Document Actions

Topic 4 - Physical Modelling of Debris Flows

Up one level
Topic 4 - Physical Modelling of Debris Flows
Slope failure is commonly caused by rainfall infiltration due to increase in pore-water pressure within the slope. In order to understand the failure mechanism of granular soil slopes, a model slope subjected to rainfall infiltration was developed and employed to perform experiment on sandy soils. Different geological conditions, fines contents of sand, and rainfall intensities were considered as variables. Infiltration of rainfall was simulated by an overland flow infiltrating uniformly into a platform on
Topic 4 - Physical Modelling of Debris Flows
The concept of friction angle as a measure of friction among bodies in static or dynamic conditions, is almost ubiquitous in Earth sciences. In spite of its importance, there is not a general agreement on its definition or standardization on the way to measure it. This study goes back to the fundamentals of friction among granular particles, presenting results from laboratory tests performed in order to measure the friction angles of particles of different shape, density and material, getting indications
Topic 4 - Physical Modelling of Debris Flows
We measured the pore water pressure distributions in miniature debris flows to assess the validity of the related constitutive equations. Our experiments used a rotating mill that allowed steady flows to be maintained easily and a Pitot tube to measure pore pressure accurately. Plastic and glass beads with particle sizes of 1–6 mm were used to simulate the debris flows. Since laboratory debris flows within a rotating mill give flow fields that differ from those of in situ debris flows, the flow characteri
Topic 4 - Physical Modelling of Debris Flows
The shear stress exerted at the bed and walls of granular flows is an important quantity for modeling and predicting runout, bulking up, channel erosion, and entrainment. Although there are some measurements of boundary shear stress for granular flows in the field and laboratory, we lack systematic measurement of shear stress for a range of flow properties such as particle size, particle shape, and fluid content, especially with natural sediment or for long durations where the flow may evolve. We used two
Topic 4 - Physical Modelling of Debris Flows
In this paper, we examine the effect of flow mass and moisture content on debris flow velocity, discharge, and runout using a series of smallscale flume tests in a geotechnical centrifuge. We found that an increase in mass and an increase in moisture content increased peak velocity during down-slope movement. However, the effect of increased moisture content is much more pronounced than that of increased mass. The maximum cross-sectional area observed did not depend on mass or moisture content, although may
Topic 4 - Physical Modelling of Debris Flows
A visibly granular debris flow front, where large boulders accumulate, is often observed in nature. Although there is abundant evidence of particle sorting and solid-fluid segregation processes, little is known about the specific segregation mechanisms and what factors control the relatively dry coarse snout. To investigate the conditions associated with the development of an unsaturated front, experiments have been conducted with grain-fluid mixtures of different compositions. To create long-lived, accessi
Topic 4 - Physical Modelling of Debris Flows
We perform rheological measurements in a rotating drum. As a starting point for using formula to calibrate rheological measurements, we first identify the possible flow phenomenon in the drum. The experiments were conducted in a drum with 0.5 m inner radius and 0.2 m width. The material used is a Kaolin/ water mixture. The rotating speeds varied from 0 rpm to 40 rpm. The sample amount used in experiments must be large enough to assure that the flow length is much larger than its height. The three flow patte
Topic 4 - Physical Modelling of Debris Flows
When debris flows grow by entraining sediment, they can become especially hazardous owing to increased volume, speed, and runout. To investigate the entrainment process, we conducted eight largescale experiments in the USGS debris-flow flume. In each experiment, we released a 6 m3 water-saturated debris flow across a 47-m long, ~12-cm thick bed of partially saturated sediment lining the 31º flume. Prior to release, we used low-intensity overhead sprinkling and real-time monitoring to control the bed-sedime
Topic 4 - Physical Modelling of Debris Flows
This paper describes a series of “small scale” laboratory flume tests designed to examine the motion and arrest of concentrated granular-fluid flows, with a view to understanding debris flows. A non intrusive optical approach which relies on the matching of the refractive index and the planar laser-induced fluorescence techniques (PLIF), is adopted to analyse the flow behaviour of a granular medium in a ‘free surface’ condition and in the context of relatively high-speed movement. A PIV (Particle Im
Statistics