Assessment of Direct Tension Tests on Compacted Sand-Clay Mixtures

The common laboratory tests for determining the tensile strength of soils can be categorized into direct and indirect methods. For direct methods, there are no standard testing apparatuses or procedures to measure the tensile strength of soils. This paper presents a modification of a direct tension apparatus and its test results on compacted soil. The major factors affecting tensile strength measurements include the size of the specimen, tensile displacement pulling rate, and the shape of the tensile apparatus mold. The effect of the tensile displacement pulling rate and the behavior of crack propagation due to the shapes of the direct tension mold were investigated. Three wedge types (triangular, trapezoidal, and rectangular) were used in the tests. Particle image velocimetry (PIV) technique was adopted to capture the crack propagation along with the development of tensile stress and to evaluate the wedges suitability. In addition, tests were conducted to measure the tensile strength of soils with different specimen depths and cross-sectional areas. The results show that there was no significant influence of the displacement rate associated with tensile force, crack propagation, and maximum tensile force. Triangular wedges are the best pick for direct tension tests. Tensile strength was found to be size dependent; the cross-sectional area and specimen depth govern the tensile strength of compacted soil mixture. However, it was found that the tensile strength was close to a constant when the area ratio exceeds a critical value.