An experimental investigation of the behavior of compacted clay/sand mixtures
Date
2010
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Compacted clay/sand mixtures can be used as engineered fills when constructing earthen levees or embankment dams. They are also a design option available to engineers that are constructing liner systems or other types of impervious buffer zones for waste disposal projects. For geotechnical engineers that are designing these types of engineered fill systems, it is useful to have an understanding of the engineering behavior of these mixtures as a function of the soil mixture and compaction process that is utilized. This study investigated the effects of various soil mixtures and compaction conditions on the strength and compressibility characteristics of compacted clay/sand mixtures. The factors investigated include the: clay mineral type, clay content, dry unit weight, compaction moisture content, and compaction energy. To simulate the field compaction process, representative Proctor specimens were prepared for each of the clay/sand mixtures at low, standard, and modified Proctor compaction energy levels. Unconsolidated-undrained triaxial strength tests were conducted at various confining pressures on test specimens prepared from each of the compacted Proctor specimens. One dimensional compression tests were also performed on test specimens prepared from each of the compacted Proctor specimens, to determine the compressibility behavior of each of the compacted soil mixtures. The experimental findings showed that the undrained strength of samples compacted at the same energy level decreased with increasing compaction moisture content. Additionally, the undrained strength increased with increasing confining pressure and compaction energy. The results also indicated that the angles of shearing resistance increased with decreasing moisture content, and were largest for specimens compacted at a very low water content with high compaction energy. The values of the cohesion intercept increased with increasing dry density, clay content, and plasticity of the clay fraction. Due to their differences in soil mineral characteristics and as-compacted soil fabric, kaolinite/sand mixtures exhibited higher φ values and lower c values than bentonite/sand mixtures at the same water content relative to the optimum water content. The values of Young's modulus measured in the triaxial test at 50% of the strength increased with clay content and were higher for dry-ofoptimum specimens. The compression test results further showed that a large percentage of compression occurred tended to occur within the first minute of loading. The compaction moisture content was found to have a more significant effect on a given mixture's compressibility behavior for samples having a high clay content.