【作者】 师晓权；

【导师】 张志强；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2012， 博士

【摘要】 目前我国各类交通土建工程如高速铁路、公路及城市地铁等建设全面展开,穿越软弱、破碎围岩等不良地质段的隧道工程不断增加。而软弱围岩隧道的修建一直是隧道设计和施工的技术难点。鉴于此,本文对软弱围岩隧道掌子面稳定性控制及预加固技术的关联性问题,开展了全面、系统、深入的研究工作。主要工作和成果如下：(1)采用极限平衡法,建立了掌子面稳定分析水平条分模型,该模型能有效克服垂直划分的条块与加固结构体锚杆等存在交叉的缺点,并提出了掌子面锚杆加固等效压力系数ka,该系数能方便用于水平条分模型中,能较为准确地对掌子面锚杆加固效果进行模拟,基于该模型,分析了土体参数、掌子面锚杆加固强度等因素对维持掌子面稳定所需极限支护力的影响进行研究。(2)基于极限分析上限定理,建立隧道掌子失稳破坏模型,该模型能考虑未支护段及掌子面锚杆加固等预加固手段对掌子面稳定性的影响。基于该模型,分析了未支护段长度、土体参数、隧道埋深、未支护段支护力、掌子面锚杆加固强度等因素,对维持掌子面稳定所需极限支护力的影响进行研究。该模型能有效模拟隧道深浅埋不同的破坏模式,并对纵向拱效应进行模拟。(3)以围岩与支护结构相互作用为基础,建立了掌子面前方围岩变基床系数下的管棚双参数弹性地基梁有限差分力学分析模型,系统分析了隧道开挖过程中的管棚的变形、受力特征及传递荷载特性,并研究了开挖进尺、基床系数、掌子面加固强度、隧道埋深等因素对管棚作用特性的影响。(4)采用GFRP筋与混凝土粘结锚固性能试验,得出钢筋与纤维筋粘结比例系数为1.2～1.5,确定了GFRP筋最小锚固长度取为20倍筋材直径。修订了GFRP筋与混凝土间粘结滑移CMR模型中的sr、β参数,该参数与试验具有较好拟合度,具有一定的可靠度及安全度。提出了GFRP筋锚杆剪切刚度求解公式,该公式对于纤维筋锚杆剪切刚度具有良好的模拟性。(5)采用大型室内相似模拟试验手段,研究了管棚作用机理,管棚能将荷载向掌子面前方传递1.25～3.75m,可认为管棚能将传递到掌子面上的荷载作用位置向掌子面前方转移约为0.1～0.3D,管棚传递荷载的特性主要是发挥荷载传力梁作用将荷载进行分散传递,减小荷载集中。(6)研究发现掌子面锚杆加固围岩稳定和控制掌子面变形机制与纵向压力拱效应密切相关。掌子面锚杆所引起的纵向压力拱的范围(0.6D)要小于管棚、小导管结果。掌子面锚杆能促进纵向拱效应在近距离内形成,充分调动和发挥围岩的自承能力,从而控制掌子面前方围岩的变形及防止围岩失稳塌方。(7)通过对采用不同加固措施条件下隧道未支护段围岩稳定性,得出小导管和管棚对上部围岩的位移控制属于“被动式”控制,其是通过控制下部围岩的位移而实现对上部围岩的位移限制；掌子面锚杆对未支护段上部围岩的位移控制属于“主动式”控制,掌子面锚杆通过前方“待挖核心土”的加固,可以促进开挖后地层拱的形成,抑制变形向深部岩体扩展。(8)研究洞内预加固(掌子面锚杆)与洞周预加固(管棚、小导管)技术联合工作特性,得出正面锚杆和超前小导管的联合使用可集合掌子面锚杆在控制掌子面挤出变形及深部岩体变形的优势和小导管在未支护段控制拱顶附近围岩变形的优势。在联合支护体系中,二者对围岩变形的控制效果不会相互抵消,正面锚杆起主要作用,小导管只起辅助作用。(9)对不同施工方法下软弱围岩隧道围岩应力、变形和塑性区综合分析,得出全断面预加固工法优于三台阶七步法,而三台阶七步法优于双侧壁导坑法。全断面预加固工法通过掌子面锚杆超前加固核心土,增加待挖核心土的强度和刚度,可以显著控制围岩的变形。与其他工法相比,全断面预加固工法开挖施工空间大,能引入大型施工机械,采用更大的开挖进尺,可兼顾工程造价、施工速度与施工安全,具有很高的综合优势。更多还原

【Abstract】 With the development and upgrade of infrastructure such as high speed railway, expressway, railway, water conveyance, urban subway and many other facilities, the NATM tunnels with soft surrounding rockmass construction are gradually increasing in China. Particular attention is focused on the design and construction of NATM tunnels with soft surrounding rockmass, which are regarded as the key issues so as to determine success of the whole transportation engineering. In view of this, the stability control of tunnel face and pre-reinforcement technology in soft surrounding rock is studied systematically and deeply in this thesis. The main works and research achievements as follows:(1) Based on the limit equilibrium analysis theory, a new model for tunnel face stability analysis is presented by use of horizontal slice method. This model can overcome the shortcomings that the intersections between the slices and the bolt by using vertical slice method to some extent. The equivalent pressure coefficient’ka’of tunnel face bolt reinforced is put forward. With this coefficient, the reinforcement effect of tunnel face bolt is simulated conveniently and reasonably by using the horizontal slice method. Furthermore, the influence of the soil parameters and the strength of tunnel face reinforce on the tunnel face limit supporting forces are studied.(2) According to the limit analysis method, the tunnel face failure model considering the factors of unsupported section and tunnel face bolt and pre-consolidation measures is established. In order to investigate the tunnel face limit support forces, the paper studies the factors such as soil parameters the length and support force of unsupported section, tunnel depth and tunnel face bolt reinforce strength. Thus, the failure modes of shallow and deep buried tunnels with longitudinal arching effect are obtained.(3) Based on the interaction between support structure and ground, a double-parameter elastic foundation beam model with variable coefficients of coefficient of subgrade reaction for pipe roof is presented and the solution of this model is given by finite difference method. The research of the mechanical behavior, deformation characteristics and load transferring effects of pipe roof are carried out. In addition, the influence of excavation length, tunnel face reinforce strength and tunnel depth on pipe roof action are studied.(4) Through the tests of bond behavior between GFRP rebar and concrete, the paper draw conclusions that the bond proportional coefficient of steel to GFRP reinforcement approximately equal to1.2～1.5and minimum anchorage length is20times diameter. The CMR model of bond-slip relationship of GFRP rebars in concrete parameters sr and P are modified. These parameters have not only high fitting degree in comparison with test results, but also have certain degree of reliability and safety. The formula for calculating shear stiffness of GFRP bolt with high degree of reliability is put forward.(5) By means of large-scale similarity model test, the mechanism of pipe roof pre-support is studied. It is found that the load can be transferred to the distance between1.25m and3.75m (i.e.0.1～0.3D) in front of tunnel face. In short, the mechanism of pipe roof pre-support is regarded as the action of load transferring with beam effect and dispersing load and decreasing stress concentration. (6) The pre-reinforcing mechanism of face bolt improving the stability of surrounding rook by controlling deformation of tunnel face is closely related to the effect of longitudinal pressure arch. In addition, the range of longitudinal pressure arch by face bolt reinforced is about0.6D, which is less than the results of small pipe reinforced and pipe roof reinforced. By face bolt promoting the formation of longitudinal pressure arch in short distance, the stability of tunnel face can be effectively improved and prevent surrounding rock collapse.(7) Though analysing of the stability of soft surrounding rockmass in unsupported section, the result shows that the deformation of the upper rock mass of tunnel is controlled by limiting the loosening ground deformation around tunnel in cases of supporting by pipe roof or small pipe, the effects of pipe roof or small pipe are regarded as the passive-control. Comparing the difference of the effects above, the deformation of surrounding rock mass of tunnel in case of face bolt supporting is effectively controlled by enhancing the rockmass strength of the core zone in front of tunnel face with forming longitudinal pressure arch, the effect is regarded as the active-control.(8) Base on the analysis of work characteristics of all kinds of the pre-reinforcement measures around face, we can benefit from the combination action of face bolt support together with small pipe, making use of face bolt advantage in controlling deformation of face extrusion and in limiting the deformation of rock mass in unsupported section around tunnel. In the combination supporting system, their controlling effects can not be counteracted. The face bolt pre-reinforcing measure is seen as the major load bearing component of the pre-support system, and the small pipe supporting measure is relatively seen as a partial load bearing component of the pre-support system.(9) By comprehensive analysing surrounding rockmass stress, deformation and plastic zone, the different tunnel construction methods in soft surrounding rockmass are studied. The result shows that the full face method with tunnel face bolt pre-reinforcing is much better than three-bench seven-step method, and the three-bench seven-step method has an advantage over the double side drifts method. Through enhancing the rockmass strength of the core zone in front of tunnel face by bolt, the surrounding rock deformation can be controlled effectively by the full face method with tunnel face bolt pre-reinforcing. In contrast with other methods, the full face method with tunnel face bolt pre-reinforcing is more competitive in terms of cost and excavation speed and construction safety, and allows the use of a large excavation area, using large construction machinery with deeper excavated length.更多还原