monograph takes the screening interpretation a step further by characterizing the liquefaction of the soils to behave in a sand-like or clay-like behavior. As pointed out by the previous methodologies, the screening often occurs within “dirty” sands and low plastic fine-grained soils. Idriss and Boulanger summarized that soils began to behave claylike once their plasticity indices were between 4 and 9, intermediate (clay-like and sand-like) with a plasticity index between 4 and 5 and sand-like when the plasticity index of the soil is less than 3.5. In one of the last industrywide accepted consensus papers, Brigham Young University’s Leslie Youd and many others (Youd et al., 2001) concluded that soils once classified as too “clayey” for liquefaction to trigger may instead suffer softening and strength loss during earthquake shaking. If your site sits on soil that behaves in a clay-like manner, you may be asking whether you are free from a seismically induced ground settlement. Like many geotechnical phenomena, it depends. Although the site may be too clayey for liquefaction to occur, settlement may still happen, but it will be at a much smaller magnitude than sand-like behavior. As illustrated in the screening methods above, the hazard of liquefaction and its potential effects on the environment can most accurately be characterized using studies incorporating more recent earthquake events and the liquefaction behavior associated with each. Unfortunately, there isn’t a “one size fits all” methodology. Your geotechnical engineer can help step you through the hazards and guide you on the potential ground movement your site may experience. These screening methods offer a fresh look at the susceptibility of soils to liquefaction and related behavior (such as settlement and cyclic softening). Taylor Hall, P.E., is a Geotechnical Engineer and the Owner and Principal of the Moab Geotechnical Group. He has a bachelor’s degree in civil engineering from the Missouri University of Science and Technology and a master’s degree in civil engineering from the University of Texas at Austin. Taylor has practiced as a professional engineer for nine years in California, Colorado and Utah, and he has been practicing in the state of Utah for the last five years. He has focused on private developments, public infrastructure and transportation projects throughout the West in various soil and rock conditions. Taylor has experience with shoring and retaining systems that incorporate dewatering for large and small excavations. He has experience with most drilling methods, fieldwork coordination, permitting and laboratory testing. His passions within the geotechnical engineering field are founded in soft soils, slope stability, foundations, ground response, and providing practicals product on time. References Bray, J.D. and Sancio, R.B., 2006, Assessment of the liquefaction susceptibility of fine-grained soils: Journal of Geotechnical and Geoenvironmental Engineering, v. 132, No. 9, pp. 1165-1177. Idriss, I.M. and Boulanger, R.W., 2008, Soil liquefaction during earthquakes: Oakland, California, Earthquake Engineering Research Institute, MNO-12, 237 pp. Youd, T.L. and Idriss, I.M., 2001, Liquefaction resistance of soils: summary report from the 1996 NCEER and 1998 NCEER/NSF workshops on evaluation of liquefaction resistance of soils: Journal of Geotechnical and Geoenvironmental Engineering, v. 127, No. 4, pp. 297-313. 47
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