Date of Graduation

12-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Coffman, Richard A.

Committee Member

Bernhardt, Michelle L.

Second Committee Member

Dennis, Norman D. Jr.

Third Committee Member

Liner, Christopher L.

Keywords

Anisotropy; Bender Element; Consolidation; CRS; Shear Wave; Small Strain

Abstract

A back-pressure saturated, constant-rate-of-strain consolidation device was modified to incorporate bender elements (BP-CRS-BE) and thus allowed for shear wave measurements during consolidation tests. This newly fabricated system has many advantages over other previous or current devices: 1) it can be utilized not only for laboratory prepared soil samples but also for field sampled soils such as Shelby tube samples, and 2) continuous compression curves, and continuous values of vertical hydraulic conductivity and coefficient of consolidation can be acquired with a significant reduction in testing time. Soil modulus values such as shear modulus and constrained modulus are also able to be accurately determined through a given test.

This proposed research included three phases: 1) fabrication of the BP-CRS-BE device and verification of system compliance, 2) input signal sensitivity analysis for the bender element tests, and 3) performance tests on soil samples. Specifically, a brass sample and kaolinite soil samples were utilized to perform the verification. The obtained soil properties such as compression index (c_c), recompression index (c_r), swell index (c_s), compression ratio (R_c), recompression ratio (R_r), swell ratio (R_s) and consolidation coefficient (c_v) as collected using the BP-CRS and BP-CRS-BE devices were compared. For the BP-CRS-BE tests on soil, Kaolinite and Illite soil type were utilized to investigate the following relationships: 1) the shear modulus as a function of the void ratio, the amount of axial strain, and/or the amount of stress; 2) the relationship between the shear modulus and the constrained modulus of the soil; and 3) the effects of anisotropic properties on the behavior of the soil.

In addition, the methodology and systematic procedures that were utilized to obtain constrained modulus (M), small strain shear modulus (Gmax), drained Poisson’s ratio values (v ), effective stress values in the horizontal direction, coefficient of lateral earth pressure (K0), and drained friction angle values were discussed. Besides acquiring accurate soil parameters for the geotechnical design, the results obtained from the BP-CRS-BE tests will also enable soil parameters to be obtained to establish a constitutive model for any given soil.

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