Drained shear strength of compacted sand with clayey fines

Abstract

The drained shear strength of silty sands and clayey sands is not well studied although sands with fines are encountered in many geological settings. There are limited studies that investigate the drained shear strength of sands with fines and their impact on the stability of geotechnical systems that are supported on these soils. The objective of this paper is to investigate the impact of replacing 10-40% of pure Ottawa sand with natural clay of intermediate plasticity on the drained shear strength of the composite. To achieve this objective, consolidated drained direct shear tests were conducted on pure sand specimens and specimens that included mixtures of sand and clay. Results indicate that the drained friction angle of Ottawa sand decreases from 36.2° to 20.2° and the drained cohesion increases from 0 to 7.7 kPa because of the replacement of 40% of the sand with clay. Examples that target the design of square footings and the stability of infinite slopes indicate that the allowable bearing capacity of footings and the factor of safety of slopes decrease significantly as the percentage of fines is increased from 0 to 40%. © 2015 W. S. Maney & Son Ltd.