【作者】 徐剑；

【导师】 张俊儒；

【作者基本信息】 西南交通大学 ， 建筑与土木工程（专业学位）， 2022， 硕士

【摘要】 粉质黏土是一种介于粉土和黏土之间的土类,广泛分布于我国各大地区,具有强度低、结构松散、力学性能不稳定及地域性差异等显著特征,隧道在穿越该地层时极易出现大变形及掌子面突变失稳等灾害,施工风险极高。对此,针对粉质黏土地层公路隧道大变形机理及控制技术进行研究显得尤为重要。本文依托工程大营坡隧道在穿越粉质黏土地层段出现了初期支护整体下沉及错台、地表开裂、掌子面坍塌及涌出等灾害,同时现场监测数据显示围岩变形具有变形量大、变形速度快、以竖向变形为主及受施工扰动影响大的特点。基于上述背景,文章综合采用室内试验、数值模拟和现场监测等研究手段,掌握第四系粉质黏土的工程特性,揭示粉质黏土地层公路隧道大变形机理,并提出基于含水率的大变形控制技术,研究成果可为类似隧道的设计和大变形控制提供借鉴。论文主要研究内容及结论如下:(1)开展自由膨胀率试验、三轴压缩试验及扫描电镜观察,试验结果表明,该粉质黏土无膨胀性,但表现出较强的水敏性,且含水率与力学参数之间呈现出明显的相关性,并基于SEM图像从结构演化特征的角度对该特性给出微观解释。(2)考虑含水率和埋深变化,采用数值模拟的方法研究粉质黏土地层公路隧道围岩变形特征。结果表明:含水率一定时,若含水率w≤25%,围岩变形随隧道埋深增加而线性增加,含水率达到30%后,围岩变形随隧道埋深增加而非线性指数式增加;埋深一定时,随着含水率的增加围岩变形也呈现出增大的变化趋势,尤其当含水率达到30%时,围岩变形急剧增加,产生突变,此时隧道极易发生大变形及突变失稳等灾害。(3)采用数值模拟的方法研究含水率变化对围岩-支护体系稳定性的影响,并将含水率对隧道稳定性的影响划分为四个区间,进一步揭示粉质黏土地层公路隧道大变形机理:是由于水的物理劣化作用导致围岩稳定性及地基承载力骤降,使得支护结构无法提供足够的抗力来限制围岩变形,隧道发生拱部围岩剪切破坏和拱脚地基冲切破坏而形成的大变形。(4)依托实际工程,在粉质黏土含水率w=30%的条件下,采用数值模拟的方法,研究不同支护措施对围岩变形的控制效果;以粉质黏土地层公路隧道大变形机理为指导依据,结合数值模拟研究结论,提出基于含水率的大变形控制技术,并在依托工程试验段通过现场测试数据验证了其应用效果,具有良好的工程应用价值。更多还原

【Abstract】 Silty clay is a kind of soil between silt and clay,which is widely distributed in major regions of China.It has significant characteristics such as low strength,loose structure,unstable mechanical properties and regional differences.When the tunnel is constructed in this stratum,it is very prone to disasters such as large deformation and sudden instability of tunnel face with a high risk of construction.Therefore,it is particularly important to study the large deformation mechanism and control technology of highway tunnel in silty clay soil layer.Dayingpo tunnel has experienced disasters such as overall subsidence and dislocation of initial support,surface cracking,tunnel face collapse and gushing in the section crossing silty clay soil.Besides,the field monitoring data show that the surrounding earth deformation has the characteristics of large deformation,fast deformation speed,mainly vertical deformation and greatly affected by construction disturbance.Based on the above background,indoor tests,numerical simulation and field monitoring are used in this paper to master the engineering characteristics of Quaternary silty clay,reveal the large deformation mechanism of highway tunnel in silty clay layer,and put forward the large deformation control technology based on water content.The research results can provide reference for the design and large deformation control of similar tunnels.The main research contents and conclusions are as follows:(1)The free expansion rate test,triaxial compression test and scanning electron microscope observation are carried out.The test results show that the silty clay has no expansion but strong water sensitivity,and there is an obvious correlation between water content and mechanical parameters.Based on SEM images,this characteristic is explained from the perspective of structural evolution characteristics.(2)Considering the variation of water content and buried depth,the deformation characteristics of surrounding earth of highway tunnel in silty clay layer are studied by numerical simulation.The results show that when the water content is constant,if the water content w ≤ 25%,the surrounding earth deformation increases linearly with the increase of tunnel buried depth.When the water content reaches 30%,the surrounding earth deformation increases nonlinearly and exponentially with the increase of tunnel buried depth.When the buried depth is certain,the surrounding earth deformation also shows an increasing trend with the increase of water content.Especially when the water content reaches 30%,the surrounding earth deformation increases sharply and has a sudden change.At this time,the tunnel is very prone to disasters such as large deformation and sudden instability.(3)Numerical simulation is used to study the influence of water content change on the stability of surrounding rock support system,and the influence of water content on tunnel stability is divided into four sections to further reveal the large deformation mechanism of highway tunnel in silty clay layer: the physical deterioration of water leads to the sudden drop of surrounding rock stability and foundation bearing capacity,so that the support structure cannot provide sufficient resistance to limit surrounding rock deformation,The tunnel has large deformation caused by shear failure of surrounding rock at the arch and punching failure of foundation at the arch foot.(4)Based on the actual project,under the condition where the water content of silty clay is 30%,the control effect of different support measures on surrounding earth deformation is studied by using the method of numerical simulation.Based on the large deformation mechanism of highway tunnel in silty clay layer and the conclusion of numerical simulation,the large deformation control technology corresponding to water content is proposed,and its application effect is verified by field test in the supporting engineering test section,which has good engineering application value.更多还原