A test method for simulating the impact driving of precast piles

Abstract

This invention discloses a test method for simulating the impact driving of precast piles, comprising the following steps: adjusting the position and irradiation direction of a laser emitter; driving the pipe pile through an impact device and measuring the penetration depth s of the pipe pile; moving the laser emitter downwards by s based on the penetration depth s to adjust the position of the laser emitter; during the impact driving process, a camera continuously captures images of the pile and soil during the driving process, and the displacement of the pile and soil is obtained through image processing technology. The displacement of the pile and soil includes the upward displacement of the pile and soil and the radial displacement on both sides of the pile and soil. The soil plugging effect of the pile and soil is evaluated based on the upward displacement of the pile and soil and the radial displacement on both sides of the pile and soil. This invention can realize the development law of pile-soil interaction with soil displacement at the pile side and pile end locations under the influence of ground stress, so as to simulate the formation of soil plug at the pile end.

Description

Technical Field

[0001] This invention relates to the field of simulation testing technology for pipe pile driving, specifically a test device for simulating dynamic driving of precast piles. Background Technology

[0002] Precast piles are widely used as a foundation type for land and water construction due to their high pile-driving efficiency and easy quality control. Common types of precast piles include steel pipe piles and PHC piles. Precast piles are generally driven using methods such as impact, vibration, and static pressure. Impact and vibration are both dynamic pile-driving methods. Dynamic pile driving is highly efficient and adaptable, making it one of the main methods for pile foundation construction.

[0003] Faced with complex and ever-changing geological environments, many pile driving projects encounter problems due to a lack of understanding of the dynamic pile driving principles or insufficient analytical experience and technology. These problems include pile slippage, hammer rejection, and failure to meet bearing capacity requirements, resulting in economic losses and safety risks. To address this issue, on-site pile testing (i.e., experimental pile driving) can be used to measure and obtain relevant parameters to calculate whether the bearing capacity requirements are met. However, on-site pile testing is too costly and difficult to fully cover all geological conditions, especially for special soils with varying properties and hardness. Therefore, indoor simulated pile driving has become a crucial method for solving this problem.

[0004] Most existing simulated pile driving test devices are small-scale model pile tests that do not consider the influence of ground stress. They mainly focus on measuring the mechanical parameters of pile-soil interaction and assess the impact parameters of pile foundation stress by measuring the changes in the pile-soil stress field around the pile during pile driving. These existing simulated pile driving test devices lack the ability to measure the penetration depth during pile driving, and in particular, they cannot effectively measure the changes in pile-soil interaction at the pile side and pile tip as the soil displacement occurs. They cannot simulate the formation of soil plugs at the pile tip, and therefore cannot establish the relationship between pile displacement and pile-soil interaction mechanical parameters, thus making it impossible to optimize pile driving technology based on this relationship. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a test method for simulating the impact driving of precast piles, which can solve the problems described in the background art.

[0006] The technical solution to achieve the objective of this invention is as follows: a test method for simulating the impact driving of precast piles, applied to a test device for simulating the dynamic driving of precast piles, the test method comprising the following steps:

[0007] Step 11: Adjust the position and irradiation direction of the laser emitter so that the laser emitted by the laser emitter is perpendicular to the sensing surface of the CCD sensor on the pipe pile;

[0008] Step 12: Install the impact device on the hammer cap, and apply hammering force to the pipe pile through the impact device to achieve impact driving of the pipe pile.

[0009] During the downward displacement of the pipe pile, the pipe pile drives the CCD sensor on the pipe pile to move downward synchronously. The position of the laser point on the CCD sensor also moves accordingly, and the position of the laser point is collected by the CCD sensor. The collected laser point position is transmitted to the computer through the wireless communication module.

[0010] Step 13: During the hammering of the pipe pile by the impact device, the penetration depth s of the pipe pile is measured by the displacement change information of the laser point on the CCD sensor over time.

[0011] Step 14: Based on the penetration depth s of the pipe pile, the laser emitter is moved downwards by s to adjust its position;

[0012] Step 15: Repeat steps 13 and 14 to achieve continuous downward driving of the pipe pile. The depth of the pipe pile into the soil is equal to the final moving distance of the laser emitter, thereby obtaining the variation curve between the final maximum moving displacement DMX, penetration s, and pile rebound c.

[0013] Step 16: Before the impact device begins driving the pipe pile, turn on the three laser lights on the grid column. The lasers emitted by the three laser lights shine through the transparent part and irradiate the pile and soil, forming speckle patterns on the pile and soil surface in the first observation area, the second observation area and the third observation area.

[0014] Step 17: Aim the camera at the observation window to capture images of the pile soil in the three observation areas.

[0015] During the impact pile driving process, a camera continuously captures images of the pile and soil during the driving process, and image processing technology is used to obtain the displacement of the pile and soil.

[0016] The displacement of the pile and soil includes the upward displacement of the soil within the pile and the radial displacement of the soil around the pile to both sides. The soil plugging effect of the pile and soil is evaluated based on the upward displacement of the soil within the pile and the radial displacement of the soil around the pile to both sides. If the change in soil displacement is less than or equal to a first threshold and the change in radial displacement of the soil around the pile to both sides is greater than or equal to a second threshold, then the soil plugging effect is considered to have occurred; otherwise, it is considered that the soil plugging effect has not occurred.

[0017] The critical point at which the soil plugging effect occurs during pile driving is determined by the pile driving depth and pile penetration degree when the soil plugging effect occurs.

[0018] Furthermore, step 17 also includes,

[0019] Using a piezoresistive sensor installed on the pipe pile, the radial stress σr at the lower end of the pipe pile and the vertical stress σv at the top end of the pipe pile are measured respectively. Based on the radial stress σr, the shear stress τ at the lower end of the pipe pile is obtained. This represents the friction angle at the pile-soil interface obtained from indoor pile-soil tests, in order to establish the curve relationship between the pile-soil shear stress and vertical displacement on the pile side of the pipe pile, and the curve relationship between the pile-soil vertical stress and vertical displacement at the pile tip of the pipe pile.

[0020] Furthermore, following step 17, the process also includes:

[0021] Step 18: Calculate the total resistance Rd of the pipe pile according to formula ①, and calculate the static resistance Rstatic of the pipe pile according to formula ②.

[0022]

[0023] In the formula, As represents the side surface area of ​​the pipe pile, Ap represents the end surface area of ​​the pipe pile, τouter represents the external skin friction of the pipe pile, and τinne represents the skin friction of the pipe pile. r The inner frictional resistance of the pipe pile is represented by d, the diameter of the pipe pile is t, the wall thickness of the pipe pile is mg, the weight of the impact hammer cap is h, and the falling height of the impact hammer cap is h.

[0024] Furthermore, the test apparatus for simulating dynamic pile driving of precast piles includes a reaction frame, a model cylinder, a sliding base, a jack, a pile driving device, a hammer cap, and an observation device. The model cylinder is installed on the sliding base, and a cavity for containing the pile soil is provided inside the model cylinder. The jack is installed at the end of the model cylinder away from the sliding base, and the jack abuts against the reaction frame.

[0025] The hammer cap is installed on the pipe pile, which serves as the precast pile. The pipe pile passes through the mold cylinder and is inserted into the soil inside the mold cylinder, with one end of the pipe pile protruding outside the mold cylinder. The hammer cap is located on the protruding end of the pipe pile.

[0026] The pile driving device is used to drive the pipe pile into the soil using dynamic pile driving, thereby simulating the dynamic pile driving process of precast piles.

[0027] The observation device is located on the outside of the model cylinder.

[0028] Furthermore, the reaction frame includes a frame body, a main crossbeam, a square base, and anchor bars installed on the frame body. The jack abuts against the main crossbeam, the square base is fixedly installed at the lower end of the frame body, and the main crossbeam spans across the frame body.

[0029] Anchor bars pass through the main crossbeam and the frame to fix the main crossbeam and the frame together. An anchor block is also installed on one end of the anchor bar that passes through the main crossbeam and the frame. The anchor bar also passes through the frame and the square base and is exposed on the outside of the square base. The anchor bar is used to penetrate into the ground and fix it to the ground to fix the reaction frame on the ground.

[0030] Furthermore, the model cylinder includes a cylinder body, an air bladder, and a pressure plate. The cylinder body includes a cavity, and the air bladder is installed inside the cavity. When inflated, the air bladder adheres to the inner wall of the cavity of the cylinder body, forming a receiving space for holding pile soil. The pressure plate covers the cylinder body or covers both the cylinder body and the air bladder. The pressure plate has through holes at its center and eccentric position.

[0031] Furthermore, the model cylinder also includes an observation window. A through-hole is drilled in both the cylinder body and the air bladder. When the air bladder is inflated and fits against the inner wall of the cylinder's cavity, the through-holes in the cylinder body and the air bladder are aligned. The through-hole in the cylinder body is fitted with grid posts embedded in it. The through-hole in the air bladder is fitted with a transparent element, with the grid posts positioned directly in front of the transparent element. When the pipe pile passes through the through-hole and is inserted into the soil, the pipe pile is directly facing the observation window.

[0032] The grid column comprises several upright columns, which are connected together in a cross shape to form an array. Each grid column is also equipped with a first laser light, a second laser light, and a third laser light facing opposite directions. These laser lights are positioned away from the observation device so that they can illuminate the soil surface inside the model cylinder.

[0033] The grid columns divide the observation window into a first observation area, a second observation area, and a third observation area in a certain direction. The first laser light is located in the first observation area, the second laser light is located in the second observation area, and the third laser light is located in the third observation area.

[0034] The pipe pile is equipped with strain gauges and CCD sensors at one end of the model cylinder, and piezoresistive sensors are installed on the inner and outer walls of the top and bottom ends of the pipe pile.

[0035] Furthermore, the sliding base includes a sliding frame, and a first snap-fit ​​plate, a second snap-fit ​​plate, a support plate, several sliding shafts, and several fixing blocks mounted on the sliding frame. The sliding shafts are arranged parallel and spaced apart. Both ends of each sliding shaft are fixedly connected to a fixing block, which is fixedly mounted on both ends of the sliding frame. The support plate is mounted on the sliding frame and located above the sliding shafts. The first and second snap-fit ​​plates are snap-fitted onto the sliding frame. The first and second snap-fit ​​plates are located on opposite sides of the support plate and fixedly connected to it. Both the first and second snap-fit ​​plates are located above the sliding frame. The model cylinder is mounted on the support plate.

[0036] The sliding shafts are arranged sequentially from low to high and then back to low along the axial direction of the sliding frame.

[0037] Furthermore, the pile driving device includes an impact device, which comprises an impact motor, an impact output shaft, a traction rope, a hammer body, a stop rod, and an impact hammer cap. The output shaft of the impact motor is connected to the impact output shaft, one end of the traction rope is wound around the impact output shaft, and the other end of the traction rope is fixedly connected to the hammer body.

[0038] The hammer body is fixedly connected to one end of the plunger rod, and the other end of the plunger rod is fixedly connected to the impact hammer cap column. The outer wall of the impact hammer cap column is provided with an external thread, and the impact hammer cap column matches the internal thread of the inner wall of the hammer cap through the external thread.

[0039] Furthermore, the observation device includes a camera, a laser emitter, a tripod, a support rod, a computer, and a wireless communication module. The camera is mounted on the top of the tripod and is communicatively connected to the computer. The laser emitter is slidably mounted on the support rod and can slide along the axial direction of the support rod. The laser emitter is electrically connected to the computer and emits laser light onto a CCD sensor.

[0040] The camera takes pictures through the observation window on the model tube, and three laser lights inside the observation window illuminate the soil surface of the pile at different locations inside the model tube.

[0041] The beneficial effects of this invention are as follows: This invention can effectively realize dynamic pile driving, including impact pile driving and vibratory pile driving. By applying pressure to the pressure plate through jacks, it acts on the pile and soil to simulate the influence of ground stress. Thus, considering the influence of ground stress, it can measure the penetration during the pile driving process and obtain the development law of pile-soil interaction with soil displacement at the pile side and pile end locations during the pile driving process, so as to simulate the formation of pile end soil plug (effect). Therefore, it can establish the relationship between pile displacement and pile-soil interaction mechanical parameters.

[0042] In addition, this test device has a simple structure, is easy to maintain, has a long service life, and can be set at the center or off-center of the pile soil as needed. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the experimental setup;

[0044] Figure 2 This is a schematic diagram of the reaction frame of the test apparatus;

[0045] Figure 3 This is a schematic diagram of the exploded structure of the model cylinder;

[0046] Figure 4 This is a schematic diagram of the grid column structure;

[0047] Figure 5 This is a front view of the grid column;

[0048] Figure 6 This is a schematic diagram showing the location between the pipe piles and the grid pattern;

[0049] Figure 7 This is a schematic diagram of the structure of the model cylinder on the sliding base;

[0050] Figure 8 This is a schematic diagram of the impact device.

[0051] Figure 9 A schematic diagram showing the structure in which the impact motor of the impact device is installed inside the inner box;

[0052] Figure 10 A schematic diagram of a structure in which the impact motor of an impact device is installed in an inner housing and the inner housing is installed in an outer housing;

[0053] Figure 11 A schematic diagram of the impact device installed inside the hammer cap;

[0054] Figure 12 This is a schematic diagram of the impact device installed inside the hammer cap from another perspective.

[0055] Figure 13 This is a schematic diagram of the vibration device.

[0056] Figure 14 This is a schematic diagram of the structure where the vibration device is installed inside the hammer cap;

[0057] Figure 15 A schematic diagram of the structure of the vibration device installed inside the hammer cap from another perspective;

[0058] Figure 16 This is a schematic diagram of the structure of the first vibration device and the second vibration device;

[0059] Figure 17 A schematic diagram illustrating the principle of the force generated by the first and second vibration devices.

[0060] Figure 18 This is a side view of the experimental setup;

[0061] Figure 19 This is a front view of the experimental setup;

[0062] Figure 20 This is a top view of the experimental setup;

[0063] Figure 21 A schematic diagram of the structure for moving the pipe pile to the center of the model cylinder;

[0064] Figure 22A schematic diagram showing the relationship between the maximum displacement DMX, penetration s, and pile rebound c;

[0065] Figure 23 Schematic diagrams showing the occurrence and absence of soil plugging effect;

[0066] Figure 24 A flowchart illustrating the test method for impact pile driving;

[0067] Figure 25 This is a flowchart illustrating the test method for vibratory pile driving.

[0068] In the diagram, 1-Main beam, 2-Pile driving device, 3-Hammer cap, 4-Jack, 5-Reaction frame, 6-Cylinder body, 7-Square base, 8-Camera, 9-Laser emitter, 10-Tripod, 11-Support rod, 12-Computer, 13-Wireless communication module, 14-Anchor bar, 15-Anchor block, 16-Pressure plate, 17-Observation window, 18-Airbag, 19-Pipe pile, 20-Grid column, 21-Ventilation valve, 22-Column rod, 23- 24-First laser light, 25-Second laser light, 26-First observation area, 27-Second observation area, 28-Third observation area, 29-Strain gauge, 30-CCD sensor, 31-First snap plate, 32-Sliding shaft, 33-Fixing block, 34-Sliding frame, 35-Second snap plate, 36-Pad, 37-Impact motor, 38-Impact output shaft, 39-Hammer body, 40-Plug rod, 41-Impact hammer 42-Hammer cap thread, 43-Traction rope, 44-Inner box, 45-Outer box, 46-Upper box, 47-Lower box, 48-Wedge block, 49-Vibrating hammer cap, 50-Column rod, 51-First vibration device, 511-First motor, 512-First gear, 513-First rotating shaft, 514-First movable cam, 515-Second rotating shaft, 516-Second movable cam, 517-First fixed cam. 518-Second gear, 519-First base, 52-Second vibration device, 521-Second base, 522-Second motor, 523-Third fixed cam plate, 524-Third gear, 525-Fourth fixed cam plate, 526-Fourth gear, 527-Third movable cam plate, 528-Third rotating shaft, 529-Fourth movable cam plate, 530-Fourth rotating shaft, 53-Bearing column, 54-Support plate, 55-Connecting column rod. Detailed Implementation

[0069] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0070] like Figures 1-23As shown, this embodiment provides a test device for simulating the dynamic driving of precast piles, including a reaction frame 5, a model cylinder, a sliding base, a jack 4, a pile driving device 2, a hammer cap 3, and an observation device. The model cylinder is installed on the sliding base, and a cavity for containing the pile soil is provided inside the model cylinder. The jack 4 is installed at the end of the model cylinder away from the sliding base, and the jack 4 abuts against the reaction frame 5. The reaction frame 5 is used to provide a reaction force to the model cylinder through the jack 4 to press the pile soil inside the model cylinder. The hammer cap 3 is installed on the pipe pile 19, which is the precast pile. The pipe pile 19 passes through the model cylinder and is inserted into the pile soil located inside the model cylinder. One end of the pipe pile 19 protrudes outside the model cylinder, and the hammer cap 3 is located on the end of the pipe pile 19 that protrudes outside the model cylinder. The pile driving device 2 is used to drive the pipe pile 19 into the pile soil through the hammer cap 3. The pile driving device 2 can realize the dynamic driving of the pipe pile 19 into the pile soil in a dynamic pile driving manner to simulate the dynamic pile driving process of precast piles. The observation device is located outside the model tube. The observation device is used to observe the relevant parameters of the pile soil, such as the pile soil displacement and pile soil resistance changes during the pile driving process, as well as the parameters of the pipe pile 19, such as the pile driving displacement and pile driving penetration rate during the pile driving process. In this way, the pile soil displacement and pile soil resistance changes can be correlated with the pile driving displacement and pile driving penetration rate of the pipe pile 19.

[0071] For example, the reaction frame 5 includes a frame body, a main crossbeam 1, a square base 7, and anchor bars 14 mounted on the frame body. The jack 4 abuts against the main crossbeam 1, the square base 7 is fixedly mounted on the lower end of the frame body, and the main crossbeam 1 spans across the frame body. The anchor bars 14 pass through the main crossbeam 1 and the frame body to fix the main crossbeam 1 and the frame body together. An anchor block 15 is also installed on one end of the anchor bars 14 that pass through the main crossbeam 1 and the frame body. The anchor bars 14 also pass through the frame body and the square base 7 and are exposed on the outside of the square base 7. In actual use, the reaction frame 5 is fixedly mounted on the ground by the anchor bars 14 penetrating into the ground, so that after the jack 4 acts on the reaction frame 5, the reaction frame 5 remains fixed and can provide a reaction force to the jack 4, which in turn acts on the pile soil inside the model cylinder of the pressure plate 16 machine.

[0072] The jack 4 abuts against the center of the main crossbeam 1. The jack 4 abuts against the main crossbeam 1 through a pad 36, which is located between the jack 4 and the main crossbeam 1. The pad 36 can be a square block.

[0073] For example, the model cylinder includes a cylinder body 6, an air bladder 18, and a pressure plate 16. The cylinder body 6 includes a cavity, and the air bladder 18 is installed inside the cavity. When inflated, the air bladder 18 adheres to the inner wall of the cavity of the cylinder body 6 and partially fills the cavity to form a receiving space for holding pile soil. The pressure plate 16 covers the cylinder body 6, or covers both the cylinder body 6 and the air bladder 18.

[0074] The pressure plate 16 has through holes at its center and eccentricity, respectively, through which the pipe pile 19 can pass, thereby allowing the pipe pile 19 to be inserted into the center of the pile soil or to the side of the pile soil.

[0075] For example, the model cylinder also includes an observation window 17. A through-hole is drilled in both the cylinder body 6 and the airbag 18; the through-hole can be square, circular, or other shapes. When the airbag 18 is inflated and fits against the inner wall of the cylinder body 6, the through-holes on the cylinder body 6 and the airbag 18 are directly opposite each other. A grid post 20 is provided in the through-hole on the cylinder body 6, embedded in the through-hole. A transparent element is provided in the through-hole on the airbag 18, serving to isolate the pile from the soil. The grid post 20 is located directly in front of the transparent element, which can be made of transparent glass or transparent acrylic sheet, or other transparent materials. When the pipe pile 19 passes through the through-hole and is inserted into the pile soil, the pipe pile 19 is directly opposite the observation window 17, allowing the pipe pile 19 to be observed through the observation window 17. This enables the observation device to observe the pile soil and the pipe pile 19 within the containment space through the observation window 17.

[0076] For example, the cylinder 6 is also equipped with a vent valve 21, which is connected to the air bladder 18 to inflate the air bladder 18 or expel gas from the air bladder 18 (i.e., de-air).

[0077] The grid column 20 includes several upright columns, which are connected together in a cross shape to form an array. The grid column 20 is also equipped with a first laser light 23, a second laser light 24, and a third laser light 25 facing in opposite directions. The first laser light 23, the second laser light 24, and the third laser light 25 are positioned away from the observation device so as to illuminate the surface of the pile and soil inside the model tube; that is, the first laser light 23, the second laser light 24, and the third laser light 25 face inwards to illuminate the surface of the pile and soil.

[0078] For example, the grid column 20 divides the observation window 17 into a first observation area 26, a second observation area 27 and a third observation area 28 in a certain direction. The first laser light 23 is located in the first observation area 26, the second laser light 24 is located in the second observation area 27 and the third laser light 25 is located in the third observation area 28.

[0079] For example, a strain gauge 29 and a CCD sensor 30 are provided on one end of the pipe pile 19 located in the model cylinder. The strain gauge 29 is used to measure the hammer force generated by the pile driving device 2 impacting the pipe pile 19 or the excitation force generated by the vibration pile driving.

[0080] Piezoresistive sensors (not shown in the figure) are installed on the inner and outer walls of the top and bottom ends of the pipe pile 19. The piezoresistive sensors are used to measure the stress on the pipe pile 19.

[0081] For example, the sliding base includes a sliding frame 34, and a first snap-fit ​​plate 31, a second snap-fit ​​plate 35, a support plate 54, a plurality of sliding shafts 32, and a plurality of fixing blocks 33 mounted on the sliding frame 34. The sliding shafts 32 are arranged parallel and spaced apart, with both ends of each shaft fixedly connected to a fixing block 33. The fixing blocks 33 are fixedly mounted on both ends of the sliding frame 34. The support plate 54 is mounted on the sliding frame 34 and located above the sliding shafts 32. The first snap-fit ​​plate 31 and the second snap-fit ​​plate 35 are snap-fitted onto the sliding frame 34. The first snap-fit ​​plate 31 and the second snap-fit ​​plate 35 are located on opposite sides of the support plate 54 and fixedly connected to it. Both the first snap-fit ​​plate 31 and the second snap-fit ​​plate 35 are located above the sliding frame 34. The model cylinder is mounted on the support plate 54.

[0082] The sliding shaft 32 is arranged in a series of low to high and then low along the axial direction of the sliding frame 34. This height change facilitates the movement of the model cylinder on the support plate 54 into and out of the sliding frame 34.

[0083] The entire sliding base supports the model cylinder and constrains its movement. It provides support for the cylindrical model cylinder and limits its displacement, offsetting the stress caused by the deformation of the model cylinder's sidewall due to the ground stress provided by the reaction force, thereby ensuring the overall stability of the model cylinder.

[0084] For example, the pile driving device 2 includes an impact device and a vibration device. The impact device and the vibration device are two independent components. When impact pile driving is required, the pile driving device 2 uses the impact device. When vibration pile driving is required, the pile driving device 2 uses the vibration device.

[0085] The impact device includes an impact motor 37, an impact output shaft 38, a traction rope 43, a hammer body 39, a stopper rod 40, and an impact hammer cap post 41. The output shaft (i.e., rotor) of the impact motor 37 is connected to the impact output shaft 38. One end of the traction rope 43 is wound around the impact output shaft 38, and the other end of the traction rope 43 is fixedly connected to the hammer body 39. The impact motor 37 rotates forward or backward to wind up or release the traction rope 43, thereby extracting or lowering the hammer body 39.

[0086] The hammer body 39 is fixedly connected to one end of the stopper rod 40, and the other end of the stopper rod 40 is fixedly connected to the impact hammer cap post 41. The outer wall of the impact hammer cap post 41 is provided with an external hammer cap thread 42. The impact hammer cap post 41 matches the internal thread on the inner wall of the hammer cap 3 through the external hammer cap thread 42, so that the impact hammer cap post 41 and the hammer cap 3 are threadedly connected, thereby connecting the impact device to the hammer cap 3 and realizing the installation of the impact device on the hammer cap 3.

[0087] For example, the impact device also includes an inner housing 44, the impact motor 37 is installed inside the inner housing 44, and the end of the impact output shaft 38 away from the impact motor 37 passes through the inner housing 44 and is exposed outside the inner housing 44.

[0088] For example, the impact device further includes an outer housing 45, an inner housing 44 located inside the outer housing 45, one end of the impact shaft exposed outside the inner housing 44 located inside the outer housing 45, and the end of the traction rope 43 away from the impact shaft passing through the outer housing 45 and connected to the hammer 39.

[0089] For example, the vibration device includes an upper housing 46, a lower housing 47, a first vibration device 51, a second vibration device 52, a connecting rod 55, a vibrating hammer cap 49, and a plurality of wedge blocks 48. The first vibration device 51 is installed inside the lower housing 47, and the second vibration device 52 is installed inside the upper housing 46. The upper housing 46 is stacked on top of the lower housing 47, and the upper housing 46 and the lower housing 47 are fixedly or detachably connected. The lower housing 47 is connected to the upper end of the connecting rod 55, and the lower end of the connecting rod 55 is fixedly connected to the vibrating hammer cap 49. The wedge blocks 48 are fixedly connected to the end of the vibrating hammer cap 49 opposite to the connecting rod 55, and the wedge blocks 48 are spaced apart.

[0090] The first vibration device 51 includes a first motor 511, a first gear 512, a second gear 518, a first rotating shaft 513, a second rotating shaft 515, a first movable cam plate 514, a second movable cam plate 516, a first fixed cam plate 517, and a first base 519. The first motor 511 is mounted on the first base 519. The output end (i.e., the rotor) of the first motor 511 is connected to the first rotating shaft 513, and the first motor 511 can drive the first rotating shaft 513 to rotate. The first gear 512 is sleeved and fixed on the first rotating shaft 513, and the first gear 512 can rotate with the first rotating shaft 513. The first movable cam plate 514 is fixedly mounted on the end of the first rotating shaft 513 away from the first motor 511, and the first gear 512 and the first movable cam plate 514 are spaced apart.

[0091] One end of the second rotating shaft 515 is rotatably mounted on the first base 519, for example, by means of a bearing or other component. The other end extends away from the first base 519 and is located on the outside of the first base 519. The second rotating shaft 515 and the first rotating shaft 513 are arranged parallel and spaced apart. The second gear 518 is sleeved and fixed on the second rotating shaft 515. The second gear 518 meshes with the first gear 512. Through the meshing transmission of the first gear 512 and the second gear 518, the first motor 511 can synchronously drive the first rotating shaft 513 and the second rotating shaft 515 to rotate. The second movable cam plate 516 is fixedly installed at the end of the second rotating shaft 515 away from the first base 519. The second movable cam plate 516 and the first movable cam plate 514 are arranged in parallel and, along the axial direction of the second rotating shaft 515, at least a portion of the first movable cam plate 514 and the second movable cam plate 516 overlap. That is, when the first movable cam plate 514 and the second movable cam plate 516 are projected along the axial direction of the second rotating shaft 515, at least a portion of the two movable cam plates overlap.

[0092] The first fixed cam plate 517 is sleeved and fixed on the second rotating shaft 515, and the second fixed cam plate is located between the first base 519 and the second gear 518. The first fixed cam plate 517 plays a protective role.

[0093] When the first motor 511 starts, it drives the first rotating shaft 513 to rotate, which in turn drives the first movable cam plate 514 to rotate. The first movable cam plate 514 rotates together with the first rotating shaft 513, achieving a 360° rotation. Simultaneously, the first motor 511 drives the second rotating shaft 515 to rotate synchronously with the first rotating shaft 513. The second rotating shaft 515 drives the second movable cam plate 516 to rotate, and the second movable cam plate 516 rotates together with the second rotating shaft 515, achieving a 360° rotation.

[0094] Since the first gear 512 drives the second gear 518 to rotate, and the rotation directions of the first gear 512 and the second gear 518 are exactly opposite, one rotates clockwise and the other rotates counterclockwise, the rotation directions of the first movable cam plate 514 and the second movable cam plate 516 are also exactly opposite.

[0095] The second vibration device 52 includes a second motor 522, a third gear 524, a fourth gear 526, a third rotating shaft 528, a fourth rotating shaft 530, a third movable cam plate 527, a fourth movable cam plate 529, a third fixed cam plate 523, a fourth fixed cam plate 525, and a second base 521. The second motor 522 is mounted on the second base 521. The output end (i.e., the rotor) of the second motor 522 is connected to the third rotating shaft 528, and the second motor 522 can drive the third rotating shaft 528 to rotate. The third gear 524 is sleeved and fixed on the third rotating shaft 528, and the third gear 524 can rotate with the third rotating shaft 528. The third movable cam plate 527 is fixedly installed at the end of the third rotating shaft 528 away from the second motor 522, and the third gear 524 and the third movable cam plate 527 are spaced apart.

[0096] One end of the fourth rotating shaft 530 is rotatably mounted on the second base 521, for example, by means of a bearing or other component. The other end extends away from the second base 521 and is located on the outside of the second base 521. The fourth rotating shaft 530 and the third rotating shaft 528 are arranged parallel and spaced apart. The fourth gear 526 is sleeved and fixed on the fourth rotating shaft 530. The fourth gear 526 and the third gear 524 are meshed and connected. Through the meshing transmission of the third gear 524 and the fourth gear 526, the second motor 522 can synchronously drive the third rotating shaft 528 and the fourth rotating shaft 530 to rotate. The fourth movable cam plate 529 is fixedly installed at the end of the fourth rotating shaft 530 away from the second base 521. The fourth movable cam plate 529 and the third movable cam plate 527 are arranged in parallel and, along the axial direction of the fourth rotating shaft 530, at least a portion of the third movable cam plate 527 and the fourth movable cam plate 529 overlap. That is, when the third movable cam plate 527 and the fourth movable cam plate 529 are projected along the axial direction of the fourth rotating shaft 530, at least a portion of the two movable cam plates overlap.

[0097] The third fixed cam plate 523 is sleeved and fixed on the third rotating shaft 528. The third fixed cam plate 523 is located between the second base 521 and the third gear 524, and the third fixed cam plate 523 serves a protective function. The fourth fixed cam plate 525 is sleeved and fixed on the fourth rotating shaft 530. The fourth fixed cam plate 525 is located between the second base 521 and the fourth gear 526, and the fourth fixed cam plate 525 serves a protective function.

[0098] When the second motor 522 starts, it drives the third rotating shaft 528 to rotate, which in turn drives the third movable cam plate 527 to rotate. The third movable cam plate 527 rotates together with the third rotating shaft 528, achieving a 360° rotation. Simultaneously, the third motor drives the fourth rotating shaft 530 to rotate in sync with the third rotating shaft 528. The fourth rotating shaft 530 drives the fourth movable cam plate 529 to rotate, and the fourth movable cam plate 529 rotates together with the fourth rotating shaft 530, achieving a 360° rotation.

[0099] Since the third gear 524 drives the fourth gear 526 to rotate, and the rotation directions of the third gear 524 and the fourth gear 526 are exactly opposite, one rotates clockwise and the other rotates counterclockwise, the rotation directions of the third movable cam plate 527 and the fourth movable cam plate 529 are also exactly opposite.

[0100] refer to Figure 17 The first movable cam plate 514 to the fourth movable cam plate 529 are all semi-arc plates, which can be semi-circular or semi-elliptical arc structures. The four movable cam plates can act on the corresponding upper housing 46 or lower housing 47, thereby generating a force on the vibrating hammer cap column 49. When the first movable cam plate 514 and the second movable cam plate 516 rotate to the first position, both the first movable cam plate 514 and the second movable cam plate 516 face downward and act vertically on the lower housing 47, and the first vibration device 51 generates a downward force with a magnitude of F. At this time, the third movable cam plate 527 and the fourth movable cam plate 529 rotate to the third position, both the third movable cam plate 527 and the fourth movable cam plate 529 face downward and act vertically on the upper housing 46, and the second vibration device 52 generates a downward force with a magnitude of F. The resultant force generated by the first vibration device 51 and the second vibration device 52 is 2F in magnitude and is directed vertically downward. No force is exerted on the upper box 46 and the lower box 47 in the horizontal direction, which is to say, no force is exerted on the vibrating hammer cap column 49. The magnitude of this force is 2F.

[0101] Similarly, when the first movable cam 514 and the second movable cam 516 are still in the first position, the third movable cam 527 and the fourth movable cam 529 rotate to the second position. Both the third and fourth movable cams 527 and 529 face upwards and act perpendicularly on the upper housing 46. The second vibration device 52 generates an upward force of magnitude F. Since the first vibration device 51 and the second vibration device 52 generate forces of equal magnitude but opposite direction, the resultant force of the first vibration device 51 and the second vibration device 52 is 0, and no force is generated on the vibrating hammer cap 49. When the first movable cam 514 and the second movable cam 516 continue to rotate and reach the second position, both the first movable cam 514 and the second movable cam 516 face upwards and act perpendicularly on the lower housing 47. The first vibration device 51 generates an upward force of magnitude F. At this time, the third movable cam 527 and the fourth movable cam 529 rotate to the fourth position. Both the third movable cam 527 and the fourth movable cam 529 face upward and act vertically on the upper housing 46. The second vibration device 52 generates an upward force with a magnitude of F. The resultant force generated by the first vibration device 51 and the second vibration device 52 is 2F in magnitude and is directed vertically upward. No force is generated horizontally on the upper housing 46 and the lower housing 47, that is, no force is generated on the vibrating hammer cap column 49. The magnitude of this force is 2F.

[0102] Therefore, by controlling the first vibration device 51 and the second vibration device 52, the magnitude of the force acting on the vibrating hammer cap column 49 can be made to change periodically along the vertical direction: ↓2F→0→↑2F→0→↓2F→0→↑2F→……. Here, ↑ indicates the direction of the resultant force is upward, ↓ indicates the direction of the resultant force is downward, and → indicates the direction of change of the resultant force. This achieves periodic vibration, controllable force magnitude, and no force is generated in the horizontal direction.

[0103] For example, the observation device includes a camera 8, a laser emitter 9, a tripod 10, a support rod 11, a computer 12, and a wireless communication module 13. The camera 8 is mounted on the top of the tripod 10 and is communicatively connected to the computer 12. The laser emitter 9 is slidably mounted on the support rod 11 and can slide along the axial direction of the support rod 11. The laser emitter 9 is electrically connected to the computer 12. The laser emitter 9 cooperates with the CCD sensor 30 to realize the penetration measurement of the pipe pile 19. The laser emitter 9 emits a laser beam onto the CCD sensor 30. The pile displacement of the pipe pile 19 is determined by the change in the position of the laser beam on the CCD sensor 30, and the laser emitter 9 is moved on the support rod 11 to the corresponding position according to the pile displacement. The CCD sensor 30 uploads the measured laser point position to the computer 12, and the computer 12 controls the position of the laser emitter 9 on the support rod according to the laser beam position.

[0104] The camera 8 captures images through the observation window 17 on the model cylinder. Three laser lights inside the observation window 17 illuminate the pile and soil surface at different locations inside the model cylinder, thus forming three observation areas. The camera 8 captures images of the pile and soil with laser speckle on the surface, and then processes the images using image algorithms to obtain pile and soil displacement data.

[0105] refer to Figure 1 and Figure 21 , Figure 1 The central pipe pile 19 is inserted into the eccentric position of the model cylinder and is located on the side. Figure 21 The central pipe pile 19 is inserted into the center (i.e., the center of the circle) of the model tube and is located in the center position. When the pipe pile 19 is inserted into the center position of the model tube, it also includes a load-bearing column 53. The two ends of the load-bearing column 53 abut against the pad plate 36 and the pressure plate 16 respectively. The jack 4 is installed on the pad plate 36 and abuts against the main crossbeam 1.

[0106] When practical use is required, the anchor bar 14 is inserted into the ground to a sufficient depth to meet the required reaction force of the reaction frame 5. The air bladder 18 is inflated through the vent valve 21 and then inflated again, with the air bladder 18 adhering to the inner wall of the cylinder 6. Simulated soil for the pile is then filled into the containment space to a preset height, for example, 0.1m from the top of the cylinder 6. Then, the pressure plate 16 is added, and the pipe pile 19, equipped with the hammer cap 3, is inserted into the pile soil. The bottom end of the pipe pile 19 is aligned with the observation window 17 of the model cylinder, for example, the bottom end of the pipe pile 19 is aligned with the middle position of the observation window 17, allowing the bottom end of the pipe pile 19 to be observed through the observation window 17.

[0107] The model cylinder, already filled with pile soil, is dragged to the middle position of the sliding base by hoisting. Then, the first locking plate 31 and the second locking plate 35 are fastened and locked onto the sliding frame 34. The hoisting jack 4 is placed onto the pressure plate 16 of the model cylinder. After the output end (i.e., plunger) of the jack 4 extends, the pad 36 is tightly attached to the bottom of the main crossbeam 1, thereby applying a vertical pressure P. Inflation is then carried out through the vent valve 21 to the air bladder 18, so that the air pressure inside the air bladder 18 reaches K times the pressure P, that is, the air pressure inside the air bladder 18 reaches K*P. K is calculated based on the Poisson's ratio of the pile soil, K=v / (1-v), where v represents the Poisson's ratio of the soil.

[0108] refer to Figure 24 Based on the aforementioned test device for simulating dynamic driving of precast piles, this embodiment also provides a test method for simulating impact driving of precast piles, which includes the following steps:

[0109] Step 11: Adjust the position and irradiation direction of the laser emitter 9 so that the laser emitted by the laser emitter 9 is perpendicular to the sensing surface of the CCD sensor 30 on the pipe pile 19.

[0110] Step 12: Install the impact device on the hammer cap 3, and control the impact motor 37 of the impact device to drive the pipe pile 19 by impact. During the downward displacement of the pipe pile 19, the pipe pile 19 drives the CCD sensor 30 on the pipe pile 19 to move downward synchronously. The position of the laser point irradiated on the CCD sensor 30 also moves accordingly, and the position of the laser point is collected by the CCD sensor 30. The collected laser point position is transmitted to the computer 12 through the wireless communication module 13.

[0111] Step 13: During the hammering of the pipe pile 19 by the impact device, the pipe pile 19 will rebound. Therefore, it is necessary to analyze the displacement change information of the laser point on the CCD sensor 30 over time during the pile driving process to accurately measure the penetration depth s of the pipe pile 19. Taking the initial position of the laser point as the reference, the maximum displacement DMX during the entire pile driving process is calculated based on the peak displacement of the laser point. The final position of the laser point is taken as the penetration depth s of the pipe pile 19. Then, the rebound c of the pipe pile 19 has the following relationship: c = DMX - s. At the same time, based on the information of the laser point displacement changing with time, the velocity time history curve of the laser point can be obtained. Then, the energy transferred to the pipe pile 19 by the hammering action of the impact device can be obtained according to the kinetic energy equation, and the conversion efficiency η of potential energy to kinetic energy can be determined.

[0112] Step 14: Based on the penetration depth s of the pipe pile 19, the laser emitter 9 is moved downwards by s to adjust the position of the laser emitter 9.

[0113] Step 15: Repeat steps 13 and 14 to achieve continuous downward driving of the pipe pile 19. The penetration depth of the pipe pile 19 is equal to the final moving distance of the laser transmitter 9, thereby obtaining the variation curve between the final maximum moving displacement DMX, penetration s, and pile rebound c. Figure 22 This is a schematic diagram showing the variation curves between the maximum displacement DMX, penetration s, and pile rebound c.

[0114] Step 16: Before the impact device starts driving the pipe pile 19, turn on the three laser lights (first laser light 23, second laser light 24 and third laser light 25) on the grid column 20. The lasers emitted by the three laser lights shine through the transparent part and irradiate the pile soil, forming speckle patterns on the pile soil surface where the first observation area 26, the second observation area 27 and the third observation area 28 are located.

[0115] Step 17: Camera 8 is aimed at observation window 17 to capture images of the three observation areas, and then the pile soil in the three observation areas is captured.

[0116] During the impact driving process, the pipe pile 19 is driven by hammering the pipe pile 19. The pipe pile 19 moves downward and squeezes the soil, causing the soil to deform. The camera 8 continuously captures images of the soil during the driving process, and the displacement of the soil is obtained through image processing technology.

[0117] The upward displacement of the pile and soil and the radial displacement of the pile and soil on both sides of the circumference within observation window 17 are used to evaluate the soil plugging effect. When the soil displacement of the pile and soil remains basically unchanged (changes within the threshold can be considered basically unchanged), and the radial displacement of the pile and soil on both sides of the circumference increases sharply (change rate exceeding the preset threshold can be considered a sharp increase), it indicates that the soil plugging effect has occurred. By correlating the pile driving control parameters such as the pile driving depth and pile penetration degree when the soil plugging effect occurs, the critical point for the soil plugging effect during pile driving can be determined.

[0118] The radial stress σ at the lower end of the pipe pile 19 was measured using a piezoresistive sensor installed on the pipe pile 19. r The vertical stress σ at the top of the pipe pile 19 v And based on radial stress σ r The shear stress τ at the lower end of the pipe pile 19 is obtained. This represents the friction angle at the pile-soil interface obtained from indoor pile-soil tests. This allows us to establish the relationship between the pile-soil shear stress and vertical displacement along the pile side of pipe pile 19, as well as the relationship between the pile-soil vertical stress and vertical displacement at the pile tip of pipe pile 19.

[0119] refer to Figure 23 Step 18: Calculate the total resistance R of pipe pile 19 according to formula ① d The static soil resistance R of pipe pile 19 is calculated according to formula ②. static :

[0120]

[0121] In the formula, A s A represents the surface area of ​​the side of pipe pile 19. p Let τ represent the surface area of ​​the pile tip of pipe pile 19. When the soil plugging effect does not occur, the surface area of ​​the pile tip of pipe pile 19 is the net area of ​​the annulus at the bottom of pipe pile 19. When the soil plugging effect occurs, the calculation becomes more complex. outer τ represents the external skin friction of the pipe pile 19. innerThe inner frictional resistance of the pipe pile 19 is represented by d, the diameter of the pipe pile 19 is represented by t, the wall thickness of the pipe pile 19 is also the side wall thickness of the pipe pile 19, mg represents the weight of the impact hammer cap column 41, and h represents the falling height of the impact hammer cap column 41 is also the hammer drop height.

[0122] For the impact pile driving test method, the impact hammer cap column 41 will experience energy loss due to air resistance and heat generated by the collision during its fall. Therefore, the conversion efficiency η needs to be considered, which represents the energy reduction efficiency. Each rotation of the impact motor 37 drives the traction rope 43 to travel a distance d. Therefore, a servo motor can be used for the impact motor 37, and the number of rotations of the impact motor 37 can be controlled. This ensures that the impact hammer cap column 41 can be raised to different heights (d, 2d, 3d, etc.) by the traction rope 43, thereby controlling the downward impact force of the impact hammer cap column 41 through the lifting height, achieving impact pile driving. The hammer impact force at the top of the pipe pile 19 can be measured by the strain coefficient ε collected by the strain gauge 29, and then the stress σ can be calculated using Hooke's law. Based on the stress and Hooke's law, the hammer impact force F is calculated as follows: F = σA, where A represents the surface area of ​​the top of the pipe pile 19.

[0123] refer to Figure 25 Based on the aforementioned test device for simulating dynamic driving of precast piles, this embodiment also provides a test method for simulating vibration driving of precast piles, which includes the following steps:

[0124] Step 21: Adjust the position and irradiation direction of the laser emitter 9 so that the laser emitted by the laser emitter 9 is perpendicular to the sensing surface of the CCD sensor 30 on the pipe pile 19.

[0125] Step 22: Install the vibration device on the hammer cap 3, and control the vibration driving of the pipe pile 19 by controlling the impact motor 37 of the vibration device. During the downward displacement of the pipe pile 19, the pipe pile 19 drives the CCD sensor 30 on the pipe pile 19 to move downward synchronously. The position of the laser point irradiated on the CCD sensor 30 also moves accordingly, and the position of the laser point is collected by the CCD sensor 30. The collected laser point position is transmitted to the computer 12 through the wireless communication module 13.

[0126] Pipe pile 19 is driven under vibration. During the driving process, the pile body of pipe pile 19 vibrates up and down. When the cumulative displacement d of pipe pile 19... t When the vertical movement range of laser emitter 9 within the CCD sensor 30 is greater than the vertical movement range of CCD sensor 30, laser emitter 9 is moved downwards by a distance d. t .

[0127] Based on the displacement of the laser position point irradiated on the CCD sensor 30 over time, the vibration acceleration characterizing the vibration of the pipe pile 19 can be further calculated, and the cumulative movement distance of the laser emitter 9 is recorded as the driving depth of the pipe pile 19 into the soil.

[0128] Vibration driving is continuously performed, and the final pile penetration depth is equal to the sum of the movement distances of the laser emitter 9 in each movement, thus forming a curve showing the change in pile penetration speed with penetration depth.

[0129] Step 23: Before the vibrating device drives the pipe pile 19, turn on the three laser lights (first laser light 23, second laser light 24 and third laser light 25) on the grid column 20. The lasers emitted by the three laser lights shine through the transparent part and irradiate the pile soil, forming speckle patterns on the pile soil surface where the first observation area 26, the second observation area 27 and the third observation area 28 are located.

[0130] The camera 8 is aimed at the observation window 17 to capture images of the three observation areas (first observation area 26, second observation area 27, and third observation area 28) on the observation window 17. The camera 8 continuously captures images of the soil within the pipe pile 19 during the pile driving process, and the soil displacement changes are obtained through image processing methods.

[0131] The soil plugging effect is assessed based on the upward displacement of the soil and the radial displacement of the pipe pile 19 along both sides of the pile circumference. If the upward displacement of the soil within the pipe pile 19 remains essentially unchanged (an upward displacement less than a threshold can be considered essentially unchanged), and the radial displacement on both sides of the pipe pile 19 increases sharply (radial displacement exceeding a threshold can be considered a sharp increase), then a soil plugging effect has occurred; otherwise, no soil plugging effect has occurred.

[0132] Step 24: Using the piezoresistive sensor installed on the pipe pile 19, measure the radial stress σ at the lower end of the pipe pile 19. r The vertical stress σ at the top of the pipe pile 19 v , and based on radial stress σ r The shear stress τ at the lower end of the pipe pile 19 is obtained. This represents the friction angle at the pile-soil interface obtained from indoor pile-soil tests. This allows us to establish the pile-soil shear stress τ and vertical stress σ along the side of pipe pile 19. v The relationship between the vibration acceleration of the pipe pile 19 and the soil weakening law under vibration load is studied based on this relationship.

[0133] After the test, the pressure of jack 4 was released, the sliding base was removed, and the gas in the airbag 18 was extracted through the vent valve 21, that is, the air was pumped out. The compacted pile soil was separated from the inner wall of the airbag 18, the pile soil was broken up and then removed from the airbag 18.

[0134] This invention can effectively realize dynamic pile driving, including impact pile driving and vibratory pile driving. By applying pressure to the pressure plate 16 through the jack 4, pressure is applied to the pile and soil to simulate the influence of ground stress. Thus, considering the influence of ground stress, the penetration depth during the pile driving process can be measured, and the displacement law of the pile and soil at the pile side and pile end can be obtained during the pile driving process to simulate the formation of the pile end soil plug (effect). In this way, the relationship between the pile displacement and the mechanical parameters of the pile-soil interaction can be established.

[0135] In addition, this test device has a simple structure, is easy to maintain, has a long service life, and can set the pipe pile 19 at the center or side of the pile soil as needed.

[0136] The impact pile driving test method can effectively assess whether the soil plugging effect occurs during the impact pile driving process, and calculate the total resistance and static soil resistance of the pipe pile 19. Furthermore, the impact force can be regularly vibrated and driven by controlling the number of rotations of the impact motor 37.

[0137] The vibratory pile driving test method can also effectively assess whether the soil plugging effect occurs during impact pile driving, as well as the pile-soil shear stress τ and vertical stress σ on the side of the 19 pipe piles. v The relationship between the vibration acceleration of the pipe pile 19 and the soil weakening law under vibration load is studied based on this relationship.

[0138] The embodiments disclosed in this specification are merely illustrative of one aspect of the invention, and the scope of protection of the invention is not limited to these embodiments. Any other functionally equivalent embodiments fall within the scope of protection of the invention. Those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the scope of protection of the claims of this invention.

Claims

1. A test method for simulating the impact driving of precast piles, characterized in that, A test apparatus for simulating dynamic driving of precast piles, the test method includes the following steps: Step 11: Adjust the position and irradiation direction of the laser emitter so that the laser emitted by the laser emitter is perpendicular to the sensing surface of the CCD sensor on the pipe pile; Step 12: Install the impact device on the hammer cap, and apply hammering force to the pipe pile through the impact device to achieve impact driving of the pipe pile. During the downward displacement of the pipe pile, the pipe pile drives the CCD sensor on the pipe pile to move downward synchronously. The position of the laser point on the CCD sensor also moves accordingly, and the position of the laser point is collected by the CCD sensor. The collected laser point position is transmitted to the computer through the wireless communication module. Step 13: During the hammering of the pipe pile by the impact device, the penetration depth s of the pipe pile is measured by the displacement change information of the laser point on the CCD sensor over time. Step 14: Based on the penetration depth s of the pipe pile, the laser emitter is moved downwards by s to adjust its position; Step 15: Repeat steps 13 and 14 to achieve continuous downward driving of the pipe pile. The depth of the pipe pile into the soil is equal to the final moving distance of the laser emitter, thereby obtaining the variation curve between the final maximum moving displacement DMX, penetration s, and pile rebound c. Step 16: Before the impact device begins driving the pipe pile, turn on the three laser lights on the grid column. The lasers emitted by the three laser lights pass through the transparent part and illuminate the pile and soil, forming speckle patterns on the pile and soil surface in the first observation area, the second observation area, and the third observation area. The experimental apparatus includes a model cylinder, which comprises a cylinder body, an air bladder, and an observation window. A through-hole is drilled in both the cylinder body and the air bladder. When the air bladder is inflated and fitted against the inner wall of the cylinder body, the through-holes in the cylinder body and the air bladder are aligned. A grid of posts is installed in the through-hole of the cylinder body, and three laser lights are mounted on each post. The grid posts are embedded in the through-hole. A transparent element is installed in the through-hole of the air bladder, with the grid posts positioned directly in front of the transparent element. When the pipe pile passes through the through-hole and is inserted into the soil, the pipe pile is directly opposite the observation window. The grid columns divide the observation window into a first observation area, a second observation area, and a third observation area in a certain direction. Step 17: Aim the camera at the observation window to capture images of the pile soil in the three observation areas. During the impact pile driving process, a camera continuously captures images of the pile and soil during the driving process, and image processing technology is used to obtain the displacement of the pile and soil. The displacement of the pile and soil includes the upward displacement of the pile and soil and the radial displacement on both sides of the pile and soil. The soil plugging effect of the pile and soil is evaluated based on the upward displacement of the pile and soil and the radial displacement on both sides of the pile and soil. When the change of soil displacement of the pile and soil is less than or equal to the first threshold and the change of radial displacement on both sides of the pile and soil is greater than or equal to the second threshold, the soil plugging effect is considered to have occurred; otherwise, the soil plugging effect is considered not to have occurred. The critical point at which the soil plugging effect occurs during pile driving is determined by the pile driving depth and pile penetration degree when the soil plugging effect occurs.

2. The test method for simulating precast pile impact driving according to claim 1, characterized in that, Step 17 also includes, The radial stress at the lower end of the pipe pile was measured using a piezoresistive sensor installed on the pipe pile. and vertical stress at the top of the pipe pile And based on radial stress The shear stress at the lower end of the pipe pile is obtained. Shear stress , This represents the friction angle at the pile-soil interface obtained from indoor pile-soil tests, in order to establish the curve relationship between the pile-soil shear stress and vertical displacement on the pile side of the pipe pile, and the curve relationship between the pile-soil vertical stress and vertical displacement at the pile tip of the pipe pile.

3. The test method for simulating precast pile impact driving according to claim 1 or 2, characterized in that, Following step 17, it also includes, Step 18: Calculate the total resistance of the pipe pile according to formula ① The static soil resistance of the pipe pile is calculated according to formula ②. : ------① ------② In the formula, Indicates conversion efficiency. This represents the lateral surface area of ​​the pipe pile. This indicates the surface area at the pile tip of the pipe pile. This represents the external skin friction of the pipe pile. The inner frictional resistance of the pipe pile is represented by d, the diameter of the pipe pile is t, the wall thickness of the pipe pile is mg, the weight of the impact hammer cap is h, and the falling height of the impact hammer cap is h.

4. The test method for simulating precast pile impact driving according to claim 1, characterized in that, The test apparatus for simulating dynamic pile driving of precast piles includes a reaction frame, a model cylinder, a sliding base, a jack, a pile driving device, a hammer cap, and an observation device. The model cylinder is mounted on the sliding base and has a cavity inside to hold the pile soil. The jack is mounted on the end of the model cylinder away from the sliding base and abuts against the reaction frame. The hammer cap is installed on the pipe pile, which serves as the precast pile. The pipe pile passes through the mold cylinder and is inserted into the soil inside the mold cylinder, with one end of the pipe pile protruding outside the mold cylinder. The hammer cap is located on the protruding end of the pipe pile. The pile driving device is used to drive the pipe pile into the soil using dynamic pile driving, thereby simulating the dynamic pile driving process of precast piles. The observation device is located on the outside of the model cylinder.

5. The test method for simulating precast pile impact driving according to claim 4, characterized in that, The reaction frame includes a frame body, a main crossbeam, a square base, and anchor bars installed on the frame body. The jack abuts against the main crossbeam, the square base is fixedly installed at the lower end of the frame body, and the main crossbeam spans across the frame body. Anchor bars pass through the main crossbeam and the frame to fix the main crossbeam and the frame together. An anchor block is also installed on one end of the anchor bar that passes through the main crossbeam and the frame. The anchor bar also passes through the frame and the square base and is exposed on the outside of the square base. The anchor bar is used to penetrate into the ground and fix it to the ground to fix the reaction frame on the ground.

6. The test method for simulating precast pile impact driving according to claim 4, characterized in that, The model cylinder also includes a pressure plate. The cylinder body includes a cavity, and an air bladder is installed inside the cavity. When the air bladder is inflated, it adheres to the inner wall of the cavity of the cylinder body, forming a receiving space for holding pile soil. The pressure plate covers the cylinder body or covers the cylinder body and the air bladder. The pressure plate has through holes at its center and eccentric position.

7. The test method for simulating precast pile impact driving according to claim 6, characterized in that, The grid column comprises several upright columns, which are connected together in a cross shape to form an array. Each grid column is also equipped with a first laser light, a second laser light, and a third laser light facing opposite directions. These laser lights are positioned away from the observation device so that they can illuminate the soil surface inside the model cylinder. The first laser light is located in the first observation area, the second laser light is located in the second observation area, and the third laser light is located in the third observation area. The pipe pile is equipped with strain gauges and CCD sensors at one end of the model cylinder, and piezoresistive sensors are installed on the inner and outer walls of the top and bottom ends of the pipe pile.

8. The test method for simulating precast pile impact driving according to claim 4, characterized in that, The sliding base includes a sliding frame, and a first snap-fit ​​plate, a second snap-fit ​​plate, a support plate, several sliding shafts, and several fixing blocks mounted on the sliding frame. The sliding shafts are arranged parallel and spaced apart. Both ends of each sliding shaft are fixedly connected to a fixing block, which is fixedly mounted on both ends of the sliding frame. The support plate is mounted on the sliding frame and located above the sliding shafts. The first and second snap-fit ​​plates are snap-fitted onto the sliding frame. The first and second snap-fit ​​plates are located on opposite sides of the support plate and fixedly connected to it. Both the first and second snap-fit ​​plates are located above the sliding frame. The model cylinder is mounted on the support plate. The sliding shafts are arranged sequentially from low to high and then back to low along the axial direction of the sliding frame.

9. The test method for simulating precast pile impact driving according to claim 1, characterized in that, The pile driving device includes an impact device, which comprises an impact motor, an impact output shaft, a traction rope, a hammer body, a stop rod, and an impact hammer cap. The output shaft of the impact motor is connected to the impact output shaft. One end of the traction rope is wound around the impact output shaft, and the other end of the traction rope is fixedly connected to the hammer body. The hammer body is fixedly connected to one end of the plunger rod, and the other end of the plunger rod is fixedly connected to the impact hammer cap column. The outer wall of the impact hammer cap column is provided with an external thread, and the impact hammer cap column matches the internal thread of the inner wall of the hammer cap through the external thread.

10. The test method for simulating precast pile impact driving according to claim 4, characterized in that, The observation device includes a camera, a laser emitter, a tripod, a support rod, a computer, and a wireless communication module. The camera is mounted on the top of the tripod and is communicatively connected to the computer. The laser emitter is slidably mounted on the support rod and can slide along the axial direction of the support rod. The laser emitter is electrically connected to the computer and emits laser light onto a CCD sensor. The camera takes pictures through the observation window on the model tube, and three laser lights inside the observation window illuminate the soil surface of the pile at different locations inside the model tube.

Images