CN114482154B - Method and system for testing static bearing capacity of pipe pile based on traveling wave tracing principle - Google Patents
Method and system for testing static bearing capacity of pipe pile based on traveling wave tracing principle Download PDFInfo
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Abstract
A method and a system for testing the static bearing capacity of a pipe pile based on a traveling wave tracing principle are disclosed, wherein the method comprises the following steps: arranging sensors on the inner wall of the tubular pile along the axial direction of the pile body, wherein the sensors of various types are arranged on the pile body in a one-to-one annular corresponding mode; hammering the pile top of the pipe pile, and synchronously acquiring and recording force wave signals and speed wave signals of each measuring point of the pile body axially transmitted along the pile body; decomposing force waves axially propagated along the pile body into uplink waves and downlink waves by a traveling wave decomposition method, and realizing traveling wave tracing of the pile body; calculating to obtain a dynamic resistance time-course curve and a pile end soil dynamic resistance time-course curve of each pile section, and determining pile side soil dynamic resistance and pile end soil dynamic resistance; and determining the maximum static bearing capacity of the tubular pile and the limit bearing capacity of the pile. The static bearing capacity of the pile body is directly evaluated through the actually measured dynamic signals of the pile body, the calculation process does not involve concrete parameters and human factors of the soil body around the pile, and the influence of the property complexity of the soil body around the pile and the subjectivity of a tester on the evaluation result of the bearing capacity is effectively avoided.
Description
Technical Field
The invention belongs to the technical field of pile foundation engineering detection, and particularly relates to a method and a system for testing static bearing capacity of a tubular pile based on a traveling wave tracing principle, which are suitable for evaluating the bearing capacity of the pile foundation.
Background
In recent years, with the rapid development of engineering construction in China, pile foundations are widely applied to various foundation construction projects such as buildings, traffic, water conservancy and municipal works. Whether the bearing capacity of the pile foundation meets the design requirement is of great importance to the safe service of the upper structure, so that the effective test of the bearing capacity of the pile foundation is an indispensable part in engineering detection, and the method has extremely important engineering practical significance.
The existing pile foundation bearing capacity test method mainly comprises two main types: static test methods and dynamic test methods. The static test method mainly refers to a static load test method widely used at present, and has the obvious advantages that the real pile foundation bearing condition is simulated, the test result has higher reliability, but the defects are obvious, the loading device is large, the loading process is complex, and the test economy and time cost are higher; in addition, under the working conditions of relatively narrow operation space such as on the sea, the difficulty of carrying out the static load test is large, and even the static load test cannot be implemented at all. The dynamic testing method is developed according to the limitation of a static load testing method, the dynamic testing method for the bearing capacity of the pile foundation which is used more domestically at present is a high-strain method, and the high-strain method is further divided into a CASE method and a waveform fitting method according to the difference of testing theories. The two pile foundation bearing capacity dynamic measurement methods are characterized in that a group of acceleration and strain sensors are symmetrically arranged at positions close to the pile top, and the ultimate bearing capacity of the pile foundation is calculated by testing the speed and stress wave signals of the pile top under the action of hammering load; the waveform fitting method selects one of the actually measured pile top speed and stress signals as an input signal to be substituted into a pre-built pile-soil theoretical model, obtains an output signal by means of huge calculation capacity of a modern computer, repeatedly compares the actually measured output signal with a theoretical inversion output signal by changing various parameters of the theoretical model until a good fitting effect is achieved, and then calculates by using the inverted pile-soil system parameter values to obtain the static bearing capacity of the pile foundation. According to the principle, the accuracy of the prediction result is greatly influenced by the theoretical model of the pre-built pile-soil system, if the pre-built theoretical model is rough, the real pile-soil interaction state cannot be reflected, and the deviation degree of the test result is large; selecting a complex theoretical model closer to reality leads to excessive parameters to be determined, excessive inversion calculation amount and poor inversion effect, and is mainly reflected in the fact that multiple parameter combinations may exist to achieve the same waveform fitting effect, thereby leading to non-uniqueness of a test result. In addition, both the CASE method and the waveform fitting method have the problem of empirical judgment of parameters, so that the subjectivity of a test result to a tester is greatly influenced. The self limitation of the testing theory and the subjectivity of the testing personnel enable the stability of the testing effect of the high strain method to be poor and lack of engineering persuasion.
Therefore, the existing pile foundation bearing capacity testing method still has many problems, the actual requirements of engineering development are difficult to meet, especially for marine large-diameter tubular piles, the traditional testing method is often difficult to obtain a good testing effect, a novel pile foundation bearing capacity testing method is urgently needed to be provided to improve the pain point of the prior art, the quick and effective testing of the tubular pile bearing characteristic is realized, and the marine engineering development and the marine resource development are further promoted.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method and a system for testing static bearing capacity of a tubular pile based on a traveling wave tracing principle aiming at the limitation of the conventional pile bearing capacity detection technology, wherein the method is not influenced by the property of soil around the pile, is suitable for researching the pile bearing capacity under various soil bodies, considers the convenience of sensor installation and the specificity of test working conditions, and is particularly suitable for predicting and evaluating the bearing capacity of a large-diameter offshore tubular pile.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the method for testing the static bearing capacity of the pipe pile based on the traveling wave tracing principle comprises the following steps of:
1) Arranging sensors on the inner wall of the tubular pile along the axial direction of the pile body, wherein the sensors comprise but are not limited to strain sensors and acceleration sensors, a plurality of strain sensors distributed along the axial direction form a distributed strain gauge, and a plurality of acceleration sensors distributed along the axial direction form a serial accelerometer; the sensors of all types are arranged on the pile body in a one-to-one corresponding mode along the ring shape, namely at least one strain sensor and one acceleration sensor are arranged at the same height in the horizontal direction (so as to be convenient for the decomposition of the up-and-down traveling wave with a specific cross section);
2) In the pile driving process or after pile sinking is finished, hammering is applied to the pile top of the pipe pile, and the hammering force is ensured to be uniformly distributed on the section of the pile top of the pipe pile as far as possible (the influence of the three-dimensional effect of the pile body is avoided);
3) Synchronously acquiring and recording force wave signals and velocity wave signals of all measuring points of the pile body axially transmitted along the pile body through a multi-channel data acquisition instrument, distributed strain gauges and a serial accelerometer which are arranged in advance;
4) Decomposing the force wave axially transmitted along the pile body into an uplink wave and a downlink wave by a traveling wave decomposition method by utilizing the force wave signal and the velocity wave signal axially transmitted along the pile body by each measuring point, and realizing traveling wave tracing of the pile body;
5) Obtaining a time domain spectrum of the upgoing wave and the downgoing wave along the depth direction through traveling wave tracing in the step 4), calculating to obtain a pile side soil dynamic resistance time course curve of each pile section, obtaining a pile end soil dynamic resistance time course curve by using the upgoing wave and the downgoing wave at the position of the pile end, and determining the pile side soil dynamic resistance and the pile end soil dynamic resistance;
6) And acquiring a speed curve of each pile section by using an acceleration sensor, and determining the maximum static bearing capacity of the tubular pile and the limit bearing capacity of the pile according to the dynamic resistance time-course curve and the speed curve of each pile section and the pile end.
According to the scheme, in the step 1), two groups of distributed strain gauges and serial accelerometers are respectively fixed at symmetrical positions (namely the annular angle is 180 degrees) on the inner wall of the tubular pile, and the distributed strain gauges and the serial accelerometers are distributed along the annular shape by 90 degrees.
According to the scheme, in the step 4), the traveling wave decomposition method specifically comprises the following steps: the method comprises the following steps of dividing a pile body into a plurality of pile sections along the axial direction according to the arrangement mode of a sensor, supposing that pile side soil dynamic resistance borne by each pile section acts on the center of the pile section in a centralized manner, decomposing force waves of each measuring point of a pile body into an upgoing wave and a downgoing wave by using measured force wave signals and speed wave signals, and accordingly forming an upgoing wave and a downgoing wave time domain wave spectrum which are distributed along the depth direction, and realizing real-time tracing of the upgoing wave and the downgoing wave through the time domain wave spectrum.
According to the scheme, assuming that all sensors have (n + 1), the sensors are numbered from top to end as 1-n +1 in sequence, and correspond to 1-n +1 measuring points on the pile body, the whole pile is divided into n pile sections by the (n + 1) sensors, taking the ith pile section as an example, the sensors at two ends of the ith pile are numbered as i and i +1, in order to realize the traveling wave decomposition of the i and i +1 measuring points, a processing method similar to the wave fitting method in the test principle is adopted, the pile side soil dynamic resistance of the i pile section is considered to act on the center position of the pile section in a centralized manner, and the force wave P (i) of the i measuring point measured by a strain sensor and the velocity wave v (i) measured by an acceleration sensor are used for decomposing the up-down traveling force waves of the two points, which is shown as the following formula:
in the formula, Pd(i) And Pu(i) The lower force wave and the upper force wave of the point i are measured, and Z is the section impedance of the pile body.
According to the scheme, the traveling wave tracing resolution is improved by increasing the arrangement density of the sensors along the axial direction; and the traveling wave tracing of a specific point position is realized by changing the arrangement position of the sensor.
According to the scheme, in the step 5), the determination of the pile side soil dynamic resistance is specifically as follows:
taking i pile section as an example, assuming that the pile side soil dynamic resistance borne by the i pile section is R (i), R (i) is concentrated on the central position of the pile section, and according to the assumption of pile foundation dynamics, considering that the influence of the damping effect of the pile body material on the propagation characteristic of force waves in the pile body is ignored, thus obtaining the following relational expression:
in the formula (I), the compound is shown in the specification,
and
respectively an upper side ascending force wave, an upper side descending force wave, a lower side ascending force wave and a lower side descending force wave of the central section of the i pile section;
and then, further deducing according to the stress balance and displacement continuity conditions of the central section of the i pile section:
determining a pile side soil dynamic resistance time course curve of the i pile section according to the up-down force waves of the i and i +1 measuring points;
the pile end soil dynamic resistance is determined as follows: the dynamic resistance time-course curve of the pile end soil adopts the upward force wave P at the pile endu(n + 1) and the down force wave Pd(n + 1) solving, and obtaining pile end soil dynamic resistance R according to the pile end section stress balance equationtoe：
Rtoe＝Pu(n+1)+Pd(n+1) (6)。
According to the above scheme, in the step 6), the determination of the maximum static bearing capacity specifically comprises:
considering the pile side soil dynamic resistance value corresponding to the first zero-returning moment after the velocity of each pile section reaches the peak value as the maximum pile side soil static resistance value, supposing that the pile side soil dynamic resistance of each pile section acts on the middle position of the pile section, correspondingly, the velocity of the central point of the pile section is also used for representing the velocity of the pile section, taking the pile section i as an example, and the velocity time-course curve of the central point of the pile section
The velocities of the two end points of the pile section measured by the serial accelerometer are obtained by the following formula:
then curve in the course of speed
First zero time after the velocity peak is determined
Finding the time course curve corresponding to the pile side soil dynamic resistance of the pile section i obtained in the step 5)
The dynamic resistance value at the moment is the maximum pile side soil static resistance value R of the pile sections(i) (ii) a Repeating the steps, respectively determining the maximum pile side soil static resistance values of all the pile sections, and performing accumulation summation to obtain the maximum pile side soil static resistance value R of the whole piles：
Determining the maximum static resistance value of the pile end soil according to the method, determining the time t (n + 1) of zeroing for the first time after determining the peak value on the speed time course curve v (n + 1) of the pile end position point, and then determining the dynamic resistance value corresponding to the time t (n + 1) on the pile end soil dynamic resistance time course curve, namely determining the maximum pile end soil static resistance value
And determining the maximum static bearing capacity R of the whole pile as the sum of the maximum pile side soil static resistance value and the maximum pile end soil static resistance value:
the impact force of the pile top directly influences the exertion of the bearing capacity of the pile side soil and the pile end soil, and when the impact force is large enough to completely stimulate the bearing capacity of the pile side soil and the pile end soil, the maximum static bearing capacity obtained by the method is the actual ultimate bearing capacity R of the pile foundationmax。
The invention also provides a system for testing the static bearing capacity of the tubular pile based on the traveling wave tracing principle, which comprises a multi-channel data acquisition instrument and sensors arranged on the inner wall of the tubular pile along the axial direction of a pile body, wherein each sensor is connected with the multi-channel data acquisition instrument, the sensors comprise but are not limited to strain sensors and acceleration sensors, the sensors of various types are arranged on the pile body in a one-to-one corresponding mode along the ring shape, namely at least one strain sensor and one acceleration sensor are arranged at the same height in the horizontal direction, the strain sensors distributed along the axial direction form a distributed strain gauge, and the acceleration sensors distributed along the axial direction form a serial accelerometer.
According to the scheme, the first sensor on the distributed strain gauge and the serial accelerometer keeps a proper distance from the cross section of the pile top and is positioned above the ground, and the last sensor is as close to the pile end as possible.
According to the scheme, the distances between the distributed strain gauges and the sensors of the serial accelerometer include, but are not limited to, equal-distance arrangement, gradual encryption from top to bottom and gradual thinning from top to bottom.
The working principle of the invention is as follows: tracing the ascending and descending force waves of each measuring point of the pile body under the action of the hammering load by arranging a sensor along the axial direction of the pile body, and further obtaining the maximum static soil resistance value of the pile body under the action of the specific hammering load by utilizing a traveling wave time domain spectrum and a speed time domain spectrum along the depth direction; when the hammering load is large enough to make the resistance of the side soil and the end soil of the pile fully exerted, the ultimate static bearing capacity of the whole pile can be obtained.
The invention has the beneficial effects that:
1. the testing process is economical and convenient, the calculation result can be quickly presented by means of computer programming calculation, and the defects of time and labor consumption of a static load test method are effectively overcome;
2. the bearing characteristics of the pile foundation at each piling stage can be rapidly tested in real time in the piling process, so that the piling quality can be monitored in real time;
3. all data are derived from actual test signals, the static bearing capacity of the pile body is directly evaluated through the actually measured dynamic signals of the pile body according to the traveling wave tracing principle, the whole data processing and calculating process does not involve artificial estimation and determination on unknown parameters, specific parameters and artificial factors of the soil body around the pile do not need to be considered, the property complexity (uncertainty) of the soil body around the pile and the subjective influence caused by the empirical judgment of testers in the traditional high-strain test method can be effectively avoided, and the method is suitable for testing the static bearing capacity of the pipe pile under the soil bodies with various properties;
4. the whole testing and data processing process does not involve the selection and calculation of soil parameters around the pile, is not influenced by the soil property around the pile, can be suitable for researching the bearing capacity of the pile foundation under various soil conditions and soil layer distribution working conditions, can also consider the existence of soil plugs in the pile, and has wider applicability; the method is particularly suitable for predicting and evaluating the bearing capacity of the offshore large-diameter tubular pile in consideration of the convenience of sensor installation and the particularity of test working conditions;
5. in the test process, the formula (4) shows that theoretically, R (i) has two calculation methods, if the consistency of R (i) obtained by the two calculation methods in the actual test is better, the test effect is better, and the obtained R (i) can be used for subsequent calculation and analysis; if the consistency is poor, the problem of the test data is shown, and repeated tests are needed, so that the test method provided by the invention has a self-verification function, the validity of the test data is more effectively ensured, and an accurate test result of the bearing capacity of the pile foundation is more favorably obtained.
Drawings
Fig. 1 is a schematic view of a pipe pile structure of a pipe pile static bearing capacity testing system based on a traveling wave tracing principle according to an embodiment of the invention;
FIG. 2 isbase:Sub>A view of the strain sensor arrangement of the pipe pile in FIG. 1 along the A-A direction;
FIG. 3 is a view of the arrangement of acceleration sensors of the pipe pile in the direction B-B in FIG. 1;
FIG. 4 is a schematic diagram of traveling wave propagation and stress analysis of an ith pile section pipe pile according to an embodiment of the invention;
FIG. 5 is a schematic diagram of the traveling wave propagation and force analysis of the pile tip according to an embodiment of the present invention;
in the figure: 1-tubular pile, 2-strain transducer, 3-connecting wire and 4-acceleration transducer.
Detailed Description
The core idea of the method is to reflect the resistance characteristics of the soil at the pile side and the pile end by utilizing the traveling wave transmitted along the pile body so as to further determine the ultimate bearing capacity of the whole pile, and the specific implementation steps of the method are described in detail below by combining the attached drawings.
The embodiment of the invention provides a method for testing static bearing capacity of a pipe pile based on a traveling wave tracing principle, which comprises the following steps:
1. and (6) installing a sensor. Before piling construction, strain sensors and acceleration sensors are distributed on the inner wall of a tubular pile 1 along the axial direction of a pile body in a specific arrangement mode, as shown in fig. 1, a plurality of strain sensors 2 distributed along the axial direction form a distributed strain gauge, a plurality of acceleration sensors 4 distributed along the axial direction form a serial accelerometer, and the distributed strain gauge and the serial accelerometer are respectively used for realizing real-time, synchronous and high-resolution acquisition of force wave signals and velocity wave signals of specific measuring points of the pile body. The spacing between the individual sensors of the distributed strain gauges and the serial accelerometers can be varied at will to assume different arrangements along the shaft, including but not limited to an equidistant arrangement at a certain distance (as shown in fig. 2 and 3), a gradual top-to-bottom encryption (sparse top and sparse bottom), and a gradual top-to-bottom sparseness (sparse top and sparse bottom). The sensors are arranged on the pile body in a one-to-one corresponding mode along the annular mode, namely at least one strain sensor and one acceleration sensor are arranged at the same height in the horizontal direction, and the strain sensor 2 and the acceleration sensor 4 are connected with a multi-channel data acquisition instrument through connecting wires 3 so as to facilitate the decomposition of up-and-down traveling waves with specific cross sections. In order to reduce the influence of pile top hammering load eccentricity as much as possible, two groups of distributed strain gauges and serial accelerometers are respectively fixed at symmetrical positions (annular angle of 180 degrees) on the inner wall of the pipe pile, and the distributed strain gauges and the serial accelerometers are distributed along an annular shape at 90 degrees, as shown in fig. 2 and 3. The first sensor on the distributed strain gauge and the serial accelerometer keeps a proper distance from the cross section of the pile top and is positioned above the ground so as to avoid the influence of the three-dimensional effect of the pile body as much as possible; the last sensor should be as close to the pile end as possible to achieve accurate decomposition of the up going and down going force waves at the pile end. Assuming that each type of sensor has (n + 1) sensors, the number of the sensors is 1-n +1 from the top to the end, and the sensors (n + 1) number 1-n + 1 corresponding to the measuring points on the pile body, and divide the whole pile into n pile sections, wherein the sensors at the two ends of the i-th pile section are numbered i and i +1, as shown in fig. 4. It should be noted that the pile section from the first sensor to the pile top is a zero-number pile section, which is located above the ground surface, so that the influence on the overall bearing capacity is small and is out of the consideration range of the method.
2. And (5) dynamic signal acquisition. In the pile driving process or after pile sinking is finished, hammering is applied to the pile top of the pipe pile, and in order to avoid the influence of the three-dimensional effect of the pile body, the hammering force is ensured to be uniformly distributed on the section of the pile top of the pipe pile as far as possible; and then, synchronously acquiring force wave and velocity wave signals of each measured point in real time by using a distributed strain meter and a serial accelerometer which are axially arranged along the pile body. Taking an i pile segment as an example, as shown in fig. 4, the strain sensors and the acceleration sensors at two ends of the i pile segment are numbered i and i +1, wherein the strain sensors can measure force waves P (i) and P (i + 1) at two ends of the i pile segment, and the acceleration sensors can measure velocity waves v (i) and v (i + 1) at two ends of the i pile segment. By analogy, P (n + 1) and v (n + 1) are respectively a stress wave and a velocity wave of the cross section of the pile end.
3. And (3) decomposing and tracing traveling waves, wherein the step mainly realizes the decomposition and tracing of the uplink and downlink force waves of each pile body measuring point. Similarly, taking the ith pile segment as an example, in order to realize the traveling wave decomposition of the i and i +1 measuring points, a processing method similar to that in the test principle of the waveform fitting method is adopted, and the pile side dynamic resistance of the ith pile segment is considered to act on the center position of the pile segment in a centralized manner, as indicated by a dotted line in fig. 4. At this time, the force wave of the point i measured by the strain sensor in the step 2 and the velocity wave of the point i measured by the acceleration sensor can be used for decomposing the uplink and downlink force waves of the two points, as shown in the formulas (1) and (2); because the tubular pile is mostly precast pile in the engineering, consequently think its pile shaft quality control good, the section impedance is the constant value. Similarly, the up-down force waves of each measuring point of the pile section can be obtained according to the traveling wave decomposition methods shown in the formulas (1) and (2). Therefore, traveling wave tracing along the axial direction of the pile body can be achieved on the basis of traveling wave decomposition.
4. The pile side soil dynamic resistance is determined, taking i pile sections as an example, assuming that the pile side dynamic resistance borne by the i pile sections is R (i), the R (i) is concentrated on the central position of the pile sections, as shown in FIG. 4, according to the common pile foundation dynamics assumption, the influence of the damping effect of the pile body material on the force wave propagation characteristic in the pile body is considered to be negligible, and therefore, the relation (3) can be obtained.
And then, a formula (4) can be further obtained according to the stress balance and displacement continuity conditions of the central section of the i pile section. Therefore, the pile side dynamic resistance time-course curve of the i pile section can be determined by the up-down force waves of the i and i +1 measuring points. Meanwhile, as can be seen from the formula (4), theoretically, there are two calculation methods for R (i), and if the consistency of R (i) obtained by the two calculation methods is better in actual test, the test effect is better, and the obtained R (i) can be used for subsequent calculation analysis; if the consistency is poor, the problem of test data exists, and repeated tests are needed. Therefore, the test method provided by the invention has a self-verification function and is more beneficial to obtaining accurate and effective results.
5. And determining the dynamic resistance of the pile end soil. The dynamic resistance time course curve of the pile end soil can adopt the upward force wave P at the pile endu(n + 1) and the down force wave Pd(n + 1) is solved, as shown in figure 5, the pile end soil dynamic resistance R can be obtained according to the pile end section stress balance equation (6)toe。
6. And determining the maximum static bearing capacity. And (5) determining the pile side soil dynamic resistance and the pile end soil dynamic resistance time course curve of each pile section through the step (4) and the step (5), and then considering that the pile side dynamic resistance value corresponding to the first zero-resetting time after the speed of each pile section reaches the peak value is the maximum static resistance value. In the method, the dynamic resistance of the soil at the side of each pile section is supposed to act on the middle position of the pile section, and accordingly, the speed of the center point of the pile section is also used for representing the speed of the pile section. Taking i pile segment as an example, the velocity time course curve (v) of the center point of the pile segmenti) The measured speeds at the two ends of the pile section can be obtained through various numerical calculation methods, and a simpler mean value calculation algorithm is selected for convenience of description, as shown in formula (7).
Then curve in speed time course
The first zero time after the upper determined peak value
Further, finding the time course curve corresponding to the i pile section pile side soil dynamic resistance obtained in the step 4
The dynamic resistance value at the moment is the maximum pile side soil static resistance value Rs(i) In that respect Repeating the steps, respectively determining the maximum pile side soil static resistance values of all the pile sections, and summing the maximum pile side soil static resistance values to obtain the maximum pile side soil static resistance value R of the whole pilesAs shown in formula (8).
Determining the maximum static resistance value of the pile end soil according to the method, determining the time t (n + 1) of zeroing for the first time after determining the peak value on the speed time course curve v (n + 1) of the pile end position point, and then determining the dynamic resistance value corresponding to the time t (n + 1) on the pile end soil dynamic resistance time course curve, namely determining the maximum pile end soil static resistance value
Accordingly, the maximum static bearing capacity (R) of the whole pile may be determined as the sum of the maximum pile-side soil static resistance value and the maximum pile-end soil static resistance value, as shown in formula (9).
7. The ultimate bearing capacity of the pile is determined. The size of the pile top hammering force directly influences the exertion of the bearing capacity of the pile side soil and the pile end soil, and when the hammering action is large enough to completely excite the bearing capacity of the pile side soil and the pile end soil, the maximum static bearing capacity obtained by the method is the actual ultimate bearing capacity R of the pile foundationmax。
The invention is not limited to the use as specified in the description and the embodiments, but various modifications and variations can be made by those skilled in the art in light of the present invention, and are intended to fall within the scope of the appended claims.
Claims (7)
1. The method for testing the static bearing capacity of the tubular pile based on the traveling wave tracing principle is characterized by comprising the following steps of:
1) Arranging sensors on the inner wall of the tubular pile along the axial direction of the pile body, wherein the sensors comprise strain sensors and acceleration sensors, a plurality of strain sensors distributed along the axial direction form a distributed strain gauge, and a plurality of acceleration sensors distributed along the axial direction form a serial accelerometer; the sensors of all types are arranged on the pile body in a one-to-one corresponding mode along the ring shape, namely at least one strain sensor and one acceleration sensor are arranged at the same height in the horizontal direction;
2) In the pile driving process or after pile sinking is finished, hammering is applied to the pile top of the pipe pile, and the hammering force is uniformly distributed on the section of the pile top of the pipe pile as far as possible;
3) Synchronously acquiring and recording force wave signals and velocity wave signals of all measuring points of the pile body axially transmitted along the pile body through a multi-channel data acquisition instrument, a distributed strain meter and a serial accelerometer which are arranged in advance;
4) Decomposing the force wave axially propagated along the pile body into an uplink wave and a downlink wave by a traveling wave decomposition method by utilizing the force wave signal and the velocity wave signal axially propagated along the pile body at each measuring point, thereby realizing the traveling wave tracing of the pile body;
5) Acquiring time domain spectrums of the upgoing waves and the downgoing waves in the depth direction through traveling wave tracing in the step 4), calculating to obtain a pile side soil dynamic resistance time course curve of each pile section, acquiring a pile end soil dynamic resistance time course curve by using the upgoing waves and the downgoing waves at the pile end position, and determining the pile side soil dynamic resistance and the pile end soil dynamic resistance;
6) And acquiring a speed curve of each pile section by using an acceleration sensor, and determining the maximum static bearing capacity of the tubular pile and the limit bearing capacity of the pile according to the dynamic resistance time-course curve and the speed curve of each pile section and the pile end.
2. The method for testing the static bearing capacity of the tubular pile based on the traveling wave tracing principle of claim 1, wherein in the step 1), two groups of distributed strain gauges and serial accelerometers are respectively fixed at symmetrical positions on the inner wall of the tubular pile, and the distributed strain gauges and the serial accelerometers are arranged along an annular shape at an angle of 90 degrees.
3. The traveling wave tracing principle-based static bearing capacity testing method of the tubular pile according to claim 1, wherein in the step 4), the traveling wave decomposition method specifically comprises the following steps: the method comprises the following steps of dividing a pile body into a plurality of pile sections along the axial direction according to the arrangement mode of a sensor, supposing that pile side soil dynamic resistance borne by each pile section acts on the center of the pile section in a centralized manner, decomposing force waves of each measuring point of a pile body into an upgoing wave and a downgoing wave by using measured force wave signals and velocity wave signals, thereby forming an upgoing wave and a downgoing wave time domain wave spectrum which are distributed along the depth direction, and realizing real-time tracing of the upgoing wave and the downgoing wave through the time domain wave spectrum.
4. The method for testing the static bearing capacity of the tubular pile based on the traveling wave tracing principle as claimed in claim 3, wherein assuming that each sensor has (n + 1) total, the number of the sensors from the top to the end is 1-n +1, and the sensors corresponding to 1-n +1 measuring points on the pile body, and the (n + 1) sensors divide the whole pile into n pile sections, taking the i-th pile section as an example, and the sensors at the two ends of the i-th pile section are numbered i and i +1, in order to realize the traveling wave decomposition of the i and i +1 measuring points, a processing method similar to the waveform fitting method test principle is adopted, and it is considered that the pile side soil dynamic resistance of the i pile section acts on the center position of the pile section in a centralized manner, and the force wave P (i) at the i measuring point measured by the strain sensor and the velocity wave v (i) measured by the acceleration sensor decompose the up-down traveling force waves at the two points, as shown in the following formula:
in the formula, Pd(i) And Pu(i) The lower force wave and the upper force wave of the point i are measured respectively, and Z is the section impedance of the pile body.
5. The method for testing the static bearing capacity of the tubular pile based on the traveling wave tracing principle according to claim 3, wherein the traveling wave tracing resolution is improved by increasing the arrangement density of the sensors along the axial direction; and the traveling wave tracing of a specific point position is realized by changing the arrangement position of the sensor.
6. The traveling wave tracing principle-based tubular pile static bearing capacity testing method according to claim 3, wherein in the step 5), the pile side soil dynamic resistance is determined specifically as follows:
taking i pile section as an example, assuming that the pile side soil dynamic resistance borne by the i pile section is R (i), R (i) is concentrated on the central position of the pile section, and according to the assumption of pile foundation dynamics, considering that the influence of the damping effect of the pile body material on the propagation characteristic of force waves in the pile body is ignored, thus obtaining the following relational expression:
in the formula (I), the compound is shown in the specification,
and
respectively an upper side ascending force wave, an upper side descending force wave, a lower side ascending force wave and a lower side descending force wave of the central section of the i pile section;
and then, further deducing according to the conditions of stress balance and displacement continuity of the central section of the i pile section:
determining a pile side soil dynamic resistance time course curve of the i pile section according to the up-down force waves of the i and i +1 measuring points;
the pile end soil dynamic resistance is determined as follows: the dynamic resistance time-course curve of the pile end soil adopts the upward force wave P at the pile endu(n + 1) and a downstream force wave Pd(n + 1) solving, and obtaining pile end soil according to the pile end section stress balance equationDynamic resistance Rtoe：
Rtoe＝Pu(n+1)+Pd(n+1) (6)。
7. The method for testing the static bearing capacity of the tubular pile based on the traveling wave tracing principle according to claim 3, wherein in the step 6), the determination of the maximum static bearing capacity is specifically as follows:
considering the pile side soil dynamic resistance value corresponding to the first zero-resetting time after the velocity of each pile section reaches the peak value as the maximum pile side soil static resistance value, assuming that the pile side soil dynamic resistance value of each pile section acts on the middle position of the pile section, correspondingly, the velocity of the center point of the pile section is also used for representing the velocity of the pile section, taking i pile section as an example, and the velocity time-course curve (v) of the center point of the pile section as an examplei) The velocities of the two end points of the pile section measured by the serial accelerometer are obtained by the following formula:
then curve in the course of speed
First zero time after the velocity peak is determined
Finding the time course curve corresponding to the pile side soil dynamic resistance of the i pile section obtained in the step 5)
The dynamic resistance value at the moment is the maximum pile side soil static resistance value R of the pile sections(i) (ii) a Repeating the steps, respectively determining the maximum pile side soil static resistance values of all the pile sections, and performing accumulation summation to obtain the maximum pile side soil static resistance value R of the whole piles：
Determining the maximum static resistance value of the pile-end soil by the same method, determining the time t (n + 1) of first zeroing after the peak value on the velocity time-course curve v (n + 1) of the pile-end position point, and then determining the dynamic resistance value corresponding to the time t (n + 1) on the pile-end soil dynamic resistance time-course curve, namely determining the maximum pile-end soil static resistance value
And determining the maximum static bearing capacity R of the whole pile as the sum of the maximum pile side soil static resistance value and the maximum pile end soil static resistance value:
the size of the pile top hammering force directly influences the exertion of the bearing capacity of the pile side soil and the pile end soil, and when the hammering action is large enough to completely excite the bearing capacity of the pile side soil and the pile end soil, the maximum static bearing capacity obtained by the method is the actual pile foundation ultimate bearing capacity Rmax。
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