Numerical analysis and field monitoring tests on shallow tunnels under weak surrounding rock

The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring tests and numerical analysis were done. The mechanical characteristics of shallow tunnels under weak surrounding rock and the stress-strain rule of surrounding rock and support were analyzed. The numerical analysis results show that the settlement caused by upper bench excavating accounts for 44% of the total settlement, and the settlement caused by tunnel upper bench supporting accounts for 56% of the total settlement. The maximum axial force of shotcrete lining is 177.2 k N, which locates in hance under the secondary lining. The maximum moment of shotcrete lining is 5.08 k N·m, which locates in the arch foot. The stress curve of steel arch has three obvious stages during the tunnel construction. The maximum axial force of steel arch is 297.4 k N, which locates in tunnel vault. The axial forces of steel arch are respectively 23.5 k N and-21.8 k N, which is influenced by eccentric compression of shallow tunnel and locates in hance. The results show that there is larger earth pressure in tunnel vault which is most unfavorable position of steel arch. Therefore, the advance support should be strengthened in tunnel vault during construction process.

Time-dependent safety of lining structures of circular tunnels in weak rock strata

Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.

In Situ Experiments on Supporting Load Effect of Large-span Deep Tunnels in Hard Rock

A section of the Nanliang high speed railway tunnel on Shijiazhuang-Taiyuan high-speed passenger railway line in China was instrumented and studied for its mechanical properties and performances. The cross section for the tunnel was300 m2and is classified as the largest cross section for railway tunnels in China. Through in situ experimental studies, mechanistic properties of the tunnel were identified, including the surrounding rock pressure, convergences along tunnel perimeter and safety of primary support and lining structure.Based on the field measured data, the surrounding rock pressure demand for large-span deep tunnel in hard rock is recommended as double peak type in the vertical direction and fold line type was recommended for horizontal pressure. The results suggested that Promojiyfakonov's theory was most close to the monitored value. Specific recommendations were also generated for the use of bolts in tunnel structures.Numerical simulation was used to evaluate the safety of the tunnel and it confirmed that the current design can satisfy the requirement of the current code.

Non-contact monitoring and analysis system for tunnel surrounding rock deformation of underground engineering

It is very important to monitor surrounding rock deformation in tunnel construction. The principle, function, development and application of the system composed of a total station and computer for monitoring and analyzing surrounding rock deformation were discussed. The new methods of two free station of 3D measurement and its mathematic adjustment mode were presented. The development of software for total station on-board and post for computer were also described. Without centering it and measuring its height, the total station controlled by the software on-board can fulfill the whole measurements to target points. Monitoring data can be processed by the post software and results of regression analysis, forecasting information of the tunnel surrounding rock deformation can be provided in time. The practical use shows that this system is practicable, highly accurate and efficient. It satisfies the needs of safety and information construction in tunnel construction of underground engineering.

公路隧道改扩建方案比选及施工工法数值模拟

为了分析公路隧道改扩建方案的可行性以及公路隧道不同改扩建施工工法时围岩扰动后的力学特性,以济南绕城高速港沟立交至殷家林枢纽段改扩建工程某公路隧道为研究对象,比选3种公路隧道改扩建方案;建立三维数值模型,对比最佳方案不同施工工法时的围岩力学特性;利用有限差分软件FLAC 3D内置的FISH语言对围岩塑性区体积求和计算,探讨左线公路隧道改扩建过程对右线公路隧道的影响。结果表明:综合考虑改扩建施工难度、运营安全性、后期提速、管养难度、工程造价等因素,确定公路隧道改扩建为双八车道隧道为公路隧道改扩建最佳方案;围岩位移随着公路隧道开挖深度的增加而增大,并且在开挖断面处增大最快;围岩的压应力集中区为公路隧道的拱脚处,而拱顶和拱底压应力较小并向拉应力转变;围岩塑性区破坏方式以剪切破坏为主,可及时施作支护结构控制围岩变形;综合考虑公路隧道改扩建施工的可行性、安全性和经济性,确定中隔壁法为公路隧道改扩建最优施工工法。

基于FLAC3D的隧道开挖过程围岩稳定性研究

针对隧道在施工开挖过程中产生的复杂应力场和位移场,应用FLAC3D 6.0三维有限差分软件进行数值模拟。地层采用Drucker-Prager准则作为岩体塑性屈服准则,计算得到隧道开挖及支护后的隧道应力场、位移场分布规律,进而确定隧道需要支护的关键位置。结果表明,支护能够抑制应力和位移的扩大,显著提高围岩的承载力。

基于质量指标的隧道围岩智能分级及精益建造研究

隧道工程围岩级别的准确判识是围岩稳定性评价及隧道开挖精益支护的基础。围岩质量指标是围岩级别评判的依据,由于围岩质量指标计算包括定性与定量因素,存在定性指标难以准确评定,围岩级别精准评价困难的问题。采用围岩质量指标分级法与机器学习算法融合构建围岩智能分级软件系统,量化分析围岩分级质量指标要素,数值法求解围岩质量指标,围岩级别判定卡采集围岩要素,卡片信息软件系统自动识读、自动分析,快速判定围岩级别,精准确定支护参数,动态优化原支护设计方案。研究成果在3项隧道工程中实践应用,实现隧道围岩精准分级、精益支护建造的目标。

基于围岩监测的隧道施工期突涌水风险预测

突涌水灾害的频发对隧道安全施工和生命财产构成严重威胁,因此精准预测并有效控制隧道施工中的突涌水风险尤为重要。本研究旨在提出一种适用于隧道施工期的突涌水风险预测方法,通过反馈施工现场监测数据确定风险概率并预测水量范围。首先,在分析施工期突涌水事故案例的基础上,综合考虑地质构造和水文地质条件,并引入开挖支护、动态监测围岩以及渗压信息,建立了包含10个指标在内的突涌水评估指标体系;其次,采用博弈论组合赋权法优化主客观权重向量,构建改进功效系数模型以计算各风险等级下的综合功效系数,并在归一化处理后确定风险发生概率;最后,根据最大隶属度原则确定风险等级并预测水量范围。以鸡公岭隧道和跃龙门隧道为例,应用该方法对施工中的突涌水风险进行了预测。结果表明:所提出的基于博弈论组合权重和改进功效系数的隧道施工期突涌水灾害风险预测方法与现场开挖结果吻合较好;该方法综合考虑评估指标和风险等级之间非线性关系使预测结果更接近实际施工情况,在评估风险等级的同时实现了风险概率和涌水量范围的预测。

大断面花岗岩公路隧道快速施工工法研究

大断面隧道施工穿越较破碎花岗岩区段时,采用台阶法开挖会造成工序之间相互影响,严重制约了大型机械的作业空间,为此在台阶法基础上提出了便于大型机械施工的快速施工工法,从而提高了施工效率。文章基于某高速公路隧道,通过有限差分软件,对快速施工工法和施工设计的台阶法留核心土开挖进行两榀开挖下的数值模拟对比分析,并结合FISH语言编程和现场监测数据验证了快速施工工法的围岩损伤及可行性。结果表明:快速施工工法与台阶法留核心土开挖相比,会增大隧道拱肩、边墙以及掌子面处的围岩变形;现场施工时要加强对隧道边墙下方和拱脚处的监测;快速施工工法是一种可应用于现场的、安全高效的施工工法。

浅埋河谷段TBM施工应用与适宜性评价

TBM施工技术应用于隧洞开挖,技术上已经成熟,并广泛应用于深埋长大隧洞施工中。影响隧洞TBM施工的因素基本清楚,一般认为穿越浅埋河谷段隧洞采用TBM施工容易发生围岩塌方、涌水事故,不适宜采用TBM施工。为了研究浅埋河谷段TBM施工适宜性,通过两个典型的穿越浅埋河谷段隧洞TBM施工的工程实例,对比详细的工程地质条件,分析塌方的原因,进行TBM施工适宜性分析,结果表明,隧洞上覆弱风化岩体大于1倍洞径段进行适当的工程处理后,采用TBM施工是适宜性的。

深大竖井开挖稳定性数值模拟分析

依托芷铜高速椿木山隧道通风竖井工程,针对竖井施工对围岩造成的扰动影响以及初期支护受力情况进行数值模拟分析,探明了竖井开挖中围岩最危险区以及初期支护参数的合理性,并根据分析结果提出相应的加固或处理措施。结果表明:竖井施工对围岩造成的扰动较小,围岩不会出现明显的塑性区,揭示了在开挖并施作初期支护后,围岩具有一定的稳定性;随着开挖深度的加大,岩体最大应力也在增大,在竖井底部达到最大值3.36 MPa,地表沉降曲线呈现出明显的V形特征,中间沉降量大,越远离中部开挖区,沉降量越小;不同性质的围岩过渡区会出现应力突变,在实际操作中应加强围岩过渡区的支护与监测频率。

松散软弱围岩煤巷高效掘进及支护工艺优化研究

针对芦岭煤矿9^(#)煤层松散软弱围岩煤巷掘进技术难题,分析松散软弱围岩煤巷高效掘进支护主要影响因素及优化关键支护工序,并实现松散软弱围岩煤巷挖底、控顶、护帮整体控制效果,采用FLAC 3D数值模拟软件对芦岭煤矿Ⅱ946回风巷掘进支护方案及高效掘进工艺进行计算机模拟,设计松散软弱煤巷围岩稳定性控制措施,即“注浆锚杆(锚索梁)超前主动支护+协同柔性支护”工艺,现场试验表明芦岭煤矿Ⅱ946回风巷每日掘进从2.4 m增加到3.0~3.6 m,控制了松散软弱围岩的变形,提高了掘进效率。

复杂地质条件下小净距浅埋深隧道施工方案分析

隧道工程由于其施工的难度及复杂性,往往是整个建设工程中的重难点部分,尤其是复杂地质条件下的小净距浅埋深隧道,其施工方案的好坏直接关系到隧道施工的安全与质量。本文将已完工的兴汕高速大旗山隧道作为案例分析,全面介绍了该类隧道施工方案以及技术特点,为今后类似隧道的施工提供指导。

不同岩体条件下双护盾TBM施工性能分析

针对复杂地质条件下城市地铁隧道双护盾TBM的掘进性能评价,依托青岛地铁6号线创石区间左、右线TBM施工段,对全线施工数据进行收集与分析,研究不同围岩类别下双护盾TBM掘进参数与施工性能参数的变化规律。不同围岩类别下TBM利用率分析表明,双护盾TBM对岩体质量较差的围岩段具有良好适应性。分析了不同围岩类别下各掘进参数与工程破岩比能SE间关系,贯入度与SE的相关性最好,更适合作为评价TBM掘进过程中能量消耗的指标,且在不同围岩类别下,贯入度与工程破岩比能SE呈较好的负幂指数关系,在Ⅱ,Ⅲ,Ⅳ,Ⅴ类围岩类别下,当贯入度分别>2,5,8,10mm/r时,其对应的工程破岩比能SE在较低水平。

富水软弱围岩小净距隧道掌子面稳定性及超前管棚支护技术研究

以义东高速公路防军隧道为例,通过理论分析与数值模拟相结合,研究了富水软弱围岩小净距隧道的掌子面稳定性与超前管棚支护技术。首先,基于管棚Winkler地基模型分析了掌子面稳定性安全系数,并采用Midas GTS NX有限元软件建立隧道模型;然后,分别分析了有、无超前管棚支护两种方案下的管棚弯矩、隧道围岩位移、衬砌应力以及特征断面掌子面稳定性的变化规律;最后,结合现场实际情况提出了富水软弱围岩隧道超前管棚的施工控制技术,并对其施工效果进行了监测。结果表明:采用超前支护与注浆加固后,可以减小裂隙水对围岩的侵蚀,提高围岩稳定性;施作超前管棚支护不仅能够改善掌子面的受力情况,使其安全系数增大了54.7%,且可减小隧道开挖时的拱顶沉降变形和有效控制掌子面塑性区发展,其中掌子面的挤出变形减小了约23%。

某山区铁路隧道工程地质综合勘察与施工验证分析

近些年,高速铁路隧道修建积累了丰富的勘察设计与施工经验,而山区隧道的勘察一直是困扰业界的难题。通过对比分析后发现,隧道区物探的异常和区域地质资料的可溶岩分布,应引起项目负责人的高度警惕。施工前应进行更加详细的地质调查、加密布置勘探孔、采用不同方法的物探验证和深孔钻孔等手段进行验证,施工时更加重视超前水平钻和地质雷达等超前地质预报工作。通过总结提炼了勘察与施工配合的相关内容,提升了我院山区铁路勘察的方法和经验,更好地指导施工期隧道地质配合。

双洞八车道特大跨度隧道Ⅴ级石质围岩开挖工法

为减小双洞八车道特大跨度隧道洞口Ⅴ级石质围岩后行导坑爆破对已完成支护结构的不利影响,该文以平潭牛寨山隧道工程为例,针对原设计双侧壁导坑法在后行的临近导坑爆破时,易将原先已施工完成的临时钢支撑震塌,提出取消临时横向支撑的变更方案1,以及带竖向支撑的上下台阶法(变更方案2),再利用有限元法计算,模拟3种不同开挖工法对隧道变形及受力的影响。计算结果表明:3种方案引起的拱顶沉降相差较小,最大相差约11.8%;变更方案2引起的围岩应力最大,但变更方案2同时取消了左右侧壁导坑的横向支撑以及左右侧壁导坑下台阶的竖向支撑,大大简化了施工工序。最后,结合监测数据进行分析,隧道结构安全稳定,变更方案2不仅合理可靠,而且加快了施工进度,节约了造价。

大断面软弱围岩隧道施工方法研究

为了解决大断面软弱围岩隧道的施工技术难题,以G30连霍高速公路某隧道工程实例为依托,通过现场隧道拱顶下沉、周边收敛及支护结构受力的监控量测情况,开展大断面软弱围岩隧道合理施工方法的研究。结果表明:微台阶环形开挖预留核心土法能够保证隧道施工安全、质量、进度要求,满足项目建设需要。

浅埋软岩大跨度双线铁路隧道沉降控制技术研究

在浅埋软岩大跨度铁路隧道施工过程中,软岩大变形是尤为常见的现象,而其中沉降现象更为突出。如何降低沉降,减小其在隧道工程施工过程中的施工风险和维护成本,是尤为必要的。鉴于此,本文依托渝昆高铁山田隧道和华山松隧道3号横洞,开展隧道沉降变形控制技术研究,通过监测施作沉降控制措施前后隧道结构的沉降变形,分析了隧道沉降措施控制效果。结果表明:在施作沉降预控措施的里程段,沉降量远小于未采取措施的里程段。该结果验证了沉降处置措施的有效性,为高速铁路软弱围岩段隧道的安全施工提供了借鉴。

邻近寺庙群高海拔隧道钻爆施工关键技术研究

为解决同赛高速隧道施工中振动风险高、作业面不足、洞身超挖的问题,自主研究开发爆破风险识别程序,基于地质背景与施工条件,采用现场试验、数值模拟、工程实测等方式,开展隧道钻爆布孔形式、装药结构、轮廓线等技术参数优化研究。现场实践表明:通过应用研发振动风险识别程序,可大幅度提高现场振动风险识别、动态控制能力,有效避免了敏感人群、建筑群受扰动风险;依据现场有效作业面设大倾角掏槽布孔,辅以扩槽孔、拱顶单排下压孔等措施,在满足掏槽、破岩要求的前提下达到了提升工效的预期;采用优化周边孔装药结构、收紧拱顶轮廓线等措施,有效降低了洞身排险后超挖量,现场初支喷混超方量由200%降低至100%以内,同时每循环节省药量约20kg,经济效益显著。