Direct Tension Test on Compacted Sand-Clay Mixture with Different Ratio of Sand to Clay and Factors Affecting Its Measurements

In geotechnical engineering practice, the tensile strength of soil is generally ignored during design and safety assessment. Compared to the compressive strength of soil and the shear strength of soil, the tensile strength of soil is too small to be considered. Furthermore, uncommon testing apparatuses and techniques for measuring the tensile strength of soil and uncompleted theories have not been adequately developed and studied. Currently, the methods of measuring the tensile strength of soil can be categorized into direct and indirect methods. Compared to direct method, the indirect methods, such as the Brazilian test, the split tension test, double punch test, unconfined penetration test, etc. have been developed. All the indirect tension tests have a defect that the orientation of tensile strain cannot be directly obtained during experiment. Therefore, in this study, direct tension method is modified and the tensile behavior of compacted lightly cemented sand is examined. The modified direct tension apparatus was developed. To examine the geometric influence in direct tension test, three affecting factors, the effect of the specimen sizes, the effect of boundary condition and the effect of the clay-sand mixed ratios, respectively, were discussed in this study. First affecting factor was examined by changing the height of specimen, 3 cm, 6 cm, 9 cm and 12 cm, respectively. Second affecting factor was examined only by triangular wedges with three different angles, 10°, 20° and 30°, respectively. The higher the triangular wedge angle, the less cross sectional area is, and the higher grabbing ability is. Therefore, the specimen size and shape should be discussed. The last affecting factor was examined by 4:1 and 3:1 mixed ratio of sand to clay by weight. All the specimens were prepared at its maximum dry density and optimum moisture content, and compacted by the tampers which fit the shape of the specimen. In addition, this direct tension apparatus was modified firstly in this study due to the unsolved problems in the previous study, such as the non-uniform compaction, the friction of guide rails and the eccentric problem during the experiment. From the results of the direct tension tests, the specimen with different fines contents could strongly influence their behavior at different geometric conditions. Besides the strength analysis, the energy analysis was used to describe the tensile behavior of soil.