黄土黏附特性评价-室内试验和微观响应机制研究

Evaluation of loess adhesion characteristics-laboratory experiment and inherent microscopic mechanism

隧道在黏土地层中开挖经常会发生堵塞,以往的工程证明黄土作为一种低塑性的黏性材料容易黏附刀盘后形成堵塞,造成盾构机向前推进,严重者导致大幅增加工期。为探究西北黄土地区盾构隧道施工的黏附机理,通过搅拌黏附试验和流动度试验,研究以砂、高岭土、膨润土为添加剂对粉土的黏附性、流动性和稠度的影响。此外采用微观原子力显微镜测试探究不同黏性材料的形貌和黏附特性,得到不同黏性材料的微观高度曲线和土样表面与金属探针的黏附力曲线,从而建立以宏观试验参数特征与微观试验的定量关系。结果表明:粉土高差最大(22nm),在土壤黏附的内在影响机制中分子间作用力占据主导地位。高差极小(小于3nm)的高岭土和膨润土则创造了水膜产生初始条件,对于这些细颗粒则由水膜张力主导黏附行为。砂对低塑性粉土有很好的降黏效果,添加砂会显著降低黏附特性,增加流动性。粉土中加入高岭石和膨润土有不同的减黏效果,由于水分难以侵入高岭石的细观结构,降低了黏附特性,然而膨润土的掺入增加了混合土的液塑性极限,增大了水膜厚度,也导致黏附特性降低。稠度指数曲线表明粉土占比更多的低稠度混合土难以结块卡住刀盘但容易黏附于刀盘上,而膨润土占比更多的混合土不仅在高稠度容易引起黏附问题,在低稠度更容易吸水团聚后黏附刀盘,影响刀盘掘进效率。

Tunnel excavation in clay stratum may often lead to clogging of shield tunneling machine.It has been proved by previous projects that loess,as a low-plastic cohesive material,is also easy to adhere to the cutter head,leading to difficulty in spoil discharge or even stoppage of work.To explore the adhesion and clogging mechanism of loess during tunnel construction in the loess area of Northwest China,the effects of sand,kaolinite,and bentonite additives on the adhesion,fluidity,and consistency of silt were studied through mixing adhesion tests and fluidity tests.In addition,the microscopic AFM tests were used to explore the morphology and adhesion characteristics of different cohesive materials,and the microscopic height curves and adhesion curves of different cohesive materials were obtained to establish the quantitative relationship between the characteristics of macroscopic experimental parameters and inherent microscopic experiments.The results show that the alitude difference of silt based on the microscopic height curve is the largest(22 nm),and the intermolecular force plays a dominant role in the internal mechanism of soil adhesion.Kaolinite and bentonite with very small altitude difference(less than 3 nm)created the initial conditions for water film generation,and water film tension dominates adhesion of these fine particles.Sand has a good adhesion-reducing effect on low-plasticity silt,and the addition of sand may significantly reduce adhesion and increase fluidity.The addition of kaolinite and bentonite to silt has different adhesion-reducing effect.For the former,the risk of clogging may be reduced because water is hard to invade non-swelling kaolinite,while for the latter,the addition of the large amount of bentonite may increase the liquid and plasticity limits of silt-bentonite mixture.The rapidly expanding liquid plasticity limit increases the thickness of the water film and results in a decrease in the adhesion.The consistency index curve shows that it is difficult for the low-consistency mixed soil with more silt to agglomerate and block the cutterhead,but this mixed soil is easy to adhere to the cutterhead.While the mixed soil with more bentonite is not only easy to cause clogging at high consistency,but also more prone to adhering to the cutter head after absorbing water and agglomerating,affecting the excavation efficiency.