老黏土地层土压盾构刀盘堵塞渣土改良效果评价方法

Evaluation method for muck conditioning of hard clay to prevent clogging in EPB tunnelling

以常州地铁2号线某盾构区间穿越老黏土地层为项目背景,对刀盘在硬塑高强度、高韧性黏土中的"堵塞"风险进行了初步评估,并设计和进行了改良渣土锥体拉拔试验,该试验方法可用于评价黏性渣土的改良效果.研究表明:黏土含水率对锥体极限拉拔强度有显著影响,含水率越高,极限拉拔强度越小;分散剂在黏土稠度指数Ic<0.75时能有效降低锥体极限拉拔强度,减小量在10kN/m^2以上;试验所用黏土在稠度指数Ic=0.5~0.75时黏附量较高,在500g/m^2以上;添加分散剂后改良渣土的黏附量明显减小,关键在于黏土与分散剂充分混合.依据试验结果及现场经验提出评价改良后黏性渣土"堵塞"风险的方案,将黏性渣土按照极限拉拔强度和黏附量划分为4个"堵塞"风险等级.

Taking the shield tunnelling of Changzhou Metro Line 2 as the project example,which passes through the hard clay layer,the"clogging"risk in hard,plastic,high strength and high toughness clay is preliminarily evaluated.The muck cone pull-out test for conditioned soil is designed and carried out to evaluate the conditioning effect of cohesive muck.The study shows that:water content in clay has a significant effect on the ultimate pulling force of muck cone,and the ultimate pulling force decreases with the increasing water content.Dispersant can effectively reduce the ultimate pulling force of the cone when the consistency index Ic<0.75,with the reduction more than 10 kN/m^2.Clayey muck is highly adhesive when the consistency index Ic=0.5~0.75,which is above 500 g/m^2.The adhesion of the conditioned clay drops significantly when the dispersant and clay are fully mixed.In addition,based on the test results,a draft for evaluating the risk of"clogging"of conditioned clay is proposed,classifying clayey muck into 4 levels of"clogging"according to the ultimate pulling force and adhesive ability.