渣土改良剂对黏土液塑限影响及机理分析

针对盾构穿越黏土地层时渣土改良剂类型和添加量难以确定的问题,进行了液塑限测定试验.通过研究不同改良剂对土样液塑限的影响特征,确定改良剂的地层适用性,对比分析分散剂对不同土样的改良效果;通过黏土颗粒Zeta电位测定和颗粒间互斥能的分析,探究分散剂的作用机理.研究表明:在黏性较大的渣土中,单独使用阴阳离子复配型泡沫剂难以达到理想的改良效果;絮凝剂能够增大黏土的液限和塑性指数,增加黏土的抗剪强度,而分散剂能够减小黏土的液塑限和塑性指数,减小黏土的抗剪强度,因此分散剂适用于黏土地层;相对于高岭土,由于高蒙混合土(高岭土与蒙脱土质量比=1∶1)和蒙脱土结合水含量高,需要更多分散剂和作用时间,改良作用才能稳定发挥;当分散剂添加至一定量后,改良效果基本不再变化;随着分散剂添加比的增加,蒙脱土、高蒙混合土、高岭土的Zeta电位减小(即负电荷增多)后趋于稳定,黏土颗粒聚团的位垒Vmax/R增高,即颗粒间排斥能增加,因此黏土利于分散.

Effect of soil conditioner on Atterberg limits of clays and its mechanism

To select ideal type and content of soil conditioner in clay formation, the Atterberg limits of clay were measured. The applicability of soil conditioners was determined and the effects of dispersant on different clays were compared by analyzing the influence of soil conditioners on the clays. The Zeta potentials with different dispersant contents and repulsive energy among particles were also measured to analyze action mechanism of the dispersants. The results show that it is difficult to achieve ideal effect only by using anionic-cationic foam individually. The flocculant increases the liquid limit and plasticity index of the bentonite, so it also contributes to the increase of the shear strength. In the contrary, the dispersant decreases the liquid limit and plasticity index of the clay, thus it can decrease the shear strength, which makes the dispersant more suitable for clay conditioning. Compared with kaolin, the mixture (the mass ratio of bentonite to kaolin is 1:1) and bentonite require much time and dispersant due to high content of bonding water in bentonite. The effect of dispersant keeps unchanged after the injection ratio of dispersant reaching a certain value. With the increase in dispersant content, the Zeta potential decreases (i.e., negative charge increased) and tends to a lower constant in bentonite, kaolin and their mixture. The mean barrier potential V_max/R of clayey particles get higher with more dispersant, thus it is more difficult for the clays to be agglomerated and easier to disperse.