Combined foundation pit support construction method

Abstract

According to the combined foundation pit supporting construction method, in a foundation pit supporting structure, the edge of a foundation pit is provided with a stirring pile waterproof curtain (1), the side of the stirring pile waterproof curtain is provided with a prestressed pipe pile (2), the side of the prestressed pipe pile is provided with c-shaped steel (3), a boundary beam (4) is arranged below a bearing platform and is a construction edge sealing concrete beam, and the outer side of the edge sealing concrete beam is provided with an additional plate (5); the additional plate is a thickened reinforced concrete cushion layer, and the method is characterized by comprising the following steps of a, setting a reinforcing measure for the boundary beam and the additional plate, b, setting a reinforcing measure for the inclined support, and c, setting a reinforcing measure for the horizontal support. The combined foundation pit support construction method has the advantages that the boundary beam additional plates are arranged below the bearing platform and connected with the engineering piles to serve as an integral structure to provide support counterforce, combined support construction is achieved, support is safe and economical, arrangement is ingenious and flexible, lateral deformation of the foundation pit support is controlled, safety of surrounding roads and pipelines is protected, and construction efficiency is improved. The smooth excavation of the pit earthwork in the edge pit is ensured; and the construction period is shortened.

Description

Technical Field

[0001] The present invention belongs to the technical field of building construction, and specifically, it is a combined foundation pit support construction method. Background Art

[0002] After the on-site foundation pit support construction is completed, due to reasons such as design changes, situations such as adjacent pit-in-pit where the elevator foundation pit moves to the edge of the pit often occur. For example, when the large surface of the bottom plate is excavated to a depth of 6m and the adjacent pit-in-pit is excavated by another 2.4m, the original embedded depth of the support pile is insufficient, resulting in difficulties in excavating the adjacent pit-in-pit and problems such as the inability to carry out subsequent processes. The anchor cable support form usually does not have basic construction conditions due to objective situations such as existing municipal roads and pipelines around the site. After the foundation pit support construction is completed, due to changes and other reasons, adjacent pit-in-pit occurs, and problems such as the inability to carry out subsequent processes arise.

[0003] Therefore, there are various inconveniences and problems in the known working conditions where the original embedded depth of the support pile is insufficient due to design changes and other reasons. Summary of the Invention

[0004] The purpose of the present invention is to propose a safe and reliable combined foundation pit support construction method for the above problems in the prior art.

[0005] To achieve the above purpose, the technical solution of the present invention is: A combined foundation pit support construction method, in which a mixing pile water stop curtain is provided at the edge of the foundation pit in the foundation pit support structure, prestressed pipe piles are provided beside the mixing pile water stop curtain, C-shaped steel is provided beside the prestressed pipe piles, a side beam is provided below the bearing platform, the side beam is a construction edge-sealing concrete beam, and an additional plate is provided outside the edge-sealing concrete beam. The additional plate is a thickened reinforced concrete cushion layer, and it is characterized by including the following steps: a. Enhancement measures are set for the side beam and the additional plate, including the following steps: (1) Steel embedment plates matching the steel supports are buried at corresponding positions on the side of the side beam. The side beam, the additional plate, and the engineering piles are combined into an overall foundation pit support structure to provide a support reaction force. b. Enhancement measures are set for the inclined support, including the following steps: (1) At the top position of the foundation pit support structure, rib plates are added and fixedly welded to the I-beams of the support piles to form the first steel waist beam. After the side beam and the additional plate reach the required strength, a steel pipe strut with a diameter of Ф609×12 is installed as the inclined support. The setting distance between adjacent two inclined supports does not exceed 10m, and a preloading force of 1 ton is applied. (2) At the top position of the foundation pit support structure, rib plates are added and fixedly welded to the I-beams of the support piles to form the first steel waist beam. After the side beam and the additional plate reach the required strength, a steel pipe strut with a diameter of Ф609×12 is installed as the inclined support. The setting distance between adjacent two inclined supports does not exceed 10m, and a preloading force of 1 ton is applied. (3) For the first step of earth excavation of the edge pit and pit-in-pit, when the earth is excavated to a level where the horizontal support members have a construction working surface, at the corresponding positions, additional rib plates are fixedly welded to the I-beams of the retaining piles to form the second steel waist beam, and lattice steel struts with a size of 600×600 are installed as horizontal struts. Hanger bars are set for the second steel waist beam; (4) For the second step of earth excavation of the edge pit and pit-in-pit to the bottom elevation, the earth excavation and the construction of the inclined struts must be closely coordinated. Follow the principle of "support first, then excavate". The earth excavation machinery shall not collide with the inclined struts. When necessary, small excavators and manual labor shall be used for cooperation in excavation; (5) The cushion layer, brick formwork, waterproofing, and foundation construction shall be carried out in sequence according to the construction process. Outside the foundation areas of the cushion layer, brick formwork, waterproofing, and foundation, a concrete replacement support strip with a thickness of at least 200 mm and the same strength as the foundation is set to top the retaining piles. The retaining piles are I-beams for easy extraction after use; c. Enhancement measures for the horizontal strut setting, including the following steps: (1) In the plane layout of the horizontal struts, the inner edges of the lattice structures of the horizontal struts on both sides are exactly flush with the edge pit and pit-in-pit. An additional horizontal strut is added in the middle to ensure that the spacing of the horizontal struts does not exceed 8 m. The horizontal struts on both sides and the connected second steel waist beam are buried under or within the foundation and are not recovered; (2) After the concrete of the foundation and the replacement support strip between the retaining piles reaches the strength requirement, the recoverable parts of the steel pipe inclined struts are removed, and the first steel waist beam connected to the inclined struts is removed; (3) After the foundation pit is used up, the I-beams used as retaining piles are extracted.

[0006] The combined foundation pit retaining construction method of the present invention can also be further realized by adopting the following technical measures.

[0007] In the foregoing method, the cross-sectional height of the side beam shall be greater than the size of the steel embedment plate buried at the corresponding position on its side and matching the steel strut.

[0008] In the foregoing method, the additional plate is cast with concrete, the thickness of the additional plate is 300 mm, and double-layer and double-directional steel bars are arranged.

[0009] In the foregoing method, the plane layout of the inclined struts shall avoid the construction of shear walls or make local adjustments.

[0010] In the foregoing method, at the positions of the inclined struts and the first steel waist beam, steel pipe force-transfer bifurcations shall be added in construction. The first steel waist beam is a double-pin 40c I-beam.

[0011] In the foregoing method, the second steel waist beam is a triple-pin 40c I-beam, and the length of the second steel waist beam extends at least 2.5 m on each side based on the length of the edge pit and pit-in-pit.

[0012] In the foregoing method, the inclined struts are provided with water-stop steel plates, which are set at the bottom slab elevation before the bottom slab is poured, with the inside closed and the outside fully welded.

[0013] The foregoing method, wherein the inclined bracing can also be changed into a lattice inclined bracing so as to minimize the influence on the underground structure wallboard, and a water-stop steel plate is arranged on the bracing.

[0014] The foregoing method, wherein the soil body in the active earth pressure area at the slope top can be subjected to a 45-degree slope cutting and soil unloading treatment.

[0015] The foregoing method, wherein there are four groups of suspension bars, each group is provided with 2 steel bars with a diameter of 20 mm, the height of the suspension bars is 1.5 m - 2 m, and the distance between adjacent suspension bars is set not to exceed 5 m.

[0016] After adopting the above technical solution, the combined foundation pit support construction method of the present invention has the following advantages: 1. By arranging a side beam additional slab connection and engineering piles under the bearing platform to provide a support reaction force for the overall structure, constructing a steel waist beam, installing a steel pipe inclined bracing, applying a pre-top force, and installing a lattice horizontal bracing, the combined support construction has the remarkable features of safe and economic support and ingenious and flexible layout; 2. The inclined bracing makes full use of the counterpressure effect and effectively reduces the horizontal displacement of the top of the support pile; 3. Control the lateral deformation of the foundation pit support, protect the safety of the surrounding existing municipal roads and pipelines, keep the water-stop curtain intact, ensure the smooth excavation of the side pit in the pit and the normal construction of subsequent processes, and shorten the construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the combined support structure of an embodiment of the present invention; Figure 2 It is a plan view of the scope of the side beam additional slab of an embodiment of the present invention; Figure 3 It is a plan view of the inclined bracing layout of an embodiment of the present invention; Figure 4 It is a plan view of the horizontal bracing layout of an embodiment of the present invention; Figure 5 It is a schematic diagram of the combined erection of the horizontal bracing and the inclined bracing of an embodiment of the present invention; Figure 6 It is a plan view of the standard section of the steel waist beam lattice of an embodiment of the present invention.

[0018] Figure 7 is Figure 6 the cross-sectional view of 1-1 in DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The present invention will be further described in detail below in conjunction with the embodiments and their accompanying drawings.

[0020] Embodiment 1 Now please refer to Figures 1-7, for the combined foundation pit support construction method of the present invention, a mixing pile water-stop curtain 1, prestressed pipe piles 2, and C-shaped steel 3 are provided in the foundation pit support structure. A side beam 4 is provided below the bearing platform, and the side beam is a construction edge-sealing concrete beam. The additional slab 5 is a thickened reinforced concrete cushion, including the following steps: a. Setting the side beam and the additional slab, including the following steps: (1) Steel embedment plates matching the steel supports need to be buried at corresponding positions on the side of the side beam. The additional slab of the side beam and the engineering piles are combined as an integral structure to provide the bearing reaction force. (2) At the jacking position, additional rib plates are added and welded firmly to the I-beams of the support piles. The first steel waist beam 6 of double-pinned I40c is constructed. After the additional slab of the side beam reaches the strength, a steel pipe strut of Ф609×12, that is, an inclined strut 7, is installed. The spacing between the two inclined struts is arranged not to exceed 10m, and a pre-jacking force of 1 ton is applied. The cross-sectional height of the side beam should be greater than the size of the steel embedment plate buried at the corresponding position on its side and matching the steel support. The additional slab is cast with concrete, and the thickness of the additional slab is 300mm, with double-layer and double-directional steel bars. The plane layout of the inclined strut should avoid the construction of shear walls or make local adjustments.

[0021] b. Setting the horizontal strut, including the following steps: (1) For the first step of earth excavation in the adjacent pit-in-pit, when the earth excavation reaches the working surface where the horizontal support member can be constructed, additional rib plates are added and welded firmly to the I-beams of the support piles. The second steel waist beam 8 of triple-pinned I40c is constructed, and a lattice steel strut of 600×600 is installed as the horizontal strut 9. Among them, the second steel waist beam is provided with suspension bars 10. The suspension bars are arranged not to exceed 5m, with a total of four groups, and each group has 2 steel bars with a diameter of 20. The height of the suspension bars is 1.5m to 2m; at the positions of the inclined strut and the first steel waist beam, steel pipe force-transfer bifurcations 11 need to be added.

[0022] (2) For the second step of earth excavation in the adjacent pit-in-pit, the earth excavation reaches the bottom elevation. The earth excavation and the construction of the inclined strut must be closely coordinated, following the principle of "support first and then excavate". The earth excavation machinery shall not collide with the inclined strut. When necessary, a small excavator and manual labor are used for excavation in cooperation. (3) The cushion, brick formwork, waterproofing, foundation construction, etc. are carried out in sequence according to the construction process. A concrete replacement strut strip with the same strength and a thickness of at least 200mm is set outside the foundation in this area to top the support piles firmly. The support piles are I-beams so that they can be pulled out after use. c. Setting the horizontal strut, including the following steps: (1) For the plane layout of the horizontal strut, the inner edges of the lattice structures of the horizontal struts on both sides are exactly flush with the adjacent pit-in-pit. One more is added in the middle to ensure that the spacing does not exceed 8m. The horizontal struts on both sides and the second steel waist beam connected to them are buried under or inside the foundation and are not recovered; the second steel waist beam is triple-pinned I40c12, and the length of the steel waist beam is at least 2.5m extended on each side based on the length of the adjacent pit-in-pit.

[0023] (2) After the foundation and the concrete of the replacement support slab belt connecting to the retaining piles reach the strength requirements, remove the recyclable parts of the steel pipe inclined supports and the first steel girders connected to the inclined supports.

[0024] (3) After the foundation pit is used up, pull out the I-beams used as retaining piles. The inclined support is provided with a water-stop steel plate and is set at the bottom slab elevation before the bottom slab is poured. It is closed inside and fully welded outside. The inclined support can also be changed into a lattice-type inclined support to minimize the impact on the underground structure wall panels passing through, and at the same time, a water-stop steel plate is provided on the support. The soil in the active earth pressure area at the slope top can be treated by cutting the slope at a 45-degree angle to unload the soil.

[0025] The present invention has substantial features and significant technical progress. The combined foundation pit support construction method of the present invention, which is a combined foundation pit support construction method of adding an additional slab to the side beam, a horizontal support, and an inclined support, can solve the problems in the prior art that after the foundation pit support construction is completed, due to changes and other reasons, there are edge pit-in-pits (such as the large-area excavation depth of the bottom slab is 6m, and the edge pit-in-pit is excavated by another 2.4m), resulting in insufficient embedded depth of the original retaining piles, difficult excavation of the edge pit-in-pits, and inability to carry out subsequent processes. It specifically has the following advantages: By setting an additional slab under the bearing platform and connecting the engineering piles as an integral structure to provide the reaction force of the support, constructing the steel girders, installing the steel pipe inclined supports, applying the pre-top force, and installing the lattice horizontal supports, the combined support construction has the remarkable characteristics of safe and economical support and ingenious and flexible layout. The inclined support makes full use of the counter-pressure effect and effectively reduces the horizontal displacement of the top of the retaining piles.

[0026] The combined foundation pit support construction method of the additional slab of the side beam, the horizontal support and the inclined support of the present invention, compared with the cable anchor support, strictly controls the lateral deformation of the foundation pit support, protects the safety of the surrounding existing municipal roads and pipelines, and the integrity of the water-stop curtain, ensures the smooth excavation of the edge pit-in-pits and the normal construction of subsequent processes, shortens the construction period, and can be popularized for use in local foundation pit supports or in combination with other support methods.

[0027] The above embodiments are only for illustrating the present invention and not for limiting the present invention. Those skilled in the relevant technical fields can also make various transformations or changes without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also belong to the scope of the present invention and should be defined by each claim.

Claims

1. A combined foundation pit support construction method. In the foundation pit support structure, a mixing pile water-stop curtain (1) is provided at the edge of the foundation pit, prestressed pipe piles (2) are provided beside the mixing pile water-stop curtain, C-shaped steel (3) is provided beside the prestressed pipe piles, a side beam (4) is provided below the bearing platform, the side beam is a construction edge-sealing concrete beam, and an additional plate (5) is provided outside the edge-sealing concrete beam. The additional plate is a thickened reinforced concrete cushion layer, and the characteristics are as follows It includes the following steps: a. Reinforcement measures are set for the side beam and the additional plate, including the following steps: (1) Steel embedment plates matching the steel supports are buried at corresponding positions on the side of the side beam. The side beam, the additional plate, and the engineering piles are connected as an integral foundation pit support structure to provide the bearing reaction force. b. Reinforcement measures are set for the inclined support, including the following steps: (1) At the top position of the foundation pit support structure, additional rib plates are added and fixedly welded to the I-beams of the support piles to form the first steel waist beam (6). After the side beam and the additional plate reach the required strength, a steel pipe brace with a diameter of Ф609×12 is installed as the inclined support (7). The spacing between adjacent two inclined supports does not exceed 10 m, and a preloading force of 1 ton is applied. (2) When the first step of earth excavation in the adjacent pit-in-pit reaches the working surface for the horizontal support members, at the corresponding position, additional rib plates are added and fixedly welded to the I-beams of the support piles to form the second steel waist beam (8). A lattice steel brace with a size of 600×600 is installed as the horizontal support (9), and suspension bars (10) are set for the second steel waist beam. (3) When the second step of earth excavation in the adjacent pit-in-pit reaches the bottom elevation, the earth excavation and the construction of the inclined support must be closely coordinated, following the principle of "support first and then excavate". The earth excavation machinery shall not collide with the inclined support. When necessary, a small excavator and manual labor are used for cooperation in excavation. (4) The cushion layer, brick formwork, waterproofing, and foundation construction are carried out in sequence according to the construction process. A concrete replacement support strip with a thickness of at least 200 mm and the same strength as the foundation is set outside the foundation in the areas of the cushion layer, brick formwork, waterproofing, and foundation to top-reinforce the support piles. The support piles are I-beams for easy removal after use. c. Reinforcement measures are set for the horizontal support, including the following steps: (1) In the plane layout of the horizontal support, the inner edges of the lattice structures of the horizontal supports on both sides are exactly flush with the adjacent pit-in-pit. An additional horizontal support is added in the middle to ensure that the spacing of the horizontal supports does not exceed 8 m. The horizontal supports on both sides and the connected second steel waist beam are buried under or inside the foundation and are not recycled. (2) After the concrete of the foundation and the replacement support strip connecting to the support piles reaches the required strength, the recyclable parts of the steel pipe inclined supports are removed, and the first steel waist beam connected to the inclined support is removed. (3) After the foundation pit is no longer in use, the I-beams used as support piles are removed.

2. The combined foundation pit support construction method according to claim 1, characterized in that, The cross-sectional height of the side beam should be greater than the size of the steel embedment plate buried at the corresponding position on its side and matching the steel support.

3. The combined foundation pit support construction method according to claim 1, characterized in that The additional plate is cast with concrete, with a thickness of 300 mm and double-layer and double-directional steel bars.

4. The combined foundation pit support construction method according to claim 1, wherein The plane layout of the inclined support should avoid the construction of shear walls or make local adjustments.

5. The combined foundation pit support construction method according to claim 1, characterized in that, At the positions of the inclined support and the first steel waist beam, a steel pipe force transfer bifurcation (11) construction should be added. The first steel waist beam (6) is a double-spliced 40c I-beam.

6. The combined foundation pit support construction method according to claim 1, characterized in that, The second steel waist beam (8) is a triple-spliced 40c I-beam (12). The length of the second steel waist beam extends at least 2.5 m on each side based on the length of the adjacent pit-in-pit.

7. The combined foundation pit support construction method according to claim 1, characterized in that The inclined support is provided with a water-stop steel plate, which is set at the bottom plate elevation before the bottom plate is poured, with the inside closed and the outside fully welded.

8. The combined foundation pit support construction method according to claim 1, characterized in that, The inclined support can also be changed to a lattice-type inclined support to minimize the impact on the underground structure wall panel. At the same time, a water-stop steel plate is set on the support.

9. The combined foundation pit support construction method according to claim 1, characterized in that, The soil in the active earth pressure area at the slope top can be treated by cutting and unloading the soil at a 45-degree angle.

10. The combined foundation pit support construction method according to claim 1, characterized in that, The hanger bars (10) are provided in four groups, with 2 steel bars with a diameter of 20 mm in each group. The height of the hanger bars is 1.5 m - 2 m, and the spacing between adjacent hanger bars is set not to exceed 5 m.

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