A method for constructing deep foundation pits for subway station main structures

Abstract

This invention relates to the field of subway foundation pit construction technology, specifically to a method for constructing a deep foundation pit for a subway station. The method includes steps S1, where a temporary partition divides the foundation pit into two construction areas; step S2, where a continuous underground wall is constructed around the foundation pit, and lattice columns are constructed on the side of the foundation pit closest to the road; step S3, where the foundation pits in both construction areas are excavated simultaneously, with transport channels reserved on both sides of the temporary partition corresponding to the two construction areas; step S4, where multiple concrete supports are constructed according to the foundation pit depth until the foundation is reached; and step S5, where the temporary partition and the reserved portions on both sides are excavated in layers, with steel supports constructed using a method of excavation and support as needed, supporting the concrete supports on both sides of the temporary partition. By dividing the foundation pit into two construction areas using temporary partitions, synchronous excavation in different zones is achieved, effectively improving construction efficiency and shortening the construction period.

Description

Technical Field

[0001] This invention belongs to the field of subway foundation pit construction technology, specifically relating to a method for constructing a deep foundation pit for a subway station. Background Technology

[0002] With the rapid development of urban rail transit, the number of subway stations is constantly increasing, and many are located in the core areas of cities, surrounded by dense buildings and heavy traffic, which brings extremely high difficulty and safety risks to deep foundation pit construction. At present, the construction of deep foundation pits for subway stations mostly adopts a single-area excavation mode, which has problems such as low construction efficiency, difficulty in controlling foundation pit deformation, and significant impact on the surrounding environment. At the same time, in the construction of foundation pit support systems, the stability of the support structure is insufficient and the installation accuracy is difficult to guarantee, which can easily lead to safety hazards such as foundation pit collapse and excessive settlement of the surrounding soil, thereby affecting the safety of existing underground pipelines and buildings.

[0003] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a method for constructing deep foundation pits for subway station main structures.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for constructing a deep foundation pit for a subway station includes the following steps: Step S1: Measure and lay out the foundation pit according to the design drawings. Temporary construction partitions divide the foundation pit into two construction areas. Step S2: Construct a diaphragm wall around the foundation pit, build a capping beam above the diaphragm wall, construct multiple lattice columns in the foundation pit, and construct the foundation pit cover plate on the side closest to the road, using the lattice columns as support. Step S3: Starting from the temporary partition, excavation of the foundation pits in two construction areas is carried out simultaneously. Transportation channels are reserved on both sides of the temporary partition corresponding to the two construction areas. Step S4: After the first layer of earthwork is excavated, the first layer of concrete support is constructed at the bottom of the first layer of earthwork. After the first layer of concrete support is constructed, the second layer of earthwork is excavated with the support. Multiple layers of concrete support are constructed according to the depth of the foundation pit until the foundation is excavated. Step S5: Excavate the temporary partition and the reserved parts on both sides in layers. During the excavation process, steel support is constructed by excavating and supporting simultaneously. The concrete supports on both sides of the temporary partition are supported by the steel supports. Step S6: Level the bottom of the foundation pit, and then pour plain concrete to seal the bottom.

[0006] Preferably, concrete supports are provided on both sides of the transport channel, and the number of steel support layers corresponds to the number of concrete support layers. Multiple steel support installation points are set along the length of the concrete supports. During the excavation process, the earthwork at the designated positions of the steel supports is excavated first. After the excavation is completed and the steel supports are installed, the entire transport channel is excavated.

[0007] Preferably, in step S1, dewatering wells are constructed, and dewatering operations are continuously carried out during the excavation of the foundation pit. The dewatering well pipes are protected during the excavation of the foundation pit. Before the dewatering operation begins, the elevation of each wellhead and the ground is measured, and the static water level is measured. After the dewatering begins, the water level is dynamically monitored and measured to assess the settlement of the soil around the foundation pit and the impact on existing underground pipelines.

[0008] Preferably, multiple lattice columns are distributed within the foundation pit, respectively supporting the foundation pit cover and concrete supports; During the construction of the foundation pit cover slab, anchor heads are installed at the top of the corresponding lattice columns, and the anchor heads extend into the steel reinforcement skeleton inside the foundation pit cover slab; the cap beam has reserved steel reinforcement corresponding to the foundation pit cover slab above it, so that the cap beam, lattice columns and foundation pit cover slab can be fixed together as one by pouring. During the construction of the concrete support, the lattice columns are cut as the excavation progresses, and the cut lattice columns are supported below the formwork of the corresponding concrete support layer; scissor bracing is installed between adjacent concrete support layers.

[0009] Preferably, the lattice column has a concrete pile foundation at its base, and the concrete pile foundation is a rotary-dug pile. The construction steps include: A rotary drilling rig is used to drill holes at preset locations. A reinforcing cage is then lowered into the hole opening, and the elevation of the upper end of the reinforcing cage is not lower than the elevation of the foundation pit. Lower the lattice column so that the lower end of the lattice column is inserted into the steel cage, and then pour concrete. The concrete pouring elevation should match the elevation of the upper end of the steel cage. After the concrete has initially set, plain soil is filled into the rotary drilling piles. During the earthwork excavation, grouting anchors are inserted into the plain soil between the lattice columns and the rotary drilling piles according to the excavation progress, and the supporting force of the plain soil is improved by grouting.

[0010] Preferably, during the concrete pouring process, the verticality of the lattice column is detected by a testing agency, and the lattice column is adjusted using adjusting components based on the test data; The adjusting components are hydraulic cylinders distributed outside the lattice column. The hydraulic cylinders are evenly distributed along the circumference of the lattice column, and a top plate corresponding to the inner wall of the rotary drilling hole is provided at the end of the hydraulic cylinder.

[0011] Preferably, a support rod is installed between the lattice column and the concrete support, depending on the progress of earthwork excavation.

[0012] Preferably, the two ends of the foundation pit are provided with "[" shaped horizontal bracing for the ends and sides of the foundation pit, and the horizontal bracing corresponds to the number of concrete support layers so as to support the bottom of each layer of concrete support respectively; The concrete supports corresponding to the cross bracing are inclined between the inner walls of the adjacent two sides of the foundation pit, and the cross bracing is fixed to the inner wall of the underground continuous wall by steel brackets.

[0013] Preferably, the diaphragm wall comprises multiple segments that are spliced ​​together and constructed using an intermittent skipping method. After the construction of two adjacent diaphragm wall segments is completed, a borehole is drilled at the joint of the diaphragm wall, and grouting anchor rods are placed in the borehole. Grouting is then used to interlock the two diaphragm wall segments together.

[0014] Beneficial effects: This invention divides the foundation pit into two construction areas by setting up temporary partitions, enabling synchronous excavation in different zones, which effectively improves construction efficiency and shortens the construction period. The use of a composite support system composed of diaphragm walls, capping beams, concrete supports, steel supports, and lattice columns, combined with a construction method of excavating and supporting simultaneously, effectively controls foundation pit deformation and surrounding soil settlement, improves construction safety and stability, and reduces the impact on existing underground pipelines and buildings. The entire construction process is standardized and highly operable, solving problems such as low efficiency, high safety risks, and significant environmental impact in existing deep foundation pit construction. It is suitable for the construction of deep foundation pits for subway stations in urban core areas. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 This is a schematic diagram of the foundation pit in a specific embodiment of the present invention.

[0016] In the diagram: 1. Diaphragm wall; 2. Excavation pit cover; 3. Concrete support; 4. Temporary partition; 5. Transportation passage; 6. Horizontal bracing. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0018] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0019] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0020] like Figure 1 As shown, a method for constructing a deep foundation pit for a subway station includes the following steps: Step S1, according to the design drawings, measurement and layout are carried out to accurately determine the excavation boundary of the foundation pit and the construction position of the temporary partition 4. The temporary partition 4 is constructed using steel sheet piles or concrete cast-in-place piles to divide the foundation pit into two independent construction areas. The height of the temporary partition 4 is adapted to the design depth of the foundation pit, and the thickness is determined based on the soil pressure calculation of the foundation pit sidewall to ensure that the temporary partition 4 has sufficient resistance to lateral displacement, providing a guarantee for subsequent synchronous excavation in different areas. At the same time, after the construction of the temporary partition 4 is completed, its verticality and flatness are tested, and any unqualified parts are rectified in a timely manner to avoid affecting subsequent construction.

[0021] In this embodiment, multiple vibration isolation holes are provided on both sides of the temporary partition 4. The vibration isolation holes are distributed at intervals along the length of the temporary partition 4, and the holes are filled with gravel to avoid mutual interference between the two construction areas.

[0022] Step S2: Construct diaphragm wall 1 around the foundation pit. Diaphragm wall 1 serves as the main support structure of the foundation pit and is constructed using an intermittent skipping method. The length of each section of diaphragm wall 1 is reasonably determined based on the performance of the construction equipment and the size of the foundation pit. During trenching, the verticality of the trench wall and the thickness of the sediment at the bottom of the trench are strictly controlled. After trenching is completed, the steel cage is hoisted and concrete is poured in a timely manner to ensure the construction quality of diaphragm wall 1. A capping beam is constructed above diaphragm wall 1. The capping beam is a reinforced concrete structure, and its cross-sectional dimensions and reinforcement are determined based on the stress calculation of the foundation pit support. The capping beam is tightly integrated with the top of diaphragm wall 1 to form an integrated support system. Multiple lattice columns are constructed in the foundation pit. On the side closest to the road, the foundation pit cover 2 is constructed with the lattice columns as supports. The lattice columns are welded from steel sections, and the foundation pit cover 2 is a cast-in-place reinforced concrete structure with a thickness of not less than 150mm to ensure that it can withstand the road traffic load and the construction load above the foundation pit. At the same time, a passage for construction personnel and equipment to enter and exit is reserved, taking into account both construction convenience and traffic needs.

[0023] Step S3: Starting from temporary partition 4, excavation of foundation pits in two construction areas is carried out simultaneously. The foundation pits are excavated in a layered and segmented manner. During the excavation process, the excavation slope and excavation speed are strictly controlled to avoid excessive soil disturbance. A certain width is reserved on both sides of the temporary partition 4 in both construction areas as a transportation channel 5. The width of the transportation channel 5 is not less than 4m.

[0024] Step S4: After the first layer of earthwork excavation is completed, the first layer of concrete support 3 is constructed at the bottom of the first layer of earthwork. The concrete support 3 is a cast-in-place reinforced concrete structure. During the pouring process, the slump and vibration quality of the concrete are strictly controlled to ensure the strength and integrity of the concrete support 3. After the first layer of concrete support 3 is constructed, the second layer of earthwork excavation is carried out with the support after the concrete strength reaches more than 70% of the design strength to avoid deformation of the foundation pit caused by excavation without support. Multiple layers of concrete support 3 are constructed according to the depth of the foundation pit. After the construction of each layer of concrete support 3 is completed, the next layer of earthwork excavation is carried out only after its strength reaches the design requirements, until the foundation is excavated. The elevation error of the foundation excavation is controlled within ±50mm to ensure that the foundation is flat.

[0025] Step S5: Excavate the temporary partition 4 and the reserved portions on both sides (transportation channels 5) in layers, with the excavation thickness controlled at 1.5-2m / layer. During the excavation process, steel support is constructed using a method of excavation and support as needed. The steel support uses structural steel supports, which connect and support the concrete supports 3 on both sides of the temporary partition 4 to form a complete support system, effectively controlling the displacement of the temporary partition 4 and the deformation of the pit sidewalls. After the steel support is installed, it is pre-tightened in a timely manner to ensure that the steel support can fully play its supporting role and avoid loosening.

[0026] Step S6: Level the bottom of the foundation pit. During the leveling process, remove loose soil, debris and water from the foundation to ensure that the foundation soil is compacted. After leveling, pour plain concrete to seal the bottom. The thickness of the plain concrete seal should not be less than 100mm and the concrete strength grade should not be lower than C15. Use a plate vibrator to compact the concrete during the pouring process. After the bottom is sealed, cure it for no less than 7 days to prevent the foundation soil from being disturbed and to provide a stable working surface for the subsequent construction of the main structure.

[0027] In some embodiments, concrete supports 3 are provided on both sides of the transport channel 5. The concrete supports 3 provide a certain degree of protection for the transport channel 5. The number of steel support layers corresponds to the number of concrete support 3 layers to ensure the integrity and stability of the support system. Multiple steel support installation points are provided along the length of the concrete support 3. The spacing between the installation points is determined according to the bearing capacity of the steel support and the stress distribution of the concrete support 3, and is generally 3-5m.

[0028] During the excavation process, the earthwork at the designated location of the steel support is first partially excavated. The excavation depth is adapted to the installation height of the steel support. After the excavation is completed, the steel support is installed and pre-tightened in a timely manner. After the steel support is installed in place, the entire layer of the transport channel 5 is excavated to avoid collapse during the excavation of the transport channel 5.

[0029] Furthermore, in step S1, dewatering wells are constructed. The number, depth, and spacing of the dewatering wells are determined based on the pit area, groundwater depth, and soil permeability coefficient. The dewatering wells are drilled using rotary drilling, and filter pipes are installed after drilling. A filter screen is wrapped around the outside of the filter pipes to prevent sediment from entering the wells. Dewatering operations are continuously carried out during the pit excavation process, with the dewatering depth controlled to 1.0m below the excavation surface to ensure the soil remains dry during excavation. The dewatering well pipes are protected during excavation by wrapping them with steel pipe sleeves to prevent excavation equipment from colliding with the pipes. Damage to well pipes may occur. Before dewatering begins, the elevation of each wellhead and the ground surface should be measured, and the static water level should be accurately measured and recorded as a benchmark. After dewatering begins, the water level should be dynamically monitored and measured every 2 hours to keep track of changes in the groundwater level in real time. At the same time, the settlement of the soil around the foundation pit and the displacement of existing underground pipelines should be monitored regularly. The impact of the settlement of the soil around the foundation pit and the existing underground pipelines should be assessed based on the monitoring data. If the monitoring data exceeds the warning value, emergency measures such as stopping excavation, adding supports, and adjusting dewatering parameters should be taken in a timely manner to ensure construction safety.

[0030] In another optional embodiment, there are multiple lattice columns, each corresponding to support the foundation pit cover 2 and the concrete support 3. During the construction of the foundation pit cover 2, anchor heads are set at the top of the corresponding lattice columns, and the anchor heads extend into the internal steel reinforcement skeleton of the foundation pit cover 2. Pre-reserved steel bars corresponding to the foundation pit cover 2 are reserved above the capping beam, so that the capping beam, lattice columns and foundation pit cover 2 can be fixed together by pouring. During the construction of the concrete support 3, the lattice columns are cut according to the excavation progress, and the cut lattice columns are supported under the formwork of the corresponding layer of concrete support 3. Shear bracing is provided between two adjacent layers of concrete support 3.

[0031] There are multiple lattice columns, correspondingly distributed within the foundation pit, used to support the foundation pit cover 2 and each layer of concrete supports 3, ensuring uniform stress distribution. At least one lattice column is provided in the middle of each concrete support 3. During the construction of the foundation pit cover 2, anchor heads are installed at the top of the corresponding lattice columns. The anchor heads are made of steel plates welded to the top of the lattice columns and extend into the internal steel reinforcement skeleton of the foundation pit cover 2, ensuring the connection strength between the lattice columns and the foundation pit cover 2. Pre-reserved steel bars corresponding to the foundation pit cover 2 are reserved above the capping beam. The specifications and quantity of the pre-reserved steel bars match the steel bars of the foundation pit cover 2, and the reserved length is not less than 150mm, so that the capping beam, lattice columns and foundation pit cover 2 can be fixed together by pouring concrete to form an integral load-bearing structure, improving the load-bearing capacity and stability of the foundation pit cover 2.

[0032] During the construction of concrete support 3, the lattice columns are cut according to the excavation progress. The cut lattice columns are supported under the formwork of the corresponding layer of concrete support 3, providing temporary support for the construction of concrete support 3. Scissor bracing is provided between two adjacent layers of concrete support 3 to enhance the overall stability of the concrete support 3 system and prevent lateral displacement of concrete support 3.

[0033] In this embodiment, the bottom of the lattice column is provided with a concrete pile foundation, which is a rotary-dug pile. The construction steps include: rotary drilling at a preset point using rotary drilling equipment, using mud slurry to protect the hole wall during the drilling process to prevent collapse; after the drilling depth reaches the design requirements, cleaning the sediment at the bottom of the hole, with a sediment thickness not exceeding 50mm; lowering a reinforcing cage into the borehole opening, ensuring that the upper elevation of the reinforcing cage is not lower than the base elevation of the foundation pit, so as to ensure that the reinforcing cage can form an effective connection with the subsequent main structure; lowering the lattice column so that the lower end of the lattice column is inserted into the reinforcing cage to an insertion depth of not less than 3m, and then pouring concrete. The concrete strength grade is not lower than C30. During the pouring process, a tremie pipe is used to prevent concrete segregation. The concrete pouring elevation is matched with the upper elevation of the reinforcing cage to ensure a tight bond between the bottom of the lattice column and the concrete pile foundation. After the concrete has initially set, plain soil is filled into the rotary drilling pile. During the earthwork excavation, grouting anchors are inserted into the plain soil between the lattice column and the rotary drilling pile according to the excavation progress. The grouting anchors are full-length bonded anchors with a diameter of not less than 22mm and a spacing of not more than 1.5m. Grouting improves the compactness and support of the plain soil, further enhancing the stability of the lattice column.

[0034] In addition, during the concrete pouring process, the verticality of the lattice column is monitored in real time by a testing agency. Based on the monitoring data, the lattice column is adjusted using adjusting components to ensure that its verticality meets the design requirements. The adjusting components are hydraulic cylinders distributed around the outside of the lattice column. The hydraulic cylinders are evenly distributed around the circumference of the lattice column, and generally 4-6 hydraulic cylinders are set in the part of the lattice column near the pile foundation. At the end of the hydraulic cylinder, there is a top plate corresponding to the inner wall of the rotary drilling hole. The top plate is made of steel plate and fits tightly against the inner wall of the rotary drilling hole. By adjusting the extension and retraction of the hydraulic cylinder, the verticality of the lattice column is adjusted until the design requirements are met. The pressure of the hydraulic cylinder is maintained until the cylinder is removed after the subsequent earthwork excavation.

[0035] As a preferred option, a support rod is installed between the lattice column and the concrete support 3 according to the earthwork excavation progress. The support rod is made of steel and transmits the force through the support rod, further enhancing the connection strength between the lattice column and the concrete support 3, improving the overall stability of the support system, and preventing the lattice column from tilting or the concrete support 3 from deforming.

[0036] In another optional embodiment, "["-shaped horizontal bracing 6 is provided at both ends of the foundation pit, supporting the ends and sides of the foundation pit. The horizontal bracing 6 extends horizontally along the inner wall of the foundation pit. The horizontal bracing 6 adopts a steel structure and corresponds to the number of layers of concrete support 3, so as to support the bottom of each layer of concrete support 3 respectively, ensuring the support stability of the foundation pit end. The concrete support 3 corresponding to the horizontal bracing 6 is inclinedly supported between the inner walls of the adjacent sides of the foundation pit, forming a triangular force structure to improve the bearing capacity of the concrete support 3. The horizontal bracing 6 is fixed to the inner wall of the underground continuous wall 1 by steel brackets. The steel brackets are made of steel plates welded to the pre-embedded steel plates of the underground continuous wall 1. The specifications and quantity of the steel brackets are determined according to the stress of the horizontal bracing 6 to ensure that the horizontal bracing 6 is firmly fixed and can effectively transmit the soil pressure at the end of the foundation pit.

[0037] The diaphragm wall 1 consists of multiple interconnected segments, constructed using an intermittent, skip-construction method. Specifically, odd-numbered segments of the diaphragm wall 1 are constructed first. Once the concrete strength of these odd-numbered segments reaches at least 70% of the design strength, the adjacent even-numbered segments are constructed next. This avoids the possibility of trench wall collapse caused by simultaneous construction of two adjacent segments. After the completion of two adjacent segments, boreholes are drilled at the joints. The borehole diameter is no less than 100mm, and the depth is no less than the height of the diaphragm wall 1. Grouting anchors are then placed inside the boreholes, using full-length grouting with cement grout. The grouting pressure is controlled between 0.5-1.0MPa. Grouting helps the two segments of the diaphragm wall 1 interlock, enhancing the integrity and impermeability of the diaphragm wall 1 and preventing groundwater leakage from the joints.

[0038] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for constructing a deep foundation pit of a subway station body, characterized in that, Includes the following steps: Step S1: Measure and lay out the foundation pit according to the design drawings. Temporary construction partitions divide the foundation pit into two construction areas. Step S2: Construct a diaphragm wall around the foundation pit, build a capping beam above the diaphragm wall, construct multiple lattice columns in the foundation pit, and construct the foundation pit cover plate on the side closest to the road, using the lattice columns as support. Step S3: Starting from the temporary partition, excavation of the foundation pits in two construction areas is carried out simultaneously. Transportation channels are reserved on both sides of the temporary partition corresponding to the two construction areas. Step S4: After the first layer of earthwork is excavated, the first layer of concrete support is constructed at the bottom of the first layer of earthwork. After the first layer of concrete support is constructed, the second layer of earthwork is excavated with the support. Multiple layers of concrete support are constructed according to the depth of the foundation pit until the foundation is excavated. Step S5: Excavate the temporary partition and the reserved parts on both sides in layers. During the excavation process, steel support is constructed by excavating and supporting simultaneously. The concrete supports on both sides of the temporary partition are supported by the steel supports. Step S6: Level the bottom of the foundation pit, and then pour plain concrete to seal the bottom.

2. The method of claim 1, wherein, Concrete supports are installed on both sides of the transport channel, and the number of steel support layers corresponds to the number of concrete support layers. Multiple steel support installation points are set along the length of the concrete supports. During the excavation process, the earthwork at the designated locations of the steel supports is excavated first. After the excavation is completed and the steel supports are installed, the entire transport channel is excavated.

3. The method of claim 1, wherein, In step S1, dewatering wells are constructed, and dewatering operations are continuously carried out during the excavation of the foundation pit. The dewatering well pipes are protected during the excavation of the foundation pit. Before the dewatering operation begins, the elevation of each wellhead and the ground is measured, and the static water level is measured. After the dewatering begins, the water level is dynamically monitored and measured to assess the settlement of the soil around the foundation pit and the impact on existing underground pipelines.

4. The method for constructing a deep foundation pit for a subway station as described in claim 1, characterized in that, Multiple lattice columns are distributed within the foundation pit, respectively supporting the foundation pit cover slab and concrete supports; During the construction of the foundation pit cover slab, anchor heads are installed at the top of the corresponding lattice columns, and the anchor heads extend into the steel reinforcement skeleton inside the foundation pit cover slab; the cap beam has reserved steel reinforcement corresponding to the foundation pit cover slab above it, so that the cap beam, lattice columns and foundation pit cover slab can be fixed together as one by pouring. During the construction of the concrete support, the lattice columns are cut as the excavation progresses, and the cut lattice columns are supported below the formwork of the corresponding concrete support layer; scissor bracing is installed between adjacent concrete support layers.

5. The method for constructing a deep foundation pit for a subway station as described in claim 1, characterized in that, The lattice column is supported by a concrete pile foundation, which is a rotary-dug pile. The construction steps include: A rotary drilling rig is used to drill holes at preset locations. A reinforcing cage is then lowered into the hole opening, and the elevation of the upper end of the reinforcing cage is not lower than the elevation of the foundation pit. Lower the lattice column so that the lower end of the lattice column is inserted into the steel cage, and then pour concrete. The concrete pouring elevation should match the elevation of the upper end of the steel cage. After the concrete has initially set, plain soil is filled into the rotary drilling piles. During the earthwork excavation, grouting anchors are inserted into the plain soil between the lattice columns and the rotary drilling piles according to the excavation progress, and the supporting force of the plain soil is improved by grouting.

6. The method for constructing a deep foundation pit for a subway station as described in claim 5, characterized in that, During the concrete pouring process, the verticality of the lattice column is tested by a testing agency, and the lattice column is adjusted using adjusting components based on the test data. The adjusting components are hydraulic cylinders distributed outside the lattice column. The hydraulic cylinders are evenly distributed along the circumference of the lattice column, and a top plate corresponding to the inner wall of the rotary drilling hole is provided at the end of the hydraulic cylinder.

7. The method for constructing a deep foundation pit for a subway station as described in claim 1, characterized in that, Support rods are installed between the lattice columns and concrete supports according to the progress of earthwork excavation.

8. The method for constructing a deep foundation pit for a subway station as described in claim 1, characterized in that, The pit is equipped with "[" shaped horizontal bracing at both ends and sides. The horizontal bracing corresponds to the number of concrete support layers, so as to support the bottom of each concrete support layer respectively. The concrete supports corresponding to the cross bracing are inclined between the inner walls of the adjacent two sides of the foundation pit, and the cross bracing is fixed to the inner wall of the underground continuous wall by steel brackets.

9. The method for constructing a deep foundation pit for a subway station as described in claim 1, characterized in that, The diaphragm wall consists of multiple interconnected segments, constructed using an intermittent skipping method. After the construction of two adjacent diaphragm wall segments is completed, a borehole is drilled at the joint of the diaphragm wall, and grouting anchor rods are placed in the borehole. Grouting is then used to interlock the two diaphragm wall segments together.

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