高速铁路大断面黄土隧道深浅埋分界深度研究

郑州-西安铁路客运专线穿越西部黄土分布的主要地区,该线含大量单洞双线隧道,其开挖面积大于160 m2,跨度大于15 m,属于超大断面隧道。由于黄土的特殊性质以及开挖跨度与断面的增大,隧道围岩压力随埋深的变化尚不清楚,目前对该类型隧道的深、浅埋分界深度界定认识不统一。通过郑西线12座隧道地表裂缝与埋深关系的现场调查,初步确定了大断面黄土隧道的深、浅埋分界范围,指出小于11 m可作为超浅埋,40～60 m为浅埋与深埋分界深度,大于60 m为深埋;基于裂缝调查,按剪切滑移破坏极限状态理论对以上分界范围进行了理论分析与验证;精心设计现场试验,在浅、深埋等地段布置17个量测断面进行围岩-初期支护间接触压力的量测,发现实测围岩压力与界定的深浅埋计算结果吻合良好,表明所给深、浅埋界定范围正确。     

大断面浅埋黄土隧道锚杆作用效果的试验研究

黄土隧道系统锚杆的作用效果问题一直是争论的焦点。结合正在修建的郑州-西安铁路客运专线大断面黄土隧道,采用现场对比试验方法对系统锚杆作用效果进行研究。为了使试验结果有可比性,选取试验条件基本相同的贺家庄隧道洞身段作为试验段,分别设置有系统锚杆段40 m和无系统锚杆段40 m。对比试验的内容包括：拱顶下沉、拱脚下沉、水平收敛、围岩压力、初支钢架应力、锚杆轴力等。试验结果表明,有系统锚杆段比无系统锚杆段的拱顶沉降大40 %左右、水平收敛大25 %左右,两者的土压力和钢架应力相差不大;锚杆轴力较小,且拱部受压。经综合分析认为,拱部锚杆的支护效果不明显,取消拱部锚杆可减少施工工序,加快隧道初期支护断面及早封闭,能更好地控制支护沉降与变形,并节约工程投资。     

隧道围岩全长黏结式锚杆界面力学模型研究

分析围岩弹塑性介质中全长黏结式锚杆的锚固界面层应力分布和变化特征,对研究隧道工程初期支护系统的力学效应具有重要意义。根据全长锚杆微段的受力平衡以及锚固界面层剪应力的传递机制建立了关于锚杆轴向位移的微分方程,通过求解锚杆轴向位移的微分方程可得到锚杆与围岩相互作用下的轴向载荷和锚固界面剪应力的分布函数。然后将锚杆界面剪应力对围岩的支护反力转化为圆形隧道轴对称径向体积力,进而求解有锚喷支护作用下圆形隧道围岩塑性区半径。在此解析模型基础上,可对隧道围岩-支护系统进行详细的分析和评判。算例分析表明,初期支护时机的选择对锚固效应和围岩稳定性有较大影响;适当增加全长黏结式锚杆的锚固层厚度能明显降低锚杆端部剪应力的应力集中度,能有效改善锚杆的锚固效果。     

浅埋风积砂质黄土隧道变形综合控制技术研究

在隧道施工前,应用数值模拟分析的方法,分析浅埋砂质黄土隧道施工力学效应和变形特征。根据浅埋砂质风积黄土隧道在施工过程中地表沉降量大和洞内施工安全风险大等特点,结合隧道实际监测数据,反演计算得到侵限段地质力学参数,为迈式管棚超前支护及径向迈式锚杆的全施工过程数值模拟提供计算依据,为控制隧道围岩变形提供数据支撑。计算结果显示,隧道侵限段地表最大沉降11.4 mm、最大拱顶下沉30.4 mm、最大水平收敛48.5 mm,隧道整体变形量减小,迈式管棚超前支护可以有效地提供纵向支撑,承受侵限土体压力、约束围岩变形和控制地表沉降,同时为支护侵限段钢拱架的安全拆换提供保障。研究结果表明:径向迈式锚杆、迈式管棚超前支护、环形支撑钢拱架和锁脚锚杆一起,构成了浅埋风积砂质黄土隧道主被动变形综合控制体系,有效地解决了浅埋风积砂质黄土隧道软弱围岩超前支护的难题。     

贵州李家寨隧道系统锚杆作用效果试验研究

隧道系统锚杆作用效果一直存在较多争议,尤其在软质围岩中,一种观点认为系统锚杆可减小围岩变形,支护效果良好,特别是边墙锚杆能发挥较好的支承和约束作用;相反观点则认为系统锚杆无明显作用效果,施作系统锚杆延误了初期支护的最佳时机并导致围岩变形量的增大,而取消系统锚杆后围岩变形和受力状态良好。本文依托贵州沿印松高速公路在建李家寨隧道Ⅳ级软质围岩地段,针对系统锚杆作用效果问题开展大量的现场试验,有、无系统锚杆对比试验段各设置3个量测断面,量测内容包括围岩压力、钢架内外应力、系统锚杆轴力、拱顶下沉、水平收敛等。得出如下结论:(1)隧道施作系统锚杆延长了初期支护闭合时间,导致围岩压力和钢架受力略大于无锚杆状态;隧道有无设置系统锚杆,围岩变形及受力都无明显差异,取消系统锚杆不影响支护结构安全。(2)拱顶系统锚杆大部分处于受压状态,作用效果较差,施作系统锚杆措施明显过于保守,存在很大优化空间;但隧道边墙锚杆可起到锁脚锚杆作用,取消系统锚杆时要保证施作锁脚锚杆。(3)李家寨隧道Ⅳ级软质围岩地段架设钢拱架并取消系统锚杆能够保证初期支护结构稳定性,技术上是安全可行的。     

小净距隧道中夹岩对拉锚杆控制机制与工程应用

小净距隧道中夹岩受到两侧开挖的剧烈扰动,处于单向或双向受力的不利状态,严重影响施工安全,而预应力全长注浆对拉锚杆常用于中夹岩的主动支护。为阐明对拉锚杆的作用模式和控制机制,建立相应的力学模型和解析方法,开展实测验证,并进行参数分析和工程应用。研究表明：对拉锚杆为中夹岩提供强力水平约束,并提高岩体力学性能,发挥挤压加固作用;对拉锚杆利用剪切摩阻改善浅层围岩受力状态,同时锚固深部岩体,具有承载传力效果;对拉锚杆轴力和剪应力均由两侧向中间非线性衰减,作用范围局限于浅层中夹岩,实测结果验证了理论方法的合理性;进行了对拉锚杆的参数分析,提出了对拉锚杆临界长度、合理锚杆直径等工程建议;结合京张高铁长城站小净距隧道实践,主动增强对拉锚杆设计参数,变更后围岩压力、拱顶沉降和水平收敛的实测均值分别降低12.2%、14.1%和10.2%,保障了隧道开挖的安全。     

非连续变形岩石断裂分析中的一种全长剪切锚杆

锚杆从锚固方式上可划分两种：端部锚固方式和全长锚固方式。全长锚固锚杆作为工程支护中的一种重要锚杆类型,具有广泛的应用前景。非连续变形分析（DDA）以及在此基础上发展的非连续变形的岩石断裂分析（DDARF）方法中锚杆为端锚形式,且只考虑了锚杆的轴向作用,而忽略了锚杆作用力对锚固岩体的侧向限制。为了更好地理解锚杆的支护机制,考虑锚杆的剪切作用,提出了DDARF中一种新的锚固形式--全长剪切锚杆支护形式。用改进的全长剪切锚杆支护方法对一公路隧道稳定性进行了分析,并与端锚支护形式进行了对比,结果表明,提出的全长剪切锚杆支护方法是有效的,锚固效果比端锚支护更好。     

大断面黄土隧道初期支护适应性研究

以兰渝铁路大断面黄土隧道为工程背景,采用三维数值模拟结合现场监测实验对现有初期支护设计参数的适应性进行研究,对大断面黄土隧道初期支护的受力与变形特性进行综合分析。通过三维数值模拟得到黄土隧道开挖扰动后初期支护的受力与变形状态,将数值计算结果与现场监控量测对比获得典型断面围岩的应力和位移发展规律并对初期支护安全性进行评价;通过FLAC3D的FISH语言开发程序分析混凝土硬化特性对初期支护受力与变形的影响;现场跟踪量测与数值模拟的计算结果基本吻合,结论可为黄土地区隧道初期支护的设计和施工提供一定的借鉴和参考,积累有益的经验     

松软地层浅埋暗挖公路隧道现场监测分析研究

针对浅埋暗挖公路隧道的特点,对厦门高崎互通下穿嘉禾路隧道进行地表下沉、拱顶下沉、洞内收敛、支撑应力等项目的监测工作。基于监测结果,分析了该隧道围岩和支护系统的变形及受力特点,指出了松软地层中浅埋暗挖隧道开挖影响的时空范围和隧道施工中有效控制围岩变形的措施,并为支护体系的优化提供依据。研究结论丰富了浅埋暗挖思想,并为国内浅埋暗挖公路隧道的设计、施工和监测提供借鉴。     

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。     

近区锚喷结构的爆破振动特性研究

选用水泥砂浆和玻璃钢分别模拟岩石和锚杆,浇筑2.5 m×1.8 m×2.1 m尺寸的岩体模型,通过模型试验研究近区锚喷结构在掏槽爆破作用下的振动特性。利用测试锚杆测得不同设置情况锚杆上的应变波。试验结果表明,端锚锚杆中部锚固段与锚杆尾部自由段测得的振动波形和变形形式完全不同,中部锚固段振动幅值稍大;在不设置喷层和预应力时,尾部自由段的应变波规律性更强,且持续时间长;随着离爆源距离的增加,锚杆的振动频率和幅值衰减明显,但振动持续时间则稍有增长;通过小波变化的时频方法分析应变波的能量,临近工作面锚杆的振动能量大,但能量分布分散,振动时间有限,稍远的锚杆虽振动能量小,但能量集中,持续时间长;两种不同能量对锚喷结构产生不同的损坏模式。试验和实践发现,爆破容易造成附近喷层的损坏和锚杆的失效,钢纤维混凝土可增加喷层的抗动载性能,调整支护工艺也是减小爆破影响的有效方法。     

Centrifuge modelling of twin-tunnelling induced ground movements in loess strata

A great concern for the safety of large cross-section tunnels, which are being or to be built in the loess strata of China, is attracted. Generally, loess is a multi-phase porous medium and develops complex stress and strain variation while executing a tunnel project. Another problem is that the soil surrounding both tunnel arches is subjected to a complex loading due to the double excavation. To obtain an in-depth knowledge of the mechanism of tunnel deformation induced by the twin-tunnelling, we conducted comprehensive centrifuge tests, which can simulate and reproduce strictly the action process of twin-tunnelling. Through the model tests, the response of twin-tunnelling on loess stratum deformation was obtained. The investigations showed that with the increase of tunnel spacing, the stratum deformation distribution near the vault changes from a single-peak V shape to a double-peak W shape. Additionally, the height of the stratum pressure arch effect increases significantly. The settlement of the preceding tunnel is slightly larger than that of the latter tunnel, and the twin-tunnelling effect gradually decreases with the increase of tunnel spacing. Through comparative analysis of the different combinations of tunnel spacing and tunnel interval, the interaction between two tunnels with different spacing and interval during tunnelling was investigated, further optimizing the reasonable tunnel spacing and construction steps, as well as providing reference for tunnel route selection in the loess strata.     

不同埋置深度的山岭隧道地震响应分析

根据大量震害资料的调查分析发现,地下结构埋置深度对其地震破坏程度影响很大。通过有限元方法计算8种不同埋置深度条件下的山岭隧道地震响应,并对计算模型的地震输入方法进行了验证,证明地震波输入处理方式的合理性。讨论埋深对结构动力响应的影响,提取衬砌关键节点的竖直向和水平向加速度、位移峰值,分析随着埋深的增大,加速度和位移峰值的变化情况,并以拱顶为例,计算每个埋深变化段的加速度和位移峰值变化率,得到了一定的规律性,如埋置深度从5 m增大到50 m,衬砌结构动力响应峰值大小下降较快。此外,还分析了埋深增大对衬砌结构内力峰值的影响。最后,提出在高烈度地震区修建隧道时其埋置深度尽可能不小于50 m,这为相关工程的修建提供了参考依据。     

Analytical and Numerical Study of the Mechanics of Rockbolt Reinforcement around Tunnels in Rock Masses

Summary  This paper addresses the problem of quantifying the mechanical contribution of rockbolts installed systematically around tunnels excavated in rock masses. The mechanical contribution referred to here is that of increased stress confinement and decreased tunnel convergences as compared with corresponding stresses and displacements obtained for non-reinforced tunnels. The problem is treated analytically first by presenting a closed-form solution for stress and displacement distributions around a circular tunnel excavated in elastic material and reinforced by grouted or anchored rockbolts. The analytical solution assumes that rockbolts are regularly spaced around the tunnel and that axi-symmetry conditions of geometry and loading apply. The results obtained with the closed-form solution are shown to be equivalent to the results of the same problem solved with traditional numerical methods. Based on the analytical and numerical results and by introducing dimensionless ratios that allow to quantify the increase of radial stresses and the decrease of radial displacements in the reinforced region of the tunnel, the paper shows that reinforcement can have a significant mechanical effect (i.e., increasing the confinement and decreasing the convergences) in tunnels excavated in rock masses of poor to very poor quality. The paper analyzes then the mechanical contribution of rockbolt reinforcement when the rock mass is assumed to behave elasto-plastically. For this case, it is shown that rockbolt reinforcement can also have a critical effect in controlling the extent of the plastic failure zone and the convergences of the tunnel. Correspondence: C. Carranza-Torres, Department of Civil Engineering, University of Minnesota, Duluth Campus, 1305 Ordean Court, Duluth, USA     

Elastic Solution for Deep Tunnels. Application to Excavation Damage Zone and Rockbolt Support

Summary  A new formulation is presented for deep circular tunnels in rock with cylindrical anisotropy. The formulation is an exact solution since it satisfies equilibrium, strain compatibility, and the anisotropic constitutive model. Complete solutions have been found for two scenarios: tunnel with excavation damage zone, and tunnel with rockbolt support. The solution is based on the assumption of a deep, circular tunnel in a medium with two homogeneous zones: an inner zone surrounding the tunnel, which is either isotropic or anisotropic, and an outer zone, for the remainder of the medium, which is isotropic. Plane strain conditions, elastic response of rock, rockbolts and support, and simultaneous excavation and support installation are also assumed. For tunnels surrounded by an excavation damage zone with reduced rock properties, the tangential stresses and the radial deformations at the tunnel wall are very sensitive to both the magnitude of stiffness reduction of the damaged rock and the size of the damaged zone. The effect of the rockbolts on the rock is approximated by treating the rockbolt-rock composite as a material with cylindrical anisotropy with stiffnesses related to the properties of the rock and rockbolts, and spacing of the rockbolts. Comparisons between the analytical solution and a numerical method show small differences and provide confidence in the approach suggested.     

浅埋人防隧洞围岩破坏机理分析

以埋深为6～13 m的某浅埋人防隧洞为研究对象,应用快速拉格朗日有限差分程序（FLAC）对不同跨距、不同岩性的隧洞顶板在不同荷载作用下的破坏规律及破坏机制进行数值模拟研究,确定了隧洞围岩破坏域,并对拱顶敏感块体进行跟踪分析。研究结果表明：隧洞跨距为2 m且顶板岩层为泥岩时,隧洞顶板有一定的承载能力,当上部荷载达到0.7 MPa时隧洞才破坏;隧洞跨距为3 m且顶板岩层为泥岩时,当上部荷载达到0.33 MPa时,隧洞就已经破坏;隧洞顶板为卵石层时,即使上部不施加荷载,在自重应力的作用下,隧洞亦破坏。该研究对类似的浅埋地下工程围岩稳定性分析具有实际意义。     

复杂地表条件下陡倾角勘探区地震数据采集研究

针对王家山地震勘探区具有目的层倾角大（30°～60°）、地表相对高差大、黄土覆盖层厚、地表条件十分复杂等地震难点,在前期调研的基础上,依据品质因数—地层衰减系数与纵波速度的关系,炸药震源与介质阻抗的耦合关系,虚反射与最高频率的关系等相关理论依据,提出了获得较好原始资料的保证措施：在厚黄土厚附近,炮点变观至基岩裸露区或厚度较小区域;炸药依据基岩、黄土等岩性差异分别选用铵锑成型炸药及2#岩石硝铵炸药;激发井深为虚反射界面深度、药柱长度及药柱顶部爆炸破坏带高度之和;组合激发井距大于2倍塑性带半径;接收束状砖块式10线8炮制观测系统;大倾角地层采用较大的偏移距,下倾激发方式。通过野外采集实验,证明了该复杂条件下陡倾角勘探区采取的三维地震勘探措施的合理性,经初步处理,野外采集的资料各项质量技术指标均达到规范要求,解释的浅部塌陷区影响边界由原来计算的100～200m控制到了50m范围之内,达到了非常理想的程度。     

基于分数阶导数理论的Q3黄土流变本构模型研究

荷载的时间效应诱发的黄土蠕变和渐进破坏会显著影响其工程构筑物的长期服役性能。特别是在我国西北地区黄土广泛分布,在荷载的长期作用下一些典型工程建构筑物(如西安地铁开挖的黄土隧道工程)可能因黄土蠕变和渐进破坏而失稳,进而对工程建设的顺利实施以及工程建设完成后其安全运营维护产生极为不利影响。可见,对黄土流变特性进行分析并揭示其流变机理进而建立其本构模型具有重要的理论和实际意义。为此,以Q₃黄土为研究对象,基于分数阶导数理论,通过对典型蠕变变形过程进行分析,提出了一种可模拟加速蠕变阶段非线性变化特征的分数阶元件模型,对其进行理论分析进而建立了分数阶改进西原模型并推导出本构方程。在此基础上对Q₃黄土的原状与重塑样开展了三轴分级循环加-卸载流变试验,以验证分数阶改进西原模型的有效性。相应的理论计算结果表明:分数阶改进西原模型既能实现对Q₃黄土减速蠕变、等速蠕变和加速蠕变3个流变阶段的模拟,又可弥补整数阶改进西原模型无法描述加速蠕变阶段的不足,而且相比于整数阶改进西原模型,其在减速蠕变及卸载阶段的预测效果更佳。研究结果为考虑黄土流变问题的建构筑物安全运营维护设计与施工方案提供了重要的理论依据。     

Comparison of Squeezing Prediction Methods: A Case Study on Nowsoud Tunnel

According to the International Society of Rock Mechanics, squeezing is a time dependent large deformation occurring during tunnel construction around the tunnel associated with creep caused by exceeding a limiting shear stress (Barla in ISRM News J 2:44–49, 1995). This research is conducted using a case study on the Nowsoud Tunnel, Iran. Being 14 km in length and 4.5 m in diameter, the tunnel is located in the western part of Iran near the Iraq border. Nowsoud tunnel, which was excavated using a double shield TBM, exhibited severe squeezing (with 8919 m) in its critical zone which resulted in excavation termination. In this research, the best approach for predicting squeezing among the recommended methods for reducing the damages caused by squeezing on TBM was determined. In this regard, approaches commonly used to predict squeezing are empirical, semi-empirical, and theoretical–analytical methods. Besides, these methods, numerical modeling is used to estimate convergence generated along the tunnel pathways, which is ultimately used to categorize squeezing. This paper compares squeezing prediction methods in 68 section of Nowsoud Tunnel. These 68 sections indicate that the empirical methods propose a general estimation/overview of squeezing. Among the semi-analytical approaches, the one proposed by Hoek and Marinos (Rock engineering in difficult rock conditions—soft rocks and karst, Taylor & Francis Group, London, pp 49–60, 2000) are compatible with the occurrence of squeezing in the critical zone. However, the degree of predicted squeezing is less than the real degree of squeezing in this zone. Based on the result of Aydan approach, 75 % of the tunnel sections are under squeezing condition. Theoretical–analytical approaches underestimate the possibility of squeezing in the critical zone. Barla?s approach (1995) demonstrated the possibility of squeezing in the critical zone with low intensity. The numerical computations in this paper were performed using Plaxis (version 8.5), a two-dimensional numerical program based on the finite element method. Plaxis results, classified by Hoek and Marinos (2000) method, show that 8800 m of the tunnel length is under the non-squeezing condition. According to all prediction methods, the squeezing zones depend on faulted zones, argillaceous limestone and shale formations such as J₁Kh, J₄Kh, J₅Kh, and Kgr. These formations were identified with a high quantity of shale and argillaceous limestone. Bedding of these geological formations is thin and their geotechnical properties are weaker than those of limestone formations. On the other hand, non-squeezing zones depend on limestone formations such as J₂Kh, J₃Kh, J₆Kh, K^abg, and Kbg. Moreover, all approaches predicted squeezing potential for the critical zone where TBM is jammed.