Simulation method of complex seismic load in triaxial test

Abstract

The present application relates to a kind of simulation method of complex seismic load in triaxial test, belong to the field of geotechnical engineering laboratory test method.The present application is mainly to overcome the deficiencies in the prior art, propose a kind of simulation method of complex seismic load in triaxial test, including obtaining near-field strong motion record, and baseline correction and filtering processing are carried out to near-field strong motion record;Near-field strong motion record is decomposed and synthesized;Time history conversion is carried out to near-field strong motion record, and experimental parameter is determined;Prepare soil-rock mixture sample, and carry out sample saturation;According to the determined experimental parameter, indoor triaxial test is carried out to saturated sample;According to the test result, the correlation between input waveform and output waveform is calculated;According to the test result, the typical dynamic characteristics of soil-rock mixture under the action of near-field strong earthquake are analyzed.The present application proposes a test data analysis method under the action of seismic load, provides a kind of indoor triaxial test method for carrying out the study on the dynamic characteristics of rock-soil mass under the action of near-field strong earthquake in active fault zone.

Description

TECHNICAL FIELD

[0001] The present application relates to a simulation method of complex seismic load in triaxial test, and belongs to the field of indoor test method of geotechnical engineering. BACKGROUND

[0002] Earthquake and its induced secondary disasters will cause great loss of personnel and property and damage to the ecological environment. More and more geotechnical engineering structures are planned and constructed in active fault zone. Compared with far-field ground motion, the asymmetry, pulse characteristics and direction difference of near-field strong motion in active fault zone will cause more serious damage to geotechnical engineering structures. As the direct hosting environment of geotechnical engineering structures, the dynamic characteristics of rock-soil mass under the action of near-field strong motion in active fault zone will have an important influence on the safe operation of geotechnical engineering structures. At the same time, it is proposed to "strengthen the detection of active faults and the assessment of urban active fault strong earthquake risk, and carry out research on the disaster-prone environment, occurrence mechanism and evolution law across countries and regions". Therefore, it is of great scientific significance and great demand background to study the dynamic characteristics of rock-soil mass under the action of near-field strong motion in active fault zone.

[0003] At present, in the research on the dynamic characteristics of rock-soil mass based on indoor triaxial test, Seed simplified method is often used to simplify irregular seismic load into sinusoidal load with specific amplitude and vibration times for consideration, and then the dynamic strength and dynamic deformation characteristics of rock-soil mass under the action of sinusoidal load are studied. The equivalent cycle amplitude A in the method is calculated based on the linear cumulative damage theory of metal, and the equivalent cycle amplitude A is obtained based on the statistical analysis of test results. The method has the following two limitations when used: first, rock-soil mass is a kind of nonlinear material, the linear cumulative damage theory of metal is not applicable to rock-soil material, which is specifically manifested in that Seed simplified method cannot consider the influence of wave sequence of irregular seismic load; second, Seed simplified method does not distinguish between different types of earthquakes and is based on the liquefaction angle of sand. Studies have shown that the load simplification coefficient of different soil bodies is different, and the method cannot represent the characteristics of near-field strong motion.

[0004] Based on this, the present application combines seismic motion statistical analysis and indoor triaxial test technology to propose a simulation method of complex seismic load in triaxial test. The method is helpful to further understand the influence of near-field strong motion on the dynamic characteristics of rock-soil mass, and provides a scientific basis for the design and construction of geotechnical engineering in active fault zone. SUMMARY

[0005] In view of the above problems, the present application mainly overcomes the deficiencies in the prior art and proposes a simulation method of complex seismic load in triaxial test.

[0006] The technical scheme provided by the present application to solve the above technical problems is: a simulation method of complex seismic load in triaxial test, comprising the following steps:

[0007] Step S10, obtaining near-field strong motion records and performing baseline correction and filtering on the near-field strong motion records;

[0008] Step S20, decomposing and synthesizing the near-field strong motion records;

[0009] Step S30, time history conversion of the near-field strong motion records and determination of experimental parameters;

[0010] Step S40, preparation of soil-rock mixture samples and saturation of the samples;

[0011] Step S50, triaxial test of the saturated samples according to the experimental parameters determined in step S30;

[0012] Step S60, calculation of the correlation between the input waveform and the output waveform according to the test results in step S50;

[0013] Step S70, analysis of the typical dynamic characteristics of the soil-rock mixture under the action of near-field strong earthquakes according to the test results in step S50.

[0014] Further technical solutions are that in step S10, the fault distribution and types near the work site and historical earthquake events are first investigated, and then the near-field strong motion records are determined by comprehensively considering the source effect and site effect.

[0015] Further technical solutions are that in step S10, the near-field strong motion records include seismic motion records representing the direction difference, asymmetry and pulse characteristics of near-field strong earthquakes.

[0016] Further technical solutions are that the specific process of step S20 is:

[0017] Step S21, the near-field strong motion records are decomposed into 60 seismic motion records within an azimuth angle of 0° to 360° with an interval angle of 6°;

[0018] Step S22, seismic motion records of any azimuth angle are obtained according to any two perpendicular seismic motion records in the horizontal plane.

[0019] Further technical solutions are that the formula in step S22 is:

[0020]

[0021] In the formula: and are any two perpendicular acceleration time history curves in the horizontal direction of the same station; θ is the azimuth angle; is the acceleration time history curve in any direction in the horizontal plane.

[0022] Further technical solutions are that the specific process of step S30 is:

[0023] Step S31, obtaining a shear stress time history curve corresponding to the acceleration time history curve according to the acceleration time history curve;

[0024] Step S32, performing normalization processing on the shear stress time history curve;

[0025] Step S33, determining an input force in combination with a specimen size and a peak value of the shear stress time history curve; and determining an input frequency of the seismic motion record according to a main frequency of the seismic motion record.

[0026] Further technical solutions are that the formula in step S31 is:

[0027]

[0028] In the formula: is a shear stress time history curve; is a ground acceleration time history curve; g is a gravitational acceleration; is a vertical stress; is a shear stress attenuation coefficient considering soil deformation; z is a buried depth; γ is a shear stress attenuation coefficient.

[0029] Further technical solutions are that the normalization formula in step S32 is:

[0030]

[0031] In the formula: is a normalized shear stress time history curve; is a shear stress time history curve; is an absolute value of a peak value of the shear stress time history curve.

[0032] Further technical solutions are that the saturation process in step S40 is: the specimen is transferred to a saturator to perform vacuum saturation, a vacuum pump is used to extract vacuum at-100 kPa on the specimen, then air-free water is injected and the specimen is soaked in the air-free water for 24 h; the specimen is transferred to a dynamic triaxial device to perform CO2 saturation, water head saturation, and back pressure saturation to make the specimen fully saturated; when the specimen B value is greater than 0.95, the saturation of the specimen is completed.

[0033] Further technical solutions are that the calculation formula in step S60 is:

[0034]

[0035] In the formula: is a correlation coefficient, and The device input waveform and the device output waveform are respectively shown in the following table.

[0036] The present application has the following advantages: the present application defines the selection principle and synthesis method of near-field strong earthquake of active fault zone, provides the conversion relationship between the acceleration time history curve and the shear stress time history curve, and proposes the test data analysis method under the action of seismic load, thereby providing an indoor triaxial test method for the research on the dynamic characteristics of rock-soil mass under the action of near-field strong earthquake of active fault zone. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a synthesis diagram of near-fault ground motion;

[0038] Figure 2 It is a comparison diagram of device input waveform and output waveform;

[0039] Figure 3 It is an effective stress path curve diagram;

[0040] Figure 4 It is a stress-strain curve diagram;

[0041] Figure 5 It is a strain time history curve diagram;

[0042] Figure 6 It is a pore pressure time history curve diagram;

[0043] Figure 7 It is a result analysis diagram of the influence of near-field strong earthquake original component and residual component on the deformation of soil-rock mixture;

[0044] Figure 8 It is a result analysis diagram of the influence of near-field strong earthquake direction difference on the development of pore pressure of soil-rock mixture;

[0045] Figure 9 It is a flowchart of the present application. DETAILED DESCRIPTION

[0046] The technical solutions of the present application will be described clearly and completely below with reference to the drawings, obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0047] As shown in the drawings, Figure 9 The present application provides a simulation method of complex seismic load in triaxial test, which comprises the following steps:

[0048] Step S10, obtaining near-field strong earthquake record, and performing baseline correction and filtering processing on the near-field strong earthquake record;

[0049] The near-field strong earthquake records are selected to represent the direction difference, asymmetry and pulse characteristics of near-field strong earthquakes.

[0050] Specifically, firstly, the fault distribution and its type near the work site and historical earthquake events are investigated; then, the seismic source effect (fault type, magnitude, focal depth, etc.) and site effect (topographic effect, site type, etc.) are comprehensively selected to select the seismic motion records;

[0051] Step S20, decompose and synthesize the near-field strong earthquake records;

[0052] For the two horizontal direction seismic motion acceleration time history curves of any station, the acceleration time history curve of any azimuth in the horizontal direction can be obtained by using formula (1) (such as Figure 1 ).

[0053] Step S21, the near-field strong earthquake records are decomposed into 60 seismic motion records within the azimuth of 0° to 360° with an interval angle of 6°, which are used to analyze the direction difference of near-fault seismic motion;

[0054] Step S22, the seismic motion record of any azimuth is obtained according to any two perpendicular seismic motion records in the horizontal plane;

[0055] (1)

[0056] In the formula, and are any two perpendicular acceleration time history curves in the horizontal direction of the same station; θ is the azimuth; is the acceleration time history curve in any direction in the horizontal plane.

[0057] Step S30, time history conversion is performed on the near-field strong earthquake records, and experimental parameters (including input force F and input frequency f ) are determined;

[0058] Step S31, the acceleration time history curve a ( t ) is converted into its corresponding shear stress time history curve τ (t) by using a simplified empirical formula;

[0059] (2)

[0060] In the formula, τ ( t ) is the shear stress time history curve; a ( t ) is the ground acceleration time history curve; g is the acceleration of gravity; σ 0 is the vertical stress;γd a shear stress decay coefficient considering soil deformation;

[0061] wherein when the depth z is in 0 ≤ z ≤ 9.15 m, γd = 1.0 - 0.00765 z (z ≤ 9.15 m);

[0062] when the depth z is in 9.15 m ≤ z ≤ 23 m, γd = 1.174 - 0.0267 z (9.15 m < z < 23 m);

[0063] and finally the shear stress time history curve considering soil deformation is obtained according to the following formula τ (t);

[0064] (3)

[0065] wherein: is the shear stress time history curve; is the ground acceleration time history curve; g is the gravity acceleration; is the vertical stress; is the shear stress decay coefficient considering soil deformation; z is the buried depth; γ is the shear stress decay coefficient;

[0066] Step S32, the shear stress time history curve τ (t) is normalized;

[0067] (4)

[0068] wherein: is the normalized shear stress time history curve; is the shear stress time history curve; is the absolute value of the peak value of the shear stress time history curve;

[0069] Step S33, the input force τ is determined in combination with the specimen size and the peak value of the shear stress time history curve max{ τ ( t )} ; F according to the main frequency of the seismic record or the input frequency of the seismic record f ;

[0070] Step S40, the soil-rock mixture specimen is made and the specimen is saturated;

[0071] The making process includes the following steps:

[0072] (1) Determine the maximum particle size of the soil-rock mixture based on the sample size. d max, the maximum particle size of a typical stone. d max and sample diameter D The ratio is less than 5.0; the boundary particle size between soil particles and boulders is 2mm, meaning that particles smaller than 2mm are considered soil particles, with a particle size range of 2mm- d `max` represents large stones; for oversized particles (particles larger than [a certain size]), the maximum value is [a certain size]; d The portion containing the maximum amount is replaced with the 2mm- using the equal substitution method. d Between max and max.

[0073] (2) Prepare soil-rock mixtures with different moisture contents, obtain compaction curves based on compaction tests, and then configure soil-rock mixtures according to the optimum moisture content in the compaction curves to obtain the curve between the number of blows and the sample density, and obtain the number of blows. N The density of the sample is determined based on the above curve, thereby determining the required mass of soil-rock mixture for the sample.

[0074] (3) Pour water into the prepared dry soil-rock mixture and stir thoroughly. Cover with plastic wrap and store in a cool place for 24 hours. Divide the loose soil-rock mixture into 5 equal parts and hammer each layer. N After that, the surface is roughened before the next layer of hammering is applied.

[0075] The saturation process is as follows: The sample is transferred to a saturator for vacuum saturation. A vacuum pump is used to evacuate the sample at -100 kPa, followed by the injection of degassed water, and the sample is immersed in the water for 24 hours. The sample is then transferred to a dynamic triaxial apparatus for CO2 saturation, head saturation, and back pressure saturation until it is fully saturated. During the back pressure saturation stage, the confining pressure and back pressure are increased in increments of 10 kPa, with each load applied for 0.5 min and maintained for 2 min. The sample is considered saturated when the sample's B value is greater than 0.95. Subsequently, the target effective confining pressure is applied to consolidate the sample. Consolidation is complete when the axial displacement or back pressure volume time history curve tends to be horizontal.

[0076] Step S50: According to the experimental parameters (axial force) determined in step S30 F and loading frequency f Indoor triaxial tests were conducted on saturated specimens;

[0077] Step S60: Calculate the correlation between the input waveform and the output waveform based on the test results in step S50;

[0078] (5)

[0079] In the formula: The correlation coefficient is... and are the input waveform and the output waveform of the device, respectively;

[0080] The present application adopts a correlation coefficient ρxy to measure the correlation between the device response waveform and the input waveform, and the larger the correlation coefficient ρxy is, the stronger the signal correlation is. Figure 2 A comparison diagram of the input waveform and the device response waveform under a certain seismic load input is given. In addition, by comparing the Fourier spectrum and the energy spectrum of the input waveform and the input waveform, the frequency distribution between the input waveform and the output waveform is analyzed.

[0081] Step S70, according to the test results in step S50, analyzes the typical dynamic characteristics of the soil-rock mixture under the action of near-field strong earthquakes;

[0082] Among them, (1) analyzes the dynamic characteristics of the soil-rock mixture under the action of near-field strong earthquakes on active faults, mainly including its effective stress path curve (as shown in Figure 3 ), stress-strain curve (as shown in Figure 4 ), strain time history curve (as shown in Figure 5 ) and pore pressure time history curve (as shown in Figure 6 );

[0083] (2) as shown in Figure 7 and Figure 8 , analyzes the influence of the direction difference of near-field strong earthquakes on the deformation of the soil-rock mixture, and analyzes the influence of the pulse characteristics of near-field strong earthquakes on the deformation of the soil-rock mixture.

[0084] The above description does not limit the present application in any form, although the present application has been disclosed by the above examples, however, it is not intended to limit the present application, any person skilled in the art, without departing from the technical solution of the present application, can make some changes or modifications to the above disclosed technical content as equivalent examples, but any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above examples, as long as it does not deviate from the technical solution of the present application, belongs to the scope of the technical solution of the present application.

Claims

1. A method for simulating complex seismic load in triaxial test, characterized in that, The method comprises the following steps: Step S10, obtaining near-field strong motion records and performing baseline correction and filtering processing on the near-field strong motion records; Step S20, decomposing and synthesizing the near-field strong motion records; Step S30, performing time history conversion on the near-field strong motion records and determining experimental parameters; Step S31, obtaining a corresponding shear stress time history curve according to the acceleration time history curve; Step S32, performing normalization processing on the shear stress time history curve; Step S33, determining an input force in combination with a specimen size and a peak value of the shear stress time history curve and determining an input frequency of the seismic motion record according to a main frequency of the seismic motion record; Step S40, preparing a soil-rock mixture specimen and performing specimen saturation; Step S50, performing indoor triaxial test on the saturated specimen according to the experimental parameters determined in step S30; Step S60, calculating correlation between input waveforms and output waveforms according to the test results in step S50; Step S70, analyzing typical dynamic characteristics of the soil-rock mixture under the action of near-field strong earthquakes according to the test results in step S50.

2. The method of claim 1, wherein, In step S10, firstly, the distribution and types of faults near the work site and historical earthquake events are investigated; then, near-field strong motion records are determined by comprehensively considering source effects and site effects.

3. The method of claim 1, wherein the complex seismic load is simulated in a triaxial test. The near-field strong motion records in step S10 include seismic motion records representing direction difference, asymmetry and pulse characteristics of near-field strong earthquakes.

4. The method of claim 1, wherein, The specific process of step S20 is as follows: Step S21, the near-field strong motion records are decomposed into 60 seismic motion records within an azimuth angle of 0° to 360° with an interval angle of 6°; Step S22, seismic motion records of any azimuth angle are obtained according to any two perpendicular seismic motion records in the horizontal plane.

5. The method of claim 4, wherein the complex seismic load is simulated by using a combination of the three types of seismic loads. The formula in step S22 is as follows: In the formula: and are any two mutually perpendicular acceleration time history curves in the horizontal direction of the same station; θ = arctan (A x / A y) is the azimuth angle; is the acceleration time history curve in any direction in the horizontal plane.

6. The method of claim 1, wherein, The formula in step S31 is as follows: wherein: is the shear stress time history curve; is the ground acceleration time history curve; g is the gravitational acceleration; is the vertical stress; is the shear stress decay factor considering soil deformation; z is the burial depth; γ = A x / A y is the shear stress decay factor.

7. The method of claim 1, wherein the complex seismic load is simulated in a triaxial test. The normalization formula in step S32 is as follows: wherein: is the normalized shear stress time history curve; is the shear stress time history curve; is the absolute value of the peak of the shear stress time history curve.

8. The method of claim 1, wherein, The saturation process in step S40 is as follows: the specimen is transferred to a saturator for vacuum saturation, a vacuum pump is used to extract vacuum from the specimen at-100 kPa, then air-free water is injected and the specimen is soaked in the water for 24 h; the specimen is transferred to a dynamic triaxial device to carry out CO2 saturation, water head saturation and back pressure saturation so as to be fully saturated; when the B value of the specimen is greater than 0.95, the saturation of the specimen is completed.

9. The method of claim 1, wherein the complex seismic load is simulated in a triaxial test. The calculation formula in step S60 is as follows: wherein: is the correlation coefficient, and are the device input and output waveforms, respectively.

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