Composite enclosure structure for deep foundation pit and construction method of composite enclosure structure

Abstract

The invention provides a composite enclosure structure for a deep foundation pit and a construction method thereof.The composite enclosure structure comprises an underground diaphragm wall arranged along the periphery of the foundation pit, a counterfort retaining wall is arranged on the inner side of the foundation pit of the underground diaphragm wall, a plurality of pile foundations are arranged below the counterfort retaining wall, and the underground diaphragm wall, the counterfort retaining wall and the pile foundations are rigidly connected; the underground diaphragm wall, the counterfort retaining wall and the pile foundation form an integral stress system to jointly resist lateral water pressure, so that the integral rigidity and the bending resistance are improved, dense horizontal temporary supports are reduced, the occupied space is small, and the internal operation space of the foundation pit is released; the pile foundation can penetrate through a potential sliding surface and provide shear resistance, so that sliding of the slope of the foundation pit is effectively restrained, the method is particularly suitable for the complex geological environment with the sliding risk of a high slope or a soft layer, and the anti-sliding stability of the foundation pit is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit retaining structure technology, and in particular to a composite retaining structure for deep foundation pits and its construction method. Background Technology

[0002] With the acceleration of urbanization and the deepening of underground space development, the geological environment faced by deep foundation pit projects is becoming increasingly complex. In particular, deep foundation pits with weak soil layers, high groundwater levels or potential sliding zones, as well as areas near important buildings (structures), place extremely high demands on the safety, stability, deformation control, and water-stopping performance of the retaining structure.

[0003] In deep foundation pit engineering, commonly used retaining structures mainly include pile support and diaphragm walls. Pile support, including cast-in-place piles and sheet piles, has advantages such as strong adaptability and flexible construction, and is widely used in foundation pit engineering under various geological conditions. However, its pile-to-pile sealing is poor, which can easily lead to water leakage. In addition, its structural rigidity is limited, requiring support or anchoring systems to share the horizontal load. Anchor support forms a reaction force by anchoring the soil outward, saving internal space in the foundation pit. It is suitable for small urban sites, but it requires high stability of the surrounding soil, has a high risk of anchoring failure, and is easily affected by underground obstacles or adjacent buildings and structures during construction. Diaphragm walls are a type of retaining structure with good continuity, high rigidity, and strong water-stopping ability. They are particularly suitable for deep foundation pits, soft soil layers, or environments with high groundwater levels. In some projects, they can also serve as permanent underground structural walls, offering high comprehensive benefits. However, under high lateral pressure, they may still experience local bending or deformation, requiring extensive temporary support and reinforcement. This significantly occupies construction space, limiting the efficiency of operations and material transportation within the foundation pit. Furthermore, diaphragm walls and internal support systems often operate independently, making it difficult to form an integrated load-bearing system, leading to localized stress concentration and uneven deformation control. In addition, existing structures generally lack flexible adjustment mechanisms, exhibiting insufficient adaptability to complex load changes or sudden events (such as heavy rain or adjacent excavation). Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite retaining structure for deep foundation pits, which can solve the problems that existing deep foundation pit retaining structures are difficult to balance support strength and construction space efficiency under complex geological conditions, and are difficult to form an integrated stress system.

[0005] Therefore, the present invention adopts the following technical solution: A composite retaining structure for deep foundation pits includes a diaphragm wall arranged along the perimeter of the foundation pit, a buttress retaining wall arranged inside the foundation pit, and a plurality of pile foundations arranged below the buttress retaining wall. The diaphragm wall, the buttress retaining wall, and the pile foundations are rigidly connected.

[0006] Based on the above technical solutions, the present invention may also employ the following further technical solutions, or combine these further technical solutions: The buttress retaining wall includes an upright wall and buttresses. The bottom of the upright wall extends toward the underground continuous wall and is rigidly connected to the underground continuous wall. Multiple buttresses are spaced apart between the upright wall and the underground continuous wall. The buttresses are right-angled triangles, and the right-angled sides of the buttresses are rigidly connected to the upright wall.

[0007] The depth of the diaphragm wall is greater than the excavation depth of the foundation pit, and the depth of the pile foundation is greater than the depth of the diaphragm wall and penetrates the potential sliding surface.

[0008] The pile foundation is a bored cast-in-place pile, and several pile foundations are arranged at intervals along the width direction and extension direction of the buttress retaining wall.

[0009] The buttress retaining wall has a filter layer on the side facing the underground continuous wall.

[0010] The buttress retaining wall has several drainage holes at different heights.

[0011] Backfill soil is provided between the buttress retaining wall and the underground continuous wall.

[0012] The top of the diaphragm wall is equipped with a capping beam.

[0013] A cement-soil mixing pile reinforcement zone is provided below the buttress retaining wall. One side of the cement-soil mixing pile reinforcement zone is closely attached to the underground continuous wall, and the other side of the cement-soil mixing pile reinforcement zone extends into the foundation pit.

[0014] The present invention also provides a construction method for a composite retaining structure for deep foundation pits, comprising the following steps: Step 1: For the local soft soil layer area on one side of the foundation pit, cement-soil mixing piles are used to reinforce the foundation. Underground continuous walls are constructed along the perimeter of the foundation pit to serve as the main body for water stop and soil retention. Step 2: Under the support of the diaphragm wall, excavate the soil in the foundation pit to the bottom design elevation of the buttress retaining wall. On the working surface, construct bored piles to form multiple pile foundations. Step 3: On the working surface, construct the buttress retaining wall. The vertical wall and the buttress are cast as a whole. The buttress retaining wall has several drainage holes pre-reserved in its body. Step 4: Lay a filter layer on the side of the buttress retaining wall facing the underground diaphragm wall; Step 5: Carry out the surface structure construction of the foundation pit.

[0015] Compared with existing technologies, this invention has the following advantages and beneficial effects: the underground continuous wall, buttress retaining wall, and pile foundation form an integrated force-bearing system, which jointly resists lateral water pressure, improves overall stiffness and bending resistance, reduces dense horizontal temporary supports, occupies less space, and releases the working space inside the foundation pit; the pile foundation can penetrate potential sliding surfaces and provide shear resistance, thereby effectively suppressing the slippage of the foundation pit slope, and is particularly suitable for complex geological environments with the risk of slippage of high slopes or weak layers, ensuring the anti-slip stability of the foundation pit. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the zoning of the foundation pit and retaining system of the present invention.

[0017] Figure 2 This is a schematic diagram of the geometric model of the enclosure structure of the present invention.

[0018] Figure 3 This is a schematic diagram of the vertical displacement deformation of the foundation pit according to the present invention. Figure 4 This is a schematic diagram of the horizontal displacement deformation of the enclosure structure in the X direction according to the present invention.

[0019] Figure 5 This is a schematic diagram of the horizontal displacement deformation of the enclosure structure in the Y direction according to the present invention.

[0020] Figure 6 This is a flowchart illustrating the design process of the building envelope of this invention.

[0021] Figure 7 This is a schematic cross-sectional view of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote elements with the same or similar functions throughout. However, it should be understood that the drawings are for illustrative purposes only and should not be construed as limiting the present invention. To better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size. It is understandable for those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present invention.

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0024] The present invention provides a composite retaining structure for deep foundation pits, including a diaphragm wall 1 arranged around the perimeter of the foundation pit 11, a buttress retaining wall arranged inside the foundation pit 11 of the diaphragm wall 1, and a plurality of pile foundations 6 arranged below the buttress retaining wall, the diaphragm wall 1, the buttress retaining wall and the pile foundations 6 being rigidly connected.

[0025] The buttress retaining wall includes an upright wall 7 and buttresses 2. The bottom of the upright wall 7 extends toward the underground continuous wall 1 and is rigidly connected to the underground continuous wall 1. Multiple buttresses 2 are spaced apart between the upright wall 7 and the underground continuous wall 1. The buttresses 2 are right-angled triangles, and the right-angled sides of the buttresses 2 are rigidly connected to the upright wall 7.

[0026] The depth of the diaphragm wall 1 is greater than the excavation depth of the foundation pit 11, and the depth of the pile foundation 6 is greater than the depth of the diaphragm wall 1 and penetrates the potential sliding surface.

[0027] Pile foundation 6 is a bored cast-in-place pile, and several pile foundations 6 are set at intervals along the width direction and extension direction of the buttress retaining wall.

[0028] A filter layer 4 is provided on the side of the buttress retaining wall facing the underground continuous wall 1.

[0029] The buttress retaining wall has several drainage holes at different heights.

[0030] Backfill soil 3 is provided between the buttress retaining wall and the underground continuous wall 1.

[0031] A capping beam 5 is installed at the top of the diaphragm wall 1.

[0032] A cement-soil mixing pile reinforcement zone 10 is set below the buttress retaining wall. One side of the cement-soil mixing pile reinforcement zone 10 is closely attached to the underground continuous wall 1, and the other side of the cement-soil mixing pile reinforcement zone 10 extends into the foundation pit 11.

[0033] This invention provides a construction method for a composite retaining structure for deep foundation pits, comprising the following steps: Step 1: For the local soft soil layer area on one side of the foundation pit, cement-soil mixing pile reinforcement zone 10 is used for foundation pre-reinforcement. The underground continuous wall 1, which serves as the main body for water stop and soil retention, is constructed around the foundation pit 11. Step 2: Under the support of the diaphragm wall 1, the excavation of the foundation pit is carried out to the bottom design elevation of the buttress retaining wall. On the working surface, the construction of bored piles is carried out to form multiple pile foundations 6. Step 3: On the working surface, construct the buttress retaining wall. The vertical wall 7 and the buttress 2 are cast in one piece. The buttress retaining wall has several drainage holes 8 pre-reserved in its body. Step 4: Lay the filter layer 4 on the side of the buttress retaining wall facing the underground continuous wall 1; Step 5: Carry out the surface structure construction of foundation pit 11.

[0034] A geological survey was conducted at the project site to determine the physical and mechanical parameters of the soil, including the compression modulus Es, cohesion c, and internal friction angle φ.

[0035] Based on the engineering geometry, the preliminary design parameters for the retaining wall structure are as follows: ①Diameter of the diaphragm wall: depth Hdlq, thickness Ddlq; ② Buttress thickness Dfb, retaining wall height Hdq; ③ Pile foundation 6: diameter Dp, length L, spacing d; The specific combination method is as follows: ①The underground diaphragm wall 1 is connected to the buttress retaining wall, and the top is cast with a capping beam 5; ② The top of pile foundation 6 is connected to the bottom of vertical wall 7; ③ The vertical wall 7 is connected to the buttress 2, and a 50cm thick reverse filter layer 4 is installed behind the vertical wall 7; ④ PVC drainage holes 8 are arranged on the vertical wall 7; ⑤ In some areas, cement-soil mixing piles can be used to reinforce unfavorable geological conditions; ⑥ Fill the backfill soil 3 behind the vertical wall 7; ⑦ The underground continuous wall 1, the buttress retaining wall, and the bored piles 6 work together to resist the lateral water and soil pressure of the slope 9, ensuring the safety of the reservoir pit.

[0036] The stability of the foundation pit slope is verified using finite element numerical simulation, and its displacement should meet the specifications. If the verification fails, the relevant engineering parameters of the composite retaining wall structure will be redesigned; if the verification passes, it will be determined as the final design scheme.

[0037] like Figures 1 to 7 The following is a brief description of the implementation process of a composite retaining wall structure for a foundation pit: (1) The physical and mechanical properties of the soil obtained from geological exploration and physical and mechanical tests are as follows: Table 1. Physical and Mechanical Parameters of Soil

[0038] (2) The depth of the foundation pit is 11.3m, and the following structural parameters are initially set: ① The depth Hdlq of the diaphragm wall is 21m, and the thickness Ddlq is 1.0m; ② The buttress thickness Dfb is 0.7m, and the retaining wall height Hdq is 7.5m; ③ The pile diameter Dp is 0.6m, the length L is 30m, and the spacing d is 1m; (3) Modeling and calculation were performed using finite element method numerical calculation software.

[0039] The geometric model of this foundation pit includes the following parts: strata, retaining system, and shaft. The retaining system consists of three parts: diaphragm walls, buttress retaining walls, and pile foundations. All geometric dimensions are determined according to the design.

[0040] Based on the description and accompanying drawings of this invention, those skilled in the art can easily manufacture or use the composite retaining structure for deep foundation pits and its construction method as described in this invention, and can achieve the positive effects described in this invention.

[0041] It should be noted that the terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. The terms "installed," "set," "equipped with," "connected," "linked," and "sleeve" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral construction; 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, or an internal connection between two mechanisms, elements, or components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] In the description of this invention, it should be understood that the terms "one end," "the other end," "outer side," "inner side," "horizontal," "end," "length," "outer end," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the mechanism 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 this invention. The terms "first" and "second" are also used only for the sake of brevity in description and do not indicate or imply relative importance.

[0043] Furthermore, in practicing the claims of this invention, those skilled in the art can understand and influence variations to the disclosed embodiments through a study of the drawings, the disclosure, and the appended claims. Additionally, in the claims and description, words such as "comprising" and "containing" do not exclude other elements or steps, and non-plural nouns do not exclude their plural forms.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes and modifications made in accordance with the present invention are covered by the scope of the claims of the present invention, and will not be listed here.

Claims

1. A composite retaining structure for deep foundation pits, characterized in that, The underground continuous wall (1) is set along the perimeter of the foundation pit (11). A buttress retaining wall is set inside the foundation pit (11) of the underground continuous wall (1). Several pile foundations (6) are set below the buttress retaining wall. The underground continuous wall (1), the buttress retaining wall and the pile foundations (6) are rigidly connected.

2. The composite retaining structure for deep foundation pits as described in claim 1, characterized in that, The buttress retaining wall includes an upright wall (7) and buttresses (2). The bottom of the upright wall (7) extends toward the underground continuous wall (1) and is rigidly connected to the underground continuous wall (1). Multiple buttresses (2) are spaced apart between the upright wall (7) and the underground continuous wall (1). The buttresses (2) are right-angled triangles, and the right-angled side of the buttresses (2) is rigidly connected to the upright wall (7).

3. The composite retaining structure for deep foundation pits as described in claim 1, characterized in that, The depth of the diaphragm wall (1) is greater than the excavation depth of the foundation pit (11), and the depth of the pile foundation (6) is greater than the depth of the diaphragm wall (1) and penetrates the potential sliding surface.

4. A composite retaining structure for deep foundation pits as described in claim 1, characterized in that, The pile foundation (6) is a bored cast-in-place pile, and several pile foundations (6) are arranged at intervals along the width direction and extension direction of the buttress retaining wall.

5. A composite retaining structure for deep foundation pits as described in claim 1, characterized in that, The buttress retaining wall has a filter layer (4) on the side facing the underground continuous wall (1).

6. A composite retaining structure for deep foundation pits as described in claim 5, characterized in that, The buttress retaining wall has several drainage holes (8) at different heights.

7. A composite retaining structure for deep foundation pits as described in claim 1 or 6, characterized in that, Backfill soil (3) is provided between the buttress retaining wall and the underground continuous wall (1).

8. A composite retaining structure for deep foundation pits as described in claim 1, characterized in that, The top of the underground continuous wall (1) is provided with a capping beam (5).

9. A composite retaining structure for deep foundation pits as described in claim 1, characterized in that, A cement-soil mixing pile reinforcement area (10) is provided below the buttress-type retaining wall. One side of the cement-soil mixing pile reinforcement area (10) is closely attached to the underground continuous wall (1), and the other side of the cement-soil mixing pile reinforcement area (10) extends into the foundation pit (11).

10. A construction method for a composite retaining structure for deep foundation pits, characterized in that, Includes the following steps: Step 1: The foundation is pre-reinforced by cement-soil mixing pile reinforcement zone (10) in the local soft soil layer area on one side of the foundation pit, and underground continuous wall (1) is constructed around the foundation pit (11) as the main body for water stop and soil retention. Step 2: Under the support of the underground continuous wall (1), the earthwork in the foundation pit is excavated to the bottom design elevation of the buttress retaining wall. On the working surface, the bored piles are constructed to form multiple pile foundations (6). Step 3: On the working surface, the buttress retaining wall is constructed. The vertical wall (7) and the buttress (2) are cast in one piece. The buttress retaining wall has several drainage holes (8) reserved in the wall body. Step 4: Lay a filter layer (4) on the side of the buttress retaining wall facing the underground continuous wall 1. Step 5: Carry out the surface structure construction of the foundation pit (11).

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