【作者】 扈世民；

【导师】 王梦恕； 张顶立；

【作者基本信息】 北京交通大学 ， 地下工程， 2012， 博士

【摘要】 黄土围岩工程特性成为隧道多类问题的根源,采用理论解析、实验室研究、数值模拟与现场工程应用相结合的方法对大断面黄土隧道围岩变形特征及控制技术进行深入研究。以典型黄土隧道为依托进行现场应用与反馈,解决围岩变形特征、失稳机理、空间位移及变形控制等关键问题,进行了大量的研究工作：(1)黄土地区隧道工程主要修建在低含水率Q2、Q3地层,其工程特性表现为显著结构性与垂直节理发育；采用室内固结排水三轴试验对黄土结构特性进行研究,将综合结构势mP由单轴应力状态应用到三轴应力状态实现黄土结构性的定量化；采用弹性圆孔应力集中分析垂直节理形成的力学机理,重力引起的水平拉力是产生垂直节理的原因；综合分析黄土工程特性,选取可考虑结构性与垂直节理双线型遍布节理模型。(2)基于黄土围岩工程特性,隧道开挖引起的围岩变形具有自身特点,具体表现在：突变性、变形值大、持续时间长、易形成地表裂缝；隧道开挖引发的应力调整经历了复杂加载与卸载过程,掌子面空间效应影响范围为2倍洞径；开挖引发围岩力学响应以洞周最为强烈,沿开挖半径向围岩深部发展；影响黄土隧道围岩变形因素主要包括黄土工程特性、地应力环境、隧道埋深、隧道断面形状与尺寸、地下水与施工组织管理等。(3)通过对大断面黄土隧道失稳案例调研与数值分析,剪切滑移与弱抗拉强度成为黄土隧道松动塌落主要原因；无支护条件下黄土围岩破坏过程表现：局部裂隙产生→局部裂隙扩展→裂隙急剧贯通→残余强度四个阶段；黄土围岩首先沿小主应力方向形成剪切破坏,随着荷载的分级施加,边墙处剪切裂隙贯通形成掉块,进而拱部围岩因边墙临空而显著下沉,拱顶松动塌落是在边墙剪切滑移破坏基础上出现；围岩深部存在环向应力升高区,承担着自重与外部土体荷载形成压力拱,自洞壁向围岩深部依次可分为：松动区→压力拱→原岩应力区。(4)通过模型试验得出型钢与喷网联合支护有效控制了黄土围岩变形发展,拱顶应力松弛得到缓解；选取拱顶部位实测数据绘制围岩与支护特征曲线,型钢与喷网联合支护结构提供的最大支护反力为围岩压力的70%,相应的拱顶沉降为5.1mm。与喷网联合支护结构起到了预想的限制效果,减小了有害松动的发生。(5)由于黄土特殊工程性质,大断面隧道深部围岩变形模式表现为围岩拱部竖向位移弱化较慢而边墙水平位移弱化较快,水平收敛普遍小于拱顶沉降,基本符合Boltzmann函数；支护结构合理调整围岩应力分布,有效改善应力集中；上台阶支护对控制拱顶沉降起关键作用,施工中应引起足够重视；支护封闭成环对整个隧道变形起到明显的控制效果,有利于开挖后围岩位移场的稳定。(6)采用数值方法对黄土围岩纵向变形及控制措施进行分析；临空面的存在使得掌子面挤出变形趋势显著,总体上边墙纵向位移小于拱顶,纵向位移与弹性模量成反比；对于纵向先期位移的预测结果,Panet经验公式为25%,Hoek经验公式为30%,数值计算结果为33%；预留核心土有效控制掌子面纵向挤出变形,使得掌子面土体由不利的双向应力状态变为三向应力状态,对于大断面黄土隧道台阶法施工,核心土的预留长度控制2R/3左右较为合适。(7)采用数值计算与理论分析绘制适用于大断面黄土隧道围岩与支护特征曲线；利用收敛约束法分析现行支护参数的适应性,支护结构最大反力大于围岩与支护特征曲线的平衡点应力值,满足适应性要求(8)基于正交试验设计对支护时机与刚度进行优化,选取合理的优化指标从而计算支护结构的优化组合；数值计算表明优化后支护结构组合具有较好适应性；根据数值计算结合现场实测制定大断面黄土隧道深、浅埋位移控制基准。更多还原

【Abstract】 The characteristics of loess are source of tunnel mult-class problems. The deformation characteristics and control measures of large-section loess tunnel have been researched deeply by using theoretical analysis, laboratory model test, numerical simulation and field measurement methods. According to field application and feedback of typical loess tunnel, the surrounding rock deformation characteristics, failure mechanism, spatial displacement and deformation control have been solved. Specific findings are highlighted below:(1)Loess tunnels were usually built in Q2or Q3loess strata which are low moisture content strata. The engineering properties of loess are significant structural and vertical joints. The loss engineering characters was analysis laboratory triaxial test, and the potential of integrated structure which is from uniaxial stress state is applied to triaxial stress state, the loess structural quantitative has been realized by applying the uniaxial stress state to the triaxial stress state. According to the stress concentration of the elastic hole, the vertical joints are caused by level tension. Comprehensive analyzed of the engineering properties of loess, Bilinear Strain-Hardening/Softening Ubiquitous-Joint Model is selected to consider the type of structural and vertical joints.(2)Based on the characteristics of loess, the deformation of wall rock is shows concretely as follows:concrete manifests of mutagenicity, the large deformation, long duration, easily formation of surface cracks; The stress adjustment experiences a complex loading and unloading process during the excavation progress and the range of tunnel face space effect is2times diameters; The mechanics respond caused by the excavation is most strongly at cavern perimeter and develops along tunnel radius; The influencing factors of deformation in loess mainly include the engineering properties, environmental stress, tunnel depth, tunnel cross-section shape and size, and groundwater and construction management, etc.(3)According to the investigation and numerical analysis of tunnel collapse in large section of loess tunnel, shear slip and weak tensile strength become the main reason for tunnel failure case. Under no-support conditions of the loess surrounding rock failure process performance:local fracture produced→local fracture extended→facture rapid transfixed→residual strength. The wedge slip body is firstly performed on the side-wall parts along direction of the minimum principal stress, then spread for vault and arch bottom and the integrity of surrounding rock is undermined. As the weak tensile strength, the lossening collapse is occurred on the vault. The tangential stress increased area is existed in the deep rock, the part rock bears weight with external load soil pressure arch formed a significant effect, since the rock wall can be divided into loose zone→pressure-arch→initial stress area.(4)According to the model test, the steel and spray net support is the effect way which can control the development of loess surrounding rock deformation and stress relaxation. The surrounding rock and support characteristic curves in vault show that Steel and spray net support provides the maximum support reaction force for70%of rock pressure and corresponding vault settlement5.1mm. The combined support structure of the steel and spray net plays the expected limit and reduces the occurrence of harmful loose.(5)Due to loess engineering properties, the deformation model of large-section loess tunnel show that the vertical displacement of crown slowly weakening and the rapid weakening of the horizontal displacement. The horizontal constringency is generally less than the crown settlement, and the law is in accordance with the Boltzmann function. The support of the upper bench plays an important role in the control of crown settlement, and the supporting structure reasonably adjusts the stress distribution and improves the stress concentration effective; The support of the upper bench plays an important role in the control of crown settlement, it should be pay more attention in the construction; The ring closure of support produces obviously restrain effect on the tunnel deformation and is beneficial to the stability of displacement field.(6)The longitudinal deformation of loess surrounding rock is analysis by site numerical analysis; the extrusion deformation trend is significant for the existence of free face. On the whole, The longitudinal deformation of the crown is smaller than the wall; For the forecast of longitudinal deformation, the empirical formula of Panet is25%, Hoek is30%and3D calculation is33%; The range of free face are effectively reduced and beneficial for the tunnel face stability; the suitable reserved length of core soil is2R/3.(7)The ground and support reaction curve of large section of loess tunne is drawn by the numerical calculation and theoretical analysis. The initial support adaptation is studied by convergence-confinement method. The maximum reaction force is larger than the stress values of the equilibrium point, so it meet the requirements for adaptability. (8)Based on orthogonal design for the optimization of supporting opportunity and stiffness, a reasonable optimal indicator is selected and the combination is calculated. It shows that better adaptability to optimize the combination. The displacement control benchmark of large section loess tunnel deep and shallow has been established based on in-situ monitoring and numerical analysis.更多还原