孙萍萍, 张茂省, 谷天峰, 等.2020.吸力可控条件下的北方红黏土蠕变特性[J].工程地质学报, 28(3):500-509.doi:10.13544/j.cnki.jeg. 2019-457.
    引用本文: 孙萍萍, 张茂省, 谷天峰, 等.2020.吸力可控条件下的北方红黏土蠕变特性[J].工程地质学报, 28(3):500-509.doi:10.13544/j.cnki.jeg. 2019-457.
    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.

    吸力可控条件下的北方红黏土蠕变特性

    CREEPING CHARACTERISTICS OF NORTHERN RED CLAY UNDER CONTROLLED MATRIC SUCTIONS

    • 摘要: 北方红黏土又称三趾马红土,在黄土高原地区呈不连续状分布于黄土之下,为典型的致滑地层。红黏土遇水后强度降低、变形增大从而构成滑动面的过程,与红黏土特别是非饱和红黏土的蠕变特性息息相关,然而相关的研究多集中于南方红黏土。我国南方和北方红黏土的工程特性差异较大,不能等同对待。本文以陕西蓝田典型的北方红黏土为研究对象,借鉴控制吸力的非饱和土研究方法,在吸力分别为0,100 kPa和200 kPa条件下分级施加围压,开展了吸力控制条件下的三轴蠕变试验,研究非饱和红黏土的蠕变特性和长期强度。试验表明,红黏土具有明显蠕变特性,不同围压下的应力-应变曲线变化特征相近,均呈现幂函数或对数函数变化特征。当围压和荷载一定时,蠕变量随吸力的减小而增大,稳定时间随吸力减小而增长。吸力越小土体的蠕变性越强,其屈服强度也较小,饱和红黏土(吸力为0)的长期强度比吸力为200 kPa时的红黏土长期强度降低了约50%,说明含水率增大会增大滑带红黏土的蠕变量,促使滑坡的形成,本研究可为红黏土致滑机理研究提供基础。

       

      Abstract: 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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