Linear diaphragm wall deep foundation pit supporting construction method

Abstract

The invention discloses a linear diaphragm wall deep foundation pit supporting construction method which comprises the following steps that S1, building envelope construction is conducted at the position where a foundation pit is located, and a building envelope is constructed through linear structural plates; s2, reinforcing operation is carried out on the base; s3, a top beam at the top of the enclosure structure is constructed, and a transversely-arranged first support is installed between enclosure bodies of the enclosure structure; s4, the foundation pit is excavated in a layered and segmented mode, and when each layer is excavated, a wedge-shaped lining consistent with the excavated layer in thickness and height is constructed immediately; s5, a temporary inner support corresponding to the excavation layer is constructed; s6, the steps S4 and S5 are circulated, and the base support is constructed; and S7, backfilling is conducted on the base, temporary inner supports are removed, a subsequent prefabricated / cast-in-place structure is constructed in the foundation pit, and deep foundation pit supporting construction is completed. According to the deep foundation pit construction method, open excavation is conducted in the whole process, underwater operation is not needed, the construction cost is greatly reduced, the linear enclosure structure is easy to construct, groove wall reinforcement is not needed, and the cost is lower compared with a T-shaped underground diaphragm wall.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit support construction methods. More specifically, this invention relates to a method for constructing a deep foundation pit support system using a linear diaphragm wall. Background Technology

[0002] Retaining structures such as piles and walls, as key structures in deep foundation pit engineering that combine soil retention, load-bearing, and seepage prevention functions, have been widely used in super high-rise buildings, subway tunnels, hydraulic engineering, and other projects. Traditional construction methods typically employ pile walls combined with anchor cables, which occupy external underground space, affect surrounding buildings, and permanent anchor cables create "underground waste," which is detrimental to the environment. Steel sheet pile-supported foundation pits are shallow and have multiple internal supports, resulting in poor waterproofing performance. The combined permanent and temporary retaining structures are complex, costly, inefficient, and difficult to guarantee in terms of quality. Summary of the Invention

[0003] To achieve these objectives and other advantages according to the present invention, a preferred embodiment of the present invention provides a method for constructing a deep foundation pit support with a linear diaphragm wall, comprising the following steps: S1. Construct the retaining structure at the location of the foundation pit, and reinforce the joints of the retaining structure with waterproofing. The retaining structure is constructed using a straight structural panel. S2. Based on the geological parameters of the strata where the foundation pit is located and the stability calculation of the foundation pit, reinforcement work is carried out on the foundation to form a foundation reinforcement body; S3, the capping beam at the top of the construction retaining structure, and the first horizontal support installed between the retaining structures; S4. Excavate the foundation pit in layers and sections. After each layer is excavated, a wedge-shaped inner lining with the same thickness and height as the excavated layer is immediately installed. The wedge-shaped inner lining is smaller at the top and larger at the bottom, and is vertically attached to the retaining structure. The next wedge-shaped inner lining is located on the previous wedge-shaped inner lining. S5. Temporary internal support for the excavation layer corresponding to the construction, wherein the temporary internal support is set perpendicular to the wedge-shaped inner lining; S6. Repeat steps S4 and S5. After excavating to the designed foundation pit base, construct the foundation support and rigidly connect the foundation support and the wedge-shaped inner lining base. S7. Backfill the foundation, covering the foundation support to the upper protection area, remove the temporary internal support, and construct and pour concrete beams in the foundation pit.

[0004] Preferably, in step S7, the temporary internal support is removed using a tiered unloading process: first, 30% of the axial force of the temporary internal support is unloaded using jacks, and after 24 hours of static monitoring of the pit deformation without any abnormalities, it is unloaded to 50%, and after another 24 hours of static monitoring of the pit deformation without any abnormalities, it is finally completely removed.

[0005] Preferably, in step S7, the initial unloading adopts a gradient pressure reduction method, reducing the axial force of the temporary internal support to 70% at a pressure reduction rate of 0.1 MPa / min. During this period, the pressure is paused for 1 minute every time the axial force value decreases by 10%, and the fluctuation of the axial force gauge data is observed. The pressure is maintained within the preset fluctuation range before continuing the next reduction. During the 24-hour static monitoring period, if the horizontal displacement rate of the foundation pit is ≤0.3 mm / d and the cumulative displacement is ≤2 mm, the second unloading can proceed. The second unloading reduces the axial force to 50% at the same rate, pausing for 1 minute every time the axial force value decreases by 5%, and the fluctuation of the axial force gauge data is observed. The pressure is maintained within the preset fluctuation range before continuing the next reduction. During the 24-hour static monitoring period, if the horizontal displacement rate of the foundation pit is ≤0.3 mm / d and the cumulative displacement is ≤2 mm, the final unloading can be implemented. Before the final unloading, the pressure of the jack is reduced to a state of equilibrium with the axial force, maintained for 10 minutes, and then slowly depressurized to zero.

[0006] Preferably, in step S2, based on the geological parameters of the strata where the foundation pit is located and the stability calculation of the foundation pit, reinforcement work is carried out on the foundation, specifically as follows: S21. Based on the stability calculation results of the foundation pit, the reinforcement depth is determined to be 1.0-1.2 times the excavation depth of the foundation pit, and the reinforcement range extends 2-3m beyond the excavation edge of the foundation pit. A reinforcement grid with a side length of 1.0-2.0m is divided. S22. At the nodes of the reinforced grid, construct micropiles with a diameter of 300-400mm, and the length of the micropiles extending into the stable rock layer shall not be less than 1.0m. S23. After the micropile construction is completed, grouting holes are arranged between adjacent micropiles. The adjacent grouting holes are deep holes and shallow holes set at an inclination, with a hole diameter of 50-70mm and an inclination angle of 10-15°. S24. Shallow-hole injection of cement-water glass dual-liquid grout, with a water-cement ratio of 1:1 and a cement to water glass volume ratio of 3:1, with initial setting time controlled at 30-60 seconds; deep-hole injection of ultrafine cement grout, with cement fineness not less than 400 μm. The water-cement ratio is 0.8:1, and the grouting pressure is dynamically adjusted according to the formation permeability coefficient. The permeability coefficient is greater than... The pressure should be 0.5-0.8 MPa, and if it is less than this value, it should be 0.8-1.2 MPa.

[0007] Preferably, on the reinforcement grid divided in S21, based on the soil layer distribution characteristics in the geological survey report, the reinforcement area is divided into three sub-regions: cohesive soil region, sandy layer region, and gravel region. The grid side length of the cohesive soil region is reduced to 1.5m, while the grid side length of the sandy layer region and gravel region is expanded to 2.0m. Furthermore, a denser grid is added at the boundary between the sandy layer region and the cohesive soil region. The denser grid has a side length of 1.0m and extends 2m to both sides to ensure the uniformity of reinforcement for different strata.

[0008] Preferably, shallow holes are grouted in the order of outer perimeter first and then middle, with each hole being grouted in 3 stages, each stage being 1.5m long. Grouting is stopped when the grouting pressure increases by 0.2MPa from the initial pressure. Before grouting deep holes, clean water is injected into the hole to wash it until the return water is clear. During the grouting process, a grouting recorder is used to collect pressure data in real time. When the pressure reaches the upper limit of the corresponding formation and the grouting volume is ≤5L / min, the pressure is maintained for 3 minutes and then grouting is stopped.

[0009] Preferably, for permeability coefficient In cohesive soil areas, vent holes are added next to the grouting holes, with the depth of the vent holes being the same as that of the grouting holes, to ensure that the grout is fully filled.

[0010] The present invention has at least the following beneficial effects: The deep foundation pit construction method of the present invention is open excavation throughout the entire process without underwater operations, which greatly reduces the construction cost. Moreover, the construction of the straight retaining structure is simple and does not require trench wall reinforcement, making it less expensive than the T-shaped diaphragm wall. The construction method of the present invention achieves stability through retaining soil, supporting force transmission, and dynamic support of the inner lining of the retaining structure. It has strong adaptability to complex geological conditions and can improve construction efficiency. Furthermore, by using the retaining structure wall pile construction as the permanent structural sidewall, the anchor cable system is not used, and no structures are left in the structural construction area, which greatly reduces the project cost.

[0011] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the deep foundation pit excavation state in this invention.

[0013] Figure 2 This is a schematic diagram of the deep foundation pit support state in this invention. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0015] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious modifications will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0016] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0017] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0018] like Figure 1-2 As shown, a preferred embodiment of the present invention provides a method for constructing a deep foundation pit support with a linear diaphragm wall, comprising the following steps: S1. Construct the retaining structure 1 at the location of the foundation pit, and reinforce the joints of the retaining structure with waterproofing. The retaining structure is constructed using a straight structural slab. This invention is constructed using a straight-line structural panel, which is simpler in structure than the conventional T-shaped diaphragm wall and requires less precision in equipment and less stability in the trench wall during construction.

[0019] S2. Based on the geological parameters of the strata where the foundation pit is located and the stability calculation of the foundation pit, the foundation is reinforced to form a foundation reinforcement body 2. The foundation reinforcement body 2 is an enhanced area formed by treating the bottom and surrounding strata of the foundation pit with a specific reinforcement process, which is used to improve the foundation's resistance to uplift and overall bearing capacity.

[0020] S3, the capping beam 3 at the top of the construction retaining structure, and the first horizontal support 4 installed between the retaining structures; The cap beam 3 is a reinforced concrete beam cast on top of the retaining structure. Its function is to connect the dispersed retaining structures 1 into a whole and improve their coordinated load-bearing performance. The first support 4 is an initial load-bearing component that is set laterally between the retaining structures 1 and bears the lateral earth pressure in the early stage of the foundation pit excavation.

[0021] S4. The foundation pit is excavated in layers and sections. After each layer is excavated, a wedge-shaped inner lining 5 with the same thickness and height as the excavated layer is immediately constructed. The wedge-shaped inner lining 5 is smaller at the top and larger at the bottom, and is vertically attached to the retaining structure. The next wedge-shaped inner lining 5 is located on the previous wedge-shaped inner lining 5. The wedge-shaped inner lining 5 is a reinforced concrete component with a wedge-shaped cross section that is smaller at the top and larger at the bottom. It is constructed simultaneously with the layered excavation of the foundation pit and is vertically attached to the inner side of the retaining structure 1 to form a dynamic support system.

[0022] S5. Temporary internal support 6 corresponding to the excavation layer during construction. The temporary internal support is set perpendicularly to the wedge-shaped inner lining 5. The temporary internal support 6 is a temporary load-bearing component that is perpendicularly matched with the wedge-shaped inner lining 5 and is used to control the deformation of the foundation pit in each excavation layer. S6. Repeat steps S4 and S5. After excavation to the designed foundation pit base, construct the foundation support 7 and rigidly connect the foundation support 7 and the wedge-shaped inner lining 5 base. The foundation support 7 is a permanent support constructed after excavation to the bottom of the foundation pit. It is rigidly connected to the wedge-shaped inner lining 5 base to form a stable bottom support. S7. Backfill the foundation, covering the foundation support to the upper protection area. Remove the temporary internal support 6 and construct and pour concrete beam 8 within the foundation pit. Concrete beam 8 is parallel to the direction of the internal support.

[0023] This invention employs open-cut excavation throughout, without any underwater construction. Open-cut excavation involves a combination of mechanical excavation and manual labor to complete the foundation pit excavation and support construction in an open environment. The linear retaining structure 1 serves as the primary retaining component, its straight structure evenly bearing the external soil pressure and transferring it to the initial support 4 and each layer of temporary internal supports 6. Furthermore, the linear diaphragm wall eliminates the need for trench wall reinforcement, reducing reinforcement materials and construction costs, while also simplifying verticality control. The wedge-shaped inner lining 5 is dynamically constructed as the open-cut excavation progresses. The wedge structure disperses lateral pressure to the lower inner lining and base support 7, forming a dynamic stress system. In this open-cut operation mode, all machinery is conventional, eliminating the need for special underwater construction equipment, significantly reducing excavation costs.

[0024] In another implementation, in step S7, the temporary internal support is removed using a tiered unloading process: first, 30% of the axial force of the temporary internal support is unloaded using jacks, and after 24 hours of static monitoring of the pit deformation without any abnormalities, it is unloaded to 50%, and after another 24 hours of static monitoring of the pit deformation without any abnormalities, it is finally completely removed.

[0025] In this implementation plan, considering that the temporary internal support 6 of this application is subjected to lateral earth pressure and is in a high-stress state during the foundation pit excavation stage, its sudden removal would cause the axial force to be released instantaneously, resulting in the loss of support for the retaining structure 1 and the wedge-shaped inner liner 5, leading to excessive deformation. The staged unloading process gradually reduces the axial force using jacks, allowing the retaining structure 1, the wedge-shaped inner liner 5, and the base support 7 sufficient time to redistribute stress and smoothly transfer the lateral pressure to the already constructed subsequent structure 8 and backfill, avoiding sudden stress changes. At the same time, the overall stiffness of the linear retaining structure 1 provides a stable foundation for the unloading process, and its uniform stress distribution reduces the risk of local stress concentration during unloading, thus reducing the difficulty of unloading control.

[0026] In another embodiment, in step S7, the initial unloading adopts a gradient pressure reduction method, reducing the axial force of the temporary internal support to 70% at a pressure reduction rate of 0.1 MPa / min. During this period, the pressure is paused for 1 minute every time the axial force value decreases by 10%, and the fluctuation of the axial force gauge data is observed. The pressure is maintained within the preset fluctuation range before the next unloading continues. During the 24-hour static monitoring period, if the horizontal displacement rate of the foundation pit is ≤0.3 mm / d and the cumulative displacement is ≤2 mm, the second unloading can proceed. The second unloading reduces the axial force to 50% at the same rate, pausing for 1 minute every time the axial force value decreases by 5%, and the fluctuation of the axial force gauge data is observed. The pressure is maintained within the preset fluctuation range before the next unloading continues. During the 24-hour static monitoring period, if the horizontal displacement rate of the foundation pit is ≤0.3 mm / d and the cumulative displacement is ≤2 mm, the final unloading can be implemented. Before the final unloading, the pressure of the jack is reduced to a state of equilibrium with the axial force, maintained for 10 minutes, and then slowly depressurized to zero.

[0027] In this implementation scheme, gradient pressure is controlled by adjusting the rate of pressure decrease and the pause intervals to allow the axial force of the temporary internal support 6 to decrease gradually, avoiding stress shocks. Pausing after each percentage decrease in axial force allows sufficient time for the retaining structure 1, wedge-shaped liner 5, and base support 7 to transfer stress, smoothly transferring soil pressure from the temporary internal support 6 to the subsequent structure 8. The uniform stress distribution of the linear retaining structure 1 further facilitates stress transfer, reducing fluctuations in monitoring data caused by localized stress concentrations and simplifying the control of gradient pressure.

[0028] In another embodiment, in step S2, based on the geological parameters of the strata where the foundation pit is located and the stability calculation of the foundation pit, reinforcement work is carried out on the foundation, specifically as follows: S21. Based on the stability calculation results of the foundation pit, the reinforcement depth is determined to be 1.0-1.2 times the excavation depth of the foundation pit, and the reinforcement range extends 2-3m beyond the excavation edge of the foundation pit. A reinforcement grid with a side length of 1.0-2.0m is divided. S22. At the nodes of the reinforced grid, construct micropiles with a diameter of 300-400mm, and the length of the micropiles extending into the stable rock layer shall not be less than 1.0m. S23. After the micropile construction is completed, grouting holes are arranged between adjacent micropiles. The hole diameter is 50-70mm and the inclination angle is 10-15°. The adjacent grouting holes are deep holes and shallow holes set at an inclination, respectively. S24. Shallow-hole injection of cement-water glass dual-liquid grout, with a water-cement ratio of 1:1 and a cement to water glass volume ratio of 3:1, with initial setting time controlled at 30-60 seconds; deep-hole injection of ultrafine cement grout, with cement fineness not less than 400 μm. The water-cement ratio is 0.8:1, and the grouting pressure is dynamically adjusted according to the formation permeability coefficient. The permeability coefficient is greater than... The pressure should be 0.5-0.8 MPa, and if it is less than this value, it should be 0.8-1.2 MPa.

[0029] In the above implementation scheme, micropiles act as a framework, transferring the base load to deep, stable strata and enhancing overall rigidity; shallow-hole dual-liquid grout sets quickly, rapidly forming initial reinforcement strength, preventing grout loss, and reducing grouting costs; deep-hole ultrafine cement grout has strong permeability, filling stratum pores and binding loose soil into a whole. The stabilizing retaining structure 1 provides a safe construction environment for base reinforcement, eliminating the need for additional temporary protection during reinforcement and reducing construction steps.

[0030] In another implementation scheme, based on the soil layer distribution characteristics in the geological survey report, the reinforcement area is divided into three sub-regions on the reinforcement grid defined in S21: cohesive soil area, sand layer area, and gravel area. The grid side length of the cohesive soil area is reduced to 1.5m, while the grid side length of the sand layer area and gravel area is expanded to 2.0m. Furthermore, a denser grid is added at the boundary between the sand layer area and the cohesive soil area. The denser grid has a side length of 1.0m and extends 2m to both sides to ensure the uniformity of reinforcement for different strata.

[0031] In this implementation plan, considering the different reinforcement needs of different strata, a differentiated grid allows for a more practical layout of micropiles and grouting holes. In cohesive soil areas, a denser grid is used to increase the number of grouting holes, solving the problem of grout penetration. In sandy and gravelly areas, the grid is expanded to utilize the natural diffusion characteristics of grout and reduce the amount of construction work. The denser grid eliminates weak points in the reinforcement of strata boundaries and avoids stress concentration.

[0032] In another implementation scheme, shallow holes are grouted in the order of outer perimeter first and then middle, with each hole being grouted in 3 stages, each stage being 1.5m long. Grouting is stopped when the grouting pressure increases by 0.2MPa from the initial pressure. Before grouting deep holes, clean water is injected into the hole to wash it until the return water is clear. During the grouting process, a grouting recorder is used to collect pressure data in real time. When the pressure reaches the upper limit of the corresponding formation and the grouting volume is ≤5L / min, the pressure is maintained for 3 minutes and then grouting is stopped.

[0033] This implementation plan adopts a shallow-hole, periphery-to-center grouting sequence. The periphery grout curtain improves the grouting pressure utilization rate in the central area, ensuring uniform grout diffusion. Segmented grouting avoids uneven grout distribution caused by single-hole grouting, effectively reinforcing each section of the formation. Deep-hole washing removes impurities, ensuring good bonding between the grout and the formation. A grouting recorder monitors data in real time; when the pressure reaches the upper limit and the flow rate decreases, it indicates that the formation pores have been densely filled. Maintaining pressure for 3 minutes further ensures quality.

[0034] In another implementation scheme, regarding the permeability coefficient In cohesive soil areas, vent holes are added next to the grouting holes, with the vent hole depth matching that of the grouting hole to ensure full filling of the grout. After drilling the vent holes, a conventional PVC vent pipe is inserted into them, with 5 mm quincunx-shaped vent holes spaced 10 cm apart on the pipe wall. The vent pipe is wrapped with geotextile to prevent soil blockage.

[0035] In this implementation plan, the low-permeability cohesive soil area has small pores and poor connectivity. During grouting, the grout compresses the gas, creating air resistance and hindering grout penetration. Vent holes provide a channel for gas to escape, eliminating air resistance and allowing the grout to fully fill the pores. The vent pipes, vent holes, and geotextile wrapping ensure gas escape while preventing soil blockage, guaranteeing stable venting function. Open-cut excavation makes vent hole construction and venting observation during grouting more convenient, allowing construction personnel to visually assess gas escape status. The stabilizing effect of the linear retaining structure 1 prevents vent hole misalignment due to foundation pit deformation during grouting, ensuring effective venting.

[0036] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A construction method for deep foundation pit support using a linear diaphragm wall, characterized in that, Includes the following steps: S1. Construct the retaining structure at the location of the foundation pit, and reinforce the waterproofing at the joints of the retaining structure. The retaining structure is constructed using a straight structural panel. S2. Based on the geological parameters of the strata where the foundation pit is located and the stability calculation of the foundation pit, reinforcement work is carried out on the foundation to form a foundation reinforcement body; S3, the capping beam at the top of the construction retaining structure, and the first horizontal support installed between the retaining structures; S4. Excavate the foundation pit in layers and sections. After each layer is excavated, a wedge-shaped inner lining with the same thickness and height as the excavated layer is immediately installed. The wedge-shaped inner lining is smaller at the top and larger at the bottom, and is vertically attached to the retaining structure. The next wedge-shaped inner lining is located on the previous wedge-shaped inner lining. S5. Temporary internal support for the excavation layer corresponding to the construction, wherein the temporary internal support is set perpendicular to the wedge-shaped inner lining; S6. Repeat steps S4 and S5. After excavating to the designed foundation pit base, construct the foundation support and rigidly connect the foundation support and the wedge-shaped inner lining base. S7. Backfill the foundation, covering the foundation support to the upper protection area, remove the temporary internal support, and construct and pour concrete beams in the foundation pit.

2. The construction method for deep foundation pit support with a linear diaphragm wall according to claim 1, characterized in that, In step S7, the temporary internal support is removed using a tiered unloading process: first, 30% of the axial force of the temporary internal support is unloaded using jacks, and after 24 hours of static monitoring of the pit deformation without any abnormalities, it is unloaded to 50%, and after another 24 hours of static monitoring of the pit deformation without any abnormalities, it is finally completely removed.

3. The construction method for deep foundation pit support with a linear diaphragm wall according to claim 2, characterized in that, In step S7, the initial unloading adopts a gradient pressure reduction method, reducing the axial force of the temporary internal support to 70% at a pressure reduction rate of 0.1 MPa / min. During this period, the pressure is paused for 1 minute every time the axial force value decreases by 10%, and the fluctuation of the axial force gauge data is observed. The pressure is maintained within the preset fluctuation range before continuing the next reduction. During the 24-hour static monitoring period, if the horizontal displacement rate of the foundation pit is ≤0.3 mm / d and the cumulative displacement is ≤2 mm, the second unloading can proceed. The second unloading reduces the axial force to 50% at the same rate, pausing for 1 minute every time the axial force value decreases by 5%, and the fluctuation of the axial force gauge data is observed. The pressure is maintained within the preset fluctuation range before continuing the next reduction. During the 24-hour static monitoring period, if the horizontal displacement rate of the foundation pit is ≤0.3 mm / d and the cumulative displacement is ≤2 mm, the final unloading can be implemented. Before the final unloading, the pressure of the jack is reduced to a state of equilibrium with the axial force, maintained for 10 minutes, and then slowly depressurized to zero.

4. The construction method for deep foundation pit support with a linear diaphragm wall according to claim 1, characterized in that, In step S2, based on the geological parameters of the strata where the foundation pit is located and the stability calculation of the foundation pit, reinforcement work is carried out on the foundation, specifically as follows: S21. Based on the stability calculation results of the foundation pit, the reinforcement depth is determined to be 1.0-1.2 times the excavation depth of the foundation pit, and the reinforcement range extends 2-3m beyond the excavation edge of the foundation pit. A reinforcement grid with a side length of 1.0-2.0m is divided. S22. At the nodes of the reinforced grid, construct micropiles with a diameter of 300-400mm, and the length of the micropiles extending into the stable rock layer shall not be less than 1.0m. S23. After the micropile construction is completed, grouting holes are arranged between adjacent micropiles. The hole diameter is 50-70mm and the inclination angle is 10-15°. The adjacent grouting holes are deep holes and shallow holes set at an inclination, respectively. S24. Shallow-hole injection of cement-water glass dual-liquid grout, with a water-cement ratio of 1:1 and a cement to water glass volume ratio of 3:1, with initial setting time controlled at 30-60 seconds; deep-hole injection of ultrafine cement grout, with cement fineness not less than 400 μm. The water-cement ratio is 0.8:1, and the grouting pressure is dynamically adjusted according to the formation permeability coefficient. The permeability coefficient is greater than... The pressure should be 0.5-0.8 MPa, and if it is less than this value, it should be 0.8-1.2 MPa.

5. The construction method for deep foundation pit support with a linear diaphragm wall according to claim 4, characterized in that, Based on the soil layer distribution characteristics in the geological survey report, the reinforcement area is divided into three sub-regions: cohesive soil, sand, and gravel, according to the reinforcement grid defined in S21. The grid side length of the cohesive soil region is reduced to 1.5m, while the grid side length of the sand and gravel regions is expanded to 2.0m. In addition, a denser grid is added at the boundary between the sand and cohesive soil regions. The denser grid has a side length of 1.0m and extends 2m to both sides to ensure the uniformity of reinforcement for different strata.

6. The construction method for deep foundation pit support with a linear diaphragm wall according to claim 4, characterized in that, For shallow holes, the grouting sequence is from the periphery to the center. Each hole is grouted in 3 stages, with a section length of 1.5m. Grouting is stopped when the grouting pressure increases by 0.2MPa from the initial pressure. Before grouting deep holes, clean water is injected into the hole to wash it until the return water is clear. During the grouting process, a grouting recorder is used to collect pressure data in real time. When the pressure reaches the upper limit of the corresponding formation and the grouting volume is ≤5L / min, the pressure is maintained for 3 minutes and then grouting is stopped.

7. The construction method for deep foundation pit support with a linear diaphragm wall according to claim 4, characterized in that, For permeability coefficient In cohesive soil areas, vent holes are added next to the grouting holes, with the depth of the vent holes being the same as that of the grouting holes, to ensure that the grout is fully filled.

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