钢纤维喷射混凝土单层永久衬砌在隧道与地下工程中的应用

软弱围岩中的初期支护采用网喷混凝土已成定式.文章对钢纤维喷射混凝土的作用机理、物理力学性能作了详细的介绍,并从技术、经济及综合效益上与普通网喷混凝土作了全面比较,指出钢纤维喷射混凝土单层永久衬砌是未来隧道与地下工程支护的新趋势.     

东巨寺沟隧道湿喷纤维混凝土支护结构和围岩稳定性位移模糊判别

湿法喷射混凝土可有效地改善隧道内作业环境、反弹量小、喷射质量高,是隧道支护结构施工值得推广的工艺。首次在宝鸡－兰州铁路复线东巨寺沟铁路隧道选取试验段,实施湿喷工艺喷射聚丙烯纤维混凝土,作为支护结构兼作永久性支护,免除二次衬砌工作,并进行水平位移收敛监测。采用非线性最小二乘法对该隧道水平收敛曲线进行回归分析,同时采用隧道稳定性模糊概率分析理论对不同断面位置处的隧道围岩稳定性进行判别分析。分析结果表明,采用湿喷纤维混凝土支护的隧道围岩处于稳定状态,可靠度指标高。     

潮湿和湿喷混凝土设备的研究与应用

锚喷支护是全世界普通采用的一种地下工程施工技术，但由于在存在喷射混凝土粉尘大，回弹多和喷层质量不稳定等主要问题，多年来同内外都在研究发展潮湿和湿喷混凝土技术与装备，本文主要介绍了－１．国内外锚喷支护技术概况，国外潮湿和湿喷设备及其所达到的主要技术指标；钢纤维喷射混凝土的发展，硅粉喷射混凝土和外加剂的开发应用，喷射机具的配套完善。２．风动湿喷设备的技术关键，防粘附转子的研究，组合型塑胶软体出料弯头的     

隧道单层衬砌设计方法研究及应用

目前,在单层衬砌设计中应用较为广泛的是基于挪威法的Q系统支护设计法,但该方法涉及的参数有6个,在施工前及施工过程中测试这些参数经验性较强,准确性不高,而且费用较高;将Q法直接移植到中国的单层衬砌设计困难较大,不适合中国国情。在此背景下,提出以屈服接近度和围岩松动圈支护理论为基础的单层衬砌设计原则和方法,并结合合武铁路大别山隧道2号斜井进行了工程实践。首先通过地质勘查得到隧道所在地区的工程地质、水文地质特征以及围岩的物理力学指标,确定隧道围岩的屈服接近度,进而提出单层衬砌支护参数及喷射混凝土的力学控制指标,完成结构的预设计;根据隧道施工过程中实测的围岩松动圈范围,运用松动圈支护理论修正设计,从而形成一套完整的单层衬砌设计方法体系。实践表明,提出的单层衬砌设计方法经济适用、对施工干扰小,适合信息化施工,且施作完成的单层衬砌结构安全可靠,具有显著的经济效益和社会效益,有较大的推广前景。     

隧道喷射混凝土强度增长规律及硬化速度对初期支护性能影响试验研究

隧道结构的围岩-支护特征曲线理论表明,初期支护强度变化及支护时机将极大地影响隧道周围围岩的变形及应力分布。相应地,作为初期支护重要组成部分的喷射混凝土,其喷射后的强度增长变化规律及硬化速度也极大地影响着围岩的变形及应力重分布。为探明喷射混凝土的强度增长规律及其硬化速度对初期支护性能的影响,结合隧道工程实践,进行了一系列喷射混凝土现场试验,建立了喷射混凝土强度和弹性模量增长规律,确定了喷射混凝土硬化速度对初期支护性能的影响规律。分析表明：（1）隧道喷射混凝土早期强度发展较快、较平稳,24 h抗压强度平均值为6.4 MPa,48 h抗压强度平均值为11.4 MPa。（2）在软弱围岩中提高喷混凝土的早期强度十分重要,是控制围岩变形和稳定的关键,喷混凝土早期强度越大,隧道初期支护作用越明显。（3）喷混凝土硬化速度对控制拱顶沉降变形效果较显著。与慢速硬化相比,喷射混凝土快速硬化时拱顶沉降减少10.4%,拱脚处减小17%,边墙水平收敛减少了30.7%。（4）喷射混凝土硬化速度对控制围岩塑性变形方面差异较小。（5）应充分考虑喷射混凝土的强度硬化过程,不考虑喷射混凝土硬化速度会在一定程度上高估初期支护性能,使其相应支护结构位移明显小于考虑硬化速度时相应的结构位移。     

隧洞衬砌中湿喷钢纤维混凝土的应用

基于湿喷钢纤维混凝土的性质，讨论了喷射混凝土的特点及其在暂时支护与永久支护中的应用。     

层布式纤维混凝土弯拉特性分析

试验研究了相同配合比下素混凝土、层布式钢纤维混凝土和层布式混杂纤维混凝土弯拉性能，采集三者试件荷载-挠度曲线和90天龄期的极限荷载，并对比三者的28天龄期及90天龄期的弯拉强度，分析其弯拉强度增强机理，得出由于聚丙烯腈纤维和钢纤维的双重阻裂效应，使层布式混杂纤维混凝土的弯拉强度比素混凝土和层布式钢纤维混凝土的弯拉强度更高。     

基于接触应力反分析的隧道初期支护结构内力研究

利用现场监控量测的数据及时分析和评价支护结构的内力是隧道动态设计和施工的关键问题,对保证隧道施工的安全具有重要意义。根据初期支护中喷射混凝土自身特点,将喷层结构视为弹性地基曲梁,并运用弹性地基曲梁理论,通过喷射混凝土与围岩接触应力推求喷层结构内力的解析解,从而得到喷层结构的应力集中部位,方便后续制定施工安全措施。经台阶法开挖的隧道工程实例分析表明,从喷层与围岩接触应力出发来求解喷层结构内力解析式是隧道内力分析一种新的有效方法,为隧道结构的安全评估提供比较可靠的依据     

基于响应面法的软岩隧道湿喷纤维混凝土支护结构可靠度分析

由于湿喷纤维混凝土支护结构物理、力学参数和喷层厚度的离散性及混凝土强度破坏准则难以用支护材料参数显式表达,对该类隧道支护结构进行可靠度分析十分困难,提出采用响应面方法计算湿喷纤维混凝土支护结构的可靠度方法,并给出了计算流程,其中围岩-支护结构的确定性分析采用非线性有限元方法,可靠度分析采用2次响应面法.以赣州-龙岩铁路金华山软岩隧道湿喷纤维混凝土支护结构为研究对象,对该支护结构的可靠度进行分析与计算.分析结果表明,金华山隧道湿喷纤维混凝土支护结构可靠度指标高,处于安全状态.     

空洞对隧道喷射混凝土爆破振动特性及安全评价的影响研究

在隧道工程施工过程中,爆破开挖与喷射混凝土支护往往交替进行,爆破振动可能会造成局部的喷射混凝土与围岩表面之间失去黏结力,二者脱离形成空洞。采用薄板振动理论模型、三维离散元程序3DEC数值模拟及现场实测振动分析相结合的方法,研究了隧道喷射混凝土与围岩之间的空洞对混凝土喷层爆破振动特性及安全评价的影响。研究结果表明,当隧道喷射混凝土与围岩之间存在空洞时,空洞处喷射混凝土的振动速度增大、振动持续时间变长、振动频率降低,振动的幅值-频率谱具有明显的单峰现象,回归分析得到的质点峰值振动速度衰减速率更快;空洞的存在导致隧道混凝土喷层爆破振动危险区域增大,致使选择的喷射混凝土支护时机滞后、采用的最大单响药量偏低,从而降低了隧道开挖的施工效率、增加了工程成本。     

隧道复合式衬砌初期支护极限状态模型试验研究

当前既有以及新建的隧道结构大多采用复合式衬砌形式,在长期使用过程中,初期支护不可避免会出现劣化甚至失效的情况,会对隧道结构整体的承载力及耐久性造成影响。通过室内模型试验,采用可劣化的石膏模型制作初期支护的各构件,对其劣化失效过程进行模拟,记录二衬结构的状态变化,再通过增加荷载确定隧道结构整体承载力的变化情况。试验结果显示,钢架和喷射混凝土层的劣化对二衬结构的影响要比锚杆劣化的影响大得多,然而单纯的初期支护失效并不会造成二衬结构的破坏,且二衬结构还有较大的安全余度;初期支护构件劣化都会造成隧道结构整体承载力的降低,锚杆的影响最为明显,钢架及喷射混凝土失效对整体承载力降低影响不大。     

爆炸平面波作用下大跨度洞室稳定性模型试验研究

通过抗爆模型试验,研究了爆炸平面波作用下大跨度毛洞和锚喷衬砌支护洞室的受力变形和稳定状态。介绍了模型试验原理及方法,根据试验实测数据分析了洞室围岩的受力特征、洞壁的运动变形特征、洞室的破坏形态及承载能力等。研究表明：设计工况和超载工况下,锚喷衬砌支护洞室侧墙部位垂直应力、拱顶加速度正峰值、拱顶位移峰值及残余值、洞壁环向应变峰值均明显小于毛洞;超载试验后,毛洞破坏严重,丧失了承载能力,而锚喷衬砌支护洞室破坏明显轻微,承载能力可提高约60%。     

Effects of tunnelling on existing support systems of perpendicularly crossing tunnels

The interactions between perpendicularly crossing tunnels in the Sydney region are investigated using a full three-dimensional (3D) finite element analysis coupled with elasto-plastic material models. Special attention is paid to the effect of subsequent tunnelling on the support system, i.e. the shotcrete lining and rock bolts, of the existing tunnel. The results of the analysis show that in a region such as Sydney, with relatively high horizontal stresses, installation of the new tunnel causes the shotcrete lining of the existing tunnel to be in tension in the side facing towards the tunnel opening and in compression at the crown and invert. The pre-stressed rock bolts are usually tensioned more in the sections closest to the tunnel opening. For this particular study, if a new tunnel is driven perpendicularly beneath an existing tunnel, significant increases are induced in the bending moments in the shotcrete lining at the lateral sides of the existing tunnel and in the axial forces at its crown and invert. The increase in side bending moments causes further tensile cracking but the crown and invert stresses remain within the thresholds for both compressive failure and tensile cracking for shotcrete lining of typical concrete quality. Moreover, the driving of the new tunnel causes the tensile forces in the existing side rock bolts to increase and those in the existing crown rock bolts to decrease. In contrast, if the new tunnel is driven perpendicularly above the existing tunnel, compressive failure of the existing shotcrete lining is induced at the crown of the deeper tunnel for concrete of typical capacity and a significant tensile force increase of the existing rock bolts around the crown. It is concluded that in order to ensure the stability of the existing tunnel, local thickening is needed at the sides of the existing shotcrete lining if the shallow tunnel is installed first and local thickening is needed at the crown if the deep tunnel is installed first.     

软弱围岩隧道取消系统锚杆的现场试验研究

在软弱围岩隧道中,提出初期支护结构由钢架+喷射混凝土+钢筋网+锁脚锚杆+纵向连接筋组成,即取消系统锚杆用钢架联结处的锁脚锚杆代替。以包家山隧道为依托工程,采用现场试验的方法,选取2个试验段,进行锁脚锚杆取代系统锚杆后,有、无拱部锚杆的对比试验研究。对比试验的内容包括：隧道初期支护的净空收敛、围岩压力、钢架应力、喷射混凝土应力、锚杆轴力和纵向连接筋应力等。研究结果表明：2个试验段初期支护变形趋于稳定,结构受力安全,说明取消系统锚杆不影响初期支护结构的安全与稳定;拱部锚杆有受拉,也有受压,但受力都不大,最大拉应力仅为钢材极限强度的11.8%,其支护作用不明显;锁脚锚杆大部分受拉,最大值达到191 MPa,钢架支护作用明显,在支护体系中发挥着重要作用。取消系统锚杆减少了施工工序,降低了工程造价,缩短了工序循环时间,有利于及早封闭围岩以形成完整的支护结构。经济价值和社会效益显著。     

高地温隧洞支护结构受力特性

高地温问题严重制约了地下工程的施工和安全运营,结合新疆某水电站引水洞存在的高岩温问题展开研究。根据地质资料设置了6种地温边界,研究隧洞围岩及支护结构在开挖、施做喷层、施做衬砌和过水等工况下的受力及变形特性,并与不考虑温度场时的分析结果进行了对比分析。研究表明:高温对隧洞稳定性有显著的影响,高温下锚杆轴力约为不考虑温度场时的294倍,衬砌环向拉应力约为不考虑温度影响时的2.13倍;保温层作用显著,若不考虑保温层的影响,锚杆轴力和衬砌拉应力会更大;过水对衬砌受力影响较大,过水后衬砌环向拉应力迅速增大为过水前的2.65倍。研究结果为类似工程的设计与施工提供借鉴。      

Practical Estimate of Deformations and Stress Relief Factors for Deep Tunnels Supported by Shotcrete

Summary. Even though ground-support interaction in the vicinity of the tunnel face is a typical 3D problem, tunnel support design is usually based on simplified plane strain models, which are strongly dependent on the assumed degree of ground stress relief at the time of lining installation. The paper focuses on tunnels supported by shotcrete close to the face, where the interaction between the loading process and progressive hardening of the green shotcrete makes the problem time-dependent. A constitutive law characterized by the time-dependent stiffness and strength of the shotcrete is employed herein. The results of an extensive parametric study based on 3D axisymmetric models are presented in the form of non-dimensional design charts, which can provide guidance to a preliminary evaluation of convergences and support loadings. Moreover a strategy is proposed to enhance the capability of simplified design methods (2D models, Convergence-Confinement Method). This consists in a “guided estimate” of stress relief factors, which again is based on the results of 3D time-dependent analyses. Finally, by way of example, the proposed method is applied to two well-documented case-histories.     

Nonlinear analysis of NATM tunnel construction with the boundary element method

This paper presents a novel approach to the simulation of NATM tunnel construction using the Boundary Element Method (BEM) as principal numerical method. This new approach has the advantage that only the excavation surface, the possible plastic zones and the tunnel lining have to be discretised. The whole rock mass is represented by the BEM whereas the Finite Element Method (FEM) is used to represent the tunnel lining only. Thus, a general coupling strategy for coupling three-dimensional boundary elements with shell finite elements (shotcrete) and beam finite elements (steel arches) is presented. To achieve realistic results the effect of hydration of the shotcrete and yielding of the steel arches is considered in the excavation process. Furthermore, the nonlinear rock behaviour is modelled more realistically by using a powerful hierarchical constitutive model which considers a large range of rock materials. The combination of these ideas results in higher user-friendliness and efficiency. Some verification tests and practical applications in tunnelling are presented.     

穿越断层隧道地震响应规律动力对比试验研究

为研究断层隧道在地震作用下的影响规律,开展了穿越断层隧道的振动台对比试验,介绍了试验材料、相似比选取及动力加载情况。试验表明：地震作用下衬砌腰侧的受力明显大于顶部和底部,在进行结构设计时应进行加强;隧道衬砌具有一定的加速度放大效应,衬砌结构的加速度傅里叶谱值主要集中于中低频,在结构临近破坏时,加速度和应变响应值将发生突变;隧道衬砌裂缝发展与结构位置密切相关,地震作用下底部裂缝由内向外发展,腰部裂缝由外向内发展;断层走向与隧道纵向夹角越小,地震对隧道的作用越大,裂缝的发育越明显;隧道的最终破坏形式为管节本身的纵向拉裂缝和管节接缝处的错台组成。该研究成果为穿越断层隧道的相关设计提供参考。     

光纤Bragg光栅传感技术在隧道模型试验中应用

在模型试验中,锚杆一般尺寸较小,应变监测较为困难,可将光纤Bragg传感技术（FBG）应用于隧道模型试验中解决该问题。基于西安地铁二号线4个典型断面实际工况进行隧道模型试验,将自行设计封装的光纤Bragg光栅传感器粘贴在锚杆模型表面,监测其在不同应力状态下的应变。根据隧道开挖前、隧道开挖后、衬砌支护后、抗裂极限状态和极限破坏状态5个应力状态的实测数据,得到锚杆轴力在隧道受力过程中的变化规律。试验结果表明,锚杆受力大小在隧道开挖前后有一定变化。衬砌支护后,随围岩压力增加,锚杆轴力基本呈增加趋势,拱顶附近锚杆承受压力,支护后压力变化不大;拱肩到墙角的锚杆承受拉力,衬砌支护后受力开始增加;锚杆在含水率大的黄土隧道中受力较大,更能发挥其作用。文中方法在模型试验中的应变监测方面提出新的可靠途径。     

Laboratory Tests on Shotcrete-Rock Joints in Direct Shear, Tension and Compression

Summary. A series of laboratory tests was performed on cemented shotcrete-rock joints to investigate the strength and stiffness of the interfaces, while simulating field conditions as close as possible. The direct shear test formed the core of the experimental work, while the tension and compression tests were complementary. To simulate loading conditions experienced in practical cases the direct shear tests were performed under fairly low normal stresses. In most practical cases when shotcrete is used with rock bolts, the normal load on shotcrete lining seldom exceeds 0.2 to 0.5 MPa. The direct shear test results show that, for such normal load range the shear strength is determined by the bond strength for genuinely bonded shotcrete-rock interfaces. For higher normal stresses (σ_n > 1.0 MPa), which rarely exist at the shotcrete-rock interface, the shear strength is largely influenced by friction resulting in the cohesive strength being less significant. Assessment of the shear surface revealed that the steel fibres in the shotcrete appeared to contribute significantly to the frictional component. The shear and normal stiffnesses of the interface were also determined, which were in principal the stiffnesses of the bond. An interesting observation was the complex interaction at the interface and the mechanisms that controlled the peak shear strength which depended on the surface roughness, the existence of natural flaws and the normal load.