A combined retaining and water-stopping structure and construction method for deep silty sand strata

Abstract

This invention belongs to the field of foundation pit excavation and support technology, and particularly relates to a combined retaining and water-stopping structure and construction method for deep silty fine sand strata. The combined retaining and water-stopping structure includes: piles, precast retaining walls, a first waler, a second waler, and several supporting beams. The piles are suspended piles, with capping beams at the top. The piles are installed close to the inner wall of the pre-excavated foundation pit to bear lateral forces. The precast retaining walls are spliced ​​precast retaining walls, spaced apart on the outside of the piles to prevent groundwater seepage. The first waler is fixed to the precast retaining wall; the second waler is fixed to the piles; and the two ends of the supporting beams are connected to the first and second walers, respectively. This invention solves the problem of ineffective water-stopping in SMW (soil-filled sand) method support structures.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit excavation and support technology, and particularly relates to a combined retaining and water-stopping structure and construction method in deep silty sand strata. Background Technology

[0002] With the rapid development of urban construction, the development and utilization of underground space is becoming increasingly in-depth. Excavation projects for foundation pits, such as high-rise building foundations, subway tunnels, highway tunnels, and civil defense projects, are increasing. Moreover, foundation pit excavation projects often encounter complex geological conditions and complex surrounding environments, which puts forward higher requirements for foundation pit excavation support technology.

[0003] The SMW (Sinking Mixer) method involves drilling to a certain depth using a multi-axis drilling and mixing machine, while simultaneously spraying cement-based solidifying material at the drill bit to repeatedly mix with the foundation soil. H-beams or steel plates are then inserted into the uncured cement-soil mixture as stress reinforcement. Once the cement hardens, a subsurface wall with sufficient strength and rigidity is formed. SMW piles are widely used due to their advantages, including minimal construction disturbance, short construction period, ease of operation, and the reusability of H-beams.

[0004] However, long-term engineering practice has revealed the following problems with the relevant technology: In deep, water-rich silty sand strata, when the excavation depth of the foundation pit is small and much smaller than the thickness of the permeable layer, the suspended SMW (Surface Water Wrap) method of support structure is often used. Because the suspended cutoff wall cannot prevent groundwater seepage, it often causes a significant drop in the water level outside the pit and substantial surface settlement outside the pit. While the bottom-mounted SMW support structure can suppress seepage inside and outside the pit, its cost is extremely high. On the other hand, due to the high velocity of groundwater, the pile quality of the SMW method is poor, easily causing engineering problems such as leakage and piping in the foundation pit sidewalls. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of this application is to overcome the shortcomings of the prior art and provide a combined retaining and water-stopping structure in deep silty sand strata to solve the problem that the SMW method support structure cannot effectively stop water.

[0006] The technical solution of this application embodiment to solve the above-mentioned technical problems is as follows: a combined retaining and water-stopping structure in a deep silty sand stratum, applied to an excavated foundation pit, the combined retaining and water-stopping structure comprising:

[0007] The piles are suspended piles with a capping beam at the top and are set close to the inner wall of the pre-excavated pit to bear lateral forces.

[0008] The precast retaining wall is a spliced ​​precast retaining wall, which is spaced out on the outside of the piles to prevent groundwater seepage;

[0009] The first waler is fixed to the precast retaining wall;

[0010] The second waler is fixed to the piles.

[0011] Several supporting beams are connected at both ends to the first waler and the second waler, respectively.

[0012] Compared with existing technologies, the above technical solutions have the following beneficial effects:

[0013] By using precast retaining walls to block external groundwater from seeping into the foundation pit, and piles to bear the lateral forces of the foundation pit, the piles and precast retaining walls are connected by support beams to form a whole. This not only effectively reduces the design parameters of the pile structure, but also avoids problems such as excessive groundwater drop and excessive surface settlement.

[0014] Furthermore, the bottom depth of the precast retaining wall is greater than the bottom depth of the pile, and the bottom of the precast retaining wall penetrates the bottom of the fine sand stratum and enters the lower waterproof layer.

[0015] Furthermore, the prefabricated retaining wall includes several prefabricated panels, which are nested and spliced ​​vertically and matched horizontally to form the prefabricated retaining wall.

[0016] Furthermore, the lower end of the precast slab is provided with at least one V-shaped protrusion, and the upper end of the precast slab is provided with a corresponding V-shaped recess that matches the V-shaped protrusion.

[0017] Furthermore, it also includes steel cables that correspondingly penetrate and tighten a vertical row of the precast slabs.

[0018] Furthermore, the thickness of the precast slab gradually decreases from bottom to top, and the stiffness of the precast slab gradually decreases from bottom to top.

[0019] Furthermore, it also includes several dewatering well pipes, which are embedded in the precast retaining wall. The top of the dewatering well pipe extends out of the top of the precast retaining wall, and the bottom end of the dewatering well pipe is bent inward and extends out of the inner side of the precast retaining wall corresponding to the bottom position of the pile.

[0020] Furthermore, a permeable protective box is installed at the bottom end of the dewatering well pipe, and filter material is filled between the permeable protective box and the dewatering well pipe.

[0021] This embodiment also discloses a construction method, which includes the following steps:

[0022] Excavate a guide trench and drill several stress relief holes around the guide trench;

[0023] Several nested precast slabs are statically pressed into the guide trench in sequence, and simultaneously, dewatering well pipe sections that penetrate the precast slabs are connected to form dewatering well pipes. A vertical row of precast slabs is fixed and tightened with steel cables.

[0024] Precast retaining walls are formed by sequentially driving in adjacent rows of precast slabs. Adjacent rows of precast slabs are connected by matching grooves and protrusions, and waterproofing agent is injected into the grooves.

[0025] Water is pumped out by connecting a dewatering well pipe to lower the water level on the side of the precast retaining wall closest to the pre-excavated foundation pit;

[0026] Piles are driven into the precast retaining wall on the side near the pre-excavated foundation pit. The piles are suspended SMW method piles, in which the concrete piles overlap each other and H-beams are driven into the piles in a one-in-one-out manner. The driving depth of the bottom of the piles is less than the depth of the bottom of the precast retaining wall.

[0027] Excavate the soil between the piles, and erect and fix the first and second walers respectively, and erect the support beams connecting the first and second walers;

[0028] After installing concrete supports on the top of the piles towards the pit side, the pit is excavated.

[0029] Furthermore, the step of sequentially and statically pressing several nested precast slabs into the guide trench, simultaneously connecting dewatering well pipe sections penetrating the precast slabs to form dewatering well pipes, and using steel cables to fix and tighten a vertical row of precast slabs specifically includes:

[0030] A solid precast slab located at the bottom is statically pressed into the guide trench. The lower end of the steel cable is fixed in the bottom solid precast slab. The upper solid precast slabs are statically pressed in sequentially to match and fit each other. The steel cables pass through the upper solid precast slabs in sequence and are then tightened and fixed by clamps.

[0031] Hollow precast slabs with accommodating dewatering well pipes are statically pressed into the top solid precast slab, and a section of dewatering well pipe is installed at the same time. Then, hollow precast slabs are pressed in one by one, and this process is repeated. Steel cables are fixed on the bottom hollow precast slab. The steel cables pass through the upper hollow precast slabs in sequence and are tightened and fixed by clamps.

[0032] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0033] 1. By using the outer-side bottom-mounted precast retaining wall, a series of problems existing in the support method of suspended SMW pile foundation when the water-rich silty sand strata are much larger than the excavation depth of the foundation pit are solved, such as excessive groundwater drop and excessive surface settlement.

[0034] 2. By excavating the soil between the double support structures, the soil pressure borne by the inner SMW method pile can be reduced, which can lower the design parameters of the SMW method pile, save costs, and better utilize the bearing capacity of the outer precast retaining wall, thereby increasing the overall stress performance.

[0035] 3. By embedding dewatering well pipes in hollow precast slabs, with the ends of the dewatering well pipes placed on the inner side of the precast retaining wall, dewatering is carried out before driving SMW method piles, providing a relatively dry environment for the driving of SMW method piles and greatly improving the driving quality of SMW method piles. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is a schematic cross-sectional view of the overall structure of the present invention.

[0038] Figure 2 This is a top view of the structure of the present invention.

[0039] Figure 3 This is a top view of the horizontal splicing of the prefabricated retaining wall of the present invention.

[0040] Figure 4 This is a longitudinal splicing side view of the prefabricated retaining wall of the present invention.

[0041] Figure 5 This is a detailed schematic diagram of the bottom end of the dewatering well pipe of the present invention.

[0042] Figure 6 This is a schematic diagram of the longitudinal splicing of the solid precast slabs of the present invention.

[0043] Figure 7 This is a schematic diagram of the longitudinal splicing of the hollow precast slab of the present invention.

[0044] Figure label:

[0045] 1. Piles; 2. H-beams; 3. Precast retaining wall; 4. Cap beam; 5. Support beam; 6. First waler; 7. Concrete support; 8. Second waler;

[0046] 9. Excavated soil; 10. Permeable protective box; 11. Groove; 12. Precast slab; 13. Filter media; 14. Dewatering well pipe; 15. Bottom end; 16. Groove; 17. Steel cable. Detailed Implementation

[0047] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0048] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0049] In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "inner", "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 the present 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, they should not be construed as limiting the present invention.

[0050] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0051] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] Example 1

[0053] like Figure 1-7 As shown in the embodiment of the present invention, a combined retaining and water-stopping structure for deep silty sand strata is applied to excavation pits. The combined retaining and water-stopping structure includes: piles, precast retaining walls, a first waler, a second waler, and several supporting beams.

[0054] The piles are suspended piles, with a capping beam at the top of each pile. The piles are set close to the inner wall of the pre-excavated pit to bear lateral forces.

[0055] The precast retaining wall is a spliced ​​precast retaining wall, specifically using SMW method piles, which are spaced out on the outside of the pile row to prevent groundwater seepage;

[0056] The first waler is fixed to the precast retaining wall, and the second waler is fixed to the piles.

[0057] Several supporting beams are connected at both ends to the first waler and the second waler respectively, forming a whole with the piles and the precast retaining wall. The supporting beams play a role in force transmission, enabling the precast retaining wall to play an auxiliary role in bearing load.

[0058] By using precast retaining walls to block external groundwater from seeping into the foundation pit, and piles to bear the lateral forces of the foundation pit, the piles and precast retaining walls are connected by support beams to form a whole. This not only effectively reduces the design parameters of the pile structure, but also avoids problems such as excessive groundwater drop and excessive surface settlement.

[0059] The precast retaining wall is driven to a greater depth than the pile foundation. The bottom of the precast retaining wall penetrates the bottom of the fine sand stratum A and enters the lower waterproof layer B, thereby preventing water from seeping into the water-rich fine sand stratum A to the side of the foundation pit to the greatest extent.

[0060] In this embodiment, the prefabricated retaining wall includes several prefabricated panels, which are nested and spliced ​​vertically and horizontally to form the prefabricated retaining wall.

[0061] Specifically, the lower end of the precast slab is provided with at least one V-shaped protrusion, and the upper end of the precast slab is provided with a corresponding V-shaped recess that matches the V-shaped protrusion. The precast slab is fitted and spliced ​​together by the matching V-shaped protrusion and V-shaped recess.

[0062] Moreover, the precast slabs have raised grooves and recesses on the left and right sides, respectively. Specifically, the recesses and raised grooves are arc-shaped recesses and arc-shaped raised grooves, which allows the horizontal precast slabs to be interlocked and spliced ​​together to form a precast retaining wall.

[0063] It also includes steel cables, which pass through and tighten a vertical row of precast slabs, fixing the row of precast slabs in place by tensioning the steel cables. Correspondingly, the steel cables pass through the center of the V-shaped protrusions and V-shaped recesses, such as... Figure 6 , 7 As shown.

[0064] like Figure 4 As shown, the thickness of the precast slab gradually decreases from bottom to top, and the stiffness of the precast slab gradually decreases from bottom to top. On the one hand, the lower precast slab is more convenient for subsequent pressing, and on the other hand, it corresponds to the distribution of earth pressure.

[0065] Specifically, the thickness of the solid precast slab is preferentially set to gradually decrease from bottom to top, and the stiffness of the solid precast slab is preferentially set to gradually decrease from bottom to top.

[0066] In this embodiment, as Figure 5 , 7As shown, it also includes several dewatering well pipes, which are embedded in the precast retaining wall. The top of the dewatering well pipe extends out of the top of the precast retaining wall, and the bottom end of the dewatering well pipe is bent inward and extends out of the inner side of the precast retaining wall corresponding to the bottom position of the pile. The water on the inner side of the precast retaining wall is pumped out through the dewatering well pipes, providing a dry environment for the inner side of the precast retaining wall and improving the quality of pile driving.

[0067] Precast slabs include hollow precast slabs and solid precast slabs. Specifically, in hollow precast slabs, two V-shaped protrusions and two V-shaped recesses are each provided, which are used to clamp the through holes of the dewatering well pipes. Figure 7 As shown, in solid precast slabs, at least one V-shaped protrusion and one V-shaped recess are provided, such as... Figure 6 As shown.

[0068] A permeable protective box is installed at the bottom end of the dewatering well pipe, and filter material is filled between the permeable protective box and the dewatering well pipe. The protective box and filter material at the bottom end of the dewatering well pipe prevent excessive sediment from passing through and causing blockage.

[0069] Specifically, the protruding length of the permeable protective box is within the thickness outline of the bottom solid precast slab. That is, the thickness of the hollow precast slab where the permeable protective box is located plus the width of the permeable protective box is less than the thickness of the bottom solid precast slab. This prevents the permeable protective box from being excessively damaged during the static pressure pressing process, thus ensuring its protective function.

[0070] Example 2

[0071] This embodiment also discloses a construction method, which includes the following steps:

[0072] S1. Excavate a guide trench and drill several stress relief holes around the guide trench to reduce the soil squeezing effect of the precast slab.

[0073] S2. Several nested precast slabs are sequentially pressed into the guide trench using static pressure. At the same time, dewatering well pipe sections that penetrate the precast slabs are connected to form dewatering well pipes. A vertical row of precast slabs is fixed and tightened using steel cables.

[0074] S3. Precast retaining walls are formed by sequentially driving in adjacent columns of precast slabs. Adjacent columns of precast slabs are connected by matching grooves and protrusions, and waterproofing agent is injected into the grooves.

[0075] S4. Use a water pump connected to a dewatering well pipe to pump water and lower the water level on the side of the precast retaining wall closest to the pre-excavated pit.

[0076] Specifically, since the precast retaining wall is bottom-mounted, the water level on the left side away from the foundation pit will not be affected. Therefore, the water level outside the pit will not decrease significantly, and there will be no settlement. This dewatering serves two purposes: firstly, it reduces the impact of groundwater flow on the quality of SMW method piles, because in general, due to the weak cementation of soil particles in silty sand strata, the strong flow of groundwater makes the grout easily dispersed. Therefore, the pile quality of SMW method piles can be greatly improved after dewatering; secondly, dewatering provides conditions for the subsequent excavation of the soil between the two structures, achieving two goals at once.

[0077] S5. Drive piles on the side of the precast retaining wall near the pre-excavated foundation pit. The piles are suspended SMW method piles, in which the concrete piles overlap each other, and the H-beams are driven into the piles in a one-in-one-out manner. The driving depth of the bottom of the piles is less than the depth of the bottom of the precast retaining wall.

[0078] S6. Excavate the soil between the piles to a depth of about 1 / 2 of the foundation pit excavation depth. Install and fix the first and second walers respectively. Install support beams connecting the first and second walers. The support beams are made of steel and are installed at horizontal intervals of 5-8m.

[0079] S7. After installing concrete supports on the top of the piles towards the pit side, excavate the pit.

[0080] In step S2, the step of sequentially pressing several nested precast slabs into the guide trench under static pressure, simultaneously connecting dewatering well pipe sections penetrating the precast slabs to form dewatering well pipes, and using steel cables to fix and tighten a vertical row of precast slabs specifically includes:

[0081] S201. A solid precast slab located at the bottom is statically pressed into the guide trench. The lower end of the steel cable is fixed in the bottom solid precast slab. The upper solid precast slabs are statically pressed into the top slabs in sequence. The steel cables pass through the upper solid precast slabs in sequence and are then tightened and fixed by clamps.

[0082] Specifically, the lower end of the solid precast slab is designed with a V-shaped protrusion, and the upper end with a V-shaped recess. The solid precast slabs are statically pressed in sequentially using the matching V-shaped protrusions and recesses. After the first solid precast slab is pressed in, the V-shaped protrusion of the second solid precast slab is inserted into the V-shaped recess of the first solid precast slab and statically pressed in, and so on, until the solid precast slabs are assembled and pressed into the soil. A steel cable is fixed to the center of the V-shaped protrusion of the bottom solid precast slab for connecting the solid precast slabs. Specifically, the V-shaped protrusions and recesses of the upper precast slabs all have round holes in their centers for steel cable connection. All solid precast slabs are connected through this steel cable. After connection, a clamp is added to the other end of the steel cable, and a jack is placed between the clamp and the solid precast slab to tighten and fix the steel cable.

[0083] The V-shaped protrusions and concave depressions facilitate static pressure and increase the water seepage path. The water-stop strip placed in the V-shaped groove provides a good water-stopping effect.

[0084] S202. A hollow precast slab with a accommodating dewatering well pipe is statically pressed into the uppermost solid precast slab, and a section of dewatering well pipe is installed at the same time. Then, hollow precast slabs are pressed in one by one, and so on. A steel cable is fixed on the lowermost hollow precast slab. The steel cable passes through the upper hollow precast slab in one by one and is tightened and fixed by a clamp.

[0085] Specifically, hollow precast slabs are spliced ​​together on top of solid precast slabs. The hollow precast slabs have through holes running vertically through them to accommodate dewatering well pipes. V-shaped protrusions are provided on both sides of the through holes at the bottom of the hollow precast slabs, and V-shaped recesses are provided on both sides of the through holes at the top of the hollow precast slabs. This is achieved by splicing the V-shaped protrusions and V-shaped recesses on the left and right sides. A section of dewatering well pipe is installed at the same time as each hollow precast slab is joined. Then, the slabs are statically pressed into the soil to complete the splicing and static pressing of a row of precast slabs.

[0086] The V-shaped protrusions on both sides of the hollow precast slab are fixed with steel cables for connecting the upper hollow precast slabs. The V-shaped recesses and V-shaped protrusions are both opened with round holes for connecting the steel cables. After the connection is completed, a clamp is added to the top of the steel cable, and a jack is placed between the clamp and the precast slab to tighten the steel cable.

[0087] The lowest precast slab penetrates the water-bearing fine sand layer A and partially enters the impermeable waterproof layer B below.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A combined retaining and water-stopping structure for use in deep silty sand strata, applied to excavated foundation pits, characterized in that, The combined retaining and water-stopping structure includes: The piles are suspended piles with a capping beam at the top and are set close to the inner wall of the foundation pit to bear lateral forces. The precast retaining wall is a spliced ​​precast retaining wall, which is spaced out on the outside of the piles to prevent groundwater seepage. The precast retaining wall includes several precast slabs, which are nested and spliced ​​vertically and matched horizontally to form the precast retaining wall. The precast retaining wall is formed by statically pressing several nested precast slabs into the guide trench, and driving adjacent rows of precast slabs into the trench. The bottom depth of the precast retaining wall is greater than the bottom depth of the piles. The bottom of the precast retaining wall penetrates the bottom of the fine sand stratum and enters the lower impermeable layer. Steel cables, which pass through and tighten a vertical row of precast slabs; The first waler is fixed to the precast retaining wall; The second waler is fixed to the piles. Several supporting beams, with their two ends connected to the first waler and the second waler respectively; Several dewatering well pipes are embedded in the precast retaining wall. The top of the dewatering well pipe extends out of the top of the precast retaining wall, and the bottom end of the dewatering well pipe is bent inward and extends out of the inner side of the precast retaining wall corresponding to the bottom position of the pile.

2. The combined retaining and water-stopping structure in deep silty sand strata according to claim 1, characterized in that, The lower end of the precast slab is provided with at least one V-shaped protrusion, and the upper end of the precast slab is provided with a corresponding V-shaped recess that matches the V-shaped protrusion.

3. The combined retaining and water-stopping structure in deep silty sand strata according to claim 1, characterized in that, The thickness of the precast slab gradually decreases from bottom to top, and the stiffness of the precast slab gradually decreases from bottom to top.

4. The combined retaining and water-stopping structure in deep silty sand strata according to claim 1, characterized in that, A permeable protective box is installed at the bottom end of the dewatering well pipe, and filter material is filled between the permeable protective box and the dewatering well pipe.

5. A construction method for a combined retaining and water-stopping structure in a deep silty sand stratum as described in claim 1, characterized in that, Includes the following steps: Excavate a guide trench and drill several stress relief holes around the guide trench; Several nested precast slabs are statically pressed into the guide trench in sequence, and simultaneously, dewatering well pipe sections that penetrate the precast slabs are connected to form dewatering well pipes. A vertical row of precast slabs is fixed and tightened with steel cables. Precast retaining walls are formed by sequentially driving in adjacent rows of precast slabs. Adjacent rows of precast slabs are connected by matching grooves and protrusions, and waterproofing agent is injected into the grooves. Water is pumped out by connecting a dewatering well pipe to lower the water level on the side of the precast retaining wall closest to the pre-excavated foundation pit; Piles are driven into the precast retaining wall on the side near the pre-excavated foundation pit. The piles are suspended SMW method piles, in which the concrete piles overlap each other and H-beams are driven into the piles in a one-in-one-out manner. The driving depth of the bottom of the piles is less than the depth of the bottom of the precast retaining wall. Excavate the soil between the piles, and erect and fix the first and second walers respectively, and erect the support beams connecting the first and second walers; After installing concrete supports on the top of the piles towards the pit side, the pit is excavated.

6. The construction method of the combined retaining and water-stopping structure in deep silty sand strata according to claim 5, characterized in that, The process of sequentially and statically pressing several nested precast slabs into the guide trench, simultaneously connecting dewatering well pipe sections penetrating the precast slabs to form dewatering well pipes, and fixing and tightening a vertical row of precast slabs with steel cables includes: A solid precast slab located at the bottom is statically pressed into the guide trench. The lower end of the steel cable is fixed in the bottom solid precast slab. The upper solid precast slabs are statically pressed in sequentially to match and fit each other. The steel cables pass through the upper solid precast slabs in sequence and are then tightened and fixed by clamps. Hollow precast slabs with accommodating dewatering well pipes are statically pressed into the top solid precast slab, and a section of dewatering well pipe is installed at the same time. Then, hollow precast slabs are pressed in one by one, and this process is repeated. Steel cables are fixed on the bottom hollow precast slab. The steel cables pass through the upper hollow precast slabs in sequence and are tightened and fixed by clamps.

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