Anti-floating calculation and control method for reinforcement cage in cast-in-situ bored pile casting process

Abstract

The invention discloses an anti-floating calculation and control method for a reinforcement cage in a cast-in-situ bored pile pouring process, which belongs to the technical field of geotechnical engineering and comprises the following steps: S1, measuring the hole diameter and the pile depth of a cast-in-situ bored pile after the cast-in-situ bored pile is formed; s2, a reinforcement cage is hoisted into the cast-in-situ bored pile, and the gravity of the reinforcement cage is determined; s3, concrete is poured after bottom cleaning and slurry changing, the acting force of the concrete on the reinforcement cage is determined, and the acting force of the concrete on the reinforcement cage comprises the sum of buoyancy, viscous force and impact force borne by the reinforcement cage; s4, comparing the gravity of the reinforcement cage with the acting force of the concrete on the reinforcement cage; and S5, according to a comparison result in the step S4, a reinforcement cage anti-floating response measure is formulated. According to the method, the gravity of the reinforcement cage and the acting force of concrete on the reinforcement cage can be scientifically determined, anti-floating countermeasures of the reinforcement cage can be formulated more comprehensively and more effectively, and the method has important theoretical guiding significance for follow-up cast-in-situ bored pile construction.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a method for calculating and controlling the anti-floating properties of a steel cage during the casting process of bored piles. Background Art

[0002] During the construction of bored cast-in-place piles, when the forces (buoyancy, viscosity and impact force) acting on the steel cage during the pouring process of concrete are greater than the gravity of the steel cage, the steel cage will float up, which may affect the quality and strength of the pile at the least, or cause the pile to be abandoned at the worst.

[0003] The existing control measures for the anti-floating of reinforced cages in bored piles are mostly based on field experience, and there are still disadvantages such as high implementation cost, difficult engineering quality control, and high experience requirements for construction personnel. There is a lack of scientific and effective measures for the anti-floating of reinforced cages. Therefore, a calculation and control method for the anti-floating of reinforced cages in the process of bored pile casting is proposed. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to solve the above problems existing in the prior art, and provides a method for calculating and controlling the anti-floating of a steel cage during the casting process of bored cast-in-place piles.

[0005] The present invention solves the above technical problems through the following technical solutions, and the present invention comprises the following steps:

[0006] S1: After the bored pile is bored, its hole diameter and pile depth are measured;

[0007] S2: Lift the steel cage into the drill hole and determine the weight of the steel cage;

[0008] S3: After cleaning the bottom and replacing the slurry, pour the concrete and determine the force exerted by the concrete on the steel cage. The force exerted by the concrete on the steel cage includes the sum of the buoyancy, viscosity and impact force exerted on the steel cage.

[0009] S4: Compare the gravity of the steel cage and the force exerted by the concrete on the steel cage;

[0010] S5: According to the comparison result of step S4, formulate the anti-floating countermeasures of the steel cage.

[0011] Furthermore, in step S1, the hole diameter D and the pile depth H are measured to see whether they meet the design requirements. If not, re-drilling and repairing the hole should be performed.

[0012] Furthermore, in the step S2, the steel cage is hoisted into the drill hole, and the steel cage is tightened by hoisting rods to prevent the bottom of the steel cage from being inserted into the mud at the bottom of the pile.

[0013] Furthermore, in step S2, the calculation formula of the reinforcement cage gravity G is as follows:

[0014]

[0015] Among them, γ is the bulk density of the steel bar; n is the number of main bars in the steel cage; H is the length of the main bars in the steel cage; d is the diameter of the main bars in the steel cage.

[0016] Furthermore, in step S3, the specific process is as follows:

[0017] S31: After the steel cage is hoisted, the bottom is cleaned and the slurry is replaced through the grouting pipe until the slurry density reaches the set range and concrete can be poured;

[0018] S32: Calculate the buoyancy of the steel cage:

[0019]

[0020] Where, F1 is the buoyancy of the steel cage; 浆 is the mud bulk density; 砼 is the concrete bulk density; h is the concrete liquid level height;

[0021] S33: Calculate the viscous force on the steel cage:

[0022] F2=πndhτ

[0023] Among them, F2 is the viscous force on the steel cage; τ is the concrete shear stress;

[0024] S34: Calculate the impact force on the steel cage:

[0025]

[0026] Among them, F3 is the impact force on the steel cage; t is the initial setting time of concrete; k is the rising speed of the concrete liquid level in the hole;

[0027] S35: Calculate the force exerted by concrete on the steel cage:

[0028] F=F1+F2+F3.

[0029] Furthermore, in step S4, when the gravity of the steel cage is greater than the force exerted by the concrete on the steel cage within a set multiple range, the steel cage will not float and no countermeasures are needed; when the gravity of the steel cage is less than the force exerted by the concrete on the steel cage within a set multiple range, anti-floating countermeasures for the steel cage need to be formulated.

[0030] Furthermore, in step S5, the anti-floating measures for the steel cage include the following three measures:

[0031] The first method is to reduce the concrete pouring speed v, thereby slowing down the concrete liquid level rising speed k and reducing the upward impact force on the steel cage caused by the rising concrete liquid level;

[0032] The second method is to prefabricate a concrete ring at the bottom of the steel cage. When the concrete is poured in, the pressure of the concrete and the mud is concentrated on the concrete ring, thereby increasing the downward gravity of the steel cage.

[0033] The third method: Before the steel cage is hoisted into the drilled hole, a set of inverted crosses are welded on the upper half of the main reinforcement of the steel cage to prevent the steel cage from floating up.

[0034] Furthermore, in the first countermeasure, the concrete liquid level rising speed k is proportional to the concrete pouring speed v, and the relationship is: By adjusting the flow rate of the concrete pump, controlling the inclination angle of the concrete delivery pipe or adjusting the size of the concrete pouring port to reduce the concrete pouring speed v, the impact force F3 on the steel cage is reduced, and the force F of the concrete on the steel cage is also reduced, thereby preventing the steel cage from floating up;

[0035] Furthermore, in the second countermeasure, as the height h of the concrete liquid level rises, the pressure of the concrete and mud on the concrete ring gradually increases, thereby preventing the steel cage from floating up;

[0036] The pressure of the concrete and slurry on the concrete ring is obtained by the following formula:

[0037]

[0038] Among them, T is the pressure of concrete and mud on the concrete ring; O is the outer diameter of the concrete ring; o is the inner diameter of the concrete ring. By adjusting the size of the inner diameter of the concrete ring, the pressure of the concrete and mud on the concrete ring can be controlled.

[0039] Furthermore, in the third countermeasure, when the steel cage is hoisted into the borehole, the inverted fork is hoisted into the borehole along with the steel cage. When the concrete is poured, the steel cage has a tendency to float up, and the inverted fork is inserted into the soil on the side wall of the borehole, thereby preventing the steel cage from floating up.

[0040] Among them, the inverted forks are symmetrically welded at intervals on the upper half of the main bars of the steel cage, the number of the inverted forks is 1 / 2 of the number of the main bars of the steel cage, the angle between the inverted forks and the main bars of the steel cage is 20°~30°, and the upper half is 0.2H~0.4H away from the top of the steel cage.

[0041] Compared with the prior art, the present invention has the following advantages: the method for calculating and controlling the anti-floating of the steel cage during the casting of bored cast-in-place piles determines the gravity of the steel cage and the force of concrete on the steel cage by measuring the bored cast-in-place pile parameters on site, not only considering the buoyancy factor, but also comprehensively considering the viscosity and impact factors, and formulating corresponding anti-floating countermeasures for the steel cage according to the comparison result of the gravity of the steel cage and the force of concrete on the steel cage; compared with the existing anti-floating control measures for the bored pile steel cage, the method can scientifically determine the gravity of the steel cage and the force of concrete on the steel cage, and formulate more comprehensive and effective anti-floating countermeasures for the steel cage, which has important theoretical guiding significance for subsequent bored cast-in-place pile construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of a method for calculating and controlling the anti-floating property of a steel cage during the casting process of bored piles in an embodiment of the present invention;

[0043] Figure 2 Schematic diagram of bored pile structure in an embodiment of the present invention;

[0044] Figure 3 Schematic diagram of the concrete ring structure in an embodiment of the present invention.

[0045] In the figure: 1-rebar cage suspension bar; 2-inverted fork; 3-rebar cage main bar; 4-rebar cage hoop bar; 5-drilled hole side wall; 6-concrete ring; 7-reserved steel bar for concrete ring; 8-hole. DETAILED DESCRIPTION

[0046] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0047] like Figure 1-3 As shown, this embodiment provides a technical solution: a method for calculating and controlling the anti-floating property of a steel cage during the casting of bored piles, comprising the following steps:

[0048] 1) After the bored pile is bored, measure its hole diameter and pile depth;

[0049] 2) Lift the steel cage into the drilled hole and determine the weight of the steel cage;

[0050] 3) Pour concrete after cleaning the bottom and changing the slurry, and determine the force of concrete on the steel cage (buoyancy, viscosity and impact force);

[0051] 4) Compare the gravity of the steel cage and the force exerted by the concrete on the steel cage;

[0052] 5) Based on the comparison results of step 4), formulate anti-floating measures for the steel cage.

[0053] In this embodiment, in step 1), the hole diameter D and the pile depth H are measured to see whether they meet the design requirements. If not, re-drilling and repairing the hole should be performed.

[0054] In this embodiment, in the step 2), the steel cage is hoisted into the drilled hole, and the steel cage is tightened by hoisting rods to prevent the bottom of the steel cage from being inserted into the mud at the bottom of the pile.

[0055] In this embodiment, in the step 2), the number of main bars n of the steel cage is determined, and the diameter d of the main bars of the steel cage is determined; according to the number of main bars n of the steel cage and the diameter d of the main bars of the steel cage, the length of the main bars of the steel cage is the same as the pile depth H, and the gravity G of the steel cage is calculated; the gravity of the steel cage is obtained by the following calculation:

[0056]

[0057] Among them, γ is the bulk density of steel bars, in N / m 3 ; n is the number of main bars in the steel cage; H is the length of the main bars in the steel cage, in m; d is the diameter of the main bars in the steel cage, in m.

[0058] In this embodiment, in step 3), after the steel cage is hoisted, the bottom is cleaned and the slurry is replaced through the grouting conduit until the slurry density is 1.10-1.25, and then the concrete can be poured.

[0059] In this embodiment, in step 3), the mud and concrete samples are injected into the container of the hydrometer using a mud hydrometer and a concrete hydrometer, and the weight is slowly moved. The bulk density γ of the mud is measured on site according to the reading of the hydrometer. 浆 and the bulk density of concrete γ 砼 , the buoyancy of the steel cage is calculated by the following formula:

[0060]

[0061] Where F1 is the buoyancy of the steel cage, in N; 浆 is the mud bulk density, in N / m 3 ; γ 砼 is the concrete density, in N / m 3 ; h is the height of concrete liquid level, in meters.

[0062] In this embodiment, in step 3), the shear stress τ of the concrete is measured on site, and the viscous force on the steel cage is calculated by the following formula:

[0063] F2=πndhτ (3)

[0064] Among them, F2 is the viscous force on the steel cage, the unit is N; τ is the concrete shear stress, the unit is Pa.

[0065] In this embodiment, in step 3), the concrete liquid level rising speed k is measured on site, and the impact force on the steel cage is calculated by the following formula:

[0066]

[0067] Among them, F3 is the impact force on the steel cage, in N; t is the initial setting time of concrete, in s; k is the rising speed of the concrete liquid level in the hole, in m / s.

[0068] In this embodiment, in step 3), the force of the concrete on the steel cage is F=F1+F2+F3; when the concrete liquid level h is equal to the pile depth H, the force reaches the maximum value, and the maximum force is calculated by the following formula:

[0069]

[0070] Among them, F max is the maximum force exerted by concrete on the steel cage, in N.

[0071] In this embodiment, in the step 4), when the weight of the steel cage is greater than 1.1 to 1.2 times the force exerted by the concrete on the steel cage, the steel cage will not float and no countermeasures are needed; when the weight of the steel cage is less than 1.1 to 1.2 times the force exerted by the concrete on the steel cage, anti-floating countermeasures for the steel cage need to be formulated.

[0072] In this embodiment, in step 5), the anti-floating measures of the steel cage include: ① reducing the concrete pouring speed v, thereby slowing down the concrete liquid level rising speed k and reducing the upward impact force on the steel cage; ② prefabricating a concrete ring at the bottom of the steel cage. When the concrete is poured, the pressure of the concrete and the mud is concentrated on the concrete ring, thereby increasing the downward gravity on the steel cage; ③ before the steel cage is hoisted into the drilled hole, a group of inverted crosses are welded on the upper half of the main reinforcement of the steel cage to prevent the steel cage from floating.

[0073] In this embodiment, in step 5), in the countermeasure ①, the concrete liquid level rising speed k is proportional to the concrete pouring speed v, and the relationship is: By adjusting the flow rate of the concrete pump, controlling the inclination angle of the concrete delivery pipe or adjusting the size of the concrete pouring port to reduce the concrete pouring speed v, the impact force F3 on the steel cage is reduced, and the force F of the concrete on the steel cage is also reduced, thereby preventing the steel cage from floating.

[0074] In this embodiment, in step 5), in the countermeasure ②, the pressure of the concrete and mud on the concrete ring is obtained by the following formula:

[0075]

[0076] Among them, T is the pressure of concrete and mud on the concrete ring, in N; O is the outer diameter of the concrete ring, in m, and its value is the same as the diameter of the steel cage; o is the inner diameter of the concrete ring, in m, and its value is larger than the diameter of the concrete conduit. By adjusting the size of the inner diameter of the concrete ring, the pressure of the concrete and mud on the concrete ring can be controlled.

[0077] In the present embodiment, in the step 5), in the countermeasure ②, as the height h of the concrete liquid level rises, the pressure of the concrete and mud on the concrete ring gradually increases, thereby preventing the steel cage from floating up, and while the concrete ring prevents the steel cage from floating up, the holes inside it ensure that the concrete is smoothly poured through the holes to the bottom of the bored pile, solidifying the sediment at the bottom of the pile and improving the bearing capacity of the pile bottom.

[0078] In this embodiment, the thickness of the concrete ring is 3 to 5 cm, and the outer diameter O of the concrete ring is 10 to 20 cm smaller than the hole diameter D of the bored pile; as a better choice, the concrete ring has the same concrete grade as the bored pile; as a better choice, the concrete ring has a built-in steel skeleton, and before the steel cage is hoisted into the drilled hole, the reserved steel bars of the concrete ring are welded to the main bars at the bottom of the steel cage.

[0079] In this embodiment, in the step 5), in the countermeasure ③, when the steel cage is hoisted into the bored pile, the inverted fork is hoisted into the borehole along with the steel cage, and when the concrete is poured, the steel cage has a tendency to float up, and the inverted fork is inserted into the soil on the side wall of the borehole to prevent the steel cage from floating up.

[0080] As a better choice, the inverted forks are symmetrically welded at intervals on the upper half of the main bars of the steel cage, the number of the inverted forks is 1 / 2 of the number of the main bars of the steel cage, the angle between the inverted forks and the main bars of the steel cage is 20°~30°, and the upper half is 0.2H~0.4H away from the top of the steel cage.

[0081] In summary, the method for calculating and controlling the anti-floating of the steel cage during the casting of bored cast-in-place piles in the above-mentioned embodiment determines the gravity of the steel cage and the force of concrete on the steel cage by measuring the bored cast-in-place pile parameters on site, and not only considers the buoyancy factor, but also comprehensively considers the viscosity and impact factors. According to the comparison results of the gravity of the steel cage and the force of concrete on the steel cage, corresponding anti-floating measures for the steel cage are formulated; compared with the existing anti-floating control measures for bored pile steel cages, it can scientifically determine the gravity of the steel cage and the force of concrete on the steel cage, and formulate more comprehensive and effective anti-floating measures for the steel cage, which has important theoretical guiding significance for subsequent bored cast-in-place pile construction.

[0082] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for calculating and controlling the anti-floating properties of steel cages during bored pile casting, characterized in that: The following steps are involved: S1: After the bored pile is bored, its hole diameter and pile depth are measured; S2: Lift the steel cage into the drill hole and determine the weight of the steel cage; S3: After cleaning the bottom and replacing the slurry, pour the concrete and determine the force exerted by the concrete on the steel cage. The force exerted by the concrete on the steel cage includes the sum of the buoyancy, viscosity and impact force exerted on the steel cage. S4: Compare the gravity of the steel cage and the force exerted by the concrete on the steel cage; S5: According to the comparison result of step S4, formulate the anti-floating countermeasures of the steel cage.

2. The method for calculating and controlling the anti-floating property of the steel cage during the casting process of bored piles according to claim 1 is characterized in that: In step S1, the hole diameter D and the pile depth H are measured to see whether they meet the design requirements. If not, re-drilling and repairing the hole should be performed.

3. The method for calculating and controlling the anti-floating property of the steel cage during the casting process of bored piles according to claim 1 is characterized in that: In step S2, the steel cage is hoisted into the drill hole, and the steel cage is tightened by hoisting rods to prevent the bottom of the steel cage from being inserted into the mud at the bottom of the pile.

4. The method for calculating and controlling the anti-floating property of the steel cage during the casting process of bored piles according to claim 2, characterized in that: In step S2, the calculation formula of the reinforcement cage gravity G is as follows: Among them, γ is the bulk density of the steel bar; n is the number of main bars in the steel cage; H is the length of the main bars in the steel cage; d is the diameter of the main bars in the steel cage.

5. The method for calculating and controlling the anti-floating property of the steel cage during the casting process of bored piles according to claim 4 is characterized in that: In step S3, the specific process is as follows: S31: After the steel cage is hoisted, the bottom is cleaned and the slurry is replaced through the grouting pipe until the slurry density reaches the set range and concrete can be poured; S32: Calculate the buoyancy of the steel cage: Where, F1 is the buoyancy of the steel cage; 浆 is the mud bulk density; 砼 is the concrete bulk density; h is the concrete liquid level height; S33: Calculate the viscous force on the steel cage: F2=πndhτ Among them, F2 is the viscous force on the steel cage; τ is the concrete shear stress; S34: Calculate the impact force on the steel cage: Among them, F3 is the impact force on the steel cage; t is the initial setting time of concrete; k is the rising speed of the concrete liquid level in the hole; S35: Calculate the force exerted by concrete on the steel cage: F=F1+F2+F3.

6. The method for calculating and controlling the anti-floating property of the steel cage during the bored pile casting process according to claim 5, characterized in that: In step S4, when the gravity of the steel cage is greater than the force exerted by the concrete on the steel cage within a set multiple range, the steel cage will not float and no countermeasures are needed; when the gravity of the steel cage is less than the force exerted by the concrete on the steel cage within a set multiple range, anti-floating countermeasures for the steel cage need to be formulated.

7. The method for calculating and controlling the anti-floating property of the steel cage during the casting process of bored piles according to claim 6, characterized in that: In step S5, the anti-floating measures for the steel cage include the following three measures: The first method is to reduce the concrete pouring speed v, thereby slowing down the concrete liquid level rising speed k and reducing the upward impact force on the steel cage caused by the rising concrete liquid level; The second method is to prefabricate a concrete ring at the bottom of the steel cage. When the concrete is poured in, the pressure of the concrete and the mud is concentrated on the concrete ring, thereby increasing the downward gravity of the steel cage. The third method: Before the steel cage is hoisted into the drilled hole, a set of inverted crosses are welded on the upper half of the main reinforcement of the steel cage to prevent the steel cage from floating up.

8. The method for calculating and controlling the anti-floating property of the steel cage during the bored pile casting process according to claim 7, characterized in that: In the first countermeasure, the concrete liquid level rising speed k is proportional to the concrete pouring speed v, and the relationship is: By adjusting the flow rate of the concrete pump, controlling the inclination angle of the concrete delivery pipe or adjusting the size of the concrete pouring port to reduce the concrete pouring speed v, the impact force F3 on the steel cage is reduced, and the force F of the concrete on the steel cage is also reduced, thereby preventing the steel cage from floating.

9. The method for calculating and controlling the anti-floating property of the steel cage during the bored pile casting process according to claim 7, characterized in that: In the second countermeasure, as the height h of the concrete liquid level rises, the pressure of the concrete and mud on the concrete ring gradually increases, thereby preventing the steel cage from floating up; The pressure of the concrete and slurry on the concrete ring is obtained by the following formula: Among them, T is the pressure of concrete and mud on the concrete ring; O is the outer diameter of the concrete ring; o is the inner diameter of the concrete ring. By adjusting the size of the inner diameter of the concrete ring, the pressure of the concrete and mud on the concrete ring can be controlled.

10. The method for calculating and controlling the anti-floating property of the steel cage during the bored pile casting process according to claim 7, characterized in that: In the third countermeasure, when the steel cage is hoisted into the borehole, the inverted fork is hoisted into the borehole along with the steel cage. When the concrete is poured, the steel cage tends to float up, and the inverted fork is inserted into the soil on the side wall of the borehole to prevent the steel cage from floating up. Among them, the inverted crosses are symmetrically welded at the upper half of the main bars of the steel cage. The number of inverted crosses is 1 / 2 of the number of main bars of the steel cage. The angle between the inverted crosses and the main bars of the steel cage is 20o~30o, and the upper half is 0.2H~0.4H away from the top of the steel cage.

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