CN103411729B - The scaling method of miniature soil pressure sensor in the free stress field of soil-structure interactions - Google Patents

Abstract

A method for calibrating a miniature earth pressure sensor in a soil medium free stress field, the steps of which mainly include: (1) hydraulic calibration test to obtain hydraulic calibration coefficient; (2) soil medium calibration test to load step by step; (3) obtain all levels soil medium modulus during loading; (4) Obtain the matching error β _i at each level of loading; (5) Establish the functional relationship between the matching error β and the soil medium modulus E _s : take the soil medium modulus E _s as the horizontal Coordinates, with the matching error β as the ordinate, the soil medium modulus at all levels of loading and matching error β _i plotted as Scatterplot with fraction function Fit the scatter diagram to obtain the fitting parameters K ₁ , K ₂ , K ₃ ; (6) Determine the soil medium calibration coefficient: the soil medium calibration coefficient is k′, This method reasonably eliminates the matching error caused by the interaction between the miniature earth pressure sensor placed in the free stress field and the soil medium, which can significantly improve the accuracy of earth pressure measurement, and provide a basis for geotechnical engineering design, construction, maintenance, etc. More reliable test basis.

Description

Calibration method of miniature earth pressure sensor in free stress field of soil medium

technical field

The invention relates to a calibration method of a miniature earth pressure sensor in a free stress field of an earth medium.

Background technique

In the field of geotechnical engineering, it is often necessary to simulate the relationship between the structural form of the engineering site, the loading mode and other working conditions of the engineering site and the stress distribution, stress and strain of the soil medium through geotechnical model tests, so as to provide support for the design, construction, maintenance, etc. of geotechnical engineering. Provide a reliable test basis. The determination of soil medium load, that is, the measurement of earth pressure, is a key issue in geotechnical model tests, which directly affects the accuracy and reliability of geotechnical model test results. The measurement of earth pressure in geotechnical model tests mostly depends on the pre-embedded miniature earth pressure sensors in the soil medium.

When the miniature earth pressure sensor is used in the geotechnical model test, due to the difference between the test system and the test system at the factory, a hydraulic calibration test is required before use, and the relationship curve between the input liquid load p _l and the output signal q _με is fitted to obtain The hydraulic calibration coefficient k=p _l /q _με of the miniature earth pressure sensor is obtained. The liquid load is used for calibration because the liquid medium has fluidity, and the applied liquid load can be transmitted to the bearing surface of the miniature earth pressure sensor without hindrance, that is, the load borne by the bearing surface of the miniature earth pressure sensor (hydraulic revision value p _t ′ ) is consistent with the real liquid load at this point, and there is no matching error problem.

However, due to the difference between the geometric dimensions and material properties of the micro earth pressure sensor and the soil medium, it will inevitably lead to the interaction (disturbance) between the micro earth pressure sensor and the soil medium, resulting in the hydraulic revision value p _t of the micro earth pressure sensor after hydraulic calibration ' is still inconsistent with the real earth pressure p' _o of the point when it is not disturbed, which leads to the problem of matching error.

To solve this problem, the commonly used method at present is to place the miniature earth pressure sensor in the soil medium that is as consistent as possible with the geotechnical model test environment for calibration tests, and perform linear function fitting on the input load p _o and the output signal q in the calibration test , and then in the geotechnical model test, the output signal q′ of the miniature earth pressure sensor is fitted and corrected with a linear function, and the earth pressure p′ _o in the soil medium is obtained. However, since the modulus of the soil medium changes continuously during the loading process, it is difficult to ensure the consistency of the soil medium modulus under the calibration test conditions and the geotechnical model test conditions, and the soil medium modulus has a great influence on the load distribution of the soil medium. Therefore, this method has a large error in the measurement results when the modulus of the soil medium changes greatly.

Contents of the invention

The purpose of the present invention is to provide a method for calibrating miniature earth pressure sensors in the free stress field of the soil medium, which reasonably eliminates the matching error problem caused by the interaction between the miniature earth pressure sensors placed in the free stress field and the soil medium, It can significantly improve the accuracy of earth pressure measurement and provide more reliable test basis for the design, construction and maintenance of geotechnical engineering.

The technical scheme adopted by the present invention to realize its object of the invention is: a kind of calibration method of miniature earth pressure sensor in the free stress field of soil medium, comprises the following steps:

(1) Hydraulic calibration test: Through the hydraulic calibration test, the hydraulic calibration coefficient k=p _l /q _με of the miniature earth pressure sensor is obtained by fitting the relationship curve of the input liquid load p _l and the output signal q _με ;

(2) Soil medium calibration test: measure the moisture content ω and compaction coefficient K of the on-site soil medium, and conduct a compaction test on the on-site soil medium to measure its maximum dry density ρ _dmax ; In the geotechnical centrifuge model box, the filling height is h, and the miniature earth pressure sensor is placed horizontally when the filling height of the soil medium is h/2; Take the centrifugal acceleration of 20g as a level, and load step by step until the centrifugal acceleration reaches 100g;

(3) Obtain the soil medium modulus: while the centrifuge is loading step by step, the displacement meter measures the soil medium settlement △h _i when the centrifugal acceleration g _i is loaded at each level, and calculates the soil medium strain at each level ε _i , ε _i =△h _i /h; the theoretical load of the soil medium on the miniature earth pressure sensor under the action of centrifugal acceleration g _i loaded at various levels , where ρ is the density of the soil medium, ρ=Kρ _dmax (1+ω); finally calculate the modulus of the soil medium under the action of centrifugal acceleration g _i at all levels ;The subscript i of each parameter symbol is the serial number of the centrifuge loaded step by step, i=1, 2, 3, 4, 5;

(4) Acquire the matching error: record the output signal q _i of the miniature earth pressure sensor when it is loaded at each level, and calculate the hydraulic correction value of the miniature earth pressure sensor when it is loaded at each level through the hydraulic calibration coefficient k obtained in step (1) , to determine the matching error β _i at each level of loading,

(5) Establish the functional relationship between the matching error β and the soil medium modulus E _s : take the soil medium modulus E _s as the abscissa, take the matching error β as the ordinate, and calculate the soil medium modulus at each level of loading and matching error β _i plotted as Scatterplot with fraction function Fit the scatter diagram to obtain fitting parameters K ₁ , K ₂ , K ₃ ;

(6) Determine the soil medium calibration coefficient: the soil medium calibration coefficient is k′, In the formula, p' _o is the corrected value of the earth pressure in the geotechnical model test, q' is the output signal of the miniature earth pressure sensor in the geotechnical model test, E _s ′ is the measured mode of the soil medium around the miniature earth pressure sensor in the geotechnical model test quantity.

Compared with prior art, the beneficial effect of the present invention is:

The applicant found that in the same geotechnical model test, the conditions such as the diameter D of the miniature earth pressure sensor, the thickness S, the equivalent deformation modulus E _g and the Poisson's ratio μ _s of the soil medium are determined; the soil in the geotechnical model test The pressure measurement matching error β only has a single-factor mapping relationship with the soil medium modulus E _s . And then the present invention adopts the unified form of classical matching error theory formula , for multiple sets of calibration tests Fit the data to determine the parameters K ₁ , K ₂ , and K ₃ of the mapping relationship between the matching error β and the soil medium modulus E _s , and then obtain the soil medium calibration coefficient k′. Compared with ignoring the influence of the soil medium modulus, the direct Using the calibration coefficient obtained by fitting the linear function, the invention effectively eliminates the matching error of the miniature earth pressure sensor in the soil medium, thereby significantly improving the accuracy of earth pressure measurement; it is useful for geotechnical engineering design, construction, Maintenance, etc. provide a more reliable test basis.

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is a comparison diagram of corrected earth pressure obtained by adopting the method of the present invention and the existing linear function fitting processing method.

Among Fig. 1: the connected straight line is the theoretical load; the point marked by " ■" is the corrected earth pressure value obtained by the method of the present invention; the point marked by "○" is the corrected earth pressure obtained by the existing linear function fitting processing method value.

Detailed ways

Example

A specific embodiment of the present invention is a method for calibrating a miniature earth pressure sensor in a soil medium free stress field, comprising the following steps:

(1) Hydraulic calibration test: Through the hydraulic calibration test, the hydraulic calibration coefficient k=p _l /q _με of the miniature earth pressure sensor is obtained by fitting the relationship curve of the input liquid load p _l and the output signal q _με ;

(2) Soil medium calibration test: measure the moisture content ω and compaction coefficient K of the on-site soil medium, and conduct a compaction test on the on-site soil medium to measure its maximum dry density ρ _dmax ; In the geotechnical centrifuge model box, the filling height is h, and the miniature earth pressure sensor is placed horizontally when the filling height of the soil medium is h/2; Take the centrifugal acceleration of 20g as a level, and load step by step until the centrifugal acceleration reaches 100g;

(3) Obtain the soil medium modulus: while the centrifuge is loading step by step, the displacement meter measures the soil medium settlement △h _i when the centrifugal acceleration g _i is loaded at each level, and calculates the soil medium strain at each level ε _i , ε _i =△h _i /h; the theoretical load of the soil medium on the miniature earth pressure sensor under the action of centrifugal acceleration g _i loaded at various levels , where ρ is the density of the soil medium, ρ=Kρ _dmax (1+ω); finally calculate the modulus of the soil medium under the action of centrifugal acceleration g _i at all levels ;The subscript i of each parameter symbol is the serial number of the centrifuge loaded step by step, i=1, 2, 3, 4, 5;

(4) Acquire the matching error: record the output signal q _i of the miniature earth pressure sensor when it is loaded at each level, and calculate the hydraulic correction value of the miniature earth pressure sensor when it is loaded at each level through the hydraulic calibration coefficient k obtained in step (1) , to determine the matching error β _i at each level of loading,

(5) Establish the functional relationship between the matching error β and the soil medium modulus E _s : take the soil medium modulus E _s as the abscissa, take the matching error β as the ordinate, and calculate the soil medium modulus at each level of loading and matching error β _i plotted as Scatterplot with fraction function Fit the scatter diagram to obtain fitting parameters K ₁ , K ₂ , K ₃ ;

(6) Determine the soil medium calibration coefficient: the soil medium calibration coefficient is k′, In the formula, p' _o is the corrected value of the earth pressure in the geotechnical model test, q' is the output signal of the miniature earth pressure sensor in the geotechnical model test, E _s ′ is the measured mode of the soil medium around the miniature earth pressure sensor in the geotechnical model test quantity.

Test verification

The soil medium calibration test in the centrifuge was carried out on the single-membrane resistance strain type miniature earth pressure sensor produced in my country. The range of the miniature earth pressure sensor is 0.2MPa, the diameter is 15mm, the thickness is 3.5mm, and the overload capacity is 20% FS. The box body material is alloy aluminum. The soil medium adopts graded medium sand, the particle density is 2.77g/cm ³ , the internal friction angle is 32.6°, and the cohesion is 11.4kPa. According to the sieving test, the coefficient of unevenness C _u =5.1, the coefficient of curvature C _c =1.2, d ₅₀ =0.4mm, the content of particles smaller than 2mm is 82.22%, and the content of particles smaller than 0.075mm is 3.79%. Obtained from the heavy-duty Z2 compaction test, its maximum dry density ρ _dmax is 1.86g/cm ³ . Use TLJ-2 type 100gt geotechnical centrifuge to carry out the following soil medium calibration test and geotechnical model test on the above-mentioned miniature earth pressure sensor:

Soil medium calibration test: the filling height of the sand in the gradation is h=260mm, the measured moisture content of the sand in the gradation is 6.6%, and the density ρ ₁ =1.78g/cm ³ . The relevant data and results obtained from the calibration test carried out on this soil medium according to the method of this example are as follows: the hydraulic calibration coefficient k=0.0982 of the miniature earth pressure sensor, the mapping relationship between the matching error β and the soil medium modulus E _s $\mathrm{\β}\left({\mathrm{E.}}_{\mathrm{the\; s}}\right)=\frac{K_1{\mathrm{E.}}_{\mathrm{the\; s}}+K_2}{{\mathrm{E.}}_{\mathrm{the\; s}}+K_3}=\frac{-0.97{\mathrm{E.}}_{\mathrm{the\; s}}+36.77}{{\mathrm{E.}}_{\mathrm{the\; s}}+1.48}$ , where the correlation coefficient is . And then get its calibration coefficient $k^{\′}=k/(1+\frac{-0.97{\mathrm{E.}}_{\mathrm{the\; s}}+36.77}{{\mathrm{E.}}_{\mathrm{the\; s}}+1.48})=0.0982/(1+\frac{-0.97{\mathrm{E.}}_{\mathrm{the\; s}}+36.77}{{\mathrm{E.}}_{\mathrm{the\; s}}+1.48}).$

Geotechnical model test: the filling height of the sand in the gradation is h=500mm, the measured moisture content of the sand in the gradation is 6%, and the density ρ ₃ =1.77g/cm ³ . Carry out the operation of method step (2) and (3) of the present invention, obtain the soil medium modulus E _s ' of this kind of soil medium when loading at various levels, it is substituted into , get the soil medium calibration coefficient k′, and then according to , calculate the corrected value of earth pressure p _o ′ when loading at various levels, that is, the point marked by “■” in Fig. 1.

At the same time, for the data obtained in steps (1) and (2) of the soil medium calibration test, and the output signal q _i of the miniature earth pressure sensor when loaded at various levels, the linear function is used according to the traditional method Fit the test data to get the fitting parameters a=0.3349, b=-36.092, where the correlation coefficient is . Then, the output signal q' in the geotechnical model test is substituted into the above fitting formula to obtain the corrected result, which is the point marked "○" in Figure 1.

It can be seen from Figure 1 that the error of the traditional method is relatively large, and the relative error between the correction result obtained by linear function fitting and the theoretical load (connected straight line in Figure 1) is between 3.31% and -54.21%, and the mean is -31.98%; while the relative error between the correction result obtained by fitting the fractional function of the present invention and the theoretical load (connected straight line in Figure 1) is only between -1.97% and 20.13%, and the average value is only 7.5%. It can be seen that adopting the calibration test method of the present invention can effectively reduce the error, the relative error range is only less than half of the existing method, and the relative error mean value is only a quarter of the existing method, and its test accuracy is high, which can be Geotechnical model test provides more accurate and reliable test basis.

Claims (1)

1. the scaling method of miniature soil pressure sensor in the free stress field of soil-structure interactions, comprises the following steps:

(1) hydraulic calibration test: tested by hydraulic calibration, by infusion fluid load p _land output signal q _{μ ε}relation curve, matching draws miniature soil pressure sensor hydraulic calibration coefficient k=p _l/ q _{μ ε};

(2) soil-structure interactions rating test: water percentage ω and the coefficient of compaction K of measuring on-the-spot soil-structure interactions, and compaction test is carried out to on-the-spot soil-structure interactions measure its maximum dry density ρ _dmax; Meanwhile, another enchashment field soil-structure interactions is filled in geotechnical centrifuge model casing, and raising is h, and when the pack height of soil-structure interactions is h/2 the miniature soil pressure sensor of horizontal positioned; After filling completes, arrange displacement meter on soil-structure interactions surface, start hydro-extractor, make hydro-extractor with centrifugal acceleration 20g for one-level, multistage loadings, until centrifugal acceleration only reaches 100g;

(3) soil-structure interactions modulus is obtained: while hydro-extractor multistage loadings, the centrifugal acceleration g of loading at different levels measured by displacement meter _itime soil-structure interactions settling amount △ h _i, and calculate the soil-structure interactions strain stress of loading at different levels _i, ε _i=△ h _i/ h; Soil-structure interactions is at the centrifugal acceleration g of loading at different levels _ito the theoretical load that miniature soil pressure sensor produces under effect wherein ρ is soil-structure interactions density, ρ=K ρ _dmax(1+ ω); Finally calculate centrifugal acceleration g at different levels _isoil-structure interactions modulus under effect wherein the subscript i of each pa-rameter symbols is the progression sequence number of hydro-extractor multistage loadings, i=1,2,3,4,5;

(4) matching error is obtained: record the output signal q of miniature soil pressure sensor when at different levels loading _i, the hydraulic calibration coefficient k obtained by (1) step, calculates the hydraulic pressure revision value of miniature soil pressure sensor when at different levels loading determine matching error β during at different levels loading _i,

(5) matching error β and soil-structure interactions modulus E is set up _sfunctional relation: with soil-structure interactions modulus E _sfor horizontal ordinate, with matching error β for ordinate, by soil-structure interactions modulus during at different levels loading with matching error β _ibe depicted as scatter diagram, adopts Fraction Functions matching is carried out to scatter diagram, obtains fitting parameter K ₁, K ₂, K ₃;

(6) soil-structure interactions calibration coefficient is determined: soil-structure interactions calibration coefficient is k ', in formula, p ' _ofor revised geotechnical model test soil pressure modified value, the miniature soil pressure sensor output signal that q ' is geotechnical model test, E ' _sfor the actual measurement modulus of soil-structure interactions around soil pressure sensor miniature in geotechnical model test.