Assessing the deformation response of double-track overlapped tunnels using numerical simulation and field monitoring

The unprecedented rate of metro construction has led to a highly complex network of metro lines.Tunnels are being overlapped to an ever-increasing degree.This paper investigates the deformation response of double-track overlapped tunnels in Tianjin,China using finite element analysis(FEA)and field monitoring,considering the attributes of different tunneling forms.With respect to the upper tunneling,the results of the FEA and field monitoring showed that the maximum vertical displacements of the ground surface during the tail passage were 2.06 mm,2.25 mm and 2.39 mm obtained by the FEA,field monitoring and Peck calculation,respectively;the heaves on the vertical displacement curve were observed at 8 m(1.25D,where D is the diameter of the tunnel)away from the center of the tunnel and the curve at both sides was asymmetrical.Furthermore,the crown and bottom produce approximately0.38 mm and 1.26 mm of contraction,respectively.The results of the FEA of the upper and lower sections demonstrated that the tunneling form has an obvious influence on the deformation response of the double-track overlapped tunnel.Compared with the upper tunneling,the lower tunneling exerted significantly less influence on the deformation response,which manifested as a smaller displacement of the strata and deformation of the existing tunnel.The results of this study on overlapped tunnels can provide a reference for similar projects in the future.

Case study of performance assessment of overlapping shield tunnels with a small curve radius

Due to the network planning of subways and their surrounding structures,increasingly more overlapping shields with a small curve radius have been constructed. A newly constructed upper tunnel partly overlaps a lower one, leading to the extremely complex uplift of the lower tunnel caused by the construction of a new tunnel. Based on the shield-driven project that runs from the Qinghe Xiaoyingqiao Station to the Qinghe Station in Beijing, which adopts the reinforcement measures of interlayer soil grouting and steel supports on site, in this study, the uplift pattern of the lower tunnel and the stress characteristics of steel supports were investigated through numerical simulations and on-site monitoring.The study results show that among all tunnel segments, the first segment of the shield witnesses a maximum uplift displacement that increases with the horizontal space between tunnels. On using either interlayer soil grouting or steel-ring bracing reinforcement, the uplift of the tunnel lining exceeds the control value;by contrast,when these two measures are jointly applied, the uplift of the tunnel lining does not exceed a maximum value of 4.87 mm, which can satisfy the requirements of deformation control. Under these two joint measures, the soil strength between two stacked shield tunnels can be enhanced and the uplift deformation can be restricted with the interlayer soil grouting. Also, the segmental deformation and overall stability of the existing tunnel can be controlled with the temporary steel supports.The deformation of circumferential supports and segments is closely related to each other, and the segmental uplift is controlled by H-shaped steel supports. With the increase in the horizontal space between twin shields, the effect of the construction would gradually weaken, accompanied by a gradual reduction of the stresses of steel supports. These findings provide a valuable reference for the engineering design and safe construction of overlapping shield tunnels with a small curve radius.

Dynamic interaction of twin vertically overlapping lined tunnels in an elastic half space subjected to incident plane waves

The scattering of plane harmonic P and SV waves by a pair of vertically overlapping lined tunnels buried in an elastic half space is solved using a semi-analytic indirect boundary integration equation method. Then the effect of the distance between the two tunnels, the stiffness and density of the lining material, and the incident frequency on the seismic response of the tunnels is investigated. Numerical results demonstrate that the dynamic interaction between the twin tunnels cannot be ignored and the lower tunnel has a significant shielding effect on the upper tunnel for high-frequency incident waves, resulting in great decrease of the dynamic hoop stress in the upper tunnel; for the low-frequency incident waves, in contrast, the lower tunnel can lead to amplification effect on the upper tunnel. It also reveals that the frequency-spectrum characteristics of dynamic stress of the lower tunnel are significantly different from those of the upper tunnel. In addition, for incident P waves in low-frequency region, the soft lining tunnels have significant amplification effect on the surface displacement amplitude, which is slightly larger than that of the corresponding single tunnel.

Deformation analysis of ground and existing tunnel induced by overlapped curved shield tunneling

The deformation caused by tunnel excavation is quite important for safety,especially when it is adjacent to the existing tunnel.Nevertheless,the investigation of deformation characteristics in overlapped curved shield tunneling remains inadequate.The analytical solution for calculating the deformation of the ground and existing tunnel induced by overlapped curved shield tunneling is derived by the Mirror theory,Mindlin solution and Euler-Bernoulli-Pasternak model,subsequently validated through both finite element simulation and field monitoring.It is determined that the overcutting plays a crucial role in the ground settlement resulting from curved shield tunneling compared to straight shield tunneling.The longitudinal settlement distribution can be categorized into five areas,with the area near the tunnel surface experiencing the most dramatic settlement changes.The deformation of the existing tunnel varies most significantly with turning radius compared to tunnel clearance and grouting pressure,especially when the turning radius is less than 30 times the tunnel diameter.The tunnel crown exhibits larger displacement than the tunnel bottom,resulting in a distinctive‘vertical egg'shape.Furthermore,an optimized overcutting mode is proposed,involving precise control of the extension speed and angular velocity of the overcutting cutter,which effectively mitigates ground deformation,ensuring the protection of the existing tunnel during the construction.

Investigation and measurement of old building response to the overlapped shield tunnel of multiple schemes in the sandy cobble stratum

Ground movements due to tunneling are becoming increasingly critical as buildings are located around construction sites.This study proposes a new combined reinforcement method using a foundation grouting oblique pipe roof.The former improves the bearing capacity of the subsoil,and the latter blocks the transmission of soil deformation,which weakens the influence of construction during overlapped tunnel under-crossing.Based on this new method,a case study of the shield tunneling response to an old building in Line 6 of China’s Chengdu Metro is presented.Additionally,three-dimensional numerical models without reinforcement,traditional foundation grouting reinforcement,and the new combined reinforcement schemes were compared.The numerical simulation performance was verified using a set of field instrumentation data,which demonstrated that the old building response to the overlapped tunnels was under control,and the maximum deformation,angular distortion,and principal tensile strain of the building were 5.25 mm,5.1010–6 rad/m,and 0.0081%,respectively.Compared with the traditional reinforcement scheme,the deformation,angular distortion,and principal tensile strain in the combined reinforcement scheme were reduced by 54.78%,71.02%,and 70.22%,respectively.These results have important implications for the design and construction of shield tunnels and their response to old buildings.

双线暗挖叠落隧道施工对地面沉降影响研究

北京地铁22号线定福庄站—管庄站双线暗挖叠落隧道工程安全风险极高,易产生严重变形和不均匀沉降问题,采用有限差分软件对隧道施工诱发地面沉降问题展开研究,基于现场监测数据证明模型的可靠性,并对不同施工方案的影响规律进行探讨。结果表明:模型计算结果与现场监测结果基本吻合,沉降差异较小,模拟结果准确可信。在施工过程中,监测点地面沉降随隧道下穿顺序依次开始增大,沉降量与隧道净距成反比,与距隧道开挖区域水平距离成反比,且沉降增量呈现两个阶段的变化特征,第一个阶段中位于砂土层中的下层隧道施工影响更加显著;不同施工方案诱发地表变形规律接近,下导洞开挖阶段变形增量相对较大,上导洞先施工的方案可显著减少最终地面沉降,施工条件允许时可以优先采用。研究结果可以为相关工程的沉降预测和施工方案选择提供参考。

软土地层三线小角度叠交盾构隧道施工影响规律及位移控制

天津地铁6号线入出段线盾构隧道上穿既有隧道,通过现场实测和数值模拟对既有隧道结构变形规律、变形影响因素、不同变形控制措施的效果进行了研究。结果表明:盾构上穿过程中既有隧道竖向位移整体呈现出隆起-沉降-隆起的变化规律;刀盘距叠交部位断面距离L=2.0D(D为隧道直径)时,叠交部位断面轴力达到最大值,L=0~2.0D时,叠交部位断面弯矩逐渐由L≤0时的横8字形转变为L≥2.0D时的三叶草形;新建隧道与既有隧道的叠交角度在15°~60°、竖向净距小于1.0D时,既有隧道竖向位移受新建隧道影响较大,实际工程中应使叠交角度大于60°,竖向净距大于1.0D;设置支撑台车后,支撑台车影响范围约为2倍台车长度,在影响范围内横断面位移得到控制,但随着支撑台车离开,原来位置处对位移的控制效果逐渐消失;与不注浆相比,深孔注浆加固后既有隧道竖向位移最大值和水平位移最大值分别减小了67.4%、76.0%。

上下重叠隧道盾构法施工引起的地面沉降分析

[目的]重叠隧道特殊的施工方式可能会导致地面沉降槽的形成及地层损失率的增加,对周边环境和建筑物造成影响。因此,有必要对重叠隧道施工中的地面沉降规律进行研究。[方法]以北京地铁昌平线清河小营桥站—学知园站区间的完全重叠段隧道为例,结合数值分析与现场监测数据,系统地研究了盾构重叠隧道施工过程中的地面沉降和地层损失情况,分析了上线隧道和下线隧道的施工顺序对地面沉降槽形态、最大沉降值及地层损失率的影响。[结果及结论]盾构重叠隧道施工中存在明显的叠加效应。上线隧道的施工会对地层造成一定的损失,并导致地面最大沉降值的增加。重叠施工情况下,上线隧道开挖造成的地层损失小于不涉及重叠施工情况下的上层隧道单独施工造成的地层损失。重叠隧道施工中的地层损失率不受隧道埋深变化的影响,且单线开挖与重叠开挖的地层损失率相差不大。在本工程类似地层中,地层损失率可大致按0.25%进行估算。

轴流压气机串列叶栅前后叶型位置匹配特性研究

采用数值和试验相结合的方法研究了高负荷轴流压气机串列叶栅前后叶型位置的匹配特性,详细分析了周向节距比和轴向重叠度2个参数对叶栅性能的影响规律和机理。结果表明,串列叶栅性能受周向节距比的影响较轴向重叠度更为显著,且在周向节距比的最优设计空间内,串列叶栅性能不再随2个参数的改变发生显著变化。周向节距比增大使缝隙流道收敛度和缝隙射流加速比增大,改变了前叶尾缘压力面和后叶前缘吸力面附近的流动特性,使前叶尾缘负荷增加,后叶前缘负荷和攻角降低,进而减弱了后叶吸力面分离。当周向节距比增大到缝隙流道闭合边界附近时,缝隙射流动量的显著降低导致分离损失显著增大。最后,采用叶栅风洞吹风试验,验证了数值计算得到的部分典型周向节距比和轴向重叠度匹配方案研究结果的可靠性。

铁路上下重叠隧道施工力学特性研究

随着我国道路交通工程建设的快速发展,不断有上下或交错重叠布置的高难度隧道工程涌现。本文依托重庆东环线铁路芭蕉沟上下重叠隧道工程,针对不同典型断面建立了多个数值模型,研究了重叠隧道施工历程中隧道拱顶位移、仰拱变形和横撑处水平收敛的变化规律以及相应的非同步开挖条件下的隧道衬砌应力分布特征,并且结合施工引起的地层应力变化规律以及塑性区分布特征分析了开挖过程的地层扰动效应。结果表明:(1)不同断面处的上层隧道施工主要引起下层隧道的拱顶沉降与净空收敛,而对仰拱部分影响较小,施工中应重点关注拱顶沉降与净空收敛;(2)当上、下层隧道相距较近时,上层隧道施工会导致下层隧道一定程度隆起,随两隧道之间距离的增加,回弹程度逐渐降低直至沉降。据此提出相应的施工扰动控制措施,从而为优化结构设计和指导现场施工服务,并可为今后类似工程提供借鉴与参考。

富水砂层盾构叠落隧道开挖步序优化

依托哈尔滨地铁3号线区间叠落盾构隧道工程,建立模拟泥水盾构机掘进施工过程的三维数值模型。通过现场监测数据与模拟数据进行比对验证,验证该模型有效性,同时进一步分析上下隧道施工顺序对地层与衬砌变形的影响。研究表明:先进行下线隧道开挖再进行上线隧道开挖更为安全,且两隧道掘进面距离越远,衬砌与周围地层变形越小;当两隧道掘进面距离10环进行施工情况下,衬砌变形与原有工况相比差距不大,可实现上线隧道与下线隧道同时掘进开挖。

重叠隧道盾构施工下穿铁路营业线施工技术研究

以合肥地铁8号线耀远路站—灵璧路站区间隧道上下重叠下穿铁路轨道群工程为例,根据工程地质条件及施工重难点,分析了施工过程中可能存在的风险,研究了盾构施工过程中的控制措施、掘进参数控制以及监测控制,以确保轨道群的运营安全及施工质量。

小转弯半径叠落盾构隧道施工相互影响研究

【目的】受地铁规划线路与周边环境的限制,小转弯半径叠落盾构隧道的应用较多,叠落段上行隧道施工引起的邻近下行隧道结构上浮规律极其复杂,相应的加固措施有待研究。为此,【方法】以北京地铁上清桥站—清河站区间隧道工程为背景,通过数值模拟和现场监测,研究夹层土注浆和钢环撑加固措施对下行隧道结构上浮的影响规律和钢环撑受力特征。【结果】结果显示:单独采取夹层土注浆或钢支撑加固措施时的下行隧道结构上浮均超过控制值,采取联合加固措施时变形为4.87 mm;下行隧道第1环管片上浮变形最大,随着盾构间距增大,隧道结构上浮呈不断减小的趋势,数值模拟得到的最大的隧道结构上浮为现场监测的1.15倍;实测的竖撑拉应力最大为5.78 MPa。【结论】结果表明:夹层土注浆提高叠落盾构井之间土体强度并对抑制下行隧道结构上浮起到一定作用,临时钢环撑施作有利于限制管片变形,其中竖撑限制管片竖向的收敛变形,横撑限制管片水平净空收敛,纵撑限制了管片的上浮。研究成果可为类似小转弯半径叠落盾构隧道工程设计与安全施工提供参考。

软土地区交叠盾构隧道施工对地层的影响

为研究软土地区交叠盾构隧道在不同施工顺序下对地层的影响,本研究模拟了六组盾构法上下交叠盾构隧道施工模型,对比了粉土、粉砂、粉质黏土三种典型天津软土的土质情况,并分别分析了在三种土质条件下,“先上后下”和“先下后上”两种施工方法引起的地层变形情况,结合工程中先建隧道的现场监测数据,得出如下规律:相同土层中“先下后上”顺序施工在隧道上部的地层位移均小于“先上后下”顺序施工,但隧道下部深层土体的位移均大于“先上后下”顺序施工;当需要控制夹层土体的竖向位移时,可以在深厚粉土层或粉砂层中选择“先上后下”顺序施工,在深厚粉质黏土层中选择“先下后上”顺序施工。

Performance of overlapped shield tunneling through an integrated physical model tests,numerical simulations and real-time field monitoring

In this work,deformations and internal forces of an existing tunnel subjected to a closely overlapped shield tunneling are monitored and analyzed using a series of physical model experiments and numerical simulations.Effects of different excavation sequences and speeds are explicitly considered in the analysis.The results of the physical model experiments show that the bottom-up tunneling procedure is better than the top-down tunneling procedure.The incurred deformations and internal forces of the existing tunnel increase with the excavation speed and the range of influence areas also increase accordingly.For construction process control,real-time monitoring of the power tunnel is used.The monitoring processes feature full automation,adjustable frequency,real-time monitor and dynamic feedback,which are used to guide the construction to achieve micro-disturbance control.In accordance with the situation of crossing construction,a numerical study on the performance of power tunnel is carried out.Construction control measures are given for the undercrossing construction,which helps to accomplish the desired result and meet protection requirements of the existing tunnel structure.Finally,monitoring data and numerical results are compared,and the displacement and joint fracture change models in the power tunnel subject to the overlapped shield tunnel construction are analyzed.

高速列车振动荷载作用下桥隧交叠结构动力响应特性研究

为研究桥隧结构在高速列车振动荷载作用下的动力响应特性,通过数值模拟和模型试验相结合的方法,以频响函数和峰值加速度为评价指标分析单点振动荷载作用下桥隧结构动力响应规律。依托西安地铁14号线下穿大西高速铁路特大桥基础工程,采用有限元计算软件建立数值模型,研究高速列车移动荷载作用下桥隧交叠结构的动力响应特性。研究结果表明:全频域单点扫频振动荷载作用下,桥隧交叠结构的动力响应随着频率的增加而增大,隧道不同位置处的动力响应呈现明显差别,靠近桩基一侧拱腰的动力响应明显大于拱顶和拱底,平均差值分别为2.48 dB和4.15 dB。考虑列车振动荷载的移动效应会增大桥隧交叠结构的动力响应,移动荷载作用下拱顶处的峰值加速度增加约358%,靠近桩基一侧拱腰处增加约358%,远离桩基一侧拱腰处增加约280%,隧道拱底处增加约206%。此外研究发现,隧道结构动力响应均在距离桥隧交叠结构附近约10 m处开始迅速增强,超过10 m范围内动力响应变化趋于稳定,应加强靠近桥隧交叠结构10 m范围内的监控量测。

软土地质条件下长距离重叠隧道施工技术

该技术依托天津地铁5号线成林道站~津塘路站区间为上下重叠隧道施工中各项难题,通过模型计算分析、先建隧道结构加强和可拆卸环形支撑加固等综合技术,有效地解决了施工中的各项难题,完成了长距离盾构重叠施工。该项技术成果取得了显著的社会效益及经济效益,对城市地铁设计和施工具有积极的借鉴意义,推广应用价值前景广阔。

基于FLAC^(3D)的砂质淤泥质土层地铁施工影响因素分析

为分析叠交地铁施工中既有隧道变形的影响因素,依托苏州市轨道交通S1线工程S1-TS-05标段,针对在砂质淤泥质土层中盾构上穿施工导致的既有隧道的沉降与变形,采用数值模拟方法分析隧道几何参数、空间位置、地层参数等因素对既有隧道的影响,结合现场监测验证数值计算的准确性。研究结果表明:在砂质淤泥质土层盾构上穿施工中,既有隧道的位移和管片变形以竖向沉降为主,且沉降量随着盾构直径的增大而增大,随着覆土层厚度、新旧隧道净距、下穿角度,以及地层弹性模量的增大而减小。现场监测数据与模拟结果较为吻合,既有隧道位移与距叠交中心距离呈负相关关系。研究结论可为同类型地层条件下叠交地铁隧道盾构施工变形控制提供参考。

盾构隧道与箱涵交叠下穿铁路开挖面稳定性上限分析

为了对盾构隧道与箱涵交叠下穿铁路同步施工开挖面的稳定性进行研究,以厦门轨道交通6号线盾构隧道与箱涵交叠下穿海沧铁路支线工程为背景,首先采用FLAC3D探究主动破坏情况下二者开挖面的模式并运用空间离散化技术构建开挖面主动破坏理论模型;然后利用极限分析上限定理考虑支护应力、列车荷载等因素求解出该破坏模式下的开挖面极限支护力;最后将所推导的理论解与数值解进行对比验证。研究结果表明:①盾构隧道与箱涵开挖面均失稳破坏时,其破坏模式与二者的埋深比有关。当盾构隧道与箱涵埋深比C/H较小时,两者的变形区域会形成联通区,随着埋深比C/H的增大,联通区消失,失稳产生的大变形主要由盾构隧道体现。②所构建出的盾构隧道与箱涵均失稳情况下开挖面破坏三维理论模型与数值模拟对比,差异均在10%以内,结果比较吻合,验证了其具有一定的合理性。③盾构隧道与箱涵均失稳时的极限支护力大小趋近于盾构隧道开挖面失稳破坏时的极限支护力,且极限支护力大小随埋深比C/H的增大逐渐减小,最终趋于定值。

空间位置对叠落盾构隧道施工影响效应分析

面对隧道叠落区间复杂施工形式及富水砂层条件,亟需探究地层位移与衬砌自身变形的响应规律,以降低潜在施工风险。依托实际工程,针对后施工上线盾构隧道与既有下线隧道相互作用问题,采用有限元数值模拟方法,结合现场监测数据与地层条件,考虑隧道连线倾角与隧道间距等空间位置的影响因素,分析盾构过程中地层沉降和衬砌应力应变的变化规律以及相互作用机制,并提出相应施工保护措施。结果发现:叠落隧道位置关系对地层与衬砌的影响显著,随着隧道中心连线倾角增大,地表沉降峰值位置发生偏移,倾角约45°时沉降达到最小,同时下线隧道拱底和拱腰变形最大;随着完全叠落两隧道间距的减小,相互作用影响增大。