A finite strain solution for the elastoplastic ground response curve in tunnelling: rocks with non‐linear failure envelopes

This paper generalizes the finite strain Coulomb solution of Vrakas and Anagnostou (Int J Numer Anal Meth Geomech 2014; 38(11): 1131–1148) for the classic tunnel mechanics problem of the ground response curve to elastoplastic grounds satisfying a non‐linear Mohr's failure criterion. A linear (Coulomb‐type) plastic potential function is used, leading to a non‐associated flow law, and edge plastic flow is considered in the plastic zone. The solution for a general non‐linear Mohr's failure criterion is semi‐analytical in that it requires the evaluation of definite integrals. In the special case of the Hoek–Brown criterion, however, these integrals are calculated analytically, resulting in a rigorous closed‐form series solution. The applicability of the derived solution is illustrated through the example of the Yacambú‐Quibor tunnel, where very large deformations were observed when crossing of weak graphitic phyllites. Copyright © 2016 John Wiley & Sons, Ltd.     

土质围岩开挖破坏模式研究

结合大量土质隧道围岩破坏调研资料和室内模型试验,研究土质围岩破坏的位置和形态,以破坏位置和特点探讨了土质围岩的破坏模式,并对各破坏模式进行了定义。研究表明,土质围岩破坏模式有未支护段破坏模式、掌子面破坏模式、未支护段和掌子面同时破坏模式及不发生破坏4种;未支护段破坏模式可分为自稳破坏、进尺破坏和不破坏;未支护段自稳破坏模式主要受洞形跨度和跨高、围岩条件控制,而进尺破坏模式主要受进尺和围岩条件控制;掌子面破坏模式的破坏面可近似为对数螺旋曲面或斜平面,未支护段破坏模式的破坏面可近似为抛物线曲面,未支护段和掌子面同时破坏模式的破坏面近似为数螺旋曲面或斜平面和抛物线曲面相交。     

人防坑道爆破掘进对施工中的电视塔的影响观测与分析

为检查人防工程主干道爆破施工对其上部正在进行主体混凝土浇灌的电视塔工程的影响,我们对人防坑道爆破瞬间的电视塔结构、电视塔附近基岩以及人防坑道底板的振动速度进行了现场测量。本文将电视塔作为一个正在连续浇灌施工的高耸建筑物,其顶部混凝土尚处于初凝期,对破坏判据的选取进行评价与分析。文中对现代城市经常出现的地面建筑物(或地下上层结构物)振动效应控制的分析,可对同类工程提供有意义的参考。     

The Observation and Analysis of Influence of Blast Driving of the People’s Air Defence Tunnel on a TV Tower under Construction

In order to investigate the influence of blast driving of the people’s air defence tunnel on a TV tower being under construction, we have measured vibration velocity of the TV tower, cornerstone and the tunnel. In this paper the TV tower is regarded as a protruding high edifice which is under construction, the assessment and analysis of the failure criteria have been given. The analysis and conclusion may contribute as a instructive reference for some similar engineering.     

非均质黏土地基中平面应变隧道最小支护压力数值模拟

土体由于沉积而具有天然的非均质性,但关于非均质地基中隧道开挖面稳定性的研究却很稀少,在实际盾构隧道工程中均按均质地基对待。但这一简化并没有考虑非均质性对保持开挖面稳定所需最小支护压力的有利作用,以及对破坏模式的影响。故文中采用基于tresca准则的弹塑性有限元法来研究黏聚力随深度线性变化的纯黏土地基中平面应变隧道的开挖面稳定性,模拟了土体失稳渐进破坏的全过程。最终验证了无量纲化的有效性,得到了各种工况时保持土体稳定的最小支护压力值,并发现了黏聚力线性变化斜率对深埋隧道破坏模式的影响,可为理论分析和工程实践提供依据。     

花岗岩隧道脆性破坏的温度效应研究

目前深埋硬岩隧道的岩爆等脆性破坏研究还较少考虑到温度的作用效应。采用精细网格数值模型,提出热-脆性-精细力学计算方法,应用能反映高地应力下硬岩脆性破坏特点的岩体劣化模型,结合能量计算指标,开展了不同温度作用下隧道硬岩脆性破坏的热力耦合分析。以瑞典APSE花岗岩隧洞岩柱为例,进行不同地温下隧道破坏区、能量释放值和应力指标的定量化对比研究。研究结果表明,隧道地温的增加将使岩体产生附加温度应力,进而增大其脆性破坏程度,计算结果与隧道现场的破坏规律基本一致。热-脆性-精细力学计算能合理描述硬岩的损伤和渐进破坏过程,计算结果较好地揭示了花岗岩等硬岩深埋隧道脆性破坏的温度作用效应,对于高应力、高地温下深部工程的稳定性评价具有指导意义。     

隧道变形失稳过程的非线性动力学分析与破坏判据研究

隧道变形失稳过程与破坏判据研究是地下工程的热点与难点之一。运用协同学与混沌动力学,分析了隧道变形失稳过程的非线性动力学演化特征,并将其划分为平衡、非平衡线性、非平衡非线性等3个演化阶段;从系统分析的角度,研究了整个隧道系统的涨落关联机制,建立了隧道变形失稳的动力学演化模型。在此基础上,分别给出了大数据量（≥3 000）与小数据量（ 3 000）条件下稳定性演化过程的动力学判别准则。结合隧道变形失稳的阶段性特征,建立了其破坏的混沌动力学判据。将以上研究应用于广州地铁某立体交叉隧道的稳定性分析中,验证了该动力学演化模型与判据的合理可靠性,对隧道稳定性状态的判别具有一定指导意义。     

深部复合地层TBM开挖扰动模型试验研究

针对全断面隧道掘进机（TBM）开挖过程掌子面岩体软硬交替变化的特点,以兰州水源地建设工程为背景,采用模型试验与数值模拟方法研究了复合地层TBM开挖过程隧洞围岩的动态响应规律。通过开展相似配比试验配制了不同围岩强度比的复合地层岩体相似材料,运用光纤光栅技术全程捕捉了隧洞开挖过程复合地层应变演化规律,并分析了隧洞围岩的宏观破裂形态。模型试验结果表明：TBM推进过程中复合地层应变变化规律体现了掌子面推进的空间效应,软岩部分应变要大于硬岩部分应变,且随着开挖步数的增加两种岩层应变差值越大;隧洞内岩体完全挖除后,围岩宏观破裂形态表明因复合地层岩体物理力学性质的差异,上覆软岩变形破坏较为严重,破裂和变形较为显著,在软、硬岩层交界面出现“变形不协调”现象。选取工程沿线某洞段的地质力学参数,基于破坏接近度（FAI）指标评价了隧洞开挖过程中复合地层围岩的稳定性,数值结果表明：开挖过程软岩中FAI变化较为明显,塑性区和破坏区分布范围更广,而下部硬岩受开挖扰动影响较小,只有拱底小范围岩体进入破坏状态。模型试验和数值结果均说明交替变化的掌子面岩体在开挖过程中其围岩在变形破坏等规律方面存在明显差异,因此,TBM在复合地层施工可采取重点部位监测预警、提前采取相应措施等手段,减少或避免卡机事故的发生。该研究成果对于指导复合地层TBM施工具有一定的借鉴和指导意义。     

Stability analysis of shotcrete supported crown of NATM tunnels with discontinuity layout optimization

For tunnel constructed by New Austrian Tunnelling Method, the crown is the upper part of tunnel section, constructed during excavation process and supported by shotcrete. The stability of the crown has great influence on the safety of tunnel itself and the buildings above, which correlates, among others, with geometrical setup of tunnel and material properties of shotcrete and soil/rock. In this paper, aiming at analyzing the stability of shotcrete supported crown, a recently presented numerical method discontinuity layout optimization is adopted, which introduces a great amount of potential discontinuities cross over one another and provides a wide search space for efficient upper limit analysis. In the analysis, a well‐established hydration model of cementitious material is implemented for accounting the hydration of shotcrete. Then assumptions based on convergence‐confinement method are used for accounting the 3‐dimensional effect in 2‐dimensional analysis, finally providing time‐space–dependent assessments of stability of shotcrete supported crown.     

隧道变形失稳的能量演化模型与破坏判据研究

隧道变形失稳过程与破坏判据研究是地下工程的热点与难点之一。运用耗散结构理论,分析了隧道变形失稳的能量耗散过程与演化特征;结合热力学基本定律,研究了整个隧道系统的能量耗散机制,建立了隧道变形失稳的能量演化模型。在此基础上,分别给出了大数据量（≥3 000）与小数据量（<3 000）条件下稳定性演化过程的能量判别准则;根据隧道系统变形失稳演化各阶段特征,提出了其失稳破坏的能量判据。将研究成果应用于广州地铁某立体交叉隧道的稳定性分析,验证了该能量演化模型与判据的合理可靠性,其结果对隧道稳定性状态的判别具有一定指导意义。     

隧道大变形机制及处治关键技术模型试验研究

大变形是隧道建设中无法完全避免的灾害之一,发生后若处治不当极有可能出现多次换拱甚至塌方等二次灾害。通过相似模型试验,采用自行设计的隧道模型开挖装置和围岩内部位移监测装置,研究了隧道开挖和埋深增大过程中围岩渐进性破坏过程及位移和应力变化规律,揭露出预防隧道大变形的重点支护部位,并进一步研究了大变形出现后处治过程中衬砌的破坏规律,明确了大变形处治时的支护措施。试验结果表明：（1）隧道产生大变形过程中,拱顶与拱底的变形量大于拱腰与拱脚的变形量,且随着埋深增大,差值逐渐增大;（2）大变形产生后隧道拱顶径向和切向应力值均减小,而拱脚切向应力值大幅上升;（3）更换变形拱架时,更换位置附近衬砌拱顶处可能出现张拉破坏,拱腰处可能出现剪切破坏,因此,大变形处治时需保留两侧衬砌的临时钢支撑,必要时需增设底部横支撑或临时仰拱。该研究结果有助于得到大变形发生时和发生后处治时的防控重点,为大变形的预防及安全处治提供指导和参考。     

Elasto‐plastic model for cement‐treated sand

This paper presents an elasto‐plastic model for non‐linear analyses of cement‐treated sand. Various laboratory tests were systematically carried out to investigate the pre‐peak and post‐peak behaviours of a cement‐treated sand. On the basis of these experimental results, the new model was built within the framework of a relatively simple elasto‐plastic theory. Two failure criteria are employed to express tensile and shear failure characteristics observed in the experimental results of the cement‐treated sand. The proposed model can describe strain‐hardening and strain‐softening responses under both failure modes. In the strain‐softening rules, the smeared crack concept is used, and a characteristic length is considered to avoid the issue of mesh‐size dependency. Since the failure criterion and strain‐hardening/softening rules are based on the experimental evidences, the model is relatively easy to understand and the parameters used in the model have clear physical meaning. The proposed model was applied to simulate the behaviour of cement‐treated sand in various laboratory tests, allowing for a reasonable comprehensive evaluation. It was demonstrated that the proposed model is suitable for describing both the tensile and shear failure behaviours of cement‐treated sand. Copyright © 2006 John Wiley & Sons, Ltd.     

A finite strain closed‐form solution for the elastoplastic ground response curve in tunnelling

The ground response to tunnel excavation is usually described in terms of the characteristic line of the ground (also called ‘ground response curve’, GRC), which relates the support pressure to the displacement of the tunnel wall. Under heavily squeezing conditions, very large convergences may take place, sometimes exceeding 10–20% of the excavated tunnel radius, whereas most of the existing formulations for the GRC are based on the infinitesimal deformation theory. This paper presents an exact closed‐form analytical solution for the ground response around cylindrical and spherical openings unloaded from isotropic and uniform stress states, incorporating finite deformations and linearly elastic‐perfectly plastic rock behaviour obeying the Mohr–Coulomb failure criterion with a non‐associated flow rule. Additionally, the influence of out‐of‐plane stress in the case of cylindrical cavities under plane‐strain conditions is examined. The solution is presented in the form of dimensionless design charts covering the practically relevant parameter range. Finally, an application example is included with reference to a section of the Gotthard Base tunnel crossing heavily squeezing ground. The expressions derived can be used for preliminary convergence assessments and as valuable benchmarks for finite strain numerical analyses. Copyright © 2014 John Wiley & Sons, Ltd.     

浅埋人防隧洞围岩破坏机理分析

以埋深为6～13 m的某浅埋人防隧洞为研究对象,应用快速拉格朗日有限差分程序（FLAC）对不同跨距、不同岩性的隧洞顶板在不同荷载作用下的破坏规律及破坏机制进行数值模拟研究,确定了隧洞围岩破坏域,并对拱顶敏感块体进行跟踪分析。研究结果表明：隧洞跨距为2 m且顶板岩层为泥岩时,隧洞顶板有一定的承载能力,当上部荷载达到0.7 MPa时隧洞才破坏;隧洞跨距为3 m且顶板岩层为泥岩时,当上部荷载达到0.33 MPa时,隧洞就已经破坏;隧洞顶板为卵石层时,即使上部不施加荷载,在自重应力的作用下,隧洞亦破坏。该研究对类似的浅埋地下工程围岩稳定性分析具有实际意义。     

Dynamic Analysis of Tunnel in Soil Subjected to Internal Blast Loading

The present work deals with the three-dimensional nonlinear finite element (FE) analyses of the tunnel in soil subjected to internal blast loading. The analyses are performed using the coupled Eulerian–Lagrangian analysis tool in FE software Abaqus/Explicit. The soil and reinforced concrete lining are modeled using the Lagrangian elements. The explosive Trinitrotoluene (TNT) is modeled using the Eulerian elements. The stress–strain response of soil, concrete, and reinforcement are simulated using strain rate dependent Drucker–Prager plasticity, concrete damaged plasticity and Johnson–Cook (J–C) plasticity models, respectively. The pressure–volume relationship of the TNT explosive is simulated using the Jones-Wilkins-Lee equation of state. Parametric sensitivity studies have been performed for different (1) tunnel lining thicknesses, (2) explosive charge weights and (3) angles of internal friction of soil. It is observed from the results that blast induced pressure on the tunnel lining increases with the increase in charge weight. Both the lining and the surrounding soil undergo significant deformation. The deformation of the tunnel lining increases with increasing charge weight and decreases with increasing lining thickness and increasing the angle of internal friction of soil. Blast-induced velocity in soil attenuates with increasing distance from the source of the blast.     

地表超载作用下隧道失稳破坏的上限有限元分析

针对地表超载作用下隧道稳定性和破坏模式问题,基于刚体平动运动单元上限有限元理论编程并计算分析,获得了浅埋隧道失稳临界超载系数上限解和刚性运动块体体系破坏模式。通过与现有的刚性块体极限分析上限法以及极限分析上、下限有限元法计算结果的对比分析,验证了上限解的可靠性。研究结果表明,（1）临界超载系数 黏聚力c之比 随土体内摩擦角 和隧道埋深C与直径D之比( )的增大而相应增大,随土体重度与黏聚力参数 的增大而减小;（2） 和 对隧道破坏模式的影响较明显; 增大,则隧道破坏范围增加;内摩擦角 增大,刚性运动块体破坏模式相互错动更加显著,相比而言, 对破坏模式的影响并不显著;（3）刚体平动运动单元上限有限元上限解精度高,所得刚性运动块体破坏模式具有滑移线形态,能精细地反映隧道失稳破坏特征。     

Stability of long circular tunnels in sloping ground

Assessment of tunnel stability has become increasingly crucial as more and more tunnels are built in difficult terrains such as sloping ground. The required support pressure on the tunnel walls associates both tunnel stability and liner design considerations. The present analysis attempts to find a uniform internal pressure which can support a circular tunnel built in a sloping ground with a particular level of stability in cohesive-frictional soils. The lower bound finite element limit analysis has been applied to find the required minimum uniform internal support pressure presented as a non-dimensional term p/c; where p is the minimum normal internal pressure on the tunnel boundary to avoid collapse and c is the cohesion of soil. The variation of p/c is presented for a range of normalised embedment depth of tunnel (H/D), stability number (γD/c), internal friction angle of soil (?) and slope angle (β); where H is the crown depth of the tunnel, D is the tunnel diameter and γ is the unit weight of soil. Appropriate comparisons have been carried out with available literature. Failure patterns of the tunnel have also been studied to understand the extent and the type of failure zone which may generate during the collapse.     

隧道结构系统可靠度研究

在结构系统可靠度研究的基础上,根据隧道结构的特点,应用概率理论及工程结构系统可靠度分析方法,对整个隧道结构系统可靠度进行了探讨。隧道结构系统可靠度研究包括衬砌断面可靠度、在各种不同围岩压力作用下衬砌断面可靠度、同种围岩地段衬砌可靠度以及整座隧道可靠度的研究。整座隧道可看作由两端洞门和洞内不同围岩地段隧道衬砌所组成的串联系统,任一围岩地段衬砌和任一洞门结构的破损,都认为该隧道破损,则运用“概率网络估算技术”（又称PNET法）可求得整座隧道系统的失效概率与可靠指标。通过实例计算得到,整座隧道系统的总体可靠指标比所有单段结构的可靠指标都要低。     

连拱隧道围岩变形和破坏形态的DDA分析

连拱隧道围岩一般为由节理结构面相互切割的非连续岩体,利用非连续性分析方法研究这类围岩的变形和破坏形态可以更好地反映工程实际情况。采用非连续变形分析方法 DDA,对金鸡山连拱隧道围岩的变形和破坏过程进行了模拟,将整个变形破坏过程划分为了3个阶段：中墙上方岩体变形、地表下沉、滑移面产生阶段、隧道左右洞两侧滑移带（或滑移面）的形成阶段以及中墙顶部块体失稳、隧道上方岩体快速塌落阶段。研究了金鸡山隧道浅埋围岩和深埋围岩的变形破坏特征,其中边墙部位、靠近中墙的内侧拱顶或拱肩部位、外侧拱肩部位会首先受到变形破坏。