Browsing by Author "Lawton, Evert C."
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Article Citation Count: 1Comparison of Methodologies for Establishing Design Properties of Horizontal Drainage in Soft Cohesive Soils(Natl Acad Sciences, 2015) Farnsworth, Clifton B.; Ozer, A. Tolga; Bartlett, Steven F.; Lawton, Evert C.Estimating the rate of settlement for foundation soils treated with vertical drains requires an understanding of the horizontal drainage behavior of the soil, because the time of consolidation settlement may be critical to the overall construction schedule and sequencing. This paper provides a case study comparison of the results of methodologies associated with obtaining design parameters for horizontal drainage for use with vertical drain design, including backcalculation of field settlement data, cone penetrometer testing for pore pressure dissipation, and laboratory Rowe cell testing, by means of the soft, cohesive Lake Bonneville soil deposits in Salt Lake City, Utah. Each of these methodologies has an inherent set of strengths and limitations that should be considered when vertical drains are being designed or time of consolidation settlement is being estimated. Backcalculation of field performance data is effective in identifying true in situ settlement behavior but is not always feasible. Rowe cell testing tends to provide values that more closely correspond with those obtained from backcalculation but is not often performed. Testing for pore pressure dissipation is the most used technique, but it can provide drainage values much higher than the other two methodologies.Article Citation Count: 17New method to determine proper strain rate for constant rate-of-strain consolidation tests(Canadian Science Publishing, Nrc Research Press, 2012) Ozer, A. Tolga; Lawton, Evert C.; Bartlett, Steven F.The development of a new semiempirical method to predict the proper strain rate for constant rate-of-strain (CRS) consolidation tests is described herein. The validity of the proposed method is analyzed using experimental results from CRS and incremental loading tests on four types of soil: Lake Bonneville clay, Massena clay, kaolinite, and montmorillonite. It is found that the maximum allowable strain rate depends on the initial void ratio of the soil and thus is related to the compressibility of the soil. The effect of the strain rate on the distribution of the pore pressure within the sample is investigated by comparing values of effective vertical stress calculated using a linear equation published by Wissa et al. in 1971 with values of effective stress at the base of the specimen determined from measured values of pore pressure. Overall, the proposed method predicts the maximum allowable strain rate very well for three of the four soils and moderately well for the other soil.