GEOSTRATA Magazine

Nearly seven million tourists visit the Big Sur area of California annually, in some cases overwhelming the two-lane Highway 1 that clings to the steep and rugged Coast Range mountains and slopes that extend to the Pacific Ocean located more than 100 m below the roadway. In 2016, the average daily vehicle count at the Big Sur River Bridge was 6,500, a 14 percent increase from 5,700 in 2011, and a 160 percent increase from the 2,500 vehicles per day when the highway opened in 1937. Throughout its operation, the highway has been closed more than 55 times by landslides, with closures up to 18 months in duration.

Sophisticated analysis tools are common in many of today's geotechnical offices. While universities teach the basics, field conditions are often complex and require specialized treatment. Observations made during and after geotechnical failures provide unique sets of data to guide sophisticated numerical analyses. These analyses, when performed carefully and thoughtfully, can serve the immediate needs of a project as well as improve the profession's understanding and ability to predict complex geotechnical behavior.

Uncrewed aircraft systems, big data, machine learning, and artificial intelligence are technologies and concepts becoming well-established in forensic engineering practice. However, standardized training and guidance supporting most applications have lagged behind rapid adoption by industry. For those new to these developments, this article will help navigate their implementation in a field that's grounded in location-specific standards, personal experience, and professional precedent.

In areas across the U.S., particularly those that are arid or semiarid, expansive clayey soils pose many infrastructure challenges. These soils present in highway embankments such as cut sections, which undergo volume changes with the seasons. During wet periods, they swell significantly due to moisture absorption, while in dry seasons, they shrink and experience cracks that can extend to depths of 10 ft or more. The persistent cycle of swelling and shrinking, driven by weather conditions, affects not only the soil's physical properties, but also its mechanical strength properties. The development of surficial soil cracks can exacerbate the potential for slope failure when the cracks become filled with water during rainfall events. Failure of embankment slopes can cause distress to infrastructure — for example, to the roads built over them — that leads to increased maintenance costs and expensive repairs. Studies have shown that the embankment soil's permeability can increase drastically after just a few cycles of wetting and drying, leading to more rapid water infiltration. This process significantly weakens the soil's shear strength, which is crucial for maintaining the stability of highway embankments and cut slopes.