上软下硬复合地层盾构渣土改良试验研究

Experimental Study on Improvement of Ground Conditioning for Shield Tunneling in Soft-Upper and Hard-Lower Composite Strata

土压平衡盾构穿越上软下硬复合地层时存在刀盘“结泥饼”、排渣不畅和刀具磨损等难题。针对以上问题,以粉质黏土-全风化花岗岩复合地层为研究对象,基于渣土改良剂的地层适应性和性能测试开展不同地层渣土改良室内试验。研究泡沫剂和膨润土泥浆等渣土改良剂及其改良方法对上软下硬地层的改良效果,以获得土压平衡盾构在复合地层中的渣土改良方案及改良剂合理添加比。结果表明:(1)采用浓度为3%的泡沫剂溶液和配合比1∶8的膨润土泥浆进行联合改良可获得良好效果;(2)粉质黏土地层采用泡沫剂进行改良,渣土坍落度随泡沫添加比增加而增大,抗剪强度、黏聚力、内摩擦角和渗透系数随之减小,改良剂合理添加比为19.7%~22.8%;(3)全风化花岗岩地层采用泡沫剂和膨润土泥浆进行联合改良,可有效改善渣土流塑性和抗渗性,当采用全泡沫改良时,合理添加比为22.2%~28.7%,当采用泡沫与膨润土泥浆联合改良时,合理添加比为24.3%~31.5%。现场应用及施工效果反馈表明,采用以上改良方案可有效改善渣土流塑性,盾构推力、刀盘扭矩以及刀具磨损均有显著改善。

When an earth pressure balance shield passes through soft-upper and hard-lower composite strata,it faces challenges such as cutterhead“mud cake”formation,inefficient muck removal,and tool wear.To address these issues,this study focused on silty clay-completely weathered granite composite strata and conducted laboratory tests on ground conditioning in different strata based on the adaptability and performance of soil conditioners.The study explored the effects of soil conditioners,such as foam agent and bentonite slurry,as well as their improvement methods on soft-upper and hard-lower strata,to determine an optimal ground conditioning scheme and the appropriate addition ratios for shield tunneling in composite strata.The results showed that:(1)Combining a 3%concentration foam agent solution with bentonite slurry at a 1∶8 ratio yielded good results.(2)The silty clay strata were improved by foam agent.The slump of the muck increased with the foam addition ratio,while the shear strength,cohesion,internal friction angle,and permeability coefficient decreased.The optimal addition ratio of the soil conditioners was between 19.7%and 22.8%.(3)The completely weathered granite strata were improved using a combination of foam agent and bentonite slurry,which effectively enhanced the flow plasticity and impermeability of the muck.When using only foam,the optimal addition ratio was between 22.2%and 28.7%,while the combined foam and bentonite slurry method required a ratio of 24.3%to 31.5%.Field application and construction feedback showed that the above improvement scheme effectively enhanced the flow plasticity of the muck,and significantly improved the shield thrust,cutterhead torque and tool wear.