Inclined strut deformation control method for implementing foundation pit engineering through reverse construction method

Abstract

The invention belongs to the field of underground space development, and relates to an inclined strut deformation control method for implementing foundation pit engineering through a reverse construction method. According to the main technical scheme, after a reverse construction structure beam plate reaches the design strength, a temporary bent frame is dismantled, and a lower inclined strut, an enclosing purlin and a stress transfer beam are constructed below the reverse construction structure beam plate; the enclosing purlins are located on the side faces of the foundation pit support structure. A supporting plate structure is arranged between the bottom of the enclosing purlin and the stress transfer beam and used for placing a servo jack in the later period; the stress transfer beams are effectively connected with the temporary supporting side columns and the lower inclined struts; one end of the lower inclined strut is connected with the stress conversion beam, and the other end is connected with the middle supporting pile; and a servo jack is arranged between the enclosing purlin and the stress transfer beam and is used for applying a jacking force. The construction method is suitable for the situation of large-depth multi-layer underground space development under the complex sensitive environment condition of the central urban area, and the construction method can effectively reduce the influence of the construction process on buildings and underground pipe networks around the foundation pit in the reverse construction method deep foundation pit engineering.

Description

Technical Field

[0001] The invention belongs to the field of underground space development, and in particular relates to a construction method under the condition that the surrounding environment of a foundation pit in a central urban area is complex and the deformation control requirements of a foundation pit retaining structure are very high. Background Art

[0002] With the rapid development of urban underground space, the design and construction of foundation pit projects have also encountered new problems and challenges. Urban underground space has changed from traditional single functions such as commerce and parking to multi-functional underground complexes, and the scale of foundation pit projects has continued to increase. In addition, foundation pit projects in central urban areas are often close to protected objects such as subways, protected buildings, and underground pipelines. The environmental conditions around the foundation pits are becoming more complex and sensitive, and the deformation control requirements for the implementation of the foundation pits are also becoming higher and higher.

[0003] The top-down method is a commonly used support method in foundation pit engineering. In this method, intermediate supporting piles are cast or driven into relevant locations inside the building as supporting structures that bear the deadweight of the upper structure and construction loads before the bottom slab is sealed during construction. The structural beams and slabs of each floor of the basement are excavated downward to serve as horizontal supports for the retaining structure. Compared with the conventional forward excavation method, the top-down method has the following outstanding advantages: (1) Since the structural beams and slabs of the first floor on the ground are completed first, the upper structure can be constructed simultaneously during the downward top-down excavation process, thereby greatly shortening the construction period; (2) It avoids the waste of temporary supports, has significant economic benefits, and is conducive to the green and sustainable development of foundation pit engineering; (3) The horizontal top-down structural beam and slab support has high rigidity and safety.

[0004] Although the top-down construction method has the above advantages, it still has certain shortcomings in controlling foundation pit deformation when the surrounding environmental protection requirements are very high: (1) The construction speed of underground top-down structural beams and slabs is usually slow. In soft soil areas such as Shanghai, soft clay has rheological properties. Before the top-down construction of the beams and slabs is completed and an effective horizontal support is formed, the foundation pit deformation will continue to accumulate and grow over time; (2) In order to ensure the construction quality and dimensional accuracy of the top-down structural beams and slabs, the top-down construction method usually requires the use of a racking method. Therefore, each stage of the foundation pit excavation process requires over-excavation to a certain depth, which is also not conducive to the control of foundation pit deformation.

[0005] At present, the research on the implementation of foundation pit engineering by reverse construction method, especially the technical means to control the deformation of foundation pit retaining structure and reduce the impact of foundation pit on the surrounding environment, is still immature. Summary of the invention

[0006] The present invention provides a method for controlling the deformation of diagonal braces used in foundation pit projects implemented using the reverse construction method. The method is particularly suitable for the development of large-depth and multi-layer underground spaces under complex and sensitive environmental conditions in central urban areas. The method can effectively reduce the impact of the construction process on the surrounding structures and underground pipelines of the foundation pit in deep foundation pit projects using the reverse construction method.

[0007] The construction steps of the present invention are: Step 1: First construct the foundation pit retaining structure, temporary supporting side columns and intermediate supporting piles in the foundation pit. The temporary supporting side columns are located outside the intermediate supporting piles.

[0008] Step 2: Excavate the foundation pit to a depth below the top-down structure beam and slab, and construct a complete top-down structure beam and slab. The top-down structure beam and slab are effectively connected with the intermediate supporting piles and the foundation pit retaining structure; temporary racks support the top-down structure beam and slab.

[0009] Step 3: After the top-down structure beams and slabs reach the design strength, the temporary racks are removed, and the lower diagonal braces, purlins and load transfer beams are constructed below the top-down structure beams and slabs; the purlins are located on the side of the foundation pit retaining structure; a pallet structure is set between the bottom of the purlin and the load transfer beam for the later placement of the servo jack; the pallet structure is connected to the purlin, and the other end is disconnected from the load transfer beam; the load transfer beam is effectively connected to the temporary supporting side columns and the lower diagonal braces; one end of the lower diagonal brace is connected to the load transfer beam, and the other end is connected to the middle supporting pile column; the servo jack is installed between the purlin and the load transfer beam and a jacking force is applied.

[0010] Step 4: Repeat steps 2 to 3 above to complete the construction of each layer of reverse-constructed structural beams and slabs and the application of servo jack thrusts in sequence; after the construction of the basement foundation slab is completed, remove the servo jacks, lower diagonal braces, purlins and load-bearing transfer beams in stages.

[0011] Based on the above technical features: the connection point between the lower diagonal brace and the middle supporting pile column is the beam-column node of the reverse-constructed structural beam-slab.

[0012] Based on the above technical features: the purlin and the foundation pit retaining structure are connected by hangers.

[0013] The concept of the above technical solution is as follows: the reverse-construction structure beams and slabs usually need to be constructed by setting up racks, so each stage of the foundation pit excavation process needs to be over-excavated to a certain depth, which is not conducive to the control of foundation pit deformation. In addition, if the basement floor height is large and the single-skin earthwork excavation depth is large, it is also easy to cause large deformation of the retaining structure. Adding lower diagonal braces to each layer of the reverse-construction structure beams and slabs is equivalent to increasing the number of temporary supports acting on the retaining structure, while giving full play to the characteristics of high stiffness and high bearing capacity of the reverse-construction structure beams and slabs. Compared with the entire layer of reverse-construction structure beams and slabs, the lower diagonal braces set only around the foundation pit can be applied quickly, and there is no need for over-excavation during the construction process, which shortens the unsupported exposure time of the retaining structure and reduces the deformation of the retaining structure. On this basis, adding a servo jack in combination with the lower diagonal brace to apply a top thrust on the retaining structure can further reduce the deformation of the foundation pit. The reaction force formed by the jack is transmitted to the reverse-construction structure beams and slabs through the lower diagonal brace, and the vertical separation generated during the force transmission process can be borne by the temporary supporting side columns.

[0014] The present invention can effectively control the deformation of the retaining structure of the deep foundation pit project implemented by the reverse construction method, thereby reducing the impact of the foundation pit excavation construction on the surrounding buildings and underground pipe networks, and plays an important role in urban renewal construction projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional schematic diagram of setting a lower diagonal brace and a servo system in combination with a foundation pit reverse-construction structural beam and slab in the present invention.

[0016] The symbols in the figure are as follows: foundation pit retaining structure 1; temporary supporting side column 2; intermediate supporting pile column 3; reverse structure beam slab 4; lower diagonal brace 5; surrounding purlin 6; load transfer beam 7; support plate structure 8; servo jack 9; hanger rod 10. DETAILED DESCRIPTION

[0017] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. These embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0018] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0019] The present invention provides a method for controlling the deformation of diagonal braces used in the reverse construction of foundation pit projects. In the development of deep and multi-layer underground spaces under complex and sensitive environmental conditions in the central urban area, the construction method can effectively reduce the impact of the construction process on the surrounding environment of the foundation pit in the reverse construction deep foundation pit project. The specific description is as follows in conjunction with the accompanying drawings.

[0020] Step 1: First, construct the foundation pit retaining structure 1, the temporary supporting side columns 2 and the middle supporting piles 3 in the foundation pit, and the temporary supporting side columns 2 are located outside the middle supporting piles 3.

[0021] Step 2: Excavate the foundation pit to a depth below the top-down structure beam and slab, and construct a complete top-down structure beam and slab 4. The top-down structure beam and slab 4 are effectively connected with the intermediate supporting piles 3 and the foundation pit retaining structure 1; temporary racks support the top-down structure beam and slab 4.

[0022] Step 3: After the top-down structure beam slab 4 reaches the design strength, the temporary bent frame is removed, and the lower diagonal brace 5, the purlin 6 and the load transfer beam 7 are constructed below the top-down structure beam slab 4; the purlin 6 is connected to the foundation pit retaining structure 1 through the hanger 10. A support plate structure 8 is set between the bottom of the purlin 6 and the load transfer beam 7 for the later placement of the servo jack 9; the load transfer beam 7 is effectively connected to the temporary supporting side column 2 and the lower diagonal brace 5. One end of the lower diagonal brace 5 is connected to the load transfer beam 7, and the other end is connected to the middle supporting pile column 3 and the beam-column node of the top-down structure beam slab 4. Under this connection, the horizontal force can be transmitted to the structural main beam of the top-down structure beam slab to ensure the safety of the column. The servo jack 6 is installed between the purlin 6 and the load transfer beam 7 and a top thrust is applied to reduce the deformation of the foundation pit retaining structure 1.

[0023] The support plate structure 8 is connected to the purlin 6, and the other end is disconnected from the force conversion beam 7, which can prevent the support plate structure 8 from being broken when the servo jack 9 applies a top thrust. In addition, if the two ends of the support plate structure 8 are connected to the purlin 6 and the force conversion beam 7 at the same time, the top thrust of the servo jack 9 will be restricted.

[0024] Step 4: Repeat steps 2 to 3 above to complete the construction of each layer of reverse-constructed structural beams 4 and the application of the top thrust of each servo jack 6 in sequence; after the construction of the basement foundation slab is completed, remove the servo jack 9, lower diagonal brace 5, surrounding purlin 6 and load transfer beam 7 in stages.

[0025] In summary, in foundation pit projects, due to the unloading of earthwork in the foundation pit, the retaining structure deforms into the foundation pit, which in turn causes the settlement and deformation of buildings and underground pipelines outside the pit. The deformation of the foundation pit retaining structure is directly related to the settlement and deformation of surrounding buildings and underground pipelines. Therefore, controlling the deformation of the retaining structure is conducive to reducing the impact of foundation pit excavation on the surrounding environment. Adding lower diagonal braces that can be quickly constructed to the beams and slabs of each layer of reverse-construction structure increases the number of supports acting on the retaining structure and shortens the unsupported exposure time of the retaining structure. On this basis, adding a servo jack in combination with the lower diagonal brace to apply a top thrust can further reduce the deformation of the foundation pit.

[0026] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A method for controlling the deformation of diagonal braces used in reverse construction of foundation pit engineering: Step 1: First, construct a foundation pit retaining structure (1), temporary supporting side columns (2) and intermediate supporting piles (3) in the foundation pit, wherein the temporary supporting side columns (2) are located outside the intermediate supporting piles (3); Step 2: the foundation pit is excavated to a depth below the top-down structural beam slab (4), the top-down structural beam slab (4) is completely constructed, the top-down structural beam slab (4) is effectively connected to the intermediate supporting piles (3) and the foundation pit retaining structure (1); a temporary bent frame is used to support the top-down structural beam slab (4); Step 3: After the top-down structural beam slab (4) reaches the design strength, the temporary bent frame is removed, and a lower diagonal brace (5), a purlin (6) and a load transfer beam (7) are constructed below the top-down structural beam slab (4); the purlin (6) is located on the side of the foundation pit retaining structure (1); a support plate structure (8) is arranged between the bottom of the purlin (6) and the load transfer beam (7) for later placement of a servo jack (9); the support plate structure (8) is connected to the purlin (6) and the other end is disconnected from the load transfer beam (7); the load transfer beam (7) is effectively connected to the temporary supporting side column (2) and the lower diagonal brace (5); one end of the lower diagonal brace (5) is connected to the load transfer beam (7) and the other end is connected to the intermediate supporting pile column (3); a servo jack (9) is installed between the purlin (6) and the load transfer beam (7) and a top thrust is applied; Step 4: Repeat the above steps 2 to 3 to sequentially complete the construction of the reverse-constructed structural beams and slabs (4) of each layer and the application of the top thrust of each servo jack (6); after the construction of the basement foundation slab is completed, remove the servo jack (9), the lower diagonal brace (5), the purlin (6) and the load-bearing conversion beam (7) in stages.

2. The method for controlling deformation of diagonal braces used in reverse construction of foundation pit engineering according to claim 1 is characterized in that: The connection point between the lower diagonal brace (5) and the intermediate supporting pile column (3) is a beam-column node of the reverse-construction structural beam slab (4).

3. The method for controlling deformation of diagonal braces used in reverse construction of foundation pit engineering according to claim 1 is characterized by: The enclosure purlin (6) is connected to the foundation pit retaining structure (1) via a suspension rod (10).

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