Prediction model of surrounding rock deformation in doublecontinuous-arch tunnel based on the ABC-WNN

Purpose–The wavelet neural network(WNN)has the drawbacks of slow convergence speed and easy falling into local optima in data prediction.Although the artificial bee colony(ABC)algorithm has strong global optimization ability and fast convergence speed,it also has the drawbacks of slow speed while finding the optimal solution and weak optimization ability in the later stage.Design/methodology/approach–This article uses an ABC algorithm to optimize the WNN and establishes an ABC-WNN analysis model.Based on the example of the Jinan Yuhan underground tunnel project,the deformation of the surrounding rock of the double-arch tunnel crossing the fault fracture zone is predicted and analyzed,and the analysis results are compared with the actual detection amount.Findings–The comparison results show that the predicted values of the ABC-WNN model have a high degree of fitting with the actual engineering data,with a maximum relative error of only 4.73%.On this basis,the results show that the statistical features of ABC-WNN are the lowest,with the errors at 0.566 and 0.573,compared with the single back propagation(BP)neural network model and WNN model.Therefore,it can be derived that the ABC-WNN model has higher prediction accuracy,better computational stability and faster convergence speed for deformation.Originality/value–This article uses firstly the ABC-WNN for the deformation analysis of double-arch tunnels.This attempt laid the foundation for artificial intelligence prediction in deformation analysis of multiarch tunnels and small clearance tunnels.It can provide a new and effective way for deformation prediction in similar projects.

Mechanical properties and influence mechanism of confined concrete arches in high-stress tunnels

Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,which makes it difficult to meet the requirements of ground control under complex conditions. As a new support form with high strength and rigidity, the confined concrete arch plays an important role in controlling the rock deformation under complex conditions. The section shape of the tunnel has an important impact on the mechanical properties and design of the support system. However, studies on the mechanical properties and influence mechanism of the new confined concrete arch are rarely reported. To this end, the mechanical properties of traditional U-shaped steel and new confined concrete arches are compared and comparative tests on arches of circular and straight-leg semicircular shapes in deep tunnels are conducted. A large mechanical testing system for underground engineering support structure is developed. The mechanical properties and influence mechanism of confined concrete arches with different section shapes under different loading modes and cross-section parameters are systematically studied. Test results show that the bearing capacity of the confined concrete arch is 2.10 times that of the U-shaped steel arch, and the bearing capacity of the circular confined concrete arch is 2.27 times that of the straight-leg semicircular arch. Among the various influencing factors and their engineering parameters,the lateral stress coefficient has the greatest impact on the bearing capacity of the confined concrete arch,followed by the steel pipe wall thickness, steel strength, and core concrete strength. Subsequently, the economic index of bearing capacity and cost is established, and the optimization design method for the confined concrete arch is proposed. Finally, this design method is applied to a high-stress tunnel under complex conditions, and the deformation of the surrounding rock is effectively controlled.

Effect of pipe characteristics in umbrella arch method on controlling tunneling-induced settlements in soft grounds

Recent developments in tunneling have stimulated design practitioners to more effectively utilize the underground spaces.However,tunneling at shallow depth in soft grounds gives rise to concerns associated with tunnel instability.Umbrella arch method(UAM),as a pre-reinforcement approach of tunnels in complex geological conditions,is widely used to maintain the tunnel stability.Quantitative assessment of the impacts of the entire approach and forepoling pipe features on tunnel stability remains challenging due to the complex nature of the UAM application.This study aimed to assess the effect of pipe design parameters on reinforcing the tunnels excavated in soft grounds.This practical investigation considered the actual field conditions attributed to the tunneling procedure and UAM deployment.Then,the tunneling process was modeled and the tunnel excavation-induced settlements were calculated.The post-processed results confirmed that deploying the UAM substantially reduced the tunnel crown and ground surface settlements by 76%and 42%,respectively.Investigation of various design parameters of pipes underscored the significance of incorporating the optimum value for each individual parameter into design schemes to more effectively control the settlements.Additionally,contrasting the settlement reduction rates(SRRs)for pipe design variables showed that the tunnel stability is more sensitive to the changes in the values of diameter and length,compared to values of the installation angle and center-tocenter distance of the pipes.

The Types of Tunnels Maintenance in Umbrella Arch Method

During tunneling in loose grounds, the ground deformation caused by drillings around the tunnel, leads to land subsidence and the adjacent tunnel which would affect tunnel structure and surrounding structures. In such situations it is necessary to improve the properties of the ground prior to drilling operations. In order to acquire tunnel face stability during excavation operations in areas with loose soil fault or areas with lack of adhesion, there are various methods such as split cross drilling, frame holder or auxiliary pre-holding methods such as umbrella arch method;pre-holding methods must provide safety when drilling and must be affordable, economically. In this study, we assessed the previous studies on methods and behaviors of umbrella arch strategy in reinforcing the concrete tunnels, reached the purpose with experimental and numerical methods and offered the latest design achievements, implementation progresses and analysis in relation with this method.

Roof collapse mechanism of weak surrounding rock for deep-buried tunnels under high geostress conditions

High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for the failure mechanism that occurs in deep-buried tunnel roofs,taking into account the influence of geostress.The limit analysis theory was utilized for deriving analytical solutions about the geometry of the collapsing surface and the limit supporting pressure.The collapsing surface obtained by the analytical solution was validated by the findings of the physical model test,which shows a high level of agreement with the actual one.An extensive investigation was done to explore the effects of the lateral pressure coefficients,the tunnel buried depth,the geological conditions of the surrounding rock,the long-short axis ratio,and the size of the tunnel profile.The findings indicate that an increase in the lateral pressure coefficient from 0.5 to 1.5 results in a reduction in the height of the collapsing zone by 2.08 m and the width of the collapsing zone by 1.15 m,while simultaneously increases the limit supporting pressure by 18.9%.The proposed upper bound method accurately determines the limit supporting pressure and the geometry of the collapsing surface,which aligns well with the results acquired through numerical modelling and on-site monitoring in actual engineering applications.The proposed analytical method can serve as a reference for similar crown failure issues of deep-buried tunnels.

山区偏压连拱隧道开挖方法适应性数值分析研究

山区常存在偏压或围岩破碎情况,隧道穿越该地层施工时,围岩变形控制困难,施工扰动容易致使隧道拱顶坍塌及支护结构破坏。依托银花隧道工程,开展了偏压地层隧道施工开挖方法的适应性数值仿真研究,对比分析了“三导洞法”和“中导洞法”两种开挖方式中不同开挖步对软弱围岩偏压隧道围岩变形、拱顶沉降、最大主应力分布的影响规律。结果表明:三导洞法随着偏压处侧导洞开挖,左洞拱顶沉降区与中导洞开挖扰动变形区会形成沉降叠加,最大工地沉降出现在正洞开挖后,为-12.35 mm,所占沉降比η达到55.23%。中导洞施工时,最大沉降值分布在偏压拱腰处且呈扇形分布,左右洞上台阶施工产生的沉降比最大达到73.57%,中、下台阶开挖对拱顶沉降影响较小,最大拱顶沉降值为-17.81 mm。两种方法的最大主应力并非严格对称,尽管中导洞法施工产生较大沉降,但考虑施工成本和效率,“中导洞法”更为合理。

大跨度地铁车站十导洞洞桩法施工变形规律及其影响因素研究

[目的]为确保大跨度地铁车站施工安全,需对十导洞洞桩法施工过程中车站结构的变形规律及其影响因素进行研究。[方法]以西黄村站为工程背景,建立了大跨度车站十导洞洞桩法施工数值模型,分析了不同施工阶段地面的沉降以及桩的水平变形规律,研究了导洞开挖顺序、导洞开挖错距及扣拱施工顺序等三种因素对地面沉降的影响规律。[结果及结论]车站上方导洞以及中间导洞施工对地面沉降的影响较大;各施工阶段的地面沉降规律均满足正态分布,最大沉降位于车站中线处,导洞施工及扣拱施工两个阶段引起的地面沉降占总沉降的74.7%。车站负二层土体开挖后,桩在水平方向的约束急剧减弱,导致桩水平变形增大。先开挖下层导洞引起的地面沉降较小;随着导洞开挖错距的增大,地面最大沉降逐渐减小;先开挖两侧扣拱再依次开挖中间扣拱的施工顺序引起的地面沉降最小。

水利隧洞工程洞身开挖与衬砌施工工艺

为了最大限度上利用水资源,我国近年建设了很多水利工程项目,其中涉及大量的隧洞工程,洞身开挖和衬砌施工是隧洞工程施工中的关键环节,直接影响着施工周期以及施工过程的安全。首先对某水利隧洞工程项目进行概述,简要分析了整体施工思路,然后从洞身开挖、仰拱开挖衬砌施工、边顶拱衬砌施工等层面详细分析了施工工艺,积累了实践经验,对于提升我国水利隧洞工程的施工技术水平具有一定的实践意义。

铁路隧道无砟轨道上拱处治技术研究

为了解决深埋大跨度铁路双线隧道受高地应力影响引起无砟轨道上拱等问题,以西南某铁路双线隧道为研究对象,提出一种“拆换仰拱+加深加厚仰拱+隧底增设长锚杆”的综合治理方法,首先建立弹塑性三维模型来分析拟定换拱结构的参数,并对拆换仰拱法控制上拱效果进行预测分析,然后布置监控量测点对仰拱和边墙变形进行实测分析,根据弹塑性三维模型预测结果,采取拆换仰拱法可有效降低无砟轨道上拱变形,总上拱量较常规处理减小85%;根据实测数据结果,采取拆换仰拱法处理后,上拱速率呈现明显“加速期、线性降速期、波动平衡期”,仰拱和边墙上拱量比值接近2。研究结果表明,针对铁路隧道受高地应力引起的无砟轨道上拱问题,采取“拆换仰拱+加深加厚仰拱+隧底增设长锚杆”的综合治理方法可有效抑制仰拱上拱变形,对隧道前期设计具有重要指导意义。

考虑拱效应的巷道断面优化研究

为减少巷道开挖工作量和有效控制巷道围岩变形量,以拱形巷道拱高、巷宽及巷高为研究变量,采用L 16(34)三因素四水平的正交模拟实验,基于FLAC 3D数值模拟研究了各种组合情况下,巷道开挖后围岩变形量及塑性区面积变化规律。结果表明:拱高与巷道顶板围岩塑性区面积成负相关,与巷道帮角的破坏呈正相关,且最优组合巷道断面参数为巷宽4.5 m、巷高3 m、拱高1 m;采用优化方案后,直墙拱形巷道比原方案矩形巷道塑性区面积减少了35.07%,顶板下沉量减少了19.2%,两帮移近量减少了22.4%,巷道断面优化后可有效减少围岩塑性区破坏范围,有利于巷道的长期稳定。

高铁长大隧道斜井进正洞挑顶施工技术

隧道斜井进正洞处相比正常掘进具有开挖断面渐变、跨度大、结构复杂等特点,且过程中初支结构需要多次的应力转化,施工难度大、安全风险高,易出现冒顶、掉块等问题。西渝高铁樊哙隧道斜井进正洞挑顶施工,对过渡段进行小导管注浆和异形钢拱架加强,先纵向、横向开挖导洞再纵向分三台阶开挖正洞,拱顶变形和围岩水平收敛符合控制要求。挑顶方案有效的控制了交叉段的变形,总体效益良好,施工方案科学合理。

硬质裂隙灰岩隧道超前长管棚套拱支护施工技术研究

硬裂缝灰岩隧道地形高陡,下切严重,局部地形变化较大,导致其稳定性差,易产生塌方。为此,论文提出了硬质裂隙灰岩隧道超前长管棚套拱支护施工技术。根据工程概况,首先,对超前长管棚套拱参数进行设计,然后,进行钻孔,管棚制作及安装,最后,灌注浆液。试验结果证明:该技术能够有效地控制试件的变形程度,防止其过度变形或损坏,从而确保隧道施工安全和质量。

Numerical simulation of airflow distribution in mine tunnels

Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels is studied. The average velocity points were analyzed quantitatively. The results show that the airflow pattern is similar for the three-center arch section under different ventilation velocities and cross sectional areas. The shape of the tunnel cross section and wall are the critical factors influencing the airflow pattern. The average velocity points are mainly close to the tunnel wall. Characteristic equations are developed to describe the average velocity distribution, and provide a theoretical basis for accurately measuring the average velocity in mine tunnels.

Numerical analyses in the design of umbrella arch systems

Due to advances in numerical modelling, it is possible to capture complex support-ground interaction intwo dimensions and three dimensions for mechanical analysis of complex tunnel support systems,although such analysis may still be too complex for routine design calculations. One such system is theforepole element, installed within the umbrella arch temporary support system for tunnels, whichwarrants such support measures. A review of engineering literature illustrates that a lack of designstandards exists regarding the use of forepole elements. Therefore, when designing such support, designersmust employ complex numerical models combined with engineering judgement. With referenceto past developments by others and new investigations conducted by the authors on the Driskos tunnelin Greece and the Istanbul metro, this paper illustrates how advanced numerical modelling tools canfacilitate understanding of the influences of design parameters associated with the use of forepole elements.In addition, this paper highlights the complexity of the ground-support interaction whensimulated with two-dimensional （2D） finite element software using a homogenous reinforced region,and three-dimensional （3D） finite difference software using structural elements. This paper further illustratessequential optimisation of two design parameters （spacing and overlap） using numericalmodelling. With regard to capturing system behaviour in the region between forepoles for the purpose ofdimensioning spacing, this paper employs three distinctive advanced numerical models： particle codes,continuous finite element models with joint set and Voronoi blocks. Finally, to capture the behaviour/failure ahead of the tunnel face （overlap parameter）, 2D axisymmetric models are employed. Finally,conclusions of 2D and 3D numerical assessment on the Driskos tunnel are drawn. The data enriched casestudy is examined to determine an optimum design, based on the proposed optimisation of designparameters, of forepole elements related to the site-specific considerations. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Optimal Deployment Patterns for k-Coverage and k-Connectivity 3D WSNs in Underground Tunnel

In this paper,we first model the mining structure as a arched shape in terms of the tunnel geometry.Based on the regularly placement of nodes in that model,a set of deployment patterns for seamless coverage and k-connectivity is proposed,i.e.1-and 2-connectivity.Further,we figure out the maximum horizontal distance of tangent plane to determine the placement of nodes for k-coverage（k=1,2）.Besides,the mathematical relations between the communication radius and the sensing radius are derived,when the network keeps k-coverage（k=1,2） and k-connectivity（k=2,3） under certain regularity constrains for various patterns.Finally,we demonstrate the optimality of several approaches that we have proposed in the aspect of energy consumption and network lifetime.

A History of the Urban Underground Tunnel (4000 B.C.E. - 1900 C.E.)

Generally hidden from public view, out of our daily thoughts, and literally under our feet, are myriad urban underground tunnels that make our modern megacities possible. From their ancient beginnings in antiquity, as a means of supplying fresh water and draining waste water from cities, underground tunnels evolved into a means of providing high capacity rail mass transit in our most densely populated urban centers. This paper provides a broad overview of the evolution of urban tunnels across a 6000 year time span and includes the specific engineering formulas/computations for the earliest 19th century subways/infrastructure projects based on the Roman vaulted arch tunnel.

高地应力软岩隧道仰拱结构受力特性与参数优化

为探索高地应力软岩隧道施工期间仰拱结构受力特性与合理支护参数,以陕西省宝汉高速公路连城山隧道工程为依托,针对仰拱施工病害及其主要影响因子,采用现场试验与数值模拟相结合的方法,探讨了不同影响因素下的仰拱结构变形与力学响应,分析了仰拱结构变形与受力对不同影响因素的敏感性,基于仰拱结构病害特征及数值模拟结果,对仰拱半径(深度)、仰拱厚度等支护参数进行了优化,并进行了工程验证。结果表明:连城山隧道施工期间仰拱二次衬砌最大接触压力达1.034 MPa,混凝土最大应力超过其抗压强度(30 MPa),出现了仰拱回填隆起、开裂等病害,仰拱设计支护参数难以保障结构稳定;地应力水平和基底围岩劣化对仰拱结构变形与受力状态均有显著影响,其中基底软化深度的影响最为突出,地应力水平次之;减小仰拱半径、增大仰拱厚度、增大仰拱钢筋直径、减小仰拱钢筋间距均能显著抑制仰拱变形,而提高混凝土强度等级对控制仰拱变形效果不明显,且经济性较差;优化后的仰拱受力得以明显改善,有效控制了仰拱结构病害,避免了频繁拆换仰拱,保障了隧道结构安全稳定。研究成果可为类似软岩隧道仰拱变形控制及病害防治提供重要借鉴。

粉煤灰堆积体大断面连拱隧道失稳破坏模式及施工力学研究

国内目前并无在粉煤灰堆积体中采用暗挖法修建大断面连拱隧道的先例,给隧道的设计和施工带来了巨大挑战。依托盐坪坝隧道工程,开展了室内相似模型试验,探讨了该地层下大断面连拱隧道塌落拱演化规律及开挖施工力学行为。研究结果表明:连拱隧道在粉煤灰堆积体中开挖极易发生失稳,将失稳过程划分为4个演化阶段,破坏模式具有突发性、剧烈性、对称性、同步性特征;塌落拱高度约为隧道开挖跨度的40%。采用单侧壁导坑法开挖时粉煤灰堆积体承载力严重不足,根据相似换算关系左、右洞拱顶沉降分别为16.86,14.91cm,需对地层实施注浆加固;地层沉降呈对称“双峰状”,先行洞相较于后行洞受开挖影响较大,中隔墙的承载作用能够有效降低地层位移,单洞压力拱向双洞压力拱转换过程中,中隔墙受到偏压作用容易向先行洞侧偏转,建议在先行洞开挖时中隔墙添加支撑物。

无导洞法连拱隧道先行洞仰拱开裂及受力分析

研究目的:为探明无导洞法连拱隧道先行洞仰拱衬砌开裂的原因,本文首先通过现场监测得到先行洞的受力规律,然后基于该受力特征提出一种考虑后行洞开挖的先行洞荷载-结构计算模型,进而结合现场监测和数值计算分析先行洞仰拱衬砌的开裂原因,最后评价先行洞二衬的安全性并给出相应的控制措施。研究结论:(1)当后行洞开挖前,先行洞二衬对称受力且各截面的安全系数大于2.4;当后行洞开挖后,先行洞二衬处于偏压受力状态,仰拱右侧的安全系数仅为1.25,其内表面恰是最大拉应力所在位置,与现场仰拱衬砌的开裂位置吻合;(2)先行洞仰拱衬砌开裂的原因是由于后行洞开挖导致的隧道偏压受力以及仰拱不均匀沉降;(3)提高支护抗力系数有助于改善衬砌结构的安全性,但支护抗力系数高于某值后安全系数变化不大;(4)本研究成果可为相关连拱隧道的设计和施工提供参考。

浅埋无中导洞连拱隧道先行洞衬砌承担围岩荷载确定方法

不同于常规隧道衬砌结构,无中导洞连拱隧道先行洞衬砌施作稳定后还要受到邻近后行洞开挖的二次扰动,后行洞开挖对先行洞衬砌受力的影响不可忽视。依托杨家寨公路隧道工程,基于考虑了后行洞开挖影响的隧道围岩压力计算方法,结合现场监测位移数据采用荷载-结构法进行位移反分析,提出了一种确定浅埋无中导洞连拱隧道先行洞衬砌承担围岩荷载的方法,最后和衬砌背后围岩荷载现场监测值进行对比验证。研究结果表明:后行洞开挖对先行洞衬砌承担围岩荷载的影响较为显著,监测点增长幅度均值高达142%;先行洞衬砌受力呈现“拱腰较小,拱顶及拱肩较大”的分布规律,且靠近后行洞一侧拱肩位置受力最大;通过现场监测位移反分析得到的先行洞衬砌受力结果和现场监测结果较为一致,论证了该方法的合理性和实用性,研究成果可为无中导洞连拱隧道结构设计提供参考。