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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Civil and Environmental Engineering

Year Degree Awarded

2018

Month Degree Awarded

September

First Advisor

Don J DeGroot

Second Advisor

Guoping Zhang

Third Advisor

Jon Woodruff

Fourth Advisor

Jason T DeJong

Subject Categories

Geotechnical Engineering

Abstract

This thesis investigates empirical correlations between consolidation design parameters and index properties of soft fine-grained soils from coastal Louisiana region, normalized undrained shear behavior of high liquid limit organic fine-grained coastal soils, and consolidation behavior of fine-grained soils.

The first phase of this research consisted of studying a database of site investigation data from 15 marsh creation projects across the coastal Louisiana region. The database includes a wide variety of fine-grained soils ranging from low-plasticity inorganic clays and silts to high-plasticity organic clays and silts with a large range of water content and liquid limit. Most of the empirical correlations in the literature do not cover the soils in this data set. Correlations between consolidation parameters (compressibility, preconsolidation stress, and coefficient of consolidation) determined from 1-D incremental loading consolidation tests and index properties (water content, void ratio, Atterberg Limits, and dry unit weight) were developed. The degree of correlation between the index parameters and different consolidation design parameters varied significantly. In many cases, considering inorganic and organic soil separately improved the correlations.

The second phase of this research investigated the undrained shear behavior of high liquid limit, organic soils from coastal Louisiana region over the consolidation effective stress range of 50 to 1600 kPa. Undrained direct simple shear (DSS) behavior of 6 resedimented natural organic soils with liquid limit ranging from 81 to 215% and two natural inorganic soils with liquid limit equal to 45% and 46% was studied. CK0UDSS tests were performed on normally consolidated samples. Normalized undrained shear strength and normalized undrained Young’s modulus decreased with increasing consolidation stress level. The organic soils had significantly higher normalized undrained shear strengths than the inorganic soils especially at lower stresses with the difference became smaller at higher stresses. The rate of decrease in normalized undrained shear strength was found to correlate well with liquid limit or organic matter and new correlations were developed to relate undrained shear strength and consolidation stress level as a function of liquid limit. Such correlations were not observed for normalized undrained modulus and liquid limit or organic matter. Thus, a collection of plots of undrained modulus normalized by undrained shear strength versus applied stress ratio for the organic soils tested are provided.

The third phase of this research involved a suite of CRS consolidation tests to investigate different methods of determining the recompression ratio (RR). Tests were performed on a variety of natural clays and silts from different quality samples (intact, highly disturbed, and resedimented) by conducting unload-reload loops at different stress levels and different unloading ratios. Seven different methods were used to determine recompression ratio from each loop resulting, on average, in over 240% difference in RR estimates from the different methods on a loop. The results showed that RR from all the methods increased with increasing stress level and unloading ratio with higher influence for higher OCR soils and sensitive clays. Recommendations for practice are provided for conduct of CRS tests and how to interpret the test results to best estimate RR.

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