Post-Wildfire Stability and Improvement of Hillslopes near Pacific Northwest Transportation Infrastructure to Increase Mobility

Abstract

An increased incidence of wildfires followed by a wet season in the Pacific Northwest of the United States has resulted in surficial stability issues (erosion, shallow landslides). If a wetting-induced shallow landslide occurs on a highway embankment or on a natural hillslope near Pacific Northwest infrastructure, in addition to human life and property loss, there are significant economic consequences when hillslope material blocks the highway, damages the transportation infrastructure, and thus reduces mobility. This study updated an existing slope stability model (level one stability analysis, LISA) by incorporating suction stress and then tested the model performance by estimating the landslide susceptibility of a past landslide. In addition, the study tested the effect of surficial application of a soil stabilizer (xanthan gum) on the shear strength of subsurface soil. The results showed that 2.8 g of xanthan gum applied on the soil surface (68.5 cm x 68.5 cm) reduced erosion by 2.9 times and increased runoff only by ~12 percent, while also increasing the normal stress-shear stress behavior of the subsurface soil at the end of three wetting events.