Evaluation of non-uniformity of sandy soil specimens compacted in the field and laboratory using triaxial tests

Abstract

The strength and deformation characteristics of compacted soils are typically evaluated using triaxial compression tests on specimens that are compacted relatively uniformly in a laboratory. Soil compacted in the field using vibration rollers is nonuniform in the vertical depth direction; this is because the gradient of the dry density and saturation degree in the depth direction of each compaction layer is large, owing to the distribution of the load transmitted from the contact surface. As a quality control method for earth-filling works, nondestructive inspection indices—such as the soil stiffness index—are applied in some cases, and the average value of the nonuniform compaction layers is measured. Further, unsaturated specimens, which were retrieved from the test fill yielded during field compaction tests, and specimens obtained via compaction using the same soil as that in the laboratory were prepared, and then triaxial compression tests were performed. Local displacement transducers were installed to obtain local deformation characteristics, based on the vertical depth of the specimen, which were then compared with the average deformation characteristics of the entire specimen. The results show that the local low-stiffness section significantly affects the overall average; this makes it non-negligible because the specimen compacted in the field is nonuniform. However, because field-compacted soil has a local lowstiffness section near the surface layer compared with laboratory-compacted soil, evaluations based on the nondestructive inspection of the surface layer may result in underestimations.