| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 103 === 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 apparatus and procedures to measure the tensile strength of soils. For direct tension tests, major affecting factors on tensile strength include the size of specimen, tensile pulling rate and the shape of apparatus mold.
A recent development of a direct tension apparatus and tensile strength testing on compacted soil are presented in this thesis. Firstly, the influence of the tensile pulling rate on tensile strength of soil was studied. Secondly, the behavior of crack propagation due to the shape of the direct tension mold was discussed. Three types of wedges were used in tests, including triangular, trapezoid-shaped and rectangular wedges. Using the particle image velocimetry (PIV) technique, the crack propagation along with the developed tensile stress was captured. The suitability of the wedges was then evaluated. In addition, tests measuring tensile strength of soils with different specimen depths and cross sectional areas were conducted. These affecting factors in the developed direct tension apparatus and measurement of tensile strength were discussed.
From the results of the direct tension tests, the displacement rate of the split box might had little influence on the tensile force versus displacement curve and crack propagation. Furthermore, the peak tensile force was not influenced by the tensile pulling rate. From the results of the PIV analyses, it is concluded that triangular wedges are suitable for direct tension experiments. Most importantly, tensile strength was found size dependent from the direct tension tests, where the cross sectional area could influence the tensile strength of compacted soil mixture. It is concluded that the tensile strength leads to a constant value when the area ratio exceeded a great value.
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