and the features in the embodiments can be combined with each other. The following will describe the present disclosure in detail with reference to the drawings and embodiments.

[0077] This embodiment provides a construction method for cutting piles of a shield underground station, as Figure 1 shown, the specific steps include:

[0078] S1. Evaluate the health status of the existing station 10 and the spatial position relationship between it and the shield tunnel 20 to determine the risk level of shield pile cutting.

[0079] Specifically, the steps include:

[0080] S11. First, detect the current deformation status of the structure of the existing station 10 itself, and perform non-destructive detection on the bottom and surrounding soil layers of the existing station 10 to determine the health status level of the existing station 10.

[0081] The detection of the current deformation status of the existing station 10 mainly aims to understand the structural diseases and current deformation status of the existing station 10. At the same time, combining the geological exploration data and supplementary exploration data of the project, within the range of 1 - 2 m inside and around the existing station 10, use non-destructive geophysical exploration methods such as ground penetrating radar to finely detect the geological conditions at the bottom and around the existing station 10, and further analyze whether there are other structures, underground obstacles or bad geology in the core area of excavation disturbance. If so, pretreatment or removal should be carried out in advance.

[0082] Among them, the health status of the existing station 10, that is, the vulnerability of the structure of the existing station 10, mainly evaluates the health status (vulnerability) level of the existing station 10 based on the requirements of the "House Structure Safety Appraisal Standard" (DB11 T637 - 2009). The specific level evaluation criteria are shown in Table 1.

[0083] Table 1 Health Status (Vulnerability) Grade Table of Existing Stations

[0084]

[0085] As can be seen from the above table, the grade determination of the health status of the existing station 10 has four grades, namely Grade A (good), Grade B (normal), Grade C (poor), and Grade D (dangerous). From Grade A to Grade D, the risk of the health status of the existing station 10 gradually increases, that is, the vulnerability of its structure gradually becomes larger.

[0086] S12. Then, based on the minimum vertical distance between the outer edge line of the shield and the structural floor slab 11 of the existing station 10, the relative net distance between the existing station 10 and the shield tunnel 20 is determined; then, based on the relative net distance between the existing station 10 and the shield tunnel 20, the grade of the spatial position between the existing station 10 and the shield tunnel 20 is determined.

[0087] In the present disclosure, the spatial position relationship between the existing station 10 and the shield tunnel 20 is the risk of the spatial position between the existing station 10 and the shield tunnel 20. Mainly based on the requirements of the Technical Specification for Structural Safety Protection of Urban Rail Transit (CJJT 202 - 2013), the grade assessment of the spatial position relationship (risk) between the existing station 10 and the shield tunnel 20 is carried out. The specific grade assessment criteria are shown in Table 2.

[0088] Table 2 Spatial Relationship (Risk) Grade Table between Existing Station and Shield Tunnel

[0089]

[0090] Note: The relative net distance (L) refers to the minimum vertical distance between the outer edge line of the shield and the floor slab of the existing station; D is the diameter of the newly built shield tunnel.

[0091] It can be seen from Table 2 that based on the relative net distance between the existing station 10 and the shield tunnel 20, the spatial relationship between the existing station 10 and the shield tunnel 20, that is, the risk, can be divided into five grades; including: Grade 1 (not close), Grade 2 (relatively close), Grade 3 (close), Grade 4 (very close), and Grade 5 (extremely close). So far, the diameter D of the shield tunnel 20 is mostly above 6m, and conservatively estimated to be 6m, then the relative net distance is L ≤ 0.5D, that is, L ≤ 3.0m. Since the present disclosure mainly focuses on the pile cutting construction of the shield tunneling under the existing station 10 at a very short distance, the relative net distance between the existing station 10 and the shield tunnel 20 is as Figure 4The vertical distance L from the top of the shield tunnel 20 shown in the figure to the structural floor slab 11 of the existing station 10 is less than or equal to 2.0 m. Therefore, according to the risk assessment level in Table 2, in this case, the level of the spatial relationship (risk) between the existing station 10 and the shield tunnel 20 in this disclosure is extremely close at level 5. Of course, this assessment method can also be extended and applied to other working conditions.

[0092] S13. Determine the risk level of shield cutting piles based on the level of the health condition of the existing station 10 and the level of the spatial position between the existing station 10 and the shield tunnel 20.

[0093] Based on the level of the health condition (vulnerability) of the existing station 10 obtained from Table 1 and the spatial position relationship (risk) between the existing station 10 and the shield tunnel 20 obtained from Table 2, and then according to the Figure 2 safety risk assessment framework diagram of the shield tunneling under the existing station 10 shown in the figure, the risk level of shield cutting piles can be obtained. For example: when the health condition (vulnerability) of the existing station 10 is at level A and the spatial position relationship (risk) between the existing station 10 and the shield tunnel 20 is at level 4, then according to the Figure 2 assessment framework shown in the figure, the risk level of grinding piles during shield tunneling under the existing station 10 is level II (low risk).

[0094] As can be seen from Figure 2 the risk levels are divided into level I, level II, level III, and level IV, and the higher the level, the higher the safety risk. Among them, when the risk level of shield cutting piles is at level I and level II, the deformation standard of the existing station is consistent with the design requirements; when the risk level of shield cutting piles is at level III, the deformation standard of the existing station is 80% of the original standard design; when the risk level of shield cutting piles is at level IV, the deformation standard of the existing station is 60% of the original standard design.

[0095] Based on the deformation control standards corresponding to each risk level shown in Table 3, the control indexes of track bed settlement, station structure displacement, station clearance convergence, and differential settlement corresponding to this risk level can be obtained.

[0096] Table 3 Deformation control standards corresponding to each risk level

[0097]

[0098] S2. Based on the risk level, preliminarily select the adaptability of the shield machine and conduct a numerical simulation test of shield cutting piles.

[0099] Refer to similar engineering cases at home and abroad and the actual geological working conditions of the current project, and preliminarily select the shield machine to be used, mainly including the excavation diameter of the shield machine, the preliminary form of the shield cutter head, etc.

[0100] When the risk level of shield pile cutting is level III or level IV, the pile cutting condition is simulated numerically to determine the unstable areas that may occur during pile cutting. Specifically, when the risk assessment results are medium risk of level III and high risk of level IV, and combined with the preliminary selection of the shield machine, the finite element / finite difference numerical simulation technology (such as: FLAC3D, ABAQUS, ANSYS, MIDAS and other software) is used to simulate and calculate the specific pile cutting condition, and the areas that may be unstable during the pile cutting process are obtained through displacement fields, plastic zones, and stress fields, which indicate the direction for the areas that need to be strengthened and controlled in the future.

[0101] When the risk level of shield pile cutting is level I or level II, there is no need to simulate the pile cutting condition. In other words, when the risk assessment result is level I safety and level II low risk, there is no need to carry out shield pile cutting numerical test. It is only necessary to strengthen the local key points according to the actual construction situation, adopt traditional construction methods and reasonable excavation construction parameters, strengthen on-site monitoring and measurement, and timely adjust the construction parameters of shield excavation to ensure the smooth penetration of the shield and pile cutting construction.

[0102] S3. Based on the numerical test of shield pile cutting, the excavation parameters of the shield pile cutting and the width of the reinforcement ring 30 are optimized.

[0103] Specifically, before construction, the finite element / finite difference numerical simulation technology is still used to simulate and calculate the specific pile cutting conditions, and the optimized shield pile cutting excavation parameters mainly include parameters such as soil bin pressure, grouting pressure and grouting filling rate. The purpose of optimizing the shield pile cutting excavation parameters is to determine the shield pile cutting excavation parameters that best match the actual engineering conditions and minimize excavation disturbance. Among them, according to the simulation results of the shield pile cutting numerical test, the shield pile cutting construction parameters are optimized, and then in the actual on-site construction process, the optimized parameters are used for shield pile cutting construction to reduce the impact and disturbance on the surrounding environment during the shield pile cutting construction process.

[0104] It also includes the optimization of the width of the MJS reinforcement ring 30. Specifically, before construction, finite element / finite difference numerical simulation is used to simulate the working conditions of different MJS reinforcement ring 30 widths to determine the optimal width of the reinforcement ring 30, avoid material waste, and reduce construction costs. Among them, the width of the optimized reinforcement ring 30 mainly refers to the width of both sides of the cross section of the reinforcement area on one side, that is, Figures 3 - 5 The horizontal width W1 and the vertical width H1 of a single side shown in the figure are omitted in the following text and will not be explained again.

[0105] S4. Based on the optimized width of the reinforcement ring 30, the MJS bottom soil layer of the existing station 10 is fully reinforced.

[0106] Specifically, before the shield tunneling starts, based on the optimized width of the MJS reinforcement ring 30, the bottom soil layer of the existing station 10 is firstly reinforced with horizontal MJS full-floor reinforcement.

[0107] Among them, the reinforcement material is PO 42.5 ordinary silicate cement, the dosage is 45-50%, the water-binder ratio of cement slurry is 1.0-1.3, the unconfined compressive strength of the solidified body after 28 days of reinforcement is ≥3.0MPa, and the permeability coefficient of the reinforcement is ≤1×10 -7 cm / s, the verticality deviation of horizontal reinforcement pile depth is ≤1 / 150.

[0108] like Figure 4 As shown, the horizontal width W1 and vertical width H1 of the reinforcement ring 30 on any single side after optimization must satisfy 1.6-1.8D, where D is the diameter of the newly built shield tunnel. The horizontal width W1 of the reinforcement ring 30 on one side after optimization does not involve the association with the structural bottom 11 of the existing station 10 and will not change. Only the vertical width H1 of the reinforcement ring 30 on one side after optimization is affected by the actual working conditions and will be associated with the structural bottom 11 of the existing station 10. Among them, when the vertical width H1 of the optimized reinforcement ring 30 does not infringe on the bottom of the existing station 10, reinforcement is performed according to the vertical width H1 of the optimized reinforcement ring 30. When the vertical width H1 of the optimized reinforcement ring 30 infringes on the bottom of the existing station 10, that is, when the upper area of ​​the contour line of the shield tunnel 20 on any single side, such as Figure 4 When the height of the F zone in the structure does not meet the optimized vertical width H1 of the reinforcement ring, under the condition that safety is permitted, it is only necessary to meet the vertical width H1 of the reinforcement ring 30 and be tangent to the point M of the structural bottom plate 11 of the existing station 10, and then the reinforcement ring 30 is reinforced vertically.

[0109] like Figure 5As shown in the figure, for the horizontal MJS reinforcement in the reinforcement ring 30, it can be reinforced by the horizontal semi-circular reinforcement piles 36 or the horizontal full-circular reinforcement piles 35, which is determined according to the actual engineering requirements, but it is necessary to ensure that other reinforcement indicators meet the requirements. At the same time, the vertical MJS reinforcement in the reinforcement ring 30 is the vertical reinforcement piles 34 constructed during the foundation pit construction of the new station 40. The reinforcement length is from the outer side of the enclosure of the main structure 42 of the foundation pit of the new station 40 to the outer side of the enclosure structure of the existing station 10. The reinforcement width is centered on the central axis of the shield tunnel 20, and the width is the optimized width obtained from the numerical simulation in step S3. To ensure the quality of the horizontal MJS reinforcement, the reinforcement sequence should follow the principle of constructing the lower row of piles first and then the upper row of piles, and the soil reinforcement is carried out from bottom to top. Before the construction of the MJS horizontal reinforcement piles, it is necessary to install a sealing valve on the lining wall to prevent the cement slurry from overflowing. After the MJS construction is completed, since the foundation pit of the new station 40 is the shield launching shaft 42, in the MJS reinforcement area around the shield portal 24, that is, in the left-line reinforcement area 31 and the right-line reinforcement area 32, 6-8 exploration holes with a diameter of 20-25 mm are evenly arranged with the central axes of the left-line shield tunnel and the right-line shield tunnel as the midlines, and the depth is the horizontal distance from the pile cutting position to the diaphragm wall at the shield portal 24 position of the foundation pit of the new station 40. The leakage of water and sand is detected through the exploration holes to detect the MJS reinforcement effect.

[0110] S5. Based on the numerical test of shield pile cutting, determine the type selection of the shield machine and transform the shield machine.

[0111] Based on the simulation results of the numerical test of shield pile cutting in step S3, finally determine the type selection of the shield machine. However, due to the requirements of pile cutting, it is necessary to transform the shield machine. The main transformation points include:

[0112] Cutter head 60 transformation: Adopt a six-spoke composite cutter head 60, in which the hob can be interchanged with the tooth cutter. The hob and the shell cutter are combined and configured on the cutter head 60, which can make full use of the characteristics of the shell cutter cutting steel bars and the hob breaking rocks. The parameters of the cutter head 60 after transformation are shown in Table 4, and the structural schematic diagram of the cutter head 60 after transformation is as Figure 8 shown.

[0113] Screw conveyor transformation: Adopt a shafted screw conveyor, and 6-8 inspection openings are designed separately on the screw conveyor to prevent the screw conveyor from getting stuck when the cut steel bars enter the soil bin. The set inspection openings can break or remove the obstacles.

[0114] Propulsion system transformation: It mainly involves the transformation of the shield machine with a slow propulsion system. Considering that the shield needs to cut the piles to be cut 12 in the existing station 10, the cutter should grind and cut the concrete and steel bars at a slow pushing speed and a small cutting depth. During the pile cutting process, the pushing speed should be controlled at 1-2 mm / min.

[0115] Table 4 Structural parameters of the cutter head after transformation

[0116]

[0117] S6. Apply additional anti - floating compensation measures to the existing station 10.

[0118] Specifically, first, arrange a row of anti - floating bored cast - in - place piles 15 with a diameter of Φ900mm and a horizontal center - to - center spacing of 1000mm on the foundation pit side of the existing station 10 far from the new station 40. The bottom elevation of the bored cast - in - place piles 13 is the same as the height of the retaining structure of the existing station 10. And arrange a coping beam 16 with a length × width of 800mm×800mm above the top plate of the existing station 10.

[0119] Then, on the foundation pit side of the existing station 10 close to the new station 40, utilize the diaphragm wall of the foundation pit of the new station 40 to add a corbel 50 and connect the corbel 50 to the existing station 10 to improve the overall anti - floating characteristics of the existing station. The relative position of the corbel 50 in the existing station 10 is as shown in Figure 4 the E area shown. Among them, the enlarged view of the corbel 50 is as shown in Figure 9 shown. In subsequent embodiments, there will be a detailed introduction to the corbel 50.

[0120] S7. Construct the shield cutter - changing area 43 and ancillary structures.

[0121] After applying additional anti - floating compensation measures to the existing station 10, it is also necessary to construct the shield cutter - changing area 43 and ancillary structures, specifically including:

[0122] After the shield machine passes under the existing station 10, select a suitable open area according to the environmental conditions around the shield construction to set the shield cutter - changing area 43. The structure of the cutter - changing area 43 is as shown in Figure 10 shown. The cutter - changing area 43 is the two shaded parts in Figure 10 , which are respectively arranged in the left - line reinforcement area 31 and the right - line reinforcement area 32. The periphery of the cutter - changing area 43 uses three - axis mixing piles 37 with a diameter of Φ850mm and a horizontal center - to - center spacing of 600mm to construct a waterproof curtain 45 in a circle from the ground. Among them, the depth from the ground to the bottom of the three - axis mixing piles 37 is all solid piles, and the cement content is 20 - 25%. The reinforcement depth is the vertical distance from the ground to the same level as the bottom end of the previous horizontal MJS reinforcement body. The reinforcement width W3 of the single - side cutter - changing area 43 is the sum of the diameter D of the shield tunnel 20 and twice the distance W2 that the outer edge of the shield tunnel 20 extends, that is, W3 = D + 2×W2. Among them, W2 is 2 - 2.5m, so the single - side reinforcement width W3 is about twice the length S1 of the reinforcement body at the cutter - head position, that is, 10 - 12m.

[0123] The cutter head position (tunnel face) of the tool changing area 43 also uses three-axis mixing piles 37 with a diameter of Φ850 mm and a horizontal center distance of 600 mm for ground reinforcement. The reinforcement length S1 is 5 - 6 m, and the width W3 extends 2 - 2.5 m outward from the shield contour line. Among them, from the ground to a depth of 2 - 2.5 m above the outer contour line of the shield excavation is the empty pile, with a cement content of 8 - 10%; while from 2 - 2.5 m above the outer contour line of the shield excavation to the pile bottom depth is the solid pile, with a cement content of 20 - 25%. Ordinary Portland cement P.O42.5 is used for the cement.

[0124] Among them, the length of the water stop curtain 45 is S2, and its width is W4. And 6 - 8 emergency dewatering wells 44 are set at a horizontal distance of 2 - 3 m from the water stop curtain 45 inside the water stop curtain 45. In this disclosure document, 6 dewatering wells 44 are provided inside the water stop curtain 45 and are divided into three groups.

[0125] S8. Based on the optimized cutting pile tunneling parameters, control before, during, and after shield cutting piles is performed.

[0126] Control before, during, and after shield cutting piles means adopting different tunneling speeds based on different stages during shield tunneling.

[0127] Specifically:

[0128] When the distance between the cutter head 60 of the shield machine and the existing pile foundation 12 to be cut remains only the width of 1 ring of the shield segment 23, the shield tunneling speed is controlled at 6 - 8 mm / min;

[0129] When the distance between the cutter head 60 of the shield machine and the existing pile foundation 12 to be cut is 20 - 30 cm, the shield tunneling speed is controlled at 3 - 5 mm / min;

[0130] When the cutter head 60 of the shield machine is exactly cutting the existing pile foundation 12 to be cut, the shield tunneling speed is controlled at 1 - 2 mm / min, and the rotation speed of the cutter head 60 is controlled at 0.8 - 1.0 rpm;

[0131] After the cutter head of the shield machine passes through the existing pile foundation 12 to be cut, it still advances forward at a tunneling speed of 1 - 2 mm / min for 25 - 30 cm to completely cut and grind the residual pile and residual steel bars of the existing pile foundation 12 to be cut.

[0132] In addition, during the process of cutting piles by shield tunneling, the thrust should be controlled at 8000 - 12000 kN, the torque should be controlled at 800 - 1200 kN·m, and the values of the soil chamber pressure, synchronous grouting pressure, and backfill rate behind the lining are all determined according to the results optimized in step S3. During the pile cutting process when the shield starts tunneling from the shield end and passes under the existing station 10, the shield needs to pass through the MJS reinforcement area, and the overexcavation cutter of the cutterhead 60 should be turned on. Therefore, it is necessary to strictly control the parallelism between the shield attitude and the axis. When the shield advances to the position of the existing pile foundation 12 to be cut, the shield soil in the soil chamber should be emptied in advance, and Hengdun mud should be injected into the soil chamber. Hengdun mud should also be injected through the radial grouting holes reserved in the front shield and the middle shield to fill the gap between the shield machine shell and the soil. In addition, during the shield construction process, according to the monitoring results obtained from the automated monitoring system mentioned in step S9, tail synchronous grouting and secondary supplementary grouting should be carried out in a timely manner. The secondary supplementary grouting uses double-fluid grout. Especially after the shield finishes cutting the pile and the shield tail exits the existing pile foundation, the synchronous grouting volume should be increased, and secondary supplementary grouting should be carried out in a timely manner.

[0133] S9. Arrangement of the automated monitoring system inside the existing station 10.

[0134] During the control process before, during, and after shield pile cutting, it also includes the arrangement of the automated monitoring system inside the existing station 10. Specifically:

[0135] An automated monitoring system is used to monitor the pile grinding process when the shield starts tunneling from the shield end and passes under the existing station 10 at multiple points. The monitoring system mainly includes: monitoring stations, control rooms, reference points, and deformation points. Among them, the reference points are arranged 80 - 120 m away from the deformation area (the attached drawing is omitted). The reference points are all arranged near the tunnel portal position and should be far from the influence range of the deformation points to be measured to improve the accuracy of the deformation monitoring results. According to the deformation control standard table 3 of each index obtained from the above risk assessment, the shield tunneling parameters should be adjusted in real time or additional deformation control measures should be taken to ensure the absolute safety and stability of the shield machine and the existing station 10.

[0136] Among them, during the pile grinding process when the shield starts tunneling from the shield end and passes under the existing station 10, it is necessary to strengthen the real-time monitoring of the structure of the existing station 10. The monitoring method can adopt the Leica GeoMoS automated monitoring system produced by Guangzhou Oulai Surveying and Mapping Technology Co., Ltd. The monitoring system mainly includes: monitoring stations, control rooms, reference points, deformation points, and total station monitoring robots. For the setting of monitoring points, as Figure 3 shown, the monitoring points include the left monitoring point 17 set on the structural floor 11 of the existing station 10 directly above the center line of the left-line tunnel 21 and the right monitoring point 18 set on the structural floor 11 of the existing station 10 directly above the center line of the right-line tunnel 22. During the daily monitoring process, an automated remote control system is used to operate and control the total station robot, and the deformation laws of each structure of the existing station 10 during the shield passing under and cutting the pile are collected in real time.

[0137] In order to more clearly understand the purpose and technical solution of the present invention, a further detailed description is now given in conjunction with specific engineering examples and drawings.

[0138] like Figure 3 As shown in the figure, the shield tunnel section of Suzhou Rail Transit Line 6 project, Sujin Station-Pinghe Road Station, is used as the engineering background. The total length of the left and right lines of this section is 865.7m and 867.3m respectively. A shield machine is used to start excavation from Pinghe Road Station. The new station 40 is Pinghe Road Station of the new subway Line 6, located at the intersection of Renmin Road and Pinghe Road, arranged along Pinghe Road in an east-west direction, and interchanges with the Pinghe Road Station Hall of Line 2, which is the existing station 10. It is located on the east side of Pinghe Road Station of Line 2 of the existing station 10. The structures of the existing station 10 and the new station 40 are shown in the figure. Figure 1 As shown, the new station 40 is excavated in two lines, namely, the left line excavation of the left line tunnel 21 and the right line excavation of the right line tunnel 22. The existing station 10 is enclosed by SMW piles 14, and the steel has been removed. A row of existing pile foundations 12 with a diameter of 850mm, a pile spacing of 3m, a pile length of 37m, and 22 anti-pulling piles with a diameter of 32mm and HRB335 steel bars are arranged in the center of the station along the longitudinal direction. A number of existing bored piles 13 are also arranged in the existing station 10. The outer diameter D of the shield tunnel 20 of the new station 40 is 6.6m. It starts from Pinghe Road Station and needs to pass under the existing station 10 at the end position. The left line tunnel 21 and the right line tunnel 22 need to remove three existing pile foundations 12 at the bottom of Pinghe Road Station respectively. The tunnels at the nodes underpassed are mainly located in silt sand and silty clay layers, in micro-confined water layers, and rich in water content. The vertical clearance L between the top of the left-line tunnel 21 and the structural bottom plate 11 in the existing station 10 is 2.68m, and the vertical clearance L between the top of the right-line tunnel 22 and the bottom of the underturned beam of the structural bottom plate 11 in the existing station 10 is 1.38m. Since the shield head starts and passes under the existing station 10 at a close distance, it is also necessary to cut off a number of existing pile foundations 12 to be cut as anti-pulling piles, which requires high requirements for the protection of the surrounding environment, great construction difficulty, and high deformation control accuracy.

[0139] The present disclosure is used to strictly control the deformation and disturbance of the existing station 10 when the shield end starts to pass through the existing station 10 at a very close distance to cut piles. The overall operation diagram of the method is shown as follows: Figures 3 - 5 As shown, the specific steps are as follows:

[0140] S1. A comprehensive investigation was conducted on the existing station 10 of Pinghe Road Station on Line 2. The results showed that the overall structure of the existing station 10 was safe, without any dangerous structures, and could remain safe and stable under normal load values. Based on the standards in Table 1, an assessment was conducted, and the health status (vulnerability) of the existing station 10 itself was graded B in the normal state. Ground penetrating radar was then used to conduct non-destructive detection of the soil layer within and 2m around the existing station 10, and no other obstacles, pipelines, or poor geological bodies were found.

[0141] From the engineering conditions of this project, it can be seen that the vertical distance between the top of the shield tunnel 20 and the structural bottom plate 11 of the existing station 10 is less than or equal to 2.0m. Based on the standards in Table 2, it can be concluded that the level of the spatial position relationship (danger) between the existing station 10 and the shield tunnel 20 is extremely close to level 5.

[0142] Therefore, based on the health status (vulnerability) of the existing station 10 and the spatial relationship (danger) between the existing station 10 and the shield tunnel 20, Figure 2 The safety risk assessment framework diagram of the shield tunneling under the existing station 10 shown in the figure shows that the risk level of the shield tunneling pile cutting is medium risk level III. Therefore, according to the deformation control standards corresponding to each risk level shown in Table 3, it can be known that the deformation standards of each control index of the existing station 10 during the construction of this project are: track bed settlement ≤8mm; station structure displacement (vertical and horizontal) ≤8mm; station clearance convergence ≤16mm; differential settlement ≤4mm.

[0143] S2. Based on the risk level, the shield machine adaptability is preliminarily selected and the shield pile cutting numerical test is carried out. Referring to the relevant engineering experience at home and abroad and the relevant technical specifications of the shield, the ZTE6830 earth pressure balance shield machine is preliminarily selected for this section. The maximum excavation diameter of the shield machine is 6.84m, and the cutter head 60 is a traditional soft soil cutter head.

[0144] Since the risk level is at the medium risk level III, the FLAC3D finite difference program is used to establish a three-dimensional numerical model of shield pile cutting corresponding to the project. Figure 6 As shown in FIG. 1 , the left tunnel 21 and the right tunnel 22 both pass through the existing pile foundation 12 to be cut. A numerical simulation analysis of shield pile cutting is carried out, and the results are shown in FIG. Figure 7 As shown, without reinforcement, after the left-line tunnel 21 and the right-line tunnel 22 were completed under the pile cutting, the maximum settlement displacement of the structural bottom plate 11 in the existing station 10 located directly above the existing pile foundation reached 3.45 cm, which is much larger than the standard limit value. Therefore, pre-reinforcement must be carried out before actual construction, and the area directly above the arch of the left-line tunnel 21 and the right-line tunnel 22 must be strengthened in particular.

[0145] S3. Based on the numerical test of shield pile cutting, optimize the excavation parameters of shield pile cutting and the width of the reinforcement circle 30. According to the opinions of the expert meeting, this project intends to use the horizontal MJS full-chamber to reinforce the lower soil layer of the existing station 10. Before the on-site reinforcement, the FLAC3D finite difference program is first used to establish multiple sets of shield pile cutting three-dimensional numerical models corresponding to the project, and optimize the excavation construction parameters of shield pile cutting, soil bin pressure, grouting pressure and wall back grouting filling rate, and the width of the horizontal MJS reinforcement circle 30. Among them, the reinforcement circle 30 includes the left line reinforcement area 31 and the right line reinforcement area 32, such as Figure 3 The optimization results show that during the shield pile cutting and excavation construction, the soil bin pressure should be controlled at 0.2-0.3MPa, the grouting pressure should be controlled at about 0.5MPa, and the grouting filling rate behind the wall should be controlled at about 200%. The optimal width of the reinforcement ring 30 is 1.6-1.8D, that is, its horizontal width W1 and vertical width H1 are both 1.6-1.8D, where D is the diameter of the shield tunnel 20 of the new station 40.

[0146] S4. Based on the optimized width of the reinforcement ring 30, the bottom soil layer of the existing station 10 is fully reinforced with MJS, that is, horizontal reinforcement piles are constructed on-site in the foundation pit of the new station 40 to fully reinforce the bottom soil layer of the existing station 10. The reinforcement material is ordinary Portland cement with a PO of 42.5, and the water-cement ratio of the cement slurry is 1.0. Among them, the horizontal MJS reinforcement uses two types of reinforcement piles, namely horizontal full-circle piles 35 and horizontal semi-circle piles 36. The reinforcement structures of the left-line tunnel 21 and the right-line tunnel 22 are the same, both of which include a row of horizontal full-circle piles 35, and the others are horizontal semi-circle piles 36. The horizontal full-circle piles 35 are full-circle cylindrical piles with a diameter of Φ2000mm, and the horizontal center spacing between two adjacent column piles is 1520mm; the horizontal semi-circle piles 36 are semi-circle cylindrical piles with a diameter of Φ2600mm, and the horizontal center spacing between two adjacent column piles is 1900mm, and the vertical center spacing is 700mm. Figure 5 The length of the full-bridge reinforcement is 23.6m, and the horizontal width W1 of the single-track tunnel reinforcement is 11.22m, that is, the optimal interval average value 1.7D is taken, and the center line of the single-track tunnel is taken as the symmetry axis, 5.61m on each side. The recommended MJS construction parameters are shown in Table 5. The exploration hole shows that there is no leakage and sand gushing, and the horizontal MJS reinforcement effect is good.

[0147] Table 5 Recommended construction parameters of MJS

[0148]

[0149] S5. Based on the shield pile cutting numerical test, the shield machine is selected and modified. That is, based on the numerical simulation of the shield pile cutting in step S3, it is finally determined to select the shield machine model ZTE6830 earth pressure balance shield machine mentioned in step S2. However, considering the need for pile cutting, the shield machine needs to be modified, mainly including the modification of the cutter head 60. According to the parameters in Table 4, the schematic diagram of the modified cutter head 60 is as follows: Figure 8 As shown, the transformation of the screw machine and the transformation of the shield machine's own slow propulsion system.

[0150] Among them, the transformation of the spiral machine: a shaft-type spiral machine is used, and 6-8 inspection ports are designed separately on the spiral machine to prevent the spiral machine from getting stuck when the cut steel bars enter the soil bin. The inspection ports can break or remove obstacles.

[0151] Propulsion system modification: mainly involves the modification of the slow propulsion system of the shield machine. Considering that the shield machine needs to cut the pile foundation 12 to be cut in the existing station 10, the cutter should grind the concrete and steel bars at a slow push speed and a small cutting depth. During the pile cutting process, the propulsion speed should be controlled at 1-2mm / min.

[0152] S6. Take additional anti-floating compensation measures for the existing station 10.

[0153] Specific as Figure 4 As shown, a row of anti-floating bored piles 15 with a diameter of Φ900mm and a horizontal center distance of 1000mm between two adjacent piles is arranged on the west side of the existing station 10. The pile bottom elevation is the same as the enclosure structure of the existing station 10, and a 800mm×800mm capping beam 16 is arranged above the top plate of the existing station 10, and a C20 plain concrete backfill is arranged below the capping beam 16; in addition, on the east side of the existing station 10, the underground continuous wall of the enclosure structure 41 of the newly built station 40 is connected to the main structure of the existing station 10 by setting a corbel 50, thereby improving the anti-floating characteristics of the existing station 10; at the same time, SMW piles 14 are arranged on both sides of the existing station 10. Among them, for the enlarged view of the corbel 50 in the E area, as shown Figure 9 As shown, it includes a plain concrete cushion layer 51 with a thickness of 200 mm, a sand cushion layer 52 with a thickness of 200 mm, a plurality of steel bars 53 with a diameter of Φ25 mm and a horizontal center distance of 150 mm between two adjacent ones, a post-cast strip 54 and a pre-buried steel bar connector 55.

[0154] S7, after the shield machine passes under the existing station 10 and cuts the pile, after passing Renmin Road, the shield cutter head changing area 43 and auxiliary structures are set up at a position about 10-15m away from Renmin Road, such as Figure 10As shown in the figure. That is: the position where the cutter head 60 is placed is the single-sided cutter changing area 43. The three-axis mixing pile 37 with a diameter of Φ850mm and a center spacing of 600mm is used for ground reinforcement. The length S1 of the solidified body formed by the three-axis mixing pile 37 at the cutter head position is 5.5m, and the width W3 is 10.6m. This width W3 is the distance D (i.e., the diameter of the shield tunnel 20) of 6.6m between the outer edges of the shield tunnel 20 plus 2m of W2 outside the shield contour lines on both sides. The purpose is to reserve conditions for inspecting the cutter head 60 of the shield. Among them, the section from the ground to 2m above the outer contour line of the shield excavation is an empty pile, and the cement content is 10%; while the section from 2m above the outer contour line of the shield excavation to the pile bottom depth is a solid pile, and the cement content is 25%. In addition, around this area, a water-stop curtain 45 is constructed with three-axis mixing piles 37 with a diameter of Φ850mm and a center spacing of 600mm. From the ground to the pile bottom depth of the three-axis mixing pile 37, it is all solid piles, and the cement content is 25%. Among them, the length S2 of the water-stop curtain 45 is 10.6m, the width W4 is 28.75m, and the depth is about 27.3m from the ground to the bottom position of the solidified body. And 6 dewatering wells 44 with a diameter of 1m are arranged inside the water-stop curtain 45. The bottom elevation of the dewatering wells 44 is the same as the wall elevation of the water-stop curtain 45.

[0155] S8. Based on the optimized shield pile-cutting tunneling parameters, implement the control before, during, and after shield pile-cutting. That is, during the shield tunneling process, when the distance between the cutter head 60 of the shield machine and the existing pile foundation 12 to be cut is only 1.2m, that is, only the width of 1 ring of the shield segment 23 remains, the shield tunneling speed should be controlled at 6 - 8mm / min; when the distance between the cutter head 60 of the shield machine and the existing pile foundation 12 to be cut is 20 - 30cm, the shield tunneling speed should be controlled at 3 - 5mm / min; when the cutter head 60 of the shield machine is cutting the existing pile foundation 12 to be cut, the shield tunneling speed should be controlled at 1 - 2mm / min, and the rotation speed of the cutter head 60 should be controlled at 0.8 - 1.0rpm; when the shield machine passes through the existing pile foundation 12 to be cut, it still advances forward at a tunneling speed of 1 - 2mm / min for 25 - 30cm to completely cut and grind the residual piles and residual steel bars of the existing pile foundation 12 to be cut.

[0156] In addition, during the shield tunneling and pile-cutting process, the thrust should be controlled at 8000 - 12000kN, the torque should be controlled at 800 - 1200kN·m, and the values of the soil chamber pressure, synchronous grouting pressure, and backfill rate behind the lining are the same as the results obtained by optimizing step S6 in this embodiment.

[0157] S9. Arrange an automated monitoring system inside the existing station 10. The specific monitoring indicators include: the settlement deformation of the track bed, the vertical and horizontal displacements of the station structure, the convergence of the station structure's clearance, and differential settlement. The positions of the left monitoring point 17 and the right monitoring point 18 are as Figure 3As shown in , and the monitoring results of the left monitoring point 17 and the right monitoring point 18 are as follows Figure 11 As shown,.

[0158] By adopting the technical solution of the present invention, the shield machine successfully realized the pile cutting construction of Pinghe Road of Line 2 passing under the existing station 10, and the vertical deformation of the structure of the existing station 10 was within the control standard range, among which the maximum vertical displacement did not exceed 2.5 mm, which was far less than the limit value of 8 mm mentioned in Table 3.

[0159] A construction method for cutting piles in an underground shield station is adopted by the disclosed design. The present invention proposes a risk assessment framework that comprehensively considers the health status (vulnerability) of the existing station and the spatial position relationship (danger) between the existing station and the shield tunnel. The safety risk level of cutting piles when the shield passes under the existing station is quantitatively evaluated in advance, the influence of human subjective factors is reduced, the accuracy of the risk level assessment of pile cutting is improved, and the foundation is laid for subsequent construction design and control.

[0160] At the same time, before the shield pile cutting, it is proposed to use numerical simulation to simulate the shield pile cutting process. According to the mechanical effect of pile cutting construction, the subsequent construction key reinforcement areas are guided, and the shield excavation construction parameters and the width of the reinforcement circle 30 are optimized to avoid the blindness of the excavation parameter setting during the construction process, improve the construction quality of shield excavation pile cutting, reduce the impact of shield pile cutting on existing stations, reduce resource waste and reduce construction costs.

[0161] In addition, through the transformation of the shield machine, the implementation of anti-floating compensation measures for the existing station, and the construction of the shield cutter changing area, it is only necessary to use the horizontal MJS full-floor reinforcement of the bottom soil layer of the existing station, and by strictly controlling the excavation construction parameters and strengthening the automatic monitoring during the construction period, it is possible to achieve the reinforcement of the starting end of the shield machine to ensure the smooth start of the shield machine; it is also possible to minimize the disturbance and impact on the existing station during the pile cutting process under the station at an ultra-close distance.

[0162] Those skilled in the art should understand that the above embodiments are only for the purpose of clearly illustrating the present disclosure, and are not intended to limit the scope of the present disclosure. For those skilled in the art, other changes or modifications may be made based on the above disclosure, and these changes or modifications are still within the scope of the present disclosure.

Claims

1. A construction method for cutting piles of a shield underground station, characterized in that the steps include: Evaluate the health status of the existing station and its spatial relationship with the shield tunnel to determine the risk level of shield pile cutting; The steps include: detecting the deformation status of the existing station structure, and conducting non-destructive detection of the bottom and surrounding soil layers of the existing station, and dividing the health status of the existing station into four levels: A, B, C, and D; detecting the minimum vertical distance between the outer edge line of the shield and the bottom plate of the existing station to determine the relative clearance between the existing station and the shield tunnel; and then dividing the spatial position between the existing station and the shield tunnel into five levels: 1, 2, 3, 4, and 5; quantitatively dividing the risk level of shield pile cutting based on the level of the health status of the existing station and the level of the spatial position between the existing station and the shield tunnel; the risk levels are divided into Level I, Level II, Level III, and Level IV, and the higher the level, the higher the safety risk; Based on the risk level, the shield machine adaptability is preliminarily selected and a shield pile cutting numerical test is carried out; when the risk level of the shield pile cutting is level III or IV, the pile cutting working condition is simulated numerically to obtain the area where instability may occur reflected by the displacement field, plastic zone and stress field during the pile cutting process; when the risk level of the shield pile cutting is level I or II, there is no need to perform a simulation numerical simulation of the pile cutting working condition; Based on the shield pile cutting numerical test, the shield pile cutting excavation parameters and the width of the reinforcement ring are optimized; the shield pile cutting excavation parameters are optimized, and the shield pile cutting excavation parameters at least include soil bin pressure, grouting pressure and grouting filling rate parameters; finite element or finite difference numerical simulation is used to simulate the working conditions of different MJS reinforcement ring widths to determine the optimized reinforcement ring width; Based on the optimized width of the reinforcement ring, the existing station bottom soil layer is fully reinforced with MJS; Based on the numerical test of shield pile cutting, the shield machine type is selected and modified; additional anti-floating compensation measures are implemented and shield cutter changing area and auxiliary structures are constructed; Based on the optimized pile cutting excavation parameters, shield tunneling control is performed before, during and after pile cutting, and different excavation speeds are adopted in different stages.

2. The construction method for cutting piles of a shield underground station according to claim 1, characterized in that When the risk level of shield pile cutting is level I and II, the deformation standard of the existing station is consistent with the design requirements; When the risk level of shield pile cutting is level III, the deformation standard of existing stations is 80% of the original standard design; When the risk level of shield pile cutting is Level IV, the deformation standard of existing stations is 60% of the original standard design.

3. The construction method of cutting piles for a shield underground station according to claim 1, characterized in that, The MJS full-floor reinforcement of the existing station bottom soil layer includes: Based on the optimized width of the MJS reinforcement ring, the existing station bottom soil layer is horizontally reinforced with MJS full-floor reinforcement; Among them, the reinforcement material uses P.O 42.5 ordinary Portland cement, with a dosage of 45 - 50%, the water-binder ratio of the cement slurry is 1.0 - 1.3, the unconfined compressive strength of the solidified body at 28 days of age after the solidified body is ≥ 3.0 MPa, and the permeability coefficient of the solidified body is ≤ 1×10 -7 cm / s, and the verticality deviation of the horizontal reinforcement pile depth is ≤ 1 / 150.

4. A construction method for cutting piles of a shield underground station according to any one of claims 1-3, characterized in that, The shield machine selection includes: Based on the simulation results of the shield pile cutting numerical test, the selection of the shield machine is finally determined; The transformation of the shield machine includes: Cutterhead modification: a six-spoke composite cutterhead is used, with a combination of hobs and shell cutters on the cutterhead; Screw machine transformation: Use a shaft-type screw machine with 6-8 inspection ports designed separately on the screw machine; Propulsion system modification: During the pile cutting process, the propulsion speed of the cutter disc is controlled at 1-2mm / min.

5. A construction method for cutting piles of a shield underground station according to claim 4, characterized in that, After the steps of selecting and determining the shield machine and modifying the shield machine, it also includes the step of taking additional anti-floating compensation measures for the existing station. Among them, The step of taking additional anti-floating compensation measures for the existing station is specifically as follows: A row of bored cast-in-place piles with a diameter of Φ900mm and a horizontal center spacing of 1000mm is arranged on the side of the existing station far from the newly built foundation pit. The bottom elevation of the bored cast-in-place piles is the same as that of the retaining structure of the existing station; And a coping beam with a length × width of 800mm × 800mm is arranged above the top plate of the existing station; On the side of the existing station close to the newly built foundation pit, a corbel is added by using the diaphragm wall of the foundation pit of the newly built station and the corbel is connected to the existing station.

6. The construction method of cutting piles for a shield underground station according to claim 5, characterized in that, After taking additional anti-floating compensation measures for the existing station, it also includes the step of constructing the shield cutter changing area and ancillary structures, specifically including: After the shield machine passes under the existing station, the shield cutter changing area is set according to the surrounding environmental conditions of the shield construction; And a water-stop curtain is constructed in a circle from the ground by using three-axis mixing piles with a diameter of Φ850mm and a horizontal center spacing of 600mm on the periphery of the cutter changing area; The cutter head position in the cutter changing area is also reinforced from the ground by using three-axis mixing piles with a diameter of Φ850mm and a horizontal center spacing of 600mm. The reinforcement length is 5 - 6m and the width is 2 - 2.5m outside the shield contour line; And 6 - 8 emergency dewatering wells are arranged at a horizontal distance of 2 - 3m from the water-stop curtain inside the water-stop curtain.

7. A construction method for cutting piles of a shield underground station according to any one of claims 1-3, 5-6, characterized in that The control before, during and after the shield cuts the pile is to adopt different tunneling speeds based on different stages during the shield tunneling process; Specifically: When the distance between the cutter head of the shield machine and the existing pile foundation to be cut is only the width of 1 ring of shield segments left, the shield tunneling speed is controlled at 6 - 8mm / min; When the distance between the cutter head of the shield machine and the existing pile foundation to be cut is 20 - 30cm, the shield tunneling speed is controlled at 3 - 5mm / min; When the cutter head of the shield machine is just cutting the existing pile foundation to be cut, the shield tunneling speed is controlled at 1 - 2mm / min and the cutter head rotation speed is controlled at 0.8 - 1.0rpm; When the cutter head of the shield machine passes through the existing pile foundation to be cut, it still advances forward at a tunneling speed of 1 - 2mm / min for 25 - 30cm to completely cut off and grind the residual piles and residual steel bars of the existing pile foundation to be cut.

8. A construction method for cutting piles of a shield underground station according to claim 7, characterized in that, During the control process before, during and after the shield cuts the pile, it also includes the step of arranging the internal automatic monitoring system of the existing station, specifically: An automatic monitoring system is used to monitor the process of the shield starting from the end and passing under the existing station and grinding the pile at multiple points. The monitoring system mainly includes: a monitoring station, a control room, a reference point and a deformation point; among them, the reference point is arranged 80 - 120m away from the deformation area.

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