Green low-carbon foundation reconstruction technology and construction method on old pile site

Abstract

The invention relates to a green low-carbon foundation reconstruction technology on an old pile site and a construction method. The green low-carbon foundation reconstruction technology comprises the following steps that old piles which need to be pulled out and old piles which can be recycled are determined through pile foundation detection; in combination with the characteristics of a stratum and a pile foundation, an optimal pile foundation pulling-out technology is selected to pull out an old pile; mgO-based carbon sequestration soil is adopted for backfilling of the pull-out holes, and a large amount of CO2 is injected through a spiral breather pipe to conduct carbonization reinforcement on a backfilled body; according to the pile foundation configuration principle and the load distribution condition of the upper layer structure, the position of a new pile is determined, and the foundation reinforcing effect of a backfill body is fully exerted; site surface soil is cleaned, and new and old pile heads are cleaned; and finally, a cushion layer and a raft are constructed and poured, and foundation construction is completed. According to the construction method, old piles are reused, the number of driven new piles can be reduced, the foundation manufacturing cost is saved, the construction period is shortened, resource waste caused by pulling out the old piles is avoided, the influence on the environment is reduced, and the positive effects of absorbing industrial solid waste, storing CO2 and improving and reinforcing a soil body are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of pile foundation engineering, and relates to a green and low-carbon foundation reconstruction technology and a construction method on an old pile site. Technical Background

[0002] The existence of old pile foundations not only affects the construction of new building pile foundations, shield tunnels, underground pipe networks and other projects, but also has an adverse impact on the construction of foundation pit support and water-stop curtains. Therefore, the treatment of old piles is crucial to the development of urban underground space.

[0003] In the process of urban renewal, old piles in good condition can be recycled to reduce resource waste, while piles that do not meet the design requirements of new buildings need to be removed. The backfilling of the holes after removal is complicated, and in the case where part of the old piles are used and part are removed and backfilled, new piles need to be installed due to the large load of the new building. This involves not only the removal technology of old piles, but also the backfill reinforcement technology of the removed holes, as well as the collaborative working mechanism of new and old piles.

[0004] Conventional pile foundation removal hole backfilling methods include backfilling with poured plain concrete or mixing fluid cement soil, or backfilling and compacting with lime soil, graded sand and gravel, or plain soil with good compaction properties in layers. Each method has its own applicable conditions and limitations. In the prior art, the backfilling of old pile removal holes mostly uses cement-based materials, which have problems such as high carbon emissions and waste of resources. The increase in the price of building materials such as cement, on the one hand, leads to an increase in the cost of cement soil, and on the other hand, cement will produce waste gas pollution such as dust and smoke during the production and use of cement, and is accompanied by a large amount of greenhouse gas CO 2 emissions, causing air pollution. The use of dynamic tamping method for construction also generates vibration and noise, which affects surrounding buildings and underground pipelines, and interferes with the lives of surrounding residents. In the process of coordinated configuration of new and old piles, the lack of systematicity in the coordinated design of new and old piles is prone to occur, resulting in insufficient integrity of the foundation. It also involves many challenges such as bearing capacity matching problems, settlement differences, and soil disturbance problems. The collaborative work of new and old piles increases the complexity of the design and also puts higher requirements on construction technology. In view of the above problems, it is urgent to propose a green and low-carbon foundation reconstruction technology and construction method on the old pile site, which can improve the safety and stability of the foundation while bringing economic and environmental benefits. The present invention combines the treatment of old piles, green backfilling, coordinated supplementary driving of new piles and overall structural reconstruction through a reconstruction technology system to achieve the dual goals of low carbonization and improvement of foundation performance. Summary of the invention

[0005] The purpose of the present invention is to provide a green and low-carbon foundation reconstruction technology and construction method on an old pile site, so as to solve the limitations of the conventional pile foundation extraction hole backfilling method mentioned in the technical background and the problem of coordinated configuration of new and old pile foundations.

[0006] The "reengineering" technology described in the present invention includes four core links:

[0007] 1. Classification of old piles: through testing and screening, old piles that can be reused and old piles that need to be removed are selected;

[0008] 2. Green backfill of extraction holes: using MgO-based carbon-fixed soil combined with CO 2 Carbonization reinforcement, CO storage 2 and improve soil strength;

[0009] 3. Coordinated configuration of new and old piles: Optimize the location of new piles based on load distribution to match the bearing capacity and settlement characteristics of new and old piles;

[0010] 4. Overall structural reconstruction: Through the construction of cushion layer and raft slab, a composite foundation form is formed in which the new and old piles and backfill body are subjected to the force synergistically.

[0011] The purpose of the present invention can be achieved by the following technical solutions:

[0012] The present invention provides a green and low-carbon foundation reconstruction technology and construction method on an old pile site, comprising the following steps:

[0013] S1. Obtain the pile foundation design drawings of the target area, determine the initial design scheme of the pile foundation in the target area (pile foundation type, number of piles, pile diameter, pile length, etc.) according to the previous drawing data, and form an overall reconstruction technology framework for the old pile site;

[0014] S2. Comprehensively inspect and evaluate the existing pile foundations in the target area to determine the old piles that need to be removed and those that can be reused;

[0015] S3. Remove old piles in the target area that do not meet the design bearing capacity requirements of new buildings;

[0016] S4. Use MgO-based carbon-fixing soil to backfill the old pile removal hole in situ. MgO-based carbon-fixing soil can be prepared by mixing solidifying materials MgO, industrial solid waste, cement and soil, etc., combined with CO 2 Carbonization reinforcement forms a green and low-carbon extraction hole backfill technology;

[0017] S5. Arrange ventilation pipe to inject high-pressure CO 2 The gas carbonizes and consolidates the MgO-based carbon soil;

[0018] S6. According to the load distribution of the superstructure, the location of the new piles is determined based on the collaborative working mechanism of the new and old piles to achieve the overall reconstruction of the foundation form;

[0019] S7. Clean the surface soil and new and old pile heads of the site;

[0020] S8. Construct the cushion layer, construct and pour the raft slab, and complete the foundation construction.

[0021] Furthermore, the construction method for removing the old piles can be selected from any one of the three methods: direct removal method, full-rotation pile removal method, and crushing and demolition method, depending on the conditions of the stratum and pile foundation.

[0022] Furthermore, the MgO-based carbon-fixing soil used is a carbon-fixing soil prepared by mixing components including solidifying material MgO, industrial solid waste, a small amount of cement and soil. The MgO carbon-fixing soil of the present invention has the effect of improving the strength of the soil, reducing the water content and porosity in the soil, and can also absorb a large amount of CO 2 The gas is then solidified in the soil, improving and strengthening the soil.

[0023] Furthermore, the CO 2 The length of the ventilation pipe is not less than the depth of the old pile removal hole.

[0024] Furthermore, the CO 2 The arrangement of the ventilation pipe in the old pile extraction hole is selected from any of the three forms: arrangement along the center of the extraction hole, arrangement along the inner wall of the extraction hole, or arrangement along the inner wall of the extraction hole in a vertical spiral direction, which is used to ensure that the required CO 2 Under ventilation pressure, ensure that the backfill body is fully carbonized and reinforced to prevent problems such as insufficient strength due to incomplete carbonization.

[0025] Furthermore, in the CO 2 The ventilation pipe is provided with multiple equidistant air outlet holes to ensure that the backfill bodies at different depths can fully contact the CO. 2 Gas undergoes carbonization reaction to prevent uneven carbonization of the backfill body from causing uneven pile strength.

[0026] Furthermore, when the ventilation pipe is arranged vertically along the inner wall of the extraction hole, the spiral spacing is 0.5 to 1.0 meters to ensure CO 2 The gas diffuses evenly over the entire cross section of the backfill body.

[0027] Furthermore, the industrial solid waste accounts for 30% to 50% of the MgO-based carbon-fixing soil, and the cement content does not exceed 5%. Through the synergistic effect of MgO and industrial solid waste, CO 2 Solidification and sealing and improvement of soil strength.

[0028] Furthermore, the amount of MgO in the backfill solid is controlled at 15% to 30%, CO 2The injection pressure is controlled at 0.5-1.5MPa, the ventilation flow rate is 10-20L / min, and the carbonization consolidation time is recommended to be no less than 12 hours. In addition, the carbonization reaction is to fully hydrate MgO to Mg(OH) 2 As a prerequisite, when CO is introduced 2 Before the gas is released, it is necessary to ensure that most of the MgO has been hydrated. MgO hydration process and Mg(OH) 2 Absorbing CO 2 The processes are all exothermic reactions. Therefore, by monitoring the temperature changes during the hydration process, it is possible to effectively determine whether the hydration process is completed. At the same time, the reaction conditions of the entire carbonization process can be monitored by monitoring the temperature changes of the backfill body.

[0029] Furthermore, by following the pile foundation configuration principles, the foundation reinforcement effect of the backfill reinforcement body can be fully utilized to achieve the matching of the bearing capacity of the new and old pile foundations, ensure the consistency of the settlement behavior of the new and old pile foundations, reduce the disturbance of the surrounding soil that may be caused by the construction of new piles, and improve economic and environmental benefits.

[0030] Furthermore, when setting the cushion layer, the pile head may be connected to the raft slab through the cushion layer or may not be connected to the raft slab according to the actual construction conditions.

[0031] Furthermore, the cushion layer is recommended to be made of medium-coarse sand or cement soil, and the thickness range is recommended to be between 1.5 meters and 3 meters.

[0032] Furthermore, the foundation reconstruction technology includes: green backfilling of old pile removal holes, reuse of old piles, coordinated driving of new piles, and integrated casting of cushion layer and raft slab, forming a new composite foundation form that is different from the original site foundation structure.

[0033] Compared with the prior art, the advantages of the present invention are as follows:

[0034] 1. MgO-based materials are hydrated to generate Mg(OH) 2 After that, with CO 2 Carbonization reaction occurs, converting gaseous CO 2 Converted into stable magnesium carbonate to achieve carbon sequestration and realize CO 2 Solidification and emission reduction benefits. MgCO 3 Crystals fill the pores in the soil, reduce the porosity and increase the density; at the same time, the cementitious material generated by the carbonization reaction enhances the compressive strength of the soil.

[0035] 2. During the construction process according to the present invention, the reusable old piles can be screened through pile foundation detection, and combined with the bearing capacity matching theory, the load distribution of new and old piles can be balanced, the reuse rate of old piles can be improved, the comprehensive cost of the project can be reduced, and the construction period can be shortened.

[0036] 3. The present invention utilizes solid waste as resources, reduces construction waste, and achieves green construction and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a front view of the combined foundation construction technology in an embodiment of the present invention;

[0038] Figure 2 is a top view of the combined foundation construction technology in an embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the backfilling and solid carbonization process in the present invention;

[0040] Figure 4 It is a construction flow chart of the present invention;

[0041] In the figure: 1-external load, 2-raft, 3-cushion, 4-old pile, 5-backfill reinforcement, 6-new pile, 7-spiral vent, 8-air outlet. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0043] In the following embodiments or examples, if there is no special description of raw materials or processing techniques, it is indicated that they are all conventional commercially available raw materials or conventional processing techniques in the art.

[0044] Embodiment: In order to solve the limitations of the conventional pile foundation extraction hole backfilling method and the problem of coordinated configuration of new and old pile foundations, the present invention provides a green low-carbon foundation reconstruction technology and construction method on the old pile site. The construction flow chart is as follows: Figure 4 As shown, the following steps are included:

[0045] S1. Obtain the pile foundation design drawings of the target area, determine the initial design scheme of the pile foundation in the target area (pile foundation type, number of piles, pile diameter, pile length, etc.) according to the previous drawing data, and form an overall reconstruction technology framework for the old pile site;

[0046] S2. Comprehensively inspect and evaluate the existing pile foundations in the target area to determine the old piles that need to be removed and those that can be reused;

[0047] S3. Remove old piles in the target area that do not meet the design bearing capacity requirements of new buildings, and retain old piles that meet the reuse conditions;

[0048] S4. Use MgO-based carbon-fixing soil to backfill the old pile removal hole in situ. MgO-based carbon-fixing soil can be prepared by mixing solidifying materials MgO, industrial solid waste, cement and soil, etc., combined with CO 2 Carbonization reinforcement forms a green and low-carbon extraction hole backfill technology;

[0049] S5. Arrange ventilation pipe to inject high-pressure CO 2 The gas carbonizes and consolidates the MgO-based carbon soil;

[0050] S6. According to the load distribution of the superstructure, the location of the new piles is determined based on the collaborative working mechanism of the new and old piles to achieve the overall reconstruction of the foundation form;

[0051] S7. Clean the surface soil and new and old pile heads of the site;

[0052] S8. Construct the cushion layer, construct and pour the raft slab, and complete the foundation construction.

[0053] In some specific implementations, the construction method for removing the old piles can be selected from any one of the three methods: direct removal method, full-rotation pile removal method, and crushing and demolition method, depending on the conditions of the stratum and the pile foundation.

[0054] In some specific embodiments, the MgO-based carbon-fixing soil used is a carbon-fixing soil prepared by mixing components including solidifying material MgO, industrial solid waste, a small amount of cement and soil. The MgO carbon-fixing soil of the present invention has the effect of improving the strength of the soil, reducing the water content and porosity in the soil, and can also absorb a large amount of CO 2 The gas is then solidified in the soil, improving and strengthening the soil.

[0055] In some specific implementations, fly ash, steel slag and other industrial solid wastes are added to the MgO-based carbon-fixing soil to replace 30% to 50% of traditional cement, reducing the carbon emission of the material by more than 50%.

[0056] In some specific embodiments, the CO 2 The length of the ventilation pipe is not less than the depth of the old pile removal hole.

[0057] In some specific embodiments, the CO 2 The arrangement of the ventilation pipe in the old pile extraction hole is selected from any of the three forms: arrangement along the center of the extraction hole, arrangement along the inner wall of the extraction hole, or arrangement along the inner wall of the extraction hole in a vertical spiral direction, which is used to ensure that the required CO 2 Under ventilation pressure, ensure that the backfill body is fully carbonized and reinforced to prevent problems such as insufficient strength due to incomplete carbonization.

[0058] In some specific embodiments, in the CO 2The ventilation pipe is provided with multiple equidistant air outlet holes to ensure that the backfill bodies at different depths can fully contact the CO. 2 Gas undergoes carbonization reaction to prevent uneven carbonization of the backfill body from causing uneven pile strength.

[0059] In some specific embodiments, when the ventilation tube is arranged vertically in a spiral along the inner wall of the extraction hole, the spiral spacing is 0.5 to 1.0 meters to ensure that CO 2 The gas diffuses evenly over the entire cross section of the backfill body.

[0060] In some specific embodiments, the industrial solid waste accounts for 30% to 50% of the MgO-based carbon-fixing soil, and the cement content does not exceed 5%. Through the synergistic effect of MgO and industrial solid waste, CO 2 Solidification and sealing and improvement of soil strength.

[0061] In some specific embodiments, the amount of MgO in the backfill solid is controlled at 15% to 30%, CO 2 The injection pressure was controlled at 0.5-1.5 MPa, the ventilation flow rate was 10-20 L / min, and CO 2 The recommended time for ventilation carbonization consolidation is no less than 12 hours. The carbonization reaction is to fully hydrate MgO to Mg(OH) 2 As a prerequisite, when CO is introduced 2 Before the gas is released, it is necessary to ensure that most of the MgO has been hydrated. MgO hydration process and Mg(OH) 2 Absorbing CO 2 The processes are all exothermic reactions. Therefore, by monitoring the temperature changes during the hydration process, it is possible to effectively determine whether the hydration process is completed. At the same time, the reaction conditions of the entire carbonization process can be monitored by monitoring the temperature changes of the backfill body.

[0062] In some specific implementations, the pile foundation configuration principles are followed to give full play to the foundation reinforcement effect of the backfill reinforcement body, which is used to achieve the matching of the bearing capacity of the new and old pile foundations, ensure the consistency of the settlement behavior of the new and old pile foundations, reduce the surrounding soil disturbance that may be caused by the construction of new piles, and improve economic and environmental benefits.

[0063] In some specific implementations, the location of the new pile driving must ensure that the distance between the new and old piles is not less than 3 times the pile diameter, and the load sharing ratio of the backfill area exceeds 30%, ensuring that the settlement difference between the new and old piles does not exceed 5 mm.

[0064] In some specific implementations, when the cushion layer is provided, the pile head may be connected to the raft slab through the cushion layer or may not be connected to the raft slab according to the actual construction conditions.

[0065] In some specific implementations, the cushion layer is recommended to be made of medium-coarse sand or cement soil, and the thickness range is recommended to be between 1.5 meters and 3 meters.

[0066] In some specific embodiments, the foundation reconstruction technology includes: green backfilling of old pile removal holes, reuse of old piles, coordinated driving of new piles, and integrated casting of cushion layer and raft slab, forming a new composite foundation form that is different from the original site foundation structure.

[0067] The above embodiments may be implemented individually or in any combination of two or more.

[0068] The above implementation is described in more detail below in conjunction with specific examples.

[0069] Embodiment 1:

[0070] Taking a certain construction site as an example, the existing technical method requires backfilling the old pile removal hole with plain concrete or mixing fluid cement soil, or using lime soil, graded sand and gravel, and plain soil with good compaction to backfill and compact in layers. This embodiment provides a green and low-carbon foundation reconstruction technology and construction method on the old pile site, and the specific implementation steps are as follows:

[0071] Step 1: Obtain the pile foundation design drawings of the target area, and determine the initial design plan of the pile foundation in the target area (pile foundation type, number of piles, pile diameter, pile length, etc.) based on the preliminary drawing data to form an overall reconstruction technical framework for the old pile site.

[0072] Step 2: Comprehensively inspect and evaluate the existing old piles 4 and 5 in the target area, and determine the old piles 5 that need to be removed and the old piles 4 that can be reused.

[0073] Step 3: Remove the old piles 5 in the target area that do not meet the requirements of the new building design bearing capacity, and retain the old piles 4 in the target area that meet the reuse conditions; the old pile removal construction method can be any of the three methods of direct removal, full-rotation pile removal, and crushing and demolition according to the conditions of the stratum and pile foundation.

[0074] Step 4: Use MgO-based carbon-fixing soil to backfill the removal hole of the old pile 4 in situ. The MgO-based carbon-fixing soil can be prepared by mixing solidifying materials MgO, industrial solid waste, cement and soil, wherein the amount of MgO is controlled at 15% to 30%. Industrial solid waste such as fly ash and steel slag are added to the MgO-based carbon-fixing soil to replace 30% to 50% of traditional cement. 2 Carbonization reinforcement forms a green and low-carbon extraction hole backfill technology.

[0075] Step 5: Arrange the spiral vent pipe 7 to inject high-pressure CO 2 The gas carbonizes and consolidates the MgO-based carbon soil, CO2 The injection pressure is controlled at 0.5-1.5 MPa, the ventilation flow rate is 10-20 L / min, the carbonization consolidation time is not less than 12 hours, and the CO 2 The length of the vent pipe 7 is not less than the depth of the hole where the old pile 5 is removed. 2 A plurality of equidistant air outlet holes are arranged on the ventilation pipe 7, CO 2 The arrangement of the vent pipe 7 in the hole for removing the old pile 5 is selected from any one of the three arrangements: arrangement along the center of the hole, arrangement along the inner wall of the hole, or arrangement in a vertical spiral along the inner wall of the hole.

[0076] Step 6: According to the distribution of the upper structure load 1 of the target site, determine the location of the new pile 6. Follow the pile foundation configuration principle. The location of the new pile must meet the requirement that the distance between the new and old piles is not less than 3 times the pile diameter, and the load sharing ratio of the backfill area exceeds 30%. Ensure that the difference in settlement between the new and old piles does not exceed 5mm, and give full play to the foundation reinforcement effect of the backfill reinforcement body.

[0077] Step 7: Clean the surface soil and new and old pile heads of the site.

[0078] Step 8: construct cushion layer 3, construct and cast raft slab 2, and complete the foundation construction. It is recommended to use medium-coarse sand or cement soil as the cushion layer, and the thickness range is recommended to be between 1.5 meters and 3 meters. The pile head can be connected to the raft slab through the cushion layer or not according to the actual construction conditions.

[0079] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those familiar with the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the scope of protection of the present invention.

Claims

1. A green and low-carbon foundation reconstruction technology and construction method on an old pile site, characterized in that: The method comprises the following steps: S1. Obtain the pile foundation design drawings of the target area, determine the initial design scheme of the pile foundation in the target area (pile foundation type, number of piles, pile diameter, pile length, etc.) according to the previous drawing data, and form an overall reconstruction technology framework for the old pile site; S2. Conduct a comprehensive inspection and evaluation of the existing pile foundations in the target area to determine the old piles that need to be removed and those that can be reused; S3. Remove old piles that do not meet the design requirements of new buildings in the target area, and retain old piles that meet the reuse conditions; S4. Use MgO-based carbon soil to backfill the old pile extraction holes in situ, and combine CO2 carbonization reinforcement to form a green and low-carbon extraction hole backfill technology; S5. Arrange ventilation pipes to inject high-pressure CO2 gas to carbonize and consolidate the MgO-based carbon soil; S6. According to the load distribution of the superstructure, the location of the new piles is determined based on the collaborative working mechanism of the new and old piles to achieve the overall reconstruction of the foundation form; S7. Clean the surface soil and new and old pile heads of the site; S8. Construct the cushion layer, construct and pour the raft slab, and complete the foundation construction.

2. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: The construction method for removing the old piles is selected from any one of the three methods: direct removal method, full-rotation pile removal method, and crushing and demolition method according to the conditions of the stratum and the pile foundation.

3. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: The MgO-based carbon-fixing soil used is a carbon-fixing soil prepared by mixing components including solidifying material MgO, industrial solid waste, cement and soil.

4. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: The length of the CO2 ventilation pipe is not less than the depth of the old pile removal hole, and the arrangement of the CO2 ventilation pipe in the old pile removal hole is selected from any of the three forms: arrangement along the center of the removal hole, arrangement along the inner wall of the removal hole, or arrangement in a circumferential spiral vertical manner along the inner wall of the removal hole.

5. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: A plurality of equidistant air outlet holes are arranged on the CO2 ventilation pipe; when the ventilation pipe is arranged vertically in a spiral along the inner wall of the extraction hole, the spiral spacing is 0.5 to 1.0 meter to ensure that the CO2 gas is evenly diffused to the entire cross-section of the backfill body.

6. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: The industrial solid waste accounts for 30% to 50% of the MgO-based carbon-fixing soil, and the cement content does not exceed 5%. Through the synergistic effect of MgO and industrial solid waste, the solidification and storage of CO2 and the improvement of soil strength are achieved.

7. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: The content of MgO in the backfill reinforcement is controlled at 15% to 30%, and the time for CO2 ventilation carbonization reinforcement is not less than 12 hours.

8. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: When setting the cushion layer, the pile head may be connected to the raft slab through the cushion layer or may not be connected to the raft slab.

9. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: It is recommended that the cushion layer be made of medium-coarse sand or cement soil, with a thickness ranging from 1.5 meters to 3 meters.

10. The green and low-carbon foundation reconstruction technology and construction method on the old pile site according to claim 1 is characterized in that: The foundation reconstruction technology includes: green backfilling of old pile removal holes, reuse of old piles, coordinated driving of new piles, and integrated casting of cushion layer and raft slab, forming a new composite foundation form that is different from the original site foundation structure.

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