Construction method for large-scale complex deep foundation pit without partition wall

Abstract

This invention relates to a construction method for replacing supports in large, complex, deep foundation pits without partition walls. One side of the support replacement location already has a completed main structure base slab, main structure columns / walls, and main structure floor slabs. Without partition walls, lattice columns and supporting connecting beams are pre-installed. Then, the foundation pit supports can be replaced by installing buttress walls and buttress columns. An automatic servo system is used to compensate for axial force, transferring the axial force of the supports to the buttress walls and buttress columns. Compared with existing technologies, this invention's method for replacing supports in large, complex, deep foundation pits without partition walls eliminates the need for segmented soil retention and excavation during actual construction. It prioritizes the completion of key construction processes for the main structure, significantly shortening the construction period and saving overall project costs.

Description

Technical Field

[0001] This invention relates to the field of building construction engineering technology, and in particular to a method for replacing supports in the construction of large, complex, deep foundation pits without partition walls. Background Technology

[0002] With rapid economic development and accelerated urbanization, urban space utilization is increasingly shifting towards three-dimensional excavation. Foundation pit projects are becoming larger and deeper, with increasingly complex surrounding environments. As the foundation pit deepens, the complexity of the support system and the number of supports increase, placing extremely stringent requirements on underground structure construction. Construction must also be accelerated, leading to increased construction time and difficulty. In deep foundation pit construction, the process of replacing supports becomes a major challenge. Due to site, safety, or funding constraints, when the foundation pit area is large or adjacent to important buildings such as subways, a segmented construction method is often adopted. If segmented construction is required in a deep foundation pit, the segmented retaining and separating system (such as retaining piles or diaphragm walls) must be completed before excavation. Subsequently, segmented construction begins. In principle, the adjacent foundation pit is excavated only after the basement structure of one pit is completed. After the construction of each segment is completed, the segmented retaining and separating system is removed to form a complete structure. This traditional method of setting up separating walls and segmenting the excavation can impact the construction progress. For example, Chinese patent CN104831736A discloses a method and structure for replacing the partition wall in the foundation pit. The replacement method involves setting up several partition walls in the middle of the foundation pit to divide it into several sub-pits. The sub-pits are constructed sequentially as required. After the underground structure of each sub-pit is completed, the partition walls are removed, and the basement structures on both sides of the partition walls are connected to form a complete structure. This requires sequential construction of each sub-pit, which affects the construction progress. Furthermore, the setting of the partition walls increases the cost of the project. Summary of the Invention

[0003] The purpose of this invention is to overcome the defects of the existing technology and provide a construction method for replacing supports in large-scale, complex, deep foundation pits without partition walls. Through this method, supports can be installed and foundation pits can be excavated simultaneously. The supports in key areas of the main structure that need to be completed first can be directly replaced, saving the overall construction period and reducing the cost of the project.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] The purpose of this invention is to provide a construction method for replacing supports in large, complex, deep foundation pits without partition walls. This method includes the following steps:

[0006] S1. Determine the priority construction area for the main structure:

[0007] For large, complex, deep foundation pits with a depth greater than 5m, prioritize the area where the main structure supports are to be replaced. This area already has completed main structure base slabs, main structure columns (walls), and main structure floor slabs. Based on the scope of the completed main structure and the upper main structure to be constructed, determine which supports to retain and which to be removed.

[0008] S2, Pre-designed lattice columns and supporting connecting beams:

[0009] If there are no lattice columns and supporting connecting beams, the lattice columns and supporting connecting beams shall be pre-installed at the locations where the supports are to be dismantled;

[0010] S3, Pre-set buttress walls and buttress columns:

[0011] Within a range of 0.1 to 1m on both sides of the lattice column at the location to be dismantled, two buttress walls are set on the floor slab of the main structure, and buttress columns and buttress beams are set within the range of each buttress wall;

[0012] S4, Support shaft force replacement:

[0013] After the buttress wall and the buttress column reach the designed concrete strength, an automatic servo system is used to press them against the support connecting beam and the buttress wall respectively, and the support to be dismantled is removed. At this time, the axial force of the retained support is transferred to the buttress wall and the buttress column.

[0014] S5, Automatic servo system axial force compensation:

[0015] The automatic servo system is used to monitor the axial force of the support after replacement in real time and to compensate for the axial force, thereby controlling the deformation of the foundation pit.

[0016] Furthermore, the longitudinal section of the buttress wall is a right-angled trapezoid, the top width of the buttress wall is 1-3m, the thickness is 0.6-1.2m, and the area of ​​the main reinforcing steel bars is 4000-20000mm². 2 The height of the buttress wall is determined by the difference between the top elevation of the retained support and the top elevation of the main structural floor slab. The height of the buttress wall does not exceed 5m, and the angle of the buttress wall is 20° to 50°.

[0017] Furthermore, the cross-sectional width or diameter of the buttress column is 0.6 to 1.2 m, and is not greater than the thickness of the buttress wall; the net height of the buttress column is determined by the difference between the top elevation of the main structure floor slab and the bottom elevation of the main structure floor slab; the distance from the center of the buttress column to the edge of the buttress wall is not less than the width of the buttress column; and the ratio of the height of the buttress column to the width of the buttress column is not greater than 14.

[0018] Furthermore, in step S5, when the axial force of the replaced support is detected to be less than 80% of the original design retained axial force, axial force compensation is achieved through the automatic servo system; when the axial force of the replaced support is detected to be greater than 80% of the original design retained axial force, the automatic servo system alarms.

[0019] Furthermore, the axial force of the retaining support is no greater than 20,000 kN.

[0020] Preferably, the retaining support is a steel support or a reinforced concrete support.

[0021] Preferably, the supporting connecting beam is a steel connecting beam or a reinforced concrete connecting beam.

[0022] Furthermore, the cross-sectional dimensions of the supporting connecting beam meet the shear resistance requirements of the axial force of the retained support.

[0023] Furthermore, the buttress columns can be either main structural columns or non-main structural columns.

[0024] Preferably, the buttress column is a reinforced concrete column, a steel column, a steel-concrete composite column, or a steel-concrete composite column.

[0025] Furthermore, the number of buttress columns is determined by the axial force of the retained support and the weight of the buttress wall, and shall be no less than two, arranged symmetrically and evenly.

[0026] Furthermore, the buttress beams are either installed separately or in combination with the floor slab beams of the main structure.

[0027] Furthermore, the automatic servo system is a support shaft force automatic servo system.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The construction method for replacing supports in large, complex, deep foundation pits without partition walls provided in this technical solution has a wide range of applications, especially for large, complex, interconnected foundation pits. It is particularly suitable for the following two complex situations: large, complex, deep foundation pits with a depth greater than 5m, especially deep foundation pits with irregular planar shapes; and foundation pits where it is necessary to shorten the construction period and save costs due to reasons such as construction period or construction sequence, and the traditional method of setting partition walls for segmented excavation and soil retention is not feasible. In order to ensure the priority completion of the main structure of key processes, the traditional method requires the removal of some supports. The buttress walls and buttress column structures in this technical solution can serve as supports for the retained supports, ensuring the smooth construction of key processes.

[0030] 2) The construction method for replacing supports in large, complex, deep foundation pits without partition walls provided by this technical solution uses an automatic servo system to transfer the axial force of the supports to the buttress wall, monitors the magnitude of the axial force in real time and realizes axial force compensation, ensuring the reliability of the axial force conversion of the foundation pit supports, effectively controlling the axial force of the supports while also controlling the deformation of the foundation pit, and ensuring the safety of the foundation pit and the surrounding environment.

[0031] 3) The method for replacing supports in large, complex, deep foundation pits without partition walls provided by this technical solution can save on the overall construction period and project cost. Traditionally, large, complex, deep foundation pits are constructed by setting up partition walls, leaving soil in sections, and excavating in sections. The construction speed is limited by the zoning of the foundation pit. The method for replacing supports provided by this technical solution can simultaneously set up supports and excavate the foundation pit. The key areas of the main structure that need to be completed first can be directly replaced with supports, which saves the overall construction period, reduces the need for setting up foundation pit partition walls, and saves the overall construction period and project cost. Attached Figure Description

[0032] Figure 1 The plan view of the foundation pit replacement support for the construction method of replacing supports for large-scale, complex, deep foundation pits without partition walls provided by the present invention.

[0033] Figure 2 Detailed drawings of the foundation pit replacement support nodes for the construction method of replacing supports for large-scale, complex, deep foundation pits without partition walls provided by the present invention.

[0034] Figure 3 The AA cross-sectional view of the foundation pit replacement support node in the construction method for replacing supports of large, complex, deep foundation pits without partition walls provided by the present invention.

[0035] Figure 4 The BB cross-sectional view of the foundation pit replacement support node in the construction method for replacing supports of large, complex, deep foundation pits without partition walls provided by the present invention.

[0036] Figure 5 Plan view of the north square foundation pit replacement support for the construction method of large-scale, complex, deep foundation pit replacement support without partition walls provided in the embodiments of the present invention.

[0037] Figure 6 Detailed diagram of the north square foundation pit replacement support node for the construction method of large-scale, complex, deep foundation pit replacement support without partition walls provided in the embodiments of the present invention.

[0038] Figure 7 AA section view of the North Square foundation pit replacement support node in the construction method of large-scale connected complex deep foundation pit replacement support without partition walls provided in the embodiment of the present invention.

[0039] Figure 8The BB section view of the North Square foundation pit replacement support node in the construction method for the replacement support of a large, complex, deep foundation pit without partition walls provided in the embodiment of the present invention.

[0040] The numbers in the diagram are as follows:

[0041] 1. Retained support; 2. Support to be dismantled; 3. Lattice column; 4. Support connecting beam; 5. Buttress wall; 6. Buttress column; 7. Buttress beam; 8. Automatic servo system; 51. Buttress wall A; 52. Buttress wall B. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0043] like Figures 1-4 As shown, the technical solution provides a construction method for replacing supports in large, complex, deep foundation pits without partition walls. This method includes the following steps:

[0044] S1. Determine the priority construction area for the main structure:

[0045] For large, complex, deep foundation pits with a depth >5m, prioritize the area where the main structure supports are removed and replaced. This area already has the main structure base slab, main structure columns (walls), and main structure floor slabs that have been completed. It is determined that support 1 should be retained and support 2 should be removed.

[0046] S2, Pre-designed lattice columns and supporting connecting beams:

[0047] If there is no lattice column 3 and supporting connecting beam 4, lattice column 3 and supporting connecting beam 4 shall be pre-installed at the location of the support 2 to be dismantled;

[0048] S3, Pre-set buttress walls and buttress columns:

[0049] Within a range of 0.1 to 1m on both sides of the lattice column 3 at the location of the support to be dismantled 2, two buttress walls 5 are set on the main structural floor slab, and a buttress column 6 and a buttress beam 7 are set within the range of each buttress wall 5.

[0050] S4, Support shaft force replacement:

[0051] After the buttress wall 5 and buttress column 6 reach the designed concrete strength, the automatic servo system 8 is used to press against the support connecting beam 4 and buttress wall 5 respectively, and the support to be dismantled 2 is removed. At this time, the axial force of the remaining support 1 is transferred to the buttress wall 5 and buttress column 6.

[0052] S5, Automatic servo system axial force compensation:

[0053] The automatic servo system 8 is used to monitor the axial force of the support after replacement in real time and realize axial force compensation to control the deformation of the foundation pit.

[0054] Figures 1-4 This is a schematic diagram of the present invention. Figures 5-8 This is a design drawing of an embodiment.

[0055] like Figures 5-8 As shown, the embodiment is a renovation and expansion project of a railway station square and station building area. The north square consists of an underground space for the railway station building, parking lot, etc., with an irregular plan shape. The pit area is approximately 33,000 square meters, and the pit depth ranges from 8 to 16.0 meters. Due to construction period constraints, the pit needs to be excavated simultaneously over a large area, making it impossible to use partition walls for segmented excavation. The main railway station building is a key node for controlling the construction period. The first support of the main station building pit needs to be removed first. The method of replacing the support with buttress walls and buttress columns is adopted to achieve priority replacement of the support in the main railway station building area. After the replacement of the support is completed, the axial force of the pit support and the deformation of the pit are well controlled during the period from the completion of the support replacement to the backfilling of the pit. With the application of this invention, the pit engineering cost is reduced by 5%, and the overall construction period is reduced by 3 months.

[0056] This invention can support large, complex, deep foundation pits with a depth >5m, wherein steel or reinforced concrete supports with an axial force not exceeding 20,000kN are retained. In this embodiment, the foundation pit depth is 8–16m, and the axial force of the retained supports ranges from 9,000 to 14,000kN, with reinforced concrete supports. The foundation pit parameters of this embodiment are within the support range of this invention, therefore the method of this invention is applicable for replacing the supports.

[0057] The specific steps of the construction method for replacing supports in large, complex, deep foundation pits without partition walls, provided in this embodiment, are as follows:

[0058] S1. Determine the priority construction area for the main structure:

[0059] The railway station building foundation pit of this project is 8m deep. The superstructure is a large-span structure, which takes a long time to construct and install. In order to save the construction period, the first support needs to be removed immediately after the completion of the underground floor slab, main structure columns (walls) and main structure floor slab to facilitate the construction of the superstructure. It is determined that support 1 will be retained and support 2 will be removed. The axial force range of support 1 is 9000~14000kN. Both support 1 and support 2 are reinforced concrete supports.

[0060] S2, Pre-designed lattice columns and supporting connecting beams:

[0061] A lattice column 3 and a support connecting beam 4 were pre-installed at the location of the support to be dismantled 2 in the foundation pit. The support connecting beam 4 is a reinforced concrete connecting beam with a cross-sectional dimension of 800×800mm, which meets the shear resistance requirements of the axial force of the retained support 1.

[0062] S3, Pre-set buttress walls and buttress columns:

[0063] Within a 0.3m range on both sides of the lattice column 3 at the location of the support to be dismantled 2, two buttress walls 5 are erected on the main structural floor slab, namely buttress wall A51 and buttress wall B52. Two buttress columns 6 and buttress beams 7 are erected within the range of each buttress wall 5. The longitudinal section of the buttress wall 5 is a right-angled trapezoid with a thickness of 0.8m, and the main reinforcing steel is configured as follows: Reinforcement area As = 14470m² 2 The buttress 5 has a height of 2.5m, an angle of 26°, a top width of 1.8m, and a bottom width of 5.4m. The buttress column 6 is a Φ600 steel-concrete composite column, 5.5m high, and has a thickness of [missing information]. The slenderness ratio (the ratio of height to width) is 9.1. The center of the buttress column 6 is 0.8m away from the side of the buttress wall 5. The buttress column 6 is a non-main structural column and is a steel-concrete composite column. The position of the buttress beam 7 is combined with the main structural floor slab beam. The cross-sectional dimensions of the buttress beam 7 are 800×700mm.

[0064] S4, Support shaft force replacement:

[0065] After the buttress wall 5 and buttress column 6 reach the designed concrete strength, the automatic servo system 8 is used to press against the support connecting beam 4 and buttress wall 5 respectively, and the support to be dismantled 2 is removed. At this time, the axial force of the remaining support 1 is transferred to the buttress wall 5 and buttress column 6.

[0066] S5, Automatic servo system axial force compensation:

[0067] Automatic servo system 8 is a support axial force automatic servo system. It monitors the axial force of the replaced support in real time and realizes axial force compensation. When the monitored support axial force is less than 80% of the original design retaining support axial force, the automatic servo system 8 realizes axial force compensation. During construction, the support axial force does not reach the monitoring alarm value. The maximum deformation increment of the foundation pit before and after the support is replaced is controlled within 8mm.

[0068] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A construction method for replacing supports in large, complex, deep foundation pits without partition walls, characterized in that... Includes the following steps: S1. Determine the priority construction area for the main structure: For large, complex, deep foundation pits with a depth >5m, the area where the main structure supports are to be replaced is identified as the priority area. The main structure base plate, main structure columns, and main structure floor slabs have been completed in this area. The supports to be retained (1) and the supports to be removed (2) are identified. S2, Pre-designed lattice columns and supporting connecting beams: If there is no lattice column (3) and supporting connecting beam (4), the lattice column (3) and the supporting connecting beam (4) shall be pre-installed at the position of the support (2) to be dismantled; S3, Pre-set buttress walls and buttress columns: Within a range of 0.1 to 1m on both sides of the lattice column (3) at the location of the support to be dismantled (2), two buttress walls (5) are set on the floor slab of the main structure, and a buttress column (6) and a buttress beam (7) are set within the range of each buttress wall (5); S4, Support shaft force replacement: After the buttress wall (5) and the buttress column (6) reach the designed concrete strength, the automatic servo system (8) is used to press against the support connecting beam (4) and the buttress wall (5) respectively, and the support to be dismantled (2) is removed. At this time, the axial force of the retained support (1) is transferred to the buttress wall (5) and the buttress column (6). S5, Automatic servo system axial force compensation: The automatic servo system (8) is used to monitor the axial force of the support after replacement in real time and realize axial force compensation to control the deformation of the foundation pit.

2. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The buttress wall (5) has a top width of 1-3m, a thickness of 0.6-1.2m, and a main reinforcing steel reinforcement area of ​​4000-20000mm². 2 The height of the buttress wall (5) is determined by the difference between the top elevation of the retained support (1) and the top elevation of the main structure floor slab. The height of the buttress wall (5) does not exceed 5m, and the angle of the buttress wall is 20° to 50°.

3. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The cross-sectional width or diameter of the buttress column (6) is 0.6 to 1.2 m and is not greater than the thickness of the buttress wall (5); The clear height of the buttress column (6) is determined by the difference between the top elevation of the main structure floor slab and the bottom elevation of the main structure floor slab. The center distance of the buttress column (6) from the side of the buttress wall (5) is not less than the width of the buttress column (6). The ratio of the height of the buttress column (6) to the width of the buttress column (6) is not greater than 14.

4. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... In step S5, when it is detected that the axial force of the support after replacement is less than 80% of the original design retained axial force, axial force compensation is achieved through the automatic servo system (8); When the detected support shaft force after replacement is greater than 80% of the original design retaining support shaft force, the automatic servo system (8) will alarm.

5. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The axial force of the retained support (1) shall not exceed 20000 kN; The reserved support (1) is a steel support or a reinforced concrete support.

6. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The supporting connecting beam (4) is a steel connecting beam or a reinforced concrete connecting beam.

7. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The cross-sectional dimensions of the supporting connecting beam (4) meet the shear resistance requirements of the axial force of the retained support (1).

8. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The buttress column (6) is a reinforced concrete column, a steel column, a steel pipe concrete column, or a steel-concrete composite column.

9. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The number of buttress columns (6) is determined by the axial force of the retained support (1) and the weight of the buttress wall (5), and shall be no less than 2, arranged symmetrically and evenly.

10. The construction method for replacing supports in a large, complex, deep foundation pit without partition walls, as described in claim 1, is characterized in that... The buttress beam (7) is set separately or in combination with the main structure floor slab beam.

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