Landslide Stability: Role of Rainfall-Induced, Laterally Propagating, Pore-Pressure Waves

Abstract

The Johnson Creek Landslide is a translational slide in seaward-dipping Miocene siltstone and sandstone (Astoria Formation) and an overlying Quaternary marine terrace deposit. The basal slide plane slopes sub-parallel to the dip of the Miocene rocks, except beneath the back-tilted toe block, where it slopes inland. Rainfall events raise pore-water pressure in the basal shear zone in the form of pulses of water pressure traveling laterally from the headwall graben down the axis of the slide at rates of 1-6 m/hr. Infiltration of meteoric water and vertical pressure transmission through the unsaturated zone has been measured at ,50 mm/hr. Infiltration and vertical pressure transmission were too slow to directly raise head at the basal shear zone prior to landslide movement. Only at the headwall graben was the saturated zone shallow enough for rainfall events to trigger lateral pulses of water pressure through the saturated zone. When pressure levels in the basal shear zone exceeded thresholds defined in this paper, the slide began slow, creeping movement as an intact block. As pressures exceeded thresholds for movement in more of the slide mass, movement accelerated, and differential displacement between internal slide blocks became more pronounced. Rainfall-induced pore-pressure waves are probably a common landslide trigger wherever effective hydraulic conductivity is high and the saturated zone is located near the surface in some part of a slide. An ancillary finding is apparently greater accuracy of grouted piezometers relative to those in sand packs for measurement of pore pressures at the installed depth.

Evidence for earthquake triggering of large landslides in coastal Oregon, USA

“…The Carmel Knoll and Johnson Creek rockslides are crossed by U.S. Highway 101 and have been periodically studied since the 1970s, providing a large amount of subsurface and laboratory data that were available for our use (ODOT Geotechnical Group, 1986;Landslide, 2004;Priest et al, 2006;Ellis et al, 2007;Schulz and Ellis, 2007;Kleutsch, 2008;Niem, 2008;Priest et al, 2011). To our knowledge, the Devils Punchbowl rockslide had not been studied previously; its impact is very limited as it occurs mostly within an undeveloped state park.…”

“…The variability in annual movement somewhat correlates with total annual rainfall (Table 1) but correlates better with the abundance of generally short-lived (hours to few days), intense rainfall events ( Fig. 4; Schulz et al, 2009;Priest et al, 2011). Although erosion of the rockslide toes by wave action also renders the slides more prone to movement, attempts to correlate movement with erosion have been unsuccessful (e.g., Priest et al, 2006).…”

“…To account for bluff retreat that has occurred since formation of the slides, we extended the bluff seaward so that its base intercepted the projection of the present-day location of the basal failure surface. Groundwater flow parallel to the water table was assumed for all analyses as this condition was indicated by monitoring observations Schulz et al, 2009;Priest et al, 2011). We used the means of moist and saturated unit weights determined in the laboratory during previous studies (ODOT Geotechnical Group, 1986;Cornforth Consultants, Inc., 2003;Landslide Technology, 2004;Shannon and Wilson, Inc., 2006;Kleutsch, 2008) for the Astoria Formation (21.2 kN/m 3 and 25.5 kN/m 3 , respectively) and marine terrace sand (18.3 kN/m 3 and 23.6 kN/m 3 , respectively) during all analyses.…”

Implication of subsurface flow on rainfall-induced landslide: a case study

“…Subsurface flow recharged from rainfall infiltration has been widely recognized as one of the main factors affecting the location, time, and type of a landslide occurrence (Leroueil 2001;Li et al 2013). This is supported by the fact that many previously reported rainfall-induced landslides did not occur during rainfall, but hours or even months after a rainfall event (Iverson and Major 1987;Priest et al 2011). Yu et al (2006) performed a detailed investigation on 63 landslide events in Taiwan after the Typhoon Nari on 15 September 2001.…”

State fusion entropy for real-time and site-specific analysis of landslide stability changing regularities

“…Secondly, external factors such as rainfall (Priest et al, 2011;Bernardie et al, 2015;Liu et al, 2016) and fluctuation of water level (Ashland et al, 2006;Huang et al, 2017) will also change landslide stability. But for now only a few literatures mentioned real-time landslide stability (Montrasio et al, 2011;Chen et al, 2014).…”