A method for making a nested foundation pit

Abstract

The application discloses a method for manufacturing a nested foundation pit, which comprises the following steps: carrying out dewatering at a site where a nested foundation pit is to be manufactured until the dewatering meets preset requirements; excavating to form a rudiment of the nested foundation pit; surrounding a core area in the rudiment of the nested foundation pit into a cylinder by using a plate; lining a brick mold to a preset height on the inner side of the cylinder, drawing out the plate, and continuing to line the brick mold; and plastering around a slope formed by the brick mold. The method for manufacturing the nested foundation pit can avoid slope instability and collapse, improve the safety of foundation pit construction, speed up the construction progress on site, and save construction cost.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, and in particular relates to a method for constructing nested foundation pits. Background Technology

[0002] When excavating sump pits or elevator pits in deep foundation pits, the quality of the nested pit formation is crucial, especially in foundations with poor soil conditions requiring dewatering. Effective control of the slope stability of the nested pit is paramount. Currently, a common construction method is to densely deploy dewatering manifolds around the sump pit or elevator pit, and then excavate the pit using either natural slope or slope protection. Natural slope excavation involves the following steps: first, determining the slope gradient based on the excavation depth and soil conditions; second, marking the top and bottom lines of the slope; and finally, excavating the sump pit or elevator pit within the slope excavation line. During excavation, it is essential to continuously monitor the slope stability for any abnormalities, such as unusual noises, cracks, or water inrush. However, this method has limitations; it is prone to collapse when the soil conditions are poor, resulting in a relatively low safety factor. Slope protection includes the following steps: First, the slope protection design is carried out to determine the slope and protection method. Then, the slope is excavated in stages, with support first and then excavation. Each layer of soil is supported after excavation until the design elevation is reached. During this process, the foundation pit is monitored according to the testing requirements. This method has a relatively high safety factor, but the cost is high and the construction period is relatively long. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for constructing nested foundation pits, which can prevent slope instability and collapse, improve the safety of foundation pit construction, accelerate on-site construction progress, and save construction costs.

[0004] The present invention provides a method for manufacturing nested foundation pits, comprising:

[0005] Dewatering is carried out at the location of the nested foundation pit to be constructed until the dewatering meets the preset requirements;

[0006] The excavation forms the initial shape of nested foundation pits;

[0007] The core area within the prototype of the nested foundation pit is enclosed by plates to form a cylindrical body;

[0008] The inner side of the cylinder is lined with brick molds to a preset height, the plate is removed, and the brick molds are lined again.

[0009] Plaster is applied around the slope formed by the brick mold.

[0010] Preferably, in the above-mentioned method for constructing nested foundation pits, before dewatering the area where the nested foundation pits are to be constructed, the method further includes:

[0011] Dewatering was carried out on the outer part of the large foundation pit.

[0012] Preferably, the above-mentioned method for constructing nested foundation pits further includes:

[0013] Before pouring the bottom cushion layer, a dewatering pipe is reserved in the dewatering well for connection to the self-priming pump.

[0014] Preferably, in the above-mentioned method for manufacturing nested foundation pits, the step of enclosing the core area within the prototype of the nested foundation pit into a cylindrical structure using sheet metal includes:

[0015] In the rectangular area at the bottom of the prototype of the nested foundation pit, a cylindrical body is formed by using a plate with a height of 2.0m to 2.5m and a length that is 1.0m to 1.2m longer than the side length of the prototype of the nested foundation pit to be made, and each side protrudes at least 0.2m to 0.3m in the length direction.

[0016] Preferably, in the above-mentioned method for constructing nested foundation pits, after the cylindrical structure is formed using sheet metal, the method further includes:

[0017] The four sides of the cylinder are supported by steel pipes.

[0018] Preferably, in the above-mentioned method for constructing nested foundation pits, the step of lining the inner side of the cylinder with brick molds to a predetermined height includes:

[0019] A brick mold with a height of 0.45mm to 0.55mm and a thickness of 0.5m is laid at a horizontal distance of 0.12m to 0.16m from the cylinder body, followed by a stepped, retreating lining of a brick mold with a height of 0.25m to 0.35m and a thickness of 0.36m to 0.38m.

[0020] The gaps inside and outside the cylinder are filled with sand and gravel to make them dense. The brick mold is supported in the short direction with steel pipes, and the top support of the cylinder is removed.

[0021] Preferably, in the above-mentioned method for manufacturing nested foundation pits, the step of extracting the plate includes:

[0022] By tying steel wire ropes to the lifting lugs of the board, the board is lifted and moved horizontally to achieve recycling.

[0023] Preferably, in the above-mentioned method for constructing nested foundation pits, the step of continuing to line the brick mold includes:

[0024] The brick formwork has a lining thickness of 0.23m to 0.25m, and the maximum slope is controlled at 1:0.5. The collapsed parts of the slope are filled with sand and gravel or original soil to form a whole lining.

[0025] Preferably, in the above-mentioned method for constructing nested foundation pits, the plastering around the slope formed by the brick mold includes:

[0026] Apply plaster around the slope using plaster mortar mixed with waterproofing agent;

[0027] Clean the bottom of the initial nested pit and pour a fine stone concrete cushion layer with a thickness of 0.09m to 0.11m.

[0028] Preferably, in the above-mentioned method for manufacturing nested foundation pits, the plate material is a steel plate.

[0029] As described above, the method for constructing the nested foundation pit provided by the present invention includes: dewatering the area to be constructed until the dewatering meets preset requirements; excavating to form a preliminary shape of the nested foundation pit; using sheet metal to enclose the core area within the preliminary shape of the nested foundation pit into a cylindrical structure; lining the inner side of the cylindrical structure with brick molds to a preset height, removing the sheet metal, and continuing to line the brick molds; and plastering the slope formed by the brick molds. Therefore, it can prevent slope instability and collapse, improve the safety of foundation pit construction, accelerate on-site construction progress, and save construction costs. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 A schematic diagram illustrating an embodiment of a method for manufacturing a nested foundation pit provided by the present invention;

[0032] Figure 2 This is a top view of the tube after the sheet metal has been used to enclose it.

[0033] Figure 3 A schematic diagram of a nested foundation pit created using the method described in this application. Detailed Implementation

[0034] The core of this invention is to provide a method for constructing nested foundation pits, which can prevent slope instability and collapse, improve the safety of foundation pit construction, accelerate on-site construction progress, and save construction costs.

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] An example implementation of the method for fabricating a nested foundation pit provided by this invention. Figure 1 As shown, Figure 1 This is a schematic diagram illustrating an embodiment of a method for fabricating a nested foundation pit provided by the present invention. The method may include the following steps:

[0037] S1: Dewater the area where the nested foundation pit is to be constructed until the dewatering meets the preset requirements;

[0038] It should be noted that the nested foundation pit can be, but is not limited to, an elevator pit or a sump pit. Before dewatering the area to be constructed in the nested foundation pit, dewatering can also be carried out in the outer large foundation pit area. After the large-scale excavation and support of the foundation pit is completed, a stable external water pressure balance system is formed. On this basis, dewatering is carried out in the center of the nested foundation pit, and the water depth in the dewatering well is observed. The foundation pit is first excavated to the bottom elevation of the cushion layer, and then dewatering continues in the dewatering wells in the nested foundation pit. The water level changes in the dewatering wells are observed. This can locally increase the dewatering gradient, and the water level can be lowered to 500mm below the bottom of the nested foundation pit to meet the needs of the nested foundation pit excavation construction.

[0039] S2: Excavation forms the initial shape of nested foundation pits;

[0040] In other words, this step is to initially excavate and obtain the prototype of the nested foundation pit. First, observe the soil conditions and quicksand areas on the slope of the nested foundation pit. Generally, slope collapse will occur 2 to 3 days after the nested foundation pit is formed. During this period, a warning line should be set up to prevent unauthorized personnel from approaching, and the intermediate dewatering wells should continue to dewater.

[0041] S3: The core area within the initial shape of the nested foundation pit is enclosed by plates to form a cylindrical structure;

[0042] Specifically, after 2 to 3 days, the slope of the nested foundation pit will show local collapse. Multiple panels can be used to protect it, and steel pipes can be used to support the top of the four sides of the cylinder. Under the action of the collapsed soil, a stable cylinder is formed, reducing the flow of quicksand into the nested foundation pit. The water inside the nested foundation pit will not stop being dewatered to prevent the groundwater level from rising and causing a large-scale slope collapse.

[0043] S4: Line the inside of the cylinder with brick molds to the preset height, remove the plates, and continue lining with brick molds;

[0044] It should be noted that after the initial shape of the nested foundation pit is stabilized by the quicksand inside the shell using plate enclosure, the quicksand is cleaned up, and the bottom is filled with sand and gravel. After compaction, brick molds are built at a certain distance from the steel plate. First, brick molds of a preset height are built, and then they are built in a stepped manner. When the brick molds are built to the preset height, the gaps between the inside and outside of the plate can be filled with sand and gravel. The brick molds are supported in the short direction with steel pipes. Then the internal support of the plate is removed, completing the conversion from plate support to brick mold support system. Then the plate can be removed and the remaining brick molds can be continued to be lined.

[0045] S5: Apply plaster around the slope formed by the brick mold.

[0046] It should be noted that after the brick formwork of the nested foundation pit is completed, the slope surface is plastered to prevent water from seeping in. The bottom can also be cleaned and a 100mm thick C20 fine stone concrete cushion layer (mixed with 5% JX-Ⅱ waterproofing agent) is poured.

[0047] As can be seen from the above description, in the embodiments of the nested foundation pit construction method provided by the present invention, since the following steps are taken: dewatering is carried out at the location of the nested foundation pit to be constructed until the dewatering meets the preset requirements; excavation is carried out to form the prototype of the nested foundation pit; the core area within the prototype of the nested foundation pit is enclosed with plates to form a cylinder; brick molds are lined inside the cylinder to a preset height, the plates are removed, and brick molds are lined again; and plaster is applied around the slope formed by the brick molds, the slope instability and collapse can be avoided, the safety of foundation pit construction can be improved, the on-site construction progress can be accelerated, and the construction cost can be saved.

[0048] In a specific embodiment of the above-described method for constructing nested foundation pits, the following steps may also be included:

[0049] Before pouring the bottom cushion layer, a dewatering pipe is pre-installed in the dewatering well for connecting to the self-priming pump. In this case, the dewatering pipe is led out along the slope to the slope surface, connected to the self-priming pump, and dewatering continues. After the main structure is completed, the garage and foundation pit backfilling is finished, and the anti-buoyancy requirements are met, the self-priming pump dewatering is stopped. It should be noted that this scheme is applicable to the excavation of nested foundation pits in silty soil. If the soil quality is relatively good and the groundwater level is low, the central dewatering system may not be necessary. If the entire dewatering system is operating well, and the groundwater level at the bottom of the sump or elevator pit is low, the self-priming pump dewatering can be stopped in advance, but the self-priming pump must still be installed to prevent groundwater from surging up, dewatering from being delayed, and the nested foundation pit from becoming instable due to water immersion.

[0050] In another specific embodiment of the above-mentioned method for constructing nested foundation pits, the core area within the prototype of the nested foundation pit may be enclosed into a cylindrical body using sheet metal, which may include:

[0051] In the rectangular area at the bottom of the prototype nested foundation pit, a cylindrical structure is formed by using plates with a height of 2.0m to 2.5m and a length 1.0m to 1.2m longer than the side length of the prototype nested foundation pit, with each side protruding at least 0.2m to 0.3m in the length direction. Further, the preferred height of the plate is 2.0m, the length is 1.0m longer than the side length of the prototype nested foundation pit, and the protrusion is at least 0.2m. Figure 2 As shown, Figure 2 This is a top view of the tube after the panels are enclosed to form a cylinder, which facilitates staggered stability.

[0052] In this case, the length of the steel plate is 1m longer than each side of the rectangular base of the nested foundation pit, ensuring that 0.5m thick masonry can be built on each of the four sides of the core area. Of course, other sizes can be selected according to actual needs, and there are no restrictions here. Moreover, the aforementioned plate can preferably be a steel plate.

[0053] In another specific embodiment of the above-mentioned method for constructing nested foundation pits, lining the inner side of the cylinder with brick molds to a preset height may include the following steps:

[0054] A brick mold with a height of 0.45mm to 0.55mm and a thickness of 0.5m is laid at a horizontal distance of 0.12m to 0.16m from the cylinder. Then, a brick mold with a height of 0.25m to 0.35m and a thickness of 0.36m to 0.38m is laid in a stepped, retreating manner.

[0055] Fill the gaps inside and outside the cylinder with sand and gravel, use steel pipes to support the brick mold in the short direction, and remove the top support of the cylinder.

[0056] Furthermore, a brick mold with a height of 0.5mm and a thickness of 0.5m can be laid at a horizontal distance of 0.15m from the cylinder, followed by a stepped, retreating brick mold with a height of 0.30m and a thickness of 0.37m. Of course, adaptive adjustments can be made according to actual needs, and there are no restrictions here.

[0057] In a preferred embodiment of the above-mentioned method for fabricating nested foundation pits, the step of extracting the plate material may specifically include:

[0058] By attaching steel wire ropes to the lifting lugs of the steel plates, the plates are lifted, raised, and moved horizontally for recycling. Specifically, one end of a steel wire rope is fixed to the end of an excavator, and the other end is tied to the lifting lug of the steel plate. The excavator lifts the steel plate, raising one end slowly. Once the steel plate is vertically detached from the top of the nested pit, it is moved horizontally to the designated position. Then, the next steel plate is lifted, and so on, until each steel plate is moved to its designated position.

[0059] In another preferred embodiment of the above-mentioned method for constructing nested foundation pits, the step of continuing to line the brick mold may specifically include:

[0060] The brick formwork has a lining thickness of 0.23m to 0.25m, with the maximum slope controlled at 1:0.5. Collapsed areas on the slope are filled and compacted with sand, gravel, or undisturbed soil, forming a monolithic lining. Alternatively, a 0.24m thick brick formwork can be used, with collapsed areas filled and compacted with sand, gravel, or undisturbed soil, forming a monolithic lining to resist flowing sand and form a stable brick retaining wall. Adjustments can be made according to actual needs; there are no restrictions here.

[0061] In another preferred embodiment of the above-mentioned method for constructing nested foundation pits, plastering around the slope formed by the brick mold may include the following steps:

[0062] Apply plaster around the slope using plaster mortar mixed with waterproofing agent;

[0063] The bottom of the initial nested foundation pit is cleaned, and a fine aggregate concrete cushion layer with a thickness of 0.09m to 0.11m is poured. More specifically, the thickness of this fine aggregate concrete cushion layer can preferably be 0.10m. Furthermore, M10 special precast plastering mortar can be used, and 5% JX-Ⅰ waterproofing agent is added during the mixing of the plastering mortar to further enhance the waterproofing effect of the slope. The final nested foundation pit will look like... Figure 3 As shown, Figure 3 A schematic diagram of a nested foundation pit created using the method described in this application.

[0064] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for fabricating nested foundation pits, characterized in that, include: Dewatering is carried out at the location of the nested foundation pit to be constructed until the dewatering meets the preset requirements; The excavation forms the initial shape of nested foundation pits; The core area within the prototype of the nested foundation pit is enclosed by plates to form a cylindrical body; The inner side of the cylinder is lined with brick molds to a preset height, the plate is removed, and the brick molds are lined again. Plaster is applied around the slope formed by the brick mold; Before dewatering the area where the nested foundation pit is to be constructed, the process also includes: Dewatering was carried out on the outer part of the large foundation pit; Also includes: Before pouring the bottom cushion layer, a dewatering pipe for connecting to the self-priming pump is reserved in the dewatering well; The core area within the prototype of the nested foundation pit is enclosed by plates to form a cylindrical structure, including: In the rectangular area at the bottom of the prototype of the nested foundation pit, a cylindrical body is formed by using plates with a height of 2.0m to 2.5m and a length that is 1.0m to 1.2m longer than the side length of the prototype of the nested foundation pit to be constructed, and each side protrudes at least 0.2m to 0.3m in the length direction. After the cylindrical body is formed by enclosing it with sheet metal, it also includes: The four sides of the cylinder are supported by steel pipes. The step of lining the inner side of the cylinder with brick molds to a preset height includes: A brick mold with a height of 0.45m to 0.55m and a thickness of 0.5m is laid at a horizontal distance of 0.12m to 0.16m from the cylinder body, followed by a stepped, retreating lining of a brick mold with a height of 0.25m to 0.35m and a thickness of 0.36m to 0.38m. The gaps inside and outside the cylinder are filled with sand and gravel to make them dense. The brick mold is supported in the short direction with steel pipes, and the top support of the cylinder is removed.

2. The method for fabricating nested foundation pits according to claim 1, characterized in that, The step of extracting the plate includes: By tying steel wire ropes to the lifting lugs of the board, the board is lifted and moved horizontally to achieve recycling.

3. The method for fabricating nested foundation pits according to claim 2, characterized in that, The continued lining brick formwork includes: The brick formwork has a lining thickness of 0.23m to 0.25m, and the maximum slope is controlled at 1:0.

5. The collapsed parts of the slope are filled with sand and gravel or original soil to form a whole lining.

4. The method for fabricating nested foundation pits according to claim 3, characterized in that, The plastering around the slope formed by the brick mold includes: Apply plaster around the slope using plaster mortar mixed with waterproofing agent; Clean the bottom of the initial nested pit and pour a fine stone concrete cushion layer with a thickness of 0.09m to 0.11m.

5. The method for fabricating nested foundation pits according to claim 4, characterized in that, The material is a steel plate.

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