盾构下穿仑头海高水压粉细砂地层渣土改良试验研究

Experimental Study on Improvement of Residual Soil in Silty Fine Sand Stratum with High Water Pressure in Luntouhai Under Shield

为解决土压平衡盾构穿越高水压粉细砂地层时易喷涌、开挖面塌陷等技术难题,依托广州地铁12号线下穿仑头海盾构工程,通过筛分试验、改良剂性能试验、砂层喷涌模拟装置设计及现场工程验证等手段,对高水压粉细砂地层下土压平衡盾构喷涌防控技术开展研究。试验研究成果:(1)针对本工程粉细砂地质特性,确定合理改良剂品种及配比,优选了膨润土膨水比、膨化时间及掺入比;(2)基于相似理论,设计了一套模拟砂层喷涌发生、评价装置,直观反映不同工作压力下改良剂改良砂样的效果,为渣土改良试验提供技术支撑;(3)通过评估喷涌发生装置砂样喷出的流速v、水平距离ΔL等参数,确定了特定级配砂样所需改良剂的相关配比及掺入量,并形成了防喷涌渣土改良实施方案。结合实际盾构穿越仑头海砂层运用效果,指导现场膨润土改良参数控制,验证了膨润土相关参数及喷涌模拟装置可靠性,避免了盾构穿越富水砂层喷涌风险。

In order to solve the technical problems of gushing and collapse of excavation surface when the earth pressure balance shield passes through the silty fine sand stratum with high water pressure,this paper studies the gushing prevention and control technology of earth pressure balance shield under the silty fine sand stratum with high water pressure by means of screening test,modifier performance test,sand layer gushing simulation device design and field engineering verification.Test and research results:1)according to the geological characteristics of silty fine sand of the project,determine the reasonable variety and proportion of modifier,and optimize the bentonite swelling water ratio,expansion time and mixing ratio;2)Based on the similarity theory,a set of device for simulating the occurrence and evaluation of sand gushing is designed to intuitively reflect the effect of modifier on sand samples under different working pressures,so as to provide technical support for residue soil improvement test;3)By evaluating the velocity v and horizontal distance of sand sample ejected from the gushing deviceΔL and other parameters,the relevant proportion and mixing amount of modifier required for specific graded sand samples are determined,and the implementation scheme of anti gushing residue improvement is formed.Combined with the actual application effect of shield tunneling through Luntou sea sand layer,guide the on-site bentonite improvement parameter control,verify the reliability of bentonite relat-ed parameters and gushing simulation device,avoid the gushing risk of shield tunneling through water rich sand layer.