Cast-in-place pile and side friction assessment method

Abstract

The invention discloses a cast-in-place pile and a side friction resistance evaluation method. The cast-in-place pile comprises a pile casing, a cone connected to the bottom of the pile casing and a plurality of windows formed in the side wall of the pile casing, and movable pieces are hinged to the windows; the device further comprises a central control column arranged in the pile casing, and the central control column is provided with push rods in one-to-one correspondence with the windows, a displacement monitoring and processing module used for monitoring the displacement of the push rods and a pressure controller used for controlling the pressure borne by the push rods. The comprehensive performance of the cast-in-place pile is remarkably improved through a mechanical structure capable of being actively controlled. The method is characterized in that a push rod is driven by a central control column to accurately eject out a movable piece hinged to the side wall of a pile casing, so that the movable piece is actively embedded into a surrounding soil body, and mechanical occlusion and lateral friction resistance between pile soil are greatly enhanced. According to the structure, mechanical and displacement data in the unfolding process of the movable piece can be collected in real time, and a high-precision and in-situ measurement data basis is provided for pile body friction resistance evaluation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of stress measurement, and particularly to a cast-in-place pile and a side friction resistance evaluation method. BACKGROUND

[0002] Under the background of accelerating urbanization, as an important facility for intensive laying of municipal pipelines, the foundation pit engineering of underground comprehensive pipe gallery faces multiple challenges in safety, economy and environmental protection of supporting structure. Although the traditional cast-in-place pile support has the advantages of large rigidity and strong adaptability, it has problems such as material waste and difficulty in recycling, which not only increases the engineering cost, but also produces a large amount of construction waste. At the same time, the foundation pit of urban pipe gallery is usually in a complex geological condition and dense building environment, and the deformation control requirement of the supporting system is extremely strict, while the existing recyclable supporting structures such as steel sheet pile and steel cement soil mixing wall have defects such as insufficient rigidity and joint leakage. At the same time, the change of pile foundation friction resistance can reflect the interaction between pile and soil and the stability of soil. By monitoring the side friction resistance of pile foundation during foundation pit construction, the influence of construction on pile foundation can be evaluated in real time, potential risks such as soil settlement and pile corrosion can be identified, and construction scheme and emergency plan can be optimized accordingly to ensure engineering safety. SUMMARY

[0003] The purpose of the present application is to provide a cast-in-place pile and a side friction resistance evaluation method, which has high supporting rigidity, low environmental impact and reusability, and can monitor and evaluate the side friction resistance of pile foundation to optimize construction safety control. To achieve the above-mentioned purpose, the present application provides the following technical scheme: In a first aspect, the present application discloses a cast-in-place pile, comprising a casing, a cone connected to the bottom of the casing, a plurality of windows opened in the side wall of the casing, and a movable piece hinged on the window; further comprising a central control column arranged in the casing, a push rod corresponding to the window on the central control column, a displacement monitoring and processing module for monitoring the displacement of the push rod, and a pressure controller for controlling the pressure borne by the push rod.

[0004] Further scheme: the central control column comprises a column body, and a grouting pipe arranged in the column body and along the axial direction of the column body.

[0005] Further scheme: the central control column is provided with an axial heater.

[0006] Further scheme: the push rod comprises a telescopic rod and a power mechanism for driving the movement of the push rod.

[0007] Further scheme: further comprising a cover arranged at the top end of the casing and a hook arranged on the cover.

[0008] In a second aspect, the present application discloses a method for evaluating the lateral friction resistance of the cast-in-place pile, characterized in that the method comprises the following steps: S1, placing the cast-in-place pile into a pre-drilled hole; S2, pushing the push rod outward to push the movable piece out of the window and into stable contact with the soil body; S3, pouring sulfur concrete into the casing, and after the sulfur concrete cools down, calculating the lateral friction resistance of the pile body according to the data collected by the pressure controller and the displacement monitoring and processing module.

[0009] Further, in step S3, the calculation process is as follows: segmentally accumulating the lateral friction resistance of a single power mechanism to obtain the initial total lateral friction resistance of the pile body; and correcting the initial total lateral friction resistance of the pile body in combination with the characteristics of the soil body to obtain the lateral friction resistance of the pile body.

[0010] Further, the lateral friction resistance of a single power mechanism is obtained by the following formula:

[0011] In the formula, is the lateral friction resistance of the i th power mechanism, with the unit of kPa; is the measured pressure of the i th power mechanism, with the unit of kPa; is the effective contact area of the movable piece with the soil body, with the unit of m 2 ; is the included angle between the movable piece and the casing, with the unit of °; The initial total lateral friction resistance of the pile body is obtained by segmentally accumulating along the pile body by the following formula:

[0012] In the formula, is the initial total lateral friction resistance of the pile body, with the unit of kPa; is the lateral friction resistance of the i th power mechanism, with the unit of kPa; is the segmental length of the pile body corresponding to the i th push rod, with the unit of m; and n is the number of push rods.

[0013] Further, the corrected total lateral friction resistance of the pile body is corrected by the following formula: ;

[0014] In the formula, is the corrected lateral friction resistance of the pile body, with the unit of kPa; is the lateral friction resistance of the i th power mechanism, with the unit of kPa; is the relative displacement of the pile-soil at the depth z, with the unit of mm; is the shear stiffness coefficient of the soil body; is the maximum slip threshold value; is a dimensionless coefficient between 0 and 1; e is a natural constant, and the value range is 2.7-2.8.

[0015] Compared with the prior art, the application has the beneficial effects that: The application significantly improves the comprehensive performance of the cast-in-place pile through the actively controllable mechanical structure. The core is that the active piece hinged to the side wall of the casing is precisely pushed out by the push rod driven by the middle control column, so that it is actively embedded in the surrounding soil, thereby greatly enhancing the mechanical engagement and lateral friction between the pile and the soil. The structure simultaneously integrates displacement and pressure monitoring modules, which can collect mechanical and displacement data during the expansion of the active piece in real time, providing a high-precision, in-situ measurement data basis for pile shaft friction evaluation.

[0016] Based on the collected data, the application further provides an accurate lateral friction evaluation method. The method not only calculates the initial friction by segment accumulation, but also innovatively introduces a nonlinear correction model considering the relative displacement of pile and soil, effectively quantifying the influence of slip effect, overcoming the large error of traditional theoretical models in complex soil, and significantly improving the reliability and accuracy of friction calculation.

[0017] In addition, the cast-in-place pile innovatively uses sulfur concrete as a filling material and integrates a heater and a top hoisting structure. After construction is completed, the concrete can be melted, and the core components such as the casing, the active piece, and the middle control column can be completely recovered, realizing the recycling of the supporting structure. This design fundamentally solves the pain points of high waste rate, much construction waste, and high cost of traditional cast-in-place piles, and has significant economic benefits and environmental value. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 is a structural schematic diagram of the cast-in-place pile of the application; Fig. 2 is a structural schematic diagram of the middle control column in the application; Fig. 3 is a structural schematic diagram of the push rod in the application; In the figure: 1-casing, 11-window, 12-cover, 13-cone, 2-hook, 3-active piece, 4-middle control column, 41-column body, 42- grouting pipe, 43-support frame, 5-push rod, 51-telescopic rod, 52-power mechanism, 6-displacement monitoring and processing module, 7-heater. DETAILED DESCRIPTION

[0019] With reference to the drawings and embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0020] In the description of the present application, it should be noted that the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings or the orientation or positional relationship commonly used when the product of the present application is used, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0021] Please refer to Figs. 1-3 In the present embodiment, a cast-in-place pile includes a casing 1, a cone 13 connected to the bottom of the casing 1, and a plurality of windows 11 provided in the side wall of the casing 1, wherein a movable piece 3 is hinged to each window 11. The pile further includes a central control column 4 provided in the casing 1, wherein the central control column 4 is provided with a push rod 5 corresponding to each window 11, a displacement monitoring and processing module 6 for monitoring the displacement of the push rod 5, and a pressure controller for detecting the pressure borne by the push rod 5. The pressure controller is built into the upper cover of the casing 1, which is not shown in the figure. The push rod 5 pushes the movable piece 3 outward, the push rod 5 is in stable contact with the soil body, and the movable piece 3 is inclinedly embedded in the soil body to improve the bearing capacity of the pile foundation. The displacement monitoring and processing module 6 and the pressure controller obtain pile-soil interaction data in situ, which is used to calculate the lateral friction of the pile body. The pressure controller adjusts the output of the push rod 5 in real time according to the hardness of the soil to prevent the movable piece 3 from being overloaded and damaged. In addition, the pressure controller and the displacement monitoring and processing module 6 are data-fused and cooperatively monitored to improve the calculation accuracy of the friction.

[0022] Further, the central control column 4 includes a column body 41 and a grouting pipe 42 arranged axially along the column body 41. The grouting pipe 42 is used to inject sulfur concrete into the column body.

[0023] Further, the central control column 4 is provided with a heater 7 arranged axially. The heater 7 is a tubular heater, which is used to heat and melt the sulfur concrete, and realizes the lossless recovery of the casing 1 and the central control column 4.

[0024] Further, the push rod 5 includes a telescopic rod 51 and a power mechanism 52 for moving the push rod 5. The telescopic rod 51 adjusts the displacement of the expansion of the movable piece 3 to adapt to different soil layers. The power mechanism 52 can be selected as a hydraulic / electric dual mode to ensure the reliability in extreme working conditions.

[0025] Further, the support frame 43 is arranged in the column body 41, which provides a solid and stable mounting base and force frame for the entire center control column system (including the push rod 5, the heater 7, the grouting pipe 2, etc.).

[0026] Further, the cover 12 arranged at the top end of the casing 1 and the hook 8 arranged on the cover 12 are also included. The hook 8 is integrated in the cover 12 to avoid welding damage to the structure. After the foundation pit construction is completed, the inside of the casing 1 is heated by the tubular heater, the sulfur concrete is then extracted, the pile foundation is pulled out through the hook 8, and the pile foundation is recycled.

[0027] The embodiment also discloses an evaluation method for the side friction of the cast-in-place pile. S1, placing the cast-in-place pile into a pre-drilled hole; S2, pushing the push rod outward to push the movable piece out of the window and into stable contact with the soil; S3, pouring sulfur concrete into the casing, and after the sulfur concrete is cooled, calculating the side friction of the pile body according to the data collected by the pressure controller and the displacement monitoring and processing module.

[0028] Further, the calculation process of step S3 is as follows: the side friction of a single power mechanism 52 is segmented and accumulated to obtain the initial total side friction of the pile body; and the initial total side friction of the pile body is corrected in combination with the characteristics of the soil to obtain the side friction of the pile body.

[0029] Further, the side friction of a single power mechanism 52 is obtained through the following formula:

[0030] In the formula, is the side friction of the i th power mechanism 52, and the unit is kPa; is the measured pressure of the i th power mechanism 52, and the unit is kPa; is the effective contact area of the movable piece 3 and the soil, and the unit is m 2 ; is the included angle between the movable piece 3 and the casing 1, and the unit is °; The initial total side friction of the pile body is segmented and accumulated along the pile body through the following formula:

[0031] In the formula, is the initial total side friction of the pile body, and the unit is kPa; is the side friction of the i th power mechanism 52, and the unit is kPa; is the length of the pile body segment corresponding to the i th push rod 5 (the overall length of the casing 1 is evenly divided according to the number of push rods 5), and the unit is m; and n is the number of push rods.

[0032] Further, the total pile side friction is modified by the following formula: ;

[0033] wherein, is the modified pile side friction, in kPa; is the side friction of the ith actuator 52, in kPa; is the relative displacement of the pile and soil at depth z, in mm; is the soil shear stiffness coefficient; is the maximum slip threshold; is the displacement modification coefficient at depth z, which is a dimensionless coefficient between 0 and 1; e is the natural constant, which has a value of 2.71828.

[0034] Although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the specification is described in this way only for the sake of clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

[0035] Therefore, the above description is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application; that is, any equivalent transformation made within the scope of the claims of the present application is within the protection scope of the claims of the present application.

Claims

1. A cast-in-place pile, characterized in that, It includes a protective sleeve (1), a cone (13) connected to the bottom of the protective sleeve (1), and multiple windows (11) opened on the side wall of the protective sleeve (1), with movable pieces (3) hinged on the windows (11); it also includes a central control column (4) located inside the protective sleeve (1), with push rods (5) corresponding to the windows (11) on the central control column (4), a displacement monitoring and processing module (6) for monitoring the displacement of the push rods (5), and a pressure controller for controlling the pressure borne by the push rods (5).

2. The cast-in-place pile according to claim 1, characterized in that, The central control column (4) includes a column body (41) and a grouting pipe (42) disposed in the column body (41) and arranged along its axial direction.

3. The cast-in-place pile according to claim 1, characterized in that, The central control column (4) is equipped with an axially arranged heater (7).

4. The cast-in-place pile according to claim 1, characterized in that, The push rod (5) includes a telescopic rod (51) and a power mechanism (52) that drives the push rod (5) to move.

5. The cast-in-place pile according to claim 1, characterized in that, It also includes a cover (12) located at the top of the protective sleeve (1) and a hook (8) located on the cover (12).

6. A method for evaluating the side friction resistance of a cast-in-place pile as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Place the cast-in-place pile into the pre-drilled hole; S2. Push the push rod outward to push the movable piece out of the window and make stable contact with the soil. S3. Pour sulfur concrete into the casing. After the sulfur concrete cools, calculate the side friction resistance of the pile body based on the data collected by the pressure controller and displacement monitoring and processing module.

7. The evaluation method according to claim 6, characterized in that, In step S3, the calculation process is as follows: the side friction resistance of a single power mechanism is accumulated in segments to obtain the initial total pile side friction resistance; combined with the soil properties, the initial total pile side friction resistance is corrected to obtain the pile side friction resistance.

8. The evaluation method according to claim 6, characterized in that, The side friction resistance of a single power mechanism is obtained by the following formula: In the formula, Let be the side friction resistance of the i-th power mechanism, in kPa; The measured pressure of the i-th power mechanism is expressed in kPa. The effective contact area between the moving part and the soil, in m². 2 ; The angle between the movable plate and the casing, in degrees; The initial total pile side friction is obtained by summing it segmentally along the pile using the following formula: In the formula, The initial total pile side friction resistance is expressed in kPa. Let be the side friction resistance of the i-th power mechanism, in kPa; is the length of the pile segment corresponding to the i-th push rod, in meters; n is the number of push rods.

9. The evaluation method according to claim 6, characterized in that, The total pile side friction resistance is corrected using the following formula: ； in, The corrected side friction resistance of the pile body is expressed in kPa. Let be the side friction resistance of the i-th power mechanism, in kPa; The pile-soil relative displacement at depth z is expressed in mm. This is the soil shear stiffness coefficient; The maximum slip threshold; The displacement correction factor at depth z is a dimensionless coefficient between 0 and 1; e is a natural constant with a value range of 2.7-2.8.

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