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Scour is often found along the shoulder of the road, especially the shoulder without pavement in suburban and rural areas. This can reduce the function of the road shoulder and increase the risk of traffic accidents. The mechanism and form of scour have not been widely discussed and need to be studied to improve road safety aspects. This study aims to investigate scour occurrence along the unpaved road shoulders. An experiment was conducted in the laboratory by creating a physical model to simulate the scouring process at unpaved road shoulder. The laboratory test used varying rainfall intensities, slopes, and sediment diameters. Results show that the scour depths are influenced significantly by those three factors. Scour depths resulting in 25% longitudinal slope is around twice deeper than these in 0% longitudinal slope. The scour depth in border between the paved road lane and the unpaved road shoulder is deeper than other part of the shoulder. It shows that the location is a susceptible-part to scouring.

To produce a hazard map and thus provide mitigation measures against natural catastrophic events such as landslides, avalanches, and debris flows, it is necessary to determine the spread distance of such flows. There is a well-documented relationship between the angle of friction and the debris flow volume, allowing one to determine the possible distance a debris flow can travel. However, the effect of mean particle size (d50) and the sorting coefficient (Sc) on the final spread distance (Df) has received mere attention. In this study, a mini conical-shaped mould was used to measure the final spread distance (Df) and angle of friction (αf) for various dry granular material samples both in air and in water. Experimental results indicated that a granular material sample with a smaller d50 travel a longer distance compared to a sample with a higher d50. However, a sample with a smaller d50 results in a smaller angle of friction than the one with a higher d50. Conversely, a well-sorted sample has a smaller spread distance and larger angle of friction. Results also indicated that the spread distance in air is slightly larger and the angle of friction is slightly smaller than in water.