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: 10/01/10 – 09/01/11
Background — Landslides and debris flows are a source of societal safety hazard and economic impact 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 the landslide hazards. A similar class of natural geotechnical hazard is the liquefaction of loose, saturated, cohesion-less soils and other granular materials during large-magnitude earthquakes. Lateral spreading induced by seismic liquefaction causes large ground displacement and shear strains that can damage and disrupt pile foundations of buildings and bridges, embankments, river dikes, pipelines and waterfront structures. Most 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 research is to establish a generic SPH-based computational framework capable of solving problems in geomechanics that involve both small and large deformations.
Approach — A SPH-based computational framework is used to predict the size, shape, and runout length of debris flows, landslide flows and liquefaction-induced lateral ground displacement. The computational framework is supported by limited experiments related to the rheology of the debris and liquefied soil. Simulations are carried out for cases where experimental data and analog site data are available. The rheological characteristics are amenable to changes in the flow characteristics, geometry and material properties for flows with free-surface deformation.
Accomplishments — The Herschel-Bulkley, Bingham plastic and the power law model in the SPHYSICS code were implemented. These are the classical non-Newtonian models used in the simulations. The models were validated against experimental data from problems involving non-Newtonian fluids. These simulations highlighted both the importance and complexity of rheology, and the effect of simulation parameters on predicted solutions. The non-Newtonian model results matched well with experimental data. A physical experiment was conducted to analyze different rheological formulations with observed data. The dynamics and motions of landslides and liquefied soils are strongly dependent on the apparent viscosity of the materials. Parametric studies of spreading of soils after liquification revealed that yield stress and viscosity play very important roles in the liquefaction process and control the extent of liquefaction. The SPH technique was found to be a very effective tool for modeling the spreading of liquefied soil.
