Large-Scale Flume Testing of Landslide Impacts on Liquefiable River Valley Floor Sediments

Abstract

Entrainment of liquefiable river valley floor sediments by a landslide can increase slide volume and mobility. Understanding landslide entrainment of liquefiable soils is therefore vital for risk assessment. However, despite the availability of real world examples for back analysis, entrainment of liquefiable soils is not well understood due to the difficulty of directly observing rapid landslides in the field. While large scale flume experiments might typically be used to create representative scenarios for investigation, the difficulty of constructing liquefiable soil layers at the low mean effective stresses typical of 1g lab environments has thus far prevented researchers from performing these experiments. The twofold aim of this dissertation is to establish an effective method for preparation of 1g liquefiable fine sand layers, and to capture and quantify, for the first time ever to the author’s knowledge, entrainment of a liquefiable soil layer by a landslide in a 1g flume. Bench scale experiments were performed to investigate the effect of sand drop height, initial moisture content, and saturation procedure on sample void ratio. These results were incorporated into sample preparation techniques for large scale flume experiments. The large scale flume experiments took place in the Queen’s University landslide flume, which consists of an 8 m long by 2 m wide slope inclined at 30° to the horizontal connected to a 30 m long horizontal runout channel. 0.4 m3 of saturated ceramic particles were released from the top of the flume slope, impacting 4 m long sand beds at a velocity of approximately 4 m/s. Flume experiments included detailed measurements of porewater pressure and deformation during impact, as well as investigation into the effect of dilative vs. contractive behaviour and liquefiable layer thickness on entrainment. These experiments demonstrated that liquefiable sand layers experience frontal plowing style entrainment when struck by landslides. Dilative layers evidenced almost no entrainment but experienced significantly more runout than liquefiable layers. Thinner liquefiable layers experienced more runout but less entrainment than thicker layers. Notably, liquefiable layer experiments were conducted on soil layers with saturations between 65-85%, showing that liquefaction can occur at lower saturations if the soil is subjected to rapid large strain loading.