Subway station ultra-wide underground diaphragm wall construction method

Abstract

The invention discloses a construction method for an ultra-wide underground diaphragm wall of a subway station. The construction method comprises the steps of construction preparation, surveying and lofting, guide wall manufacturing, grooving excavation, groove cleaning and slurry changing, reinforcement cage manufacturing and hoisting, concrete pouring, quality detection and the like. The construction method for the ultra-wide underground diaphragm wall of the subway station is suitable for construction of the underground diaphragm wall with the groove width of 9 m under the complex geological condition of a reclamation area, the efficiency is improved by adjusting the length of the groove width unit of the underground diaphragm wall, increasing groove wall reinforcement and forming grooves through combination of different devices, and truss ribs and I-shaped steel joints are optimized; it is ensured that the integrity, the anti-seepage function and the hoisting safety of the underground diaphragm wall meet the design requirements; and meanwhile, the hoisting in-place requirement of the prefabricated parts of the laminated assembly type subway station can be met.

Description

Technical Field

[0001] The present invention relates to the field of building construction technology, and in particular to a construction method for an ultra-wide underground continuous wall of a subway station, which is particularly suitable for the construction of an underground continuous wall with a width of 9m under complex geological conditions in a reclamation area. Background Art

[0002] With the continuous development of urban rail transit, prefabricated station technology will be increasingly widely used. In future urban rail transit construction, prefabricated station technology will provide effective technical support for rapid construction. To ensure the hoisting of prefabricated components, the size and support spacing of the underground diaphragm walls supporting the station foundation pit are adjusted and widened according to the width of the prefabricated components.

[0003] However, traditional conventional underground diaphragm walls mostly use a slot width design of 6m or less. Although mature in common geological conditions, they have the following drawbacks in complex geological environments such as reclamation areas: 1) Long construction period and low efficiency: Conventional underground continuous wall trenches are relatively small, resulting in an increased number of wall sections per unit pit length. Each section of the wall must undergo repeated processes, including trenching, hole cleaning, steel cage installation, and concrete pouring. This significantly increases the number of construction links and the time required for cross-operation. This is particularly true in reclamation areas, where the geology is often characterized by poor soil layers such as miscellaneous fill, silt, and loose sand. Trenching is difficult and inefficient, and the frequent repetition of processes further prolongs the retaining structure construction period, hindering the subsequent installation of prefabricated components and the construction of the main structure. 2) High Joint Management and Quality Risk: Conventional trenches require joints (such as I-beam joints) between each wall. The greater the number of walls, the greater the joint management workload. Under the complex hydrogeological conditions of reclamation areas, mud inclusion and leakage are common at joints due to poor slurry protection and incomplete cleaning. This not only affects the anti-seepage performance of the underground continuous wall but can also lead to safety hazards such as sidewall instability and soil erosion during foundation pit excavation, increasing the cost and difficulty of subsequent joint repairs.

[0004] 3) Insufficient wall integrity and limited support safety: Underground diaphragm walls with a span of 6m or less have poor wall integrity due to their numerous sections. This can lead to cracking and excessive deformation in soft soil strata in reclamation areas due to uneven settlement or lateral earth pressure. Prefabricated stations, on the other hand, place even higher demands on deformation control in the foundation pit support system. The insufficient integrity of conventional underground diaphragm walls makes it difficult to meet the stringent requirements for retaining structure stability during the hoisting phase of the composite prefabricated structure, potentially adversely affecting the installation accuracy and construction safety of prefabricated components.

[0005] 4) Poor compatibility with prefabricated construction processes: The slot width division of conventional underground diaphragm walls fails to fully consider the hoisting dimensions and segmented construction requirements of prefabricated components, resulting in poor integration between the construction processes of the retaining structure and the main structure. For example, the hoisting path of prefabricated components may be restricted by the location of wall joints, or additional adjustments to the hoisting plan may be required to avoid obstructions in the support structure, increasing the complexity and cost of construction organization. Summary of the Invention

[0006] In order to overcome the problems in the prior art of underground continuous walls with a width of 6m or less, such as long construction period, large amount of joint processing, insufficient integrity and poor adaptability to assembly processes under complex geological conditions in reclamation areas, the present invention provides a construction method for ultra-wide underground continuous walls in subway stations.

[0007] The technical solution of the present invention is as follows: A construction method for an ultra-wide underground continuous wall in a subway station comprises the following steps: Construction preparation: set up temporary facilities, complete temporary water and electricity connections, conduct technical briefings, safety education, equipment and material inspections, and pave construction access roads; Surveying and setting out: Use calibrated measuring instruments to establish control reference points, divide the slot into sections and mark them on the guide walls; Guide wall production: including site preparation, measurement and positioning, trench excavation, reinforced concrete construction, corner treatment and formwork removal; Trench excavation: A trencher and a double-wheel slot milling machine are used in combination. The width of the first excavation is the trench width plus 1200mm. The trencher is used to excavate the soft soil layer, and the double-wheel milling machine or impact drill is used to process the rock layer. Tank cleaning and slurry replacement: remove mud skin from joints by brushing the wall, use air lift reverse circulation method to clean the hole, and control the thickness of sediment at the bottom of the tank and the slurry density; Fabrication and hoisting of steel cage: The steel cage is equipped with 8 longitudinal truss bars and transverse truss bars with a spacing of 3m. It is hoisted by two cranes and hoisted into the slot as a whole. Concrete pouring: Concrete pouring is carried out through three discharge ports using the conduit method. The buried depth of the conduit is controlled to be 2-4m, and the height difference of the concrete between adjacent conduits is not more than 0.5m. Quality inspection: inspect the integrity of the excavated trench section and underground continuous wall.

[0008] As a preferred embodiment of the present invention, the construction preparation step specifically includes the following sub-steps: Temporary facilities: set up a steel bar processing site, mud box, waste dump and car wash pool within the construction site; Water and electricity connection: Temporary water is connected to various water points through the water supply pipes on site, and temporary electricity is connected to the trenching machine and mud pump through the transformer. Technology and safety management: Organize operators to be familiar with drawings and specifications, complete safety and quality technical briefings and three-level safety education; Equipment and material inspection: Acceptance of incoming machinery and equipment, checking of certificates of conformity and operating permits, and materials entering the site in batches. After sampling and inspection, materials are stored according to regulations; Laying of construction access roads: Laying construction access roads for construction machinery to travel along the underground continuous wall.

[0009] As a preferred embodiment of the present invention, the measuring and setting out step specifically includes the following sub-steps: Instrument calibration: Test and calibrate measuring instruments and obtain test certificates; Establishment of control network: Set up the measurement control network according to the design institute's benchmark points and take protective measures; Slot section identification: Slot section divisions are marked on the guide wall according to the slot section number and elevation, and a closure check is performed on the on-site slot section divisions.

[0010] As a preferred solution of the present invention, the guide wall manufacturing step specifically includes the following sub-steps: Site preparation: level the site, remove debris, replace soft soil and compact it, plan driving routes and keep a safe distance from the trench; Measurement and positioning: Calculate the coordinates of the corner points of the center line of the ground-connected wall, set up guard piles after measurement and report to the supervisor for review; the center line of the guide wall is set 100mm outward, and the two sides of the side line are set 25mm outward; Trench excavation: Construction should be carried out in sections, with a length of 30-50m, avoiding ground-connected wall joints, clearing obstacles and sealing the broken ends of abandoned pipelines; Reinforced concrete construction: The bottom formwork is fixed with low-grade concrete, and the side formwork is supported by wooden formwork square timber with a spacing of 1000mm; C12 threaded steel bars are tied, with the main and horizontal bars spaced 150mm apart, and the main bars are anchored in the hardened ground; concrete is poured symmetrically on both sides; Corner treatment: The guide wall at the corner should be extended outward along the axis by no less than 0.4m; Formwork removal: After the concrete strength reaches 70%, the formwork is removed, wooden beams are erected for support, and the dividing lines and width numbers are marked on the top wing surface of the guide wall.

[0011] As a preferred embodiment of the present invention, the trenching step specifically includes the following sub-steps: Staking and preparation: The width of the first excavation is the trench width plus 1200mm; measure the elevation of the top of the guide wall, mark the location and number of the trench, put the trenching machine and dump truck in place, and inject mud to 50cm below the top of the guide wall; Equipment combination trenching: trenching machine and double-wheel milling machine are used for trenching operation, and the trenching machine should be ≥2.5m away from the guide wall; trenching machine is used to excavate soft soil layer, and double-wheel milling machine is used to excavate rock layer; Trench control: The standard unit trench section adopts the three-grab trenching method, with an excavation speed of 1.5m / h. The verticality is corrected as the trench is excavated, and the excavation depth of the trench bottom in the same trench section is kept consistent. When encountering trench sections of the same width but different depths, the shallower ones are excavated first and the deeper ones are excavated later.

[0012] As a preferred embodiment of the present invention, the tank cleaning and slurry replacement step includes the following sub-steps: Brushing: Use a steel brush to brush the joints of the unit slot sections until there is no mud on the brush; Hole cleaning: Use the air lift reverse circulation method to clean the hole. The lower end of the slurry discharge pipe should be 20-30 cm away from the top surface of the sediment at the bottom of the hole. Add high-quality mud until the sediment thickness and mud density at the bottom of the tank meet the standards.

[0013] As a preferred embodiment of the present invention, the steel cage production and hoisting steps include the following sub-steps: Steel cage production: Set up 8 longitudinal truss bars and transverse truss bars with a spacing of 3m, and use an integral production process to process the entire piece on the bottom form; Hoisting construction: Double crawler cranes are used to lift the steel cage. The main hoist and auxiliary hoist are equipped with 2 rows of longitudinal and 6 horizontal lifting points. After the whole cage is straightened, it will be put into the groove at one time.

[0014] As a preferred embodiment of the present invention, the concrete pouring step includes the following sub-steps: Conduit installation: Install the conduit within 4 hours after the steel cage is placed. Set up 3 discharge ports, with the lower port of the conduit 30-50cm away from the bottom of the trench, and the upper port of the conduit connected to a funnel; Pouring control: Use the conduit method to pour underwater concrete, with a slump of 180±20mm at the outlet; the buried depth of the lower end of the conduit in the concrete is controlled at 2-4m, and the height difference of the concrete in two adjacent conduits is not greater than 0.5m; reduce the pouring speed when pouring to the top of the wall, and reduce the minimum buried depth of the conduit to 2m.

[0015] As a preferred embodiment of the present invention, the quality inspection step includes the following sub-steps: Excavation trench inspection: Check the trench length, thickness, depth, inclination and position deviation of embedded parts on the wall; Concrete quality testing: Core extraction test and ultrasonic testing methods are used to test the wall concrete strength, sediment thickness at the bottom of the wall, properties of the rock and soil layer at the bottom of the wall, and wall integrity.

[0016] As a preferred embodiment of the present invention, in the core pulling test, each project has no less than 15% and no less than 10 slot sections, and each slot section has no less than 3 holes; in the ultrasonic testing, 45% of the total wall width of each project is pre-buried with acoustic testing pipes, the number of tested wall widths is no less than 30%, and each slot section has no less than 5 testing holes.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Short construction period: Under the condition that the processing time of underground continuous wall steel cage is the same, the ultra-wide underground continuous wall concrete pouring volume is larger at one time, which improves construction efficiency and shortens the overall construction period; 2. Low overall cost: Compared with conventional underground continuous wall trench width, the ultra-wide underground continuous wall construction requires less joint processing, which reduces the project cost while ensuring construction quality and safety; 3. Strong adaptability: The 9m channel width design can meet the requirements of segmented construction of the cast-in-place main structure and the hoisting requirements of prefabricated components of the composite assembled subway station; 4. Good integrity: Compared with the conventional 6m trough width, the 9m trough width can be cast in one time to form a larger volume and the wall has stronger integrity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a flow chart of a method for constructing an ultra-wide underground continuous wall in a subway station according to one embodiment of the present invention; Figure 2 A specific flow chart of the construction preparation steps in one embodiment of the present invention; Figure 3 A specific flow chart of the measurement and setting out steps in one embodiment of the present invention; Figure 4 A specific flow chart of the guide wall manufacturing steps in one embodiment of the present invention; Figure 5 A specific flow chart of the trenching excavation step in one embodiment of the present invention; Figure 6 This is a specific flow chart of the tank cleaning and slurry replacement steps in one embodiment of the present invention; Figure 7 A specific flow chart of the steps of making and hoisting a steel cage in one embodiment of the present invention; Figure 8 A specific flow chart of the concrete pouring steps in one embodiment of the present invention; Figure 9 This is a specific flow chart of quality detection in one embodiment of the present invention. DETAILED DESCRIPTION

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. It should also be noted that the embodiments described below are intended only to illustrate the present invention and are not intended to limit the present invention.

[0021] See also Figure 1 This embodiment provides a method for constructing an ultra-wide underground continuous wall in a subway station, comprising the following steps: Step S1, construction preparation: set up temporary facilities, complete temporary water and electricity connections, conduct technical briefings, safety education, equipment and material inspections, and pave construction access roads; Step S2, measurement and layout: using calibrated measuring instruments to establish control reference points, divide the slot into sections and mark them on the guide wall; Step S3, guide wall fabrication: including site preparation, measurement and positioning, trench excavation, reinforced concrete construction, corner treatment and formwork removal; Step S4, trenching and excavation: A trenching machine and a double-wheel trenching machine are used in combination. The width of the first excavation is the trenching width plus 1200 mm. The soft soil layer is excavated by the trenching machine, and the rock layer is processed by a double-wheel milling machine or an impact drill. Step S5, tank cleaning and slurry replacement: remove the mud skin at the joint by brushing the wall, use air lift reverse circulation method to clean the hole, and control the thickness of the sediment at the bottom of the tank and the slurry density; Step S6, fabrication and installation of the steel cage: The steel cage is provided with 8 longitudinal truss bars and transverse truss bars with a spacing of 3m, and is hoisted integrally into the slot using a double crane; Step S7, concrete pouring: pouring through three discharge ports using the conduit method, controlling the buried depth of the conduit to 2-4m, and the height difference of the concrete between adjacent conduits to be no more than 0.5m; Step S8, quality inspection: inspect the integrity of the excavated trench section and the underground continuous wall.

[0022] See also Figure 2 In this embodiment, the construction preparation step S1 specifically includes the following sub-steps: (1) Temporary facility installation Temporary facilities such as steel bar processing yard, mud box, slag yard and car wash pool are set up in the construction site to provide convenient conditions for subsequent construction and ensure the orderly development of construction material processing, storage and on-site sanitation cleaning.

[0023] (2) Water and electricity connection Temporary water supply is connected to various water points on the construction site, such as the car wash tank and mud tank, through the on-site water supply pipe. Temporary electricity is provided by laying cables through transformers on the construction site and connecting them to the trough forming machine, mud pump, etc. By completing the temporary water and electricity connection, we ensure that all water points on the construction site have sufficient water sources and various construction machinery and equipment have a stable power supply, ensuring smooth construction.

[0024] (3) Technology and safety management Organize operating personnel to be familiar with drawings and specifications so as to master various technical requirements and construction methods, complete safety and quality technical briefings, and complete safety and quality technical briefings and three-level safety education, so that operating personnel can master technical requirements and construction methods, enhance safety awareness, and reduce technical errors and safety accidents during construction.

[0025] (4) Inspection of equipment and materials Acceptance inspection is conducted on incoming machinery and equipment, including equipment certificates, inspection and testing reports, and special operator certificates. All incoming machinery and equipment must be installed and inspected before they are put into use. This ensures that the machinery and equipment perform well and that the materials are of qualified quality, guaranteeing construction quality and safety. Steel bars, concrete, and other materials are delivered in batches according to the material delivery plan. Incoming materials undergo on-site acceptance inspection, with sampling and reporting required for inspection. Only after passing inspection can they be put into use. During construction, concrete test blocks and weld strength test pieces must be submitted for inspection according to design and specification requirements. Materials must be stored or stacked in the specified location and manner, with the quality, specifications, and quantity of materials and components labeled and protected for ease of management and use.

[0026] (5) Construction access road paving A construction access road is arranged around the underground continuous wall to meet the travel needs of construction machinery such as hydraulic grab trenching machines, double-wheel milling machines, rotary drilling rigs, rotary grouting machines, crawler cranes and concrete tankers. The construction access road utilizes the original hardened road surface. When necessary, 20mm steel plates are laid on the road to ensure the safety of crawler cranes and other equipment. Mud and debris are removed in a timely manner during the construction process to ensure construction safety and efficiency.

[0027] See also Figure 3 In this embodiment, the measurement and setting out step specifically includes the following sub-steps: (1) Instrument calibration The total station, level, steel ruler and other measuring instruments used in the inspection are inspected and calibrated, and inspection certificates are obtained to ensure the accuracy of the measurement data and provide reliable basic data for construction.

[0028] (2) Establishment of control network In order to ensure the accuracy of the construction control network, a surveying control network is set up according to the design institute's benchmark points during construction. Each control point of the surveying control network has permanent coordinate piles and horizontal benchmark piles, and protective measures are taken to prevent damage. The surveying control network is used to control and correct the axis, elevation, etc. to ensure construction accuracy.

[0029] (3) Slot segment identification On-site technicians use red paint to mark the slot section divisions on the guide wall according to the slot section number and elevation to facilitate construction, and perform closure checks on the on-site slot section divisions so that construction personnel can clearly understand the slot section location and size, facilitating accurate construction.

[0030] See also Figure 4 In this embodiment, the guide wall manufacturing step specifically includes the following sub-steps: (1) Site treatment Arrange the construction site reasonably according to the requirements, level the site, remove debris, replace soft and loose soil, and compact it; after leveling the site, plan the driving route of excavators and concrete tankers, and keep a certain distance between the access road and the trench position to avoid affecting the stability of the trench wall.

[0031] (2) Measurement and positioning The guide wall is the reference object on the surface of the underground continuous wall. The plane position of the guide wall determines the plane position of the underground continuous wall. Therefore, the construction layout of the guide wall must be correct.

[0032] a. Calculate the coordinates of the centerline corner points of the underground continuous wall based on the coordinates provided in the design drawings. After the calculation results are internally verified to be correct, they are measured and laid out, and guard piles are prepared. The results are then reported to the supervisor for review.

[0033] b. To ensure that the clearance of the foundation pit structure in the later stage meets the requirements, the center line of the guide wall is placed 100mm outward. At the same time, to prevent the steel cage from getting stuck when entering the groove, the edge line of the guide wall is placed 25mm outward on both sides, for a total of 50mm.

[0034] c. After the excavation of the guide wall trench is completed, the center line should be immediately introduced under the trench to control the template construction and ensure that the center line of the guide wall is correct.

[0035] d. Before pouring the guide wall concrete, the top surface elevation of the guide wall should be placed on the formwork surface to control the top surface elevation of the guide wall.

[0036] e. After the guide wall formwork is removed, check whether the center line, flatness and verticality of the guide wall meet the requirements.

[0037] f. After the guide wall construction is completed, immediately make the dividing lines on the top surface of the guide wall and measure the elevation of the hanging point position of the steel cage of each trough section to control the length of the hanging bars.

[0038] (3) Trench excavation The guide wall is constructed in sections, and the length of each section is controlled within 30-50m according to the template length and specification requirements. This will neither increase the construction difficulty and extend the construction period due to sections being too long, nor increase the workload of connecting the section construction due to sections being too short. This is conducive to reasonably arranging the construction progress and improving construction efficiency. Among them, the guide wall segmentation line avoids the ground-connected wall joints, which can avoid interference of the guide wall construction on the ground-connected wall joints, reduce stress concentration or construction damage at the ground-connected wall joints that may be caused by the guide wall construction, thereby ensuring the construction quality of the ground-connected wall joints and enhancing the structural stability of the underground continuous wall; before the guide wall is excavated, the excavation width of the guide wall is staked out on site according to the measurement and stakeout results and the thickness of the underground continuous wall, which can ensure that the excavation size of the guide wall meets the design requirements; the guide wall construction joints on the plane are staggered with the underground continuous wall joints to avoid the connection of leakage channels, reduce the probability of water leakage after the underground continuous wall construction is completed, improve the waterproof performance of the underground continuous wall, and ensure the safety and durability of the underground project; when excavating the guide wall, if there are obstacles such as abandoned pipelines, they should be removed, and the broken ends of the abandoned pipelines should be tightly sealed to prevent them from becoming mud leakage channels.

[0039] (4) Reinforced concrete construction a. Immediately after the guide wall trench is excavated, the center line of the guide wall is led into the trench. The bottom formwork made of square timber is placed in the trench and adjusted to the designed position. It is then fixed with self-mixed low-grade concrete. The side wall formwork adopts wooden formwork, and the formwork is supported and reinforced with square timber, one above and one below, with a horizontal spacing of 1000mm. The formwork should be firmly reinforced to prevent formwork from running, and the accuracy of the axis and clearance should be guaranteed. Before pouring concrete, check whether the verticality, center line and clear distance of the formwork meet the requirements.

[0040] b. After the bottom formwork construction is completed, the guide wall reinforcement is tied. The guide wall reinforcement is designed to use C12 threaded steel bars. During construction, it is arranged in a single layer. The main reinforcement and horizontal reinforcement are arranged at a distance of 150mm. The horizontal reinforcement is placed on the inside. The C12 threaded steel main reinforcement needs to be anchored into the surrounding hardened site. After the reinforcement construction is completed and passed the three inspections, fill out the hidden project acceptance form and report it to Party A and the supervisor for acceptance. Only after passing the acceptance can the next construction process be carried out.

[0041] c. The strength grade of the guide wall concrete is C20. Concrete pouring is done by manual labor combined with concrete tankers. The pouring is carried out symmetrically and alternately on both sides to prevent formwork deviation. If formwork deviation occurs, the pouring of concrete should be stopped immediately, the formwork should be reinforced again, and the joints between the guide walls can be poured only after it is corrected to the designed position.

[0042] d. Use a φ50 vibrating rod to vibrate the concrete. Insert quickly and pull out slowly during the vibration process to ensure uniform vibration of the concrete structure from top to bottom. Since the wall concrete thickness is 200mm, single-row vibration is adopted. The moving spacing of the vibrating rod is about 400mm. The vibration time at each point is 20-30S. The vibrating rod should be inserted 50mm into the lower layer of concrete when the concrete surface no longer sinks significantly, no bubbles appear, and mortar appears on the surface. The vibrating rod should be avoided from colliding with steel bars and formwork during vibration.

[0043] (5) Corner processing At the corner of the guide wall, the grab bucket of the trenching machine is in an arc shape, and due to the width of the divided trench, in order to ensure that the trenching of the underground continuous wall can proceed smoothly and the corner section is complete, the guide wall at the corner is extended outward along the axis by no less than 0.4m.

[0044] (6) Template removal a. Remove the formwork after the guide wall concrete strength reaches 70%. Removing the formwork at this strength can ensure that the guide wall structure has sufficient bearing capacity and will not cause quality problems such as deformation and cracking due to external forces during the formwork removal process; immediately recheck the central axis and clearance size of the guide wall and the pouring quality of the side wall concrete after removing the formwork. If it is found that the side wall concrete intrudes into the clearance or there is a cavity in the wall, repair or seal it in time, call relevant personnel to analyze and discuss the cause of the accident, and formulate corresponding measures to prevent similar problems from happening again.

[0045] b. After the formwork is removed, 80×80mm wooden beam supports or plain concrete supports are immediately erected, with one support above and below, with a horizontal spacing of 2000mm and a spacing of 1.5m in the length direction of the guide wall. This can provide effective lateral support for the guide wall to prevent the guide wall from shifting or deforming due to factors such as soil pressure and construction load during the subsequent construction process, ensure the geometric size and position accuracy of the guide wall, and provide accurate guidance for subsequent processes such as trenching construction. At the same time, the support is not allowed to be removed before trenching construction to avoid displacement of the guide wall; in addition, the dividing lines and width numbers are marked on the top wing surface of the guide wall with red paint to provide clear positioning and identification for subsequent processes such as trenching construction and steel cage hoisting, which is convenient for construction personnel to operate accurately and improve construction efficiency and accuracy.

[0046] See also Figure 5 In this embodiment, the trenching step specifically includes the following sub-steps: (1) Staking out and preparation Before trenching the unit trench segments, a 600 mm gap is added to the initial excavation width based on the trenching width (b) of the segment, taking into account any deviations in verticality during trenching. The initial excavation width is the trench segment width plus 1200 mm. This allows for construction errors and ensures that the rebar cage can be lowered smoothly into place after trenching is complete. This avoids problems with cage installation due to insufficient trench segment width, thus ensuring the integrity and construction quality of the diaphragm wall structure. Furthermore, joints between unit trench segments must be avoided at corners. Corners are areas of stress concentration due to soil and water pressure, as well as loads transmitted from the superstructure, acting on the diaphragm wall. If unit trench segment joints are located at these locations, they become weak links in the structure and are more susceptible to cracking and damage under the repeated effects of complex stresses, compromising the overall structural safety and stability of the diaphragm wall.

[0047] b. Measure the elevation of the top of the guide wall to calculate the size of the steel cage suspension bar, and mark the unit slot section position and unit slot section number with red paint to roughly mark the position of each grab width and the steel cage placement position, provide clear construction guidance for construction personnel, reduce construction errors, improve construction accuracy and efficiency, and also facilitate quality inspection and management during the construction process.

[0048] c. The trenching machine and dump truck (dump truck within the site) are positioned. After the trenching machine is positioned, the automatic positioning and orientation device on the machine is activated to ensure that the level gauge on the trenching machine is level. The slurry worker lays the slurry delivery pipe to the trench section to be excavated.

[0049] d. Seal both sides of the trench section, remove garbage and debris from the guide wall, and inject mud to the specified elevation (50cm below the top surface of the guide wall) to ensure the smooth progress of the trench construction.

[0050] (2) Equipment is combined into slots The trenching operation is carried out by combining an XG50 trenching machine with a verticality correction function and an SDC120 double-wheel trenching machine. The trenching machine is ≥2.5m away from the edge of the guide wall. If the trenching machine is too close to the guide wall, its crawler or supporting structure may cause lateral extrusion of the guide wall, causing deformation or displacement of the guide wall, thereby affecting the trenching accuracy. The trenching machine is used to excavate soft soil layers (standard penetration number <70), and the double-wheel milling machine is used for excavation of massive strongly weathered and moderately weathered rock layers, so as to give full play to the advantages of different equipment, improve construction efficiency, and shorten the trenching period.

[0051] During the trenching construction of underground continuous walls, if large boulders and other underground obstacles prevent the trenching machine from taking soil normally, a double-wheel milling machine is used to clear the underground obstacles; the double-wheel milling teeth mill and crush the surrounding rock and replace it through the mud circulation system.

[0052] During the trenching process for underground continuous walls, if large, isolated boulders or other underground obstacles prevent the hydraulic grab from removing soil properly, a percussion drill can be used to clear the underground obstacle. Once the percussion drill is in place, the hammer is aimed at the isolated boulders and repeatedly impacts them until they are shattered and replaced through slurry circulation. However, if the underground obstacle is half inside the trench and half outside, direct impact can easily result in an oblique hole. Different treatments should be adopted for different situations: If the underground obstacle is a probe rock, high-quality clay blocks or gravel should be filled in, and low-hammer intensive impacts should be used. The hole should be repeatedly swept until the probe rock is shattered and the debris is replaced through slurry circulation.

[0053] (3) Grooving control a. The standard unit trench section adopts the three-claw trenching method. The trenching machine excavation speed is controlled at about 1.5m / h. The verticality is corrected as the trench is excavated to ensure a vertical accuracy of more than 3 / 1000. This ensures the verticality of the underground continuous wall, improves the wall's bearing capacity and waterproof performance, and enables the underground continuous wall to better play its role as a retaining structure. b. The excavation depth of the trench bottom within the same trench section should be kept consistent. If trench sections of the same width but different depths are encountered, dig shallower first and then deeper. This can avoid the problem of uneven trench bottom caused by inconsistent excavation depth, ensure the flatness and stability of the bottom of the underground continuous wall, and help improve the overall quality of the wall.

[0054] c. The grab bucket of the trenching machine must move up and down vertically and evenly during the trenching process to minimize disturbance to the side walls.

[0055] d. If a collapse occurs, it may not be treated if it is not serious. If it seriously affects the operation or the surrounding environment, clay or cement soil should be backfilled and excavation can be resumed after it is consolidated and stabilized.

[0056] e. For the trench sections designed for rock penetration, timely rock sampling should be performed to determine the degree of rock weathering and serve as a basis for final trenching. The first rock sample should be taken 300 mm into the rock, followed by one sample every 500 mm thereafter. Each trench section should contain at least two groups of at least three samples. This provides accurate geological information for trenching construction, helps control trenching depth and quality, and provides a reliable basis for project acceptance. Rock samples should be sealed and stored until the project is completed and accepted.

[0057] f. After the trench section is excavated and the trench depth and trench wall verticality meet the design requirements, the trench can be cleaned and the slurry replaced. This can ensure that the slurry performance in the underground continuous wall trench meets the requirements and improve the concrete pouring quality of the wall.

[0058] See also Figure 6 In this embodiment, the tank cleaning and slurry replacement step includes the following sub-steps: (1) Wall brushing Use a steel brush to brush the joints of the unit slot sections, brushing the walls up and down for no less than 20 times until there is no mud on the brush surface of the wall brush. The wall brush uses an eccentric hanging brush to ensure close contact between the steel brush surface and the joint surface to achieve a cleaning effect.

[0059] (2) Clearing the pores After the wall brushing is completed, the air lift reverse circulation method is used to clean the hole. The lower end of the slurry discharge pipe is 20-30 cm away from the top surface of the sediment at the bottom of the hole; then the air compressor is turned on to supply air, and high-quality mud is added to the hole. The mud sucked out of the hole is discharged into the mud pool (mud box) through the mud separator for recycling; until the sediment accumulation thickness and mud density at the bottom of the tank meet the standards.

[0060] The air lift reverse circulation method uses an air compressor to deliver air to the lower end of the slurry discharge pipe through an air pipeline, creating a negative pressure in the pipe. This causes the mud and sediment at the bottom of the hole to be drawn into the pipe due to the pressure difference and then discharged out of the hole. The air lift reverse circulation method has the advantages of high hole cleaning efficiency and thorough hole cleaning. Maintaining an appropriate distance between the lower end of the slurry discharge pipe and the top surface of the sediment ensures that the sediment is fully absorbed while preventing the pipe from being clogged by sediment due to a close distance, thus affecting the hole cleaning effect. Using the air lift reverse circulation method to clean the hole can effectively reduce the thickness of sediment accumulation at the bottom of the trench, meeting the requirements for trench bottom cleanliness for underground continuous wall construction.

[0061] See also Figure 7 In this embodiment, the steel cage production and hoisting steps include the following sub-steps: (1) Steel cage production A standard 6m-wide underground continuous wall typically has four longitudinal truss bars and transverse truss bars spaced 4m apart. The steel cage is manufactured as a whole, formed in one piece on a full-length bottom formwork, and then hoisted into the groove as a whole. The 9m-wide underground continuous wall of the present invention, however, uses eight longitudinal truss bars and transverse truss bars spaced 3m apart when manufacturing the steel cage. The addition of additional longitudinal truss bars can more evenly distribute the load borne by the cage, reduce local stress concentration, and effectively resist greater deformation caused by increased length and weight. By reducing the spacing between the transverse truss bars, the connection of the cage in the width direction is further strengthened, allowing the cage to better maintain its shape during hoisting, avoiding problems such as sagging or twisting in the middle due to excessive width, thereby meeting the requirements for hoisting large-sized cages.

[0062] (2) Hoisting construction Because the extra-wide diaphragm wall reinforcement cages at subway stations are heavy and long, a construction method was adopted in which the cages were hoisted with dual crawler cranes, hoisted and straightened as a whole, and then slotted in a single step. This reduced the need for segmented cages and multiple hoisting and connection processes, significantly shortening construction time and improving efficiency. Furthermore, slotting in a single step ensures the integrity and continuity of the cages, avoiding potential quality issues associated with segmented slotting, such as loose rebar connections and loose concrete pouring. This method improves the overall quality and waterproofing performance of the underground diaphragm wall.

[0063] Both the main and auxiliary hoists are equipped with two longitudinal rows and six transverse lifting points. The two longitudinal rows of lifting points distribute the lifting force according to the length of the rebar cage, keeping the cage level during the hoisting process and reducing bending deformation caused by uneven force. The six transverse lifting points further enhance the hoisting stability, better controlling the width balance of the rebar cage and preventing it from tipping or twisting during the hoisting process. This rational arrangement of lifting points ensures the safety and stability of the rebar cage during the hoisting process.

[0064] See also Figure 8 In this embodiment, the concrete pouring step includes the following sub-steps: (1) Catheter installation After the steel cage is placed, the trench wall is in a relatively unstable state. Over time, the trench wall may collapse and the mud may settle and thicken. Therefore, it is necessary to install a conduit within 4 hours of the steel cage placement and set up three discharge ports to ensure a more even distribution of concrete within the trench section. The conduit is lowered section by section during the concrete pouring, connecting them as they are lowered. Before installation, the conduit length is calculated to ensure that the lower end of the conduit is 30-50cm from the trench bottom and the upper end of the conduit is connected to a funnel. Keeping the lower end of the conduit 30-50cm from the trench bottom allows the concrete to form a stable accumulation during the initial pour, gradually covering the sediment at the bottom of the trench and ensuring a good bond between the concrete and the trench bottom.

[0065] (2) Casting control When pouring underwater concrete using the conduit method, the slump at the exit is 180±20mm. This slump ensures good concrete fluidity and facilitates pouring through the conduit underwater. Because underwater concrete requires good workability, the maximum coarse aggregate diameter for underwater concrete should not exceed 30mm. Medium or coarse sand should be used, and the sand content of the concrete mix should be no less than 40%.

[0066] During concrete pouring, the lower end of the conduit is buried within the concrete at a depth of 2-4m. This ensures that the concrete exerts sufficient pressure on the conduit, allowing the concrete to flow smoothly out of the conduit while preventing mud from entering the conduit. The height difference between adjacent conduits is no more than 0.5m, ensuring that the concrete rises evenly within the trench section and avoiding problems such as uneven stress on the trench wall due to excessive concrete height differences, resulting in trench wall collapse or loose concrete pouring. During the pouring process, the concrete surface elevation and the buried depth of the conduit should be observed and measured at all times to prevent the conduit opening from being lifted above the concrete surface. When removing the conduit, the concrete surface rise, the pouring volume, and the buried depth of the conduit should be measured to monitor the concrete surface rise, the pouring volume, and the buried depth of the conduit to prevent the lower end of the conduit from being exposed to the mud, which could cause mud to flow into the conduit. When the concrete is poured to the top of the wall, the concrete in the duct is not easy to flow out. First, reduce the pouring speed to reduce the impact of the concrete on the concrete in the duct, so that the concrete can flow out of the duct more smoothly, and then reduce the minimum burial depth of the duct to 2m. This can ensure the density of the concrete at the top of the wall, avoid quality problems such as looseness and voids on the top of the concrete due to excessive burial depth of the duct, and improve the strength and durability of the top of the underground continuous wall.

[0067] See also Figure 9 In this embodiment, the quality detection step includes the following sub-steps: (1) Excavation trench section inspection Check the length, thickness, depth, inclination of the trench section and the position deviation of the embedded parts on the wall to ensure that the trench section size and position meet the design requirements and the construction quality of the underground continuous wall; the length and inclination of the trench section should meet the following requirements: a. The allowable deviation of the slot length is ±50mm; b. The allowable deviation of the groove thickness is ±10mm; c. The allowable depth deviation is ±100mm; d. The inclination is not greater than 1 / 300; e. The position deviation of embedded parts on the wall shall not exceed 100mm horizontally and 50mm vertically.

[0068] (2) Concrete quality testing Core sampling tests and ultrasonic testing methods are used to test the wall concrete strength, sediment thickness at the bottom of the wall, properties of the rock and soil layer at the bottom of the wall, and the integrity of the wall. Through a reasonable sampling ratio and judgment method, the quality of the wall is accurately judged, and treatment measures are proposed for the slot sections that do not meet the design requirements to ensure the quality and safety of the underground continuous wall.

[0069] In core sampling tests, no less than 15% of each project and no fewer than 10 slot sections, with no fewer than three holes per slot section, should be included. By sampling multiple slot sections and holes, we can gain a comprehensive understanding of the concrete quality at different locations and promptly identify any local quality issues.

[0070] During ultrasonic testing, acoustic testing tubes are embedded in 45% of the total wall width for each project, with no less than 30% of the wall width tested, and no fewer than five testing holes in each slot section. Ultrasonic testing is a non-destructive testing method that facilitates the testing of wall concrete using embedded acoustic testing tubes. This optimal placement of embedded acoustic testing tubes, number of testing tubes, and testing holes ensures an effective assessment of the wall concrete's integrity, providing more comprehensive coverage of the wall interior and improving testing accuracy.

[0071] If core pulling tests reveal any sections that fail to meet design requirements, the sampling inspection is doubled for the sections that fail. If sections still fail to meet design requirements during the expanded sampling, all sections in that batch are tested. This gradually expanded sampling mechanism allows for the timely identification of the scope and severity of quality issues, preventing the quality of individual sections from impacting the overall project quality. Failure to expand sampling inspections after discovering unqualified sections may result in the omission of other problematic sections, leading to potential project quality risks.

[0072] If ultrasonic testing reveals any discrepancies with design requirements, core testing is performed on the remaining sections. If the core testing also reveals discrepancies, all sections in that batch are tested. This combined approach leverages the strengths of both methods. Ultrasonic testing can quickly and extensively screen for quality issues in wall concrete, while core testing allows for further verification and detailed analysis of suspected problem areas, improving the reliability and accuracy of quality testing.

[0073] After spot checks of underground diaphragm walls, an assessment is made of the wall's concrete strength, sediment thickness at the wall base, the properties of the rock and soil layer at the wall base, and the wall's integrity. This assessment follows the relevant provisions of the Shenzhen Standard "Regulations for Testing Building Foundation Pile Foundations" (SJG09). Based on the assessment results, treatment measures are proposed.

[0074] In summary, the construction method of the ultra-wide underground continuous wall of the subway station of the present invention is suitable for the construction of underground continuous walls with a trench width of 9m under complex geological conditions in reclamation areas. By adjusting the unit length of the underground continuous wall trench width, increasing the trench wall reinforcement, using a combination of different equipment to improve the trenching efficiency, and optimizing the truss reinforcement and I-beam joints, it is ensured that the integrity, anti-seepage function, and lifting safety of the underground continuous wall meet the design requirements; at the same time, it can also meet the lifting and placement requirements of prefabricated components of the composite assembled subway station.

[0075] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to the process, method, product, or apparatus.

[0076] Furthermore, although the operations of the method of the present invention are described in a particular order in the accompanying drawings, this does not require or imply that these operations must be performed in this particular order, or that all illustrated operations must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

[0077] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

[0078] The above is an exemplary description of the patent of the present invention in conjunction with the accompanying drawings. It is obvious that the implementation of the patent of the present invention is not limited to the above-mentioned method. As long as various improvements are made by adopting the method concept and technical solution of the patent of the present invention, or the concept and technical solution of the patent of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A construction method for an ultra-wide underground continuous wall in a subway station, characterized in that: The following steps are involved: Construction preparation: set up temporary facilities, complete temporary water and electricity connections, conduct technical briefings, safety education, equipment and material inspections, and pave construction access roads; Surveying and setting out: Use calibrated measuring instruments to establish control reference points, divide the slot into sections and mark them on the guide walls; Guide wall production: including site preparation, measurement and positioning, trench excavation, reinforced concrete construction, corner treatment and formwork removal; Trench excavation: A trencher and a double-wheel slot milling machine are used in combination. The width of the first excavation is the trench width plus 1200mm. The trencher is used to excavate the soft soil layer, and the double-wheel milling machine or impact drill is used to process the rock layer. Tank cleaning and slurry replacement: remove mud skin from joints by brushing the wall, use air lift reverse circulation method to clean the hole, and control the thickness of sediment at the bottom of the tank and the slurry density; Fabrication and hoisting of steel cage: The steel cage is equipped with 8 longitudinal truss bars and transverse truss bars with a spacing of 3m. It is hoisted by two cranes and hoisted into the slot as a whole. Concrete pouring: Concrete pouring is carried out through three discharge ports using the conduit method. The buried depth of the conduit is controlled to be 2-4m, and the height difference of the concrete between adjacent conduits is not more than 0.5m. Quality inspection: inspect the integrity of the excavated trench section and underground continuous wall.

2. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The construction preparation step specifically includes the following sub-steps: Temporary facilities: set up a steel bar processing site, mud box, waste dump and car wash pool within the construction site; Water and electricity connection: Temporary water is connected to various water points through the water supply pipes on site, and temporary electricity is connected to the trenching machine and mud pump through the transformer. Technology and safety management: Organize operators to be familiar with drawings and specifications, complete safety and quality technical briefings and three-level safety education; Equipment and material inspection: Acceptance of incoming machinery and equipment, checking of certificates of conformity and operating permits, and materials entering the site in batches. After sampling and inspection, materials are stored according to regulations; Laying of construction access roads: Laying construction access roads for construction machinery to travel along the underground continuous wall.

3. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The measuring and setting out step specifically includes the following sub-steps: Instrument calibration: Test and calibrate measuring instruments and obtain test certificates; Establishment of control network: Set up the measurement control network according to the design institute's benchmark points and take protective measures; Slot section identification: Slot section divisions are marked on the guide wall according to the slot section number and elevation, and a closure check is performed on the on-site slot section divisions.

4. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The guide wall manufacturing step specifically includes the following sub-steps: Site preparation: level the site, remove debris, replace soft soil and compact it, plan driving routes and keep a safe distance from the trench; Measurement and positioning: Calculate the coordinates of the corner points of the center line of the ground-connected wall, set up guard piles after measurement and report to the supervisor for review; the center line of the guide wall is set 100mm outward, and the two sides of the side line are set 25mm outward; Trench excavation: Construction should be carried out in sections, with a length of 30-50m, avoiding ground-connected wall joints, clearing obstacles and sealing the broken ends of abandoned pipelines; Reinforced concrete construction: The bottom formwork is fixed with low-grade concrete, and the side formwork is supported by wooden formwork square timber with a spacing of 1000mm; C12 threaded steel bars are tied, with the main and horizontal bars spaced 150mm apart, and the main bars are anchored in the hardened ground; concrete is poured symmetrically on both sides; Corner treatment: The guide wall at the corner should be extended outward along the axis by no less than 0.4m; Formwork removal: After the concrete strength reaches 70%, the formwork is removed, wooden beams are erected for support, and the dividing lines and width numbers are marked on the top wing surface of the guide wall.

5. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The trenching step specifically includes the following sub-steps: Staking and preparation: The width of the first excavation is the trench width plus 1200mm; measure the elevation of the top of the guide wall, mark the location and number of the trench, put the trenching machine and dump truck in place, and inject mud to 50cm below the top of the guide wall; Equipment combination trenching: trenching machine and double-wheel milling machine are used for trenching operation, and the trenching machine should be ≥2.5m away from the guide wall; trenching machine is used to excavate soft soil layer, and double-wheel milling machine is used to excavate rock layer; Trench control: The standard unit trench section adopts the three-grab trenching method, with an excavation speed of 1.5m / h. The verticality is corrected as the trench is excavated, and the excavation depth of the trench bottom in the same trench section is kept consistent. When encountering trench sections of the same width but different depths, the shallower ones are excavated first and the deeper ones are excavated later.

6. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The tank cleaning and slurry replacement step includes the following sub-steps: Brushing: Use a steel brush to brush the joints of the unit slot sections until there is no mud on the brush; Hole cleaning: Use the air lift reverse circulation method to clean the hole. The lower end of the slurry discharge pipe should be 20-30 cm away from the top surface of the sediment at the bottom of the hole. Add high-quality mud until the sediment thickness and mud density at the bottom of the tank meet the standards.

7. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The steel cage production and hoisting steps include the following sub-steps: Steel cage production: Set up 8 longitudinal truss bars and transverse truss bars with a spacing of 3m, and use an integral production process to process the entire piece on the bottom form; Hoisting construction: Double crawler cranes are used to lift the steel cage. The main hoist and auxiliary hoist are equipped with 2 rows of longitudinal and 6 horizontal lifting points. After the whole cage is straightened, it will be put into the groove at one time.

8. The method for constructing an ultra-wide underground continuous wall in a subway station according to claim 1, characterized in that: The concrete pouring step includes the following sub-steps: Conduit installation: Install the conduit within 4 hours after the steel cage is placed. Set up 3 discharge ports, with the lower port of the conduit 30-50cm away from the bottom of the trench, and the upper port of the conduit connected to a funnel; Pouring control: Use the conduit method to pour underwater concrete, with a slump of 180±20mm at the outlet; the buried depth of the lower end of the conduit in the concrete is controlled at 2-4m, and the height difference of the concrete in two adjacent conduits is not greater than 0.5m; reduce the pouring speed when pouring to the top of the wall, and reduce the minimum buried depth of the conduit to 2m.

9. The method for constructing an ultra-wide underground continuous wall for a subway station according to claim 1, characterized in that: The quality inspection step includes the following sub-steps: Excavation trench inspection: Check the trench length, thickness, depth, inclination and position deviation of embedded parts on the wall; Concrete quality testing: Core extraction test and ultrasonic testing methods are used to test the wall concrete strength, sediment thickness at the bottom of the wall, properties of the rock and soil layer at the bottom of the wall, and wall integrity.

10. The method for constructing an ultra-wide underground continuous wall in a subway station according to claim 9, characterized in that: In the core pulling test, no less than 15% and no less than 10 slot sections of each project shall be tested, and no less than 3 holes shall be installed in each slot section; in the ultrasonic testing, 45% of the total wall width of each project shall be pre-buried with acoustic testing pipes, the number of tested wall widths shall be no less than 30%, and no less than 5 testing holes shall be installed in each slot section.

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