Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelas...Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged.In such scenarios,as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area,internal variables that signify these microstructural changes should be established within this zone.Thus,localized deformation characteristics of rocks are studied here by the preset angle shear experiment.A method based on shear displacement and shear stress differences is proposed to identify the compaction,yielding,and residual points for enhancing the model's effectiveness and minimizing subjective influences.Next,a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band.Incorporating damage theory and an elasto-plastic model,a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure.Subsequently,a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern.Thereafter,an innovative damage model is proposed to effectively encompass diverse rock material behaviors,including elasticity,plasticity,and softening behaviors.Ultimately,the effects of the preset angles,temperature,normal stresses and the residual shear strength are carefully discussed.This discovery enhances rock research in the proposed damage model,particularly regarding shear failure mode.展开更多
When assessing seismic liquefaction potential with data-driven models,addressing the uncertainties of establishing models,interpreting cone penetration tests(CPT)data and decision threshold is crucial for avoiding bia...When assessing seismic liquefaction potential with data-driven models,addressing the uncertainties of establishing models,interpreting cone penetration tests(CPT)data and decision threshold is crucial for avoiding biased data selection,ameliorating overconfident models,and being flexible to varying practical objectives,especially when the training and testing data are not identically distributed.A workflow characterized by leveraging Bayesian methodology was proposed to address these issues.Employing a Multi-Layer Perceptron(MLP)as the foundational model,this approach was benchmarked against empirical methods and advanced algorithms for its efficacy in simplicity,accuracy,and resistance to overfitting.The analysis revealed that,while MLP models optimized via maximum a posteriori algorithm suffices for straightforward scenarios,Bayesian neural networks showed great potential for preventing overfitting.Additionally,integrating decision thresholds through various evaluative principles offers insights for challenging decisions.Two case studies demonstrate the framework's capacity for nuanced interpretation of in situ data,employing a model committee for a detailed evaluation of liquefaction potential via Monte Carlo simulations and basic statistics.Overall,the proposed step-by-step workflow for analyzing seismic liquefaction incorporates multifold testing and real-world data validation,showing improved robustness against overfitting and greater versatility in addressing practical challenges.This research contributes to the seismic liquefaction assessment field by providing a structured,adaptable methodology for accurate and reliable analysis.展开更多
The current aseismic design has seldom considered the effect caused by underlain tunnels.Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation.This paper...The current aseismic design has seldom considered the effect caused by underlain tunnels.Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation.This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests.Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions.The soil-rock site is classified as four micro-zones with varying conditions,to mount observation stations of acceleration sensors.Dynamic characteristics of the four zones are identified by the transfer function(TF)method,and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models.The test results indicate that the tunnel effect varies with the site conditions.Distinctively,a significant amplification effect is observed at the A4 zone,located on the soil deposit near the soil-rock interface.Then,it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification,revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.展开更多
基金supported by the China Scholarship Council Program(Grant No.202008320274)it is also supported by Technical University of Munich.
文摘Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged.In such scenarios,as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area,internal variables that signify these microstructural changes should be established within this zone.Thus,localized deformation characteristics of rocks are studied here by the preset angle shear experiment.A method based on shear displacement and shear stress differences is proposed to identify the compaction,yielding,and residual points for enhancing the model's effectiveness and minimizing subjective influences.Next,a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band.Incorporating damage theory and an elasto-plastic model,a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure.Subsequently,a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern.Thereafter,an innovative damage model is proposed to effectively encompass diverse rock material behaviors,including elasticity,plasticity,and softening behaviors.Ultimately,the effects of the preset angles,temperature,normal stresses and the residual shear strength are carefully discussed.This discovery enhances rock research in the proposed damage model,particularly regarding shear failure mode.
文摘When assessing seismic liquefaction potential with data-driven models,addressing the uncertainties of establishing models,interpreting cone penetration tests(CPT)data and decision threshold is crucial for avoiding biased data selection,ameliorating overconfident models,and being flexible to varying practical objectives,especially when the training and testing data are not identically distributed.A workflow characterized by leveraging Bayesian methodology was proposed to address these issues.Employing a Multi-Layer Perceptron(MLP)as the foundational model,this approach was benchmarked against empirical methods and advanced algorithms for its efficacy in simplicity,accuracy,and resistance to overfitting.The analysis revealed that,while MLP models optimized via maximum a posteriori algorithm suffices for straightforward scenarios,Bayesian neural networks showed great potential for preventing overfitting.Additionally,integrating decision thresholds through various evaluative principles offers insights for challenging decisions.Two case studies demonstrate the framework's capacity for nuanced interpretation of in situ data,employing a model committee for a detailed evaluation of liquefaction potential via Monte Carlo simulations and basic statistics.Overall,the proposed step-by-step workflow for analyzing seismic liquefaction incorporates multifold testing and real-world data validation,showing improved robustness against overfitting and greater versatility in addressing practical challenges.This research contributes to the seismic liquefaction assessment field by providing a structured,adaptable methodology for accurate and reliable analysis.
基金supported by the National Natural Science Foundation of China(Grant Nos.51778487&51478343)Joint Funds of the National Natural Science Foundation of China(Grant No.U1934210)National Natural Science Foundation of China Projects of International Cooperation and Exchanges(Grant No.52061135112).
文摘The current aseismic design has seldom considered the effect caused by underlain tunnels.Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation.This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests.Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions.The soil-rock site is classified as four micro-zones with varying conditions,to mount observation stations of acceleration sensors.Dynamic characteristics of the four zones are identified by the transfer function(TF)method,and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models.The test results indicate that the tunnel effect varies with the site conditions.Distinctively,a significant amplification effect is observed at the A4 zone,located on the soil deposit near the soil-rock interface.Then,it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification,revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.
