Degree Type

Dissertation

Date of Award

2016

Degree Name

Doctor of Philosophy

Department

Civil, Construction, and Environmental Engineering

Major

Civil Engineering

First Advisor

David J. White

Abstract

This study set out to independently evaluate the quality of compaction using the current specifications. The independent testing results showed that higher rates of data fell outside of the target limits, while in many cases the contractor QC and the agency quality assurance (QA) data fell within the target limits. Statistical analysis results from this study showed some improvements over results from previous projects in terms of the percentage of data that fell within the specification limits. However, QC/QA results are not consistently meeting the target limits/values. Intelligent compaction (IC) technology offers a new and alternative way to control compaction quality. In this study, comparative IC results and in situ point test results involving traditional moisture-density test measurements and performance-based measurements such as light weight deflectometer elastic modulus and dynamic penetration index values were evaluated. Results show that this alternative method can contribute to improved process control, but careful calibration is required.

Based on the field observation of often wet materials at various sites, a laboratory and numerical study was performed to evaluate an approach to assess compaction quality in terms of controlling post-construction settlement of the fill. Results indicated that this approach can be helpful, but empirical relationships between moisture-density-soil index property and consolidation parameters are required to be able to effectively implement such an approach. Some correlations were developed in this study, but must be further validated.

Embankment subgrade soils in Iowa are generally rated as fair to poor as construction materials with low bearing strength, high volumetric instability, and durability problems. Cement stabilization offers opportunities to improve these soils conditions. A laboratory investigation was designed and executed in this study with the main objective of developing correlations between soil index properties, unconfined compressive strength (UCS) and cement content. A total of 28 granular and non-granular materials obtained from 9 active construction sites in Iowa were tested using 4 to 12% type I/II portland cement contents. Specimens were prepared using Iowa State University 2 in. by 2 in. compaction apparatus and tested for 28 day UCS with and without vacuum saturation. Results indicated that statistically significant relationships exist between soil index properties, UCS and cement content.

Copyright Owner

Shengting Li

Language

en

File Format

application/pdf

File Size

296 pages

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