Research Projects

Background. Landslides entail downhill flow of a large amount of mass, typically soil and other granular matter, and constitute a major geological hazard in India. Climate change, deforestation and other anthropogenic activities have greatly escalated the frequency and detrimental impact of these events.   Landsliding is generally accompanied by large rocks –boulders– that are either part of the original collapse or are entrained by the flow. Such boulders are the cause of a significant percentage of the overall damage from these events, because of the much larger momentum per unit volume that they carry. At the same time, boulders – whether entrained or stationary – can and do affect the downhill flow in important ways. In particular, it is critical to evaluate the impact of boulder laden flows on landslide barrier, -- Aim. The above motivates the present study of entrainment and transport of boulders by granular flows. In particular, we seek to address the following questions How are stationary boulders entrained by a granular flow?  How do boulders move in a granular flow? And where are they finally deposited? How is a granular flow affected by entrained boulders? How is the flow’s runout and its spread affected? Can we formulate a simple boulder-flow interaction law? Is it possible develop a physics-based framework to design landslide barriers? -- Methodology. To answer these questions we need, at a fundamental level, to understand the forces that act between a granular flow and a stationary or an entrained boulder, and the effect of system parameters.   For this, we will pursue experiments, discrete element (DE) simulations and continuum modeling. Experiments will be conducted on a long (3m) variable-inclination granular flow setup and will involve flow visualization, force measurement and boulder tracking. Generally, we will focus on shallow granular flows and squat cylindrical boulders with circular or more complex cross-sections. But, we will also consider simple three-dimensional objects, such as sticky or faceted (e.g. golf balls) spheres, that have non-zero and quantifiable rolling resistance. Our experiments will consider (a) entrainment of a static boulder, (b) boulder transport, (c) flow alteration and (d) impact on landslide barriers. Experiments will be complemented by DE simulations that will offer access to phenomena that remain hidden in experiments because of the opacity of granular flows. We will also be better able to investigate three-dimensional boulders. More importantly, we will be able to consider the effect of mimicking large-scale field phenomena by lab-scale experiments. The low overburden pressure in lab experiments that model geophysical granular processes causes some real-world physics to be lost. This scaling-effect may be prevented by artificially augmenting the value of gravity in simulations. Finally, we will create a continuum model, by extending shallow landslide theory to granular flows with an immersed boulder taken as a mobile rigid body. The model will be refined using results from experiments and simulations. -- Impact. We envisage the following important applications: - Disaster management: Knowledge of parameters that ease entrainment of static boulders and allow them to be transported large distances will help identify boulders that must be protected against. Information about boulder momentum and migration will inform design of landslide barriers. - Landslide modeling: This work will provide detailed mechanics of how inclined granular flow mobilize obstacles, and the dynamic coupling between rigid intruders (boulders) and surrounding granular flow. - Planetary science: There is interest in boulder motion on small planetart bodies–such as moons and asteroids. Regolith motion, boulder tracks and their emplacement on these bodies offer a window into their geological and dynamical evolution histories, as well as inform possible landing sites. Our results will be directly relevant.