# Fluid-Dynamics Based Analysis of Landslides, Debris Flow, and Liquefaction Induced Ground Displacement for Hazard Assessment, 20-R8089

**Principal Investigators**
Debashis Basu

Kaushik Das

Steve Green

Ron Janetzke

John Stamatakos

Inclusive Dates: 10/01/11 – 03/01/12

**Background** — Landslides and debris flows represent
severe natural disasters and are a source of societal hazard throughout the
world. The occurrence of a landslide depends on a number of factors including
bedrock geology, geotechnical properties of surface materials, rheology and
groundwater conditions. The large spectrum of landslide phenomena makes it
difficult to define a single standard technique to evaluate landslide hazards
and risk. However, a detailed analysis of the relationship between landslides
and their various causes not only provides insight into landslide mechanisms,
but can also form a basis for predicting the occurrence of future landslides and
assessing landslide hazards. A similar class of natural geotechnical hazards is
the liquefaction of loose, saturated, cohesionless soils and other granular
materials during large-magnitude earthquakes. Lateral spreading induced by
seismic liquefaction causes large ground displacement and shear strains that can
cause extensive damage and disruption to pile foundations of buildings and
bridges, embankments, river dikes, pipelines, and waterfront structures. Most of
the prior analyses of debris and landslide flow and liquefaction-induced lateral
spreading employed numerical techniques such as the finite element method (FEM)
and discrete element method (DEM). Compared to FEM and DEM, a mesh-free
computing method such as smoothed particle hydrodynamics (SPH) provides a
significant advantage in handling large deformation and postfailure analysis.
The broad overall objective of this project is to establish a generic SPH-based
computational framework capable of solving problems in geomechanics that involve
both small and large deformations.

**Approach** — This project developed a SPH-based computational
framework for predicting the size, shape, and runout length of debris flows,
landslide flows, and liquefaction-induced lateral ground displacement. The
simulations were carried out using an adaptation of a SPH 2-Dimensional (2–D)
code. The computational effort was also supported by limited experiments related
to the rheology of the debris material and flow of landslide debris material
along an inclined plane. The experimental test setup consists mainly of a ramp
with an adjustable angle. A sample of clay slurry mud is placed in the reservoir
at the top of the ramp and released. The motion of the mud down the ramp is
recorded digitally through clear acrylic sidewalls. Simulated results were
compared with the experimental results. A detailed analysis on the various
non-Newtonian rheology models was also carried out as part of the project.
These experimental investigations coupled with simulations from the
SPH-based computational tool emphasized the importance of landslide and debris
flow geometry, viscosity of the material and treatment of non-Newtonian
viscosity. The project established a generic SPH-based computational framework
capable of solving problems in geomechanics that involve both small and large
deformations.

**Accomplishments ** — One peer-reviewed conference paper and
one conference presentation resulted from the project. These conference papers
described the different aspects of landslides and debris flow modeling as well
as the treatment of non-Newtonian viscosity in liquefaction-induced lateral
spreading analysis. An existing SPH 2–D code (SPHYSICS) was modified and further
developed for implementation of non-Newtonian viscosity rheological formulae.
A code for generating complex geometry for the SPH model was developed. These tools are also expected to be useful in work involving
deformable geometries and coastal hydraulics analysis. Project staff used
results from this completed project to prepare a National Science Foundation
proposal on hybrid analysis with the SPH framework for geomaterials and SPH
framework for quasi incompressible/ incompressible water flow. The SPH technique
was found to be a very effective tool for modeling the spreading of liquefied
soil.