Seismic site response analysis with porewater pressure generation

Xing, Guangchao

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https://hdl.handle.net/2142/121260 Copy

Description

Title

Seismic site response analysis with porewater pressure generation

Author(s)

Xing, Guangchao

Issue Date

2023-07-13

Director of Research (if dissertation) or Advisor (if thesis)

Hashash, Youssef M. A.

Doctoral Committee Chair(s)

Hashash, Youssef M. A.

Committee Member(s)

• Olson, Scott M.
• Baser, Tugce
• Ziotopoulou, Katerina

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Liquefaction
• Site response
• Numerical modeling
• Validation
• Parametric study

Abstract

Evaluation of the performance of the nonlinear effective stress soil model for liquefaction modeling remains a challenge in numerical analysis. A simplified three-dimensional nonlinear effective stress model, the I-soil model, has been successfully applied in multiple total stress seismic soil-structure interaction problems. However, using it for effective stress analysis, especially for liquefaction problems, has not been validated. This study evaluates the performance of the I-soil model for liquefaction analysis from element level to system level, then applies it to a large-scale parametric study focusing on liquefaction triggering. Multiple caveats were identified and highlighted throughout this study to ensure the successful application of the I-soil model for effective stress analysis. These include (1) calibrating the model parameter controlling dilatancy behavior based on constant volume friction angle; (2) maintaining the shear strength ratio when subdividing soil layers; (3) ensuring the stress-strain pairs for backbone curve have positive and monotonically decreasing tangent shear modulus; (4) applying correct initial vertical and horizontal stress state in total stress analysis and effective stress analysis; (5) modeling water table as a phreatic boundary, instead of a non-flow boundary. Besides, the calibration of the I-soil model only uses soil properties that are easy to assess with field measurements, empirical correlations, and laboratory tests. The model parameter generation and one-dimensional shear beam model development are automized in a programming project. Element level evaluation of the I-soil model, based on empirical correlations and laboratory tests, indicates that the model can capture the empirical correlations and laboratory observed soil behaviors. Although some deficiencies are notified at the element level, they do not affect the model’s performance at the system level. At the system level, the evaluation indicates that the I-soil model can capture the characteristics of recorded accelerometer and porewater pressure transducer measurements, in liquefaction centrifuge tests and field case histories, at various depths. Two-/three-dimensional models are more suitable for problems with geometric and boundary effects. The large-scale parametric for liquefaction triggering is developed based on real liquefiable soil profiles in United States, Japan, and New Zealand. A broad range of recorded motions is selected to capture the uncertainties in earthquake motion intensity and frequency components. Randomization in shear wave velocity and compatible shear strength profiles were applied to capture the variability in soil profiles. Varies water tables were selected to capture the effects of water table fluctuation. The results show that porewater pressure could amplify the effects of resonance; the difference between total stress analysis and effective stress analysis become significant when excess porewater pressure is large. In addition, using the I-soil model on the LS-DYNA platform has excellent computational performance and is efficient for large-scale parametric study.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Guangchao Xing

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