富水砂层土压平衡盾构渣土改良技术研究

Soil Conditioning Technology for EPB Shield in Water-Rich Sandy Stratum

富水砂层土体具有流塑性差、渗透性强的特点,土压平衡盾构施工时易造成排土困难和喷涌事故。针对西安地铁10号线穿越富水砂层的土压平衡盾构工程,采用膨润土泥浆和泡沫剂改良盾构渣土,提出了改良渣土流塑性的评价方法,基于其流塑性和渗透性确定最佳改良方案,为工程提供借鉴和参考。结果表明:(1)当改良渣土塌落后无开裂或坍塌、塌落形状为梨形、塌落度为180~210 mm、塌落渣土与地面接触角θ为0°~90°时,流塑性合适,此时改良渣土的渗透系数于90 min内稳定在10-5cm/s,满足工程要求;(2)最佳改良方案为:渣土、膨润土、水三者质量比保持在200∶1∶40~200∶1.5∶44之间,泡沫剂溶液体积比浓度为2%,泡沫注入比为6%。

The water-rich sand has the characteristics of poor flow plasticity and high permeability,which is easy to cause unsmooth soil dumping and water spewing during the Earth Pressure Balance(EPB)shield construction.For the EPB shield project of Xian Metro Line 10 crossing the water-rich sandy stratum,this paper used bentonite slurry and foam agent to condition the flow plasticity and decrease permeability of sand,put forward the flow plasticity evaluation method for conditioned sand,and determined the optimum conditioning scheme with workable flow plasticity and permeability,so as to provide reference for the project.The following conclusions are drawn from the study.(1)The flow plasticity is workable when the conditioned sand after slumping has no cracking or collapse,the slump shape is pear shaped,the slump is 180~210 mm,and the contact angleθbetween the slumped sand and the ground is 0°~90°.At this time,the permeability coefficient of the conditioned sand with workable flow plasticity is about 10-5 cm/s within 90 minutes,meeting the engineering requirements.(2)The optimum conditioning scheme is to maintain the mass ratio of sand,bentonite and water between 200∶1∶40~200∶1.5∶44,with a volume specific concentration of foam agent solution of 2%and a foam injection ratio of 6%.