Large-Scale Experimental Investigation of Strength Properties of Composite Clay

Composite clay is a mixture of clay and coarse-grained materials which can particularly be applied in practice as the core of earth dams and the platform for construction of buildings and roads. They are especially used when the appropriate materials are not available or the present mixed soils have not the required properties. The soil strength measurement for various types of soils including the cohesive and gravelly soils is an important issue in geotechnical engineering. Therefore, this paper is intended to compare the resistance of samples with different percentages of clay and gravel with a maximum grain size of 19 mm by performing large-scale direct shear tests. The samples consisted of clay and gravel with the gravel content of 30%, 50%, 70% (by dry weight of clay), respectively. First, to ensure the required compaction, modified Proctor compaction tests were performed. Then, large scale direct shear tests were conducted on the samples to measure the shear strength properties of soil. The results clearly reveal that by increasing the percentage of gravel in the mixture, the maximum dry density increased and the optimum moisture content decreased. It was also observed that increasing the gravel content leads to an increase in the soil internal friction angle and shear strength.