Use of pore-size distribution: The control of subgrade resilient modulus

Nihal Chand Bohra, Purdue University

Abstract

The present study begins with a brief review of structure and fabric of soil followed by a discussion on the mercury intrusion porosimetry technique. Fabric is represented by a pore-size distribution curve determined by the mercury intrusion porosimetry technique. One of the primary goals of this study was to find a laboratory compaction technique capable of replicating the field-compacted fabric. This was achieved by comparing more than 260 laboratory and field compacted pore-size curves, available from a previous study, based on different compaction methods, molding water content and compaction energy. Another goal of the study focused on the experimental investigation of pore-size distribution of five fine-grained soils typically used as pavement subgrade soils in Indiana. Pore-size distribution of uncompacted (powdered) soils was also studied to determine the effect of compaction on the created fabric, and for developing correlations between pore-size parameters and clay fraction and maximum attainable dry unit weight. Parallel to the pore-size studies, the same soil types were investigated for the laboratory and field compacted resilient modulus. Post-compacted water content changes were simulated by injecting moderate quantities of water into the laboratory compacted samples using an hypodermic needle. Field compacted pore-size data were used to predict the moisture characteristic curves for the pavement subgrades. In the final phase of the study, the resilient modulus data were examined in light of the fabric results. Regression equations and correlations were developed to show the influence of fabric and pore water on the resilient modulus. It is concluded that, for high-clay soils, a laboratory impact compaction using Standard Proctor energy at optimum to two percent wet is capable of replicating the field compacted fabric. Pore-size data on uncompacted samples suggest a correlation between clay content, maximum dry unit weight, and pore-size parameters. Finally, it has been found that resilient modulus values may be predicted from the fabric parameters and pore water for soils with high clay fraction. (Abstract shortened by UMI.)

Degree

Ph.D.

Advisors

Altschaeffl, Purdue University.

Subject Area

Civil engineering

COinS