Modelling debris flow entrainment: analytical model, numerical experiment and case study

Chao Kang, Peng Cui, Dave Chan

In the proceedings of: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Landslides and Geohazards II (Liquefiable Soils)

ABSTRACT: Debris flows that entrain sediment by undermining channel beds or scouring channel banks can become exceptionally mobile and destructive. Therefore, the calculation of entrainment plays an important role in debris flow runout analysis. An entrainment model has been developed that takes into account surface erosional effects by considering progressive scouring on the channel bedused to calculate the acceleration, velocity, and displacement of the erodible material. To understand the entrainment process in granular flow, a flow channel of 8 m long with 15-degree slope is simulated using the Discrete Element Method (DEM). Results of the numerical experiment are compared with analytical calculations. The variation of the depth and the rate of erosion are used to verify the analytical model. The results indicate that the entrainment model is able to capture the mechanism of erosion and it can be used in the calculation of the rate of erosion for granular material. The analytical entrainment model is incorporated into a runout model to study a rock avalanche occurred on April 9, 2000 at Yigong Tibet, China. During entrainment, it is considered that the total mass is changing due to basal erosion. In addition, the profile of the channel bed is adjusted accordingly due to erosion in each calculation step. Measurements obtained from site investigation, including deposition depth and flow height at specific location, are used to verify the model. It is found that the calculated runout distance and the modified deposition height agree with field observations. KEYWORDS debris flow, entrainment, modelling, numerical experiment, case study

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