摘要
土压平衡盾构在富水粗粒土地层中掘进时易发生喷涌现象,仅采用泡沫改良往往无法满足渣土抗渗性要求,膨润土泥浆虽能增强泡沫堵水效果,且具有一定的稳泡作用,但在水压较高、颗粒较粗的条件下泥浆容易流失,需引入高分子聚合物进行组合改良。针对泡沫-膨润土泥浆-聚丙烯酰胺(PAM)组合改良砾砂,开展坍落度试验与渗透试验。试验结果表明:黏性较小的泡沫与膨润土泥浆难以稳定赋存在砾砂的较大孔隙中,改良土呈散粒状且易析浆、析泡沫;加入高分子聚合物能将土颗粒聚团并减小土体内摩擦角,从而提高改良土塑性及流动性,避免析浆、析泡沫。高分子聚合物含量较低时膨润土泥浆与泡沫在渗流过程中容易流失,改良土渗透系数将在短时间内突破10^(-4)m·s^(-1),不满足盾构掘进过程中渣土渗透系数小于10^(-5)m·s^(-1)的持续时间要大于90 min的抗渗要求;增加高分子聚合物含量能延长渗透系数初始稳定期并显著减小渗流末期渗透系数,改良土渗透系数能长期稳定在10^(-5)m·s^(-1)以下,且高分子聚合物含量越高,渗透系数降低效果越明显。合适塑流性的组合改良土不一定具有合适的渗透性,建议盾构在富水粗粒土地层中掘进时综合评价渣土塑流性和渗透性。最后,结合光学显微镜观察试验,探究泡沫-泥浆-聚合物组合改良机理。研究可知单用泡沫或泡沫与膨润土泥浆无法有效改良试验土,高分子聚合物能增大膨润土泥浆黏度,使改良剂有效填充于土体孔隙中,且能通过减缓泡沫排液、粗化、聚并等效应来增强泡沫稳定性,改善土体塑流性与抗渗性。
During earth pressure balance shield tunneling in the coarse-grained soil stratum with rich water,water spewing often occurs,and the use of foam for soil conditioning alone cannot guarantee anti-permeability of the soil.In particular,bentonite slurry can enhance the water plugging effect and stability of foam.However,under the condition of high water pressure and coarse-grained soil,slurry is easily lost;thus,the addition of a polymer is required to condition soil.Accordingly,in this study,slump and permeability tests were carried out for foam-bentonite slurry-polyacrylamide(PAM)conditioned gravelly sand.The results indicate the difficulty for the foam and bentonite slurry with little viscosity to remain in the large pores of gravelly sand,and the conditioned soil was granular with slurry and foam loss.Whereas,with addition of the polymer,the soil particles were aggregated,the internal friction angle of the soil was reduced,the plasticity and fluidity of the conditioned soil were improved,and no slurry or foam was lost.When the polymer content was low,the bentonite slurry and foam easily was discharged from the soil,the permeability coefficient of the conditioned soil exceeded 10^(-4) m·s^(-1) in a short time.This does not meet the anti-permeability requirement that a permeability coefficient of less than 10^(-5) m·s^(-1) should be stable for more than 90 min during shield tunneling.Increasing polymer content could lengthen the initial stable period of the permeability coefficient,and significantly reduce it when permeation tended to be stable.The permeability coefficient was stable below 10-5 m·s-1 for a long time,and the higher the polymer content,the more obvious the effect of permeability coefficient reduction.The conditioned soil with suitable flow plasticity might not have suitable permeability.It was suggested that the flow plasticity and permeability of soil should be evaluated synthetically considering shield tunneling in the coarse-grained soil stratum with rich water.Finally,the foam-slurry-polymer
作者
王树英
陈宇佳
钟嘉政
令凡琳
WANG Shu-ying;CHEN Yu-jia;ZHONG Jia-zheng;LING Fan-lin(School of Civil Engineering,Central South University,Changsha 410075,Hunan,China;Tunnel and Underground Engineering Research Center,Central South University,Changsha 410075,Hunan,China;Hunan Provincial Key Laboratory for Disaster Prevention and Mitigation of Rail Transit Engineering Structures,Central South University,Changsha 410075,Hunan,China)
出处
《中国公路学报》
EI
CAS
CSCD
北大核心
2023年第8期214-224,共11页
China Journal of Highway and Transport
基金
国家自然科学基金项目(52022112)。
关键词
隧道工程
粗粒土
试验研究
组合改良剂
塑流性
渗透性
土压平衡盾构
tunnel engineering
coarse-grade soil
experimental research
combinatorial soil conditioner
flow plasticity
permeability
EPB shield
