THESIS
2021
1 online resource (7 unnumbered pages, xii, 186 pages) : illustrations (some color)
Abstract
Estimation of coseismic landslides is of particular importance for seismic hazards assessment
and mitigation strategies. To realitically and efficiently simulate the complete
landslide process during earthquake from triggering to post-failure large movements, a robust
computational tool is necessary. In this thesis, a physics-based numerical framework
is developed based on the Material Point Method (MPM) for estimating coseismic landslides
under the influence of wave motion, topographic amplification and hydrogeological
conditions. Various numerical examples are simulated with an emphasis on the failure
mechanisms and the large deformation behavior. The major findings from the thesis are
summarized below:
(i) A two-layer hydro-mechanically coupled Material Point Method has been formulat...[
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Estimation of coseismic landslides is of particular importance for seismic hazards assessment
and mitigation strategies. To realitically and efficiently simulate the complete
landslide process during earthquake from triggering to post-failure large movements, a robust
computational tool is necessary. In this thesis, a physics-based numerical framework
is developed based on the Material Point Method (MPM) for estimating coseismic landslides
under the influence of wave motion, topographic amplification and hydrogeological
conditions. Various numerical examples are simulated with an emphasis on the failure
mechanisms and the large deformation behavior. The major findings from the thesis are
summarized below:
(i) A two-layer hydro-mechanically coupled Material Point Method has been formulated
in the framework of unsaturated soil mechanics. The method employs two
layers of material points to represent coupling effects between the solid and fluid
phases. Several numerical examples demonstrate unique features of the method,
including free water infiltration into the unsaturated soil and dynamic soil-water
interaction in an example of underwater soil collapse. Furthermore, rainfall-induced
failure in unsaturated soil slopes is analyzed. The proposed method can well capture
change in matric suction, development of shallow and deep-seated shear bands,
and finally, large-deformation post-failure behavior. Parametric studies also demonstrate
soil cohesion, dilatancy and friction angle play significant roles on the slope
failure mechanisms.
(ii) The Material Point Method is further developed to simulate dynamic slope stability
and liquefaction-induced embankment failure under earthquake loading. First, by
using elastic or elastoplastic models, topographic amplification and different slope
failure modes are analyzed considering the effects of slope geometry, soil properties
and excitation frequencies etc. The MPM model is then applied to predict a cascading
slope failure process, including triggering, shear band formation, runoff and final
deposition. Finally, a fully nonlinear bounding surface soil model is implemented
in the two-phase soil-water coupled MPM framework to investigate the liquefaction
mechanism and associated dam failure, using Success Dam and Lower San Fernando Dam as two examples. The numerical results are generally comparable
with the post-failure profiles obtained from field investigation, which highlight the
advantage of MPM in handling liquefaction-induced large deformation. The MPM
shows great promise to quantitatively assess risk and consequence associated with
seismic slope failure and soil liquefaction, thereby, advance the performance-based
engineering design and analysis.
(iii) A computational framework based on Spectral Element Method (SEM) and Material
Point Method (MPM) has been developed for multiscale, large-deformation
analysis of coseismic landslides. At a regional scale, SEM is used to model elastic
wave propagation from seismic source to a local site, such that topographic amplification,
soil response and near-field characteristics of earthquake shaking can be
simulated. At a local scale, the progressive landslide process and large deformation
behavior are simulated by a fine-scale nonlinear MPM model. The SEM and MPM
models are coupled through a domain reduction method, which is validated through
a benchmark example. In this study, the coupled SEM-MPM method is used to
simulate the massive Hongshiyan landslide triggered by the 2014 M
s 6.5 Ludian
earthquake in China, in which a whole picture from fault rupture to regional-scale
seismic wave propagation to landslides triggering, runoff and deposition is simulated.
The post-failure morphologies of the landslide simulation are generally in
agreement with those from field investigations, showing the SEM-MPM method
is a promising physics-based numerical tool for a multiscale analyses of regional
coseismic landslides.
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