红黏土工程性状的干湿循环效应试验研究

Experimental investigation on engineering behaviors of red clay under effect of wetting-drying cycles

为研究湿热多雨气候条件诱发的干湿循环过程对红黏土长期性能的影响规律,对制样过程中干湿循环含水率变化幅度控制技术进行改进,制备不同干湿循环次数以及含水率变化幅度试样。利用固结排水三轴剪切与压缩试验,研究了干湿循环次数与干湿循环含水率变化幅度对压实红黏土工程性状的影响规律。结果表明,压实红黏土的黏聚力c与内摩擦角φ均随干湿循环次数N的增加而衰减,首次干湿循环之后衰减效应最显著,其后较弱并趋于稳定,φ的衰减程度小于c,且在低围压下的抗剪强度随干湿循环衰减更加显著;压缩模量E_(1-2)随N的总体衰减规律与强度参数类似,但衰减幅度小于c而大于φ;随着干湿循环含水率变化幅度增大,压实红黏土c与E_(1-2)略有减小,φ基本不变,压实红黏土含水率在ω_(opt)±4%变化范围内,具有相对稳定的力学特性。该研究表明,红黏土不宜直接用于填筑路床与边坡表层的填料,可以作为上下路堤堤心的填料,但必须采取防排水工程措施与边坡防护措施。

To investigate the influence of wetting-drying cycles in seasonal variation on the long-term performance of red clay,the traditional sample preparation method is improved,and the moisture content variation of compacted soil during wetting-drying cycles is controlled in the regime of saturation from the optimum water content oω_（opt） to full saturation.Considering the dripping humidification,the ω_（opt） ± 2% and oω_（opt） ± 4% water content samples experienced by the wetting-drying cycles were prepared.The consolidated drained triaxial shear test and compression test were conducted to analyze the effects of wetting-drying cycles and moisture change amplitude on the engineering properties of compacted red clay.The results show that cohesion c and internal friction angle φ decrease with increasing cycle number N,and the decrease is significant in the first wetting-drying cycle and then becomes stable.However,the rate of decrease of φ is less than that of c,and the decrease of shear strength under low confining pressure is more drastic than that under high confining pressure during the cyclic wetting-drying process.Compression modulus E_（1-2） also decreased with increasing N and the decrease rate is less than that of c but larger than that of φ.Similarly,c and E_（1-2） decrease slightly with increasing moisture change amplitude of the cyclic wetting-drying compacted red clay samples.At the moisture content in range of oω_（opt） ± 4%,the compacted red clay shows relatively stable mechanical behavior.It is suggested that the red clay should not be directly used as the backfill material,but can be used as the backfill material of the embankment core,if the drainage and slope protection measures are taken effectively.