April 1, 2024

Speaker: Scott Rugg

Topic: Factors Affecting the Interpretation of Faulting in Cone Penetrometer Test Sounding Investigations

When: Monday, April 1 (6:00PM – 8:30PM)


Cone Penetrometer Test (CPT) soundings are an often-used method to characterize subsurface soil behavior properties mostly in soft material conditions. The method has many geotechnical applications, some of which include liquefaction analysis, mapping of alluvial deposits and fill, evaluation of soil density improvement and determination of seismic S- and P-wave velocities. When a series of CPTs is advanced, the subsurface stratigraphy can be profiled. This was recognized early on and soon CPTs were engaged to identify stratigraphic disruptions indicative of faulting. This method is now widely used in the coastal province of Southern California, mostly in upper Quaternary materials. Oftentimes, only several feet or less of vertical differential across unit horizons or thickness variations in strata are used to identify potential faulting. This means it is imperative that depth recording of CPTs are as accurate as possible.

Several factors can cause errors in depth readings, leading to erroneous interpretations of faulting. These factors will be discussed in this presentation as well as a quality control procedure to track actual depths and thus mitigate errors. In addition, several examples will be presented where inaccurate depth readings resulted in misinterpretation of faulting. Finally, both the advantages and limitations of the CPT method will be discussed.


Speaker Bio:

Mr. Rugg has 38 years of experience in the fields of engineering geology and geotechnical engineering, having worked on thousands of sites throughout California and the Southwest. He has focused his vocation on fault and seismic hazard assessment, having worked extensively on all types of projects including high-rise buildings, hospitals, water and wastewater treatment plants, airports, dams, transportation, education facilities, and residential sites. Early in his career he evaluated hundreds of sites damaged during the 1986 Palm Springs, 1987 Whittier Narrows, 1989 Loma Prieta, and 1994 Northridge earthquakes. A sampling of fault hazard projects he has led are the Master-plan Investigation of San Diego International Airport, San Diego, CA, – Mid-Coast Trolley Extension, San Diego, CA, – Airfield Expansion, Naval Weapons Station, China Lake, CA, – Biosolids and Clarifiers Replacement, Orange County Sanitation District, Huntington Beach, CA – Exxon Mobil Carbon Capture Facility, Baytown, Tx – Camp Blaz Satellite Facility, US Territory Guam, and the Automated People Mover, Inglewood, CA. . He has proficiency in all methods of fault investigation with extensive experience in the use of Cone Penetrometer Test Soundings for fault hazard analysis.