Sun Pingping, Zhang Maosheng, Gu Tianfeng, et al.2020.Creeping characteristics of northern red clay under controlled matric suctions[J].Journal of Engineering Geology, 28(3):500-509.doi: 10.13544/j.cnki.jeg.2019-457.
    Citation: Sun Pingping, Zhang Maosheng, Gu Tianfeng, et al.2020.Creeping characteristics of northern red clay under controlled matric suctions[J].Journal of Engineering Geology, 28(3):500-509.doi: 10.13544/j.cnki.jeg.2019-457.

    CREEPING CHARACTERISTICS OF NORTHERN RED CLAY UNDER CONTROLLED MATRIC SUCTIONS

    • The red clay in northern China is also known as the Sanzhima red clay. It is discontinuously distributed under laying loess at the Loess Plateau, where is a typical slide-prone stratum. We can usually observe the exposed red clay in the valleys. The mechanical properties of the red clay can decrease with the increase of its water content. Accordingly, its deformation can increase and the sliding can occur. It is believed that all these behavior of the red clay are closely related to its creeping characteristics. Most of the recent related studies focus on the red clay in southern China. However, the engineering properties of the red clay in the south and north of China are quite different. We cannot treat them as the same. We take the red clay in Lantian County at Shaanxi Province as an example. There is widely distributed red clay. The landslides related to loess and red clay soil are also intensively developed along the loess tableland there. We study the long-term strength and deformation characteristics of the red clay taken from the section at the Lantian County. Based on the theory of unsaturated soil mechanics, the triaxial creeping test under different confining pressures and different matric suctions are conducted. The unsaturated triaxial test apparatus, FSR-60, is used. The pressure sensor is updated to improve the accuracy and long-term stability. According to the range of the volumatric water content(from 11.4%to 22.3%) of the studied red clay, the suction is controlled as 0, 100 kPa and 200 kPa respectively in the test. The step-loading method is used. The deformation less than 0.01 mm within 1 day is taken as the criterion for stability. During the process of adding load step by step, the lasting time for each step is about 1 to 2 weeks. The test and analysis results show the follows: (1)The red clay in northern China is characterized with obvious creeping property. The changes of stress with strain under different confining pressures are similar, which obey the law of power function or logarithm function. (2)When the value of deviatoric stress is less than the failure load, the instantaneous strain is first observed, and then the deformation decreased until stable. When the value of deviatoric stress is close to the failure load, creeping deformation occurs, then the deformation accelerates until the tested sample failure. When the value of deviatoric stress is bigger than the failure load, the tested sample is quickly destroyed during the loading process. (3)When the confining pressure and load are constant, the creep deformation increases with the decrease of suction, and the lasting time for stability increases with the decrease of suction. The creep probability increase and yield strength decrease under small suction. (4)The long-term strength for the saturated red clay(with the suction of 0) is about 50%lower than that of red clay with a suction of 200 kPa, indicating that the increase of water content can increase the creep deformation of the red clay and led to the occurrence of landslides. This study can provide a basis for the study on the mechanism of landslide related to red clay at the loess plateau.
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