A method for triaxial test of dynamic pore pressure and deformation of overburden soil reflecting seismic loading history

Abstract

The application discloses a kind of overburden soil dynamic pore pressure-deformation indoor triaxial test methods reflecting seismic loading history, belong to geotechnical engineering and earthquake engineering field.First, create numerical geometric model, input soil physical and mechanical parameters;Second, carry out dynamic time-history response analysis, output the seismic stress response time-history of different positions, different depth soil units in numerical simulation results, and convert it into test control load;Third, carry out indoor dynamic test, load test control load, collect the dynamic response data of soil under the action of seismic motion;Finally, based on dynamic response data, using interpolation method, according to stress state and dynamic strain amplitude interpolation determines all units of overburden dynamic test results, completes dynamic characteristic analysis.The application can avoid the over-simplification and blind test of traditional test, significantly improve the authenticity and accuracy of foundation soil dynamic test, and is suitable for accurate evaluation of dynamic characteristics of super-deep soft overburden foundation soil.

Description

Technical Field

[0001] This invention belongs to the fields of geotechnical engineering and earthquake engineering, and relates to an indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil that reflects the earthquake loading process. It is particularly suitable for the dynamic characteristic test control optimization and seismic dynamic response assessment of ultra-deep soft overburden foundations, and can provide scientific basis and data support for subsequent foundation liquefaction resistance assessment, deformation control and overall stability evaluation. Background Technology

[0002] High dam construction is a crucial foundation for hydropower development. With the continued deepening of development efforts, the geological conditions for selecting sites for water conservancy projects in my country have become increasingly complex in recent years. Dam construction in areas prone to strong earthquakes and with deep overburden foundations is "unavoidable." The dynamic stability of ultra-deep overburden foundations is key to ensuring the overall structural safety of the project. Accurately assessing the dynamic characteristics of the foundation soil under strong earthquakes (such as dynamic pore pressure-deformation characteristics) is a core prerequisite for seismic design and safety evaluation.

[0003] Currently, the engineering community primarily relies on the following methods to assess the dynamic properties of foundation soil: simplified analysis methods based on empirical formulas (such as the Seed-Idriss simplified method), and traditional indoor unit dynamic tests (such as standard cyclic triaxial tests) for analyzing the dynamic properties of foundation soil. Existing technologies typically employ the "equivalent substitution" approach, which involves determining the equivalent cyclic vibration number based on an earthquake magnitude table and applying a standard sinusoidal load with a fixed equivalent dynamic stress amplitude to simulate the effect of an earthquake on the soil.

[0004] However, as engineering projects extend into deep overburden layers with complex geological conditions, the limitations of the aforementioned traditional methods have become increasingly apparent. This is mainly manifested in neglecting the significant alteration of seismic wave spectral characteristics by ultra-deep, weak soil layers as natural "filters" (i.e., filtering out high frequencies and amplifying low frequencies), and still directly determining the equivalent vibration order of indoor dynamic tests based on the simplified "magnitude-order" relationship. This simplification easily leads to distorted test results, making the assessment conclusions inconsistent with reality.

[0005] To address the above issues, scholars both domestically and internationally have conducted relevant research and proposed some solutions. For example, Chinese invention patent 201610979655.7 provides a method for determining the dynamic strength parameters of deep overburden soil considering in-situ structural effects. Based on the characteristics of deep overburden soil, in-situ field tests are conducted to determine the benchmark value of dynamic strength under in-situ conditions. Then, based on laboratory test results, the magnitude proportionality coefficient, the overlying effective stress correction coefficient, and the initial shear stress correction coefficient are determined, thus considering the in-situ structural effects to determine the dynamic strength parameters of deep overburden soil. However, its laboratory tests still use simplified analysis methods based on empirical formulas and do not consider the filtering effect of the actual deep overburden on seismic waves. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a laboratory triaxial test method for dynamic pore pressure-deformation of overburden foundation soil reflecting the seismic loading process. This invention first analyzes the filtering mechanism and stress transmission law of ultra-deep overburden through dynamic numerical calculations. Then, it uses the actual stress time history to replace the equivalent harmonic wave as the test control signal to conduct laboratory tests. Based on the obtained test control signal, dynamic stress is applied to obtain the dynamic characteristics of soil elements. Finally, the dynamic characteristics of all elements are obtained by interpolation using the laboratory test results. This solves the problem of traditional tests using equivalent simplification methods and not considering the filtering effect of deep overburden, thus obtaining soil dynamic test results that more closely reflect actual seismic action.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for indoor triaxial testing of dynamic pore pressure-deformation in overburden foundation soil reflecting seismic loading history, the method comprising the following steps:

[0009] Step S1: Create a numerical geometric model based on the distribution of deep overburden soil and specification requirements, input the physical and mechanical parameters of the soil, and use the ground motion time history that matches the engineering site for dynamic analysis.

[0010] Furthermore, the physical and mechanical parameters of the soil include density, void ratio, dynamic elastic modulus decay curve, and damping ratio growth curve;

[0011] Furthermore, the numerical geometric model adopts an equivalent linear constitutive model. The parameters of the equivalent linear constitutive model are directly determined through dynamic modulus and damping ratio tests. This equivalent linear constitutive model can reasonably determine the acceleration, shear stress, and shear strain response of the soil during an earthquake, effectively avoiding the uncertainty of parameter values ​​in complex constitutive models. This allows the numerical simulation to obtain a soil seismic response that is more consistent with real-world phenomena. The boundary of the equivalent linear constitutive model adopts a viscoelastic artificial boundary or a viscous boundary to simulate an infinite domain and suppress seismic wave reflection.

[0012] Step S2: Based on the numerical geometric model created in step S1, perform dynamic time history response analysis and output the seismic stress response time history of soil elements at different locations and depths in the numerical simulation results.

[0013] Furthermore, based on the soil layer distribution, the output soil elements output the seismic stress response time histories of the upper, middle, and lower soil elements of different types of soil layers from the numerical simulation results. This facilitates the subsequent interpolation of the indoor dynamic test results of these soil elements to obtain the dynamic test results of all soil elements in the overburden layer.

[0014] Step S3: Based on the seismic stress response time history extracted from the numerical simulation in Step S2, convert it into experimental control loads using the following method. The specific method is as follows:

[0015] Step S3.1: When conducting indoor tests, first perform isobaric consolidation. After the isobaric consolidation has stabilized, apply deviatoric stress. q = s 1- s 3. Perform biased consolidation, and after the biased consolidation stabilizes, conduct dynamic tests, including... s 1 indicates the vertical stress on the surface during the indoor test. s 3 indicates the confining pressure during indoor testing.

[0016] Furthermore, the indoor test was subjected to vertical stress. s 1. The overburden pressure corresponding to the final state is obtained by static numerical simulation; the confining pressure of the indoor test s 3. The lateral horizontal stress corresponding to the final state was obtained by static numerical simulation.

[0017] Step S3.2: The extracted soil element seismic stress response time histories are processed according to the formula... Perform the conversion, where t d (t) represents the seismic shear stress response time history extracted from the numerical simulation results. This represents the test control load; the converted result is used as the dynamic loading waveform for indoor dynamic testing.

[0018] Step S4: Conduct indoor dynamic tests, apply the test control load obtained in step S3, and simultaneously collect dynamic response data on deformation development and pore water pressure changes throughout the entire dynamic test process of the specimen to obtain dynamic response data of the soil under seismic motion.

[0019] Step S5: Based on the dynamic response data obtained in Step S4, an interpolation method is used to determine the dynamic test results of all units in the overburden layer according to the stress state and dynamic strain amplitude, thus completing the dynamic characteristic analysis of all units. The dynamic test results include deformation-pore pressure development.

[0020] Furthermore, the interpolation methods include Kriging interpolation and multiple quadratic interpolation, which can transform discrete indoor unit test results into continuous and reasonable dynamic response characteristic results of all units in the cover layer, making the test results more realistic and accurate.

[0021] The beneficial effects of this invention are:

[0022] (1) Compared with the prior art, the present invention abandons the simplified processing mode of equivalent vibration number based on magnitude conversion and fixed sinusoidal wave loading in traditional tests. It fully considers the filtering and amplification effect of ultra-deep overburden on seismic waves under strong earthquake action. The indoor test is carried out by extracting the real dynamic stress time history through numerical simulation, so that the laboratory loading path is highly consistent with the real stress state of the soil in the overburden, which greatly improves the authenticity and accuracy of the test results in reflecting the actual dynamic behavior of the soil.

[0023] (2) Compared with the prior art, the present invention avoids the waste of resources in blindly carrying out a large number of conventional cyclic triaxial tests in the traditional method. It extracts soil layer units at different locations and depths based on numerical simulation for indoor tests and uses real seismic loads for indoor dynamic tests, which can significantly improve the pertinence, test efficiency and resource utilization of foundation dynamic stability assessment.

[0024] (3) Compared with the existing technology, the present invention has a complete system. Combining numerical simulation and indoor test, the test results are more realistic and can be applied to various soil types (sand, silt, improved soil, etc.) and various engineering scenarios (from building foundation to earth-rock dam), and has a wide range of promotional value. Attached Figure Description

[0025] Figure 1 This is a flowchart of the overall method of the present invention.

[0026] Figure 2 This is a numerical simulation diagram of the stress state of a certain unit in an embodiment of the present invention.

[0027] Figure 3 This is a time history diagram of shear stress extracted from a certain unit in a numerical simulation of an embodiment of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0029] Example 1

[0030] This embodiment uses a project in western China as an example. The site has a cover layer thickness greater than 20m, belonging to a deep and weak cover layer foundation. The seismic fortification intensity of the project is 8 degrees (0.30g). The method described in this invention is used to conduct dynamic characteristic tests and evaluations of the foundation soil. The specific steps are as follows: Figure 1 As shown below:

[0031] Step S1: Create a numerical geometric model based on the distribution of deep overburden soil and specification requirements, input the physical and mechanical parameters of the soil, and use the ground motion time history that matches the engineering site for dynamic analysis.

[0032] In this embodiment, the dynamic response analysis adopts an equivalent linear model, with the initial shear modulus obtained from previous conventional tests as input. G max Parameters such as dynamic modulus decay curve with dynamic shear strain amplitude and damping ratio increase curve with dynamic shear strain amplitude; boundary conditions: set viscoelastic artificial boundary or viscous boundary.

[0033] Step S2: Based on the numerical geometric model created in Step S1, conduct dynamic time history response analysis and output the seismic stress response time histories of soil elements at different locations and depths in the numerical simulation results. Simulated seismic response: Select a seismic time history matching the engineering site as input, with the input location being the bedrock interface at the bottom of the model. During this process, the numerical model automatically simulates the process of seismic waves traveling upwards from the bedrock through a thick, weak soil layer.

[0034] The filtering effect is evident in the calculation results, which show that the high-frequency components of the seismic waves are significantly attenuated, while the low-frequency components are amplified, demonstrating the significant filtering and amplification effects of the ultra-deep overburden.

[0035] Step S3: Based on the seismic stress response time history extracted from the numerical simulation in Step S2, convert it into experimental control loads using the following method. The specific method is as follows:

[0036] Step S3.1: When conducting indoor tests, first perform isobaric consolidation. After the isobaric consolidation has stabilized, apply deviatoric stress. q = s 1- s 3. Perform biased consolidation. After the biased consolidation stabilizes, conduct dynamic tests, including... s 1 indicates the vertical stress on the surface during the indoor test. s 3 indicates the confining pressure during indoor testing.

[0037] In this embodiment, the indoor test is covered with vertical stress. s 1. The overburden pressure corresponding to the final state was obtained by static numerical simulation; the confining pressure of the indoor test was also obtained. s 3. The lateral horizontal stress corresponding to the final state is obtained by static numerical simulation. In the numerical model, the sandy soil element located 35m below the ground surface is selected as the "target element" in this example. Figure 2 This is a stress state diagram of a certain element in a numerical simulation according to an embodiment of the present invention. The diagram shows the final state of the element obtained from the static numerical simulation, including: s 1 means the overlying pressure is 400 kPa. s3. That is, the lateral horizontal stress is 200 kPa.

[0038] Step S3.2: The extracted soil element seismic stress response time histories are processed according to the formula... Perform the conversion; in the formula t d (t) represents the seismic shear stress response time history extracted from the numerical simulation results. This represents the test control load; the converted result is used as the dynamic loading waveform for indoor dynamic testing.

[0039] In the numerical model, this example selects a sandy soil element located 35m below the ground surface as the "target element." Time history data extraction: The seismic shear stress response time history of this target element is extracted. Stress transformation is performed according to the above process. The resulting stress time history is an irregular curve, rather than a traditional constant-amplitude sine wave. Figure 3 This refers to the seismic shear stress response time history extracted for the target unit in the embodiments of the present invention, which is significantly different from the simplified mode of traditional equivalent sinusoidal loading.

[0040] Step S4: Conduct indoor dynamic tests, apply the test control load obtained in step S3, and simultaneously collect dynamic response data on deformation development and pore water pressure changes throughout the entire dynamic test process of the specimen to obtain the dynamic response of the soil under seismic motion.

[0041] Due to the difficulty in obtaining undisturbed sand samples at a depth of 35m, remolded samples were used. Remolded sand samples with the same relative density as those in the field were prepared. The sample dimensions were cylinders with a diameter of 100mm and a height of 200mm, and vacuum saturation was performed to ensure a B-value > 0.95. Initial state simulation: Consolidation confining pressure was applied to the sample according to the soil depth. s After isobaric consolidation at 3=200kPa, deviatoric stress is applied. q =200kPa, eccentric consolidation was performed. Dynamic load application: The actual dynamic stress time history obtained in step three was converted and imported into the control system of the dynamic triaxial apparatus. Irregular axial stress, completely consistent with the numerical simulation results, was applied to the specimen. According to the pre-set test criteria, the test was stopped after the criteria were met, and the test data were collected and analyzed.

[0042] Step S5: Based on the dynamic response data obtained in Step S4, an interpolation method is used to determine the dynamic test results of all units in the overburden layer according to the stress state and dynamic strain amplitude, thus completing the dynamic characteristic analysis of all units. The dynamic test results include deformation-pore pressure development.

[0043] Conclusion: This embodiment demonstrates that traditional methods severely underestimate the destructive effect of low-frequency seismic waves on soil after filtering through ultra-deep overburden layers. However, the method of this invention successfully reproduces the true dynamic pore pressure-deformation behavior of the soil, providing accurate pore pressure-deformation control basis for seismic design. The various implementation steps of this invention are closely linked, establishing reasonable physical relationships between parameters. This solves the key problem of traditional laboratory dynamic tests using simplified methods to determine the equivalent cyclic vibration number of indoor tests based on the relationship between magnitude and equivalent vibration number, without considering the filtering effect of deep overburden layers under strong earthquakes. Ultimately, this ensures that the final results conform to both theoretical laws and meet the needs of engineering practice.

[0044] The above specific embodiments further illustrate the purpose, technical solution and beneficial effects of this application. It should be understood that the above are only specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solution of this application should be included within the scope of protection of this application.

Claims

1. A method for indoor triaxial testing of dynamic pore pressure-deformation in overburden foundation soil reflecting seismic loading history, characterized in that, The indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil includes the following steps: Step S1: Create a numerical geometric model based on the distribution of deep overburden soil and specification requirements, input the physical and mechanical parameters of the soil, and use the ground motion time history that matches the engineering site during dynamic analysis; the physical and mechanical parameters of the soil include density, void ratio, dynamic elastic modulus decay curve and damping ratio growth curve. Step S2: Based on the numerical geometric model created in step S1, perform dynamic time history response analysis and output the seismic stress response time history of soil elements at different locations and depths in the numerical simulation results. Step S3: Based on the seismic stress response time history extracted from the numerical simulation in Step S2, convert it into experimental control loads; specifically: Step S3.1: When conducting indoor tests, first perform isobaric consolidation. After the isobaric consolidation has stabilized, apply deviatoric stress. q = σ 1- σ 3. Perform biased consolidation, and after the biased consolidation stabilizes, conduct dynamic tests, including... σ 1 indicates the vertical stress on the surface during the indoor test. σ 3 indicates the confining pressure during indoor testing; Step S3.2: The extracted soil element seismic stress response time histories are processed according to the formula... Perform the conversion, where τ d (t) represents the seismic shear stress response time history extracted from the numerical simulation results. The test control load is represented; the converted result is used as the dynamic loading waveform for indoor dynamic testing. Step S4: Conduct indoor dynamic tests, apply the test control load obtained in step S3, and simultaneously collect dynamic response data on deformation development and pore water pressure changes throughout the entire dynamic test process of the specimen to obtain dynamic response data of the soil under seismic motion. Step S5: Based on the dynamic response data obtained in step S4, an interpolation method is used to determine the dynamic test results of all units of the overburden layer according to the stress state and dynamic strain amplitude, and the dynamic characteristic analysis of all units is completed; among which, the dynamic test results include deformation-pore pressure development.

2. The indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil reflecting seismic loading history, as described in claim 1, is characterized in that... In step S1, the numerical geometric model adopts an equivalent linear constitutive model, and the parameters of the equivalent linear constitutive model are determined by dynamic modulus and damping ratio experiments.

3. The indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil reflecting seismic loading history, as described in claim 1, is characterized in that... In step S2, based on the soil layer distribution, the seismic stress response time histories of soil units at the top, middle, and bottom of different types of soil layers in the numerical simulation results are output.

4. The indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil reflecting seismic loading history, as described in claim 3, is characterized in that... In step S3.1, the indoor test is covered with vertical stress. σ 1. The overburden pressure corresponding to the final state is obtained by static numerical simulation; the confining pressure of the indoor test σ 3. The lateral horizontal stress corresponding to the final state was obtained by static numerical simulation.

5. The indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil reflecting seismic loading history, as described in claim 1, is characterized in that... The interpolation method in step S5 includes Kriging interpolation or multiple quadratic interpolation.

Images