原状黄土的反压饱和法试验研究

Experimental Study on the Back Pressure Saturation Method of Undisturbed Loess

含水量是黄土液化特性研究中的一个至关重要的参数,对原状黄土进行充分饱和是饱和黄土动三轴试验中一个不可回避的课题。以WF公司生产的WF12440型空心圆柱扭剪仪为实验平台,运用反压饱和法,对室内原状黄土进行了饱和试验研究。该仪器提供3种不同加压方式增加围压和反压(孔压),即手动加压、自动加压和线性持续加压,通过检测孔隙压力系数B值是否达到0.95以上来判断黄土是否完全饱和。试验表明,即便是初始饱和度较低的原状黄土,也可以采用反压饱和法,在较短的时间内使孔压系数B值达到0.95以上,实现完全饱和,具体可以采用线性连续加压方式;初始压力差,即围压和反压之差一般可设为10 kPa,起始围压也设为10 kPa,太大或太小都会对试样造成破坏;如果孔压在1分钟内的变化值小于围压和反压之间压力差的5%,则认为孔压稳定,即可进行B值检测。

Water contents play an important role in study of liquefaction of loess.Saturation of undisturbed loess samples is an inevitable step in the liquefaction study.Taking WF12440 hollow cylinder apparatus as a testing platform,the back pressure method is used to saturate loess fully.The apparatus provides 3 ways to increase confining pressure and back pressure,i.e.manual stepping,automatic stepping,and continuous ramping.The pore water pressure parameter B is automatically checked to see whether the loess is fully saturated.Testing results show that even for undisturbed loess samples with low initial saturation degree,the back pressure method can be used to make B reach 0.95 and fully saturate the samples.The continuous ramping is the most efficient and convenient way,where the initial pressure difference of 10 kPa and initial confining pressure of 10 kPa should be kept.Otherwise,the samples could be damaged.If the change of pore pressure in one minute is less than the 5% of difference between the cell pressure and the back pressure,the pore pressure is considered stable and B value can be checked.