Research On Frozen-Thaw Behavior Affect The Mechanical Property Of Chengdu Clay

Chengdu had experienced an unusual low temperature period during the beginning of 2008. The temperature dropped to -5°C and even lower. Such period also included snow and ground frozen process. The unusual weather influenced the mechanics behaviors of rock and soil which distribute around Chengdu city, due to Chengdu clay have been found commonly on the east part of Sichuan basin, which covered more than thousands kilometers area. In order to find out the influence of the short- period freezing-thaw behavior occurs to the soil strength of Chengdu clay, The paper designed a series of experiments which frozen-thaw soil samples have been tested by different experiments and provided the related methods of data collection and data analysis, tend to accumulate some in-site experience for the future researches on the strength affecting factor of temporary frozen soil under unusual weather conditions.In the beginning, some laboratory experiments about the basic Chengdu clay physical property have been carried on, which included the water content, density, liquid limit, plastic limit, modulus of compressibility and the elastic ratio under the room-temperature condition. These data will be used for the reference when later comparison with the frozen-thaw soil sample and also as the evidence for how to explain the soil strength changing with different index changing. By the second part, it gives two important factors which are frozen period and frozen temperature to use as the experiment design factors in the later experiments.Then, the paper designed two types of shear strength tests to find out how the freezing-thaw behavior affected on the shear strength of Chengdu clay, they are tri-axial compression test and direct shear test. Four different frozen periods and three different frozen temperatures have been design and the values of C andФunder different condition have been collected. The tendencies curves have been drawn by the multiple regression analysis methods. All the curves of the tendency of shear strength index developing have been drawn and the tendencies have been analyzed. Besides, the frozen-thaw circle test has been carried on; the results have also been collected for analysis. For further explanation of the tendencies developments, the paper showed the SEM photos which were taken for the micro-structure analysis, it tried to analyze the influence on the inner structure of soil sample during the freezing-thaw process to see how shear strength changed under different test conditions. From the photos of micro-structure of Chengdu clay, it has been discovered the micro-structure before the frozen behavior is layer-structure and the micro-structure after the frozen-thaw behavior turned out to be the flocculent-structure or granular-structure, which indicate the shear strength become smaller after the frozen-thaw behavior because of the structure differences.In the end, the paper designed the unconfined compressive strength test to get the compression strength, the affect factors designs are the same with the tri-axial compression test: with four different frozen periods and three different frozen temperatures as well as one group of frozen-thaw circle strength test. The tendencies of the compression strength developed with the different frozen temperature and different frozen periods have been record and analyzed. In order to analysis in which degree the structure affect the strength of Chengdu clay, the sensitivity of Chengdu clay also been calculated to indicate the structure affect the strength of Chengdu clay in a high degree. At last, Numerical experiment was provided to simulate the deformation and failure process of soil sample by setting different parameters of two different types of soil samples which were disturbed ones and undisturbed ones ,the results of numerical simulation were successfully proved two different types of deformation and failure processes, in the hope of recording some case studies for the further numerical experiment on soil strength research.