Impulse waves generated by gravitationally-accelerated granular landslides in a large scale flume

Abstract

Landslide-generated impulse waves are a risk to coastal areas near possible sources of large and rapid landslides. A better understanding of the generation of these waves is important for the prediction of the size of these waves. High quality experimental data of a range of different landslide parameters is essential for the development of empirical relationships between landslide and the resulting wave. The existing established relationships are based on physical models that feature pneumatically accelerated slide masses, either using solid blocks or granular material. These tests have short and dense landslides which may not represent all the landslide types. The present study adds to the existing data set using a large scale flume and high speed cameras, which can model very large, gravity accelerated landslides. These types of landslides may be more representative of certain types of large, rapid landslides. A total of twenty-two tests were performed in the large scale flume with eight different water depths. The landslide volume was constant between all tests, while the water depth varied, to change the relative size and velocity of the landslide compared to the water body. The effect of the landslide mass, length, and volume fraction were more pronounced than has been observed in previous studies featuring smaller and denser landslide types. The relative landslide parameters are compared to the maximum wave amplitudes and observed wave types. Although three different wave types were generated in the near-field to the impact site, these waves were observed to transition into solitary waves. The speed and shape of the waves closely matched solitary wave theory in the far-field. The run-up of the waves on a smooth impermeable slope closely matched predictions for run-up of solitary waves. The observed maximum wave amplitudes are also compared to existing empirical wave generation equations. An effective mass reduction factor is introduced to account for the large size and long length of the slides tested. Long, gravity accelerated granular landslides were found to behave significantly different during the wave generation phase than experiments conducted using both solid block landslides and granular block landslides reported in the literature.