Compendium of Student Papers: Transportation Scholars Conference, Iowa State University, November 15, 1999

(1999) Compendium of Student Papers: Transportation Scholars Conference, Iowa State University, November 15, 1999. Iowa State University

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Abstract

An evaluation of Iowa highway embankment quality was initiated in 1997 as a result of internal Iowa Department of Transportation (Iowa DOT) studies that raised concerns about the quality of recently constructed soil embankments. Some embankments reportedly exhibited slope stability problems, and rough pavements had been observed shortly after being opened to traffic (1). This raised the question as to whether the current Iowa DOT embankment design and construction methods were adequate. Research began with an investigation of several embankments under construction during summer 1997 through summer 1998. As part of the investigation, Iowa DOT resident construction engineers and field inspectors and earthwork contractors were interviewed to develop an understanding of current knowledge of specifications, engineering soil classification and properties, and desired embankment quality. From these interviews and discussions it became apparent that there were problems with some earthwork specifications and construction methods. Foremost it was observed that the current state-of-knowledge regarding soil identification and placement was lower than anticipated. Field personnel and contractors appeared to be generally conscientious and trying to do a good job, but they were misidentifying soils in the field during construction and lacked the equipment to perform field identifications. Soil identification problems arose when soils were mixed during borrow excavation and when boring data was insufficient. With further field testing, including density and moisture tests and in-situ drilling operations it was discovered that embankment fill materials on several projects, regardless of soil type, were being placed wet of "optimum" and saturated. Fill materials compacted with high moisture contents were frequently observed and caused instability under construction equipment.