Soft soil foundation pit supporting structure and construction method thereof

Abstract

The invention relates to the technical field of building construction, and discloses a soft soil foundation pit supporting structure and a construction method thereof.The soft soil foundation pit is arranged in a sloping mode and comprises an inner supporting structure, an enclosure structure, stand column piles and reinforcing row piles; the inner supporting structure is located at the bottom of the soft soil foundation pit. The enclosure structure is located in a soil body below the soft soil foundation pit and located at the bottom of the inner supporting structure, and at least part of the top of the stand column pile is fixedly connected with the inner supporting structure; and the first row piles are connected with the stand column piles through the reinforcing row piles. An open area with a large area can be formed in the foundation pit, mechanical excavation of the soft soil foundation pit is facilitated, and the construction speed is increased; the construction method is simple in process and high in construction speed, deformation of the foundation pit is effectively controlled, and the construction requirement for supporting the foundation pit in the soft soil area is well met.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a soft soil foundation pit support structure and its construction method. Background Technology

[0002] Due to the low strength, high compressibility, and high sensitivity of foundation pits in soft soil areas, cracking and settlement are common problems. Deformation control is the core of foundation pit support in soft soil areas, ensuring project safety and minimizing the impact on the surrounding environment. Retaining structures are commonly used in foundation pit support construction. When high deformation control requirements are needed, a retaining structure combining pile foundations and reinforced concrete internal bracing is often used. However, internal bracing occupies construction space inside the foundation pit. Especially after the retaining structure is completed and mechanized deep excavation is required, the presence of internal bracing makes it inconvenient for machinery to enter and exit the pit, increasing the difficulty of excavation, soil transportation, and underground structure construction. Summary of the Invention

[0003] The purpose of this invention is to provide a soft soil foundation pit support structure and its construction method, which can form a large open area inside the foundation pit, which is conducive to the mechanized excavation of the soft soil foundation pit and improves the construction speed.

[0004] The present invention provides the following technical solution: a soft soil foundation pit support structure, wherein the soft soil foundation pit is set in a sloping manner, including: an internal support structure, a retaining structure, column piles and reinforcing piles;

[0005] The internal support structure is located at the bottom of the soft soil foundation pit;

[0006] The retaining structure is located in the soil below the soft soil foundation pit and at the bottom of the inner support structure. The retaining structure includes a first row of piles, a water-stop curtain, and a second row of piles. The first row of piles is arranged in a ring, and the water-stop curtain is arranged around the outer periphery of the first row of piles. The second row of piles is arranged in a ring along the bottom slope of the soft soil foundation pit and is arranged around the outer periphery of the water-stop curtain. The first row of piles, the water-stop curtain, and the second row of piles are all fixedly connected to the inner support structure.

[0007] The column pile is located in the soil enclosed by the first row of piles, and the top of the column pile is at least partially fixedly connected to the internal support structure.

[0008] The reinforced piles are located in the soil enclosed by the first piles, and the first piles are connected to the column piles through the reinforced piles.

[0009] Preferably, the water-stop curtain is a three-axis mixing pile water-stop curtain.

[0010] Preferably, the diameter of the piles of the water-stop curtain is 650mm to 850mm.

[0011] Preferably, the pile diameter of the first row of piles is d1, 800mm < d1 < 1000mm, and the pile spacing of the first row of piles is greater than the pile diameter of the water-stop curtain. The pile diameter of the second row of piles is d2, 1000mm < d2 < 12000mm, and the pile spacing of the second row of piles is d2 to 2d2. The row spacing between the first row of piles and the second row of piles is 2d1 to 5d1.

[0012] Preferably, the first row of piles consists of cast-in-place piles with alternating lengths.

[0013] Preferably, the column pile includes a pile body and a lattice column, the lattice column is fixedly connected above the pile body, and the top of the lattice column is at least partially fixedly connected to the internal support structure.

[0014] Preferably, the internal support structure includes a cap beam and an internal support beam. The cap beam is in the shape of a grid and connects the first row of piles, the water-stop curtain, and the second row of piles into one unit. The cap beam has an opening along the inner periphery of the first row of piles. The internal support beam is located in the opening, and both ends of the internal support beam are fixedly connected to the cap beam. The top of the grid column is at least partially fixedly connected to the internal support beam.

[0015] Preferably, a dewatering well is also provided inside the opening.

[0016] Preferably, the perimeter of the soft soil foundation pit is provided with wire mesh and shotcrete.

[0017] This application also provides a construction method for a soft soil foundation pit support structure, including:

[0018] S1. Complete the leveling and layout of the construction site, and determine the location of the three-axis mixing pile water-stop curtain, reinforcement piles, first pile, second pile, column piles and dewatering wells;

[0019] S2. The three-axis mixing pile water-stop curtain is constructed using the set-driving process and the two-mixing and two-spraying construction process. The pile diameter of the water-stop curtain is 650mm to 850mm. PO42.5R cement is used, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0 to 1.5.

[0020] S3. The reinforcement piles are constructed using a two-mixing and two-spraying construction process. The reinforcement piles are three-axis mixing piles that are evenly distributed in rows. PO42.5R cement is used, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0 to 1.5.

[0021] S4. Construct the first and second rows of piles. Both the first and second rows of piles shall be constructed using the bored pile method.

[0022] S5. For the construction of the column pile, first construct the cast-in-place pile to the designed pile bottom elevation, put the cast-in-place pile reinforcement cage into the hole, and then put in the lattice column. Weld the longitudinal reinforcement of the lattice column to the reinforcement cage of the pile body, and then use lifting equipment to hoist the whole structure. After ensuring that the verticality of the center point is correct, finally lower the guide pipe and pour underwater concrete.

[0023] S6. Construction dewatering well, with a depth of 2m below the bottom of the soft soil foundation pit;

[0024] S7. Excavate the soft soil foundation pit. The slope excavation method is adopted to excavate from both ends of the excavation site towards the middle. The bottom line of the slope is the edge line of the cap beam. In this stage, the soil layer is excavated to the elevation of the cap beam. The soft soil foundation pit slope is constructed with wire mesh and shotcrete. The first drainage ditch and guardrail are set at the top of the soft soil foundation pit slope, and the second drainage ditch is set at the bottom of the soft soil foundation pit.

[0025] S8. Continue to excavate the soft soil foundation pit to the design depth of the cap beam, check the pile deviation, and after completing the pile cutting work, level and compact the bottom of the soft soil foundation pit, and mark the position of the cap beam and the inner support beam.

[0026] S9. Construction of cap beam and inner support beam. The cap beam and inner support beam are 1m thick, and the inner support beam is 4m wide. The steel bars at the ends of the support beam are connected to the reserved horizontal longitudinal steel bars at the cap beam. The steel bars at the center of the inner support beam are connected to the lattice column.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The soft soil foundation pit is excavated using a sloped method, and reinforced piles and columns are arranged at the bottom of the pit to strengthen it, thereby improving the bearing capacity and deformation resistance of the soft soil foundation pit. The water-stop curtain, first drainage ditch, and second drainage ditch effectively delay or prevent groundwater from flowing into the foundation pit, avoiding ground subsidence around the pit due to a drop in the groundwater level. The design of the internal support structure allows for a large open area within the soft soil foundation pit, facilitating large-scale mechanized excavation and increasing construction speed. By deploying the internal support structure in conjunction with the retaining structure and columns, water and soil pressure is effectively transferred and balanced, enhancing the overall strength and rigidity of the retaining system. The construction method described in this application is simple, fast, and effectively controls the deformation of the soft soil foundation pit, well meeting the construction requirements for foundation pit support in soft soil areas. Attached Figure Description

[0029] Figure 1 This is a plan view of the soft soil foundation pit support structure of this application;

[0030] Figure 2 This is a cross-sectional view of the soft soil foundation pit support structure of this application;

[0031] Figure 3 This is a plan view of the reinforced piles for this application.

[0032] In the picture:

[0033] 1. Soft soil foundation pit; 11. First drainage ditch; 12. Second drainage ditch; 13. Slope bottom line; 14. Dewatering well; 15. Wire mesh shotcrete; 2. Internal support structure; 21. Cap beam; 211. Opening; 22. Internal support beam; 3. Retaining structure; 31. First row of piles; 32. Water-stop curtain; 33. Second row of piles; 4. Column piles; 41. Pile body; 42. Lattice column; 5. Reinforcement piles. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0035] In the description of the embodiments of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "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 the embodiments of this application 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 limitations on the embodiments of this application. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a replaceable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0037] Combination Figure 1-3As shown, a soft soil foundation pit support structure is provided. The soft soil foundation pit 1 is sloped and includes: an internal support structure 2, a retaining structure 3, column piles 4, and reinforcing piles 5. The internal support structure 2 is located at the bottom of the soft soil foundation pit 1. The retaining structure 3 is located in the soil below the soft soil foundation pit 1 and at the bottom of the internal support structure 2. The retaining structure 3 includes a first row of piles 31, a water-stop curtain 32, and a second row of piles 33. The first row of piles 31 is arranged in a ring, the water-stop curtain 32 is arranged around the outer periphery of the first row of piles 31, and the second row of piles 33... The second row of piles 33 is arranged in a ring along the bottom line 13 of the soft soil foundation pit 1, and the second row of piles 33 is arranged on the outer periphery of the water-stop curtain 32. The first row of piles 31, the water-stop curtain 32 and the second row of piles 33 are all fixedly connected to the inner support structure 2. The column pile 4 is located in the soil enclosed by the first row of piles 31, and the top of the column pile 4 is at least partially fixedly connected to the inner support structure 2. The reinforcing pile 5 is located in the soil enclosed by the first row of piles 31, and the first row of piles 31 and the column pile 4 are connected by the reinforcing pile 5.

[0038] For example, the soil surrounding the retaining structure 3 is excavated using a sloping method. When the excavation depth of the deep soft soil foundation pit 1 exceeds 5m, a layered and graded sloping method is adopted, with a slope of 1:2. Reinforcing piles 5 and column piles 4 are arranged at the bottom of the pit to reinforce the soft soil bottom, which can improve the bearing capacity and deformation resistance of the foundation and reduce the risk of settlement and heave of the soft soil foundation. The reinforcing piles 5 are uniformly distributed triaxial mixing piles, and the piles are arranged in a manner of mutual contact, overlap, or spacing. A water-stop curtain 32 is used to enclose and cut off water. A first drainage ditch 11 and a second drainage ditch 12, constructed of bricks, are appropriately arranged at the top and bottom of the soft soil foundation pit 1 to delay or prevent groundwater from flowing into the soft soil foundation pit 1, thus avoiding ground settlement around the soft soil foundation pit 1 caused by a drop in the groundwater level. The first row of piles 31 and the second row of piles 33 are both bored cast-in-place piles, primarily used to bear lateral loads. Due to the significant rheological and thixotropic properties of soft soil, it undergoes slow creep under various loads during construction. The first row of piles 31 and the second row of piles 33, acting as retaining piles, effectively reinforce the soil layers surrounding the soft soil pit 1, ensuring the structural stability of the soft soil pit 1 and its surrounding soil layers. Vertical support piles 4 are installed at the center of the pit bottom. The top of the retaining structure 3 is connected to the internal support structure 2, and the support piles 4 are also connected to the retaining structure 3. This effectively transfers and balances the water and soil pressure acting on the retaining structure 3, improving the overall strength and stiffness of the entire retaining system. During the excavation of the soft soil pit 1, the reinforced internal support structure 2 provides temporary support to the sidewalls of the soft soil pit 1, preventing soil collapse. This design creates an open working surface within the soft soil foundation pit 1, meeting the turning radius requirements of excavating machinery and facilitating the smooth operation of multiple large excavating machines, thereby shortening the earthwork construction period.

[0039] In some embodiments, the water-stopping curtain 32 is a triaxial mixing pile water-stopping curtain 32. Triaxial mixing piles involve injecting cement into the soil and thoroughly mixing it, causing a physicochemical reaction between the cement and the soil, hardening the soft soil, thereby increasing the strength of the soft soil foundation. After the construction of the triaxial mixing pile water-stopping curtain 32, due to its continuity and good compaction, it can effectively prevent or reduce the inflow of groundwater from the sidewalls and bottom of the soft soil foundation pit 1 into the soft soil foundation pit 1, exhibiting a significant water-stopping effect.

[0040] In some embodiments, the pile diameter of the water-stop curtain 32 is 650mm to 850mm. Exemplarily, the three-axis mixing pile construction of the water-stop curtain 32 uses PO42.5R ordinary Portland cement, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0-1.5, employing a two-mixing and two-spraying construction process; it also uses a driving technique, with the pile tip penetrating the sand layer by ≥1m or entering strongly weathered limestone by ≥0.5m, and penetrating the bottom of the soft soil foundation pit by at least 2m. This effectively ensures the water-stopping effect of the water-stop curtain 32.

[0041] In some embodiments, the pile diameter of the first row of piles 31 is d1, 800mm < d1 < 1000mm, and the pile spacing of the first row of piles 31 is greater than the pile diameter of the water-stop curtain 32. The pile diameter of the second row of piles 33 is d2, 1000mm < d2 < 12000mm, and the pile spacing of the second row of piles 33 is d2 to 2d2. The row spacing between the first row of piles 31 and the second row of piles 33 is 2d1 to 5d1.

[0042] For example, the embedment depth of the pile tip of the second row of piles 33 is greater than 1.0h for silty soil, greater than 1.2h for silt, and greater than 0.6h for general cohesive soil and sandy soil, where h is the depth of the soft soil foundation pit 1. The net distance between the water-stop curtain 32 and the first row of piles 31 should preferably be less than 200mm. This effectively ensures the supporting effect of the second row of piles 33 and the first row of piles 31 on both sides of the water-stop curtain 32.

[0043] In some embodiments, the first row of piles 31 consists of cast-in-place piles with staggered lengths. Support piles for soft soil foundations need to be embedded deeper into the soil layer. Combining long and short piles can effectively save costs. The first row of piles 31 is arranged with alternating long and short piles, using sequential arrangements such as "short-long-short," "short-long," and "long-short-long." The length of the long piles must meet the design requirements for embedment length and rock penetration. The staggered lengths of the support piles can adapt to different geological conditions and the depth requirements of the soft soil foundation pit 1. In cases of complex geological conditions or significant variations in the depth of the soft soil foundation pit 1, adjusting the length of the support piles can better ensure the stability and safety of the soft soil foundation pit 1. Longer piles can be embedded deeper into the soil layer, providing greater resistance, while shorter piles can be used in shallower soil layers, forming a composite support system. Simultaneously, using support piles of different lengths not only meets support requirements but also reduces material usage and lowers project costs.

[0044] In some embodiments, the column pile 4 includes a pile body 41 and a lattice column 42, the lattice column 42 being fixedly connected above the pile body 41, and the top of the lattice column 42 being at least partially fixedly connected to the inner support structure 2. This allows the column pile 4 to bear part of the self-weight of the inner support structure 2 while providing effective constraint to the inner support structure 2, thereby improving the overall structural strength.

[0045] In some embodiments, the inner support structure 2 includes a cap beam 21 and an inner support beam 22. The cap beam 21 connects the first row of piles 31, the water-stop curtain 32, and the second row of piles 33 into one unit. The cap beam 21 has an opening 211 along the inner periphery of the first row of piles 31. The inner support beam 22 is located at the opening 211, and both ends of the inner support beam 22 are fixedly connected to the cap beam 21. The top of the lattice column 42 is at least partially fixedly connected to the inner support beam 22.

[0046] For example, a formwork is set at the designed location of the cap beam 21, then a steel reinforcement frame is laid inside the formwork, and then concrete is poured to form a cap beam 21 that meets the specifications. After the cap beam 21 is formed, it can connect the various enclosure structures 3 into a whole, thereby enhancing the overall structural strength. Horizontal longitudinal reinforcement bars are reserved near the middle of the opening 211 of the cap beam 21 for connection with the reinforcement bars at the ends of the inner support beam 22, preferably by welding. Figure 2 As shown, the inner support beam 22 is a single brace. The steel reinforcement at the center of the inner support beam 22 is welded to the lattice column 42 of the column pile 4, further improving the support strength of the soft soil foundation pit support structure. The number of inner support beams 22 can be set according to the support requirements, and is not limited to one.

[0047] In some embodiments, a dewatering well 14 is also provided within the opening 211. This helps reduce the water content of the soil within the soft soil foundation pit 1, decreases the soil's fluidity, and thus prevents the collapse of the soft soil foundation pit 1 wall, ensuring construction safety. The number and location of the dewatering wells 14 can be adjusted according to specific construction conditions, with the depth of the dewatering wells 14 extending 2m below the bottom of the soft soil foundation pit 1. During the excavation of the soft soil foundation pit 1, groundwater within the soft soil foundation pit 1 preferentially concentrates within the dewatering wells 14. At this time, pumps or other facilities can be used to extract groundwater from the dewatering wells 14, lowering the groundwater level inside and outside the soft soil foundation pit 1, preventing groundwater from flowing into the soft soil foundation pit 1 through the sidewalls and foundation, and ensuring the dryness and stability of the soft soil foundation pit 1. Depending on the actual situation, the dewatering wells 14 can be used in conjunction with the retaining structure 3, internal support structure 2, reinforcing piles 5, and water-stop curtain 32 to improve the stability of the soft soil foundation pit 1.

[0048] For example, the perimeter of the soft soil foundation pit 1 is provided with wire mesh and shotcrete 15. This helps to strengthen the perimeter support of the soft soil foundation pit 1 and prevent the slope of the soft soil foundation pit 1 from collapsing due to long-term exposure to the sun or rain.

[0049] This application also provides a construction method for a soft soil foundation pit support structure, including:

[0050] S1. Complete the leveling and layout of the construction site, and determine the positions of the three-axis mixing pile water-stop curtain 32, the reinforced pile 5, the first pile 31, the second pile 33, the column pile 4, and the dewatering well 14.

[0051] S2. The three-axis mixing pile water-stop curtain 32 is constructed using the set-driving process and the two-mixing and two-spraying construction process. The pile diameter of the water-stop curtain 32 is 650mm to 850mm. PO42.5R cement is used, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0 to 1.5.

[0052] S3. The reinforcement piles 5 are constructed using a two-mixing and two-spraying construction process. The reinforcement piles 5 are three-axis mixing piles that are evenly distributed in rows. PO42.5R cement is used, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0 to 1.5.

[0053] S4. Construct the first row of piles 31 and the second row of piles 33. Both the first row of piles 31 and the second row of piles 33 shall be constructed using the method of bored cast-in-place piles.

[0054] S5. For the construction of column pile 4, first construct the cast-in-place pile to the designed pile bottom elevation, put the cast-in-place pile reinforcement cage into the hole, and then put in the lattice column 42. Weld the longitudinal reinforcement of the reinforcement cage of the lattice column 42 to the pile body 41, and then use lifting equipment to hoist the whole structure. After ensuring that the verticality of the center point is correct, finally lower the guide pipe and pour underwater concrete.

[0055] S6, Construction dewatering well 14, the depth of dewatering well 14 extends 2m below the bottom of soft soil foundation pit 1;

[0056] S7. Excavate the soft soil foundation pit 1. The slope excavation method is adopted to excavate from both ends of the excavation site towards the middle. The bottom line of the slope 13 is the edge line of the cap beam 21. In this stage, the soil layer is excavated to the elevation of the cap beam 21. The slope of the soft soil foundation pit 1 is constructed with wire mesh and shotcrete. The first drainage ditch 11 and guardrail are set at the top of the slope of the soft soil foundation pit 1, and the second drainage ditch 12 is set at the bottom of the soft soil foundation pit 1.

[0057] S8. Continue to excavate the soft soil foundation pit 1 to the design depth of the cap beam 21, check the pile deviation, and after completing the pile cutting work, level and compact the bottom of the soft soil foundation pit 1, and mark the positions of the cap beam 21 and the inner support beam 22.

[0058] S9. Construction cap beam 21 and inner support beam 22. The cap beam 21 and inner support beam 22 are 1m thick, and the inner support beam 22 is 4m wide. The steel bars at the ends of the support beam are connected to the reserved horizontal longitudinal steel bars at the cap beam 21. The steel bars at the center of the inner support beam 22 are connected to the lattice column 42.

[0059] For example, Figure 3 A layout diagram of a triaxial mixing pile reinforcement row 5 is provided. The top of the reinforcement piles 5 is at the same depth as the soft soil foundation pit 1. The pile diameter and pile tip can be designed according to construction requirements, but they should be uniformly distributed in a row. In actual construction, the mixing piles can also be set up in contact with each other, overlapping, or spaced apart. The strength and stiffness of the reinforcement piles 5 are much higher than that of the original soil, forming a composite foundation with a certain strength, thereby improving the seepage prevention performance of the soil and reducing problems such as groundwater leakage and sudden surge during the excavation of the soft soil foundation pit 1.

[0060] The construction method for bored piles is as follows: A drilling machine is used to drill a hole to the pile bottom elevation; the specific dimensions are selected according to actual construction requirements. After drilling, a reinforcing cage is placed inside the hole, and concrete is poured into the hole to form the bored pile. The strength of the formed bored pile must meet the design specifications to ensure reliable support.

[0061] In S5, for example, as shown Figure 1 , Figure 2 As shown, a 500mm×500mm column pile 4 is vertically set at the center of the pit bottom. However, the number of column piles 4 can be set according to the support requirements, and is not limited to one.

[0062] In S6, for example, such as Figure 1 As shown, a collection well is installed every 30-40m for drainage at the bottom of the pit, and the water is pumped to the surface. The number and location of the 14 dewatering wells can be adjusted according to the specific construction conditions.

[0063] When excavating the first stage of the soft soil foundation pit 1, for deep soft soil foundation pit 1 with an excavation depth exceeding 5m, the slope should be layered and graded with a gradient of 1:2. After the excavation of this layer is completed, slope protection construction should be carried out promptly, including slope mesh and shotcrete construction using C20 shotcrete. A guardrail should be installed at the top of the slope of the soft soil foundation pit 1.

[0064] After the first phase of slope construction is completed, excavation of cap beam 21 begins, reaching the designed depth of cap beam 21, with a 20cm margin reserved for manual cleaning. Pile misalignment is checked, and pile cutting can only proceed after the pile strength reaches at least 75% and passes inspection, according to the measured elevation. After the soft soil foundation pit 1 is excavated to the bottom elevation of the cap beam, an excavator and rammer are used for leveling and compaction, followed by the construction of the foundation layer, with an outer edge of 100mm. After the foundation layer construction is completed, according to the drawings, such as... Figure 1 , Figure 2 As shown, the positions of the cap beam 21 and the inner support beam 22 are marked with a chalk line. The inner support beam 22 uses a pad layer as the bottom formwork.

[0065] The cap beam and inner support beam 22 are 1m thick and 4m wide. This design makes the plane inside the soft soil pit 1 open working surface, which meets the requirements of the turning radius of the excavating machinery and is conducive to the free operation of multiple large excavating machines. This can increase the excavation speed by more than three times and achieve the goal of shortening the earthwork construction period.

[0066] It is important to note that during construction, the lower layers of soil cannot be excavated until the concrete supports, such as bored piles, triaxial mixing piles, and cap beams, have reached at least 80% of their design strength. Furthermore, the curing time for each mixing pile must exceed 28 days, and excavation of the lower layers can only proceed after the piles have passed inspection. When continuing excavation, a vertical excavation method should be used. The excavation depth for each layer in the slope section and the vertical support section should be consistent, excavating to the same bottom elevation. Excavation should be carried out in layers, sections, and symmetrically to ensure symmetrical stress distribution in the soft soil foundation pit 1. Over-excavation is not permitted. When the bottom elevation of the soft soil foundation pit 1 is reached, the construction of the second drainage ditch 12 and the sump should begin immediately to establish an effective groundwater collection and drainage system in the shortest possible time, reducing groundwater intrusion into the bottom of the soft soil foundation pit 1. After the basement construction is completed, the sump and drainage ditch should be sealed with coarse sand in a timely manner.

[0067] The construction method described in this application is simple and fast, effectively controlling the deformation of the soft soil foundation pit 1, and well meeting the construction requirements for foundation pit support in soft soil areas.

[0068] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A soft soil foundation pit support structure, characterized in that, The soft soil foundation pit is set in a sloping manner and includes: internal support structure, retaining structure, column piles and reinforcement piles; The internal support structure is located at the bottom of the soft soil foundation pit; The retaining structure is located in the soil below the soft soil foundation pit and at the bottom of the inner support structure. The retaining structure includes a first row of piles, a water-stop curtain, and a second row of piles. The first row of piles is arranged in a ring, and the water-stop curtain is arranged around the outer periphery of the first row of piles. The second row of piles is arranged in a ring along the bottom slope of the soft soil foundation pit and is arranged around the outer periphery of the water-stop curtain. The first row of piles, the water-stop curtain, and the second row of piles are all fixedly connected to the inner support structure. The column pile is located in the soil enclosed by the first row of piles, and the top of the column pile is at least partially fixedly connected to the internal support structure. The reinforced piles are located in the soil enclosed by the first piles, and the first piles are connected to the column piles through the reinforced piles.

2. The soft soil foundation pit support structure as described in claim 1, characterized in that, The water-stopping curtain is a three-axis mixing pile water-stopping curtain.

3. The soft soil foundation pit support structure as described in claim 2, characterized in that, The diameter of the piles for the water-stop curtain is 650mm to 850mm.

4. The soft soil foundation pit support structure as described in claim 3, characterized in that, The diameter of the first row of piles is d1, 800mm < d1 < 1000mm, and the spacing between the piles in the first row is greater than the diameter of the water-stop curtain. The diameter of the second row of piles is d2, 1000mm < d2 < 12000mm, and the spacing between the piles in the second row is d2 to 2d2. The distance between the first row of piles and the second row of piles is 2d1 to 5d1.

5. The soft soil foundation pit support structure as described in claim 1, characterized in that, The first row of piles consists of cast-in-place piles with alternating lengths.

6. The soft soil foundation pit support structure as described in claim 1, characterized in that, The column pile includes a pile body and a lattice column, the lattice column being fixedly connected above the pile body, and the top of the lattice column being at least partially fixedly connected to the internal support structure.

7. The soft soil foundation pit support structure as described in claim 6, characterized in that, The internal support structure includes a cap beam and an internal support beam. The cap beam is in the shape of a grid and connects the first row of piles, the water-stop curtain, and the second row of piles into one unit. The cap beam has an opening along the inner periphery of the first row of piles. The internal support beam is located in the opening, and both ends of the internal support beam are fixedly connected to the cap beam. The top of the grid column is at least partially fixedly connected to the internal support beam.

8. The soft soil foundation pit support structure as described in claim 7, characterized in that, A dewatering well is also provided inside the opening.

9. The soft soil foundation pit support structure as described in claim 1, characterized in that, The perimeter of the soft soil foundation pit is equipped with wire mesh and shotcrete.

10. A construction method for a soft soil foundation pit support structure, characterized in that, include: S1. Complete the leveling and layout of the construction site, and determine the location of the three-axis mixing pile water-stop curtain, reinforcement piles, first pile, second pile, column piles and dewatering wells; S2. The three-axis mixing pile water-stop curtain is constructed using the set-driving process and the two-mixing and two-spraying construction process. The pile diameter of the water-stop curtain is 650mm to 850mm. PO42.5R cement is used, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0 to 1.

5. S3. The reinforcement piles are constructed using a two-mixing and two-spraying construction process. The reinforcement piles are three-axis mixing piles that are evenly distributed in rows. PO42.5R cement is used, with a cement content of 480kg per cubic meter and a water-cement ratio of 1.0 to 1.

5. S4. Construct the first and second rows of piles. Both the first and second rows of piles shall be constructed using the bored pile method. S5. For the construction of the column pile, first construct the cast-in-place pile to the designed pile bottom elevation, put the cast-in-place pile reinforcement cage into the hole, and then put in the lattice column. Weld the longitudinal reinforcement of the lattice column to the reinforcement cage of the pile body, and then use lifting equipment to hoist the whole structure. After ensuring that the verticality of the center point is correct, finally lower the guide pipe and pour underwater concrete. S6. Construction dewatering well, with a depth of 2m below the bottom of the soft soil foundation pit; S7. Excavate the soft soil foundation pit. The slope excavation method is adopted to excavate from both ends of the excavation site towards the middle. The bottom line of the slope is the edge line of the cap beam. In this stage, the soil layer is excavated to the elevation of the cap beam. The soft soil foundation pit slope is constructed with wire mesh and shotcrete. The first drainage ditch and guardrail are set at the top of the soft soil foundation pit slope, and the second drainage ditch is set at the bottom of the soft soil foundation pit. S8. Continue to excavate the soft soil foundation pit to the design depth of the cap beam, check the pile deviation, and after completing the pile cutting work, level and compact the bottom of the soft soil foundation pit, and mark the position of the cap beam and the inner support beam. S9. Construction of cap beam and inner support beam. The cap beam and inner support beam are 1m thick, and the inner support beam is 4m wide. The steel bars at the ends of the support beam are connected to the reserved horizontal longitudinal steel bars at the cap beam. The steel bars at the center of the inner support beam are connected to the lattice column.

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