A new low-strain testing method for pile in soft soil layer

Abstract

The application discloses a novel environment-friendly soft soil layer pile low-strain detection method, which comprises the following steps: (1) checking the pile condition: the pile body strength should not be lower than 70% of the design strength, and should not be lower than 15 MPa; the material, strength and cross-section size of the pile head should be basically the same as those of the pile body; the pile top surface should be flat, compact and basically perpendicular to the pile axis; (2) after the pile head reaches the ideal height, the pile head is cleaned to ensure that the pile head is flat and undamaged; (3) setting the test parameters; (4) measuring sensor installation and excitation operation: the sensor installation should be perpendicular to the pile top surface; when the coupling agent is bonded, the coupling agent should have sufficient bonding strength; wherein the knocking device is arranged on the reinforcement cage to knock the excitation point, so that the excitation point avoids the influence of the main reinforcement of the reinforcement cage, and the excitation direction should be along the pile axis direction; (5) signal acquisition and screening; (6) analysis and determination of the detection data.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of land layers, and particularly relates to a novel low-strain detection method for a soft soil layer foundation pile. BACKGROUND

[0002] Low-strain detection refers to applying a dynamic force (dynamic load) on the pile top. The dynamic force can be a transient impact force or a steady-state excitation force. The pile-soil system produces a dynamic response under the action of the dynamic force. Different function sensors are used to measure the dynamic response signals (such as displacement, velocity, and acceleration signals) on the pile top. The structural integrity of the pile is determined through time domain analysis or transfer function analysis of the signals. The reflection wave method is used to repeatedly test each single pile to be detected for more than twice. For the same foundation pile, the three waveform curves formed by three hammering should be basically consistent in shape, amplitude, and phase. The collected data is calculated to be qualified.

[0003] At present, a high-pile cap pile foundation multi-measurement point low-strain detection method is disclosed in Chinese Patent No. CN112663689, published on April 16, 2021, which includes the following steps: arranging three velocity sensors vertically and equidistantly along the exposed part of the pile body on the ground surface to receive the horizontal or vertical pile body velocity response component; applying a test excitation to the pile body above all sensors; decomposing the velocity response signals collected by the sensors into upgoing and downgoing waves, and constructing a frequency domain wideband response function through integral transformation; obtaining a virtual velocity response result that eliminates the vibration characteristics of the complex upper structure by the wideband response function and a virtual half-sine excitation; using the existing pile vibration analytical solution, adjusting the pile length in the analytical solution, fitting the virtual velocity response result, searching for the pile length at the optimal fitting time as the estimated value, and judging the pile body integrity based on the estimated value.

[0004] When the excitation point is struck by the excitation force hammer, the operator usually holds the excitation force hammer to strike the excitation point. However, the actual striking position may deviate from the excitation point when the human force strikes, which affects the final detection data. Meanwhile, when the steel cage exists on the circumferential side of the upper end surface of the solid foundation pile, it is very inconvenient to strike the excitation point by the excitation force hammer, and the steel cage is easily disturbed. SUMMARY

[0005] The purpose of the present application is to provide a novel low-strain detection method for a soft soil layer foundation pile, which can accurately strike the excitation point in the environment of a solid foundation pile with a steel cage.

[0006] The above technical purpose of the present application is achieved by the following technical solution: a novel low-strain detection method for a soft soil layer foundation pile, which includes the following steps:

[0007] (1) Check the condition of the detection pile: the strength of the pile body should not be less than 70% of the design strength, and should not be less than 15 MPa; the material, strength and cross-sectional size of the pile head should be basically the same as those of the pile body; the pile top surface should be flat, dense and basically perpendicular to the pile axis;

[0008] (2) After determining that the pile head reaches the ideal height, clean it up to ensure that the pile head is flat and undamaged. In addition, in order to facilitate the installation of the sensor, 2-4 smooth surfaces with a diameter of 8-10 cm need to be polished;

[0009] (3) Set the test parameters: the time period length of the time domain signal recording should be continued for not less than 5 ms after 2L / c time; the upper limit of the frequency range of the amplitude-frequency signal analysis should be not less than 2000 Hz; the set pile length should be the construction pile length from the pile top measuring point to the pile bottom; the set pile body cross-sectional area should be the construction cross-sectional area; the pile body wave speed can be preliminarily set according to the test value of the same type of pile in the local area; the sampling time interval or sampling frequency should be reasonably selected according to the pile length, pile body wave speed and frequency domain resolution; the time domain signal sampling point number should not be less than 1024 points; the set value of the sensor should be set according to the measurement verification or calibration result;

[0010] (4) Measure the sensor installation and excitation operation: the sensor installation should be perpendicular to the pile top surface; when using coupling agent for bonding, it should have sufficient bonding strength; the knocking device is arranged on the steel reinforcement cage to knock the excitation point, so that the excitation point avoids the influence of the main reinforcement of the steel reinforcement cage, and the excitation direction should be along the pile axis direction;

[0011] (5) Signal acquisition and screening: according to the size of the pile diameter, 2-4 installation sensors are symmetrically arranged at the detection points in the pile core: the excitation point of the solid pile should be selected at the pile center, and the detection point should be at 2 / 3 of the radius from the pile center;

[0012] (6) Analysis and determination of detection data: for the determination of the average value of the pile body wave speed, when the pile length is known and the pile bottom reflection signal is clear, the average value of the pile body wave speed of not less than 5 piles with complete pile body should be calculated under the same foundation condition, pile type and piling process; when it cannot be determined according to the above, the average value of the wave speed can be determined comprehensively according to the measured value of other pile foundation engineering of the same pile type and piling process in the local area, combined with the aggregate variety and strength grade of the pile body concrete.

[0013] By adopting the above technical scheme, the knocking device can be arranged on the steel reinforcement cage to knock the excitation point, replacing the manual knocking mode by using a knocking hammer in the prior art, so that accurate knocking of the excitation point can be realized in the environment of the solid pile foundation pile with the steel reinforcement cage.

[0014] Further arrangement of the present application is that in step (5), when the pile diameter is large or the upper cross section size of the pile is irregular, in addition to collecting signals at the specified excitation point and detection point position as in the above paragraph, signals should also be collected by changing the position of the excitation point and detection point according to the characteristics of the measured signals; when the consistency of the time domain signals measured at different detection points and multiple times is poor, the reasons should be analyzed and the number of detection points should be increased; the way of changing the position of the excitation point and increasing the number of detection points should be determined according to the integrity of the pile body reflected by the measured signals to determine whether to test again or end the test; the signal should not be distorted and zero drift, and the signal amplitude should not exceed the range of the measurement system; the number of effective signals recorded at each detection point should not be less than 3.

[0015] By adopting the above technical scheme, when the consistency of the time domain signals measured at different detection points and multiple times is poor, the reasons should be analyzed and the number of detection points should be increased, so as to improve the accuracy of the detection result.

[0016] Further arrangement of the present application is that the knocking device comprises a fixed sleeve extending in the vertical direction, a double-shaft motor embedded in the fixed sleeve, a plurality of connecting arms arranged on the side of the fixed sleeve and used for connecting the reinforcement cage, a knocking hammer arranged below the fixed sleeve and used for knocking the excitation point of the foundation pile after falling, a rubber hammer pad arranged at the lower end of the knocking hammer, and a release assembly arranged between the fixed sleeve and the double-shaft motor and used for releasing the knocking hammer below the fixed sleeve after the double-shaft motor rotates.

[0017] By adopting the above technical scheme, the fixed sleeve is connected to the reinforcement cage by the connecting arms, so that the fixed sleeve is positioned at the central excitation point of the foundation pile, and then the knocking hammer below the fixed sleeve is released by the release assembly after the double-shaft motor rotates, and the knocking hammer falls under its own action to accurately knock the excitation point below through the rubber hammer pad; at the same time, the knocking force can be adjusted by replacing the weight of the knocking hammer.

[0018] Further arrangement of the present application is that a grinding wheel is arranged on the output shaft at the upper end of the double-shaft motor, a first ring groove is formed on the side of the fixed sleeve, a second ring groove is formed on the inner walls of the upper and lower sides of the first ring groove, a third ring groove with a circular cross section is formed on the inner wall of the second ring groove, a swing sleeve is arranged at one end of the connecting arm, a movable shaft is arranged on the swing sleeve and located in the first ring groove, and a sliding ball is arranged at the upper and lower ends of the movable shaft and embedded in the third ring groove through the second ring groove.

[0019] By adopting the technical scheme, in order to facilitate the installation of the sensor, a light surface is polished on the upper surface of the pile, at this time, the polishing abrasive wheel arranged on the output shaft of the upper end of the double-shaft motor can be used, the plurality of connecting arms are sleeved on the movable shaft by means of the swing sleeve, and the sliding ball at the end of the movable shaft is embedded in the third ring groove, at this time, the connecting arm can rotate along the circumferential side of the fixed sleeve, and the connecting arm can also swing around the movable shaft, at this time, the plurality of connecting arms can be combined together to form a handle for holding the double-shaft motor, and after the operator holds the connecting arm, the polishing abrasive wheel can be driven by the double-shaft motor to polish the upper surface of the pile, and finally, the polishing of the upper surface of the pile can be realized while the knocking device realizes the knocking operation.

[0020] Further provided in the application is that the upper end of the double-shaft motor is sleeved with a cleaning ring, and the cleaning ring comprises an elastic ring sleeved on the upper end of the double-shaft motor and a plurality of brush parts arranged on the circumferential side of the elastic ring and uniformly distributed along the circumferential side of the elastic ring.

[0021] By adopting the technical scheme, after the polishing abrasive wheel polishes the upper surface of the pile, the elastic ring is elastically expanded to wrap around the circumferential side of the polishing abrasive wheel, so that the polishing abrasive wheel drives the cleaning ring to rotate when rotating, at this time, the brush parts on the circumferential side of the elastic ring can clean the polished upper surface of the pile, thereby facilitating the smoothness of the polished surface.

[0022] Further provided in the application is that the end of the connecting arm away from the fixed sleeve is provided with a mounting sleeve sleeved on the steel bars in the reinforcement cage, and an internally threaded sleeve is arranged on the mounting sleeve, and a locking bolt for abutting against the steel bars is threadedly connected to the internally threaded sleeve.

[0023] By adopting the technical scheme, the locking bolt is threadedly connected to the internally threaded sleeve and abuts against the steel bars, at this time, detachable connection between the connecting arm and the reinforcement cage can be realized, which is beneficial to the quick disassembly and assembly between the connecting arm and the reinforcement cage.

[0024] The further arrangement of the present application is that the releasing assembly comprises a lifting sleeve sleeved on the output shaft at the lower end of the double-shaft motor, a guide ring arranged at the upper end of the lifting sleeve, a bevel part opened at one side of the guide ring, a guide column with the upper end connected with the output shaft of the double-shaft motor and the lower end abutting against the upper surface of the guide ring and the bevel part, a plurality of guide columns arranged at the circumferential side of the lower end surface of the fixing sleeve, a plurality of guide holes opened at the circumferential side of the lifting sleeve and respectively embedded with the lower ends of the plurality of guide columns, a reset spring sleeved on the guide column and fixed at the upper end with the fixing sleeve and at the lower end with the lifting sleeve, connecting grooves opened at the two sides of the lower end of the lifting sleeve, wedge-shaped blocks arranged in the connecting grooves and inclined upward, sliding shafts arranged at the end of the wedge-shaped blocks away from the central axis of the lifting sleeve, through holes opened on the inner wall of the connecting grooves and passed through by the sliding shafts, connecting springs sleeved on the sliding shafts, clamping columns arranged at the upper end of the knocking hammer and embedded in the lifting sleeve, a first bevel part opened at the upper end of the clamping column and clamped with the wedge-shaped block, and a second bevel part opened at the upper end of the clamping column and located at the upper side of the first bevel part, and the first bevel part and the second bevel part form a ">" shape.

[0025] By adopting the above technical scheme, the operator inserts the clamping column into the lower end of the lifting sleeve, and at this time the guide column is located at the position of the upper surface of the guide ring, the wedge-shaped block abuts against the second bevel part, the two wedge-shaped blocks move to the side away from each other, and the connecting spring is compressed, then the second bevel part can pass the wedge-shaped block, after the first bevel part moves to the position of the wedge-shaped block, under the elastic restoring force of the connecting spring, the two wedge-shaped blocks clamp the clamping column at the position of the first bevel part, thereby completing the clamping of the clamping column in the lifting sleeve and realizing the connection of the knocking hammer at the lower end of the lifting sleeve.

[0026] When it is necessary to release the knocking hammer, the double-shaft motor is started, so that the double-shaft motor drives the guide column to rotate around the output shaft of the double-shaft motor, at this time the guide column abuts against the upper surface of the guide ring and the bevel part, when the guide column moves from the position of the upper surface of the guide ring to the position of the bevel part, under the elastic restoring force of the reset spring, the lifting sleeve moves upward along the guide column, at this time the wedge-shaped block moves upward along the first bevel part and then moves to the second bevel part, after losing the clamping effect of the wedge-shaped block, the clamping column can be separated from the lifting sleeve, then the knocking hammer can fall under the action of its own gravity, and finally the knocking hammer can knock the vibration point below.

[0027] The further arrangement of the present application is that the output shaft at the lower end of the double-shaft motor is fixed with a thrust auxiliary spring for abutting against the upper end surface of the clamping column.

[0028] By adopting the above technical scheme, when the clamping column is inserted into the lower end of the lifting sleeve, the clamping column abuts against the thrust auxiliary spring, so that the thrust auxiliary spring is compressed, and when the knocking hammer is released, under the elastic restoring force of the thrust auxiliary spring, the clamping column can be quickly separated from the lifting sleeve.

[0029] The further arrangement of the present application is that the lower part of the lifting sleeve is provided with a guide sleeve for the falling of the knocking hammer, the upper end of the guide sleeve is provided with a first internal thread ring, the lower end of the lifting sleeve is provided with a first external thread ring for thread connection of the first internal thread ring, the lower end of the guide sleeve is provided with a magnet ring, the circumferential side of the magnet ring is provided with a second internal thread ring, the lower end of the guide sleeve is provided with a second external thread ring for thread connection of the second internal thread ring, the rubber hammer pad is cylindrical and the circumferential side is sleeved with a snap ring for suction on the magnet ring, and the snap ring is internally provided with a support for supporting after the rubber hammer pad falls back after rebounding.

[0030] By adopting the above technical scheme, the guide sleeve can guide the falling of the knocking hammer. In order to avoid the knocking hammer from knocking again after rebounding after falling and knocking once, thereby affecting the collection of detection point data, the snap ring is sleeved on the rubber hammer pad before the knocking hammer falls. After the knocking hammer drives the snap ring to fall together, the rubber hammer pad can pass through the magnet ring to complete the knocking action with the upper surface of the pile. At this time, the snap ring can be attracted to the magnet ring. After the knocking hammer rebounds, the snap ring can be separated from the rubber hammer pad. Then, the support can support the rubber hammer pad falling back after rebounding, so as to avoid the rubber hammer pad from knocking and colliding with the upper surface of the pile after passing through the magnet ring again. Finally, the falling of the knocking hammer can only produce one knocking action, which is beneficial to the collection of data by the sensor of the detection point.

[0031] The further arrangement of the present application is that the support includes an annular cavity opened on the inner wall of the circumferential side of the snap ring, a swing arm hinged at one end to the inner wall of the annular cavity, and a mounting spring connected at one end to the end of the swing arm and connected at the other end to the inner wall of the annular cavity. When the mounting spring is in a natural state, the swing arm swings to the center of the snap ring.

[0032] By adopting the above technical scheme, when the snap ring needs to be sleeved on the rubber hammer pad, the operator drives the swing arm to swing towards the side away from the center of the snap ring, and the mounting spring is stretched. When the snap ring is separated from the rubber hammer pad, the swing arm can swing back to the center of the snap ring under the elastic restoring force of the mounting spring, so as to support the rubber hammer pad when it falls back after rebounding.

[0033] In summary, the present application has the following beneficial effects: firstly, the upper surface of the pile is polished, the connecting arms are combined together to form a handle for holding the double-shaft motor, the operator can hold the connecting arms and drive the polishing grinding wheel to polish the upper surface of the pile through the double-shaft motor, and after polishing, the elastic ring is elastically expanded and wrapped around the polishing grinding wheel, so that the polishing grinding wheel drives the cleaning ring to rotate when rotating, and the brush part on the side of the elastic ring can clean the polished upper surface of the pile, thereby ensuring the smoothness of the polishing surface and facilitating the installation of the sensor;

[0034] Then the fixing sleeve is sleeved on the steel bar through the mounting sleeve of the connecting arm, and then the locking bolt is threadedly connected to the inner threaded sleeve and abuts against the steel bar, so that the detachable connection between the connecting arm and the steel cage is realized, and the fixing sleeve is positioned at the center excitation point of the pile;

[0035] Then the operator inserts the clamping column into the lower end of the lifting sleeve and abuts against the thrust auxiliary spring, and the guide column is located at the position of the upper surface of the guide ring, the wedge blocks abut against the second inclined surface, the two wedge blocks move away from each other, and the connecting spring is compressed, then the second inclined surface can pass the wedge blocks, and after the first inclined surface moves to the position of the wedge blocks, the two wedge blocks clamp the clamping column at the position of the first inclined surface under the elastic restoring force of the connecting spring, thereby completing the clamping of the clamping column in the lifting sleeve and realizing the connection of the knocking hammer at the lower end of the lifting sleeve; then the clamping ring is sleeved on the rubber hammer pad, and the swing arm swings away from the center of the clamping ring, and the guide sleeve is connected to the lower side of the lifting sleeve and guides the falling of the knocking hammer through the guide sleeve;

[0036] When the knocking hammer needs to be released, the double-shaft motor is started, so that the double-shaft motor drives the guide column to rotate around the output shaft of the double-shaft motor, the guide column abuts against the upper surface of the guide ring and the inclined surface, when the guide column moves from the position of the upper surface of the guide ring to the position of the inclined surface, the lifting sleeve moves upward along the guide column under the elastic restoring force of the reset spring, the wedge blocks move upward along the first inclined surface and then move to the second inclined surface, the clamping column is quickly separated from the lifting sleeve under the auxiliary action of the thrust auxiliary spring after losing the clamping action of the wedge blocks, and then the knocking hammer falls under the action of its own gravity;

[0037] When the knocking hammer drives the clasp ring to fall, the rubber hammer pad can pass through the magnet ring and knock the upper surface of the pile, at this time the clasp ring is attracted to the magnet ring, and after the rebound of the knocking hammer, the clasp ring is separated from the rubber hammer pad, and then under the action of the elastic restoring force of the installed spring, the swing arm swings reversely and swings to the center of the clasp ring, thereby supporting the rubber hammer pad when it rebounds and falls, avoiding the knocking collision of the rubber hammer pad with the upper surface of the pile after passing through the magnet ring again, and finally making each falling of the knocking hammer produce only one knocking action, which is beneficial to the data collection of the sensor of the detection point. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0039] Figure 1 is a structural schematic view of the knocking device in combination with the pile and the reinforcement cage in the present application;

[0040] Figure 2 is a structural schematic view of the knocking device in the present application;

[0041] Figure 3 is a partial sectional view of the connection relationship between the fixed sleeve, the double-shaft motor, the polishing grinding wheel and the connecting arm in the knocking device in the present application;

[0042] Figure 4 is a partial sectional view of the structure at the lower part of the fixed sleeve in the knocking device, at this time the guide column is located on the upper surface of the guide ring, and the wedge-shaped block is clamped to the first inclined surface position;

[0043] Figure 5 is a partial sectional view of the structure at the lower part of the fixed sleeve in the knocking device, at this time the guide column is located at the position of the inclined surface part, and the wedge-shaped block is located at the second inclined surface position to push the knocking hammer to fall;

[0044] Figure 6 is a partial sectional view of the connection relationship between the rubber hammer pad, the clasp ring and the supporting piece;

[0045] Figure 7 is an enlarged view of the partial structure of the knocking device, at this time the plurality of connecting arms rotate around the fixed sleeve;

[0046] Figure 8 is a structural plan view of the knocking device, at this time the plurality of connecting arms are combined together to form a handle for holding the double-shaft motor, and the operator can hold the connecting arm by hand to drive the polishing grinding wheel to polish the upper surface of the pile by the double-shaft motor.

[0047] In the figure, 1, fixed sleeve; 11, first ring groove; 12, second ring groove; 13, third ring groove; 2, double-shaft motor; 21, polishing grinding wheel; 22, cleaning ring; 221, elastic ring; 222, brush part; 23, thrust auxiliary spring; 3, connecting arm; 31, swing sleeve; 32, movable shaft; 321, sliding ball; 33, mounting sleeve; 331, internal threaded sleeve; 332, locking bolt; 4, knocking hammer; 41, rubber hammer pad; 5, release assembly; 51, lifting sleeve; 511, first external threaded ring; 52, guide ring; 53, inclined surface part; 54, guide column; 55, guide post; 56, guide hole; 57, return spring; 58, connecting groove; 59, wedge block; 501, sliding shaft; 502, through hole; 503, connecting spring; 504, clamping column; 505, first inclined surface; 506, second inclined surface; 6, guide sleeve; 61, first internal threaded ring; 62, second external threaded ring; 7, magnet ring; 71, second internal threaded ring; 8, clamping ring; 9, support; 91, annular cavity; 92, swing arm; 93, mounting spring. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work belong to the protection scope of the present application.

[0049] A novel low-strain detection method for a pile in an environmental-friendly soft soil layer, comprising the following steps:

[0050] (1) checking the pile to be detected: the strength of the pile body should be no less than 70% of the design strength, and should be no less than 15 MPa; the material, strength and cross-sectional size of the pile head should be basically the same as those of the pile body; the pile top surface should be flat, compact and basically perpendicular to the pile axis;

[0051] (2) after determining that the pile head reaches the ideal height, cleaning the pile head to ensure that the pile head is flat and undamaged, and in addition, polishing 2-4 smooth surfaces with a diameter of 8-10 cm for the convenience of installing the sensor;

[0052] (3) Set the test parameters: the length of the time domain signal record should be continued for not less than 5 ms after 2L / c time; the upper limit of the frequency range of the amplitude-frequency signal analysis should be not less than 2000 Hz; the set pile length should be the construction pile length from the pile top measuring point to the pile bottom; the set pile body cross-sectional area should be the construction cross-sectional area; the pile body wave velocity can be preliminarily set according to the test value of the same type of pile in the region; the sampling time interval or sampling frequency should be reasonably selected according to the pile length, pile body wave velocity and frequency domain resolution; the time domain signal sampling point number should be not less than 1024 points; the set value of the sensor should be set according to the measurement verification or calibration result;

[0053] (4) Measure the sensor installation and excitation operation: the sensor installation should be perpendicular to the pile top surface; when bonding with the coupling agent, it should have sufficient bonding strength; the knocking device is erected on the reinforcement cage to knock the excitation point, so that the excitation point avoids the influence of the main reinforcement of the reinforcement cage and the excitation direction should be along the pile axis direction;

[0054] (5) Signal acquisition and screening: according to the pile diameter, 2-4 installation sensors are symmetrically arranged at the detection points in the pile center: the excitation point of the solid pile should be selected at the pile center, and the detection point should be at 2 / 3 of the radius from the pile center; when the pile diameter is large or the upper cross-sectional size of the pile is irregular, in addition to collecting signals at the specified excitation point and detection point positions according to the above paragraph, the positions of the excitation point and the detection point should be appropriately changed to collect signals according to the characteristics of the measured signals; when the consistency of the time domain signals of different detection points and multiple measurements is poor, the reasons should be analyzed and the number of detection points should be increased; the signal should not be distorted and zero drift, and the signal amplitude should not exceed the range of the measurement system; the effective signal number recorded at each detection point should be not less than 3;

[0055] (6) Analysis and determination of detection data: for the determination of the average value of the pile body wave velocity, when the pile length is known and the pile bottom reflection signal is clear, the average value of the pile body wave velocity of not less than 5 piles with complete pile body should be calculated in the foundation conditions, pile type and pile forming process of the foundation pile; when it is not possible to determine according to the above paragraph, the average value of the wave velocity can be determined comprehensively according to the measured values of other pile foundation engineering of the same pile type and pile forming process in the region, combined with the aggregate variety and strength grade of the pile body concrete.

[0056] Reference Figure 1 , Figure 2 , Figure 3The knocking device in step (4) comprises a fixed sleeve 1, a double-shaft motor 2, connecting arms 3, a knocking hammer 4, a rubber hammer pad 41 and a release assembly 5. The fixed sleeve 1 extends in the vertical direction, and the double-shaft motor 2 is embedded in the fixed sleeve 1 by bolts. The double-shaft motor 2 is a variable frequency speed regulating motor, and the rotating speed of the upper and lower output shafts can be adjusted to meet different requirements. The connecting arms 3 are arranged in plurality and uniformly distributed along the circumferential side of the fixed sleeve 1, and are used for connecting the reinforcement cage. The circumferential side of the fixed sleeve 1 is provided with a first annular groove 11. The inner walls of the upper and lower sides of the first annular groove 11 are provided with a second annular groove 12, and the inner wall of the second annular groove 12 is provided with a third annular groove 13 with a circular cross section. One end of the connecting arm 3 is welded with a swing sleeve 31, and the swing sleeve 31 is provided with a movable shaft 32 penetrating through the swing sleeve 31 and located in the first annular groove 11. The upper and lower ends of the movable shaft 32 are integrally provided with sliding balls 321, which are embedded in the third annular groove 13 after penetrating through the second annular groove 12. The end of the connecting arm 3 away from the fixed sleeve 1 is welded with a mounting sleeve 33 sleeved on the reinforcement of the reinforcement cage. The mounting sleeve 33 is welded with an internally threaded sleeve 331, and the internally threaded sleeve 331 is screwed with a locking bolt 332 used for abutting against the reinforcement. At this time, the detachable connection between the connecting arm 3 and the reinforcement cage can be realized.

[0057] Referring to Figure 2 , Figure 3 , Figure 4 The knocking hammer 4 is arranged below the fixed sleeve 1 and used for knocking the base pile excitation point after falling. The rubber hammer pad 41 is bonded and fixed at the lower end of the knocking hammer 4. The knocking hammer 4 is in contact with the upper surface of the base pile through the rubber hammer pad 41, and the rubber hammer pad 41 is in the shape of a cylinder. The output shaft at the upper end of the double-shaft motor 2 is connected with a grinding wheel 21, which can grind the surface of the detection point of the sensor installed on the upper surface of the base pile. The upper end of the double-shaft motor 2 is also sleeved with a cleaning ring 22. The cleaning ring 22 comprises an elastic ring 221 and a brush part 222. The elastic ring 221 is made of elastic fabric and sleeved at the upper end position of the double-shaft motor 2. The brush part 222 is composed of a plurality of brushes and arranged in plurality. The plurality of brush parts 222 are bonded to the circumferential side of the elastic ring 221 and uniformly distributed along the circumferential side of the elastic ring 221.

[0058] Referring to Figure 2 , Figure 4 , Figure 5The release assembly 5 is disposed between the fixed sleeve 1 and the dual-axis motor 2 and is used to release the hammer 4 after the dual-axis motor 2 rotates. This release assembly 5 includes a lifting sleeve 51, a guide ring 52, an inclined surface 53, a guide post 54, a guide post 55, a guide hole 56, a return spring 57, a connecting groove 58, a wedge block 59, a sliding shaft 501, a through hole 502, a connecting spring 503, a locking post 504, a first inclined surface 505, and a second inclined surface 506. The lifting sleeve 51 is sleeved on the lower end of the dual-axis motor 2. On the shaft, the guide ring 52 is integrally mounted on the upper end of the lifting sleeve 51, while the inclined part 53 is opened on one side of the guide ring 52. The guide post 54 is welded to the output shaft of the dual-axis motor 2 at its upper end and abuts against the upper surface of the guide ring 52 and the inclined part 53 at its lower end, and the lower end surface of the guide post 54 is spherical. Multiple guide posts 55 are provided, and their upper ends are welded to the periphery of the lower end surface of the fixed sleeve 1. Multiple guide holes 56 are also provided and opened on the periphery of the lifting sleeve 51, and the multiple guide holes 56 respectively supply multiple guide posts 55. The lower end of the guide post 55 is embedded, and the return spring 57 is sleeved on the guide post 55. The upper end of the return spring 57 is welded to the fixed sleeve 1 and the lower end is welded to the lifting sleeve 51. The connecting groove 58 is opened on both sides of the lower end of the lifting sleeve 51, and the wedge block 59 is embedded in the connecting groove 58 with its inclined surface facing upward. The sliding shaft 501 is integrally set at the end of the wedge block 59 away from the central axis of the lifting sleeve 51. The through hole 502 is opened on the inner wall of the connecting groove 58 and allows the sliding shaft 501 to pass through. 03 is sleeved on the sliding shaft 501, while the locking post 504 is integrally set on the upper end of the hammer 4 and is used to be embedded in the lifting sleeve 51. The output shaft at the lower end of the dual-axis motor 2 is welded with a thrust auxiliary spring 23 for abutting against the upper end surface of the locking post 504. At the same time, the first inclined surface 505 is opened on the upper end of the locking post 504 and is used for the wedge block 59 to engage, while the second inclined surface 506 is opened on the upper end of the locking post 504 and is located above the first inclined surface 505. The first inclined surface 505 and the second inclined surface 506 form a ">" shape.

[0059] Reference Figure 2 , Figure 4 Below the lifting sleeve 51, a guide sleeve 6 is provided for the hammer 4 to fall. The upper end of the guide sleeve 6 is integrally provided with a first internal threaded ring 61, and the lower end of the lifting sleeve 51 is welded with a first external threaded ring 511 for threaded connection of the first internal threaded ring 61. At this time, the guide sleeve 6 and the lifting sleeve 51 can be detachably connected. At the same time, a magnet ring 7 is also provided at the lower end of the guide sleeve 6, and a second internal threaded ring 71 is bonded to the periphery of the magnet ring 7. The lower end of the guide sleeve 6 is integrally provided with a second external threaded ring 62 for threaded connection of the second internal threaded ring 71. At this time, the magnet ring 7 can be detachably connected to the lower end of the guide sleeve 6. After the guide sleeve 6 is installed below the lifting sleeve 51, there is a gap between the magnet ring 7 and the upper surface of the foundation pile, and the length of the rubber hammer pad 41 is greater than the sum of the gap width and the thickness of the magnet ring 7.

[0060] Referring to Figure 4 、 Figure 6 , the rubber hammer pad 41 is further sleeved with a snap ring 8 for attracting the magnet ring 7, and the snap ring 8 is in interference fit with the rubber hammer pad 41, but the friction between the snap ring 8 and the rubber hammer pad 41 is smaller than the attraction between the snap ring 8 and the magnet ring 7, wherein the snap ring 8 is further provided with a supporting piece 9 for supporting when the rubber hammer pad 41 rebounds and falls, and the supporting piece 9 includes an annular cavity 91, a swing arm 92 and a mounting spring 93, the annular cavity 91 is opened on the inner wall of the circumference of the snap ring 8, one end of the swing arm 92 is hinged to the inner wall of the annular cavity 91, and one end of the mounting spring 93 is welded with the end of the swing arm 92 and the other end is welded with the inner wall of the annular cavity 91, when the mounting spring 93 is in a natural state, the swing arm 92 swings to the center of the snap ring 8.

[0061] Principle: first, the surface of the pile is polished, the guide sleeve 6 and the knocking hammer 4 are removed, and the connecting arms 3 are combined together to form a handle for taking the double-shaft motor 2 (refer to Figure 7 、 Figure 8 ), the operator can hold the connecting arm 3 and drive the polishing grinding wheel 21 to polish the upper surface of the pile through the double-shaft motor 2, and after polishing, the elastic expansion of the elastic ring 221 is wrapped around the polishing grinding wheel 21, so that the polishing grinding wheel 21 drives the cleaning ring 22 to rotate when rotating, and the brush part 222 on the circumference of the elastic ring 221 can clean the polished upper surface of the pile, so as to facilitate the installation of the sensor.

[0062] Then the fixing sleeve 1 is sleeved on the steel bar by the mounting sleeve 33 of the connecting arm 3, and then the locking bolt 332 is threadedly connected to the inner threaded sleeve 331 and abuts against the steel bar, at this time, the detachable connection between the connecting arm 3 and the steel cage can be realized, so as to position the fixing sleeve 1 at the center excitation point of the pile.

[0063] Subsequently, the operator inserts the clamping column 504 of the knocking hammer 4 into the lower end of the lifting sleeve 51 and abuts against the thrust auxiliary spring 23, while the guide column 54 is located at the position of the upper surface of the guide ring 52, at this time, the wedge-shaped blocks 59 abut against the second inclined surface 506, so that the two wedge-shaped blocks 59 move towards the side away from each other, and the connecting spring 503 is compressed, then the second inclined surface 506 can pass the wedge-shaped blocks 59, after the first inclined surface 505 moves to the position of the wedge-shaped blocks 59, under the elastic restoring force of the connecting spring 503, the two wedge-shaped blocks 59 clamp the clamping column 504 at the position of the first inclined surface 505, thereby completing the clamping of the clamping column 504 in the lifting sleeve 51, realizing the connection of the knocking hammer 4 at the lower end of the lifting sleeve 51; then the clamping ring 8 is sleeved on the rubber hammer pad 41, and the swing arm 92 swings towards the side away from the center of the clamping ring 8, and then the guide sleeve 6 is connected to the lower side of the lifting sleeve 51 and plays a guiding role in the falling of the knocking hammer 4 through the guide sleeve 6.

[0064] When it is necessary to release the knocking hammer 4, the double-shaft motor 2 is started, so that the double-shaft motor 2 drives the guide column 54 to rotate around the output shaft of the double-shaft motor 2, at this time, the guide column 54 abuts against the upper surface of the guide ring 52 and the inclined surface part 53, when the guide column 54 moves from the position of the upper surface of the guide ring 52 to the position of the inclined surface part 53, under the elastic restoring force of the reset spring 57, the lifting sleeve 51 moves upward along the guide column 55, at this time, the wedge-shaped blocks 59 move upward along the first inclined surface 505 and then move to the second inclined surface 506, after losing the clamping of the wedge-shaped blocks 59, the clamping column 504 can quickly separate from the lifting sleeve 51 under the auxiliary action of the thrust auxiliary spring 23, then the knocking hammer 4 falls under the action of its own gravity.

[0065] When the knocking hammer 4 falls together with the clamping ring 8, the rubber hammer pad 41 can pass through the magnet ring 7 and complete the knocking action with the upper surface of the pile, at this time, the clamping ring 8 can be attracted to the magnet ring 7, and after the knocking hammer 4 rebounds, the clamping ring 8 can be separated from the rubber hammer pad 41, then under the elastic restoring force of the installation spring 93, the swing arm 92 swings reversely and then swings to the center of the clamping ring 8, thereby supporting the rubber hammer pad 41 when it rebounds and falls, avoiding the rubber hammer pad 41 from colliding with the upper surface of the pile after passing through the magnet ring 7 again, finally, the knocking hammer 4 can only produce one knocking action when it falls each time, which is conducive to the data collection of the sensor of the detection point.

Claims

1. A percussion device for low-strain testing of foundation piles in soft soil strata, characterized in that: The system includes a fixed sleeve (1) extending vertically, a dual-axis motor (2) embedded in the fixed sleeve (1), multiple connecting arms (3) arranged around the fixed sleeve (1) for connecting to the reinforcing cage, a hammer (4) arranged below the fixed sleeve (1) for striking the excitation point of the foundation pile after falling, a rubber hammer pad (41) arranged at the lower end of the hammer (4), and a release assembly (5) arranged between the fixed sleeve (1) and the dual-axis motor (2) for releasing the hammer (4) after the dual-axis motor (2) rotates; a grinding wheel (21) is provided on the output shaft at the upper end of the dual-axis motor (2), a first annular groove (11) is provided on the periphery of the fixed sleeve (1), and a second annular groove (12) is provided on the inner walls of the upper and lower sides of the first annular groove (11). The inner wall of the second annular groove (12) is provided with a third annular groove (13) with a circular cross section. A swing sleeve (31) is provided at one end of the connecting arm (3). A movable shaft (32) is provided on the swing sleeve (31) and passes through the swing sleeve (31) and is located in the first annular groove (11). Both the upper and lower ends of the movable shaft (32) are provided with sliding balls (321) that pass through the second annular groove (12) and are embedded in the third annular groove (13). An installation sleeve (33) is provided on the end of the connecting arm (3) away from the fixed sleeve (1) and is fitted on the steel bar in the steel cage. An internal thread sleeve (331) is provided on the installation sleeve (33), and a locking bolt (332) for abutting against the steel bar is threaded on the internal thread sleeve (331).The release assembly (5) includes a lifting sleeve (51) sleeved on the output shaft of the lower end of the dual-axis motor (2), a guide ring (52) set on the upper end of the lifting sleeve (51), a beveled part (53) opened on one side of the guide ring (52), a guide post (54) whose upper end is connected to the output shaft of the dual-axis motor (2) and whose lower end abuts against the upper surface of the guide ring (52) and the beveled part (53), a plurality of guide posts (55) set on the periphery of the lower end face of the fixed sleeve (1), a plurality of guide holes (56) opened on the periphery of the lifting sleeve (51) and for the lower ends of the plurality of guide posts (55) to be inserted, a return spring (57) sleeved on the guide post (55) whose upper end is fixed to the fixed sleeve (1) and whose lower end is fixed to the lifting sleeve (51), a connecting groove (58) opened on both sides of the lower end of the lifting sleeve (51), and a wedge set in the connecting groove (58) with its beveled surface facing upward. The device includes a wedge block (59), a sliding shaft (501) located at one end of the wedge block (59) away from the central axis of the lifting sleeve (51), a through hole (502) on the inner wall of the connecting groove (58) for the sliding shaft (501) to pass through, a connecting spring (503) sleeved on the sliding shaft (501), a locking post (504) located at the upper end of the hammer (4) and embedded in the lifting sleeve (51), a first inclined surface (505) located at the upper end of the locking post (504) for the wedge block (59) to engage, and a second inclined surface (506) located at the upper end of the locking post (504) and above the first inclined surface (505), wherein the first inclined surface (505) and the second inclined surface (506) are in a ">" shape; a thrust auxiliary spring (23) for abutting against the upper surface of the locking post (504) is fixed on the output shaft at the lower end of the dual-axis motor (2).

2. The percussion device for low strain testing of foundation piles in soft soil as described in claim 1, characterized in that: The upper end of the dual-axis motor (2) is fitted with a cleaning ring (22), which includes an elastic ring (221) fitted on the upper end of the dual-axis motor (2) and a plurality of brush parts (222) arranged around the elastic ring (221) and evenly spaced along the elastic ring (221).

3. The percussion device for low strain testing of foundation piles in soft soil as described in claim 1, characterized in that: The lower part of the lifting sleeve (51) is provided with a guide sleeve (6) for the hammer (4) to fall. The upper end of the guide sleeve (6) is provided with a first internal thread ring (61). The lower end of the lifting sleeve (51) is provided with a first external thread ring (511) for the first internal thread ring (61) to be threadedly connected. The lower end of the guide sleeve (6) is provided with a magnet ring (7). The periphery of the magnet ring (7) is provided with a second internal thread ring (71). The lower end of the guide sleeve (6) is provided with a second external thread ring (62) for the second internal thread ring (71) to be threadedly connected. The rubber hammer pad (41) is cylindrical and the periphery is provided with a retaining ring (8) for attracting onto the magnet ring (7). The retaining ring (8) is provided with a support member (9) for supporting the rubber hammer pad (41) after it rebounds and falls.

4. The percussion device for low strain testing of foundation piles in soft soil as described in claim 3, characterized in that: The support member (9) includes an annular cavity (91) opened on the inner wall of the circumference of the retaining ring (8), a swing arm (92) with one end hinged to the inner wall of the annular cavity (91), and a mounting spring (93) with one end connected to the end of the swing arm (92) and the other end connected to the inner wall of the annular cavity (91). When the mounting spring (93) is in its natural state, the swing arm (92) swings to the center of the retaining ring (8).

Images