A foundation treatment method for setting a flywheel energy storage device in a collapsible loess area

Abstract

This invention belongs to the field of civil engineering technology in the field of flywheel energy storage in thermal power plants. It discloses a foundation treatment method for setting up flywheel energy storage devices in collapsible loess areas. The method involves excavating 2-3 meters downwards from the surface of the collapsible loess layer, then installing bored piles for the flywheel well on the surface after the first excavation. A second excavation is then carried out on the surface corresponding to the flywheel well, reaching the lower elevation of the flywheel well's bottom slab. The loose pile portion is then removed, and the flywheel well is installed above the bored piles. Backfill soil is used to the surface height after the first excavation, followed by a layer of lime-soil. A second backfill is then used to the ground floor level, and finally, a hardened ground surface is constructed. This invention features a short construction period, low engineering cost, and a foundation treatment scheme combining bored piles and lime-soil, making it particularly suitable for the characteristics of flywheel energy storage project structures.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering technology in the field of flywheel energy storage in thermal power plants, and also to the field of foundation treatment for building structures. Specifically, it relates to a foundation treatment method for setting up flywheel energy storage devices in collapsible loess areas. Background Technology

[0002] In the global journey towards low-carbon, sustainable energy development, energy storage technology has become a key support. Flywheel energy storage, as an advanced physical energy storage method, boasts numerous advantages such as high power density, rapid charging and discharging, long lifespan, and environmental friendliness, demonstrating enormous application potential in many fields, including power system peak shaving and valley filling, new energy grid integration, distributed energy microgrids, rail transit energy recovery, and uninterruptible power supplies (UPS). With continuous technological advancements, flywheel energy storage systems are gradually moving from theoretical research to large-scale engineering practice, and their market size is showing a steady growth trend.

[0003] Civil engineering, as the foundational element for the implementation of flywheel energy storage systems, directly impacts the safety, stability, and operational efficiency of the entire system. From geological surveys and environmental considerations during site selection and planning, to load-bearing capacity and vibration control in foundation design, to the optimization of building structure layout and space utilization, and the coordinated design of supporting facilities, every detail of civil engineering plays a decisive role in the long-term, reliable operation of the flywheel energy storage system. A well-designed civil engineering system can effectively reduce construction costs, shorten the construction period, and improve overall system efficiency; conversely, a poorly designed system may lead to safety hazards, operational failures, and even significant economic losses.

[0004] Therefore, conducting research on the civil engineering design of flywheel energy storage is of paramount practical significance. On the one hand, it helps to fill the current gaps in systematic research in the field of flywheel energy storage civil engineering, providing scientific and comprehensive theoretical guidance for subsequent engineering practices. On the other hand, it can promote the deep integration of flywheel energy storage technology and civil engineering, accelerate the implementation and promotion of flywheel energy storage projects, and thus provide strong support for energy transition, grid optimization, and sustainable development.

[0005] The primary task in selecting a flywheel energy storage site is to conduct a detailed investigation of the geographical and geological conditions. This is the cornerstone for ensuring the long-term stable operation of the flywheel energy storage system. Before site selection, it is essential to thoroughly study the local geological survey report to fully understand key information such as the stratigraphic structure, soil and rock properties, and groundwater level. Based on the "Code for Geotechnical Investigation" (GB 50021-2001), a scientific assessment of the site's stability and suitability must be conducted to ensure that the selected site can withstand the dynamic and static loads of the flywheel energy storage system during operation, avoiding equipment failures or safety accidents caused by foundation settlement, uneven deformation, and other problems. The foundation treatment method is particularly important for collapsible loess areas.

[0006] The main collapsible soil layer at the proposed plant site is layer ②, a loess-like silt. This layer is distributed on the upper part of the foundation soil and is approximately 40m thick. Collapsibility was calculated using a correction factor obtained from field immersion tests. According to Table 4.4.7 of the "Code for Construction in Collapsible Loess Areas" (GB50025-2004), the plant site is classified as a self-weight collapsible loess site, with a foundation collapse level ranging from II (moderate) to VI (very severe), predominantly VI (very severe). The lower limit of collapse is the bottom of layer ② and the top surface of layer ③, the gravel layer.

[0007] The characteristics of flywheel energy storage structures are as follows: flywheel wells have large loads and deep burial depths, with the foundation bottom elevation ranging from 5 to 7.8 meters. Flywheel wells have very high requirements for settlement and tilt. Transformer prefabricated cabin foundations and flywheel cooling system foundations have smaller loads and shallower burial depths; the foundation bottom elevation only needs to be above the frost line, generally around -1 to 2 meters. Equipment foundations and flywheel cooling systems have very low requirements for settlement and tilt. Flywheel energy storage projects in thermal power plants are generally new projects implemented later, with fewer suitable sites available. They also need to be close to the main plant to avoid reducing cable lead lengths and lowering project investment. Therefore, the available site locations are limited, the site dimensions are small, and existing surrounding buildings have significant impacts. According to the "Code for Building Construction in Collapsible Loess Areas," the planar treatment scope of collapsible loess foundations should comply with the following regulations: 1. When the treatment is localized, the treatment area should be larger than the area of ​​the foundation bottom surface. In non-collapseable loess sites, each side should exceed 1 / 4 of the foundation bottom surface width, and should not be less than 0.50m; in collapsible loess sites, each side should exceed 3 / 4 of the foundation bottom surface width, and should not be less than 1m.

[0008] 2. When treating a whole area, the treatment area should be larger than the area of ​​the building's ground floor plan, extend beyond the outer edge of the building's exterior wall foundation, and each side should not be less than 1 / 2 of the thickness of the treated soil layer, and should not be less than 2m.

[0009] According to the "Code for Building Construction in Collapsible Loess Areas", the commonly used treatment methods for collapsible loess foundations are: cushion layer method, dynamic compaction method, compaction method, and pre-soaking method. The thickness of the treated soil layer on each side should not be less than 1 / 2 of the thickness, which is 20m. However, the renovation project has many surrounding buildings and structures, making such a large area unsuitable for implementation. Summary of the Invention

[0010] To address the problems existing in the prior art, the present invention aims to provide a foundation treatment method for setting up flywheel energy storage devices in collapsible loess areas. The present invention has a short construction period and low engineering cost, and adopts a foundation treatment scheme of bored piles and 3:7 lime-soil combination, which is particularly suitable for the characteristics of flywheel energy storage project structures.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for foundation treatment of flywheel energy storage devices in collapsible loess areas includes the following process: The first excavation begins on the surface of the collapsible loess layer, to a depth of 2-3 meters. Then, bored piles for the flywheel well are installed on the surface after the first excavation. After the bored piles are completed, a second excavation is carried out on the corresponding area of ​​the flywheel well, extending to the lower elevation of the flywheel well's bottom slab. The loose pile portion is then removed, and the flywheel well is installed above the bored piles. After the flywheel well is completed, backfill is performed for the first time, to the surface level of the first excavation. A layer of lime-soil is then applied to the surface after the first excavation, followed by a second backfill to the bottom elevation of the ground surface. Finally, the hardened ground surface is constructed.

[0012] Preferably, the height of the flywheel well does not exceed 7.5m, and the height of the flywheel well protruding from the hardened ground does not exceed 300mm.

[0013] Preferably, the thickness of the lime-soil layer is 1~2m.

[0014] Preferably, the height of the lime-soil layer from the surface of the collapsible loess layer is 2-3m.

[0015] Preferably, the lime-soil layer uses a 3:7 lime-soil ratio.

[0016] Preferably, the bored cast-in-place pile is deeply embedded in the bottom of the collapsible loess layer, and extends into the bottom of the collapsible loess layer by a length not less than one pile diameter.

[0017] Preferably, after the lime-soil layer is completed, the foundation of the flywheel transformer prefabricated cabin and the foundation of the flywheel cooling system are constructed on the surface of the lime-soil layer, and then the lime-soil layer is backfilled a second time.

[0018] Preferably, when carrying out the first and second backfilling, the backfill soil is required to be compacted in layers, with a layer thickness of no more than 300mm, a compaction coefficient of no less than 0.96, and a bearing capacity characteristic value of no less than 180kPa.

[0019] Preferably, the backfill soil is plain soil with an organic matter content of no more than 5%.

[0020] The present invention also provides a foundation for setting up a flywheel energy storage device in a collapsible loess area, obtained by the foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area described above.

[0021] This invention patent has the following beneficial effects: This invention patent discloses a foundation treatment method for setting up flywheel energy storage devices in collapsible loess areas. Compared with the commonly used treatment methods for collapsible loess foundations in the "Building Code for Collapsible Loess Areas," this method reduces the thickness and range of the treated soil layer, making it more suitable for similar renovation projects with limited site space. It features lower construction costs and a shorter construction period. This method reduces the impact of dynamic compaction on the operating unit and significantly saves construction time, meeting the tight schedule requirements of renovation projects. Compared with the conventional method of hammer-driven pipe-drived compacted soil pile foundation, it can save approximately 200,000 yuan in construction costs and more than 10 days of construction time. The original excavation depth of the flywheel well exceeded 5 meters, falling within the scope of a high-risk sub-project exceeding a certain scale. Therefore, a specialized design by a qualified construction unit and expert review were required. The first large-scale excavation reached the bottom of the 3:7 lime-soil mixture, followed by a second localized excavation to the bottom of the flywheel well. Both excavation depths did not exceed 5 meters, thus eliminating the need for specialized design and expert review. This invention patent discloses a foundation treatment method for setting up flywheel energy storage devices in collapsible loess areas. This method can be applied in multiple flywheel energy storage projects to achieve significant economic and social benefits. Attached Figure Description

[0022] Figure 1 This is a plan view of the foundation for a flywheel energy storage device installed in a collapsible loess area according to an embodiment of the present invention; Figure 2 This is an elevation view of the foundation for a flywheel energy storage device installed in a collapsible loess area, according to an embodiment of the present invention.

[0023] Among them, 1 is the flywheel well, 2 is the collapsible loess layer, 3 is the bored pile, 4 is the lime-soil layer, 5 is the backfill soil, 6 is the hardened ground, 7 is the flywheel transformer prefabricated cabin foundation, and 8 is the flywheel cooling system foundation. Detailed Implementation

[0024] 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.

[0025] Combination Figure 1 and Figure 2 The ground treatment method for setting up a flywheel energy storage device in a collapsible loess area in this embodiment includes the following process: The first excavation begins from the surface of the collapsible loess layer 2, extending downwards to a depth of 2-3 meters. The bottom of this initial excavation will be the subsequent layer of lime-soil 4 (see...). Figure 2The bottom of the first excavation was not more than 5m deep; then, bored piles 3 for the flywheel well 1 were installed downwards on the surface after the first excavation. After the bored piles 3 were installed, the surface after the first excavation (i.e., the bottom of the flywheel well 1) was excavated. Figure 2 The bottom of the shown lime-soil layer 4) and the area corresponding to the flywheel well 1 were excavated a second time downwards. The second excavation reached the lower elevation of the bottom plate of the flywheel well 1, so the depth of the second excavation did not exceed 5m; then the virtual pile part (i.e. Figure 2 In the previous steps, the portion of the bored pile 3 located between the bottom plate of the flywheel well 1 and the bottom of the lime-soil layer 4 is constructed. Then, the flywheel well 1 is constructed on top of the bored pile 3 (at this point, the virtual pile portion has been removed). After the flywheel well 1 is constructed, the first backfill is carried out with backfill soil, and the first backfill is carried out to the surface height after the first excavation (i.e., backfill to). Figure 2 The bottom of the ash layer 4 shown, that is Figure 2 The backfill soil 5 shown in the diagram is located at the bottom. Then, a layer of lime-soil 4 is applied to the surface after the first excavation (including the surface after the first backfill). After that, a second backfill is carried out on the lime-soil layer 4 (i.e., backfilling to the bottom). Figure 2 The portion between the top of the ash layer 4 and the hardened floor 6 shown, that is... Figure 2 The backfill soil 5 shown in the figure is backfilled a second time to the bottom elevation of the ground, and then the hardened ground 6 is implemented.

[0026] The above-described solution of this invention applies to flywheel wells 1 with a height not exceeding 7.5m. After final construction, the height of flywheel well 1 protruding above the hardened ground 6 does not exceed 300mm. In the above-described solution of this invention, the thickness of the lime-soil layer 4 is 1-2m. The height of the lime-soil layer 4 from the surface of the collapsible loess layer 2 is 2-3m. That is to say, when the thickness of the lime-soil layer 4 is 2m, the thickness of the secondary backfill layer above the lime-soil layer 4 is 0-1m. When the thickness of the secondary backfill layer is 0m, the hardened ground 6 can be directly implemented on the surface of the lime-soil layer 4 without the need for backfilling.

[0027] In a preferred embodiment of the present invention, the lime-soil layer 4 is a 3:7 lime-soil mixture. The bored pile 3 penetrates to the bottom of the collapsible loess layer 2, extending into the bottom of the collapsible loess layer 2 by a length not less than one pile diameter. After the lime-soil layer 4 is completed, the flywheel transformer prefabricated cabin foundation 7 and the flywheel cooling system foundation 8 are constructed on the surface of the lime-soil layer 4, followed by a second backfilling of the lime-soil layer 4.

[0028] In the above-described scheme of this invention, the backfill soil is plain soil with an organic matter content not exceeding 5%. During the first and second backfilling processes, the backfill soil is required to be compacted in layers, with each layer no thicker than 300mm, a compaction coefficient no less than 0.96, and a bearing capacity characteristic value no less than 180kPa. After the above process, the uniformity and density of the backfill soil are guaranteed. If the backfill is too thick at once, the lower layers may not be sufficiently compacted, leading to uneven settlement. Layered treatment ensures that the density of each layer meets the standard, reduces voids, and improves overall stability. Layered compaction also effectively improves bearing capacity, prevents post-construction settlement, and avoids structural cracking. Simultaneously, good compaction reduces water seepage and improves impermeability. Furthermore, layered construction reduces the load on mechanical equipment, avoiding equipment inefficiency or damage caused by excessively thick soil layers.

[0029] Example In this embodiment, the height of the flywheel well 1 is 7.5m. After the final construction is completed, the height of the flywheel well 1 exposed above the hardened ground 6 is 300mm. The lime-soil layer 4 adopts a 3:7 lime-soil ratio and has a thickness of 1.5m.

[0030] like Figure 1 and Figure 2 As shown in this embodiment, a foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area includes the following process: First, the entire collapsible loess layer area was mechanically excavated on a large scale for the first time to the extent that... Figure 2 The shown is lime-soil layer 4 (at this point, lime-soil layer 4 has not yet been implemented; this description needs to be combined with other information). Figure 2 (This is intended to illustrate the depth of the first large-area mechanical excavation.) In this embodiment, the depth of the first large-area mechanical excavation is 2.5m.

[0031] Secondly, bored piles 3 are installed at the bottom plane of the first excavation well 1, with the top elevation of bored pile 3 controlled at the bottom of the well 1. The pile position of the well 1 is determined, and the drilling equipment, once in place, should be level and stable to prevent tilting or movement during construction. The drilling equipment should have clear control scales for drilling depth to ensure the verticality of the hole meets design requirements. During the fabrication, transportation, and hoisting of the reinforcing cage (whether as a whole or in sections), measures should be taken to prevent overall deformation and twisting. The reinforcing cage should be slowly lowered to the center of the pile hole, and immediately fixed upon reaching the design position, with the upper edge of the cage securely fixed to the borehole casing. After the reinforcing cage is in place, concrete must be poured continuously and promptly, controlling the pouring speed to prevent pile breakage or diameter reduction. Finally, the bored pile 3 is implemented.

[0032] Next, after the bored piles 3 are completed, the area corresponding to the flywheel well 1 is excavated with a slope (i.e., a second excavation) to the lower elevation of the flywheel well 1 bottom plate. In this embodiment, the depth of the second excavation is 4.5m (less than 5m). At this time, part of the bored piles 3 that have been implemented is above the lower elevation of the flywheel well 1 bottom plate. Therefore, it is necessary to remove the dummy pile part (that is, remove the part of the bored piles 3 that is above the lower elevation of the flywheel well 1 bottom plate) and conduct dynamic testing to verify the vertical compressive bearing capacity and the integrity of the pile body.

[0033] Then, the reinforcing bars were tied, formwork was erected, and reinforced concrete base slabs and sidewalls were poured to construct flywheel well 1. After flywheel well 1 was completed, the formwork was further removed, and the foundation pit was backfilled to -2.5m (i.e., the first backfilling was carried out here). Next, the leveled area was replaced with 3:7 lime-soil to the bottom of the flywheel transformer prefabricated cabin foundation 7 and the flywheel cooling system foundation 8 (i.e., lime-soil layer 4 was constructed, with a thickness of 1.5m). Then, the equipment foundations such as the flywheel transformer prefabricated cabin foundation 7 and the flywheel cooling system foundation 8 were further constructed. Finally, plain soil was backfilled (i.e., the second backfilling was carried out, with a backfill depth of 1.0m) to the bottom elevation of the hardened ground. During the first and second backfilling, the backfill soil was required to be compacted in layers, with a layer thickness not exceeding 300mm, a compaction coefficient ≥0.96, and a bearing capacity characteristic value ≥180kPa. The organic matter content of the backfill soil shall not exceed 5%, and the backfill soil shall not be mixed with construction waste, cultivated soil, silty soil or soil containing chemical corrosive substances.

[0034] Finally, a 200mm thick C30 concrete floor was constructed to harden the floor.

[0035] Special attention should be paid to the following during implementation: when constructing the foundation, the construction unit should take effective measures to reduce the heat of hydration to ensure that the equipment foundation and related concrete structures do not crack. An epoxy asphalt coating with a thickness of ≥300μm should be applied to the concrete surface in contact with the soil.

[0036] The 3:7 lime-soil mixture used in the above-mentioned scheme of this invention, also known as 3:7 lime-soil, is a high-strength building material made by mixing lime and clay in a volume ratio of 3:7. This invention utilizes 3:7 lime-soil due to its low cost: both lime and clay are common materials, cheaper than cement. Furthermore, 3:7 lime-soil exhibits good impermeability: the reaction between lime and soil forms a dense calcium silicate gel, which acts as a dense waterproof layer, providing waterproofing and moisture protection. It also has low compressibility, resulting in good load-bearing capacity after compaction. At its optimal moisture content (18%-22%), the dry density reaches 1.6-1.7 g / cm³. Its load-bearing capacity is also good, with a 28-day unconfined compressive strength ≥0.8 MPa, equivalent to the strength of C15 concrete. Environmentally, lime is a natural material, more environmentally friendly than industrial materials. Construction is also flexible, allowing for on-site mixing or plant mixing to meet different project needs. In addition, it has low maintenance costs, good durability, and long-term stability.

[0037] As can be seen from the above-described scheme of this invention, the foundation treatment scheme of the present invention, which combines bored piles 3 and 3:7 lime-soil (i.e., lime-soil layer 4), further supplements the commonly used foundation treatment methods in collapsible loess areas in the "Code for Building Construction in Collapsible Loess Areas": cushion layer method, dynamic compaction method, compaction method, and pre-soaking method. The foundation treatment scheme of the present invention, which combines bored piles 3 and 3:7 lime-soil (i.e., lime-soil layer 4), is particularly suitable for the characteristics of flywheel energy storage project structures. Another feature of the technical solution of this invention is that the flywheel well 1, which has a large load in the collapsible loess layer 2 area, adopts the foundation treatment method of bored piles 3. The present invention adopts the foundation treatment method of 3:7 lime-soil replacement for the flywheel transformer prefabricated cabin foundation 7 and flywheel cooling system foundation 8, which have a smaller load in the collapsible loess layer 2 area. In existing technology, the original excavation depth of flywheel well 1 exceeded 5m, which falls within the scope of a relatively large-scale and dangerous sub-project. Therefore, it requires specialized design by a qualified construction unit and expert review. However, in this invention, the first large-area excavation reaches the bottom of the 3:7 lime-soil layer (i.e., lime-soil layer 4) at a depth of 2.5m, followed by a second partial excavation to the bottom of flywheel well 1 at a depth of 4.5m. Both excavation depths do not exceed 5m, thus eliminating the need for specialized design and expert review. In the above-mentioned scheme of this invention, the 3:7 lime-soil layer is placed on top of the collapsible loess layer 2, and its thickness meets the specifications.

[0038] In summary, the above-mentioned solution of the present invention effectively overcomes the shortcomings of commonly used treatment methods for collapsible loess foundations in the prior art.

[0039] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for foundation treatment of a flywheel energy storage device in a collapsible loess area, characterized in that, The process includes the following: The first excavation is carried out from the surface of the collapsible loess layer (2) to a depth of 2-3m. Then, the bored pile (3) of the flywheel well (1) is installed on the surface after the first excavation. After the bored pile (3) is installed, the second excavation is carried out on the surface after the first excavation and the area corresponding to the flywheel well (1) to the bottom elevation of the flywheel well (1). Then, the dummy pile is removed and the flywheel well (1) is installed on the top of the bored pile (3). After the flywheel well (1) is installed, the first backfill is carried out with backfill soil to the surface height after the first excavation. Then, the lime-soil layer (4) is installed on the surface after the first excavation. Then, the second backfill is carried out on the lime-soil layer (4) to the bottom elevation of the ground. Then, the hardened ground (6) is installed. The height of the flywheel well (1) shall not exceed 7.5m, and the height of the flywheel well (1) protruding from the hardened ground (6) shall not exceed 300mm; The thickness of the lime-soil layer (4) is 1~2m; The height of the lime soil layer (4) from the surface of the collapsible loess layer (2) is 2~3m.

2. The foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area according to claim 1, characterized in that, The lime-soil layer (4) uses a 3:7 lime-soil ratio.

3. The foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area according to claim 1, characterized in that, The bored pile (3) penetrates to the bottom of the collapsible loess layer (2) and extends into the bottom of the collapsible loess layer (2) for a length not less than 1 times the pile diameter.

4. The foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area according to claim 1, characterized in that, After the implementation of the lime-soil layer (4), the flywheel transformer prefabricated cabin foundation (7) and the flywheel cooling system foundation (8) are implemented on the surface of the lime-soil layer (4), and then the lime-soil layer (4) is backfilled for the second time.

5. The foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area according to claim 1, characterized in that, When carrying out the first and second backfilling, the backfill soil must be compacted in layers, with a layer thickness of no more than 300mm, a compaction coefficient of no less than 0.96, and a bearing capacity characteristic value of no less than 180kPa.

6. The foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area according to claim 1, characterized in that, The backfill soil is plain soil, and the organic matter content in the plain soil does not exceed 5%.

7. A foundation for setting up a flywheel energy storage device in a collapsible loess area, obtained by the foundation treatment method for setting up a flywheel energy storage device in a collapsible loess area as described in any one of claims 1-6.

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