A combined inclined pile foundation pit support structure and its construction method

Abstract

A combined inclined pile foundation pit support structure and its construction method are disclosed. The support structure includes a row of vertical first retaining piles and a row of inclined second retaining piles arranged at intervals. A first capping beam and a second capping beam are respectively provided at the top of the piles, and the two are rigidly connected by a concrete connecting plate. A water-stop curtain is installed tightly against the outside of the first retaining piles. A first reinforcing body is provided in the soil between the first and second retaining piles. A second reinforcing body is provided at the bottom of the foundation pit, tightly against the inside of the first retaining piles. The construction method includes: positioning, constructing the first retaining piles and water-stop curtain, constructing the second retaining piles, constructing the first reinforcing body, integrally casting the capping beam and connecting plate, constructing the second reinforcing body, excavating and constructing the bottom slab and force transmission strip. This invention forms a spatial triangular stable system through "vertical piles + inclined piles + rigid connecting plate," combined with multiple reinforcement and water-stopping measures. It has advantages such as high stiffness, small deformation, small footprint, clear force transmission, and good water-stopping effect, and is suitable for deep and large foundation pit projects in complex surrounding environments.

Description

Technical Field

[0001] This invention relates to the field of civil engineering construction technology, specifically to a combined inclined pile foundation pit support structure and its construction method. Background Technology

[0002] With the continuous development and construction of cities, foundation pit projects are gradually becoming deeper and larger, and the surrounding environment is becoming increasingly complex. For deep foundation pit projects with complex environments, engineering practice often adopts a retaining structure system of retaining piles + supports or anchors. For supports, horizontal or diagonal supports are often used to extend into the pit; for anchors, they are generally installed outside the pit, utilizing the frictional resistance between the anchors and the soil to achieve support. Currently, there are relatively few technologies for diagonal bracing structures outside the pit.

[0003] A search revealed a Chinese patent with application number CN115652952B, which describes a method for supporting foundation pits without internal bracing using a combination of anti-tension piles and retaining piles. This method involves adding inclined piles between the retaining piles to form a support system. The patent primarily utilizes the frictional resistance between the inclined piles and the soil to generate anti-tension force, similar to the force-bearing principle of anchor bolts.

[0004] A search revealed a Chinese patent with application number CN22218336.2U, which describes a composite foundation pit support structure consisting of anchor bolts and inclined piles. The structure includes vertical piles and a capping beam, as well as inclined piles and anchor bolts arranged alternately with the vertical piles. The inclined piles are inclined inwards into the foundation pit, while the anchor bolts are inclined outwards. This patent primarily utilizes the frictional resistance provided by the outer anchor bolts and the direct frictional resistance between the inner inclined piles and the soil.

[0005] A search revealed a Chinese patent with application number CN212336036U, which includes front and rear rows of piles for insertion into the soil layer of an excavation pit. Both the front and rear rows of piles have a certain inclination angle, and the front and rear rows of piles are connected by a connecting beam. This patent requires a large site space, and the excavation and backfilling work between the front rows of piles and the outer wall is extensive. Summary of the Invention

[0006] The purpose of this invention is to provide a combined inclined pile foundation pit support structure and its construction method, which aims to solve the problems of insufficient stiffness of inclined piles and difficulty in effectively controlling deep soil deformation in existing inclined and straight pile combination systems; the problems of large space occupation and large earthwork volume of front and rear rows of inclined piles; the problems of weak connection between retaining piles and permanent structure and uncoordinated force transmission; and the problems of insufficient reinforcement of soil between piles and pit bottom, and poor stability and leakage caused by loose connection of water-stop curtain.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A combined inclined pile foundation pit support structure includes first retaining piles, second retaining piles, a water-stop curtain, a first reinforcing body, and a second reinforcing body. There is one set of first retaining piles, spaced apart along the edge of the foundation pit. Each first retaining pile is a vertical pile, and a first capping beam is provided at the top of the pile. There is also one set of second retaining piles, arranged outside the first retaining pile set and corresponding one-to-one with the first retaining piles. The second retaining piles are inclined piles, and a second capping beam is provided at the top of the pile. The first capping beam and... The second crown beams are rigidly connected by concrete connecting plates; the water-stop curtain is installed on the outside of a set of first retaining piles, and the water-stop curtain is set tightly against the first retaining piles; the first reinforcement body is set in the soil between the first retaining piles and the second retaining piles; the second reinforcement body is set at the bottom of the foundation pit; the first reinforcement body is set in the soil between the water-stop curtain and the second retaining piles; the second reinforcement body is set in the soil at the bottom of the foundation pit, and the top surface elevation of the second reinforcement body is flush with the bottom surface elevation of the basement floor slab; the second reinforcement body is set tightly against the inside of a set of first retaining piles.

[0009] Preferably, the concrete connecting slab is provided with a first upper anchor bar and a first lower anchor bar, one end of the first upper anchor bar and the first lower anchor bar are anchored into the first cap beam, and the other end of the first upper anchor bar and the first lower anchor bar are anchored into the second cap beam.

[0010] Preferably, the first retaining pile is a cast-in-place pile or a precast pile; the second retaining pile is a cast-in-place pile or a precast pile; when the first and second retaining piles are precast piles, the precast piles are prestressed concrete pipe piles or solid square piles.

[0011] Preferably, the clear distance between the first retaining piles is not less than 200mm, and the length of the first retaining pile is inserted into the soil below the bottom of the foundation pit; the inclination angle between the pile body and the vertical direction of the second retaining pile is 5°~15°, and the clear distance between the piles is not less than 200mm; the length of the second retaining pile is inserted into the soil below the bottom of the foundation pit.

[0012] Preferably, the water-stopping curtain is a three-axis mixing pile, which is constructed using the single-hole splicing method to form a continuous cement-soil curtain, and the bottom elevation of the water-stopping curtain is at least 7m below the bottom of the foundation pit.

[0013] Preferably, the first solidified body is a solidified body formed by sleeve valve grouting or jet grouting; the second solidified body is a pit bottom reinforcement layer formed by high-pressure jet grouting or mixing pile technology.

[0014] Preferably, it also includes a base plate force transmission strip; the base plate force transmission strip is continuously arranged on the top of the second reinforced body along the perimeter of the foundation pit, and the base plate force transmission strip is located at the gap between the basement base plate and the first retaining pile.

[0015] A construction method for a combined inclined pile foundation pit support structure includes the following steps: Step 1, On-site positioning: Based on the design drawings, conduct surveying and layout, and mark the construction positions of the first retaining pile, the second retaining pile, and the water-stop curtain on site.

[0016] Step two: Construct the first retaining piles and the water-stop curtain.

[0017] Step 3: Construct the second retaining pile.

[0018] Step four: Reinforce the soil between the water-stop curtain and the second retaining pile to form the first reinforced body.

[0019] Step 5: Construct the concrete connecting slab, the first cap beam, and the second cap beam, and rigidly connect the concrete connecting slab with the first cap beam and the second cap beam.

[0020] Step six: Reinforce the soil below the basement floor slab to be constructed in the foundation pit and inside the first retaining pile to form a second reinforced body.

[0021] Step 7, Excavation of the foundation pit and construction of the underground main structure: Excavate the foundation pit to the design bottom elevation and construct the basement floor slab.

[0022] Preferably, in step five, when pouring the concrete connecting slab, the anchor bars on the first upper plate and the anchor bars on the lower plate inside the concrete connecting slab are anchored into the first cap beam and the second cap beam to be poured, so as to achieve the overall pouring of the three.

[0023] Preferably, in step seven, the foundation pit adopts multi-level slope and is excavated in layers and blocks. Over-excavation is strictly prohibited during the excavation process. After excavation reaches the design elevation, a concrete cushion layer and basement floor slab are poured in a timely manner. Subsequently, before constructing the basement floor slab, a base slab force transmission strip is continuously set on the top of the second reinforced body and along the perimeter of the foundation pit.

[0024] Compared with the prior art, the present invention has the following features and beneficial effects.

[0025] 1. This invention combines a vertical first retaining pile with an inclined second retaining pile, and connects them at the top of the piles with a rigid concrete connecting plate and a capping beam, forming a stable spatial triangular force-bearing system, which significantly improves the overall stiffness and stability. This system effectively transmits and disperses earth pressure. The second retaining pile not only utilizes its frictional resistance with the soil, but more importantly, it acts as an inclined bracing member, working together with the vertical piles to significantly improve the overall overturning resistance and deformation control capability of the support structure, solving the problem that in the prior art, inclined piles only act as anchor rods and have insufficient stiffness.

[0026] 2. In this invention, the second inclined retaining pile is placed immediately outside the vertical first retaining pile, and its inclination angle of 5° to 15° is determined through calculation. This makes the entire support structure compact and greatly reduces the space occupied on the outside of the foundation pit. Compared with the traditional front and rear row inclined pile scheme, the structural arrangement of this invention optimizes the spatial layout, which can significantly reduce unnecessary earthwork excavation and backfilling, not only reducing earthwork volume and saving project costs, but also reducing disturbance to the surrounding environment.

[0027] 3. This invention, by setting a second reinforcing body tightly attached to the inner side of the first retaining pile and setting a force transmission strip in the gap between the basement slab and the first retaining pile, forms a clear force transmission path from the basement basement slab → force transmission strip → first retaining pile, achieving coordinated work between the temporary and permanent structures. This allows the basement basement slab and its superstructure to participate in the permanent support of the foundation pit, effectively limiting the deformation of the retaining piles during long-term use and improving the integrity and safety of the underground structure.

[0028] 4. This invention employs a multi-layered protection strategy consisting of a "water-stopping curtain + first reinforcement body between piles + second reinforcement body at the bottom of the pit." The outer water-stopping curtain (such as deep-mixed piles) forms the first line of defense against waterlogging; the first reinforcement body between piles (such as grouting material) not only enhances the stability of the soil between piles, preventing soil erosion and voids, but also fills the gap between the water-stopping curtain and the second retaining piles, forming an auxiliary water-stopping layer; the second reinforcement body at the bottom of the pit significantly improves the soil resistance in the passive zone, effectively controlling pit bottom heave and pile inward movement. These three measures work together to greatly enhance the stability and reliability of the foundation pit's water-stopping mechanism. Attached Figure Description

[0029] The present invention will now be described in further detail with reference to the accompanying drawings.

[0030] Figure 1 This is an overall schematic diagram of the combined inclined pile foundation pit support structure of the present invention.

[0031] Figure 2 This is a schematic diagram of the connection structure between the anchor bars on the first plate, the anchor bars on the second plate, and the cap beams on both sides in this invention.

[0032] Figure 3 This is a schematic diagram of the planar structure of the first retaining pile and the second retaining pile connected as a whole in this invention.

[0033] Figure 4 This is a schematic diagram of the structure of the first retaining pile and the water-stop curtain in this invention.

[0034] Figure 5 This is a schematic diagram of the vertical structure in which the first retaining pile and the second retaining pile are connected as a whole in this invention.

[0035] Attached reference numerals: 1 - First retaining pile, 2 - Second retaining pile, 3 - First capping beam, 4 - Second capping beam, 5 - Water-stop curtain, 6 - Concrete connecting slab, 6.1 - Anchor bars on the first slab, 6.2 - Anchor bars on the second slab, 7 - First reinforced body, 8 - Second reinforced body, 9 - Basement floor slab, 10 - Force transmission strip on the floor slab, 11 - Exterior wall. Detailed Implementation

[0036] like Figure 1-5 As shown, this combined inclined pile foundation pit support structure includes a first retaining pile 1, a second retaining pile 2, a water-stop curtain 5, a first reinforcing body 7, and a second reinforcing body 8; there is a set of first retaining piles 1, which are spaced along the edge of the foundation pit; each first retaining pile 1 is a vertical pile, and a first capping beam 3 is provided on the top of the pile of the set of first retaining piles 1; there is a set of second retaining piles 2, which are arranged outside the set of first retaining piles 1 and are arranged one-to-one with the first retaining piles 1; the second retaining piles 2 are inclined piles, which gradually tilt outward from bottom to top, and their pile bodies form an inclined angle with the vertical direction. A second capping beam 4 is installed on the top of a set of second retaining piles 2; the first capping beam 3 and the second capping beam 4 are rigidly connected by a concrete connecting plate 6; the first retaining pile 1, the second retaining pile 2, the first capping beam 3, the second capping beam 4 and the concrete connecting plate 6 together form a spatial triangular stable support system to jointly resist the soil pressure outside the foundation pit. To prevent soil loss between piles and enhance waterproofing, the water-stop curtain 5 is installed on the outside of a set of first retaining piles 1, and the water-stop curtain 5 is set tightly against the first retaining piles 1; the first reinforcing body 7 is installed in the soil between the first retaining piles 1 and the second retaining piles 2; the second reinforcing body 8 is installed at the bottom of the foundation pit to improve the soil resistance in the passive zone at the bottom of the pit; to further improve soil stability, the first reinforcing body 7 is installed in the soil between the water-stop curtain 5 and the second retaining piles 2; the second reinforcing body 8 is installed in the soil at the bottom of the foundation pit, and the top surface elevation of the second reinforcing body 8 is flush with the bottom surface elevation of the basement floor slab 9; the second reinforcing body 8 is set tightly against the inside of a set of first retaining piles 1.

[0037] In this embodiment, the concrete connecting slab 6 is provided with a first upper upper anchor bar 6.1 and a first lower upper anchor bar 6.2. One end of the first upper upper anchor bar 6.1 and the first lower upper anchor bar 6.2 is anchored into the first cap beam 3, and the other end of the first upper upper anchor bar 6.1 and the first lower upper anchor bar 6.2 is anchored into the second cap beam 4.

[0038] In this embodiment, the first retaining pile 1 is a cast-in-place pile or a precast pile; the second retaining pile 2 is a cast-in-place pile or a precast pile; when the first retaining pile 1 and the second retaining pile 2 are precast piles, the precast piles are prestressed concrete pipe piles or solid square piles, and are driven by static pressure or hammering.

[0039] In this embodiment, the net distance between the first retaining pile 1 is not less than 200mm, and the length of the first retaining pile 1 is inserted into the soil below the bottom of the foundation pit; the angle between the pile body and the vertical direction of the second retaining pile 2 is 5°~15°, and the net distance between the piles is not less than 200mm; the length of the second retaining pile 2 is inserted into the soil below the bottom of the foundation pit.

[0040] In this embodiment, the water-stop curtain 5 is a three-axis mixing pile, which is constructed using the single-hole splicing method to form a continuous cement-soil curtain. The bottom elevation of the water-stop curtain 5 is at least 7m below the bottom of the foundation pit.

[0041] In this embodiment, the first solidified body 7 is a consolidated body formed by sleeve valve grouting or jet grouting, used to improve the cohesion and shear strength of the soil between piles; the second solidified body 8 is a pit bottom reinforcement layer formed by high-pressure jet grouting or mixing pile, used to improve the soil resistance in the passive zone of the foundation pit.

[0042] In this embodiment, a base plate load transfer strip 10 is included to transfer the load of the superstructure to the retaining piles and also to provide a limiting function. The base plate load transfer strip 10 is formed of plain concrete or reinforced concrete and is continuously installed along the perimeter of the foundation pit on top of the second reinforced structure 8, located at the gap between the basement floor slab 9 and the first retaining piles 1. The base plate load transfer strip 10 is used to transfer the load of the superstructure to the retaining piles. An external wall 11 is provided on top of the basement floor slab 9, inside the base plate load transfer strip 10.

[0043] The construction method for this combined inclined pile foundation pit support structure includes the following steps.

[0044] Step 1, On-site positioning: Based on the design drawings, conduct surveying and layout, and mark the construction positions of the first retaining pile 1, the second retaining pile 2, and the water-stop curtain 5 on site.

[0045] Step 2: Construct the first retaining pile 1 and the water-stop curtain 5.

[0046] Step 3: Construct the second retaining pile 2.

[0047] Step four: Reinforce the soil between the water-stop curtain 5 and the second retaining pile 2 to form the first reinforced body 7.

[0048] Step 5: After the pile body strength reaches the required level, excavate the soil at the top of the pile, tie the reinforcing bars, construct the concrete connecting plate 6, the first capping beam 3, and the second capping beam 4, and make the concrete connecting plate 6 rigidly connected to the first capping beam 3 and the second capping beam 4.

[0049] Step 6: Reinforce the soil below the basement floor slab 9 to be constructed in the foundation pit and inside the first retaining pile 1 to form a second reinforced body 8.

[0050] Step 7, Excavation of the foundation pit and construction of the underground main structure: Excavate the foundation pit to the design bottom elevation and construct the basement floor slab 9.

[0051] In this embodiment, in step five, when pouring the concrete connecting slab 6, the first upper anchor bar 6.1 and the first lower anchor bar 6.2 inside the concrete connecting slab 6 are anchored into the first cap beam 3 and the second cap beam 4 to be poured, so as to achieve the overall pouring of the three.

[0052] In this embodiment, in step seven, the foundation pit adopts multi-level slope and is excavated in layers and blocks. Over-excavation is strictly prohibited during the excavation process. After excavation reaches the design elevation, the concrete cushion layer and the basement floor slab 9 are poured in time. Then, before constructing the basement floor slab 9, the base slab force transmission strip 10 is continuously set on the top of the second reinforcement 8 and along the perimeter of the foundation pit.

[0053] In this embodiment, special attention is paid to binding the upper anchor bar 6.1 and the lower anchor bar 6.2 of the first concrete connecting slab 6 to the reinforcing cage of the first capping beam 3 and the second capping beam 4, respectively. Then, the formwork is erected as a whole, and the concrete of the first capping beam 3, the second capping beam 4, and the concrete connecting slab 6 is poured in one go.

[0054] The above embodiments are not exhaustive examples of specific implementation methods, and other embodiments are also possible. The purpose of the above embodiments is to illustrate the present invention, rather than to limit the scope of protection of the present invention. All applications derived from simple variations of the present invention fall within the scope of protection of the present invention.

Claims

1. A combined inclined pile foundation pit support structure, characterized in that: The structure includes a first retaining pile (1), a second retaining pile (2), a water-stop curtain (5), a first reinforcing body (7), and a second reinforcing body (8); there is one set of the first retaining piles (1), which are spaced apart along the edge of the foundation pit; each first retaining pile (1) is a vertical pile, and a first capping beam (3) is provided on the top of the pile of the first retaining pile (1); there is one set of the second retaining piles (2), which are arranged outside the first retaining piles (1) and are set one-to-one with the first retaining piles (1); the second retaining piles (2) are inclined piles, and a second capping beam (4) is provided on the top of the pile of the second retaining piles (2); the first capping beam (3) and the second capping beam (4) The two are rigidly connected by a concrete connecting plate (6); the water-stop curtain (5) is arranged on the outside of a set of first retaining piles (1), and the water-stop curtain (5) is set close to the first retaining piles (1); the first reinforcement body (7) is set in the soil between the first retaining pile (1) and the second retaining pile (2); the second reinforcement body (8) is set at the bottom of the foundation pit; the first reinforcement body (7) is set in the soil between the water-stop curtain (5) and the second retaining pile (2); the second reinforcement body (8) is set in the soil at the bottom of the foundation pit, and the top surface elevation of the second reinforcement body (8) is flush with the bottom surface elevation of the basement floor slab (9); the second reinforcement body (8) is set close to the inside of a set of first retaining piles (1).

2. The combined inclined pile foundation pit support structure according to claim 1, characterized in that: The concrete connecting slab (6) is provided with a first upper upper anchor bar (6.1) and a first lower upper anchor bar (6.2). One end of the first upper upper anchor bar (6.1) and the first lower upper anchor bar (6.2) is anchored into the first cap beam (3), and the other end of the first upper upper anchor bar (6.1) and the first lower upper anchor bar (6.2) is anchored into the second cap beam (4).

3. The combined inclined pile foundation pit support structure according to claim 1, characterized in that: The first retaining pile (1) is a cast-in-place pile or a precast pile; the second retaining pile (2) is a cast-in-place pile or a precast pile; when the first retaining pile (1) and the second retaining pile (2) are precast piles, the precast piles are prestressed concrete pipe piles or solid square piles.

4. The combined inclined pile foundation pit support structure according to claim 1, characterized in that: The net distance between the first retaining pile (1) is not less than 200mm, and the length of the first retaining pile (1) is inserted into the soil below the bottom of the foundation pit; the angle between the pile body and the vertical direction of the second retaining pile (2) is 5°~15°, and the net distance between the piles is not less than 200mm; the length of the second retaining pile (2) is inserted into the soil below the bottom of the foundation pit.

5. The combined inclined pile foundation pit support structure according to claim 1, characterized in that: The water-stop curtain (5) is a three-axis mixing pile, which is constructed by the single-hole splicing method to form a continuous cement-soil curtain. The bottom elevation of the water-stop curtain (5) is at least 7m below the bottom of the foundation pit.

6. The combined inclined pile foundation pit support structure according to claim 1, characterized in that: The first solidified body (7) is a solidified body formed by sleeve valve grouting or jet grouting; the second solidified body (8) is a pit bottom reinforcement layer formed by high-pressure jet grouting or mixing pile.

7. The combined inclined pile foundation pit support structure according to claim 1, characterized in that: It also includes a base plate force transmission strip (10); the base plate force transmission strip (10) is continuously set on the top of the second reinforced body (8) along the perimeter of the foundation pit, and the base plate force transmission strip (10) is located at the gap between the basement base plate (9) and the first retaining pile (1).

8. A construction method for the combined inclined pile foundation pit support structure according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1, On-site positioning: Based on the design drawings, conduct surveying and layout, and mark the construction positions of the first retaining pile (1), the second retaining pile (2) and the water-stop curtain (5) on site; Step 2: Construct the first retaining pile (1) and the water-stop curtain (5); Step 3: Construct the second retaining pile (2); Step 4: Reinforce the soil between the water-stop curtain (5) and the second retaining pile (2) to form the first reinforced body (7); Step 5: Construct the concrete connecting slab (6), the first cap beam (3), and the second cap beam (4), and rigidly connect the concrete connecting slab (6) with the first cap beam (3) and the second cap beam (4); Step 6: Reinforce the soil below the basement floor slab (9) to be constructed in the foundation pit and inside the first retaining pile (1) to form a second reinforced body (8). Step 7, Excavation of the foundation pit and construction of the underground main structure: Excavate the foundation pit to the design bottom elevation and construct the basement floor slab (9).

9. The construction method of the combined inclined pile foundation pit support structure according to claim 8, characterized in that: In step five, when pouring the concrete connecting slab (6), the first upper anchor bar (6.1) and the first lower anchor bar (6.2) inside the concrete connecting slab (6) are anchored into the first cap beam (3) to be poured and the second cap beam (4) to be poured, so as to achieve the overall pouring of the three.

10. The construction method of the combined inclined pile foundation pit support structure according to claim 8, characterized in that: In step seven, the foundation pit adopts multi-level slope and is excavated in layers and blocks. Over-excavation is strictly prohibited during the excavation process. After excavation reaches the design elevation, the concrete cushion layer and the basement floor slab (9) are poured in time. Then, before constructing the basement floor slab (9), the floor slab force transmission strip (10) is continuously set on the top of the second reinforcement (8) and along the perimeter of the foundation pit.

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