Elastic compression amount correction calculation method based on actually measured elastic modulus of pile body

Abstract

The elastic compression amount correction calculation method based on the actually-measured elastic modulus of the pile body comprises the steps that S1, a plurality of stressometers are installed at the calibrated section of the pile body, and the stress change and the temperature change of a foundation pile are monitored through the stressometers; s2, stressometer test data parameter analysis at the calibrated section is carried out, and elastic modulus change characteristics of the calibrated section of the pile body are summarized; s3, inverting parameters of the model of the elastic modulus of the calibrated section of the pile body changing along with the micro-strain by using the change characteristics of the existing monitoring data; s4, according to the actually measured compressive strength values of the concrete core samples at different depths of the pile body, a curve of the elastic modulus of the pile body concrete changing along with the depth is calculated; and S5, calculating a curve of the elastic modulus of the pile body concrete along with the comprehensive change of the micro-strain and the depth, and correcting the elastic compression amount of the pile body. According to the method, the elastic modulus of the pile body is actually measured and calibrated through the indoor concrete test block, the variable elastic modulus is substituted into the elastic modulus of the pile body for calculation, the corrected elastic compression amount of the pile body is obtained, and the actual calculation precision is improved.

Description

Technical Field

[0001] This invention belongs to the field of building monitoring technology, and in particular relates to a method for correcting the elastic compression based on the measured elastic modulus of the pile. Background Technology

[0002] Pile foundation settlement is a significant factor affecting building safety, including the effects of superstructure loads and construction activities such as subway construction and foundation excavation near the building. With the increasing prevalence of ultra-long piles, the proportion of elastic compression in pile settlement calculations is also growing. Standards such as the Technical Specification for Building Pile Foundations (JGJ 94-2008), the Technical Specification for Testing Building Foundation Pile (JGJ 106-2014), and the Specification for Testing Building Foundations (DBJ / T 15-60-2019) all require consideration of elastic compression when pile lengths exceed 25m or 40m. However, due to the unavailability of accurate elastic modulus of the pile concrete and internal force distribution, the elastic compression of the pile is mostly calculated using empirical values. When faced with significant settlement data, this can directly impact the interpretation of static load test results for the pile.

[0003] Currently, the conventional formula for calculating the elastic compression of piles uses the concrete elastic modulus as a fixed value, based on the designed concrete grade. However, due to the non-uniformity and complexity of the concrete material in cast-in-place piles, as well as the influence of factors such as construction quality, measuring instruments, and environmental conditions during testing, the concrete elastic modulus, a crucial parameter for calculating the elastic compression of piles, is not a constant. Moreover, data from core drilling measurements of the compressive strength of pile concrete show that the concrete elastic modulus gradually increases with depth. Summary of the Invention

[0004] The purpose of this invention is to provide a simple and easy-to-implement method for calculating elastic compression based on the measured elastic modulus of the pile body, which can improve calculation accuracy and thus improve detection precision.

[0005] The objective of this invention is achieved through the following technical measures: a method for correcting and calculating elastic compression based on the measured elastic modulus of a pile, characterized by comprising the following steps:

[0006] S1. Install multiple stress gauges at the pile body calibration section, collect the internal force test data of the pile body calibration section and the compressive strength values ​​of concrete core samples at different depths of the pile body, and calculate the micro-strain of the stress gauges under different levels of load based on the test data.

[0007] S2. Based on the micro-strain obtained in step S1, calculate the curve of the elastic modulus at the pile calibration section as a function of micro-strain.

[0008] S3. Fit the measured compressive strength values ​​of concrete core samples at different depths of the pile body to invert the parameters in the curve of elastic modulus versus microstrain at the calibration section of the pile body.

[0009] S4. Based on the measured compressive strength values ​​of concrete core samples at different depths in the pile body, calculate the curve of the elastic modulus of the pile body concrete as a function of depth.

[0010] S5. Calculate the curve of the elastic modulus of the pile concrete as a function of micro-strain and depth, and correct the elastic compression of the pile.

[0011] This invention employs a method of on-site measurement of the elastic modulus of the pile body and calibration using indoor concrete test blocks. Based on this, the variable elastic modulus formula is substituted into the calculation formula for the elastic modulus of the pile body to obtain the corrected elastic compression of the pile body based on the measured elastic modulus of the pile body. This solves the problem of directly using the value of the elastic modulus of the pile body concrete in the calculation formula for the elastic compression of the pile body without considering the calibration using test data, and significantly improves the actual calculation accuracy and the degree of theoretical interpretability.

[0012] The test data described in this invention includes stress gauge frequency data, temperature data, and static load test data.

[0013] In step S3 of this invention, the elastic modulus E at the calibration section of the pile body is fitted. b The linear or exponential relationship with the micro-strain ε is used to invert the constant values ​​within it;

[0014] Elastic modulus E at the marked section of the pile body b When the relationship with micro-strain ε is linear:

[0015] E b =E0+mε formula ⑴;

[0016] Elastic modulus E at the marked section of the pile body b When the relationship with micro-strain ε is exponential:

[0017] E b =A0+ B0exp(-C0ε) formula (2);

[0018] Where ε is the stress and corresponding microstrain of the pile reinforcement calculated based on the stress gauge calibration coefficient after temperature calibration; E0 and m are the intercept and slope when fitting the linear relationship; A0, B0, and C0 are constant values ​​when fitting the exponential relationship.

[0019] In step S4 of this invention, the relationship between the compressive strength value fcu,h of the concrete core sample and the depth z is as follows:

[0020] f cu,z =f cu,0 +n∙z formula⑶;

[0021] Among them, f cu,0 The standard value of the compressive strength of concrete core samples near the calibration section of the pile body;

[0022] Based on the compressive strength values ​​fcu,z of concrete core samples at different depths z, and using the calibrated cross-section of the pile body as a basis, the elastic modulus of other sections of the pile body is fitted. The relationship between the elastic modulus Ez of the pile body concrete and the depth z is as follows:

[0023] Ez = Eb + n∙z Formula (4);

[0024] Where n is the magnitude of the compressive strength value fcu,h of the concrete core sample as a function of depth z, and the untested depth can be obtained by interpolation.

[0025] In step S5 of this invention, the relationship between the elastic modulus E(ε(z)) of the pile concrete and the micro-strain ε and depth z is as follows:

[0026] When the elastic modulus Eb at the pile's calibration section has a linear relationship with the micro-strain ε:

[0027] E(ε(z))=E0+mε(z)+n∙z Formula ⑸;

[0028] Elastic modulus E at the marked section of the pile body b When the relationship with micro-strain ε is exponential:

[0029] E(ε(z))=A0+ B0exp(-C0ε)+n∙z Formula ⑹;

[0030] Wherein, E(ε(z)) is the elastic modulus of the pile concrete, which simultaneously considers the micro-strain of the pile body and the depth correction;

[0031] Substitute formulas (5) and (6) into the formula for calculating the elastic compression of the pile body to calculate the corrected elastic compression of the pile body.

[0032] In step S5② of the present invention, when the elastic modulus E at the calibrated section of the pile body... b When the relationship with micro-strain ε is linear:

[0033] q s (z)=q s,t +(q s,b - q s,t ) / L×z formula⑺;

[0034] Q(z) = Q0 - Cq s,t zC / 2L×(q s,b -q s,t )×z 2 Formula ⑻;

[0035] Formula ⑼;

[0036] Formula ⑽;

[0037] Among them, S e,修 q represents the corrected elastic compression of the pile body. s,b q s,t q represents the side friction at the pile top and pile end when the Geddes trapezoidal side resistance distribution is represented; s Q(z) and Q(z) are the side friction and axial force at a certain cross section z of the pile, respectively; A, C, and L are the cross-sectional area, perimeter, and length of the pile, respectively.

[0038] In step S5② of the present invention, when the elastic modulus E at the calibrated section of the pile body... b When the relationship with micro-strain ε is exponential:

[0039] qs(z)=qs,t+(qs,b- qs,t) / L×z formula ⑺;

[0040] Q(z) = Q0 - Cq s,t zC / 2L×(q s,b -q s,t )×z 2 Formula ⑻;

[0041] Formula ⑾;

[0042] Formula ⑿.

[0043] Compared with the prior art, the present invention has the following significant effects:

[0044] This invention employs a method of on-site measurement of the elastic modulus of the pile body and calibration using indoor concrete test blocks. Based on this, the variable elastic modulus formula is substituted into the calculation formula for the elastic modulus of the pile body to obtain the corrected elastic compression of the pile body based on the measured elastic modulus of the pile body. This solves the problem of directly using the value of the elastic modulus of the pile body concrete in the calculation formula for the elastic compression of the pile body without considering the calibration using test data, and significantly improves the actual calculation accuracy and the degree of theoretical interpretability. Attached Figure Description

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0046] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0047] like Figure 1 As shown, the present invention provides a method for correcting the elastic compression amount based on the measured elastic modulus of the pile, comprising the following steps:

[0048] S1. Install multiple stress gauges at the pile calibration section, for example, arrange four stress gauges symmetrically at a depth of 1m below the pile top on the pile calibration section. Monitor the stress and temperature changes of the pile using the stress gauges, collect internal force test data of the pile calibration section, including stress gauge frequency data, temperature data, and static load test data; and analyze the data of the four stress gauges at the pile calibration section based on the test data, mainly referring to the stress of the pile reinforcement and the corresponding micro-strain calculated according to the stress gauge calibration coefficient after temperature calibration, that is, calculate the micro-strain of the stress gauges under different levels of load;

[0049] The compressive strength values ​​of concrete core samples at different depths obtained by core drilling of the pile body are the actual measured compressive strength values ​​of concrete core samples at different depths of the pile body.

[0050] S2. Based on the micro-strain obtained in step S1, calculate the curve of the elastic modulus at the pile calibration section as a function of micro-strain.

[0051] Analyze the parameters of the stress gauge test data at the calibration section (data under different load levels), summarize the characteristics of the elastic modulus variation at the calibration section of the pile body, that is, analyze the test data at the calibration section in step S1, and calculate the elastic modulus E at the calibration section (1 to 2 times the pile diameter from the pile top). b Plot the curve of the elastic modulus of the pile body calibration section as a function of micro-strain.

[0052] S3. Fit the measured compressive strength values ​​of concrete core samples at different depths of the pile body to invert the parameters in the curve of elastic modulus versus microstrain at the calibration section of the pile body.

[0053] This step utilizes existing monitoring data to invert the parameters of the model showing the change in elastic modulus of the pile calibration section with microstrain. Specifically, it includes fitting the elastic modulus E at the pile calibration section using measured data and the data analysis results from step S2. b The linear or exponential relationship with the micro-strain ε is used to invert the constant values ​​within it;

[0054] Elastic modulus E at the marked section of the pile body b The formula that has a linear relationship with the micro-strain ε is:

[0055] E b =E0+mε formula ⑴;

[0056] Elastic modulus E at the marked section of the pile body b The formula that has an exponential relationship with the micro-strain ε is:

[0057] E b =A0+ B0exp(-C0ε) formula (2);

[0058] Where ε is the stress and corresponding microstrain of the pile reinforcement calculated according to the stress gauge calibration coefficient after temperature calibration; E0 and m are the intercept and slope when fitting the linear relationship, that is, E0 is the initial value and m is the slope of change; A0, B0, and C0 are constant values ​​when fitting the exponential relationship. When m or C0 is zero, it means that the elastic modulus at the calibration section of the pile body does not change.

[0059] S4. Based on the measured compressive strength values ​​of concrete core samples at different depths in the pile body, calculate the curve of the elastic modulus of the pile body concrete as a function of depth.

[0060] This step specifically includes: analyzing the indoor test value f of the compressive strength of concrete core samples. cu,z The variation of the concrete core sample compressive strength f with the pile depth z was used to obtain the indoor test value of the compressive strength f. cu,z The relationship between the pile depth z and the pile body depth z is as follows:

[0061] f cu,z =f cu,0 +n∙z formula⑶;

[0062] Among them, f cu,0 n represents the standard value of the compressive strength of the concrete core sample near the calibration section of the pile body, where n is the variation range.

[0063] Based on the compressive strength values ​​fcu,z of concrete core samples at different depths z obtained by the core drilling method for pile body concrete, and using the calibrated cross-section of the pile body as a basis, the elastic modulus of other sections of the pile body is fitted. The relationship between the elastic modulus Ez of the pile body concrete and the depth z is as follows:

[0064] Ez = Eb + n∙z Formula (4);

[0065] Where n is the magnitude of the compressive strength value fcu,h of the concrete core sample as a function of depth z, and the untested depth can be obtained by interpolation.

[0066] S5. Calculate the curve of the elastic modulus of the pile concrete as a function of micro-strain and depth, and correct the elastic compression of the pile.

[0067] Steps S4 and S5 determine the model of the change of the concrete modulus of the pile body with depth based on the elastic modulus relationship at the pile body calibration section established in step S3 and the indoor compressive strength test data of the pile body concrete core sample. By comprehensively applying the pile body cross-sectional strain and depth data, the conventional fixed elastic modulus value is corrected and the elastic compression of the pile body is calculated.

[0068] This step S5 specifically includes: the relationship between the elastic modulus E(ε(z)) of the pile concrete and the micro-strain ε and depth z is as follows:

[0069] When the elastic modulus Eb at the pile's calibration section has a linear relationship with the micro-strain ε:

[0070] E(ε(z))=E0+mε(z)+n∙z Formula ⑸;

[0071] Elastic modulus E at the marked section of the pile body b When the relationship with micro-strain ε is exponential:

[0072] E(ε(z))=A0+ B0exp(-C0ε)+n∙z Formula ⑹;

[0073] Wherein, E(ε(z)) is the elastic modulus of the pile concrete, which simultaneously considers the micro-strain of the pile body and the depth correction;

[0074] Substitute formulas (5) and (6) into the formula for calculating the elastic compression of the pile body, respectively, to calculate the elastic modulus of the pile body after the strain and depth correction of the pile body section, that is, to calculate the corrected elastic compression of the pile body.

[0075] Here, we take a pile with a load of Q0 at the top and a pile perimeter and length of C and L as an example. Specifically, it can be divided into three steps: 1) Determine the pile side resistance distribution pattern roughly according to the Technical Specification for Building Pile Foundations (JGJ 94-2008), taking the common Geddes trapezoidal side resistance distribution as an example (q...). s,b q s,t (E(ε(z)) represents the side skin friction at the pile top and pile end, respectively). Calculate the elastic modulus E(ε(z)) and side skin friction q at a certain cross-section z of the pile. s (z) Axial force Q(z), calculated using formulas (5) to (8). 2) Calculate the strain ε(z) at a certain section z of the pile body when the load at the pile top is Q0, using formula (9); 3) Calculate the elastic compression S of the pile body. e,修 After considering the correction for the elastic modulus of the pile, the calculation formula is formula (10). An iterative algorithm is used to solve it.

[0076] The elastic modulus E of the concrete in the pile body section is used as the standard. b For example, the linear relationship with micro-strain ε:

[0077] q s (z)=q s,t +(q s,b - q s,t ) / L×z formula⑺;

[0078] Q(z) = Q0 - Cq s,t zC / 2L×(q s,b -q s,t )×z 2 Formula ⑻;

[0079] Formula⑼

[0080] Formula ⑽.

[0081] Among them, S e,修 q represents the corrected elastic compression of the pile body. s,b q s,t q represents the side friction at the pile top and pile end when the Geddes trapezoidal side resistance distribution is represented; s Q(z) and Q(z) are the side friction and axial force at a certain cross section z of the pile, respectively; A, C, and L are the cross-sectional area, perimeter, and length of the pile, respectively.

[0082] When the elastic modulus E at the marked section of the pile body b When the relationship with micro-strain ε is exponential:

[0083] q s (z)=q s,t +(q s,b - q s,t ) / L×z formula⑺;

[0084] Q(z) = Q0 - Cq s,t zC / 2L×(q s,b -q s,t )×z 2 Formula ⑻;

[0085] Formula ⑾;

[0086] Formula ⑿.

[0087] The conventional formula for calculating the elastic compression of a pile is as follows: ξ is the elastic compressibility coefficient, which is related to the distribution of pile side friction. If it follows the conventional Geddes trapezoidal side friction distribution, the calculation formula is:

[0088] ;

[0089] The value of the elastic modulus of the pile concrete is E. pThe value is a fixed value, such as 30.0 GPa corresponding to the design grade C30 of the pile concrete, which has no direct correlation with field and indoor measured data. For precast piles with good curing conditions, the error is relatively small, but for cast-in-place piles with cast-in-place concrete, there is a significant difference. In contrast, the elastic modulus of the pile section in this invention is a function of strain and depth, taking into account the heterogeneity of concrete materials and the differences in field construction quality. Therefore, this invention fully utilizes existing measured data, inverting and correcting the elastic modulus of the pile through measured data, and finally using it in the calculation of the elastic compression of this foundation pile. The value is more reasonable, and the calculation results are more reliable. Furthermore, the measured methods used are conventional testing elements and methods, and the data is easy to obtain.

[0090] Example:

[0091] Internal force testing was conducted on a certain foundation pile. The pile diameter was 1m, the pile length L=50.0m, and the concrete cross-sectional area A=0.785m². 2 The perimeter is C = 3.141m. The relationship between the microstrain measured by four steel bar stress gauges at the calibration section, the inversion parameters, and the calculated elastic compression of the pile body and the load at the pile top is shown in the table below:

[0092]

[0093] (Table 1)

[0094] The elastic modulus of concrete has a significant impact on the calculation results of pile elastic compression. Directly using the elastic modulus corresponding to the design concrete grade makes it difficult to account for the calibration and inversion effects of existing test data, and fails to reflect the differences in on-site construction quality and the non-homogeneity of concrete piles. Therefore, this invention is based on a classic theoretical model for calculating pile elastic compression, using measured data for parameter inversion and correction of the calculated pile elastic compression. During the correction, measured data is used for fitting, which to some extent verifies the variation of the pile concrete elastic modulus with strain.

Claims

1. A method for correcting the elastic compression amount based on the measured elastic modulus of the pile body, characterized by The method comprises the following steps: S1, installing a plurality of stress meters at the pile body calibration section, collecting the internal force test data of the pile body calibration section and the concrete core sample compressive strength values measured at different depths of the pile body, and calculating the micro-strain of the stress meter under different levels of load according to the test data; S2, calculating the curve of the elastic modulus of the pile body calibration section varying with the micro-strain according to the micro-strain obtained in step S1; S3, fitting the concrete core sample compressive strength values measured at different depths of the pile body to inverse the parameters in the curve of the elastic modulus of the pile body calibration section varying with the micro-strain; S4, calculating the curve of the elastic modulus of the pile body concrete varying with the depth according to the concrete core sample compressive strength values measured at different depths of the pile body; S5, calculating the curve of the elastic modulus of the pile body concrete varying with the micro-strain and the depth, and correcting the elastic compression amount of the pile body.

2. The method for correcting the elastic compression amount based on the measured elastic modulus of the pile body according to claim 1, characterized in that: The test data includes stress meter frequency data, temperature data and static load test data.

3. The method for pile shaft modulus-based elastic compression correction calculation according to claim 2, characterized in that: In the step S3, the elastic modulus E at the calibration section of the pile body is fitted b a linear or exponential relationship with the micro-strain ε, and the constant value therein is inverted. Elastic modulus E at the calibrated section of the pile body b When the micro-strain ε is linearly related to the strain ε: E b =E0+mε Equation (1); Elastic modulus E at the calibrated section of the pile body b When the relationship with the micro-strain ε is exponential: E b =A0+ B0exp(-C0ε) Equation 2; Wherein, ε is the micro-strain corresponding to the stress of the pile body steel after temperature calibration and calculated according to the stress meter calibration coefficient; E0 and m are the intercept and slope when fitting the linear relationship; A0, B0, C0 are constant values when fitting the exponential.

4. The method for correcting the elastic compression amount based on the measured elastic modulus of the pile body according to claim 3, characterized in that: In the step S4, the relationship between the concrete core sample compressive strength value fcu,h and the depth z is: f cu,z =f cu,0 +n∙z Equation 6; wherein f cu,0 is the standard value of the core sample compressive strength of the concrete near the calibrated section of the pile body; According to the concrete core sample compressive strength value fcu,z at different depths z, the elastic modulus of the pile body other sections is fitted based on the pile body calibration section, and the relationship between the elastic modulus Ez of the pile body concrete and the depth z is: Ez=Eb+n∙z Formula 4; Wherein, n is the amplitude of the concrete core sample compressive strength value fcu,h varying with the depth z, and the untested depth can be obtained by interpolation.

5. The method for calculating the elastic compression amount correction based on the measured elastic modulus of the pile body according to claim 4, characterized in that: The step S5 comprises: ①The relationship between the elastic modulus E(ε(z)) of the pile body concrete and the micro-strain ε, the depth z is: When the elastic modulus Eb at the pile body calibration section and the micro-strain ε are in a linear relationship: E(ε(z))=E0+mε(z)+n∙z Formula 5; Elastic modulus E at the calibrated section of the pile body b When the relationship with the micro-strain ε is exponential: E(ε(z))=A0+ B0exp(-C0ε)+n∙z Formula 6; Wherein, E(ε(z)) is the elastic modulus of the pile body concrete considering the correction of the micro-strain and the depth of the pile body at the same time; ②Substitute formula 5 and formula 6 into the pile body elastic compression amount calculation formula respectively to calculate the corrected pile body elastic compression amount.

6. The method for calculating the elastic compression amount correction based on the measured elastic modulus of the pile body according to claim 5, characterized in that: In the step S5 2, when the elastic modulus E of the pile body at the calibration section b When the micro-strain ε is linearly related to the strain ε q s (z)=q s,t +(q s,b - q s,t ) / L×z formula⑺; Q(z) = Q0- Cq s,t z - C / 2L x (q s,b -q s,t ) x z 2 Equation (7); Formula (16); Official (10); where S e,修 is the corrected elastic compression of the pile; q s,b , q s,t represents the side friction at the top and the end of the pile when the Geddes normal trapezoidal side resistance distribution is used; q s (z), Q(z) are the side friction and the axial force at a certain cross section z of the pile; A, C, L are the cross-sectional area, the circumference and the length of the pile, respectively.

7. The method for pile shaft modulus-based elastic compression correction calculation according to claim 5, characterized in that: In the step S5 2, when the elastic modulus E of the pile body at the calibration section b When the relationship between the micro-strain ε and the micro-deformation δ is exponential: q s (z)=q s,t +(q s,b - q s,t ) / L×z formula⑺; Q(z) = Q0- Cq s,t z - C / 2L x (q s,b -q s,t ) x z 2 Equation (7); Official (11); Formula (XII).

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