Horizontal variable-stiffness foundation pit supporting structure for soft soil area

Abstract

The utility model discloses a horizontal variable stiffness foundation pit support structure for soft soil area, including H-shaped steel, crown beam, cast-in-situ bored pile, arch truss, energy-absorbing cell body and force transfer member, H-shaped steel is provided in the inner cavity of cast-in-situ bored pile, crown beam is provided at the top end of cast-in-situ bored pile, arch truss is connected with cast-in-situ bored pile through force transfer member, and the energy-absorbing cell body is connected with the cast-in-situ bored pile. The energy absorption cell bodies are arranged between the cast-in-situ bored piles and the soil body, and the prestressed steel strands are arranged at the two ends of the arch feet of the arch truss. The energy absorption cell body is arranged between the cast-in-situ bored pile and the soil body behind the pile, a negative Poisson's ratio structure is adopted, excellent energy absorption capacity is achieved, impact and damage of the soil body in front of the pile to a supporting structure due to the phenomena of mutual wedge-caulking of soil particles, soil stress redistribution, main stress direction deviation and the like can be effectively relieved, and the supporting effect is improved. The stability and the non-deformability of the foundation pit are enhanced; an arch truss is arranged in an area with insufficient rigidity, the horizontal supporting rigidity is improved, deformation and uneven deformation are reduced, and stability and safety are enhanced.

Description

Technical Field

[0001] The utility model belongs to a foundation pit supporting structure, in particular to a horizontal variable rigidity foundation pit supporting structure used in soft soil areas. Background Art

[0002] With the continuous deepening of the development and utilization of urban underground space, the number of "deep, large, tight, and close" foundation pit projects has increased day by day, and the construction foundation pits are developing in the direction of larger and deeper, which increases the danger of foundation pit construction. However, soft soil is soft, with low strength and stiffness, and can provide less horizontal resistance and ability to resist deformation, resulting in large deformation of the retaining structure and surrounding soil of soft soil foundation pits. With the increasing scale of foundation pits and the increasing complexity of adjacent environmental facilities, reasonable evaluation and control of foundation pit deformation and its impact on the surrounding environment have become important challenges facing soft soil foundation pit projects. Formulating reasonable deformation control standards can not only provide clear control indicators for design, construction and management departments, but also ensure safety and reduce resource waste.

[0003] Although the existing foundation pit support structure can limit the deformation of the foundation pit to a certain extent, most foundation pit support methods do not take into account the spatial effect of the foundation pit, ignore the fact that the foundation pit inner corner can effectively suppress the deformation of the foundation pit support structure, and do not solve the problem of uneven deformation of the foundation pit. Utility Model Content

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the utility model is to provide a horizontal variable stiffness foundation pit support structure with high stability and safety for use in soft soil areas.

[0005] Technical solution: The utility model discloses a horizontal variable stiffness foundation pit support structure for soft soil areas, including H-shaped steel, crown beam, bored pile, arch truss, energy absorbing cell and force transmission member. The H-shaped steel is arranged in the inner cavity of bored pile, the crown beam is arranged at the top of bored pile, the arch truss is connected with bored pile through force transmission member, the energy absorbing cell is arranged between bored pile and soil, and prestressed steel strands are arranged at both ends of arch foot of arch truss. By applying pre-tension, the deformation of arch truss when bearing load is reduced, so as to achieve the purpose of improving the bearing capacity and durability of arch truss.

[0006] Furthermore, the energy absorbing cell is welded with the H-shaped steel to form an energy absorbing component. The surfaces of the energy absorbing cell and the H-shaped steel are provided with a friction reducing layer, which can play a lubricating role, reduce the friction when the H-shaped steel and the energy absorbing cell are inserted into the bored pile as a whole, ensure the smooth insertion process, and facilitate the demoulding of the H-shaped steel when it is subsequently pulled out for reuse.

[0007] Furthermore, the energy-absorbing cell is a hollow structure with a wall thickness of 15 to 25 mm, preferably 20 mm, and an inwardly concave hexagonal plastic space structure is formed inside, and the inward concave angle is 20° to 30°. The energy-absorbing cell has a negative Poisson's ratio structure and has the ability to absorb energy. Most of the energy-absorbing cells are exposed in the soil behind the pile. While shrinking vertically under the load, due to the negative Poisson's ratio effect, they shrink laterally in the direction perpendicular to the load, producing a "tensile expansion" effect, which strengthens the mechanical properties of the compressed part. The negative Poisson's ratio energy-absorbing cell has relatively excellent compressive resistance and energy dissipation capacity, effectively ensuring the safety of the support structure. When the energy-absorbing cell is welded to the H-shaped steel, its vertical arrangement is characterized by that the distance d1 between the energy-absorbing cells in the excavation section is 1 / 2 to 1 / 3 of the distance d2 between the energy-absorbing cells in the embedded section, that is, the energy-absorbing cells in the excavation section are arranged more compactly. The energy-absorbing components are arranged in a plum blossom shape in the vertical direction, which can effectively alleviate the effects of the wedging of local soil particles in front of the pile, the redistribution of soil stress, and the shift of the main stress direction.

[0008] Furthermore, the span of the arch truss in the mid-span area is smaller than the span of the two end areas; the arch feet of the arch truss are all located on the same horizontal line. Preferably, the span of the arch truss in the mid-span area is 1 / 2 to 1 / 4 of the span of the two end areas. The arch truss is set to a reasonable arch axis, which plays a vital role in the bearing capacity of the structure. At this time, the arch ring only generates axial pressure under the action of external loads, without other bending moments and shear forces, so that the performance of the compressed material can be fully exerted.

[0009] Furthermore, the arched truss includes an upper truss and a lower truss that are connected to each other. The span of the upper truss is smaller than the span of the lower truss. Preferably, the span of the upper truss is 1 / 3 to 1 / 4 of the span of the lower truss. The arched truss has a steel support member with a double truss. The support structure is designed with horizontal variable stiffness, and the support structure is evenly divided into three sections. Two arched trusses are set in the middle section area with insufficient stiffness to increase the stiffness, thereby reducing the large deformation of the mid-span end of the support structure and improving the horizontal support stiffness of the foundation pit support structure.

[0010] Furthermore, one end of the force transmission member is fixedly connected to the bored pile, and the other end is fixedly connected to the arch truss.

[0011] Construction method:

[0012] Step 1: site leveling, surveying and laying out, casing processing and burying;

[0013] Step 2: Drilling, secondary hole cleaning, lowering and installing the steel cage, and pouring concrete;

[0014] Step 3: The energy absorbing cell is welded to the H-shaped steel, and a friction reducing agent is applied on the surface to form a friction reducing layer. Before the bored pile slurry solidifies, the energy absorbing component is vertically inserted into the bored pile to construct the cap beam;

[0015] Step 4: After the foundation pit construction is completed and the fertilizer trough on the side wall of the foundation pit is backfilled, the energy absorbing component is pulled out and then backfilled with cement mortar;

[0016] Step 5: a force transmission component is arranged on the supporting structure in the foundation pit, an arch truss is horizontally supported on the force transmission component, and a prestressed steel strand is tensioned at the arch foot;

[0017] Step six, release the prestress in the area where the arch truss is removed and remove the arch truss.

[0018] Beneficial effects: Compared with the prior art, the utility model has the following characteristics:

[0019] 1. By setting up energy-absorbing cells between bored piles and the soil behind the piles, a negative Poisson's ratio structure is adopted, which has excellent energy absorption capacity. This design can effectively alleviate the deformation of the foundation pit caused by the wedging of soil particles, the redistribution of soil stress, and the deviation of the main stress direction during the excavation of the foundation pit, significantly reduce the impact and damage of the soil on the support structure, and improve the stability and anti-deformation capacity of the foundation pit.

[0020] 2. The energy-absorbing components can be pulled out by mechanical equipment after backfilling and can be reused after proper treatment. This feature not only reduces the cost of engineering support, but also embodies the concept of environmental protection and sustainable development, and has good economic and social benefits.

[0021] 3. Considering the corner effect of the foundation pit, the support structure adopts a variable stiffness design. Multiple arch trusses are set in the area with insufficient stiffness, which effectively reduces the deformation in the span of the support structure and improves the horizontal support stiffness of the foundation pit support structure. This design not only reduces deformation and uneven deformation, but also enhances the stability and safety of the overall structure;

[0022] 4. The arched truss described in the utility model is a special support structure with a double-track structure. The upper truss is shorter than the lower truss. Compared with the traditional support form, this design can provide greater lateral support stiffness, so there is no need to set up additional space supports and columns. This facilitates soil excavation and underground structure construction while saving support materials and reducing project costs. In addition, the recyclable nature of the arched truss further reduces the project cost. It is a green and low-carbon support structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the utility model;

[0024] Figure 2 This is a view of an energy absorbing cell 5 added to a bored cast-in-place pile of the utility model;

[0025] Figure 3 It is a schematic diagram of the structure of the energy-absorbing cell 5 of the utility model;

[0026] Figure 4 It is a partial enlarged view of the arched truss 4 of the utility model;

[0027] Figure 5 It is a cross-sectional view of the utility model. DETAILED DESCRIPTION

[0028] like Figure 1 The horizontal variable stiffness foundation pit support structure for soft soil areas includes an H-shaped steel 1, a crown beam 2, a bored pile 3, an arch truss 4, a prestressed steel strand 41, an energy absorbing cell 5 and a force transmission member 6, and is characterized in that: the H-shaped steel 1 is arranged in the inner cavity of the bored pile 3, the crown beam 2 is arranged at the top of the bored pile 3, the arch truss 4 is connected to the bored pile 3 through the force transmission member 6, the energy absorbing cell 5 is arranged between the bored pile 3 and the soil, and the prestressed steel strand 41 is arranged at both ends of the arch foot of the arch truss 4. The H-shaped steel 1 serves as the main supporting structure of the support system, providing vertical supporting force for the side walls of the foundation pit, ensuring that the side walls of the foundation pit remain stable under soft soil conditions and preventing side wall collapse due to soil pressure. The crown beam 2 can connect and fix the tops of the bored piles 3 to form the top frame of the overall support structure, thereby enhancing the overall stability of the support structure and preventing overall destruction due to local instability. The bored piles 3 serve as the main bearing part of the support structure. Through the piles that penetrate deep into the soil, the soil pressure is transferred to the deep soil to ensure the safety and stability of the foundation pit. The arch truss 4 is combined with the bored piles 3 to form a horizontal supporting structure at the top of the foundation pit to provide additional supporting force. The prestressed steel strands 41 prestress the arch truss 4 to improve the overall stiffness and bearing capacity of the truss. Through the tensioning of the prestressed steel strands 41, the arch truss 4 can maintain a good shape and stability when subjected to soil pressure, while improving the bearing capacity of the entire support structure.

[0029] like Figures 2-3 The energy absorbing cell 5 is welded to the H-shaped steel 1 to form a new type of energy absorbing component. The surfaces of the energy absorbing cell 5 and the H-shaped steel 1 are coated with a friction reducer to form a friction reducing layer. The cross-sectional shape of the energy absorbing cell 5 is wide at the top and narrow at the bottom, that is, the area of ​​the upper cross section of the energy absorbing cell 5 is larger than the area of ​​the lower cross section, and the width of the upper narrow side exposed to the soft soil is greater than the lower narrow side welded to the H-shaped steel, and the wall thickness is preferably 20 mm, and it is made of steel plate welding. The energy absorbing cell 5 is a hollow structure, and a concave hexagonal plastic space structure is formed inside, and the concave angle is 20° to 30°, preferably 25°.

[0030] The energy-absorbing cell 5 is arranged between the bored pile 3 and the soil, and is used to absorb and disperse the deformation energy of the soil to reduce the impact on the support structure. The energy-absorbing cell 5 has a negative Poisson's ratio structure and has the ability to absorb energy. Most of the energy-absorbing cell 5 is exposed in the soil behind the pile. While it shrinks vertically under the action of the load, it shrinks laterally in the direction perpendicular to the load due to the negative Poisson's ratio effect, producing a "tension" effect, which strengthens the mechanical properties of the compressed part. The negative Poisson's ratio energy-absorbing cell 5 has relatively excellent compressive resistance and energy dissipation capacity, which effectively ensures the safety of the support structure. The hollow structure of the energy-absorbing cell 5 and the concave hexagonal plastic space structure design enable it to undergo plastic deformation when the soil is deformed, thereby absorbing and dispersing the deformation energy of the soil and reducing the impact and damage to the support structure. The energy-absorbing component is arranged in a plum blossom shape in the vertical direction, which can effectively alleviate the effects of the wedging of local soil particles in the soil in front of the pile, the redistribution of soil stress, and the shift of the main stress direction. When the energy absorbing cells are welded to the H-shaped steel, the vertical arrangement characteristics are that the distance d1 between the energy absorbing cells in the excavation section is 1 / 2 to 1 / 3 of the distance d2 between the energy absorbing cells in the embedded section, that is, the energy absorbing cells in the excavation section are arranged more compactly.

[0031] like Figure 4 The supporting structure consists of two end areas and a mid-span area. Two arch trusses 4 are arranged in the mid-span area, and one arch truss 4 is arranged in each of the two end areas. The span of the two arch trusses 4 in the mid-span area is 1 / 2 to 1 / 4 of that at the two ends. The arch feet of all arch trusses 4 are located on the same horizontal line. The arch trusses 4 consist of an upper truss and a lower truss, and the span of the upper truss is designed to be 1 / 3 to 1 / 4 of the span of the lower truss.

[0032] Through the design of the arch truss 4, the horizontal soil pressure is converted into the pressure inside the arch structure, thereby reducing the lateral pressure on the bored piles 3 and improving the stability of the support structure. In this process, the reasonably selected arch axis plays a crucial role. When the arch ring is under the action of external load, its unique structural form makes the pressure mainly transmitted along the arch axis, thereby avoiding the generation of bending moment and shear force, so that the performance of the compressed material is fully utilized, and the efficiency and safety of the support structure are further improved.

[0033] like Figure 5 One end of the force transmission member 6 is fixedly connected to the bored pile 3 through a compact cross section, and the other end is fixedly connected to the arch truss 4 through a larger cross section.

[0034] The force transmission component 6 connects the bored piles 3 and the arched trusses 4 to achieve force transmission and distribution. Through the design of the force transmission component 6, it is ensured that the force between the bored piles 3 and the arched trusses 4 can be effectively transmitted and distributed, thereby improving the collaborative working ability and stability of the entire support structure.

[0035] The construction method of the horizontal variable stiffness foundation pit support structure for soft soil areas comprises the following steps:

[0036] Step 1: site leveling, surveying and laying out, casing processing and burying;

[0037] Step 2: Drilling, secondary hole cleaning, lowering and installing the steel cage, and pouring concrete;

[0038] Step 3: The energy absorbing cell 5 is welded to the H-shaped steel 1, and a friction reducing agent is applied on the surface to form a friction reducing layer. Before the bored pile 3 slurry solidifies, the energy absorbing component is vertically inserted into the bored pile 3 to construct the cap beam 2;

[0039] Step 4: After the foundation pit construction is completed and the fertilizer trough on the side wall of the foundation pit is backfilled, the energy absorbing component is pulled out and then backfilled with cement slurry;

[0040] Step 5: a force transmission member 6 is arranged on the supporting structure in the foundation pit, the arch truss 4 is horizontally supported on the force transmission member 6, and the prestressed steel strand 41 is tensioned at the arch foot;

[0041] Step six, releasing the prestress in the area where the arch truss 4 is removed and removing the arch truss 4.

Claims

1. A horizontal variable stiffness foundation pit support structure for soft soil areas, characterized by: The invention comprises an H-shaped steel (1), a crown beam (2), a bored pile (3), an arch truss (4), an energy absorbing cell (5) and a force transmission component (6), wherein the H-shaped steel (1) is arranged in the inner cavity of the bored pile (3), the crown beam (2) is arranged at the top of the bored pile (3), the arch truss (4) is connected to the bored pile (3) via the force transmission component (6), the energy absorbing cell (5) is arranged between the bored pile (3) and the soil, and prestressed steel strands (41) are arranged at both ends of the arch foot of the arch truss (4).

2. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 1 is characterized by: The energy absorbing cell (5) is welded with the H-shaped steel (1) to form an energy absorbing component.

3. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 2 is characterized by: The surfaces of the energy absorbing cells (5) and the H-shaped steel (1) are both provided with a friction reducing layer.

4. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 1 is characterized by: The energy absorbing cell (5) is a hollow structure with a wall thickness of 15 to 25 mm, and forms an inwardly concave hexagonal plastic space structure inside, with an inwardly concave angle of 20° to 30°.

5. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 1, characterized in that: The span of the arched truss (4) in the mid-span region is smaller than the span of the regions at both ends; and the arch feet of the arched truss (4) are all located on the same horizontal line.

6. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 5, characterized in that: The span of the arched truss (4) in the mid-span region is 1 / 2 to 1 / 4 of the span of the two end regions.

7. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 1, characterized in that: The arched truss (4) comprises an upper truss and a lower truss which are connected to each other.

8. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 7, characterized in that: The span of the upper truss is smaller than the span of the lower truss.

9. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 7, characterized in that: The span of the upper truss is 1 / 3 to 1 / 4 of the span of the lower truss.

10. The horizontal variable stiffness foundation pit support structure for soft soil areas according to claim 1, characterized in that: One end of the force transmission component (6) is fixedly connected to the bored pile (3), and the other end is fixedly connected to the arch truss (4).

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