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Western Dam Engineering <br /> Technical Note <br /> <br /> <br />2 <br />Soil Characterization – Here’s the <br />Dirt (Part 1) <br /> <br />Introduction <br />Soil characterization can be a dirty job. So dirty that it <br />makes jobs on Mike Rowe’s Dirty Jobs TV show look <br />clean by comparison. There’s the obvious dirt involved <br />with drilling and soil sample collection in the field, then <br />it gets even dirtier in the laboratory where soil gets <br />scooped, mixed, wetted, baked, squeezed, and shaken <br />in an effort to discover its properties. Perhaps the <br />“dirtiest” (i.e., not clean or straightforward) aspect of <br />soils characterization happens in the engineer’s office <br />where the usually challenging task of characterizing <br />soil properties and utilizing the results begins. But the <br />trail of dirt actually begins long before drill rigs <br />mobilize and samples get shuttled to the laboratory. <br />The need for site-specific soil characterization is <br />usually justified with a trigger event such as: <br /> Dam hazard reclassification <br /> Owner’s decision to significantly modify the dam <br /> Flooding or a seismic event that puts an <br />unprecedented or extreme loading on the dam <br /> Periodic dam inspection that identifies a dam <br />safety deficiency. <br />The trigger event can lead to a dam safety evaluation <br />or other study, which in turn may trigger geotechnical <br />investigation, analyses, and dam modification. Soil <br />characterization is a critical step in the dam <br />modification process – it is the culmination and <br />product of data review, use of empirical correlations, <br />and/or geotechnical investigation, and it is the basis of <br />analyses and design. <br />For a Dam Owner or small engineering firm with <br />limited dam design experience, trying to understand <br />soil characterization can seem daunting. This article <br />helps the reader through the soil characterization <br />labyrinth by presenting the fundamentals of soil <br />characterization pertinent to dam design and providing <br />some key resources that can be useful. So let’s dig in <br />and get dirty! <br />The Challenge of Soil Characterization <br />Failure to develop meaningful, representative soil <br />parameters can result in faulty analyses and design, <br />unacceptable dam safety risks, and wasted money. <br />The acronym GIGO (Garbage In - Garbage Out) <br />captures it well: the outcome of geotechnical <br />analyses, design, and construction will only be as good <br />as the input soil parameters upon which they are <br />based. <br />Soil characterization is usually an inexact process, <br />requires considerable experience and judgment, and <br />sometimes resembles more of an art than a science. <br />To the unenlightened, dirt is…well, just plain ol’ dirt. <br />But to the geotechnical engineer and enlightened Dam <br />Owner, dirt is anything but, considering the following: <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> There are many types of soils used as <br />engineering materials, each with different <br />properties and behavior <br /> <br /> There are a plethora of soil characterization <br />tools to choose from – investigation methods, <br />laboratory tests, equations, correlations, “index” <br />properties, classification systems, and soil <br />behavior models <br /> <br /> Unlike other engineering materials with uniform <br />or isotropic composition / behavior such as steel <br />or concrete, soil is a 3-phase material (solid <br />particles, water, and air) with potential for <br />complex physical interactions among the three <br />constituents and under various loadings <br />