The Small Strain Characterization of Unbound Highway Base Course Materials

This dissertation, The Small Strain Characterization of Unbound Highway Base Course Materials, investigated the influence of several variables on the resilient modulus of unbound base course aggregate materials. The following variables that affect the resilient modulus were investigated: gradation, varying degrees of saturation and undrained Conditions, parent material type, stress ratio and stress history, resilient Poisson's ratio and volume change, and the effects of data acquisition methods on final results.;This research program utilized testing protocols AASHTO T 307 The Standard Method of Test for Resilient Modulus of Unbound Granular Base/Sub-base Materials and Sub-grade Soils (AASHTO 2002) and NCHRP Project 1-28A Harmonized Test Methods for Laboratory Determination of Resilient Modulus for Flexible Pavement Design - Task II: Unbound Materials (NCHRP 2004). Unique test protocols and methods were also developed for this dissertation's testing regimes. This includes large scale saturated - undrained cyclic triaxial tests. These types of tests are uncommon due to their complexity. It is believed the undrained-saturated large scale specimen test program at Michigan Tech was the most ambitious test program to date.;While it is quite difficult to monitor the volumetric behavior of soil specimens while they are being subjected to resilient modulus determinations, it is essential to determine Poisson's ratio for the materials being tested in order to understand the effects of the test variables used in the standard protocol. This required the development and manufacture of unique instrumentation that would attach to the compacted specimen while inside the triaxial chamber, and measure both lateral and axial cyclic, small strain deformations during testing.;This unique instrumentation allowed for original work regarding the stress history, strain hardening, lateral and volumetric deformations, and Poisson's ratio of engineered unbound aggregates. These topics are discussed relative to gravel/base course performance and traditional assumptions regarding small strain behavior of coarse aggregate materials. Finally a qualitative model describing the small strain behavior of unbound coarse aggregates is presented.