Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Richard Coffman

Committee Member

Michelle Bernhardt-Barry

Second Committee Member

Clinton Wood

Third Committee Member

Paul Millett

Keywords

Fabric Anisotropy, Intrinsic Properties of Soil, Reconstituted Soils, Small-strain, Stress Path, Triaxial Testing

Abstract

Reconstituted specimens are often utilized to characterize engineering properties of cohesive soils. A series of undrained triaxial tests were conducted on reconstituted soil specimens to evaluate 1) the influence of stress path, 2) the intrinsic shear strength behavior, and 3) the small-strain characteristics. The stress path tests were conducted on kaolinite specimens reconstituted from slurries with water content values of one and one-half times the liquid limit of the soil (1.5LL). To evaluate the intrinsic undrained shear strength and the intrinsic small-strain properties, the triaxial tests were performed on kaolinite and illite specimens that were reconstituted at two levels of slurry water content of 1.5LL and three times the corresponding liquid limit of the soil. Bender elements were employed with the triaxial device to measure shear wave velocity during the triaxial tests that were performed to evaluate the small-strain characteristics.

The stress-strain behavior of the normally consolidated kaolinite specimens was similar to the typical behavior of the overconsolidated specimens. Identical stress-strain behavior was observed from the stress paths tests at the same orientation of the principal stresses. A new interpretation method was proposed to normalize the undrained shear strength values of the overconsolidated specimens based on the concept of void index. By utilizing this method, better correlation was obtained between the undrained shear strength values and the intrinsic shear strength line. The values of the shear wave velocity and shear modulus were also normalized to the void index to evaluate the intrinsic small-strain characteristics. The values of both the shear wave velocity and the shear modulus did not normalize with respect to the void index values.

As discussed herein, the triaxial compression test and the reduced triaxial extension test are adequate to represent the different loading and unloading conditions in the field. Unlike previous recommendations of preparing soil slurries at water contents of 1.25 times the liquid limit, soil slurries should be prepared at water content values of at least 3LL. By preparing soil slurries with a water content of 3LL, undrained shear strength and small-strain characteristics that are in better agreement with those for natural soils will be obtained.

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