A foundation pit enclosure structure applied to ground rail transit station construction

Abstract

This application relates to the field of underground construction in subway construction, and particularly to a foundation pit retaining structure applied to the construction of subway stations. It includes an external diaphragm wall and an internal diaphragm wall. Multiple reinforcing piles are cast at equal intervals along the extension direction of the foundation pit sidewall near the external diaphragm wall. An internal support structure is provided between the external diaphragm wall and the internal diaphragm wall. The internal support structure includes: longitudinal beams, horizontally arranged in three layers, dividing the internal support structure into four layers, with the lower two layers being higher than the upper two layers; columns, vertically arranged in two rows along the length of the longitudinal beams; a top slab and a bottom slab, both sides of which are connected to the external and internal diaphragm walls; and foundation piles, arranged in a row below the internal support structure. This invention has the effect of comprehensively improving the waterproof performance inside the foundation pit and enhancing the strength of the foundation pit sidewalls to reduce the risk of foundation pit collapse.

Description

Technical Field

[0001] This application relates to the field of underground construction in subway construction, and in particular to a foundation pit retaining structure for use in the construction of subway stations. Background Technology

[0002] Currently, my country's rail transit industry is developing rapidly, with urban subway construction in full swing. In emerging first-tier cities, subway travel has become a common mode of transportation. Subways and subway stations are constructed using the open-cut method.

[0003] The cut-and-cover method involves excavating a large, deep pit on the ground to create a construction area. A supporting structure is then built within the construction area to support the pit walls and prevent collapse. Excavators are then used to excavate multiple working faces simultaneously in a sequential manner to excavate the earthwork for the tunnel. The cut-and-cover method offers advantages such as high controllability, fast construction speed, and relatively minimal disruption to the surrounding environment.

[0004] During subway station construction, the strength requirements for the retaining structure vary depending on the geological environment. In areas with complex geological conditions, the bottom layer, from top to bottom, consists of artificial fill, silty clay (containing medium sand lenses in some areas), gravelly sand, strongly weathered argillaceous sandstone, and moderately weathered argillaceous sandstone. Generally, this type of soil is soft on top and hard at the bottom, and there is a serious problem of groundwater. To achieve water avoidance and waterproofing during construction, an additional diaphragm wall needs to be constructed in the construction pit of the water-rich soil to prevent water seepage from the underground soil from entering the construction area of ​​the pit. However, conventional underground retaining structures cannot meet the requirements for retaining support, which can easily lead to the collapse of the pit sidewalls and water leakage, affecting the construction progress and quality.

[0005] Regarding the aforementioned technologies, the inventors believe that the main reason for the collapse and leakage of commonly used retaining structures during construction in water-rich sandy soil is the weak waterproofing and insufficient structural strength of the reinforcement structure between the foundation pit and the diaphragm wall. Based on this, structural improvements can be made to the traditional diaphragm wall to strengthen the connection between the diaphragm wall and the side wall of the foundation pit, thereby improving the overall waterproofing performance inside the foundation pit and enhancing the strength of the side wall of the foundation pit to reduce the risk of foundation pit collapse. Summary of the Invention

[0006] In order to improve the overall waterproof performance of the foundation pit and enhance the strength of the pit sidewalls to reduce the risk of pit collapse, this invention provides a foundation pit retaining structure for use in the construction of subway stations.

[0007] The present invention provides a foundation pit retaining structure for use in the construction of subway stations, which adopts the following technical solution:

[0008] A foundation pit retaining structure for construction of a subway station includes an external diaphragm wall and an internal diaphragm wall. The external diaphragm wall is located near the side wall of the foundation pit. Multiple reinforcing piles are cast at equal intervals along the extension direction of the side wall of the foundation pit in the portion of the foundation pit near the external diaphragm wall. An internal support structure is provided between the external diaphragm wall and the internal diaphragm wall.

[0009] The internal support architecture includes;

[0010] The longitudinal beams are horizontally arranged and distributed in three layers in the vertical direction. Each layer of longitudinal beams contains multiple beams. The three layers of longitudinal beams divide the inner support structure into four layers. The height of the lower two layers of the inner support structure is greater than the height of the upper two layers.

[0011] The columns are vertically arranged and distributed in two rows along the length of the longitudinal beams. Each row of columns includes multiple columns, and each column is simultaneously connected to three longitudinal beams in the vertical plane. Two columns that are simultaneously connected to three longitudinal beams form a group.

[0012] The top plate and the bottom plate are both horizontally arranged, and both sides of the top plate and the bottom plate are connected to the external ground wall and the internal ground wall.

[0013] The foundation piles are arranged in a row below the internal support structure. The foundation piles are vertically arranged and the top of the foundation piles are connected to the base plate.

[0014] By adopting the above technical solution, the retaining structure still uses a combination of diaphragm walls and internal supports. However, the difference lies in changing the traditional single-layer diaphragm wall waterproofing structure. Instead, a double-layer diaphragm wall with an internal support structure is used to enhance the basic physical performance and waterproofing effect of the foundation pit retaining structure. The reinforcing piles are generally made using triaxial mixing piles for casting, thus reinforcing the foundation pit sidewalls. Compared to the traditional method, the performance of the internal support structure in this solution is enhanced, reducing the number of reinforcing piles at the foundation pit sidewalls. The internal support structure is then constructed on the side of the diaphragm wall away from the reinforcing piles. This internal support structure, consisting of three layers of longitudinal beams and two columns, forms a stable four-layer, double-column, three-span frame structure. Furthermore, foundation piles connect the bottom slab, reducing the probability of overall subsidence of the internal support structure. In summary, the stable internal support structure reinforces the retaining structure, enabling the foundation pit to withstand water and water. The pit sidewalls withstand greater impact forces, reducing the probability of pit collapse and the likelihood of debris falling into the pit, thus minimizing potential safety hazards. Furthermore, it's worth noting that the three-layer longitudinal beams in the internal support structure serve as the foundation for subsequent construction of different levels of the station structure. In the early stages of construction, they also provide support to prevent the pit excavated using the open-cut method from collapsing. To illustrate the construction process of the subway station, after closing the section, workers use excavators to excavate directly from the ground. After excavation, longitudinal beams are laid at the bottom layer to support the sidewalls. Then, a portion is excavated downwards as the foundation for the second underground level. An excavator is then hoisted into the second underground level to continue excavation, and so on. After excavating the second, third, and fourth underground levels, an excavator is hoisted into each level for further excavation. The soil is then transported out using a stepped construction method.

[0015] Optionally, the inner support structure is enclosed by pouring concrete around its four sides, and side beams are provided on the two side walls of the inner support structure near the outer ground diaphragm wall and the inner ground diaphragm wall.

[0016] The three-layer longitudinal beam consists of a top longitudinal beam, a middle longitudinal beam, and a bottom longitudinal beam. The side beam is located below the bottom longitudinal beam, and one end of the side beam is fixed inside the bottom longitudinal beam.

[0017] By adopting the above technical solution, the internal support structure is enclosed into a whole structure. The longitudinal beams and columns support and reinforce the enclosed sidewalls. As the only support in the horizontal and vertical directions, the enclosed sidewalls can provide counter-support for the longitudinal beams. The side beams connected to the sidewalls support the bottom longitudinal beams that are under the greatest pressure, thereby strengthening the structural strength of the internal support structure.

[0018] Optionally, the bottom longitudinal beam and the middle longitudinal beam are both supported by concrete, and the top longitudinal beam and the side beam are both supported by steel.

[0019] The pillars are made of cast concrete.

[0020] By adopting the above technical solutions, steel supports have the advantages of fast installation and convenient dismantling, making them suitable for construction situations where the support position is frequently moved and adjusted. Concrete supports have excellent compressive strength and bearing capacity, as well as good stability and durability. From the perspective of early construction, the two lower layers serve as the base layer, with concrete providing stable support to the upper layers. The side beams further support the side walls, providing stable support during the underground construction phase of the subway station. The top longitudinal beam is located above the soil, so the requirements for support strength are lower. The use of steel support structures that can be quickly installed and flexibly dismantled can accelerate construction efficiency and allow for early excavation of the soil below. From the perspective of later finalization, the columns of the internal support structure can serve as an extension foundation for the main support structure of the subway station.

[0021] Optionally, the internal support architecture also includes;

[0022] A beam is erected, with both ends connected to the base plate. The beam is parallel to the length direction of the longitudinal beam and passes through both columns.

[0023] The through beam is horizontally positioned between the middle longitudinal beam and the bottom longitudinal beam. One end of the through beam is fixed inside the side wall of the inner support structure near the outer ground ties, and the other end of the through beam is inserted into and passes through the two columns.

[0024] By adopting the above technical solution, since the column is simultaneously supported by three longitudinal beams and vertically connects the top and bottom walls of the inner support structure, it is necessary to support the column to prevent it from bending or breaking and causing the construction area to collapse. By using a beam to simultaneously support two columns, the area at the bottom of the column with greater pressure is reinforced horizontally to strengthen the foundation of the inner support structure. On the basis of reinforcing the bottom, an additional beam is assumed on the layer above the beam to fix the column horizontally again to prevent the middle part of the column from bending. Thus, the column plays a stable supporting role in the two foundation layers of the inner support structure.

[0025] Optionally, the internal support architecture also includes;

[0026] A concrete interface is provided, with one concrete interface cast on the top side and one on the bottom side of the base plate. The concrete interface on the top side of the base plate corresponds to the column, and the concrete interface on the bottom side of the base plate corresponds to the foundation pile. The concrete interface is used to fix the column and the foundation pile.

[0027] By adopting the above technical solution, the concrete interface serves as an auxiliary reinforcing structure for fixing the columns to the base plate and the foundation piles to the base plate. On the top of the base plate, a concrete interface is set at the bottom of one of the two rows of columns as a connection foundation. Utilizing the force transmission properties of the high-strength rigid support structure, it can achieve the effect of supporting two columns simultaneously. A concrete interface is set in the row below the base plate to expand the connection point between the foundation piles and the internal support structure and strengthen the strength of the connection.

[0028] Optionally, a waterproof layer is provided between the internal support structure and the external ground ties.

[0029] By adopting the above technical solution, in order to ensure the strength and stability of the internal support structure, an additional waterproof layer is required to prevent groundwater and vapor from eroding the internal support structure, while the external diaphragm wall is connected to the reinforcing piles of the foundation pit sidewall, which acts as the first barrier to prevent water vapor from entering. However, it cannot avoid the humid environment between the internal support structure and the internal diaphragm wall. Therefore, a waterproof layer needs to be placed in front of the internal support structure to block moisture and vapor. A water-stop curtain can be used for the waterproof layer.

[0030] Optionally, the internal support architecture also includes;

[0031] Auxiliary support beams are provided in a row for each layer of the inner support structure. The length direction of the auxiliary support beams is parallel to the length direction of the longitudinal beams, and both ends are fixed inside the two side walls of the inner support structure.

[0032] The auxiliary support beam is made of steel.

[0033] By adopting the above technical solution, the auxiliary support beam runs through the entire internal support structure, fixing the internal support structure to the internal diaphragm wall and the external diaphragm wall, preventing the internal support structure from shifting. The auxiliary support beam is set for each floor of the internal support structure, relieving the pressure on the two columns and three longitudinal beams and strengthening the strength of the internal support structure. In addition, the auxiliary support beam is set at the bottom of each floor, close to the bottom plate and the three longitudinal beams respectively. When the subsequent longitudinal beams serve as the ground auxiliary support beams of the station floor, the auxiliary support beams can work with the longitudinal beams to reinforce the ground of each floor.

[0034] Optionally, three vertical high-pressure jet grouting piles are cast at the joint between the external diaphragm wall and the internal diaphragm wall, and the high-pressure jet grouting piles are used for water sealing at the joint.

[0035] By adopting the above technical solution, the gap at the interface between adjacent diaphragm wall sidewalls is a vertical line. Using easy-to-operate mixing piles, three high-pressure jet grouting piles are driven into the gap inside the diaphragm wall to form an encircling shape, blocking the diaphragm wall joint. For the joint at the corner of the diaphragm wall, high-pressure jet grouting piles are driven into the diaphragm wall to block water intrusion into the joint while reinforcing the structural strength of the corner of the diaphragm wall. For the joint between the sidewalls of the same diaphragm wall, the middle root is used for water stoppage. The protruding middle root high-pressure jet grouting pile is directly connected to the waterproof layer to enhance the water stoppage effect.

[0036] In summary, this application includes at least one of the following beneficial technical effects:

[0037] 1. A combined diaphragm wall and internal bracing method is used for the retaining structure. However, unlike the traditional single-layer diaphragm wall waterproofing structure, this method uses a double-layer diaphragm wall with an internal bracing framework to enhance the basic physical performance and waterproofing effect of the foundation pit retaining structure. The reinforcing piles are typically constructed using triaxial mixing piles to reinforce the pit sidewalls. Compared to traditional methods, this scheme enhances the performance of the internal bracing framework, thus reducing the number of reinforcing piles on the pit sidewalls. The internal bracing framework is then constructed on the side of the diaphragm wall away from the reinforcing piles. This internal bracing framework, consisting of three layers of longitudinal beams and two columns, forms a stable four-layer, double-column, three-span frame structure. Furthermore, foundation piles connect the base slab to the base slab, reducing the probability of overall subsidence of the internal bracing framework. In summary, the stable internal bracing framework reinforces the retaining structure, enabling the pit sidewalls to withstand [the stresses of water pressure]. The greater impact force reduces the probability of pit collapse and the probability of debris falling into the pit, thus reducing potential safety hazards. Furthermore, it's worth mentioning that the three-layer longitudinal beams in the internal support structure can serve as the foundation for subsequent construction of different levels of the station structure. In the early stages of construction, they also provide support to ensure that the excavated pit, created using the open-cut method, does not collapse. To illustrate the construction process of the subway station, after the workers close the section, they choose to excavate directly from the ground using excavators. After excavation, longitudinal beams are laid at the bottom layer to support the side walls. Then, a portion is excavated downwards as the foundation for the second underground level. An excavator is then hoisted into the second underground level to continue excavating, and so on. After excavating the second, third, and fourth underground levels, an excavator is hoisted into each level for excavation, and the soil is transported out using a stepped construction method.

[0038] 2. The internal support structure is enclosed into a whole structure. The longitudinal beams and columns support and reinforce the closed sidewalls. As the only support in the horizontal and vertical directions, the closed sidewalls can provide counter-support for the longitudinal beams. The side beams connected to the sidewalls support the bottom longitudinal beams that are under the greatest pressure, thereby strengthening the structural strength of the internal support structure.

[0039] 3. Steel supports offer advantages such as rapid installation and easy dismantling, making them suitable for construction situations requiring frequent movement and adjustments of support positions. Concrete supports possess excellent compressive strength and load-bearing capacity, exhibiting good stability and durability. From an early construction perspective, the two lower layers serve as the base course, with concrete providing stable support to the upper layers. Side beams further support the sidewalls, ensuring stability during the underground construction phase of the subway station. The upper longitudinal beam, located above the soil, has lower requirements for support strength. Utilizing the quickly installable and easily dismantled steel support structure accelerates construction efficiency and allows for earlier excavation beneath the soil. From a later positioning perspective, the columns of the internal support structure can serve as an extension foundation for the main support structure of the subway station. (See attached diagram for details.)

[0040] Figure 1 This is an overall application diagram of an embodiment of this application.

[0041] Figure 2 This is a cross-sectional view created to highlight the internal support architecture.

[0042] Figure 3 This is a structural diagram designed to highlight the main internal structure of the internal support architecture.

[0043] Figure 4 yes Figure 1 Enlarged view of part A.

[0044] Explanation of reference numerals in the attached drawings: 1. Excavation pit sidewall; 2. Reinforcing pile; 3. External diaphragm wall; 31. High-pressure jet grouting pile; 4. Waterproof layer; 5. Internal support structure; 51. Longitudinal beam; 511. Top longitudinal beam; 512. Middle longitudinal beam; 513. Bottom longitudinal beam; 52. Column; 521. Concrete interface; 53. Top slab; 54. Bottom slab; 55. Auxiliary support beam; 56. Beam support; 57. Side beam; 58. Through beam; 59. Foundation pile; 6. Internal diaphragm wall. Detailed Implementation

[0045] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0046] This application discloses a foundation pit retaining structure used in the construction of subway stations. (Refer to...) Figure 1 A foundation pit retaining structure for use in the construction of a subway station includes an external diaphragm wall 3 and an internal diaphragm wall 6. The external diaphragm wall 3 is located near the foundation pit sidewall 1. Reinforcing piles 2 are cast between the external diaphragm wall 3 and the foundation pit sidewall 1. The sidewalls of the reinforcing piles 2 are fixed to the foundation pit sidewall 1 and the external diaphragm wall 3, respectively. An internal support structure 5 is provided between the external diaphragm wall 3 and the internal diaphragm wall 6. The external diaphragm wall 3, the internal support structure 5, and the internal diaphragm wall 6 constitute the water-blocking retaining structure of this embodiment, used to reinforce the traditional foundation pit sidewall 1.

[0047] In this embodiment, a double-wall waterproofing method is adopted. The thickness of both the outer wall 3 and the inner wall 6 is 1000mm, and the height is adjusted according to the actual situation to obtain a suitable waterproofing capacity. The outer wall 3 is used to block water vapor, and the inner wall 6 is used as the contact surface at the excavation site of the foundation pit to prevent the stones on the side wall 1 of the foundation pit from collapsing and sliding into the construction area.

[0048] In this embodiment, the number of outer reinforcing piles 2 should be reduced while ensuring structural strength. Construction costs should be reduced when strength requirements are saturated. In addition, to accelerate the construction efficiency of the subway station, the reinforcing piles 2 can be cast using triaxial mixing piles. The specifications of the reinforcing piles 2 are φ800mm×1200mm. The height of the reinforcing piles 2 should be higher than the outer diaphragm wall 3. The part of the reinforcing piles 2 that is higher than the diaphragm wall should be inserted into the ground to ensure the overall strength of the foundation pit sidewall 1.

[0049] Reference Figure 2 and Figure 3 The internal support structure 5 includes three layers of parallel longitudinal beams 51 and two rows of parallel columns 52. Each of the three layers of longitudinal beams 51 contains multiple horizontally arranged longitudinal beams 51, and each of the two rows of columns 52 contains multiple vertically arranged columns 52. The three longitudinal beams 51 within the same longitudinal section are, from top to bottom, a top longitudinal beam 511, a middle longitudinal beam 512, and a bottom longitudinal beam 513. The three longitudinal beams 51 within the same longitudinal section form a group, and the two columns 52 within the same longitudinal section form a group. Each group of columns 52 is connected to the corresponding three longitudinal beams 51. In this embodiment, the bottom longitudinal beam 513 and the middle longitudinal beam 512 are supported by concrete, while the top longitudinal beam 511 is supported by steel.

[0050] The internal support structure 5 has a top plate 53 and a bottom plate 54 respectively at the top and bottom of the two rows of columns 52. The internal support structure 5 has side walls respectively at both ends of the three-layer longitudinal beams 51. The top plate 53, the bottom plate 54 and the two side walls are all made of concrete. Since the thickness of the bottom plate 54 should be greater than that of the top plate 53, in this embodiment the thickness of the bottom plate 54 is 1000mm, which is equivalent to the thickness of the external ground diaphragm wall 3 and the internal ground diaphragm wall 6. The thickness of the top plate 53 is 800mm. The thickness of the two side walls is not required and is only a necessary structural element.

[0051] In this embodiment, when casting the two-layer column 52, it is cast in an interlocking manner with the middle longitudinal beam 512 and the bottom longitudinal beam 513, and the top longitudinal beam 511 serves as a steel support member to simultaneously connect the two columns 52.

[0052] Reference Figure 2 and Figure 3 The top plate 53, top longitudinal beam 511, middle longitudinal beam 512, bottom longitudinal beam 513 and bottom plate 54 divide the internal support structure 5 into four layers, of which the two lower layers have the same height, the two upper layers have the same height, and the two lower layers have a greater height than the two upper layers.

[0053] The three-layer longitudinal beams 51 and two rows of columns 52 serve as the main structural foundation of the internal support structure 5. Then, concrete is poured to enclose the internal support structure 5, forming a high-strength waterproof layer 4. This not only increases the strength of the pit sidewall 1 but also achieves the effect of water avoidance and waterproofing. Among them, the top longitudinal beam 511 in the internal support structure 5 utilizes the flexible characteristics of the steel support structure. The top layer has low earthwork pressure and is easy to disassemble after construction. The height of the two upper layers is smaller than that of the two lower layers. After construction, the top longitudinal beam 511 is disassembled, so that the two upper layers are merged into a new underground construction layer, which serves as the construction foundation for the underground first floor of the subway station with high passenger flow.

[0054] Reference Figure 2 Each layer of the inner support structure 5 has an auxiliary support beam 55 horizontally installed below it. Both ends of the auxiliary support beam 55 penetrate the side walls of the inner support structure 5 and are fixed inside the outer ground diaphragm wall 3 and the inner ground diaphragm wall 6. In this embodiment, the auxiliary support beam 55 is made of φ800mm steel pipe and is erected on the inner support structure 5 of each layer in the form of steel supports. After construction is completed, the longitudinal beam 51 can serve as the foundation for the construction of each underground layer of the subway station. The auxiliary support beam 55 of each layer can work together with the longitudinal beam 51 and the base plate 54 of the corresponding layer to reinforce the foundation of the underground layer.

[0055] Reference Figure 2 The base plate 54 of the inner support structure 5 is provided with a beam 56 corresponding to each set of columns 52. The beam 56 is horizontally set at the bottom layer of the inner support structure 5. Both ends of the beam 56 are fixed to the base plate 54. The beam 56 passes through two columns 52 at the same time. In this embodiment, the beam 56 is supported by steel.

[0056] Reference Figure 2 A side beam 57 is fixed to the bottom plate 54 of the inner support structure 5 near the two side walls. The top of the side beam 57 abuts against and supports the bottom longitudinal beam 513. The top side of the inner support structure 5 is fixed inside the side wall of the inner support structure 5. In this embodiment, the side beam 57 is made of steel.

[0057] Reference Figure 2 The inner support structure 5 has a through beam 58 horizontally arranged on the third layer between the middle longitudinal beam 512 and the bottom longitudinal beam 513. One end of the through beam 58 is fixed inside the side wall of the inner support structure 5, and the other end of the through beam 58 passes through two columns 52 and is fixed inside the columns 52. In this embodiment, the through beam 58 is supported by steel.

[0058] The beam 56, the through beam 58, and the side beam 57 are all fixed structures for the longitudinal beam 51 and the column 52 in this embodiment of the application. The side wall supported by the column 52 and the longitudinal beam 51 is further reinforced by the beam 56, the through beam 58, and the side beam 57.

[0059] Reference Figure 2A row of foundation piles 59 is installed in the middle of the bottom side of the internal support structure 5. All foundation piles 59 are vertically installed, and their distribution direction is parallel to the distribution direction of the two rows of columns 52. The top of each foundation pile 59 connects to the bottom plate 54 of the internal support structure 5. A row of concrete interfaces 521 is installed on the top and bottom sides of the bottom plate 54. The concrete interfaces 521 on the bottom side of the bottom plate 54 correspond to the foundation piles 59 and are located at the connection points between the foundation piles 59 and the bottom plate 54. The concrete interfaces 521 on the top side of the bottom plate 54 correspond to one of the rows of columns 52 and are located at the connection points between the columns 52 and the bottom plate 54. The concrete interfaces 521 are installed at the connection points between the columns 52 and the foundation piles 59 to strengthen the connection structure, increase the contact area between the columns 52 and the bottom plate 54, and between the foundation piles 59 and the bottom plate 54, thereby increasing the structural strength of the connection points and, to some extent, preventing the foundation piles 59 and the columns 52 from tilting.

[0060] The foundation piles 59 are inserted into the soil below the internal support structure, which can effectively prevent the internal support structure from sinking. In this embodiment, φ1000mm concrete components are used as foundation piles 59. In addition, due to the force transmission properties of rigid materials, two concrete interfaces 521 achieve the same stability effect as one concrete interface 521. To save costs, in this embodiment, concrete interfaces 521 are only set at the bottom of one row of columns 52.

[0061] Reference Figure 2 and Figure 4 A waterproof layer 4 is installed between the external diaphragm wall 3 and the internal support structure 5. The waterproof layer 4 is attached to the sidewalls of both the external diaphragm wall 3 and the internal support structure 5. In this embodiment, the waterproof layer 4 is a 600mm thick TED water-stop curtain. The groundwater vapor blocked by the external diaphragm wall 3 is completely blocked by the water-stop curtain, preventing the internal support structure 5 from being eroded by moisture and reducing its structural strength. This embodiment uses a water-stop curtain because it has high waterproof performance, can form a continuous watertight barrier, and is economical, improving long-term stable waterproofing and reducing the cost of later maintenance and repair. More importantly, the water-stop curtain has the advantage of simple construction, which can effectively improve the efficiency of underground construction.

[0062] Reference Figure 2 and Figure 4 Three high-pressure jet grouting piles 31 are installed at the connection points of adjacent side walls of the external diaphragm wall 3 and the internal diaphragm wall 6. The three high-pressure jet grouting piles 31 are all φ800mm concrete components. The high-pressure jet grouting piles 31 are the joint water-stopping structures of the diaphragm walls. Traditional diaphragm walls are prone to water erosion over time, and cracks easily form at the four corners. The high-pressure jet grouting piles 31 serve to reinforce the four corners of the concrete structure, pre-seal the cracks, and the reinforced four corners of the concrete are not prone to cracking.

[0063] In this embodiment, each row of foundation piles 59, each row of columns 52, and each layer of longitudinal beams 51 are distributed at equal intervals.

[0064] For ease of observation, the foundation pit shown in the figure is a cube. The shape of the foundation pit should be determined according to the actual construction area during construction.

[0065] The implementation principle of the foundation pit retaining structure applied to the construction of a subway station in this application embodiment is as follows: the retaining structure is constructed by combining underground diaphragm walls and internal supports. The diaphragm walls are double-layered, with an outer diaphragm wall 3 and an inner diaphragm wall 6 set on the inner and outer sides respectively. An internal support structure 5 is set between the outer diaphragm wall 3 and the inner diaphragm wall 6 as the main structural reinforcement to strengthen the side wall 1 of the foundation pit. The outer diaphragm wall 3 acts as a barrier to groundwater, and the internal TED water-stop curtain completely blocks water vapor, creating a dry construction environment inside the foundation pit.

[0066] The reinforcing piles 2 of the pit sidewall 1 reinforce the connection between the external diaphragm wall 3 and the pit sidewall 1, making the external diaphragm wall 3 more stable. Through the reinforcement of the internal support structure of the double-column, four-story, three-span frame, the internal diaphragm wall 6 and the external diaphragm wall 3 can withstand greater impact forces, reducing the probability of pit collapse and greatly enhancing construction safety. Furthermore, the external diaphragm wall 3 and the internal diaphragm wall 6 can form a closed baffle for the pit sidewall 1, reducing the probability of debris from the pit sidewall 1 falling into the pit and minimizing potential safety hazards.

[0067] The top longitudinal beam 511, middle longitudinal beam 512, and bottom longitudinal beam 513 serve as supports in the early stages of construction, facilitating the subsequent construction of different floors of the subway station main structure. The auxiliary support beam 55, as a steel support component, can be flexibly removed or used to reinforce the ground of the corresponding construction floors, assisting the top longitudinal beam 511, middle longitudinal beam 512, and bottom longitudinal beam 513. Another reason for using steel supports for the top longitudinal beam 511 is that during construction, the hoisting method of materials makes it easy for the hoisting bucket to collide with the top longitudinal beam 511. The flexibility of the steel support component allows for easy replacement after the top longitudinal beam 511 is deformed due to repeated collisions.

[0068] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A foundation pit enclosure structure applied to the construction of a ground rail transit station, characterized in that: It includes an external diaphragm wall (3) and an internal diaphragm wall (6). The external diaphragm wall (3) is set near the side wall (1) of the foundation pit. The part of the foundation pit near the external diaphragm wall (3) is cast with multiple reinforcing piles (2) at equal intervals along the extension direction of the side wall (1) of the foundation pit. An internal support structure (5) is set between the external diaphragm wall (3) and the internal diaphragm wall (6). The internal support architecture (5) includes; The longitudinal beam (51) is horizontally arranged and has three layers in the vertical direction. Each layer of the longitudinal beam (51) contains multiple beams. The three layers of longitudinal beams (51) divide the inner support structure (5) into four layers. The height of the lower two layers of the inner support structure (5) is greater than the height of the upper two layers. The column (52) is vertically arranged and distributed in two rows along the length direction of the longitudinal beam (51). Each row of columns (52) includes multiple columns. Each column (52) is simultaneously connected to three longitudinal beams (51) in the vertical plane. Two columns (52) that are simultaneously connected to three longitudinal beams (51) form a group. Top plate (53) and bottom plate (54), both the top plate (53) and the bottom plate (54) are horizontally arranged, and both sides of the top plate (53) and the bottom plate (54) are connected to the external ground connecting wall (3) and the internal ground connecting wall (6); Foundation piles (59) are arranged in a row below the inner support structure (5). The foundation piles (59) are vertically arranged and the top of the foundation piles (59) are connected to the base plate (54).

2. The foundation pit enclosure structure applied to the construction of a ground rail transit station of claim 1, characterized in that: The inner support structure (5) is enclosed by pouring concrete on its four sides. Side beams (57) are provided on the two side walls of the inner support structure (5) near the outer ground diaphragm wall (3) and the inner ground diaphragm wall (6). The three-layer longitudinal beam (51) consists of a top longitudinal beam (511), a middle longitudinal beam (512) and a bottom longitudinal beam (513). The side beam (57) is located below the bottom longitudinal beam (513), and one end of the side beam (57) is fixed inside the bottom longitudinal beam (513).

3. The foundation pit retaining structure for construction of a subway station according to claim 2, characterized in that: The bottom longitudinal beam (513) and the middle longitudinal beam (512) are both supported by concrete, while the top longitudinal beam (511) and the side beam (57) are both supported by steel. The column (52) is made of concrete.

4. The foundation pit enclosure structure applied to the construction of the ground rail transit station of claim 2, characterized in that: The internal support architecture (5) also includes; A beam (56) is provided, with both ends of the beam (56) connected to the base plate (54). The beam (56) is parallel to the length direction of the longitudinal beam (51) and passes through the two columns (52). Through beam (58), which is horizontally arranged between the middle longitudinal beam (512) and the bottom longitudinal beam (513), one end of the through beam (58) is fixed inside the side wall of the inner support structure (5) near the outer ground connecting wall (3), and the other end of the through beam (58) is inserted into and passes through the two columns (52).

5. The foundation pit enclosure structure applied to the construction of the ground rail transit station of claim 1, characterized in that: The internal support architecture (5) also includes; A concrete interface (521) is cast on the top and bottom sides of the base plate (54). The concrete interface (521) on the top side of the base plate (54) corresponds to the column (52), and the concrete interface (521) on the bottom side of the base plate (54) corresponds to the foundation pile (59). The concrete interface (521) is used to fix the column (52) and the foundation pile (59).

6. The foundation pit enclosure structure applied to the construction of the ground rail transit station of claim 1, characterized in that: A waterproof layer (4) is provided between the internal support structure (5) and the external ground connecting wall (3).

7. The foundation pit enclosure structure applied to the construction of the ground rail transit station of claim 1, characterized in that: The internal support architecture (5) also includes; Auxiliary support beams (55) are provided in a row for each layer of the inner support structure (5). The length direction of the auxiliary support beams (55) is parallel to the length direction of the longitudinal beams (51), and both ends are fixed inside the two side walls of the inner support structure (5). The auxiliary support beam (55) is made of steel.

8. The foundation pit retaining structure for construction of a subway station according to claim 1, characterized in that: Three vertical high-pressure jet grouting piles (31) are poured at the joint between the external ground connecting wall (3) and the internal ground connecting wall (6). The high-pressure jet grouting piles (31) are used to stop water at the joint.

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