带压环境下泥浆-泡沫组合改良级配不良砂剪切特性研究  

Shear behavior of slurry-foam-conditioned poorly graded sand under pressure

作　　者：王树英[1,2] 钟嘉政 倪准林 郑响凑 WANG Shu-ying;ZHONG Jia-zheng;NI Zhun-lin;ZHENG Xiang-cou(School of Civil Engineering,Central South University,Changsha,Hunan 410075,China;College of Civil and Transportation Engineering,Shenzhen University,Shenzhen,Guangdong 518060,China)

机构地区：[1]中南大学土木工程学院,湖南长沙410075 [2]深圳大学土木与交通工程学院,广东深圳518060

出　　处：《岩土力学》2024年第10期2879-2888,共10页Rock and Soil Mechanics

基　　金：中国博士后科学基金(No.2023TQ0382)。

摘　　要：盾构穿越富水砂性地层时易出现排渣不畅或喷涌等风险,仅采用泡沫改良往往无法有效改善级配不良渣土的流动性与抗渗性,归因于泡沫易消散和流失,故须引入膨润土泥浆进行组合改良。正确认识土舱压力环境泥浆-泡沫组合改良级配不良砂土的剪切大变形行为有助于优化满足盾构安全掘进的渣土组合改良方案。因此,开展了泥浆-泡沫组合改良级配不良砂土的加压十字板剪切试验,研究结果表明:在土舱压力环境下,组合改良砂土的初始孔隙比和饱和度随泥浆注入比(bentonite injection ratio,简称BIR)增加而增大,有效应力降低,进而导致峰值强度和残余强度降低;然而剪切强度的剪切率相关性和有效内摩擦角对BIR的敏感性较弱;BIR增加还使大变形后改良砂土的屈服应力有所降低。此外,对比常压下流动性相似的3类不同改良砂土带压剪切大变形行为,表明带压环境下提高BIR或泡沫注入比(foam injection ratio,简称FIR)均可提高孔隙比且减小有效应力,但相较于纯泡沫改良砂土,组合改良砂土具有更低的有效应力和剪切强度。该类级配不良砂土的合适组合改良参数为FIR=20%、BIR=10%~15%。最后,细观成像结果揭示了膨润土对改良砂土剪切强度的双重削弱作用:(1)吸附砂土颗粒表面,降低颗粒间摩擦力;(2)延缓泡沫衰变,使得小粒径气泡较均匀分布于孔隙中,进而有效削弱土骨架强度。During an earth pressure balance shield tunneling in water-rich coarse-grained stratum,muck spewing or discharge stagnation often occurs.Only foam conditioning cannot improve the fluidity and anti-permeability of poorly graded muck due to foam dissipation and loss.Therefore,bentonite slurry must be added.Understanding the large shear deformation of slurry-foam-conditioned poorly graded sand under chamber pressure can optimize the conditioning scheme to ensure safe tunneling.In this study,a series of pressurized vane shear tests on slurry-foam-conditioned poorly graded sand was conducted.The results show that increasing the bentonite injection ratio(BIR)raises the initial void ratio and saturation of conditioned sand under pressure,resulting in a decrease in effective stress,peak strength,and residual strength.However,the shear-rate dependence of shear strength and effective internal friction angle are found to be insensitive to BIR.Moreover,increasing BIR reduces the yield stress of the conditioned sand after large deformation.A comparison of the large shear deformation under pressure of three types of conditioned soils with similar workability at atmospheric pressure indicates that increasing the slurry or foam injection ratio can enlarge the void ratio and reduce the effective stress under pressure.Notably,slurry-foam-conditioned sand exhibits lower effective stress and shear strength than foam-conditioned sand.The suitable conditioning parameters for testing poorly graded sand are FIR=20%and BIR=10%–15%.Microscopic images reveal the dual weakening effect of bentonite on the shear strength,including the bentonite adsorption on the surface of sand particles to reduce inter-particle friction and the deceleration of foam degradation,leading to a uniform distribution of small-size bubbles in pores and effectively weakening the soil skeleton strength.

关 键 词：泥浆-泡沫组合改良砂土 泥浆注入比 加压十字板剪切试验 剪切强度特性 强度削弱机制 

分 类 号：TU41[建筑科学—岩土工程]