Dr. David K. Crapps Lecture

Two Case Histories Involving Soil-like Materials and Innovative Testing Strategies

For many environmental projects, geotechnical engineers often play a supporting role assisting those responsible for environmental remediation. For example, if the remediation requires excavation of contaminated soils below the ground water table, the design by a geotechnical engineer is required of dewatering and earth support systems. However, in some cases the environmentally compromised materials themselves present a challenge and geotechnical characterization poses significant challenges. Often, the ensuing results are surprising and unexpected.

Two fascinating geoenvironmental case history examples are presented that resulted in surprising material behavior. The first case history involves characterization of the total and differential settlement of municipal solid waste (MSW). Conventional practice often relies on laboratory tests conducted on remolded large-diameter specimens. While these test results are often adequate in estimating the mechanical compression of the MSW, confidently assessing potential differential settlements is difficult, recognizing that these results may have adverse impacts on the protective liner and leachate collection systems at modern MSW landfills. Surprising results are presented from a 10.5-acre test fill and an innovative settlement monitoring system that quantified potential differential settlements. The second case history involves the geotechnical characterization of ponded coal combustion residuals (CCRs) (i.e., fly ash from coal combustion) and their potential for static liquefaction. Conventional geotechnical tests and non-conventional rheologic tests were conducted on samples obtained from across the U.S. Unexpected and surprising results are presented that explain recent failures of CCR impoundments and mine tailing dams in the absence of static liquefaction.

About the Speaker Dr. Bachus obtained his B.S. and M.S at the University of Illinois and Chicago Circle. After completing his Ph.D. at Stanford University, he joined the faculty at the Georgia Institute of Technology where he taught undergraduate and graduate classes in geotechnical engineering for 11 years. During this time he conducted research and published on insitu testing, developed design procedures for stone columns and mechanically stabilized earth structures, and studied the beneficial use of CCRs. He then joined Geosyntec Consultants where he spent 35 years as a geotechnical and geoenvironmental consultant where he worked extensively on the design, construction, and performance monitoring of landfills; laboratory and insitu testing of soils, rocks, solid waste, and geosynthetics; landslide investigation and stabilization, earth dam performance assessment and rehabilitation, behavior of ponded CCRs, and geotechnical data management. At Geosyntec he continued publishing and presenting on his research and practice. He is the past Chairman of the Site Characterization and Soil and Rock Properties Committee of the Transportation Research Board (TRB). He was the Cross USA lecturer for the Geo-Institute (G-I) in 2019 and 2020. He recently had the pleasure of conducting a face-to-face interview with Dr. John Schmertmann, when Dr. Schmertmann was recognized by the G-I as a Geo-Legend.

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