Pore-water pressure accumulation under dynamic loadings

Jung, Hyunil

Permalink

https://hdl.handle.net/2142/132680 Copy

Description

Title

Pore-water pressure accumulation under dynamic loadings

Author(s)

Jung, Hyunil

Issue Date

2025-12-02

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

Stark, Timothy D.

Doctoral Committee Chair(s)

Stark, Timothy D.

Committee Member(s)

• Mesri, Gholamreza
• Cha, Eun Jeong
• Shuttle, Dawn

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Liquefaction
• Dams
• Embankments
• Slopes
• Flow failure
• Numerical analysis
• State parameter.

Abstract

The primary objective of this dissertation is to study the impact of closely spaced low-magnitude earthquakes or other dynamic events on the stability of upstream raised tailings dam. For this purpose, a series of numerical analyses were conducted and the level of excess pore-water pressure accumulated during closely spaced earthquakes was investigated. Results of laboratory triaxial compression tests, drained, undrained, and cyclic direct simple shear tests on loose sandy tailings were used to calibrate the soil constitutive model under low applied vertical stress conditions. The seismically induced pore-water pressures calculated from the numerical analysis are compared with previous analytical methods to how that empirical correlations can be used for estimating seismically induced pore-water pressures when performing a complex seismic numerical analysis is not feasible. Flow failure stability analyses were also performed with the calculated values of seismic-induced pore-water pressures to evaluate the decrease in stability with increasing pore-water pressure accumulation. This analysis was needed because localized liquefied strength may not result in a flow failure of the entire dam. The inverse analysis of a 2015 tailings dam failure shows the subject dam was stable before the earthquakes. However, the closely-spaced earthquakes, high static piezometric level, which saturated most of the tailings deposit, and loose sand tailings resulted in positive pore-water pressures being generated during each earthquake. The decrease in the factor of safety against flow failure (FoSFlow) due to pore-water pressure accumulation under closely spaced earthquakes indicates this failure mechanism should be considered for future design and/or periodic stability assessments. Triggering of liquefaction due to accumulation of positive pore-water pressure, however, could not be explained using previous flow failure assessment procedures. Therefore, a new procedure was developed to assess the susceptibility of sandy soils to decrease in mean effective stress and undrained shear strength loss that could result in mobilizing a liquefied strength under static or dynamic conditions in dams and embankments. This procedure is based on the critical state soil mechanics framework in the effective stress domain and no longer uses a state parameter or an assessment of contractive/dilative shear behavior. Instead, the effective stress ratio (p’0/p’cs) for segments along the potential failure surface are estimated from cone penetration test measurements and used to classify the soil behavior and estimate the amount of excess pore-water pressure needed to mobilize the liquefied strength. This enables identification of zones that could mobilize a liquefied strength during static or low-level shaking/disturbances as well as high-level earthquake. Moreover, a cone penetration test (CPT) based procedure was developed to determine the in-situ density and state parameter (ψ) of cohesionless soils. To date several correlations have been developed to estimate ψ from CPT results, but most correlations are based on limited calibration testing and/or require soil constitutive parameters from laboratory shear tests. The new framework is based on a limit pressure calculated using cavity expansion theory and a semi closed-form solution that is scaled to existing calibration chamber data using a chamber shape factor. This enables estimation of ψ directly from CPT results, which makes it practical and theoretically sound. This facilitates determining ψ for use in flow failure assessment procedures for dams and embankments if needed.

Graduation Semester

2025-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/132680

Copyright and License Information

Copyright 2025 Hyunil Jung

Owning Collections