边坡影响下连拱隧道施工方案优化分析

随着我国公路隧道建设的发展,连拱隧道也越来越多.连拱隧道一般应用于中短隧道,常常与边坡结合在一起,同时连拱隧道施工过程非常复杂,不同的施工方案带来不同的力学行为,故有必要对连拱隧道在施工方案进行优化分析,尤其是在边坡影响的情况下.文章建立了连拱隧道施工动态有限元模型,分别模拟先开挖边坡外侧和先开挖内侧隧道的施工过程,并通过对中墙应力、围岩稳定性的比较,分析了边坡影响下两种施工方案的优劣.     

连拱隧道支护体系变形的现场监测及分析

与普通公路隧道相比,连拱隧道因隧道施工复杂,工序转换繁多,其变形特征更加复杂。结合某连拱隧道工程实践,在连拱隧道施工中对支护体系变形进行现场监测的基础上,分析连拱隧道支护体系变形随时间变化的规律及不同开挖工序下支护体系变形特征。监测结果表明:采用台阶法施工,能较好地控制连拱隧道的变形;在隧道施工过程中,右导洞上、下台阶开挖对支护变形影响较大,是隧道结构稳定性主要控制点;左洞上台阶和右洞下台阶开挖的纵向影响距离约为隧道跨度的2倍,右洞上台阶和左洞下台阶开挖的纵向影响距离大致为一倍隧道跨度。     

龙山浅埋大跨度连拱隧道施工方案优化分析

连拱隧道在线路平面、洞口位置选择上均较分幅修建隧道优越,其所占比例也越来越大。而按照我国公路隧道设计规范设计连拱隧道时,常将围岩和支护结构隔离开来,分析结果不能完全反映施工过程的实际情况,故有必要对连拱隧道施工方案进行优化分析。针对龙山隧道具有浅埋、大跨度、连拱的特点,建立了连拱隧道施工动态有限元分析程序,模拟三导洞法和上下台阶法开挖双连拱隧道的施工过程,并通过对拱顶沉降、地表沉降、中墙应力、围岩稳定性的分析,从施工工序与施工力学角度对2种施工方法的优劣进行比较分析,从而使得实际隧道施工方案得到优化。     

基于数值模拟的山区高速公路连拱隧道稳定性研究

为确保山区高速公路连拱隧道的施工安全,在分析隧道所在地段地质条件基础上,通过数值模拟分析了山区高速公路隧道开挖过程中隧道稳定性,结果表明,山区高速公路连拱隧道围岩自稳性较差,尤其是中拱墙部分,需要在开挖后应及时进行支护,以避免隧道拱顶或侧壁塌方。     

基于流固耦合理论的连拱隧道围岩稳定性分析

以湖南省常吉高速公路新修建的一些大跨度连拱隧道为工程背景，基于流固耦合分析理论，利用快速拉格朗日有限差分法对连拱隧道围岩稳定性进行分析。主要考虑流固耦合效应作用时，围岩级别、隧道埋深、地下水位以及施工工法和初期支护等因素对围岩稳定性的综合影响，得到Ⅲ，Ⅳ，Ⅴ级围岩在各种情况下隧道开挖后围岩最大主应力、洞周位移、塑性区、孔隙水压力分布以及喷锚支护受力特征等结果，探讨连拱隧道开挖渗流机制，并分析深埋连拱隧道开挖后的孔隙水压力场分布特征。研究结果直接指导该高速公路二期工程中的隧道防排水施工和支护措施的改进提高，为富水地层条件下的隧道工程开挖设计提供一定的理论参考。     

双连拱隧道无导洞法施工断面对隧道稳定性影响

为了对比分析采用无导洞法施工连拱隧道时最安全稳定的开挖断面形式,提高施工过程中衬砌结构的安全性和稳定性,以福建某连拱隧道作为工程背景,按照中墙顶部回填量从大到小的顺序选取了三种不同的施工断面方案,应用数值模拟方法,研究了最终状态衬砌结构安全系数、临时支撑和中墙稳定性三个方面,对三种方案稳隧道结构的稳定性及其变化规律进行了详细对比分析,发现后行洞上台阶开挖与支护的过程是衬砌结构受力变化最大的过程;无论哪种方案,在浇筑中墙后立刻回填中墙顶部的空隙总是对衬砌结构有利。可见,选择方案三作为无导洞法施工连拱隧道的断面形式,并及时回填中墙顶部,可以有效提高连拱隧道结构的安全性与稳定性,是最优的断面形式。     

连拱隧道-边坡耦合作用:连拱隧道滑坡

连拱隧道一般用于中、短隧道和隧道接线部位,除在隧道的进山、出山口遭遇仰坡和侧向边坡外,隧道主体也常处于边坡地形之中,需要对边坡的稳定性进行分析论证。连拱隧道开挖断面大,多次开挖支护以及应力的平衡、转换可能对边坡的稳定性产生显著影响,在极端不利情况下,甚至可能诱发滑坡。连拱隧道主体与边坡相互作用模式可概括为4种:隧道位于滑面以下;隧道穿越滑面;隧道位于滑面以上的坡顶;隧道位于滑面以上的坡脚,可采用修正的不平衡推力传递法分析其稳定性。对于边坡滑面不能预先判定情况,可采用数值计算方法,分析隧道开挖工法对边坡稳定性的影响。按强度折减法分析,在三导洞工法中先开挖远山侧更有利于边坡的稳定。     

连拱隧道围岩压力的释放率分析

连拱隧道作为公路隧道新的结构型式,理论上还不成熟.以云南省元磨高速公路的两座连拱隧道作为工程背景,按弹性阶段相似原则进行两组连拱隧道室内模型试验,包括隧道处于常规应力状态下和偏压状态下的模型试验.采用压力盒量测施工过程中隧道围岩压力,并提出了围岩压力释放率的概念,对连拱隧道开挖过程中围岩压力的变化特征进行了分析,同时对两种应力状态下的试验结果进行了对比分析.得出的结论对连拱隧道的设计和施工有积极的指导作用.     

连拱隧道开挖技术研究

随着全国公路里程的不断增加,公路隧道施工技术也越来越成熟,隧道开挖新技术、新工艺也不断涌现,以王格尔塘3号隧道为例,分析了连拱隧道洞口段施工、中导洞开挖、Ⅳ级围岩和Ⅴ级围岩开挖技术在隧道施工中的应用,为后期连拱隧道施工提供经验。     

偏压连拱隧道渗流-应力耦合分析及处治技术研究

基于渗流-应力耦合分析理论模拟偏压连拱隧道开挖过程,分析连拱隧道在偏压条件下围岩位移变形特性及稳定性的影响,给出偏压连拱隧道施工过程中左洞上台阶与中隔墙连接处、以及右洞拱腰处为相对薄弱位置并有针对性地进行处治。     

龙山浅埋大跨连拱隧道施工过程的数值模拟

采用美国MSC公司的大型通用有限元软件MARC对龙山浅埋大跨连拱隧道的施工过程进行数值计算,模拟隧道施工过程中围岩与支护结构的力学行为,结果表明相邻隧道的施工进度、支护方式都将影响隧道围岩的稳定性和支护结构的承载情况,得到一些有意义的结论,指导后续施工。     

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 in-equidimensional noncircular tunnel.     

Investigation of response of metro tunnels due to adjacent large excavation and protective measures in soft soils

The inevitable influence of large excavation in soft soils on nearby tunnels is of great concern in practice. In this paper, the influence of a nearby large excavation on existing metro tunnels of the Ningbo Metro Line 1 in sensitive soft soils is investigated and presented. Considerable displacement in the left tunnel closer to the excavation induced by the nearby excavation was revealed by field monitoring. Visible cracks and leakages were observed in left tunnel linings. Three dimensional numerical simulations are conducted to investigate the responses of the ground and left tunnel due to the adjacent excavation. The development of bending moment and displacement of the left tunnel during different construction stages of the nearby excavation is obtained. Then the interaction mechanism between the nearby excavation, surrounding soils and existing twin tunnels is investigated, which is of significance to the interpretation of the influence of the nearby excavation on the existing twin tunnels. Several protective measures for alleviating the influence of adjacent excavation on left tunnel are studied, including divided excavation, soil improvement and a cut-off wall. It is found that the left tunnel is influenced to varying degrees during different construction stages and the time effect is distinct for this large excavation in soft soils, which would be suggestive to engineers to pay more attention to the protection of adjacent tunnel during the crucial construction stages. The bending moment and displacement of the left tunnel is strongly related to the unloading effects and displacement of surrounding soils, which can be alleviated by means of proper improvement of excavation sequence. Comparatively, longitudinally divided excavation is more effective in protecting the left tunnel than soil improvement or a cut-off wall. This study is of certain reference value for protecting metro tunnels adjacent excavation in soft soils.     

殿会坪连拱隧道边仰坡稳定性分析及整治

连拱隧道边仰坡具有开挖范围大、受到多次开挖扰动的特点.以常吉高速公路中的殿会坪隧道为例,进行了边仰坡和隧道洞内的现场测试,从地质条件、地形地貌、地下水情况、施工方法和施工质量等方面分析该连拱隧道仰坡稳定性的影响因素,提出了整治措施,在实际中获得成功应用.     

Rockburst response in hard rock owing to excavation unloading of twin tunnels at great depth

This study aims to investigate the rockburst characteristics of hard rock during the successive excavation unloading of twin circular tunnels subjected to high active stresses. The entire evolution process of the rockburst phenomena around the tunnels is reproduced. The numerical results indicate that the unloading rates, burial depths, and presence of structural planes between the twin tunnels play important roles in the occurrence and damage degrees of rockbursts. The failure intensity and dynamic responses are aggregated with the increase of the unloading rate of the subsequent adjacent tunnel. The rockburst damage degree is exacerbated with increasing buried depth, and the rock response of the twin tunnels becomes more sensitive to the dynamic disturbance (as compared to a single tunnel at a great depth). The presence of a structural plane between the twin tunnels has both favourable and unfavourable effects on the stability of the surrounding rock. When the structural plane is parallel to the maximum tangential stress, the dynamic disturbance from the adjacent tunnel can be attenuated by the structural plane or rock joints via reflection and scattering, thus reducing the dynamic response between the twin tunnels. However, for those structural planes oblique to the maximum tangential stress, a violent rockburst is more prone to be induced, owing to the integrated response to shearing and sliding along the structural plane, and slabbing from the excavation unloading process. It is also found that the effect of the structural plane on the rockburst response is largely dependent on the burial depth.

     

平行隧道开挖引起上方既有隧道的纵向变形研究

城市地铁隧道大多数采用平行双洞的布置形式作为隧道设计施工方案,根据不同的地层条件等因素采用盾构法或暗挖法施工。由于城市地下空间变的越来越拥挤,研究新建平行双洞隧道施工过程中对邻近既有隧道的影响程度问题显得尤为重要。本文基于两阶段分析方法研究预测平行双洞隧道开挖引起上方已建隧道的纵向变形的简化解析方法。首先,采用两高斯曲线叠加,计算新建平行双洞隧道施工引起的作用在既有隧道上的附加荷载。然后,将既有隧道考虑为Winkler 地基上的Timoshenko梁,建立既有隧道纵向变形的基本微分方程,并基于Galerkin 法进行求解。将本文提出的简化解析方法得到的结果与工程沉降实测数据进行对比以验证本文提出的预测方法的合理性。最后,进行了参数敏感性分析,研究了不同隧道相互位置、地层损失率、相对抗弯刚度和地层土性参数等对结果的影响规律。     

Three-dimensional numerical simulation of a mechanized twin tunnels in soft ground

The increase in transportation in large cities makes it necessary to construct of twin tunnels at shallow depths. Thus, the prediction of the influence of a new tunnel construction on an already existing one plays a key role in the optimal design and construction of close parallel shield tunnels in order to avoid any damage to the existing tunnel during and after excavation of the new tunnel.Most of the reported cases in the literature on parallel mechanized excavation of twin tunnels have focused on the effects of the ground condition, tunnel size, tunnel depth, surface loads, and relative position between the two tunnels on tunnel behaviour. The numerical investigation performed in this study, using the FLAC^3D finite difference element programme, has made it possible to include the influence of the construction process between the two tunnels. The structural forces induced in both tunnels and the development of the displacement field in the surrounding ground have been highlighted.The results of the numerical analysis have indicated a great impact of a new tunnel construction on an existing tunnel. The influence of the lagged distance between the two tunnels faces has also been highlighted. Generally, the simultaneous excavation of twin tunnels causes smaller structural forces and lining displacements than those induced in the case of twin tunnels excavated at a large lagged distance. However, the simultaneous excavation of twin tunnels could result in a higher settlement above the two tunnels.     

特大断面隧道支护结构现场试验与三维效应分析

与普通公路隧道相比,双洞八车道特大断面隧道的结构受力更加复杂、施工方法更为多样化。结合目前国内规模最大的四车道特大断面隧道,对特大断面隧道进行现场试验,并基于现场试验结果,详细地分析特大断面隧道双侧壁导洞法开挖引起支护结构变形及受力的三维效应。研究结果表明:在特大断面隧道施工过程中,左导洞下台阶和核心土上台阶开挖对支护结构受力及变形影响较大,是支护稳定性控制的主要工序;特大断面隧道开挖的纵向影响距离大致为1~1.5倍导洞跨度,约为8~12m。研究成果可为日后类似工程的设计、施工和研究提供有益的借鉴和参考。     

连拱隧道施工方法对边坡稳定性的影响分析

结合某工程,建立了三维弹塑性有限元模型,就隧道的开挖施工过程进行了数值模拟,用强度折减法原理计算得到在左洞先挖和右洞先挖两种施工方法下边坡的安全系数,并探讨了不同开挖顺序对隧道和边坡稳定性的影响.得出了坡体的安全系数随施工的进行逐渐减小、最后趋于稳定的结论,以及对于偏压连拱隧道,先开挖靠边坡外侧的隧洞对边坡的稳定和隧道的安全更加有利.文章最后分析了边坡的破坏失稳机理,提出需加强观测以及采取一定加固措施的建议.其结论对隧道的施工方法具有指导意义.