Advancement of Pore Pressure Measurement Techniques and Investigation of Granular Flow Mechanisms in Labratory Landslide Experiments

Abstract

Granular flows are a class of landslide that can result in loss of life and severe infrastructure damage. Grain-scale processes such as pore fluid-particle interactions, flow instabilities or surges, and flow dilation greatly influence the mobility and destructive potential of these granular flows. Yet many of these processes remain poorly understood. Flume and rotating drum experiments provide a controlled environment where the impact of these phenomena on granular flow can be explored. This work investigates factors influencing fluid pressure measurement, surge development, and dilation of granular materials in physical landslide experiments. In this work, a novel hypothesis that flow turbulence may complicate pore fluid pressure measurements in saturated granular flows was tested using large scale flume experiments. Results showed that pressure sensor filter configuration correlated to varying degrees of sensor measurement amplification. A novel method to ensure appropriate sensor configuration prior to testing is presented. Following the validation of this hypothesis, the relationship between the sensor amplification phenomena and flow velocity was investigated in small scale flume experiments. Measurements demonstrated the magnitude of amplification increases with the flow velocity and a scaling relationship between sensor amplification and the Froude Number was found. A rotating drum test series conducted on angular sands and semi-spherical granules had a twofold objective: test the hypothesis that frictional characteristics of dry, uniform granular material influences the development of flow instabilities that instigate surges, and to quantify surge occurrence. Results found the sands consistently experienced instabilities over a range of rotational velocities and the granules did not, validating the hypothesis. Capturing flow front displacement and surface velocity measurements successfully allowed surge frequencies to be identified and signals reproduced. An investigation into the influence of variable test conditions (i.e., flow mass and shear rate) on collisional dilation in ideal and natural granular material employed a vertical rotating drum. Measurements of effective friction, volume fraction, and basal normal stress fluctuations were used to assess collisional dilation. Effective friction and volume fraction results found agreement with μ(I) rheology literature. Normal stress fluctuations and μ(I) relations highlighted the behavioural difference between ideal and natural materials subjected to similar experimental conditions.