Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation




Civil Engineering

First Advisor

Dr. Sebastian Bryson


The objective of this research study is to determine whether the soil stiffness, from which the small-strain shear modulus is determined, can be used to predict the shearing resistance of compacted clay soil, which are invariably under conditions of partial saturation. The research program developed for this objective included three major soil testing programs of matric suction, shear modulus, and strength.

A method to estimate matric suction of field compacted clay soil was presented and it is based on the quantified effect of change in initial void ratio on the soil water characteristic behaviors. With the use of a non-nuclear soil stiffness gauge used in an incremental compaction laboratory scale model test (a field simulation), the nuclear footprint was eliminated when compared to the use of a nuclear density gauge typically used for soil compaction verification.

An enhanced void ratio function based on the effect of void ratio on shear modulus was developed using the resulting small-strain shear moduli determined from the use of the propagated shear waves in the laboratory scale model tests.

Simulating an as-compacted condition, which is generally during construction and for a limited time thereafter, within the soil strength program, plastic shear strains were shown to occur within the zone that is classically represented as a purely elastic zone. With the use of a flow rule to represent the occurrence of plastic shear strains within this zone a constitutive soil model was developed and presented that can use a field determined shear modulus parameter as input to predict the shearing resistance of the compacted clay soil.