Aspect’s Principal Geotechnical Engineer Henry Haselton and Principal Engineering Geologist Dave McCormack will participate as faculty at The Seminar Group's Landslides program on October 25, 2018 at the Washington Athletic Club in Seattle. This seminar covers the science behind slope movement and landslides in Washington and discusses the liability concerns for a wide audience of attorneys, claims professionals, and real estate experts.
As the Washington Boulevard landslide continues to move, it threatens to cut numerous Kingston residents off from the town and emergency responders.
Since a significant slide in 2006, Aspect has provided geotechnical services at Washington Boulevard, including gathering data and monitoring and studying movement along the slope. Recently, Kitsap County Public Works decided to implement a slope dewatering system to remove groundwater from the landslide mass and increase the stability of the hillside and roadway.
Aspect’s Andy Holmson provides some insight to the solution in this Kitsap Daily News article.
Geology is on everyone’s mind in Yakima County as officials grapple with the ongoing Rattlesnake Ridge slide and how to help the community below it. This drone footage captures the surface features of the slide in detail.
Given the geology of the area, Aspect’s Principal Engineering Geologist Dave McCormack summarizes the likely forces behind the slide: “Geologic studies have shown that slides of this nature are fairly common on the flanks of the numerous anticlinal ridges in central Washington. While most are ancient and have not moved during recent history, there are examples, including the Nile Valley landslide of 2009, where old slides have reactivated, or new slides began. These slides occur where basalt flows are interbedded with sedimentary strata. While the basalt strata may be relatively strong, the sedimentary interbeds are often weathered and weak.
When the gravitational driving forces acting on these dipping strata exceed the resisting strength of the weathered sedimentary strata, they begin to slide. There are multiple factors in the delicate balance of gravitational forces versus resisting strength, including the properties of the rock, degree of weathering, groundwater levels, the geometry of the slope, etc.
Triggers for activation of landslides can include increases in groundwater level, strong earthquake shaking, or changes in slope geometry from natural causes like river migration, or human-caused grading. Because of the multiple factors involved, teasing out the exact triggers of a slope failure can be challenging, and the expected type of failure (fast debris runout, slow creeping failure, rockfalls, etc.) difficult to predict.”
Geologic insight will continue to be relied on as the slide keeps moving.
The Puget Sound area has been deluged with rain over the last few days, all within an already almost-record-breaking month of precipitation. With increased rain comes increased risk for landslides, and Aspect staff have responded to multiple ones over the last few days. This MyNorthwest article gives an explanation of landslide risks in our region with tips how to spot warning signs.