Method for simulating complex earthquake load in triaxial test

Abstract

The invention relates to a method for simulating a complex earthquake load in a triaxial test, and belongs to the field of geotechnical engineering indoor test methods. The invention mainly overcomes the defects in the prior art, and provides a simulation method for complex earthquake load in a triaxial test, which comprises the following steps: acquiring a near-field strong earthquake record, and carrying out baseline correction and filtering processing on the near-field strong earthquake record; decomposing and synthesizing the near-field strong earthquake record; performing time-history conversion on the near-field strong earthquake record, and determining experimental parameters; preparing a soil-rock mixture sample, and saturating the sample; performing an indoor triaxial test on the saturated sample according to the determined experimental parameters; calculating the correlation between the input waveform and the output waveform according to the test result; and analyzing typical dynamic characteristics of the soil-rock aggregate under the action of the near-field strong earthquake according to a test result. The invention provides a method for analyzing test data under the action of earthquake load, and provides an indoor triaxial test method for carrying out research on dynamic characteristics of a rock-soil body by near-field strong shock of an active fault zone.

Description

Technical Field

[0001] This invention relates to a method for simulating complex seismic loads in triaxial tests, belonging to the field of indoor testing methods in geotechnical engineering. Background Technology

[0002] Earthquakes and their induced secondary disasters cause significant loss of life and property, as well as ecological damage. An increasing number of geotechnical engineering structures are being planned and constructed in active fault zones. Compared to far-field ground motions, the asymmetry, pulse characteristics, and directional differences inherent in near-field strong earthquakes along active fault zones lead to more severe damage to geotechnical engineering structures. As the direct environment in which geotechnical engineering structures exist, the dynamic characteristics of soil and rock under near-field strong earthquakes along active fault zones will significantly impact the safe operation of these structures. Furthermore, it is proposed to "strengthen active fault detection and urban active fault strong earthquake hazard assessment, and conduct research on the nurturing environment, occurrence mechanism, and evolution of transnational and transregional mega-disasters." Therefore, research on the dynamic characteristics of soil and rock under near-field strong earthquakes along active fault zones has significant scientific importance and a crucial demand.

[0003] Currently, in the study of dynamic properties of soil and rock masses based on indoor triaxial tests, the Seed simplification method is often used to simplify irregular seismic loads into sinusoidal loads with specific amplitudes and orders, thereby studying the dynamic strength and deformation characteristics of soil and rock masses under sinusoidal loads. The equivalent cyclic order N in this method is calculated based on the linear cumulative damage theory of metals, and the equivalent cyclic amplitude A is obtained based on statistical analysis of experimental results. This method has two limitations: first, soil and rock masses are nonlinear materials, and the linear cumulative damage theory of metals is not applicable to soil and rock masses; specifically, the Seed simplification method cannot consider the wave sequence effect of irregular seismic loads; second, the Seed simplification method does not distinguish between earthquake types and is based on the liquefaction angle of sandy soil. Existing research shows that different soil types have different load simplification coefficients, and this method cannot characterize the characteristics of near-field strong earthquakes.

[0004] Based on this, this patent proposes a method for simulating complex seismic loads in triaxial tests, combining ground motion statistical analysis and indoor triaxial testing technology. This method is beneficial for gaining a deeper understanding of the impact of strong near-field earthquakes on the dynamic characteristics of soil and rock masses, and also provides a scientific basis for the design and construction of geotechnical engineering projects in active fault zones. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to overcome the shortcomings of existing technologies by proposing a method for simulating complex seismic loads in triaxial tests.

[0006] The technical solution provided by this invention to solve the above-mentioned technical problems is: a method for simulating complex seismic loads in triaxial tests, comprising the following steps: Step S10: Obtain near-field strong earthquake records and perform baseline correction and filtering on the near-field strong earthquake records; Step S20: Decompose and synthesize the near-field strong earthquake records; Step S30: Perform time history transformation on the near-field strong earthquake records and determine the experimental parameters; Step S40: Prepare soil-rock mixture samples and saturate the samples; Step S50: Perform an indoor triaxial test on the saturated sample according to the experimental parameters determined in step S30; Step S60: Calculate the correlation between the input waveform and the output waveform based on the test results in step S50; Step S70: Analyze the typical dynamic characteristics of soil-rock mixture under near-field strong earthquake action based on the test results in step S50.

[0007] A further technical solution is that, in step S10, the distribution and types of faults near the work site and historical earthquake events are first investigated; then, the near-field strong earthquake records are determined by combining the source effect and the site effect.

[0008] A further technical solution is that the near-field strong earthquake record in step S10 includes ground motion records that characterize the directional differences, asymmetry, and pulse characteristics of near-field strong earthquakes.

[0009] A further technical solution is that the specific process of step S20 is as follows: Step S21: Using an interval angle of 6°, decompose the near-field strong earthquake records into 60 ground motion records within the azimuth angle from 0° to 360°. Step S22: Obtain ground motion records at any azimuth angle based on any two mutually perpendicular ground motion records in the horizontal plane.

[0010] A further technical solution is that the formula in step S22 is:

[0011] In the formula: and These are any two mutually perpendicular acceleration time history curves within the same station in the horizontal direction; θ It is the azimuth angle; This represents the acceleration time history curve in any direction within the horizontal plane.

[0012] A further technical solution is that the specific process of step S30 is as follows: Step S31: Obtain the corresponding shear stress time history curve based on the acceleration time history curve; Step S32: Normalize the shear stress time history curve; Step S33: Determine the input force by combining the sample size and the peak value of the shear stress time history curve; determine the input frequency of the ground motion record based on the dominant frequency of the ground motion record.

[0013] A further technical solution is that the formula in step S31 is:

[0014] In the formula: This is the shear stress time history curve; This is the time history curve of ground acceleration; g It is the acceleration due to gravity; Vertical stress; The shear stress attenuation coefficient is used to account for soil deformation; z For burial depth; γ This is the shear stress attenuation coefficient.

[0015] A further technical solution is that the normalization formula in step S32 is:

[0016] In the formula: The normalized shear stress time history curve; This is the shear stress time history curve; This represents the absolute value of the peak value of the shear stress time history curve.

[0017] A further technical solution is that the saturation process in step S40 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, then degassed water is injected and the sample is soaked in it for 24 hours; the sample is transferred to a dynamic triaxial device to carry out CO2 saturation, water head saturation, and back pressure saturation to fully saturate it; the sample saturation is completed when the sample B value is greater than 0.95.

[0018] A further technical solution is that the calculation formula in step S60 is:

[0019] In the formula: The correlation coefficient is... and These are the device's input waveform and output waveform, respectively.

[0020] The beneficial effects of this invention are as follows: This invention clarifies the selection principle and synthesis method of near-field strong earthquakes in active fault zones, gives the conversion relationship between the time history curve of ground motion acceleration and the time history curve of shear stress, proposes a method for analyzing test data under seismic loading, and provides an indoor triaxial test method for studying the dynamic characteristics of rock and soil masses caused by near-field strong earthquakes in active fault zones. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of near-fault ground motion synthesis. Figure 2 A schematic diagram comparing the input and output waveforms of the device; Figure 3 This is a graph showing the effective stress path. Figure 4 This is a stress-strain curve diagram; Figure 5 This is a strain time history curve; Figure 6 This is a time history curve of pore pressure. Figure 7 Figure showing the analysis of the influence of the original and residual components of a near-field strong earthquake on the deformation of soil-rock mixture; Figure 8 Figure showing the results of the analysis of the influence of near-field strong earthquake directional differences on the development of pore pressure in soil-rock mixtures; Figure 9 This is a flowchart of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] like Figure 9 As shown, the present invention provides a method for simulating complex seismic loads in triaxial tests, comprising the following steps: Step S10: Obtain near-field strong earthquake records and perform baseline correction and filtering on the near-field strong earthquake records; Among them, ground motion records that characterize the directional differences, asymmetry, and pulse characteristics of near-field strong earthquakes were selected; Specifically, the first step is to investigate the distribution and types of faults near the work site, as well as historical earthquake events; then, the seismic motion records are selected by combining the source effects (fault type, magnitude, source depth, etc.) and site effects (topographic effects, site type, etc.). Step S20: Decompose and synthesize the near-field strong earthquake records; For the ground motion acceleration time history curves in two horizontal directions of any station, the acceleration time history curves at any azimuth angle in the horizontal direction can be obtained using formula (1) (e.g., Figure 1 (As shown).

[0024] Step S21: Using an interval angle of 6°, the near-field strong earthquake record is decomposed into 60 ground motion records within the azimuth angle from 0° to 360°, which are used to analyze the directional differences of near-fault ground motion. Step S22: Obtain ground motion records at any azimuth angle based on any two mutually perpendicular ground motion records in the horizontal plane; (1) In the formula: and These are any two mutually perpendicular acceleration time history curves within the same station in the horizontal direction; θ It is the azimuth angle; This represents the acceleration time history curve in any direction within the horizontal plane.

[0025] Step S30: Perform time history transformation on the near-field strong earthquake records and determine the experimental parameters (including input force). F and input frequency f ); Step S31: Use simplified empirical formulas to convert the acceleration time history curve a ( t Transform it into its corresponding shear stress time history curve τ (t); (2) In the formula: τ ( t ( ) represents the shear stress time history curve; a ( t ( ) represents the ground acceleration time history curve; g It is the acceleration due to gravity; σ 0 represents vertical stress; γd The shear stress attenuation coefficient is used to account for soil deformation; Where the depth z is 0 ≤ z ≤ 9.15 m, γd =1.0-0.00765 z (z ≤ 9.15 m); When the depth z is 9.15m ≤ z ≤ 23m, γd =1.174-0.0267 z (9.15 m) <z<23 m); Finally, the shear stress time history curve considering soil deformation is obtained according to the following formula. τ (t); (3) In the formula: This is the shear stress time history curve; This is the time history curve of ground acceleration; g It is the acceleration due to gravity; Vertical stress; The shear stress attenuation coefficient is used to account for soil deformation; z For burial depth; γ This is the shear stress attenuation coefficient; Step S32: Check the shear stress time history curve τ (t) is normalized; (4) In the formula: The normalized shear stress time history curve; This is the shear stress time history curve; This represents the absolute value of the peak value of the shear stress time history curve; Step S33: Combining specimen size and shear stress time history curve τ Peak value of (t) max{ τ ( t )} Determine the input force F Based on the dominant frequency of the ground motion record or the input frequency of the ground motion record. f ; Step S40: Prepare soil-rock mixture samples and saturate the samples; The production process includes the following steps: (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.

[0026] (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.

[0027] (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.

[0028] 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.

[0029] 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; Step S60: Calculate the correlation between the input waveform and the output waveform based on the test results in step S50; (5) In the formula: The correlation coefficient is... and These are the device's input waveform and output waveform, respectively. This invention uses correlation coefficient ρxy The correlation coefficient is used to measure the correlation between the device's response waveform and the input waveform. ρxy The larger the value, the stronger the signal correlation. Figure 2 A schematic diagram comparing the input waveform and the device response waveform under a certain seismic load is presented. Furthermore, the frequency distribution between the input and output waveforms is analyzed by comparing the Fourier spectrum and energy spectrum of the input waveform.

[0030] Step S70: Analyze the typical dynamic characteristics of soil-rock mixture under near-field strong earthquake action based on the test results in step S50; Among them, (1) analyzes the dynamic characteristics of soil-rock mixtures under strong near-field earthquakes in active fault zones, mainly including their effective stress path curves (such as...). Figure 3 As shown), stress-strain curves (as shown) Figure 4 (as shown), strain time history curve (as shown) Figure 5 (as shown) and pore pressure time history curves (as shown) Figure 6 (as shown) (2) For example Figure 7 and Figure 8 As shown, the influence of the directional differences of near-field strong earthquakes on the deformation of soil-rock mixtures is analyzed, as well as the influence of the pulse characteristics of near-field strong earthquakes on the deformation of soil-rock mixtures.

[0031] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall fall within the scope of the present invention.

Claims

1. A method for simulating complex seismic loads in triaxial tests, characterized in that, Includes the following steps: Step S10: Obtain near-field strong earthquake records and perform baseline correction and filtering on the near-field strong earthquake records; Step S20: Decompose and synthesize the near-field strong earthquake records; Step S30: Perform time history transformation on the near-field strong earthquake records and determine the experimental parameters; Step S40: Prepare soil-rock mixture samples and saturate the samples; Step S50: Perform an indoor triaxial test on the saturated sample according to the experimental parameters determined in step S30; Step S60: Calculate the correlation between the input waveform and the output waveform based on the test results in step S50; Step S70: Analyze the typical dynamic characteristics of soil-rock mixture under near-field strong earthquake action based on the test results in step S50.

2. The method for simulating complex seismic loads in a triaxial test according to claim 1, characterized in that, In step S10, the distribution and types of faults near the work site and historical earthquake events are first investigated; then, the near-field strong earthquake records are determined by combining the source effect and the site effect.

3. The method for simulating complex seismic loads in a triaxial test according to claim 1, characterized in that, The near-field strong earthquake records in step S10 include ground motion records that characterize the directional differences, asymmetry, and pulse characteristics of near-field strong earthquakes.

4. The method for simulating complex seismic loads in a triaxial test according to claim 1, characterized in that, The specific process of step S20 is as follows: Step S21: Using an interval angle of 6°, decompose the near-field strong earthquake records into 60 ground motion records within the azimuth angle from 0° to 360°. Step S22: Obtain ground motion records at any azimuth angle based on any two mutually perpendicular ground motion records in the horizontal plane.

5. The method for simulating complex seismic loads in a triaxial test according to claim 4, characterized in that, The formula in step S22 is: In the formula: and These are any two mutually perpendicular acceleration time history curves within the same station in the horizontal direction; θ It is the azimuth angle; This represents the acceleration time history curve in any direction within the horizontal plane.

6. The method for simulating complex seismic loads in a triaxial test according to claim 1, characterized in that, The specific process of step S30 is as follows: Step S31: Obtain the corresponding shear stress time history curve based on the acceleration time history curve; Step S32: Normalize the shear stress time history curve; Step S33: Determine the input force by combining the sample size and the peak value of the shear stress time history curve; determine the input frequency of the ground motion record based on the dominant frequency of the ground motion record.

7. The method for simulating complex seismic loads in a triaxial test according to claim 6, characterized in that, The formula in step S31 is: In the formula: This is the shear stress time history curve; This is the time history curve of ground acceleration; g It is the acceleration due to gravity; Vertical stress; The shear stress attenuation coefficient is used to account for soil deformation; z For burial depth; γ This is the shear stress attenuation coefficient.

8. The method for simulating complex seismic loads in a triaxial test according to claim 6, characterized in that, The normalization formula in step S32 is: In the formula: The normalized shear stress time history curve; This is the shear stress time history curve; This represents the absolute value of the peak value of the shear stress time history curve.

9. The method for simulating complex seismic loads in a triaxial test according to claim 1, characterized in that, The saturation process in step S40 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. Then, degassed water is injected and the sample is immersed in it for 24 h. The sample is transferred to a dynamic triaxial device to carry out CO2 saturation, water head saturation, and back pressure saturation to fully saturate it. The sample saturation is completed when the sample B value is greater than 0.

95.

10. The method for simulating complex seismic loads in a triaxial test according to claim 1, characterized in that, The calculation formula in step S60 is: In the formula: The correlation coefficient, and These are the device's input waveform and output waveform, respectively.

Images