Covering layer foundation soil dynamic pore pressure-deformation indoor triaxial test method for reflecting earthquake loading process

Abstract

The invention discloses a covering layer foundation soil dynamic pore pressure-deformation indoor triaxial test method for reflecting an earthquake loading process, and belongs to the field of geotechnical engineering and earthquake engineering. Firstly, a numerical geometric model is created, and soil physical and mechanical parameters are input; secondly, carrying out power time history response analysis, outputting seismic dynamic stress response time histories of soil mass units at different positions and different depths in a numerical simulation result, and converting the seismic dynamic stress response time histories into test control loads; thirdly, carrying out an indoor dynamic test, loading a test control load, and collecting dynamic response data of the soil body under the earthquake action; and finally, on the basis of the dynamic response data, determining dynamic test results of all units of the covering layer by adopting an interpolation method according to stress states and dynamic strain amplitude interpolation, and completing dynamic characteristic analysis. According to the method, excessive simplification and blind test of a traditional test can be avoided, the authenticity and accuracy of the foundation soil dynamic test are remarkably improved, and the method is suitable for accurate evaluation of the dynamic characteristics of the ultra-deep soft covering layer foundation soil.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of geotechnical engineering and earthquake engineering, and relates to a method for a dynamic pore pressure-deformation triaxial test of an overburden soil reflecting a seismic loading history, which is particularly suitable for the test control optimization of dynamic characteristics and the evaluation of seismic dynamic response of an ultra-deep and thick soft overburden soil foundation, and can provide scientific basis and data support for subsequent foundation anti-liquefaction discrimination, deformation control and overall stability evaluation. BACKGROUND

[0002] High dam construction is an important basis for water energy development. With the continuous deepening of development work, in recent years, the geological conditions of water conservancy engineering sites in China have become increasingly complex. It is difficult to avoid building dams in strong earthquake areas and deep overburden soil foundation conditions. The dynamic stability of ultra-deep and thick overburden soil foundation is the key to ensuring the safety of the overall engineering structure. Accurate evaluation of the dynamic characteristics (such as dynamic pore pressure-deformation characteristics) of soil under strong earthquakes is the core prerequisite for seismic design and safety evaluation.

[0003] At present, the evaluation of the dynamic characteristics of the foundation soil in the engineering field mainly relies on the following methods: simplified analysis method based on empirical formula (such as Seed-Idriss simplified method), and traditional indoor unit dynamic test (such as standard cyclic triaxial test) for analyzing the dynamic characteristics of the foundation soil. The existing technology usually adopts the idea of "equivalent replacement", that is, the equivalent cycle number is determined according to the seismic magnitude table, and a standard sinusoidal wave load with a fixed equivalent dynamic stress amplitude is applied to simulate the effect of earthquakes on soil.

[0004] However, with the extension of engineering construction to deep overburden with complex geological conditions, the limitations of the above traditional methods have become increasingly prominent, mainly manifested in the neglect of the significant change of the ultra-deep and thick soft soil layer as a natural "filter" to the frequency spectrum characteristics of the seismic wave (i.e. filtering high frequency and amplifying low frequency), and still directly determining the equivalent cycle number of the indoor dynamic test according to the "magnitude-cycle" simplified relationship. This simplified treatment is easy to cause distortion of the test results, making the evaluation conclusion not in line with the actual situation.

[0005] In view of the above problems, domestic and foreign scholars have carried out related research and put forward some solutions. For example, Chinese invention patent 201610979655.7 provides a method for determining the dynamic strength parameters of deep overburden soil considering the in-situ structure effect, which determines the dynamic strength reference value of deep overburden under in-situ conditions according to the characteristics of deep overburden, and then determines the magnitude proportionality coefficient, the overburden effective stress correction coefficient and the initial shear stress correction coefficient according to the laboratory test results, so as to determine the dynamic strength parameters of deep overburden soil considering the in-situ structure effect. However, the indoor test still uses the empirical formula simplified analysis method for test, and does not consider the filtering effect of the actual deep overburden on the seismic wave. SUMMARY

[0006] In order to solve the above problems, the present application provides a method for triaxial test of dynamic pore pressure and deformation of overburden soil reflecting seismic loading history.

[0007] To achieve the above object, the present application provides the following technical scheme: The method for triaxial test of dynamic pore pressure and deformation of overburden soil reflecting seismic loading history comprises the following steps: Step S1: creating a numerical geometric model according to the distribution of deep overburden soil and the requirements of the specification, inputting the physical and mechanical parameters of the soil, and using the seismic time history matched with the engineering site as the seismic time history during dynamic analysis.

[0008] Further, the physical and mechanical parameters of the soil include density, void ratio, dynamic elastic modulus decay curve and damping ratio growth curve. Further, the numerical geometric model uses an equivalent linear constitutive model, the parameters of which are directly determined by dynamic modulus and damping ratio test, which can reasonably determine the acceleration, shear stress and shear strain response of the soil during the earthquake, effectively avoiding the uncertainty of parameter selection of complex constitutive model, so that the numerical simulation can obtain soil seismic response consistent with the actual law; the boundary of the equivalent linear constitutive model uses viscoelastic artificial boundary or viscous boundary to simulate infinite domain and suppress seismic wave reflection.

[0009] Step S2: based on the numerical geometric model created in step S1, carrying out dynamic time history response analysis, and outputting the seismic stress response time history of soil units at different positions and depths in the numerical simulation results.

[0010] Further, the output soil units output the seismic stress response time history of soil units at different positions and depths in the numerical simulation results according to the distribution of soil layers, so as to facilitate subsequent interpolation of all soil unit dynamic test results of the overburden layer based on the indoor dynamic test results of these soil units.

[0011] 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: 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.

[0012] Furthermore, the indoor test was subjected to 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.

[0013] 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. This represents the test control load; the converted result is used as the dynamic loading waveform for indoor dynamic testing.

[0014] 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 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.

[0015] 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.

[0016] The beneficial effects of this invention are: (1) Compared with the prior art, the application discards the simplified processing mode based on magnitude scaling equivalent vibration order and fixed sinusoidal wave loading in traditional tests, fully considers the filtering and amplification effect of super-deep overburden layer on seismic waves under strong earthquake action, and carries out indoor tests through the real dynamic stress time history extracted by numerical simulation, so that the laboratory loading path is highly consistent with the real stress state of the soil in the overburden layer, and the authenticity and accuracy of the test results reflecting the actual dynamic behavior of the soil are greatly improved.

[0017] (2) Compared with the prior art, the application avoids the resource waste of blindly carrying out a large number of conventional cyclic triaxial tests in the traditional method, carries out indoor tests according to the different positions and different depths of the soil layer unit extracted by numerical simulation, and uses real seismic dynamic load for indoor dynamic tests, which can significantly improve the pertinence, test efficiency and resource utilization rate of foundation dynamic stability evaluation.

[0018] (3) Compared with the prior art, the application system is complete, combines numerical simulation and indoor tests, so that the test results are more authentic, can be applied to various soils (sand, silt, improved soil, etc.) and various engineering scenarios (from building foundation to earth-rockfill dam), and has wide popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the overall method flowchart of the application.

[0020] Figure 2 is the stress state diagram of a unit simulated by the embodiment of the application.

[0021] Figure 3 is the shear stress time history diagram extracted by a unit simulated by the embodiment of the application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0023] Embodiment one This embodiment takes a certain engineering in the west as an example, the thickness of the overburden layer of the site is greater than 20m, which belongs to deep and weak overburden layer foundation. The engineering seismic fortification intensity is 8 degrees (0.30g). The method described in the application is used for foundation soil dynamic property test and evaluation, and the specific steps are as shown in Figure 1 as follows: 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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: 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. 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.

[0028] In this embodiment, the indoor test is covered with vertical stress. σ 1. The overburden pressure corresponding to the final state was obtained using static numerical simulation; the confining pressure in the indoor test was also measured. σ 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: σ 1 means the overlying pressure is 400 kPa. σ 3. That is, the lateral horizontal stress is 200 kPa.

[0029] Step S3.2: converting the extracted stress response time history of the soil element into a test control load according to the formula , wherein τ d (t) is the extracted stress response time history of the seismic shear stress in the numerical simulation result, and the converted result is used as a dynamic loading waveform for the indoor dynamic test.

[0030] In the numerical model, the sand soil element at a depth of 35 m below the ground is selected as the target element in this example. The extracted time history data is the extracted stress response time history of the seismic shear stress of the target element. The stress conversion is converted according to the above process. The stress time history obtained at this time is an irregular curve, rather than a traditional equal-amplitude sinusoidal wave. Figure 3 That is, the extracted stress response time history of the seismic shear stress of the target element in the embodiment of the present application, which is significantly different from the simplified mode of the traditional equivalent sinusoidal wave loading.

[0031] Step S4: carrying out an indoor dynamic test, loading the test control load obtained in step S3, collecting the dynamic response data of the deformation development and the pore water pressure change in the whole process of the sample dynamic test, and obtaining the dynamic response of the soil under the action of the earthquake.

[0032] Since it is difficult to obtain the undisturbed sand sample at a depth of 35 m, a remolded sample is used. A remolded sand sample with a relative density consistent with the field is prepared. The sample size is a cylinder with a diameter of 100 mm and a height of 200 mm, and vacuum saturation is performed to ensure that the B value is greater than 0.95. Initial state simulation: according to the depth of the soil layer, the sample is subjected to consolidation confining pressure σ 3=200kPa after isostatic consolidation, and then a deviatoric stress q =200kPa is applied for bias consolidation. Dynamic load loading: the real stress time history calculated and converted in step three is imported into the control system of the dynamic triaxial apparatus. The sample is subjected to irregular axial stress consistent with the numerical simulation result. According to the pre-set test standard, the test is stopped after the standard is reached, and the test data is analyzed.

[0033] Step S5: for the dynamic response data obtained in step S4, an interpolation method is used to determine the dynamic test results of all elements of the overburden layer according to the stress state and dynamic strain amplitude, and the dynamic characteristic analysis of all elements is completed. The dynamic test results include deformation-pore pressure development.

[0034] Conclusion: this example proves that the traditional method seriously underestimates the damage of low-frequency seismic waves filtered by super-deep overburden to the soil; and by using the method of the application, the real dynamic pore pressure-deformation behavior of the soil is successfully reproduced, providing accurate pore pressure-deformation control basis for engineering seismic design. The various implementation links of the application are closely connected, and the parameters are reasonably physically related, which can solve the key problem that the traditional laboratory dynamic test uses the relationship between the magnitude and the equivalent vibration times to determine the equivalent cyclic vibration times of the indoor test by using the traditional simplified method, without considering the filtering effect of deep overburden under strong earthquake action, and finally ensures that the final result not only conforms to the theoretical law but also meets the engineering practice demand.

[0035] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made on the basis of the technical solutions of the present application shall be included in the protection scope of the present 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 for dynamic analysis; 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 test control loads. 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... The physical and mechanical parameters of the soil in step S1 include density, void ratio, dynamic elastic modulus decay curve, and damping ratio growth curve.

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 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.

4. 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.

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... Step S3 specifically involves: 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. This represents the test control load; the converted result is used as the dynamic loading waveform for indoor dynamic testing.

6. The indoor triaxial test method for dynamic pore pressure-deformation of overburden foundation soil reflecting seismic loading history, as described in claim 5, 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.

7. 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.

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