Pore-forming cast-in-place pile grouting method for improving foundation bearing capacity under independent foundation

Abstract

The invention discloses a pore-forming cast-in-place pile grouting method for improving the bearing capacity of a foundation under an independent foundation, which comprises the following steps: S1, measuring the porosity P of a coal gangue backfill stratum, and determining the dosage of cement slurry, cement mortar and superfluid concrete slurry of a pile hole; s2, a pile hole with the preset depth h is drilled in the lower portion of the building foundation; s3, cement paste is injected into the bottom of the pile hole; s4, cement mortar continues to be injected into the bottom of the pile hole; s5, the superfluid concrete grout determined in the step S1 is injected into a pile hole while a drill is lifted; and S6, the reinforcement cage is put into the pile hole, and the super-fluid concrete grout is reinjected for the second time after the pile is formed. Cement paste is poured firstly, coal powder on the surfaces of the coal gangues is scoured, gaps between the coal gangues are enlarged, the coal gangues are bonded together, and the foundation strength is preliminarily enhanced. Then cement mortar is poured to fill gaps among the coal gangue, and the strength of the foundation is enhanced; and finally, the pressure is increased, the super-fluid concrete slurry is poured, and the strength of the foundation is further enhanced due to the fact that small-particle stones are squeezed into gaps among the coal gangues.

Description

Technical Field

[0001] The invention belongs to the technical field of foundation treatment, and in particular relates to a method for grouting bored piles to improve the bearing capacity of a foundation under an independent foundation. Background Art

[0002] In terms of foundation treatment for construction projects, the use of coal gangue backfill strata in coal mining subsidence areas as foundation for construction projects can not only make secondary use of the abandoned coal gangue backfill strata area, but also reduce the cost of land acquisition for construction. It is a comprehensive utilization measure that fully utilizes the coal industry waste dump and reduces environmental pollution.

[0003] Many mining areas in my country have carried out gangue backfilling in coal mining subsidence areas. Gangue is a material between gravel and clay, with good particle gradation and large porosity, and is a typical unsaturated soil. At present, the main method of improving the bearing capacity of the foundation by gangue backfilling is the strong tamping reinforcement method. The principle is to squeeze out the air in the gangue stratum through the tamping process, so that the porosity changes greatly. The method is to use a steel heavy hammer to be hoisted to a high place, and then make it do free fall motion, hammer the gangue ground, and break and compact the shallow gangue stratum. For example, the construction process selected for a certain building project is to use lifting equipment (generally 8-40t) to lift to a great height (generally 10-40m); then let the heavy hammer fall freely, acting on the coal gangue foundation with a large impact energy (2000-8000Kn.m), causing shock waves and impact stresses in the coal gangue soil, forcing the voids in the coal gangue soil to be compressed, the soil to be partially liquefied, and cracks to be generated around the tamping point, forming a good drainage channel, allowing pore water and gas to overflow, and the coal gangue soil to be rearranged and compacted to achieve consolidation, thereby improving the bearing capacity of the coal gangue backfill stratum foundation.

[0004] Using the strong tamping reinforcement method to improve the bearing capacity of the foundation of the gangue backfill stratum is economical and applicable, but it can only improve the bearing capacity of the surface foundation through strong tamping, and has no effect on the deeper strata. The shortcomings of shallow and low strength of the stratum are exposed in improving the bearing capacity of the foundation of the gangue backfill stratum through the strong tamping reinforcement method. Due to the poor stability of the soil in the gangue stratum, when the weight of the upper building structure is slightly larger, it will destroy the stability of the shallow gangue stratum, causing the lower soil to collapse under the action of the upper gravity. When building industrial plants and other buildings on the gangue backfill stratum, the foundation of the construction project will produce a certain amount of settlement under the action of the upper building load, affected by the filling thickness and compaction degree, so it is necessary to consider the consolidation and improvement of the foundation bearing capacity.

[0005] In order to improve the bearing capacity of the foundation of the gangue backfill stratum so that it can reach a greater strength to facilitate the construction of larger construction projects, it is urgent to develop an economical and applicable construction method to improve the bearing capacity of the foundation of the gangue backfill stratum. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to use a bored cast-in-place pile grouting method to consolidate and improve the bearing capacity of the gangue backfill stratum suitable for the foundation under an independent foundation.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for grouting bored piles for improving the bearing capacity of a foundation under an independent foundation, characterized in that it comprises the following steps:

[0009] S1. Determination of the porosity P of the coal gangue backfill formation 孔隙率 , and determine the amount of cement paste, cement mortar and superfluid concrete paste for the pile hole;

[0010] S2, drilling a pile hole with a preset depth of h at the lower part of the building foundation;

[0011] S3, injecting cement slurry determined in S1 into the bottom of the pile hole;

[0012] S4, continue to inject the cement mortar determined in S1 into the bottom of the pile hole;

[0013] S5, injecting the superfluid concrete slurry determined in S1 into the pile hole while lifting the drill;

[0014] S6, lowering the steel cage into the pile hole and filling the superfluid concrete slurry after the pile is formed;

[0015] S7. Compact the shallow coal gangue backfill at the bottom of the foundation.

[0016] In the above technical solution, the present invention provides a method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation, which has the following beneficial effects:

[0017] First, pour cement slurry to wash away the coal powder on the surface of the gangue, increase the gaps between the gangue, and bond the gangue together to initially strengthen the foundation strength. Then pour cement mortar to fill the gaps between the gangue to enhance the foundation strength; finally, increase the pressure to pour in superfluid concrete slurry. As small particles of stone squeeze into the gaps between the gangue, the foundation strength is further strengthened. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a schematic diagram of the influence range of the foundation bearing capacity of the strong compaction reinforcement method disclosed in the prior art;

[0020] Figure 2 It is a schematic diagram of the influence range of the foundation bearing capacity of the bored pile grouting method disclosed in the present invention;

[0021] Figure 3 The present invention is a schematic diagram of the process of the bored pile grouting method disclosed in the present invention. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] like Figure 2-3 A method for grouting bored piles to improve the bearing capacity of the foundation under an independent foundation is shown, comprising the following steps:

[0024] S1. Determination of the porosity P of the coal gangue backfill formation 孔隙率 , and determine the amount of cement slurry, cement mortar and superfluid concrete slurry for the pile hole; the amount of cement slurry, cement mortar and superfluid concrete slurry for the pile hole can be determined through actual tests or calculated through the methods described below.

[0025] S2. Drill a pile hole with a preset depth of h at the lower part of the building foundation.

[0026] For example, a hole-drilling machine is used to drill a hole 3m below the building foundation, and the pile diameter is 0.8m. 0.6-0.8m is a conventional construction value. This process uses a 0.8m pile diameter to take into account the larger load of the upper building. A smaller pile diameter affects the orderly construction, and a larger pile diameter will cause waste.

[0027] S3. Inject the cement slurry determined in S1 into the bottom of the pile hole.

[0028] Specifically, cement slurry is poured downward from the bottom of the pile hole through the conduit to cement the gangue together and wet the pores between the gangue. One end of the conduit is connected to the concrete grouting pump, and the other end is connected to the upper part of the grouting pipe of the drill rod of the drilling rig. The slurry is pressurized by the concrete grouting pump, poured into the middle grouting pipe of the drill rod of the drilling rig through the conduit, and then poured into the bottom of the cast-in-place pile through the grouting pipe of the drill rod.

[0029] S4. Continue to inject the cement mortar determined in S1 into the bottom of the pile hole.

[0030] Specifically, cement mortar is poured in after cement slurry is poured in to fill the gaps between the gangue and improve the stress properties of the gangue backfill stratum. Since the drilling machine drill rod does not extend beyond the pile body, the lower part of the pile body is a closed space, and sufficient cement mortar can be pressed in through a concrete pump. One end of the conduit is connected to the concrete grouting pump, and the other end is connected to the upper part of the drilling rig drill rod grouting pipe. The slurry is pressurized by the concrete grouting pump and poured into the middle grouting pipe of the drilling rig drill rod through the conduit. After the cement slurry is poured in, cement mortar is poured in and then poured into the bottom of the cast-in-place pile through the drill rod grouting pipe.

[0031] S5. Inject the superfluid concrete slurry determined in S1 into the pile hole while lifting the drill.

[0032] Specifically, the superfluid concrete aggregate is determined by observing the porosity of the gangue and the gaps between the gangue. When the pores are large, fine stone is used as the aggregate, and when the pores are small, melon seed stone with a smaller particle size is used as the aggregate, so that the aggregate can fill the gaps between the gangue. A sufficient amount of C30 superfluid concrete slurry is pressed in by increasing the pressure of the concrete pump to strengthen the stress strength of the gangue backfill stratum. Pour in cement mortar and then lift the drill to pour C30 superfluid concrete slurry into the pile body.

[0033] S6, lowering the steel cage into the pile hole and filling the superfluid concrete slurry after the pile is formed;

[0034] Specifically, during construction, after the superfluid concrete slurry is poured, the steel cage should be pressed in immediately. It is necessary to ensure that the superfluid concrete is in a fluid state and that the steel cage can be pressed in smoothly. The operator lifts the qualified steel cage to the vicinity of the hole in advance, lifts it vertically into the hole using the auxiliary hook provided by the drilling rig, measures the cage top elevation with a level, and fixes it at the designed cage top elevation. Then, the thickness of the main reinforcement protective layer must be ensured when fixing the steel cage. The steel cage is placed using the auxiliary hook provided by the drilling rig, and the anchor pile steel cage should be hoisted at a good lifting point to avoid excessive bending. Lower the steel cage into the hole, control the verticality while lowering, and sink it to the designed elevation. If it does not sink into place, it can be pressed in with a vibrator or external force.

[0035] During the process of pressing into the steel cage, the liquid level of the poured superfluid fine stone concrete will sink, causing the pile top surface to be lower than the designed elevation, and a secondary injection of C30 superfluid concrete slurry is required. The method is to insert the catheter into the pile hole below the concrete liquid level within 2 hours after the pile is formed, and pour concrete until the liquid level reaches 50 cm above the pile top to ensure the quality of the pile head. To ensure the quality of the pile head, the poured pile top should be 0.5-1m higher than the designed elevation, and the over-pouring part should be chiseled off before construction.

[0036] S7. Compact the shallow coal gangue backfill at the bottom of the foundation.

[0037] The principle of the bored pile grouting method is to use bored piles to fill the coal gangue backfill stratum below the preset depth h in the lower part of the building foundation, and respectively inject cement slurry, cement mortar and superfluid concrete slurry. First, pour in cement slurry to wash the coal powder on the surface of the coal gangue, so that it gathers at the edge and increases the gap between the coal gangue. Cement slurry can also stick the coal gangue together to initially strengthen the foundation strength. Then pour in cement mortar to fill the gaps between the coal gangue and enhance the foundation strength. Finally, increase the pressure and pour in superfluid concrete slurry. Because the small particles of superfluid concrete squeeze into the gaps between the coal gangue, the foundation strength is further strengthened. A method of consolidating and improving the bearing capacity of the foundation of the coal gangue backfill stratum using three grouting materials. This construction method is not suitable for large-scale pile construction, but only for strengthening the foundation bearing capacity under an independent foundation.

[0038] The injection of cement paste, cement mortar and superfluid concrete paste is carried out continuously. If the interval of the next process is too long, the cement paste or cement mortar will block the gaps between the coal gangue, making it impossible for the next paste to be injected through the gaps between the coal gangue. The interval time is based on the interval time when the previous paste becomes fluid and does not solidify.

[0039] Among them, considering the thickness of the gangue stratum and the load size of the upper building, this process prefers to use a pile length of h = 3m, which is suitable for medium-sized industrial buildings. If the thickness of the gangue stratum and the load of the upper building are large, it can be appropriately lengthened. The pile length is given priority to 3m because the gangue stratum is relatively loose, and a pile length that is too long is prone to landslides. In addition to the bearing capacity of the cast-in-place pile itself on the independent foundation, the gangue stratum also has a certain bearing capacity on the independent foundation. If the pile body is too short, the bearing capacity of the gangue stratum will not be able to be transmitted downward. Therefore, a 3m pile length is more suitable.

[0040] Among them, 32.5R ordinary Portland cement can be used, the fine aggregate is medium sand with a particle size of 0.5mm-0.25mm, the coarse aggregate is fine stone with a maximum particle size of no more than 15mm, and when the pores between the coal gangue are small, the coarse aggregate uses melon seed stone with a particle size of 5-10mm.

[0041] The method for determining the amount of cement paste, cement mortar and superfluid concrete paste in S1 is:

[0042] S1-1. Determine the foundation pressure P according to the building foundation 帕设计值 、The load on the foundation F 地基承载力 , according to formula (1) determine the foundation load area M 灌浆料受力面积 ;

[0043] M 灌浆料受力面积 =F 地基承载力 / P 帕设计值 (1)

[0044] Among them, P帕设计值 =k*P 帕标准值 , k is the pressure insurance coefficient, which can be taken as 0.5, and P 帕标准值 =2*P 帕设计值 , P 帕标准值 is the standard pressure;

[0045] S1-2, set the cement slurry, cement mortar and superfluid concrete slurry at the bottom of the pile hole to form three layers of grouting balls, and the radius of the cement slurry grouting ball is r 水泥浆 , the radius r of the cement mortar grouting ball 水泥砂浆 , the radius r of the superfluid concrete slurry grouting ball is r 水泥浆 :r 水泥砂浆 :r=3:2:1; Theoretically, these three layers of grouting materials are in the shape of a teardrop, but considering that the lower force-bearing area is spherical and the teardrop shape is roughly similar to the sphere, the calculation is based on the sphere.

[0046] S1-3, set the force area M of the cement grouting ball 水泥浆受力面积 The ratio of the surface area of ​​the cement mortar grouting ball to the surface area of ​​the cement mortar grouting ball is n1, and the force bearing area of ​​the preset cement mortar grouting ball is M 水泥砂浆受力面积 The ratio of the surface area of ​​the cement mortar grouting ball to the surface area of ​​the cement mortar grouting ball is n2, and the force bearing area of ​​the preset superfluid concrete slurry grouting ball is M 超流态混凝土浆料受力面积 The ratio of the surface area of ​​the superfluid concrete slurry grouting ball to the surface area of ​​the superfluid concrete slurry grouting ball is n3, so the surface area of ​​the cement slurry grouting ball M 水泥浆受力面积 , the force bearing area M of cement mortar grouting ball 水泥砂浆受力面积 , the force bearing area M of the superfluid concrete slurry grouting ball 超流态混凝土浆料受力面积 It can be expressed by the following formulas (2)-(4):

[0047] M 水泥浆受力面积 =n 1* 4π(3r) 2 (2)

[0048] M 水泥砂浆受力面积 =n 2* 4π(2r) 2 (3)

[0049] M 超流态混凝土浆料受力面积 =n 3* 4πr 2 (4)

[0050] S1-4, set the force area M of the cement grouting ball 水泥浆受力面积 , the force bearing area M of cement mortar grouting ball 水泥砂浆受力面积 , the force bearing area M of the superfluid concrete slurry grouting ball 超流态混凝土浆料受力面积 Respectively with the foundation load area M 灌浆料受力面积The ratios are m1, m2, and m3, then:

[0051] M 灌浆料受力面积 =m 1* M 水泥浆受力面积 +m 2* M 水泥砂浆受力面积 +m 3* M 超流态混凝土浆料受力面积 (5)

[0052] The three layers of materials are injected separately, so that the density of the gangue stratum increases towards the middle of the cast material body, and the corresponding compressive strength increases. Since the pressure spreads at a 45-degree angle from the root of the cast-in-place pile to the lower stratum, the pressure decreases as it goes down. The three layers of slurry of different materials bear corresponding pressures at corresponding positions. The pressure-bearing area increases as it goes down, the force per unit area decreases, and the required density decreases.

[0053] S1-5. Substitute formula (2)-(4) into formula (5) to obtain the radius r of the superfluid concrete slurry grouting ball:

[0054]

[0055] S1-6. According to the volume formula of the ball, the volume of cement slurry V in S1 is obtained. 水泥浆 , Volume of cement mortar V 水泥砂浆 The volume dosage of the superfluid concrete slurry can be expressed by the following formulas (7)-(9):

[0056] V 水泥浆 =P 孔隙率* 4 / 3π3r 3 (7)

[0057] V 水泥砂浆 =P 孔隙率* 4 / 3π2r 3 (8)

[0058] V 超流态混凝土浆料 =P 孔隙率* 4 / 3πr 3 (9).

[0059] Preferably, according to construction experience, m1=m2=m3=1 / 3, n1=n2=n3=1 / 4 are set, and the radius r of the superfluid concrete slurry grouting ball is expressed by formula (10):

[0060]

[0061] A trial pile test can be made before construction to determine the final specific values ​​of various parameters. When the test pile compressive strength does not meet the requirements, the amount of superfluid fine stone concrete slurry is increased to increase the force-bearing area at the bottom of the pile. Preferably, after determining the amount of cement slurry, cement mortar and superfluid concrete slurry in S1, it also includes steps S1-2, when grouting the bored piles for multiple pile holes, the pile holes outside the building foundation area are first tested for construction, and the compressive strength of the pile body is measured after the test pile, if the compressive strength is unqualified, the volume amount of cement slurry, cement mortar and superfluid concrete slurry is increased in equal proportion, and the test pile is continued until the compressive strength of the pile body is qualified, and the volume amount of cement slurry, cement mortar and superfluid concrete slurry when the compressive strength of the pile body is qualified is used as the cement slurry, cement mortar and superfluid concrete slurry in steps S3, S4 and S5. Compressive strength can be obtained by the test pile compression static load test.

[0062] Preferably, the concrete strength grade of the superfluid concrete slurry is C30.

[0063] The process flow during construction is:

[0064] Test piles → Lay out lines and determine pile positions → Put pile driver in place → Drill holes → Prepare grouting materials → Press grouting liquid → Press into steel cage → Grouting → Inspection → Pile head maintenance → Testing → Compact independent foundation → Construction of independent foundation.

[0065] Specific:

[0066] 1. Test pile: Before large-scale construction of bored pile grouting method in coal gangue backfill stratum, test pile construction should be carried out to determine the construction technical parameters. The parameters obtained after the test pile are required to be the volume of grouting material and injection time of the three materials. When the compressive strength of the test pile does not meet the requirements, the solution is to increase the amount of superfluid fine stone concrete slurry and increase the bearing area of ​​the pile bottom.

[0067] 2. Laying out the lines and determining the pile positions: Lay out the center positions of the piles according to the control axis and construction drawings, and mark them with white lime dots.

[0068] 3. Pile driver in place

[0069] 4. Drilling: After the superfluid concrete spiral drill is in place and aligned with the pile site, it must be leveled to ensure the verticality of the hole. According to the actual situation of the site, sleepers or steel plates should be laid to stabilize the support of the drill to ensure that it does not tilt or move during construction. In order to accurately control the depth of the hole, a scale for controlling the depth should be set on the pile frame or drill rod. When drilling, after the drill bit is aligned with the pile site, start the drill to drill down. The drilling speed should be stable to prevent the drill from tilting and dislocating during drilling. When encountering large pieces of coal gangue and unable to drill down during drilling, the drill should be stopped and replaced with an impact drill to break up the large pieces of coal gangue, and then the superfluid concrete spiral drill should be replaced to continue drilling. After the drill reaches the designed bottom elevation of the hole, first lift the drill 20 cm, and then start the grouting construction.

[0070] 5. Prepare grouting materials and pressure grouting liquid: Prepare grouting materials before drilling and during drilling construction. Calculate the amount of cement slurry, cement mortar, and C30 super fluid fine stone concrete slurry based on the calculation parameters.

[0071] The grouting raw materials are 32.5R ordinary Portland cement, fine aggregate with a particle size of 0.5mm-0.25mm, fine stone with a maximum particle size of no more than 15mm, and when the pores are small, the coarse aggregate is melon seed stone with a particle size of 5-10mm.

[0072] The volume ratio of cement paste raw materials is (cement: water = 1:10), the volume ratio of cement mortar raw materials is (cement: medium sand: water = 1:2:10), the weight ratio of C30 super fluid fine stone concrete slurry raw materials is (cement: medium sand: fine stone: II grade fly ash = 1:2.3:2:0.25, water-binder ratio 0.6), and C30 super fluid fine stone concrete is provided by the commercial mixing station. The volume ratio of cement paste, cement mortar and fluid fine stone concrete is 27:8:1.

[0073] Use a concrete pump to connect the grouting port on the top of the drill rod of the superfluid concrete spiral drill. First, pressurize the cement slurry, and pressurize a sufficient amount of cement mortar before the cement slurry initially sets. Then pressurize a sufficient amount of C30 superfluid concrete slurry under increased pressure. Finally, grouting and lifting the drill, pouring C30 superfluid fine stone concrete into the pile body. During the process of lifting the drill, always keep the amount of concrete slurry pumped into the hole greater than the volume of the drill rod lifted to prevent pile breakage.

[0074] 6. Press in the steel cage: Lower the steel cage into the hole, control the verticality while lowering it, and sink it to the designed elevation. If it does not sink into place, use a vibrator or external force to press it in.

[0075] 7. Grouting: During the process of pressing into the steel cage, the liquid level of the poured C30 super fluid fine stone concrete will sink, causing the pile top surface to be lower than the designed elevation, and a secondary injection of C30 super fluid fine stone concrete is required. The method is to insert the catheter into the pile hole below the concrete liquid level within 2 hours after the pile is formed, and pour concrete until the liquid level reaches 50 cm above the pile top to ensure the quality of the pile head. To ensure the quality of the pile head, the poured pile top should be 0.5-1m higher than the designed elevation, and the over-pouring part should be chiseled off before construction.

[0076] 8. Pile head maintenance: Cover the top of the pile head with a film and water it for 7 days.

[0077] 9. Inspection test: The completed pile body shall be subjected to compressive strength and integrity test. The number of piles to be inspected shall not be less than 0.5% of the total number of piles, and shall not be less than 3.

[0078] 10. Compact the independent foundation: compact the shallow coal gangue backfill foundation at the bottom of the foundation.

[0079] 11. Independent foundation construction: After breaking the pile head, construct the building foundation according to the drawings.

[0080] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation, characterized in that: The following steps are involved: S1. Determination of the porosity P of the coal gangue backfill formation 孔隙率 , and determine the amount of cement paste, cement mortar and superfluid concrete paste for the pile hole; S2, drilling a pile hole with a preset depth of h at the lower part of the building foundation; S3, injecting cement slurry determined in S1 into the bottom of the pile hole; S4, continue to inject the cement mortar determined in S1 into the bottom of the pile hole; S5, injecting the superfluid concrete slurry determined in S1 into the pile hole while lifting the drill; S6, lowering the steel cage into the pile hole and filling it with superfluid concrete slurry; S7. Compact the shallow coal gangue backfill at the bottom of the foundation.

2. A method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation according to claim 1, characterized in that: The method for determining the amount of cement paste, cement mortar and superfluid concrete paste in S1 is: S1-1. Determine the foundation pressure P according to the building foundation 帕设计值 、Load F borne by the foundation 地基承载力 , according to formula (1) determine the foundation load area M 灌浆料受力面积 ; M 灌浆料受力面积 =F 地基承载力 / P 帕设计值 (1) Among them, P 帕设计值 =k*P 帕标准值 , k is the pressure insurance coefficient, P 帕标准值 is the standard pressure; S1-2. The cement slurry, cement mortar and superfluid concrete slurry at the bottom of the preset pile hole form three layers of grouting balls respectively, and the corresponding radius ratio relationship of the cement slurry grouting ball, cement mortar grouting ball and superfluid concrete slurry grouting ball is r 水泥浆 :r 水泥砂浆 :r=3:2:1; S1-3, preset force area M of cement grouting ball 水泥浆受力面积 The ratio of the surface area of ​​the cement mortar grouting ball to the surface area of ​​the cement mortar grouting ball is n1, and the force bearing area of ​​the preset cement mortar grouting ball is M 水泥砂浆受力面积 The ratio of the surface area of ​​the cement mortar grouting ball to the surface area of ​​the cement mortar grouting ball is n2, and the force bearing area of ​​the preset superfluid concrete slurry grouting ball is M 超流态混凝土浆料受力面积 The ratio of the surface area of ​​the superfluid concrete slurry grouting ball to the surface area of ​​the superfluid concrete slurry grouting ball is n3, so the surface area of ​​the cement slurry grouting ball M 水泥浆受力面积 , the force bearing area M of cement mortar grouting ball 水泥砂浆受力面积 , the force bearing area M of the superfluid concrete slurry grouting ball 超流态混凝土浆料受力面积 It can be expressed by the following formulas (2)-(4): <h2 style=";text-align:left;direction:ltr">M<h2 style=";text-align:left;direction:ltr"> 水泥浆受力面积 <h2 style=";text-align:left;direction:ltr"> =n1*4π(3r)<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> (2) M 水泥砂浆受力面积 =n2*4π(2r) 2 (3) M 超流态混凝土浆料受力面积 =n3*4πr 2 (4) S1-4, preset force area M of cement grouting ball 水泥浆受力面积 , the force bearing area M of cement mortar grouting ball 水泥砂浆受力面积 , the force bearing area M of the superfluid concrete slurry grouting ball 超流态混凝土浆料受力面积 Respectively with the foundation load area M 灌浆料受力面积 The ratios are m1, m2, and m3, then: M 灌浆料受力面积 =m1*M 水泥浆受力面积 +m2*M 水泥砂浆受力面积 +m3*M 超流态混凝土浆料受力面积 (5) S1-5. Substitute formula (2)-(4) into formula (5) to obtain the radius r of the superfluid concrete slurry grouting ball: S1-6. According to the volume calculation formula of the ball, the volume of cement slurry V in S1 is obtained. 水泥浆 , Volume of cement mortar V 水泥砂浆 And the volume of superfluid concrete slurry V 超流态混凝土浆料 It can be expressed by the following formulas (7)-(9): <h2 style=";text-align:left;direction:ltr">V<h2 style=";text-align:left;direction:ltr"> 水泥浆 <h2 style=";text-align:left;direction:ltr"> =P<h2 style=";text-align:left;direction:ltr"> 孔隙率 <h2 style=";text-align:left;direction:ltr"> *4 / 3π(3r)<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> (7) V 水泥砂浆 =P 孔隙率 *4 / 3π(2r) 3 (8) V 超流态混凝土浆料 =P 孔隙率 *4 / 3πr 3 (9)。 3. A method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation according to claim 2, characterized in that: If m1=m2=m3=1 / 3 and n1=n2=n3=1 / 4, the radius r of the superfluid concrete slurry grouting ball can be expressed by formula (10):

4. A method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation, characterized in that: After determining the amount of cement paste, cement mortar and superfluid concrete paste in S1, the method also includes step S1-2, firstly conducting a construction test on the pile holes outside the building foundation area when grouting bored piles for multiple pile holes, and measuring the compressive strength of the pile body after the test pile. If the compressive strength is unqualified, the volume amount of cement paste, cement mortar and superfluid concrete paste is increased in proportion until the compressive strength of the pile body is qualified, and the volume amount of cement paste, cement mortar and superfluid concrete paste when the compressive strength of the pile body is qualified is used as the amount of cement paste, cement mortar and superfluid concrete paste in steps S3, S4 and S5.

5. A method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation, characterized in that: The preset depth h is 3m.

6. A method for grouting bored piles for improving the bearing capacity of the foundation under an independent foundation, characterized in that: The concrete strength grade of superfluid concrete slurry is C30.

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