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In developing a constitutive model that could predict the settlement due to the collapse, several goals needed to be met. These were to gain an understanding of the collapse phenomenon, knowing the soil properties at the natural water content and how they change after collapse, and develop and test the new model. It was felt that laboratory testing could be of use. The types of test conducted included use of the Oedometer, Pressuremeter, and Triaxial tests. The material that was used for the testing was a "generic" soil manufactured out of diatomite. In all of the tests the soil was tested dry and saturated in order to establish state limits of the soil. Next, the soil was loaded dry then inundated which initiated the collapse of the soil. The stress and strains were continually recorded. From the testing it was concluded that there is a stress-strain region where after collapse the soil looses considerable strength. With increasing stress and strain the soil eventually becomes stronger. From the triaxial tests, the stress-strain data from this "region of collapse" was used in a constitutive model. Stress paths from the Oedometer and Pressuremeter tests were then successfully applied to the model. The constitutive model used was an elasto plastic model. The elastic and plastic strain components were provided using functions for yielding, hardening, plastic potential, and failure as proposed by Paul Lade in his work on cohesionless, frictional materials. Results from the conventional triaxial shear tests and isotropic compression tests were used to derive the values of the functions for the model. The end result was three dimensional surfaces for failure, yielding, plastic work and plastic potential for the dry and saturated soil in the zone of collapse.

Optimization of compaction in granular material without the use of traditional ground improvement methods may be possible by optimizing the percentage of finer material and the median grain size ratio in binary soil mixtures. In this study, the median grain size ratio D50/d50 was explored as a fundamental parpmeter affecting the compaction characteristics of binary mixes made from natural sands as opposed to singular measurements such as fines content and mean grain size traditionally used to represent granular soils. A total of 18 binary granular mixes were synthetically generated from natural sands obtained from Longboat Key, Florida and evaluated through grain size analysis, laboratory compaction and determination of relative density. Results indicate that the D50/d50 ratio shows promise as a fundamental parameter for compaction optimization in binary mixes with values exceeding six approaching the densest packing configuations. / by Tara Devine Brenner. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.