| In the theory of soil mechanics, strength of soil generally refered to the compressive strength and shear strength. Since the new century, the tensile strength of soil gradually caused the attention of scholars with the deepening of the research in the geotechnical engineering field and the engineering construction. In fact, the destruction of many earth structures related to the tension of soil: such as hydraulic fracturing phenomenon, the damage of high earth-rock fill dam core wall, and the tensile fracture in the airport or the road surface, etc. Further study of tensile properties of soil had important theory value and practical significance of improving the soil strength theory and guiding the engineering practice.A new stress type axial tensile device that was able to accurately measure tensile strength and tensile displacement of soil mass had been designed. Unsaturating “bao LAN loess” as test object, by using the latest design of soil tensile test device, the proper size of the sample, the tensile properties of undisturbed loess, the tensile properties of remolded loess, and the comparison and analysis of the tensile strength of undisturbed loess and remolded loess were mainly studied. Through the collection and analysis of test datas, the main conclusions were as follows:(1) A horizontal axial tensile tester was developed, the sample were imposed stress by adding weight, tensile displacement was read by the dial indicator connected to the sample. By installing the adjustable bolt rod, indicating the axis, using smooth glass plate and designing of the fixture of three sides which were flexible, etc., the current defects of geotextile tensile tester had been overcome. Sample always in the axial tensile state were ensured, sample damaged in the fixture end were prevented, the frictional resistance at the bottom was eliminated. The mould of making sample was cuboid which was stainless and grooved, cuboid specimen was made of 2 cm,2.5 cm,3 cm,3.5 cm,4 cm of normal section, and 2,2.5,3,3.5,4 of slenderness ratio, the mould could be repeated to use.(2) Remolded loess as the research object, through the newly designed tensile device, when dry density and moisture content of the sample were determined, it had been studied that the different sample sizes(different cross section and different slenderness ratio) effected on the tensile strength and the tensile displacement, the test datas for discrete analysis were made through mathematical methods, difficulty level of the actual sample preparation had been also considered, the article obtained that the reasonable size of sample was normal section of a = 2.5 cm length, and slenderness ratio of l/a = 3.(3) According to the reasonable sample size, uniaxial tensile test had been done for the undisturbed loess, the different moisture content of samples was got through the water distribution. The test got Tensile stress- displacement curve of the undisturbed loess. When the dry density was determined, undisturbed loess tensile strength decreased with the increased of moisture content, they were power relationship. The tensile strength of undisturbed loess and direct shear cohesion were linear relationship. By the observation of test process, the failure mode of undisturbed loess was analyzed.(4) According to the reasonable sample size, uniaxial tensile test had been done for the remolded loess, under the existing test conditions, the influence that a full moisture content and dry density to the tensile properties of remolded loess was got through the expansion of moisture content and the maximum dry density range. After finished the experiment data analysis, tensile stress- displacement curve of remolded loess had been gotten, the influence of dry density and moisture content on the tensile properties had been got. The article showed that the tensile strength of remolded loess had a peak value along with the change of moisture content, the moisture content that the peak corresponded to was ω=14.0%. The exponential relationship between the tensile strength of remolded loess and dry density had been obtained, the experiment also showed that the limit displacement had a linear relation with the dry density, the tensile strength of remolded loess had a linear relation with the direct shear cohesion. Through the observation of the experiment, the influence of moisture content to the sample failure pattern had been analyzed when moisture content was higher or below than the plastic limit.(5) The comparative study of the tensile strength of undisturbed loess and remolded loess had been carried on. When the sample had the same dry density and moisture content, tensile strength of undisturbed loess was much bigger than the tensile strength of remolded loess. The concept of differential value of tensile strength had been introduced, the experiment showed that a power function relationship existed between the remolded loess and moisture content, and that the tensile strength of undisturbed loess increased with the increased of differential value of tensile strength. |
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