基质吸力与黏粒含量对砂土抗剪强度的影响

Influence of Matrix Suction and Clay Content on Shear Strength of Clay Sand

当前对于非饱和土的研究,主要集中在纯砂土和纯黏土的土水特征和抗剪强度,而实际工程中,基质吸力对含黏粒砂土的抗剪强度具有显著的影响。根据实际工程中含黏粒砂土的级配,采用高岭土和细砂配制不同黏粒含量的砂土,利用5 bar压力板仪得出含黏粒砂土的土-水特征曲线,利用非饱和土四联直接仪得出不同基质吸力条件下含黏粒砂土的抗剪强度指标。研究结果表明:随着黏粒含量的增加,含黏粒砂土的残余含水率增加;随着基质吸力的增加,含黏粒砂土的抗剪强度大部分呈现增大的趋势;但当黏粒含量为15%时,随着基质吸力的增加,含黏粒砂土的抗剪强度先增大后减小,出现了"黏粒效应"。最后,从含黏粒砂土的微观颗粒结构出发,揭示了含黏粒砂土的抗剪强度主要受土体含水量的大小、颗粒之间弯月形水面的数量的多少和面积大小三方面的影响。

The current research of unsaturated soil research is focused on the pure sand and pure clay. In practical engineering,the matrix suction has a significant impact on shear strength of clay sand. According to the clay sand grading in actual engineering,the kaolinite is used in clay sand with different contents. The soil water characteristic curve of unsaturated containing clay sand could be analyzed by the 5 bar pressure plate apparatus test,on the basis of the soil and water characteristic curve,the suction control direct shear tests under different suction conditions to analyze the relationship between the matrix suction and the shear strength of unsaturated clay sandy soil.The results show that the residual moisture content of clay sand is increasing with the increase of clay content. With the increase of the matrix suction,the shearing strength of the clay sand mostly is increasing. When the percentage of the clay sandy soil is 15,with the increase of the matrix suction,the shearing strength of the clay sandy soil is increasing firstly,then decreasing,which is a ＂clay effect＂. This shows that the increase of the matrix suction dose not have effect on the increase of the shear strength in all time for the clay sandy soil. Finally,from the microscopic analysis of soil particle structure,the shear strength of clay sand is decided by the size of the soil water content,the quantity and size of the meniscus of water between soil particles.