A series solution for surface motion amplification due to underground twin tunnels:incident SV waves

A series solution of displacement response of the ground surface in the presence of underground twin tunnels subjected to excitation of incident plane SV waves is derived by using Fourier-Bessel series expansion method.The numerical parametric study shows that underground twin tunnels significantly amplify the nearby surface ground motion.It is suggested that the effect of subways on ground motion should be considered when the subways are planned and designed.

World’s first implementation of close-fit pipe jacking of twin tunnels for construction of subway station--Innovation in equipment and construction technology

1 Project overview The Shasan station of Phase II of Shenzhen’s urban rail transit Line 12 is situated in Bao’an District,Shenzhen.It comprises a two-level underground island platform station,measuring 212 m in length,and 22.6 m in width,with an overburden thickness of about 7.0 m.Fig.1 illustrates the presence of a large underground reinforced concrete stormwater culvert,measuring 11.5 m by 3.6 m,traversing the station’s center.

Numerical investigation on the responses of existing single piles due to adjacent twin tunneling considering the lagging distance

This paper presents an assessment of the influence of the lagging distance between two horizontal tunnel faces of the side-by-side twin tunnels on the responses of the adjacent existing single pile by a series of three-dimensional numerical analyses.Two different relative positions between the pile tip and the tunnel are considered to cover the short and long pile behaviors.The responses of the existing pile in terms of pile head settlement,axial force,lateral movement and bending moment are considered and discussed.The numerical results indicate that the lagging distance between twin tunnel faces significantly affects not only the soil movements but also the responses of the existing single pile.The critical case that produces unsatisfactory pile responses due to twin tunneling is when the lagging distance between the second tunnel and the preceding tunnel equals to the shield length.It is recommended that the lagging distance be not less than three times of shield length when the two tunnels need to be concurrently excavated.

Prediction of lining response for twin tunnels constructed in anisotropic clay using machine learning techniques

Excessive structural forces generated inside tunnel linings could affect the safety and serviceability of tunnels,emphasizing the need to accurately predict the forces acting on tunnel linings during the preliminary design phase.In this study,an anisotropic soil model devel-oped by Norwegian Geotechnical Institute(NGI)based on the Active-Direct shear-Passive concept(NGI-ADP model)was adopted to conduct finite element(FE)analyses.A total of 682 cases were modeled to analyze the effects of five key parameters on twin-tunnel struc-tural forces;these parameters included twin-tunnel arrangements and subsurface soil properties:burial depth H,tunnel center-to-center distance D,soil strength s_(u)^(A),stiffness ratio G_(u)=s_(u)^(A),and degree of anisotropy ss_(u)^(P)=s_(u)^(A).The significant factors contributing to the bending moment and thrust force of the linings were the tunnel distance and overlying soil depth,respectively.The degree of anisotropy of the surrounding soil was found to be extremely important in simulating the twin-tunnel construction,and severe design errors could be made if the soil anisotropy is ignored.A cutting-edge application of machine learning in the construction of twin tunnels is presented;multivariate adaptive regression splines and decision tree regressor methods are developed to predict the maximum bending moment within the first tunnel’s linings based on the constructed FE cases.The developed prediction model can enable engineers to estimate the structural response of twin tunnels more accurately in order to meet the specific target reliability indices of projects.

Effect of constructing twin tunnels under a building supported by pile foundations in the Sydney central business district

In congested cities such as Sydney,competition for underground space escalates within the built environment because various assets require finite geotechnical strength and support.Specific problems such as damage to buildings may develop when high-rise buildings on piled foundations are subject to ground movements as tunnels are constructed.This paper focuses on the risks of tunneling beneath Sydney’s Martin Place and how buildings are subject to additional loads caused by tunneling.The key objective of this study is to improve the understanding of tunnel-rock-pile interactions and to encourage sustainable development.A finite element model is developed to predict the interaction between tunnel construction and piled foundations.The tunnel,rock,and pile components are studied separately and are then combined into a single model.The ground model is based on the characteristics of Hawkesbury Sandstone and is developed through a desktop study.The piles are designed using Australian Standards and observations of high-rise buildings.The tunnel construction is modeled based on the construction sequence of a tunnel boring machine.After combining the components,a parametric study on the relationship between tunnel location,basements,and piles is conducted.Our findings,thus far,show that tunneling can increase the axial and flexural loads of piles,where the additional loading exceeds the structural capacity of some piles,especially those that are close to basement walls.The parametric study reveals a strong relationship between tunnel depth and lining stresses,while the relationship between tunnel depth and induced pile loads is less convincing.Furthermore,the horizontal tunnel position relative to piles shows a stronger relationship with pile loads.Further research into tunnel-rock-pile interactions is recommended,especially beneath basements,to substantiate the results of this study.

Comparison of rectangular and circular bored twin tunnels in weak ground

The recent innovation of a rectangular tunnel boring machine(TBM),and its use in the Hongzhuan Road tunnel underpass by the China Railway Engineering Group(CREG),has revitalized shallow depth soft soil tunneling.This paper presents the findings of a numerical study using PLAXIS to determine the surface settlements and moments produced in tunnel linings for circular and rectangular twin tunnels.The effects of the relative positions of twin tunnels,critical distances,volume losses,depths of burial,and tunnel sizes for both circular and rectangular tunnels are the key parameters of this investigation.The results indicate that rectangular tunnels are suitable for shallow depths in weak ground as they have lesser settlement compared with circular tunnels.This is crucial for tunneling beneath important structures such as railway lines and existing roads.However,the maximum bending moment produced in the rectangular tunnel lining is higher than that for circular tunnels.The use of rectangular TBMs is an unconventional method in modern day tunneling;however,the analysis in this project recommends that tunnel industry engineers consider this method for shallow depth weak ground tunneling.

Safe range analysis of clear distance of twin shallow tunnels based on limit analysis and reliability theory

A method of analyzing the stability of twin shallow tunnels was presented using both limit analysis with nonlinear failure criterion and reliability theory.In the condition of nonlinear failure criterion,the critical clear distancesof twin shallow tunnels were obtained by analyzing the change of surrounding pressure.A reliability model was established based on limit state equation,and the failure probability was solved by virtue of Monte Carlo method.Safety factor and corresponding clear distance of different safety levels were obtained by introducing a target reliability index.The scope of clear distance for different safety levels is described,which can be used as a supplement and improvement to the design codes of tunnels.

Energy analysis of stability of twin shallow tunnels based on nonlinear failure criterion

Based on nonlinear Mohr-Coulomb failure criterion, the analytical solutions of stability number and supporting force on twin shallow tunnels were derived using upper bound theorem of limit analysis. The optimized solutions were obtained by the technique of sequential quadratic programming. When nonlinear coefficient equals 1 and internal friction angle equals 0, the nonlinear Mohr-Coulomb failure criterion degenerates into linear failure criterion. The calculated results of stability number in this work were compared with previous results, and the agreement verifies the effectiveness of the present method. Under the condition of nonlinear Mohr-Coulomb failure criterion, the results show that the supporting force on twin shallow tunnels obviously increases when the nonlinear coefficient, burial depth, ground load or pore water pressure coefficients increase. When the clear distance is 0.5to 1.0 times the diameter of tunnel, the supporting force of twin shallow tunnels reaches its maximum value, which means that the tunnels are the easiest to collapse. While the clear distance increases to 3.5 times the diameter of tunnel, the calculation for twin shallow tunnels can be carried out by the method for independent single shallow tunnel. Therefore, 3.5 times the diameter of tunnel serves as a critical value to determine whether twin shallow tunnels influence each other. In designing twin shallow tunnels,appropriate clear distance value must be selected according to its change rules and actual topographic conditions, meanwhile, the influences of nonlinear failure criterion of soil materials and pore water must be completely considered. During the excavation process, supporting system should be intensified at the positions of larger burial depth or ground load to avoid collapses.

Interaction of Twin Circular Shallow Tunnels in Soils—Parametric Study

In big and crowded cities with limited urban areas, it is sometimes necessary to build twin tunnels to overcome transportation problems. In a city like Riyadh in Saudi Arabia, tunneling becomes very essential to solve effectively traffic conjunctions and associated problems. The city started to construct big tunneling projects and it is expected in the near future to start building twin tunnels. If the design and construction process of twin tunnels are not understood and considered, damage to the tunnel lining or excessive ground surface settlement may take place. In this study, the interaction between adjacent tunnels excavated through soils in Saudi Arabia has been investigated using FE analysis and the range of the encountered soil properties. The investigation considered the effect of spacing between the twin tunnels and ground conditions on tunnel behavior. The analysis focused on the effect of constructing twin tunnels on ground surface settlement, contact pressure between lining and ground, and change in tunnel diameter. Based on the results obtained, it was observed that as the compressibility ratio, c, and spacing between tunnels decreased, the interaction effect between tunnels increased. For compressibility ratio of 0.01, the excavation of the new tunnel caused an increase in the lining deformation of the old one in the range of 0.1% to 0.3%. Furthermore, the excavation of the new tunnel leads to an increase in the contact pressure at the crown of the old one by 7% - 9%. At the spring line level, the excavation of the new tunnel had almost no effect on the far side of the old one. On the other hand, and for low compressibility ratio, the new tunnel excavation significantly affected contact pressure at the near side of the old one. For an expected tunnel life of 100 years, the results show an increase in the normalized contact pressure at the crown of the old tunnel due to the excavation of the new one in the range of 2% - 7% for compressibility ratio ranging between 0.01 - 0.1, respectively.

隧道施工引发粉土地面沉降模拟与分析

为研究黄泛区粉土地层内开挖双线地铁隧道对地上及其周边地面沉降的影响,以某双线地铁隧道开挖工程为例,考虑地下水、隧道间距对地面沉降的影响,采用流固耦合数值方法和理论分析方法对隧道施工引起的地面沉降规律进行分析。将数值模拟数据与Peck公式进行反演计算,并考虑隧道间隔和埋深的影响提出修正Peck公式,再结合叠加原理建立适用于双线隧道开挖引起地面沉降的修正叠加公式。结果表明:隧道开挖扰动地层将引起超静孔隙水压力现象;数值模拟与理论计算得到隧道间隔为4 m时,地面沉降曲线呈现“V”型,隧道间隔为8 m、12 m时,则沉降曲线呈现“U”形;粉土内开挖双线地铁隧道,地面容易受到扰动且沉降量大,随着隧道间距的增加,隧道上方土体沉降量逐渐减小;基于修正Peck公式计算结果与数值模拟结果基本一致,相对误差在3%左右,表明该公式具有很好的实用性。研究可为粉土地区隧道及地下工程建设提供理论依据和技术支撑。

钻爆法隧道下穿既有双连拱隧道施工技术研究

钻爆法隧道穿越新建既有双连拱隧道结构,下穿隧道为大跨度隧道,高度大、埋深较深,且在穿越既有隧道时,不能影响其安全运营和造成结构破坏,施工难度大、风险高。采用有限元软件Midas GTS NX对钻爆法隧道下穿既有隧道的变形和受力情况进行数值模拟计算,并研究了下穿施工前对上方隧道间地层采用大管棚和锚杆联合加固产生的效果。研究表明:未加固时,施工侧隧道结构的沉降要大于另一侧,呈现出“一峰二谷”变形形状,既有隧道上下部极易发生结构破坏。采用大管棚及锚杆联合加固,有效地转移了应力集中现象,降低了结构破坏风险,并且既有隧道沉降量仅为前者变化量的1/1.83,在控制标准以内。

双洞隧道地铁运行引起的软土地基振动及孔压研究

建立双洞隧道的三维有限差分模型,通过车轨耦合计算得到地铁运行中隔振器的力时程,以集中力的形式施加到地铁轨道对应的节点上,分析探讨了软土地基中振动加速度和超静孔隙水压力的变化规律及影响范围等。结果表明:左侧隧道和右侧隧道振动及孔隙水压力的变化基本一致,在地铁的一次相向运行过程中,软土地基的地表竖向振动加速度在两隧道中心处出现最大值,在距隧道中心轴约25 m处存在地表振动加速度放大现象,在距隧道中心轴150 m外,地表加速度峰峰值衰减至2 gal以下。软土地基中的超静孔隙水压力随着远离隧道而快速减小,在距隧道中心轴80 m外,超静孔隙水压力便衰减至100 Pa以下。白天地铁运行过程中,超静孔隙水压力出现较平稳的振荡,晚间地铁停运后,超静孔隙水压力出现一定程度下降,且随着地铁的反复运行下降幅度减小。

资阳市纵二路隧道内爆炸易损性问题研究

隧道作为重要的交通基础设施,其在内部爆炸荷载作用下的动力响应特性与易损性问题的研究具有重要的工程意义。针对四川省资阳市临空经济区纵二路双洞隧道,开展了内爆作用下的易损性问题研究。基于Hypermesh前处理软件建立了双洞隧道有限元数值模型,确定隧道内爆后损伤指标并对计算结果进行分析,采用非参数方法绘制双洞隧道易损性曲线。结果表明:炸药当量在0~1000 kg范围内,隧道损伤程度主要是轻度破坏;1000~2000 kg范围内,隧道内爆后出现中度破坏;2000~8000 kg范围内,隧道内爆损伤以重度损伤为主;一旦炸药当量>8000 kg,隧道损伤达到完全破坏。此外,当炸药当量≯8000 kg时,双洞隧道完全破坏的概率<25%。

软土地层双线隧道地表沉降计算公式修正

由于双线隧道存在复杂的耦合作用,盾构施工引起的地表沉降规律极为复杂,所以准确计算地表沉降较为困难。基于Peck公式和Chapman修正参数,考虑先行隧道的施工影响和双线隧道的相对位置关系,通过参数的经验量化,建立双线隧道地表沉降的计算公式。此外,依托苏州市轨道交通S1号线工程,讨论公式在不同土层中的适用性及参数取值范围,在此基础上采用PLAXIS 3D有限元软件对双线隧道盾构施工进行了数值模拟。结果表明:在软土地层中进行盾构施工,应用所建修正公式计算得到的地表沉降值与数值模拟和现场实测结果均较为吻合。所建修正公式考虑了双线隧道的位置信息,可以定量反映隧道埋深和双线隧道间距对地表沉降的影响。研究成果可为软土地区双线隧道盾构施工沉降计算提供参考。

Numerical analysis of surface subsidence in asymmetric parallel highway tunnels

Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels(Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and inequidimensional noncircular tunnel.

基于能量法的双线下穿既有隧道沉降研究

针对双线隧道穿越施工造成的复杂影响问题,基于能量方法,提出了考虑地层损失率差异的双线下穿开挖作用下既有隧道沉降的计算方法。基于经典的Peck和Mair理论,在计算新建隧道开挖引起的地层位移时,引入Hunt双线开挖沉降修正系数,考虑双线隧道先后穿越引起的地层损失率差异性所造成的影响;基于Rayleigh-Ritz法和弹性地基梁理论,写出系统各部分功能关系式,建立系统总势能方程;利用变分法求解总控制方程,得到考虑地层损失率差异的双线隧道下穿引起既有隧道沉降的理论解析,并将理论计算结果与已有文献报道的工程实测沉降数据进行对比验证;以双线隧道下穿既有隧道为例,对双线中心间距、新建隧道直径以及新旧隧道净距展开参数分析。结果表明:理论计算结果与实测数据整体趋势一致,二者吻合较好,验证了所提方法的可行性;新建隧道先后下穿引起的地层损失率差异对既有隧道的沉降有显著影响;随着新建双线中心间距和新旧隧道净距的增大,既有隧道的沉降量随之减小;随着新建隧道直径的增大,既有隧道的沉降量随之增加,且第二次下穿施工产生的沉降影响会越发明显。研究成果可快速且合理评估既有隧道受新建隧道穿越施工影响时的纵向变形响应,对类似的双线隧道工程起到一定的理论支持和指导意义。

基于等效理论的水下双孔隧道渗流场半解析研究

为研究隧道设计参数对水下双孔隧道渗流场的影响,建立了水下双孔平行隧道渗流计算模型。运用Abaqus软件构建数值模型,以隧道埋深、双孔间距和支护结构参数为影响因素,分析各因素对解析解计算误差的影响以及支护结构外水压力的变化特征,并采用灰色关联理论研究各影响因素的敏感度。最后,基于数值计算结果对解析解进行修正,得到计算精度较高的半解析解。结果表明:二次衬砌结构参数对初期支护外水压力的折减幅度影响较大,埋深、间距和注浆圈参数对初期支护外水压力的折减幅度影响较小。支护结构渗透系数对拱顶处解析解计算误差影响较大,支护结构厚度对拱底处解析解计算误差影响较大。埋深与等效半径之比小于19时,解析解计算误差大致为12%。注浆圈渗透系数与二次衬砌渗透系数之比小于20时,拱顶处解析解计算误差超过10%。注浆圈渗透系数对拱顶处解析解计算误差影响较大,隧道埋深对拱底处解析解计算误差影响较大。

煤矿掘进机系统数字孪生技术研究

针对煤矿巷道掘进作业中,地质结构复杂、现场环境恶劣、掘进设备智能化程度低、安全事故频发等问题,提出了一种数字孪生解决方案。通过融合物联网、互联网、数字孪生和虚拟现实等技术,以PLC为硬件核心、MQTT协议和EMQX服务为基础、建立参数矩阵映射规则和故障原因分析表,实现了掘进作业数据采集与处理、设备与孪生模型间的数据映射、数据存储、作业过程仿真、远程遥控、智能故障检测与预警等功能,提升了煤矿掘进作业过程的数字化、智能化水平。研究结果表明,该方案在煤矿掘进作业过程中具备较强的可行性、可靠性和实用性,具有推广应用价值。

基于数字孪生技术的煤矿掘进机自动截割方法研究

为了解决目前掘进工作面设备自动化控制存在的缺乏可视化人机交互控制、缺乏掘进工作面数字孪生动态建模、缺乏巷道模型与掘进机定位导航系统融合的问题,提出一种基于三维数字孪生技术的煤矿掘进机自动截割方法;该方法利用三维数字孪生技术的巷道模型生成截割模板,实现掘进机对预设截割断面的自动化截割,可达到人工远距离、可视化控制掘进机安全自动作业的目的。介绍了数字化巷道和掘进机模型的构建方法以及数据驱动逻辑,并对掘进机自动截割控制方法进行了详细阐述。结果表明,该方法避免了粉尘等对掘进机自动化截割的影响,降低了人员现场作业风险和劳动强度,解决了掘进机远程截割精确度低、巷道断面成型质量差等问题。

地铁隧道穿越地裂缝段暗挖施工对地表影响规律分析

基于有限元分析软件,对穿越地裂缝的隧道开挖引起的地表横向变形、地表竖向位移和隧道变形规律进行分析。结果表明:(1)地表横向最终变形曲线呈现出“W型”,两个凹槽分别位于左右线隧道的中心处,且受到双洞效应的影响,左线地表横向沉降要大于右线;(2)隧道左右线开挖过程中沿开挖方向地表沉降变形在开挖进尺为5 m时,地表表现出局部隆起的趋势;且距地裂缝的距离越近,地表沉降和横向变形越大;(3)当地裂缝位于隧道正上方时,地表沉降变形规律可划分为三个阶段:平稳变形阶段,加速变形阶段,变形稳定阶段;(4)左右线隧道拱顶拱底最大变形位置均在地裂缝附近,左线隧道拱顶拱底最大变形分别为-48、47 mm,右线隧道拱顶拱底最大变形分别为-45、44 mm。建议在地裂缝主变形带内设置沉降缝,预留净空变形量,并加强隧道的结构刚度,提高抗变形能力,并预留轨道、接触网等的调整高度。