Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering

First Advisor

Louay N. Mohammad


The cone penetration test may be applied for estimation of the resilient modulus of subgrade soil. The main objectives of this study were to assess the applicability of the intrusion technology in evaluating the resilient characteristics of subgrade soil, develop models among the cone penetration test parameters, resilient modulus, soil properties, and stresses of subgrade soil, and to validate these models. Field cone penetration and laboratory tests were performed on different soil types. Disturbed and undisturbed soil samples were obtained close to the cone penetration test locations. Laboratory tests were also performed to obtain the resilient modulus, strength parameters, compaction characteristics, and physical properties of subgrade soil. The results of the laboratory soil properties, resilient modulus, and eight field cone penetration tests are presented. The models, among the cone penetration parameters, resilient modulus, moisture content, dry unit weight, and stress levels, were developed. Both in-situ stresses and induced traffic stresses were considered. Four models were developed for fine-grained and coarse-grained soil with in-situ and traffic stress conditions. These models were calibrated using the field test results of two soil types and used to predict the resilient modulus of different soil types. The cone penetration, resilient modulus, and soil property tests were also performed on the laboratory compacted soil samples to investigate the effects of the variation in the moisture content and unit weight on the resilient modulus as well as to validate the proposed models. A special test equipment and a miniature cone with a straight push rod were developed for the laboratory cone testing. Four soil types and three levels of moisture contents, such as dry side, optimum, and wet side, were selected for this testing. The results of the laboratory soil property, resilient modulus, and twelve laboratory cone penetration tests are presented. Simplified design charts, based on the cone penetration parameters and resilient modulus, were also developed. The proposed models were implemented in the selected road rehabilitation projects.