A method for evaluating low-strain waveform data of pile foundations

Abstract

The present invention discloses a method for evaluating the low-strain waveform data of a pile foundation, which includes: calculating the theoretical waveform result of the pile top dynamics by using the vibration control equation of the Rayleigh-bar model; obtaining the measured waveform result of the pile top dynamics; respectively extracting the characteristic values of the measured waveform result and the theoretical waveform result; identifying the characteristics of the pile foundation defects based on the characteristic values of the measured waveform result and the theoretical waveform result; analyzing the defects of the theoretical waveform result, and correcting the measured waveform result according to the defects of the theoretical waveform result. The present invention does not require professional knowledge. By inputting basic parameters and waveform curves, the integrity evaluation index of the pile body can be obtained, and the influences of factors such as pile diameter and soil around the pile can be considered.

Description

Technical Field

[0001] The present invention belongs to the technical field of pile foundation evaluation, and particularly relates to a method for evaluating low-strain waveform data of pile foundations, which is particularly applicable to pile foundation evaluation under complex geological conditions. Background Art

[0002] In infrastructure construction, various types of pile foundations (such as cast-in-place piles, pipe piles, etc.) are widely used. Detecting and evaluating the quality of formed piles by certain test methods is of great significance for ensuring the safety of buildings and structures. At present, the commonly used detection method is a non-destructive detection method mainly based on small-strain detection, which has the advantages of high detection efficiency and low cost. However, in actual operation, there is a possibility that the detection results are artificially interfered by the detection unit and the pile foundation construction unit, resulting in the construction unit and the supervision unit being unable to accurately grasp the true quality of the formed piles, and there are potential safety hazards. Once the situation of misreporting unqualified piles as qualified piles occurs, it will seriously affect the bearing capacity of the pile foundation and endanger the safety of the superstructure, and the consequences are very serious. Even if problems are found before the construction of the superstructure, the best opportunity for pile foundation repair will be missed, and the pile foundation needs to be reworked, which not only seriously affects the construction period but also greatly increases the construction cost. In view of this, it is an urgent problem to be solved at present to enable non-professionals (such as construction units and supervision units) to accurately and timely grasp the true situation of the quality of formed piles through appropriate measures. The most direct and effective method is for non-professionals to be specifically responsible for and carry out small-strain detection of pile foundations and analyze the small-strain waveform results. For this method, carrying out small-strain detection only requires training of personnel to complete, but the small-strain waveform results often need to be compared and analyzed in combination with professional knowledge such as soil characteristics and pile types and long-term experience, and it is difficult for non-professionals to be competent even through training. For non-professionals, how to process the small-strain waveform results of pile foundations under complex geological conditions is a technical difficulty in this field.

[0003] The invention with the publication number CN114482154A mentions a method for testing the static bearing capacity of pipe piles based on the traveling wave tracing principle, including the steps of: arranging sensors along the axial direction of the pile body on the inner wall of the pipe pile, and the arrangement of various types of sensors on the pile body is in a one-to-one correspondence along the ring; applying a hammer blow to the top of the pipe pile, synchronously collecting and recording the force wave signals and velocity wave signals propagating along the axial direction of the pile body at each measuring point; decomposing the force wave propagating along the axial direction of the pile body into an upward traveling wave and a downward traveling wave through the traveling wave decomposition method to realize the traveling wave tracing of the pile body; calculating the dynamic resistance time history curves of each pile section and the dynamic resistance time history curve of the pile tip soil, and determining the dynamic resistance of the pile side soil and the dynamic resistance of the pile tip soil; determining the maximum static bearing capacity of the pipe pile and the ultimate bearing capacity of the pile. This invention directly evaluates the static bearing capacity through the actually measured dynamic signals of the pile body. The calculation process does not involve specific pile surrounding soil parameters and human factors, effectively avoiding the influence of the complexity of the pile surrounding soil properties and the subjectivity of the testing personnel on the bearing capacity evaluation results. However, this invention does not involve the analysis and identification of pile foundation defects. Summary of the Invention

[0004] Technical problems to be solved: In order to overcome the deficiencies of the above-mentioned prior art, the present invention proposes a method for evaluating low-strain waveform data of pile foundations. Without the need for professional knowledge, by inputting basic parameters and waveform curves, the integrity evaluation index of the pile body can be obtained, and factors such as pile diameter and pile surrounding soil can be considered.

[0005] Technical solutions:

[0006] A method for evaluating low-strain waveform data of pile foundations, the evaluation method includes the following steps:

[0007] S1, using the vibration control equation of the Rayleigh-bar model, calculate the theoretical dynamic waveform result of the pile top;

[0008] S2, obtain the measured dynamic waveform result of the pile top; respectively extract the characteristic values of the measured waveform result and the theoretical waveform result;

[0009] S3, identify the characteristics of pile foundation defects based on the characteristic values of the measured waveform result and the theoretical waveform result;

[0010] S4, analyze the defects of the theoretical waveform result, and correct the measured waveform result according to the defects of the theoretical waveform result.

[0011] Further, in step S1, the vibration control equation of the Rayleigh-bar model is:

[0012]

[0013] In the formula: u pi = u pi(z, t) is the vertical displacement of the i-th pile segment. The value range of i is determined by the total number of divided pile segments n. For example, if it is divided into 10 segments, the value range of i is from 1 to 10. The total number of pile segments n is determined by the number of soil layers within the pile length depth; z and t represent depth and time respectively; E pi , A pi , ρ pi , μ pi and r pi represent the elastic modulus, cross-sectional area, density, Poisson's ratio and radius of the pile respectively; f i = f i (r pi , z, t) represents the pile-soil interface friction; Solving the control equation gives the dimensionless velocity admittance H v (ω) as:

[0014]

[0015] In the formula:

[0016]

[0017]

[0018] where θ i = ωt i , and are all dimensionless quantities; j is a complex number, t i is the time required for the elastic wave to propagate in the i-th pile segment, ω is the angular frequency; h ik and q ik satisfy the following relationship between the two parameters: v i and ρ i are the shear wave velocity and density of the soil around the i-th pile respectively; v pi , ρ pi , r pi , μ pi and l i are the longitudinal wave velocity, density, radius, Poisson's ratio and length of the i-th pile segment respectively; is the dimensionless bearing stiffness between soil layers; D si and D vi are the hysteretic damping ratios related to shear strain and volume respectively; η i is the ratio of the longitudinal wave velocity to the shear wave velocity of the soil mass; M i and N i are both coefficients determined by the boundary conditions, and the ratio of the two can be expressed as:

[0019]

[0020] Among them: Epi and A pi are respectively the elastic modulus and cross-sectional area of the i-th pile segment; Z p(i-1) is the displacement impedance at the bottom of the i-th pile segment.

[0021] Furthermore, in step S2, the characteristic value of the measured waveform result is the extreme point on the measured waveform curve in the same direction as the incident wave; the characteristic value of the theoretical waveform result is the extreme point on the theoretical waveform curve in the same direction as the incident wave.

[0022] Furthermore, in step S3, the process of identifying the characteristics of pile foundation defects based on the characteristic values of the measured waveform result and the theoretical waveform result includes the following steps:

[0023] S31, taking time as the reference, obtain the corresponding relationship between the extreme points on the measured waveform curve in the same direction as the incident wave and the extreme points on the theoretical waveform curve in the same direction as the incident wave;

[0024] S32, analyze the extreme points. If there are no reverse extreme points before and after this characteristic value, it is determined that the pile foundation defect is a reduction in cross-section; if there is a reverse extreme point in front of this characteristic value and no reverse extreme point behind it, it is determined that the pile body has an enlarged diameter; if there is no reverse extreme point in front of this characteristic value and there is a reverse extreme point behind it, it indicates that the pile body has necking or broken pile.

[0025] Furthermore, in step S4, the process of correcting the measured waveform result according to the defect of the theoretical waveform result includes the following steps:

[0026] Remove the defect at the same position on the measured waveform curve according to the defect reflected by the theoretical waveform.

[0027] Beneficial effects:

[0028] Compared with the prior art, a method for evaluating low-strain waveform data of pile foundation of the present invention does not require professional knowledge. By inputting basic parameters and waveform curves, the integrity evaluation index of the pile body can be obtained, and the influence of factors such as pile diameter and soil around the pile can be considered. Description of the Drawings

[0029] Figure 1 is the flow chart of the method for evaluating low-strain waveform data of pile foundation in an embodiment of the present invention;

[0030] Figure 2 is the result display diagram of the method for evaluating low-strain waveform data of pile foundation in an embodiment of the present invention; among them, (a) is the original measured waveform diagram, (b) is the processed measured waveform diagram, and (c) is the processed analysis diagram. Detailed Embodiments

[0031] The following embodiments can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0032] See Figure 1 , an embodiment of the present invention proposes a method for evaluating the low-strain waveform data of a pile foundation, and the evaluation method includes the following steps:

[0033] S1. Using the vibration control equation of the Rayleigh-bar model, calculate the theoretical waveform result of the pile top dynamics.

[0034] S2. Obtain the measured waveform result of the pile top dynamics; respectively extract the characteristic values of the measured waveform result and the theoretical waveform result.

[0035] S3. Identify the pile foundation defect characteristics based on the characteristic values of the measured waveform result and the theoretical waveform result.

[0036] S4. Analyze the defects of the theoretical waveform result, and correct the measured waveform result according to the defects of the theoretical waveform result.

[0037] I. Prepare basic data

[0038] The basic data includes pile body parameters such as design length, design strength grade, shear wave velocity, bottom restraint condition, pile diameter and pile body density, and pile surrounding soil parameters such as the depth, density and shear wave velocity of each soil layer, etc.

[0039] II. Analytically calculate the theoretical waveform result of the pile top dynamics using the vibration control equation of the Rayleigh-bar model

[0040] The vibration control equation of the Rayleigh-bar model in this embodiment is:

[0041]

[0042] In the formula: u Pi = u pi (z, t) is the vertical displacement of the i-th pile segment, and the value range of i is determined by the total number of pile segment divisions n. For example, if it is divided into 10 segments, the value range of i is from 1 to 10, and the total number of pile segments n is determined by the number of soil layers within the pile length depth; z and t respectively represent depth and time; E pi , A pi , ρ pi , μ pi and r pi respectively represent the elastic modulus, cross-sectional area, density, Poisson's ratio and radius of the pile; f i = f i (r pi , z, t) represents the pile-soil interface friction force; solving the control equation can obtain the dimensionless velocity admittance H v (ω) as:

[0043]

[0044] In the formula:

[0045]

[0046]

[0047] where θ i = ωt i 、 and are all dimensionless quantities; j is a complex number, t i is the time required for the elastic wave to propagate in the i-th section of the pile, ω is the angular frequency; h ik and q ik satisfy the following relationship between the two parameters v i and ρ i are respectively the shear wave velocity and density of the soil around the i-th layer of the pile; v pi 、ρ pi 、r pi 、μ pi and l i are respectively the longitudinal wave velocity, density, radius, Poisson's ratio and length of the i-th section of the pile; is the dimensionless bearing stiffness between soil layers; D si and D vi are respectively the hysteretic damping ratios related to shear strain and volume; η i is the ratio of the longitudinal wave velocity to the shear wave velocity of the soil mass; M i and N i are both coefficients determined by the boundary conditions, and the ratio of the two can be expressed as:

[0048]

[0049] where: E pi and A pi are respectively the elastic modulus and cross-sectional area of the i-th section of the pile; Z p(i-1) is the displacement impedance at the bottom of the i-th section of the pile.

[0050] III. Extract the characteristic values of the measured waveform results and the theoretical waveform results respectively

[0051] Obtain the measured dynamic waveform results at the pile top. Analyze the theoretical dynamic waveform curve at the pile top obtained by analysis and the measured dynamic waveform results at the pile top. Take the extreme points in the same direction as the incident wave on the measured waveform curve as the characteristic values of the measured waveform results; take the extreme points in the same direction as the incident wave on the theoretical waveform curve as the characteristic values of the theoretical waveform results.

[0052] IV. Identify the characteristics of pile foundation defects based on the characteristic values

[0053] Analyze the extreme points of the measured and theoretical waveform results that are in the same direction as the incident wave. If there are no reverse extreme values before and after this eigenvalue, the pile foundation defect is considered to be a cross-sectional reduction; if there is a reverse extreme value before this eigenvalue and no reverse extreme value after it, it indicates that the pile body has expanded in diameter; if there is no reverse extreme value before this eigenvalue and there is a reverse extreme value after it, it indicates that the pile body has necked down or broken.

[0054] V. Modify the measured waveform curve

[0055] Specifically, analyze the defect of the theoretical result to correct the measured result, and remove the defect at the same position of the measured waveform curve according to the defect reflected by the theoretical waveform. Figure 2 It is a result display diagram of the low-strain waveform data evaluation method for pile foundations in the embodiments of the present invention; among them, (a) is the original measured waveform diagram, (b) is the processed measured waveform diagram, and (c) is the processed analysis diagram.

[0056] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0057] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A method for evaluating low-strain waveform data of pile foundations, characterized in that, the evaluation method comprises the following steps: S1, using the vibration control equation of the Rayleigh - rod model, calculating to obtain the theoretical waveform result of the pile top dynamics; S2, obtaining the measured waveform result of the pile top dynamics; respectively extracting the eigenvalue of the measured waveform result and the eigenvalue of the theoretical waveform result; S3, identifying the characteristics of pile foundation defects based on the eigenvalue of the measured waveform result and the eigenvalue of the theoretical waveform result; S4, analyzing the defects of the theoretical waveform result, and correcting the measured waveform result according to the defects of the theoretical waveform result; In step S1, the vibration control equation of the Rayleigh - rod model is: where: u pi = u pi (z, t) is the vertical displacement of the i-th pile segment, i = 1, 2, …, n, and the total number of pile segments n is determined by the number of soil layers within the pile length depth; z and t represent depth and time respectively; E pi , A pi , ρ pi , μ pi and r pi represent the elastic modulus, cross-sectional area, density, Poisson's ratio and radius of the i-th pile segment respectively; f i = f i (r pi , z, t) represents the pile-soil interface friction force; solving the control equation gives the dimensionless velocity admittance H v (ω) as: In the formula: Among them, θ i = ωt i , and are all dimensionless quantities; j is a complex number, t i is the time required for the elastic wave to propagate in the i-th section of the pile, ω is the angular frequency; h ik and q ik satisfy the following between the two parameters: v i and ρ i are respectively the shear wave velocity and density of the soil around the i-th layer of the pile; v pi and l i are respectively the longitudinal wave velocity and length of the i-th section of the pile; is the dimensionless bearing stiffness between soil layers; D si and D vi are respectively the hysteretic damping ratios related to shear strain and volume; η i is the ratio of the longitudinal wave velocity of the soil to the shear wave velocity; M i and N i are both coefficients determined by the boundary conditions, and the ratio of the two is expressed as: where: E pi and A pi are the elastic modulus and cross-sectional area of the i-th pile segment respectively; Z p(i-1) is the displacement impedance at the bottom of the i-th pile segment.

2. The method for evaluating low-strain waveform data of pile foundations according to claim 1, characterized in that, in step S2, the eigenvalue of the measured waveform result is the extreme point on the measured waveform curve in the same direction as the incident wave; the eigenvalue of the theoretical waveform result is the extreme point on the theoretical waveform curve in the same direction as the incident wave.

3. The method for evaluating low-strain waveform data of pile foundations according to claim 2, characterized in that, in step S3, the process of identifying the characteristics of pile foundation defects based on the eigenvalue of the measured waveform result and the eigenvalue of the theoretical waveform result comprises the following steps: S31, taking time as the reference, obtaining the corresponding relationship between the extreme points on the measured waveform curve in the same direction as the incident wave and the extreme points on the theoretical waveform curve in the same direction as the incident wave; S32, analyzing the extreme points. If there are no reverse extreme points before and after this eigenvalue, it is determined that the pile foundation defect is a cross-sectional reduction; if there is a reverse extreme point in front of this eigenvalue and no reverse extreme point behind it, it is determined that the pile body has an enlarged diameter; if there is no reverse extreme point in front of this eigenvalue and there is a reverse extreme point behind it, it indicates that the pile body has a necking or a broken pile.

4. The method for evaluating low-strain waveform data of pile foundations according to claim 1, characterized in that, in step S4, the process of correcting the measured waveform result according to the defects of the theoretical waveform result comprises the following steps: Removing the defects at the same position on the measured waveform curve according to the defects reflected by the theoretical waveform.

Images