PC steel pipe pile with foundation pit inside and outside divided cavity dewatering and pit bottom pressure reduction functions and construction method

Abstract

The invention discloses a PC steel pipe pile with foundation pit inside and outside separated cavity dewatering and pit bottom pressure reduction functions and a construction method. The PC steel pipe pile is divided into a top reserved section, a cavity division dewatering section, a conventional standard section, a pit bottom pressure reduction section and a bottom grouting head from top to bottom. Filtering holes are evenly formed in the pile body steel pipe in the elevation range of the cavity division dewatering section in the annular direction, and two waterproof partition plates extending to the elevation of the bottom of the cavity division dewatering section from the pile top are arranged in an annular space formed between the pile body steel pipe and the pit bottom pressure reducing pipe in a clamped mode. The annular space is divided into two semi-annular spaces which are respectively used as an out-pit dewatering cavity and an in-pit dewatering cavity; and meanwhile, filter holes are annularly and uniformly formed in the pile body steel pipe within the elevation range of the pit bottom pressure reduction section, and a pit bottom pressure reduction cavity is formed between the pile body steel pipe and the backfilling pipe in a clamping mode. The PC steel pipe pile has the functions of foundation pit inner and outer cavity division dewatering and pit bottom pressure reduction, the construction cost of foundation pit engineering can be reduced, and the construction efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of construction technology, and particularly relates to a PC steel pipe pile with functions of cavity separation and dewatering inside and outside a foundation pit and pressure reduction at the bottom of the pit and a construction method. BACKGROUND

[0002] With the rapid advancement of urbanization, underground space development has entered a new stage, and deep foundation pit projects are increasing. The commonly used enclosure piles for deep foundation pit projects include cast-in-place piles, SMW method piles, and Larsen steel sheet piles. In recent years, PC method combined steel pipe piles have emerged as a new force and become another commonly used type of enclosure piles. The PC method combined steel pipe pile is composed of a PC steel pipe pile and a Larsen steel sheet pile, wherein the PC steel pipe pile mainly serves as a soil retaining function, and the Larsen steel sheet pile mainly serves as a water stopping function. The PC method combined steel pipe pile has large rigidity and can be recycled and reused, which conforms to the concept of green construction and is welcomed by construction units, design units, and construction units. At present, it has been widely used in 1-2 layer basement foundation pit projects.

[0003] In the silty sand stratum in the southeast coastal area, the PC method combined steel pipe pile is often used with pit inside and outside dewatering wells. Pit outside dewatering can reduce the water pressure acting on the enclosure structure, and pit inside dewatering can speed up the earthwork excavation progress. It is worth mentioning that in recent years, pit heave accidents have occurred from time to time. The bottom pressure of the pit bottom exceeds the gravity of the overburden after the earthwork is excavated to the bottom, which is the most common cause of pit heave accidents. The most effective and commonly used method to avoid pit heave accidents is to set a pressure relief well in the pit. Taking Hangzhou Binjiang District as an example, the underlying soil layer is often silt, which serves as an impermeable layer. The underlying layer of the impermeable layer is often the confined water layer. Therefore, the pit inside pressure relief well is deep and has high cost. In addition, the pit inside pressure relief well cannot be cut off or damaged during the earthwork excavation process, and it needs to be connected and fixed with each horizontal inner support to prevent overturning.

[0004] However, the above methods have the following disadvantages:

[0005] (1) Pit inside and outside dewatering wells need to be set separately. For deep and large foundation pit projects, the pit inside and outside dewatering wells are deep and have a large number, resulting in high construction cost and long construction period of the pit inside and outside dewatering wells;

[0006] (2) The pit inside dewatering well is often made of PVC corrugated pipe, which is difficult to protect during the earthwork excavation process and is easily damaged after being collided by mechanical equipment. Once the number of dewatering wells is insufficient, it needs to be supplemented, which increases the cost;

[0007] (3) The pit inside pressure relief well needs to be set separately, which has high cost. In addition, for the case where no horizontal support is set inside the pit, it is difficult to find a suitable connection and fixing point for the pressure relief well, and there is a risk of overturning during use;

[0008] (4) The pressure relief wells in the pit are usually made of steel pipes with an outer diameter of 273 mm and a wall thickness of 4 mm. The pressure relief wells are difficult to protect during the excavation process and are easily damaged after collision with mechanical equipment. Once the number of pressure relief wells is insufficient, additional ones must be added, which increases costs.

[0009] (5) Design units often require construction units to fill the underground voids while removing the PC steel pipe piles. However, due to site conditions, cost factors, and construction period factors, backfilling work is often overlooked by construction units. Therefore, after the PC steel pipe piles are removed, surrounding roads, pipelines, and houses often experience unpredictable settlement. Summary of the Invention

[0010] The purpose of the present invention is to solve the above problems in the prior art and provide a PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and decompressing the pit bottom and a construction method.

[0011] The specific technical solutions adopted in the present invention are as follows:

[0012] In the first aspect, the present invention provides a PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and decompressing the pit bottom. The PC steel pipe pile is divided from top to bottom into a top reserved section, a dewatering section, a conventional standard section, a pit bottom decompression section, and a bottom grouting head;

[0013] The PC steel pipe pile has a bottom pressure relief pipe coaxially sleeved inside the pile body steel pipe, and the bottom pressure relief pipe extends from the pile top to the top of the pit bottom pressure relief section; the bottom pressure relief pipe has a backfill pipe coaxially sleeved inside the pit bottom pressure relief pipe, and the backfill pipe extends from the pile top to the grouting head that penetrates the bottom;

[0014] The top reserved section is used to connect the reinforced crown beam during the foundation pit construction process;

[0015] Filter holes are evenly distributed in the annular direction on the pile body steel pipe within the elevation range of the sub-cavity dewatering section, and two impermeable partitions extending from the pile top to the bottom elevation of the sub-cavity dewatering section are provided in the annular space formed by clamping between the pile body steel pipe and the pit bottom pressure reducing pipe, thereby dividing the annular space into two semi-annular spaces, which serve as the pit outside dewatering chamber and the pit inside dewatering chamber respectively; at the same time, an annular end plate is provided at the bottom elevation position of the sub-cavity dewatering section, and the bottoms of the two semi-annular spaces are sealed by the annular end plate; the outer wall of the pile body steel pipe is provided with a locking structure for connecting the Larsen steel sheet pile along the boundary line on both sides of the two dewatering chambers;

[0016] No filter holes are provided on the pile steel pipe within the conventional standard section elevation range;

[0017] Filter holes are evenly opened in an circumferential direction on the pile body steel pipe within the elevation range of the pit bottom decompression section, and a pit bottom decompression chamber is formed by clamping between the pile body steel pipe and the backfill pipe. The bottom of the pit bottom decompression chamber is closed by the top of the bottom grouting head, and the top of the pit bottom decompression chamber is connected to the external space through the pit bottom decompression pipe.

[0018] As a preferred embodiment of the first aspect, the two impermeable partitions are symmetrically arranged along the diameter direction on the cross section of the annular space, so that the precipitation cavity outside the pit and the precipitation cavity inside the pit formed by dividing the pit equally are also mirror-symmetrical.

[0019] As a preferred embodiment of the first aspect, outer walls of the pile body steel pipes of the chamber dewatering section and the pit bottom decompression section are both covered with filter screens.

[0020] As a preferred embodiment of the first aspect, the bottom grouting head adopts a conical cross pile tip with a backfill hole, and the bottom of the backfill pipe passes through the backfill hole connected to the center of the conical cross pile tip.

[0021] As a preferred embodiment of the first aspect, a horizontal force transfer plate is welded to the outer wall of the pile body steel pipe in the top reserved section to improve the connection strength with the reinforced crown beam.

[0022] As a preferred embodiment of the first aspect, the pit bottom pressure relief pipe and the backfill pipe are both made of steel pipes.

[0023] In the second aspect, the present invention provides a foundation pit retaining structure, which is formed by a plurality of Larsen steel sheet piles and PC steel pipe piles to form a PC method combined steel pipe pile, wherein one or more PC steel pipe piles adopt the PC steel pipe piles with the functions of dewatering the inside and outside of the foundation pit and decompressing the pit bottom as described in the first aspect above.

[0024] As a preferred embodiment of the second aspect, in the PC steel pipe piles having the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the pit bottom, the length of the dewatering section is the same as that of the Larsen steel sheet pile.

[0025] In a third aspect, the present invention provides a method for dewatering inside and outside a foundation pit and for reducing pressure at the bottom of the pit, comprising:

[0026] S1. When deepening the design of the PC method combined steel pipe piles required for the foundation pit retaining structure, one or more PC steel pipe piles in the retaining structure are replaced with PC steel pipe piles with the functions of dewatering the inside and outside of the foundation pit and decompressing the pit bottom as described in the first aspect above, and the corresponding PC steel pipe piles are manufactured according to the design parameters;

[0027] S2. Before excavation of the foundation pit, the PC steel pipe piles are sequentially sunk. When sinking the PC steel pipe piles with the functions of dewatering the inside and outside chambers of the foundation pit and reducing pressure at the pit bottom, it should be ensured that the bottom ends of the dewatering sections and the Larsen steel sheet piles on both sides enter the impermeable layer, and that the dewatering chamber outside the pit faces the outside of the foundation pit, while the dewatering chamber inside the pit faces the inside of the foundation pit. At the same time, it should be ensured that the dewatering section at the pit bottom is located in the confined water layer.

[0028] S3. During the excavation of the foundation pit, according to the construction organization plan, the water level outside the pit is controlled by pumping water from the dewatering cavity outside the pit, and the water level inside the pit is controlled by pumping water from the dewatering cavity inside the pit. At the same time, the pressure of the pressurized water is released through the pit bottom pressure relief cavity and the pit bottom pressure relief pipe;

[0029] S4. When the PC steel pipe piles are pulled out after the foundation pit construction is completed, clay soil is simultaneously backfilled through the backfill pipe during the process of pulling out the PC steel pipe piles with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit. The PC steel pipe piles are recovered and the backfill of the pile bottom gap is completed at the same time.

[0030] As a preferred embodiment of the third aspect, the PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit needs to temporarily block the backfill hole at the end of the backfill pipe before sinking, and the pressure of the backfill soil is used to break through the temporary blockage during backfilling.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The PC steel pipe piles designed in the present invention have both the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit. Therefore, there is no need to set up dewatering wells outside the pit, which saves space around the foundation pit and is conducive to the connection of surrounding roads. The number of dewatering wells inside the pit along the edge of the pit is significantly reduced. For foundation pits with smaller areas, there is no need to set up additional dewatering wells inside the pit. In summary, the number of dewatering wells inside and outside the pit is greatly reduced, which reduces costs and saves construction time.

[0033] (2) Compared with traditional precipitation wells made of PVC corrugated pipes, the new PC steel pipe piles designed in the present invention are made of steel, which not only has greater rigidity but also belongs to the enclosure structure and is not easily damaged during the excavation process, which helps to ensure the continuity of precipitation operations and reduce the costs that may be incurred by well repairs;

[0034] (3) In actual projects, the dewatering requirements inside and outside the foundation pit are often different. The new PC steel pipe pile designed in the present invention is divided into a dewatering cavity inside the pit and a dewatering cavity outside the pit in the dewatering section. The dewatering depth can be adjusted according to the dewatering requirements inside and outside the foundation pit;

[0035] (4) The PC steel pipe piles designed in the present invention significantly reduce the number of relief wells in the pit. For foundation pits with smaller areas, there is no need to set up additional relief wells in the pit, thus reducing costs. In addition, the present invention avoids the potential safety hazards that may be induced by the difficulty in connecting and fixing the relief wells in the pit;

[0036] (5) The new PC steel pipe pile designed by the present invention has the function of reducing pressure at the bottom of the pit and is more rigid than the traditional pressure relief well. In addition, the new PC steel pipe pile is a retaining structure and is not easily damaged during the excavation process, which helps to ensure the continuity of the pressure relief operation and reduce the cost of well repair.

[0037] (6) The new PC steel pipe pile designed by the present invention can be backfilled synchronously during the extraction process, reducing the impact of extraction on surrounding roads, pipelines, and houses, which is conducive to the further promotion and application of PC steel pipe piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the new PC steel pipe pile of the present invention;

[0039] Figure 2 This is a schematic structural diagram of the novel PC steel pipe pile of the present invention;

[0040] Figure 3 This is an exploded schematic diagram of the novel PC steel pipe pile of the present invention;

[0041] Figure 4 A schematic diagram of the structural cross-section and dimensions of a chamber precipitation section in an embodiment of the present invention;

[0042] Figure 5 A schematic diagram of the structural cross-section and dimensions of a conventional standard segment in an embodiment of the present invention;

[0043] Figure 6 A schematic diagram of the structural cross-section and dimensions of the pit bottom decompression section in an embodiment of the present invention;

[0044] Figure 7 A schematic diagram of the structure cross section and dimensions of a bottom grouting head in an embodiment of the present invention;

[0045] Figure 8 A schematic diagram of the structural cross-section and dimensions of the top reserved section in an embodiment of the present invention;

[0046] Figure 9 This is a schematic diagram of the traditional PC method combined steel pipe pile;

[0047] Figure 10 This is a schematic diagram of the new PC method combined steel pipe pile;

[0048] Figure 11 This is a schematic diagram of the first process step of basement construction in an embodiment of the present invention;

[0049] Figure 12 This is a schematic diagram of the second process step of basement construction in an embodiment of the present invention;

[0050] Figure 13 This is a schematic diagram of the third process step of basement construction in an embodiment of the present invention;

[0051] Figure 14 This is a schematic diagram of the fourth process step of basement construction in an embodiment of the present invention;

[0052] Figure 15 This is a schematic diagram of the fifth process step of basement construction in an embodiment of the present invention;

[0053] Figure 16 This is a schematic diagram of the sixth process step of basement construction in an embodiment of the present invention;

[0054] Figure 17 This is a schematic diagram of the seventh process step of basement construction in an embodiment of the present invention;

[0055] Figure 18 This is a schematic diagram of the eighth process step of basement construction in an embodiment of the present invention;

[0056] The accompanying drawings are marked as follows: top reserved section P1, chamber dewatering section P2, conventional standard section P3, pit bottom dewatering section P4 and bottom grouting head P5, pile body steel pipe 1, pit bottom dewatering pipe 2, backfill pipe 3, impermeable partition 4, backfill hole 5, annular end plate 6, force transmission plate 7, locking structure 8, filter hole 9, dewatering cavity outside the pit 10, dewatering cavity inside the pit 11, and pit bottom dewatering cavity 12. DETAILED DESCRIPTION

[0057] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0058] In the description of the present invention, it should be understood that when an element is considered to be "connected" to another element, it can be directly connected to the other element or indirectly connected, that is, there are intermediate elements. On the contrary, when an element is said to be "directly" connected to another element, there are no intermediate elements.

[0059] like Figure 1As shown, in a preferred embodiment of the present invention, a PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and decompression of the pit bottom is provided. For the convenience of description, it will be referred to as a new type of PC steel pipe pile hereinafter. The new type of PC steel pipe pile is divided into five functional sections from top to bottom, namely, the top reserved section P1, the dewatering section P2, the conventional standard section P3, the pit bottom decompression section P4 and the bottom grouting head P5. It has the dual functions of dewatering the inside and outside of the foundation pit and decompression of the pit bottom, which can reduce the need to set up separate dewatering wells inside and outside the pit and decompression wells inside the pit during the use of the PC steel pipe pile. However, it should be specially noted that the division of the top reserved section P1, the dewatering section P2, the conventional standard section P3, the pit bottom decompression section P4 and the bottom grouting head P5 in the new type of PC steel pipe pile is based on function, and does not mean that the entire pile is decomposed into five independently processed and assembled pile sections.

[0060] The overall structure of the new PC steel pipe pile and the specific structure of each pile segment are described in detail below.

[0061] like Figure 2 As shown, the new PC steel pipe pile has a bottom pressure relief pipe 2 coaxially sleeved inside the pile body steel pipe 1, and the bottom pressure relief pipe 2 extends from the pile top to the top of the pit bottom pressure relief section P4; the bottom pressure relief pipe 2 has a backfill pipe 3 coaxially sleeved inside, and the backfill pipe 3 extends from the pile top to the bottom grouting head P5. Theoretically, the material of the bottom pressure relief pipe 2 and the backfill pipe 3 is not limited, as long as the strength and performance requirements of the pipeline are met. Considering the cost and performance requirements, the bottom pressure relief pipe 2 and the backfill pipe 3 can generally be made of steel pipes. The bottom of the bottom pressure relief pipe 2 and the pile body steel pipe 1 can be fixed by welding through an annular end plate. Figure 3 The following is a schematic diagram of the exploded structure of the new PC steel pipe pile with different structures, wherein the force transfer plate 7 is not shown and can be added according to actual needs.

[0062] The function of the above-mentioned top reserved section P1 is to connect the reinforced crown beam during the foundation pit construction process. In order to improve the connection strength between the top reserved section P1 and the reinforced crown beam, a horizontal force transfer plate 7 can be welded to the outer wall of the pile body steel pipe 1 corresponding to the top reserved section P1. The force transfer plate 7 can generally be realized by using a steel plate, and a circular hole with the same size as the outer diameter of the pile body steel pipe 1 is provided in the steel plate. Therefore, before the reinforced crown beam is cast, the steel plate can be put on the pile body steel pipe 1 in the middle of the elevation range of the above-mentioned top reserved section P1 and welded and fixed. After the reinforced crown beam is cast, a force transfer plate 7 that is tightly connected with the concrete can be formed to strengthen the connection between the new PC steel pipe pile and the reinforced crown beam, forming a force transmission system.

[0063] Filter holes 9 are evenly arranged in an annular direction on the pile body steel pipe 1 within the elevation range of the above-mentioned sub-cavity dewatering section P2, and two impermeable partitions 4 extending from the pile top to the bottom elevation of the sub-cavity dewatering section P2 are arranged in the annular space formed by clamping between the pile body steel pipe 1 and the pit bottom pressure reducing pipe 2, thereby dividing the annular space into two semi-annular spaces. The groundwater of the soil outside the pile body can enter the two semi-annular spaces through the filter holes 9 opened on the pile body steel pipe 1, so that the water levels in the two semi-annular spaces can be kept consistent with the water levels of the soil they are in contact with, and can serve as the pit outside dewatering chamber 10 and the pit inside dewatering chamber 11 respectively. The filter holes 9 should be opened as evenly as possible, but need to avoid the position of the impermeable partition 4. At the same time, an annular end plate 6 is provided at the bottom elevation position of the sub-cavity dewatering section P2, and the bottom of the two semi-annular spaces is sealed by the annular end plate 6. The annular end plate 6 can be made of steel plate and is welded between the pile body steel pipe 1 and the pit bottom pressure relief pipe 2. It blocks the bottom surface of the two semi-annular spaces and prevents water from seeping into the conventional standard section P3. In addition, since this new PC steel pipe pile will later replace ordinary PC steel pipe piles and then be combined with Larsen steel sheet piles to form the PC construction method combined steel pipe piles required for foundation pit protection, the outer wall of the pile body steel pipe 1 needs to be equipped with a locking structure 8 for connecting the Larsen steel sheet piles. Furthermore, since the dewatering chamber 10 outside the pit and the dewatering chamber 11 inside the pit are provided in the dewatering section P2 of the present invention to receive the groundwater outside the pit and the groundwater inside the pit respectively, there are two oppositely distributed boundary lines between the dewatering chamber 10 outside the pit and the dewatering chamber 11 inside the pit. Therefore, the locking structures 8 on both sides of the outer wall of the pile body steel pipe 1 need to be respectively provided along the boundary lines on both sides of the two dewatering chambers, thereby ensuring that after the two sides of the new PC steel pipe pile are respectively engaged with the Larsen steel sheet pile through the locking structures 8, the groundwater outside the pit can only enter the dewatering chamber 10 outside the pit and not the dewatering chamber 11 inside the pit. Similarly, the groundwater inside the pit can only enter the dewatering chamber 11 inside the pit and not the dewatering chamber 10 outside the pit. The above-mentioned locking structure 8 can be designed with reference to the locking structures of conventional PC steel pipe piles and Larsen steel sheet piles, which will not be explained in detail. In actual use, the bottom of the sub-cavity dewatering section P2 needs to be kept flush with the bottom of the Larsen steel sheet pile, and pass through the phreatic layer into the impermeable layer to fully ensure the isolation of groundwater inside and outside the pit.

[0064] Since the new type of PC steel pipe pile can generally be used in non-corner straight areas in the PC method combination steel pipe pile, the two impermeable partitions 4 are symmetrically arranged along the diameter direction on the cross section of the annular space, thereby completely dividing the annular space into equal parts. The dewatering cavity outside the pit and the dewatering cavity inside the pit formed by the equal division are mirror-symmetrical, and the locking structures 8 on both sides are also symmetrically arranged along the diameter direction. The new type of PC steel pipe pile can be installed with two Larsen steel sheet piles along a 180° plane on both sides. Of course, in theory, the new type of PC steel pipe pile can also be used in the corner area of ​​the PC method combination steel pipe pile. In this case, the corresponding dewatering cavity outside the pit and the dewatering cavity inside the pit and the orientation of the locking structures 8 on both sides also need to be adaptively adjusted.

[0065] The pile body steel pipe 1 within the elevation range of the conventional standard section P3 is not provided with filter holes 9, and the main body of the conventional standard section P3 is located in the impermeable layer. During foundation pit construction, the conventional standard section P3 often needs to bear certain lateral loads. Therefore, the pit bottom pressure relief pipe 2 needs to be extended to this pile section to strengthen the structural strength of the pile section, so that the structural strength of the pile section between the chamber dewatering section P2, the conventional standard section P3, and the pit bottom pressure relief section P4 has a relatively smooth transition, avoiding structural damage during pile sinking or use.

[0066] Filter holes 9 are evenly distributed circumferentially on the pile body steel pipe 1 within the elevation range of the pit bottom pressure relief section P4, and a pit bottom pressure relief chamber 12 is formed between the pile body steel pipe 1 and the backfill pipe 3. The bottom of the pit bottom pressure relief chamber 12 is sealed by the top of the bottom grouting head P5, and the top of the pit bottom pressure relief chamber 12 is connected to the external space through the pit bottom pressure relief pipe 2. After the pile is sunk, the pit bottom pressure relief section P4 is located in the confined water layer. As a result, the groundwater in the confined water layer will enter the pit bottom pressure relief chamber 12 through the filter holes 9 in the pile section. When the water in the pit bottom pressure relief chamber 12 is filled, the water level will continue to rise through the annular pipe between the pit bottom pressure relief pipe 2 and the backfill pipe 3, thereby achieving pit bottom pressure relief. At the same time, the annular pipe between the pit bottom pressure relief pipe 2 and the backfill pipe 3 has a small cross-section and can sensitively reflect the water head height of the confined water layer. This water head height can be observed at any time at the top of the pile through the pit bottom pressure relief pipe 2.

[0067] The bottom grouting head P5 is preferably a tapered cross-shaped pile tip with a backfill hole 5. The bottom of the backfill pipe 3 extends through the backfill hole 5, which connects to the center of the tapered cross-shaped pile tip. During the pile extraction process, backfill soil can be injected into the backfill pipe 3 from the top of the pile. The backfill soil then flows through the backfill hole 5 and into the area below the pile tip, thereby filling the void at the bottom of the pile formed by the pile extraction.

[0068] It should also be noted that during the actual pile sinking process, the outer walls of the pile body steel pipe 1 of the chamber dewatering section P2 and the pit bottom decompression section P4 can be pre-coated with one or more layers of filter screen to prevent soil and rock particles from clogging the filter holes 9.

[0069] It should also be noted that the specific dimensions and structural parameters of the above-mentioned new PC steel pipe piles can be reasonably adjusted according to actual needs. In the embodiment of the present invention, taking the foundation pit with an excavation depth of 9m as an example, the total length of the new PC steel pipe pile can be designed to be 20.8m, the top reserved section P1 is 0.8m long, the chamber dewatering section P2 is 11.2m long, the conventional standard section P3 is 5.0m long, the pit bottom pressure relief section P4 is 3.0m long, and the bottom grouting head P5 is 0.8m long. In the embodiment of the present invention, based on these pile segment sizes, the specific structure of each pile segment and the internal corresponding Figure 1 The dimensions of the five sections AA, BB, CC, DD, and EE are as follows:

[0070] like Figure 4As shown, in this embodiment of the present invention, the sub-cavity dewatering section P2 is the same length as the Larsen steel sheet piles on both sides. The pile body steel pipe 1 has an outer diameter of 915 mm and a wall thickness of 14 mm. Inside it is a pit bottom pressure relief pipe 2 with an outer diameter of 500 mm and a wall thickness of 14 mm. Inside the pit bottom pressure relief pipe 2, a built-in backfill pipe 3 with an outer diameter of 200 mm and a wall thickness of 14 mm is installed along the entire length of the pile body. A 14 mm thick steel plate is installed in the middle of the cross-section of the sub-cavity dewatering section P2 as a watertight partition 4, dividing the annular cavity between the pile body steel pipe 1 and the pit bottom pressure relief pipe 2 into two semi-circular rings. The one closer to the foundation pit is the pit dewatering chamber, responsible for internal pit dewatering, and the one farther from the foundation pit is the pit dewatering chamber, responsible for external pit dewatering. The sub-cavity dewatering section has 10 mm diameter filter holes along the circumference (avoiding the dividing steel plate), with a total of 22 filter holes per section (11 filter holes each for the pit inside and pit outside dewatering chambers), with the filter holes spaced 100 mm apart along the length of the pile body. Before the pile body is pressed in, the outer periphery of the sub-cavity dewatering section is wrapped with 3 layers of 60-mesh nylon mesh and then 1 layer of 7-mesh galvanized wire mesh.

[0071] like Figure 5 As shown, a 14mm-thick annular steel plate is installed at the top of the conventional standard section P3. This annular steel plate only covers the bottoms of the in-pit and out-pit dewatering cavities, completely separating them from the sub-cavity dewatering section while ensuring vertical access to the pit bottom pressure relief pipe 2 and backfill pipe 3. Within conventional standard section P3, extending from the sub-cavity dewatering section P2, a pit bottom pressure relief pipe 2 and a backfill pipe are extended, with no circumferential filter holes. The bottom of the pit bottom pressure relief pipe 2 is sealed between the pile body steel pipe 1 and the bottom of the pile bottom pressure relief pipe 2 by a 14mm-thick annular steel plate.

[0072] like Figure 6 As shown, a backfill pipe 2 extends from the conventional standard section P3 inside the pit bottom pressure relief section P4. Each section has 24 filter holes arranged circumferentially, with a center-to-center spacing of 100 mm along the length of the pile. Before the pile is driven in, the pit bottom pressure relief section is wrapped with three layers of 60-mesh nylon mesh and then one layer of 7-mesh galvanized wire mesh.

[0073] like Figure 7 As shown, the pile end grouting head P5 is a tapered cross-shaped pile tip with a backfill hole 5, welded from 14mm thick steel plates. This reduces the end resistance during pile installation. The backfill hole 5 is temporarily sealed with tape during pile installation. During backfilling, the pressure of the backfill soil breaks through the tape for simultaneous backfilling.

[0074] like Figure 8As shown, the steel pipe piles are interconnected through a reinforcing crown beam 13. The reinforcing crown beam 13 is made of reinforced concrete and has a size of 1800mm×800mm. In addition, a force transfer plate 7 (a 14mm thick circular double-piece steel plate with an outer diameter of 1500mm can be used) is welded on the periphery of the pile body steel pipe 1 at the height center of the reinforcing crown beam 13. After the concrete of the reinforcing crown beam 13 is poured, the force transfer plate 7 is fixed to form a force transmission system. The center of the steel pipe pile remains hollow, and the precipitation depth inside and outside the pit can be adjusted at any time, and the pressure head elevation can also be observed at any time. In addition, when the steel pipe pile is pulled out, it can be backfilled synchronously through the backfill hole 5.

[0075] Of course, the specific structure and size parameters of the above-mentioned pile segments can be reasonably designed and adjusted according to actual needs. The above is only a preferred exemplary description.

[0076] The present invention also provides a foundation pit retaining structure comprising a plurality of Larsen steel sheet piles and precast concrete (PC) steel pipe piles, forming a PC composite steel pipe pile structure. One or more of the PC steel pipe piles utilize the novel PC steel pipe piles described in the aforementioned embodiment. In the novel PC steel pipe piles, the length of the compartmentalized dewatering section P2 is generally designed to be the same as that of the Larsen steel sheet piles.

[0077] In order to better compare and understand, the traditional PC method combined steel pipe piles and the PC method combined steel pipe piles with new PC steel pipe piles of the present invention are respectively shown in the structure diagram. Figure 9 As shown, the schematic diagram of the PC method combined steel pipe pile with the new PC steel pipe pile in the present invention is as shown Figure 10 As shown. Figure 10 As shown in Section 2-2, the new PC steel pipe piles can be used in conjunction with traditional PC steel pipe piles on the construction site, depending on design requirements. For example, if the design drawings indicate that the center spacing along the pit edge for both the internal and external dewatering wells and the internal pressure relief wells is 14m, the new PC steel pipe piles can be arranged with a center spacing of 14m, with the nine central piles being traditional PC steel pipe piles. If increased dewatering capacity is required, the density of the new PC steel pipe piles can be further increased, replacing more traditional PC steel pipe piles with the new PC steel pipe piles. In theory, all PC steel pipe piles in the PC method steel pipe pile system can be replaced with the new PC steel pipe piles if necessary.

[0078] In addition, the present invention also provides a construction method for dewatering inside and outside the foundation pit and reducing the pressure at the bottom of the pit, which specifically includes the following steps:

[0079] S1. When deepening the design of the PC method combined steel pipe piles required for foundation pit retaining, one or more PC steel pipe piles in the retaining structure are replaced with the above-mentioned new PC steel pipe piles, and the corresponding new PC steel pipe piles are processed according to the design parameters.

[0080] It should be noted that the specific size parameters of the new PC steel pipe piles and the number and position of the PC method combined steel pipe piles can be designed according to the actual working conditions, focusing on factors such as the plane size of the foundation pit, excavation depth and hydrogeological conditions.

[0081] S2. Before excavation of the foundation pit, the PC method combined steel pipe piles are sunk in sequence. When sinking each new type of PC steel pipe pile, it should be ensured that the bottom ends of the chamber dewatering section P2 and the Larsen steel sheet piles on both sides enter the impermeable layer, and that the dewatering cavity outside the pit faces the outside of the foundation pit, while the dewatering cavity inside the pit faces the inside of the foundation pit. At the same time, it should be ensured that the decompression section at the bottom of the pit is located in the confined water layer.

[0082] S3. During the excavation and construction of the foundation pit project, according to the construction organization plan, the water level outside the pit is controlled by pumping water from the dewatering cavity outside the pit, and the water level inside the pit is controlled by pumping water from the dewatering cavity inside the pit. At the same time, the pressure of the pressurized water is released through the pit bottom pressure relief cavity and the pit bottom pressure relief pipe.

[0083] It should be noted that the height of the water level inside and outside the pit needs to be determined according to the specific construction organization plan and is not restricted here.

[0084] S4. When the foundation pit construction is completed and the PC steel pipe piles are pulled out, clay soil is backfilled synchronously through the backfill pipe 3 during the process of each new type of PC steel pipe pile being pulled out, and the backfill of the pile bottom void is completed while the PC steel pipe piles are recovered.

[0085] As mentioned above, before sinking the new PC steel pipe pile, it is best to temporarily block the backfill hole 5 at the end of the backfill pipe 3 to prevent soil from entering the backfill hole 5 during the pile sinking process. Temporary blocking can be achieved by using a blocking material such as tape that can be broken by the pressure of the backfill soil during backfilling.

[0086] The following example uses the construction of a basement to demonstrate the specific implementation of the aforementioned pit dewatering construction method. In this example, the corresponding construction process is as follows: fabrication of new PC steel pipe piles → sinking of new PC steel pipe piles → construction of the first support → construction of the second support → construction of the basement slab → removal of the second support and construction of the basement floor slab → removal of the first support and construction of the top slab → commencement of extraction of the new PC steel pipe piles and simultaneous backfilling → complete extraction of the new PC steel pipe piles and completion of backfilling. The following describes the key operational points for each process step by step.

[0087] (1) Production of new PC steel pipe piles

[0088] Support design and in-depth design are carried out according to the plane size of the foundation pit, excavation depth and hydrogeological conditions, and the number and total length of the new PC steel pipe piles, as well as the lengths of the top reserved section, cavity dewatering section, conventional standard section and pit bottom decompression section are determined, and then they are manufactured.

[0089] (2) Sinking of new PC steel pipe piles

[0090] like Figure 11 As shown, according to the design drawings and construction plan, the new PC steel pipe piles and the Larsen steel sheet piles between them were sunk. The sub-cavity dewatering sections of the new PC steel pipe piles and the bottoms of the Larsen steel sheet piles on both sides should be embedded in the impermeable layer to ensure effective dewatering inside and outside the pit. Furthermore, the entire decompression section at the pit bottom should be embedded in the confined water layer to ensure effective decompression at the pit bottom.

[0091] (3) Construction of the first support

[0092] like Figure 12 As shown, the water level outside the pit was lowered according to the design requirements, and the water level inside the pit was lowered to 500mm below the planned excavation surface before each excavation. Drainage ditches outside the pit, reinforced crown beams, and the first concrete support were constructed.

[0093] (4) Construction of the second support

[0094] like Figure 13 As shown, the water level in the pit dropped to 500mm below the second support, and the purlin and the second concrete support were constructed.

[0095] (5) Construction base

[0096] like Figure 14 As shown, the water level in the pit drops to 500mm below the bottom plate, and the bottom plate and power transmission belt are constructed.

[0097] (6) Remove the second support and construct the underground floor slab

[0098] like Figure 15 As shown, the second concrete support is chiseled out and the underground floor slab and force transfer belt are constructed.

[0099] (7) Remove the first supporting construction top plate

[0100] like Figure 16 As shown, the first concrete support is removed and the top slab is constructed. The fertilizer trough is backfilled with clay soil and the reinforcing crown beam is removed.

[0101] (8) New PC steel pipe piles begin to be pulled out and backfilled simultaneously

[0102] like Figure 17 As shown in the figure, the new PC steel pipe piles begin to be pulled out and clay is backfilled simultaneously through the backfill pipe.

[0103] (9) The new PC steel pipe piles are completely pulled out and backfilled

[0104] like Figure 18 As shown in the figure, the new PC steel pipe piles are completely pulled out and the void at the pile bottom is backfilled. The pulled-out new PC steel pipe piles are recycled.

[0105] The embodiments described above are merely some preferred implementations of the present invention and are not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit, characterized in that: The PC steel pipe pile is divided into a top reserved section (P1), a cavity dewatering section (P2), a conventional standard section (P3), a pit bottom decompression section (P4) and a bottom grouting head (P5) from top to bottom; A pit bottom pressure relief pipe (2) is coaxially sleeved inside the pile body steel pipe (1) of the PC steel pipe pile, and the pit bottom pressure relief pipe (2) extends from the pile top to the top of the pit bottom pressure relief section (P4); a backfill pipe (3) is coaxially sleeved inside the pit bottom pressure relief pipe (2), and the backfill pipe (3) extends from the pile top to a grouting head (P5) that penetrates the bottom; The top reserved section (P1) is used to connect the reinforced crown beam during the foundation pit construction process; Filter holes (9) are evenly arranged in an annular direction on the pile body steel pipe (1) within the elevation range of the sub-cavity dewatering section (P2), and two impermeable partitions (4) extending from the pile top to the bottom elevation of the sub-cavity dewatering section (P2) are provided in the annular space formed by clamping between the pile body steel pipe (1) and the pit bottom pressure reducing pipe (2), thereby dividing the annular space into two semi-annular spaces and serving as the pit outside dewatering chamber (10) and the pit inside dewatering chamber (11) respectively; at the same time, an annular end plate (6) is provided at the bottom elevation position of the sub-cavity dewatering section (P2), and the bottoms of the two semi-annular spaces are sealed by the annular end plate (6); the outer wall of the pile body steel pipe (1) is provided with a locking structure (8) for connecting the Larsen steel sheet pile along the boundary line on both sides of the two dewatering chambers; No filter holes (9) are provided on the pile body steel pipe (1) within the elevation range of the conventional standard section (P3); Filter holes (9) are evenly and circumferentially formed on the pile body steel pipe (1) within the elevation range of the pit bottom decompression section (P4), and a pit bottom decompression chamber (12) is formed by clamping between the pile body steel pipe (1) and the backfill pipe (3). The bottom of the pit bottom decompression chamber (12) is closed by the top of the bottom grouting head (P5), and the top of the pit bottom decompression chamber (12) is connected to the external space through the pit bottom decompression pipe (2).

2. The PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit as claimed in claim 1 is characterized in that: The two impermeable partitions (4) are symmetrically arranged along the diameter direction on the cross section of the annular space, so that the precipitation cavity outside the pit and the precipitation cavity inside the pit formed by equal division are also mirror-symmetrical.

3. The PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit as claimed in claim 1 is characterized in that: The outer walls of the pile body steel pipes (1) of the chamber dewatering section (P2) and the pit bottom decompression section (P4) are both covered with filter screens.

4. The PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit as claimed in claim 1 is characterized in that: The bottom grouting head (P5) adopts a conical cross pile tip with a backfill hole (5), and the bottom of the backfill pipe (3) passes through the backfill hole (5) connected to the center of the conical cross pile tip.

5. The PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit as claimed in claim 1 is characterized in that: In the top reserved section (P1), a horizontal force transmission plate (7) is welded to the outer wall of the pile body steel pipe (1) to improve the connection strength with the reinforced crown beam.

6. The PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit as claimed in claim 1 is characterized in that: The pit bottom pressure relief pipe (2) and the backfill pipe (3) are both made of steel pipes.

7. A foundation pit retaining structure, characterized in that: A PC method combined steel pipe pile is formed by enclosing a plurality of Larsen steel sheet piles and PC steel pipe piles, wherein one or more PC steel pipe piles are the PC steel pipe piles with the functions of dewatering the inside and outside of the foundation pit and decompressing the pit bottom as claimed in claim 1.

8. The foundation pit retaining structure according to claim 7, characterized in that: In the PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the pit bottom, the length of the dewatering section (P2) is the same as that of the Larsen steel sheet pile.

9. A construction method for dewatering inside and outside the pit and reducing pressure at the bottom of the pit in a foundation pit project, characterized in that: include: S1. When deepening the design of the PC method combined steel pipe piles required for the foundation pit retaining structure, one or more PC steel pipe piles in the retaining structure are replaced with the PC steel pipe piles with the functions of dewatering the inside and outside of the foundation pit and decompressing the pit bottom as described in claim 1, and the corresponding PC steel pipe piles are processed according to the design parameters; S2. Before excavation of the foundation pit, the PC steel pipe piles are sequentially sunk. When sinking the PC steel pipe piles with the functions of dewatering the inside and outside chambers of the foundation pit and reducing pressure at the pit bottom, it should be ensured that the bottom ends of the dewatering sections (P2) and the Larsen steel sheet piles on both sides enter the impermeable layer, and the dewatering chamber outside the pit faces the outside of the foundation pit, while the dewatering chamber inside the pit faces the inside of the foundation pit. At the same time, it should be ensured that the dewatering section at the pit bottom is located in the confined water layer. S3. During the excavation of the foundation pit, according to the construction organization plan, the water level outside the pit is controlled by pumping water from the dewatering cavity outside the pit, and the water level inside the pit is controlled by pumping water from the dewatering cavity inside the pit. At the same time, the pressure of the pressurized water is released through the pit bottom pressure relief cavity and the pit bottom pressure relief pipe; S4. When the foundation pit construction is completed and the PC steel pipe piles are pulled out, clay soil is simultaneously backfilled through the backfill pipe (3) during the process of pulling out the PC steel pipe piles having the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit, so that the PC steel pipe piles are recovered and the backfilling of the pile bottom space is completed at the same time.

10. The method for dewatering inside and outside the foundation pit and reducing pressure at the bottom of the pit according to claim 9, characterized in that: The PC steel pipe pile with the functions of dewatering the inside and outside of the foundation pit and reducing the pressure at the bottom of the pit needs to temporarily block the backfill hole (5) at the end of the backfill pipe (3) before sinking, and the pressure of the backfill soil is used to break through the temporary blockage during backfilling.

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