2012 IR&D Annual Report

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.

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