Probabilistic analysis of tunnel face seismic stability in layered rock masses using Polynomial Chaos Kriging metamodel

Face stability is an essential issue in tunnel design and construction.Layered rock masses are typical and ubiquitous;uncertainties in rock properties always exist.In view of this,a comprehensive method,which combines the Upper bound Limit analysis of Tunnel face stability,the Polynomial Chaos Kriging,the Monte-Carlo Simulation and Analysis of Covariance method(ULT-PCK-MA),is proposed to investigate the seismic stability of tunnel faces.A two-dimensional analytical model of ULT is developed to evaluate the virtual support force based on the upper bound limit analysis.An efficient probabilistic analysis method PCK-MA based on the adaptive Polynomial Chaos Kriging metamodel is then implemented to investigate the parameter uncertainty effects.Ten input parameters,including geological strength indices,uniaxial compressive strengths and constants for three rock formations,and the horizontal seismic coefficients,are treated as random variables.The effects of these parameter uncertainties on the failure probability and sensitivity indices are discussed.In addition,the effects of weak layer position,the middle layer thickness and quality,the tunnel diameter,the parameters correlation,and the seismic loadings are investigated,respectively.The results show that the layer distributions significantly influence the tunnel face probabilistic stability,particularly when the weak rock is present in the bottom layer.The efficiency of the proposed ULT-PCK-MA is validated,which is expected to facilitate the engineering design and construction.

A three-dimensional numerical study on the stability of layered rock spillway tunnels in alpine canyon areas

Rock masses in alpine canyon areas exhibit strong heterogeneity,discontinuity,and are subject to strong tectonic effects and stress unloading,leading to extremely complex distribution of in-situ stress.In addition,the occurrence of layered rock masses makes it more complex,with obvious anisotropic mechanical properties.This study proposes a comprehensive method for evaluating the stability of layered rock spillway tunnels in a hydropower station in an alpine canyon.First,the failure criterion and mechanical model of layered rock masses considering the anisotropy induced by the bedding plane and the true triaxial stress regime were established;an inversion theory and calculation procedure for in-situ stress in alpine canyon areas were then introduced.Finally,by using a self-developed numerical tool,i.e.CASRock,the stability of the layered rock spillway tunnel in a hydropower station was numerically analyzed.The results show that,affected by geological structure and stratigraphic lithology,there is significant differentiation in the in-situ stress in alpine canyons,with horizontal tectonic stress as the main factor.The occurrence of layered rock masses in the region has a significant impact on the stability of surrounding rock,and the angle between the bedding strike and the tunnel axis as well as the bedding dip both exert a significant influence on the failure characteristics of the surrounding rock.

Face stability analysis of circular tunnels in layered rock masses using the upper bound theorem

An analysis of tunnel face stability generally assumes a single homogeneous rock mass.However,most rock tunnel projects are excavated in stratified rock masses.This paper presents a two-dimensional(2D)analytical model for estimating the face stability of a rock tunnel in the presence of rock mass stratification.The model uses the kinematical limit analysis approach combined with the block calculation technique.A virtual support force is applied to the tunnel face,and then solved using an optimization method based on the upper limit theorem of limit analysis and the nonlinear Hoek-Brown yield criterion.Several design charts are provided to analyze the effects of rock layer thickness on tunnel face stability,tunnel diameter,the arrangement sequence of weak and strong rock layers,and the variation in rock layer parameters at different positions.The results indicate that the thickness of the rock layer,tunnel diameter,and arrangement sequence of weak and strong rock layers significantly affect the tunnel face stability.Variations in the parameters of the lower layer of the tunnel face have a greater effect on tunnel stability than those of the upper layer.

Integrated simulation and monitoring to analyze failure mechanism of the anti-dip layered slope with soft and hard rock interbedding

The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding.In order to reveal the landslide mechanism,taking the north slope of Fushun West Open-pit Mine as an example,this paper analyzed the failure mechanism of different landslides with monitoring and field surveys,and simulated the evolution of landslides.The study indicated that when the green mudstone(hard rock)of the anti-dip slope contains siltized intercalations(soft rock),the existence of weak layers not only aggravates the toppling deformation of anti-dip layered slope with high dip,but also causes the shear failure of anti-dip layered slope with stable low dip.The shear failure including subsidence induced sliding and wedge failure mainly exists in the unloading zone of the slope.Its failure depth and failure time were far less than that of toppling failure.In terms of the development characteristics of deformation,toppling deformation has the long-term and progressive characteristics,but shear failure deformation has the abrupt and transient characteristics.This study has deepened the understanding of such slope landslide mechanism,and can provide reference for similar engineering.

Modification of rock mass rating system:Interbedding of strong and weak rock layers

Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.

3D FEM analysis for layered rock considering anisotropy of shear strength

An empirical expression of cohesion （C） and friction angle （Ф） for layered rock was suggested. This expression was compared with a test result made by the former researchers. The constitutive relationship of a transversely isotropic medium and Mohr-Coulomb criterion in which C and Ф vary with directions were employed, and a relative 3D elasto-plastic FEM code was developed, in which the important thing was to adopt a search-trial method to find the orientation angle （p） of shear failure plane （or weakest shear plane） with respect to the major principal stress as well as the corresponding C and Ф Taking an underground opening as the calculation object, the numerical analyses were carried out by using the FEM code for two cases of transversely isotropic rock and isotropic rock, respectively, and the computation results were compared. The results show that when the rock is a transversely isotropic one, the distributions of displacements, plastic zones and stress contours in the surrounding rock will be non-axisymmetric along the tunnel＇s vertical axis, which is very different from that of isotropic rock. The stability of the tunnel in transversely isotropic rock is relatively low.

动静荷载下层状围岩隧道应力集中分布特征

针对圣加旺水电站层状围岩引水隧道工程,设计物理模型相似试验,考虑不同的静荷载、动荷载及围岩倾角,采用LSDYNA分析层状岩体应力波的传播特性及分布特征.通过正交试验分析不同因素对围岩峰值应力及二次平衡应力的敏感性,基于量纲分析建立多因素影响下应力预测模型,确定围岩安全荷载控制范围.结果表明,高地应力条件下隧道围岩存在初始应力集中,动力扰动对应力集中数值的影响显著,应力波波阵面受层理的影响呈不连续分布.动、静载与围岩峰值应力、二次平衡应力呈正线性相关,围岩峰值应力及二次平衡应力随倾角增大呈“∧”型分布,不同因素对围岩峰值应力及二次平衡应力的敏感性顺序均为动载>静载>倾角.当围岩倾角为90°(0°)、75°(15°)、60°(30°)及45°时,静载极限值分别为0.731、0.555、0.479及0.456 MPa,动载极限值分别为0.624、0.523、0.477及0.463 MPa.

双向荷载作用下层状岩体变形模量参数取值试验研究

在龙滩特大桥拱座基础中,针对层状强风化—中风化粉砂质泥岩,采用刚性承载板法进行拱座受垂向荷载及水平荷载作用下,层面倾角为38°~40°的岩体变形模量试验。结果表明:拱座基底受垂向荷载的变形模量为0.4542 GPa~0.8329 GPa,拱座受水平荷载的变形模量为0.066 GPa~0.088 GPa。研究深入分析了层状岩体的变形机制和规律,揭示了不同加载条件下的变形规律,提出了确定垂直和水平方向变形模量在综合模量中的权重比例的方法。该研究对层状岩体变形特性和大跨度拱桥的理论计算具有重要参考价值。

不同抵抗线影响下层状岩体爆破的破岩规律

层状岩体是地下工程建设常见的地质构造,钻爆法施工在层状岩体中表现为爆破成型效果差、超欠挖现象严重、振动传播不均衡等问题。抵抗线是影响爆破效果的关键参数,本研究以最小抵抗线为控制指标,研究初始应力与节理角度等影响下的层状岩体爆破破岩规律。以Ⅲ级围岩为地质背景,采用分层浇筑的方法制备不同节理参数的混凝土试块作为层状岩体的模拟材料,进行了一系列不同爆破条件下的爆破试验,结合高速摄影机、动态信号分析系统以及智能五段爆速仪等设备监测了试验过程;利用LS-DYNA三维数值仿真模型,分析了地应力静载与爆炸动载耦合作用下层状岩体的损伤及应力波传规律。研究结果表明:节理对爆破应力波地传播有阻隔作用,改变了裂纹扩展的方向和形态,应力波传至节理面后大量能量发生反射现象,少量能量发生透射现象穿过节理面,爆破效果上表现为主裂纹首先沿节理弱面贯穿,垂直于节理方向迎爆侧的岩石裂纹发育优于背侧裂纹,迎爆侧岩石内的应变强度大于背爆侧;随着抵抗线在6~10 cm增大,层状岩体爆破产生的爆破粉碎区及裂隙区范围逐渐减小,但爆破空腔范围先增大后减小,抵抗线较小时爆炸能量主要以气体形式逸出造成能量浪费,较大时爆炸能量作用于岩石内部难以抛掷岩石,当抵抗线为H=8 cm时,爆破产生的破岩效果最好;节理面迎爆侧有效应力随最小抵抗线的增加呈现先增大后减小趋势,合速度呈现先减小后增大趋势,节理面背爆侧有效应力峰值和合速度峰值变化趋势平缓。研究成果有助于加深对地下工程中层状岩石爆破破岩机理的认识。

层状岩体磷矿床采空区失稳风险定量评价方法研究

现有层状岩体磷矿床采空区失稳分析方法很少考虑岩体力学参数的空间变异性。以杉树垭磷矿为研究背景,构建了能够表征岩体力学参数自相关性、互相关性及非高斯性的随机场,以层状岩体破坏接近度(FAI)为评价指标,建立了岩体单元破坏的极限状态方程,并借助Hermite随机多项式建立了随机岩体力学参数输入场与网格单元FAI输出场间的显式函数表达式。最后,采用蒙特卡洛法计算磷矿采空区网格单元破坏概率,实现了磷矿采空区失稳风险的定量评价。结果表明:参数随机场能够很好表征岩体力学参数的空间变异性,采空区失稳高风险区域(破坏概率≥70%)位于矿柱高度的中间部位,矿柱表面的破坏深度在2m以内,与实际矿柱破坏位置与破坏深度相吻合。常规数值计算因计算结果指标分布差异,常面临难以判定磷矿采空区是否失稳的问题,而本文数值计算方法既考虑了层状岩体力学参数自相关性、互相关性及非高斯性的客观空间变异性特征,又实现了基于破坏概率的磷矿采空区失稳风险定量评价。

软破矿岩条件下胶结充填法转分段崩落法研究及应用

金川集团龙首矿西二采区上部中段充填采场发生失稳事故后,采矿方法由下向分层进路式胶结充填法转为无底柱分段崩落法时,面临着软破矿岩条件下覆盖层形成和采场稳定性问题。采用数值计算和现场试验等方法,对这2个关键技术问题进行了研究。数值模拟结果表明,随着崩落法首采分段回采工作的进行,采场复合顶板经历了破坏裂纹萌生、零星散块冒落、拱形批量冒落和柱塞状整体冒落等阶段,当首采分段回采结束时,顶板复合岩层冒落能够为崩落法采场提供足够厚度的覆盖层,且在崩落法采动地压下软破矿岩采场能够保持稳定。现场工业试验表明,在崩落法采场首采分段采用“阶梯式退采均匀扩展采空区+总量控制出矿”的技术方案,能够安全、高效地形成覆盖层,并通过增补“钢拱架+钢筋网+锚杆”的技术方案,解决在崩落法采动地压下维持破碎矿岩采场稳定性的问题,为无底柱分段崩落法在西二采区的扩大应用奠定了技术基础。

葫芦素煤矿上覆岩体运移规律及“上三带”发育高度

为研究大采宽条件上覆岩体运移与离层空间发育规律及“上三带”的关系,以内蒙葫芦素煤矿21406工作面与21101工作面为研究对象。采用多种方法如理论预测、建立模型进行数值模拟、钻探取芯观测岩性与裂隙发育、注水测量漏失量与窥视等方法研究了回采面开采后上覆岩层移动与变形规律与“上三带”发育关系。21406工作面位移呈“中间大、两边小”的分布态势,其运动速度先增加后减小,并在推过钻孔138 m处取得极大值;工作面推过138~178 m的范围内,为离层演化和发育的核心区间,并在322 m开始减弱并发生闭合;离层空间分布在距离煤层约260 m向上区域。21101工作面随着推进距离的增加,裂隙发育范围由“拱形”逐步演化为“马鞍形”,其发育的高度在推进80 m时达到61.6 m的最大值;注水实测导水裂隙带高度为65.39 m,裂采比为22.54倍。离层空间含水层发育在煤层上方260 m以上,远离导水裂隙带范围。本文研究结果为离层注浆与顶板疏放水提供了较为扎实的设计依据。

超厚中风化层高陡边坡稳定性研究

风化作用使岩石强度降低,进而导致边坡岩体的力学性能大幅度下降,因此露天矿山高陡边坡主要以微风化岩体为主,而以中风化岩体为主的边坡通常设计较为平缓,高度也多为30~50 m。对某钼矿完整性好的超厚中风化层高陡边坡稳定性进行研究,采用极限平衡法计算爆破振动力作用下的边坡安全系数,并根据计算结果对边坡参数进行优化,为下一步的设计提供技术支持。结果表明:边坡稳定性主要受到岩石强度和岩体完整性2个方面因素的影响,深部的中风化层如果节理裂隙发育减少,岩体完整性提升,边坡的稳定性也得到改善,完整性好的超厚中风化层也可以设计为高陡边坡。

Crack evolution of soft–hard composite layered rock-like specimens with two fissures under uniaxial compression

Acoustic emission and digital image correlation were used to study the spatiotemporal evolution characteristics of crack extension of soft and hard composite laminated rock masses(SHCLRM)containing double fissures under uniaxial compression.The effects of different rock combination methods and prefabricated fissures with different orientations on mechanical properties and crack coalescence patterns were analyzed.The characteristics of the acoustic emission source location distribution,and frequency changes of the crack evolution process were also investigated.The test results show that the damage mode of SHCLRM is related to the combination mode of rock layers and the orientation of fractures.Hard layers predominantly produce tensile cracks;soft layers produce shear cracks.The first crack always sprouts at the tip or middle of prefabricated fractures in hard layers.The acoustic emission signal of SHCLRM with double fractures has clear stage characteristics,and the state of crack development can be inferred from this signal to provide early warning for rock fracture instability.This study can provide a reference for the assessment of the fracture development status between adjacent roadways in SHCLRM in underground mines,as well as in roadway layout and support.

高地应力水平岩层隧道初期支护适应性研究

研究目的:蒙华铁路宜川县境内隧道地层多为水平砂泥岩互层地层,区域水平地应力高,在地应力和水平岩层共同作用下,隧道初期支护发生大面积起皮、开裂、掉块、钢架扭曲,对施工带来较大安全隐患,针对高地应力水平岩层采取什么类型的措施是亟须研究解决的问题。本次共研究了常规支护、加强型支护、加筋底板+长锚杆、限阻耗能型支护四种支护类型,结合3DEC离散元软件以及现场实际变形应力量测数据对四种支护类型效果进行对比分析,从而得出高地应力水平岩层应对工程措施。研究结论:(1)高地应力水平岩层开裂主要表现为拱顶喷混凝土剥皮、掉块、钢架扭曲;(2)单一加强支护参数方案、加筋底板+长锚杆支护方案对控制变形收敛具有效果,但拱部仍然存在开裂掉块现象,不能完全解决施工安全风险;(3)限阻耗能型支护可达到释放围岩压力的效果,限阻结构变形后初期支护未出现开裂现象;(4)在高地应力水平岩层中采用限阻耗能型支护在经济性、安全性上成效显著,推广应用效果良好。

水平层状围岩离层特征及离层影响因素研究

以南宁市东风路水平层状岩体隧道为背景,通过理论分析和现场试验,研究了水平层状围岩的离层特征及离层影响因素。离层的形成,是由于相邻岩层间的不协调变形引起的。当相邻岩层的层厚或力学性质差异较大时,隧道围岩离层便会产生。此外,离层的产生还受到岩体结构、围岩力学特性、地应力以及洞室尺寸等因素的影响。离层的产生及发展范围还受到关键层所在位置的影响,关键层距开挖断面越近,受到关键层的支撑和阻挡作用,离层所能影响范围越小,当围岩中不存在关键层时,离层影响范围大致为洞室跨度的一半。研究对类似工程具有借鉴意义。

水平层状围岩变形规律及渐进破坏机理研究

层状岩体受结构面影响,其破坏模式和破坏机制明显不同于其他岩体。在层状岩体中修建隧道,围岩稳定性问题比较突出。以东风路隧道为背景,针对层状岩体隧道围岩的破坏模式及渐进变形破坏机制进行了研究,结论如下:水平层状岩体隧道围岩稳定性影响因素主要有地质因素、施工因素、工程因素;水平层状岩体的变形破坏模式主要为顺层滑移破坏和弯折破坏;层状围岩渐进变形破坏具有典型的逐层递进性演化特征,靠近初始临空条件的岩层优先出现离层,随后逐层垮塌破坏,垮塌破坏的跨度则逐层减小,直至平衡后,最终形成梯形拱的破坏形态。

薄层层状岩体三轴试验强度变化规律研究

围绕岩体开展的研究一直是世界各国讨论的焦点,而岩体的各向异性更是研究的热点与难点问题之一。以西成铁路为工程背景,针对层状岩体,围绕影响层状岩体强度的各因素展开敏感性分析。为更客观真实地模拟表现实际工程岩体的特性,通过离散元软件3DEC模拟不同围压下层状岩体三轴压缩实验,对炭质千枚岩夹板岩薄层各向异性层状岩体的固有强度关系进行研究,通过研究不同岩体内摩擦角及黏聚力、不同结构面内摩擦角及黏聚力等强度参数,综合得出岩体强度参数。从研究结果可以看出不同层理倾角下,岩体强度关系变化都大致呈现出U形;采用三角函数的形式对强度参数进行拟合,所得表达式总体上能够体现出各向异性岩体的固有强度关系。研究结果能够为数值模拟软件本构关系二次开发提供参考。

西延高铁隧道缓倾层状岩体破坏机理及防治措施

针对西延高铁新延安隧道侏罗系下统页岩夹砂岩缓倾层状岩体初支变形及破坏问题,采用workbench静态结构及特征值屈曲模块进行支护结构建模,对初支结构破坏机理进行分析,对支护措施进行优化研究。研究表明:(1)缓倾层状岩体隧道围岩及支护结构变形破坏,主要受缓倾层状岩体岩性及缓倾层理构造等地质因素影响;(2)支护结构的破坏模式为支护结构面内屈曲,在围岩压力达到初支结构材料承载极限时出现失稳,压力继续增加时呈现压溃破坏;(3)缓倾层状岩体隧道围岩变形复杂,隧道开挖后围岩变形时间长,宜采用刚性支护,采用型钢支护相较于原设计的格栅支护在缓倾层状岩体变形控制及承载方面更合理。

注浆加固在破碎煤岩体中的应用与研究

破碎煤岩体注浆加固对控制围岩稳定具有重大意义,分层注浆效果检验是检测注浆工程合格的重要环节。通过设计分层注浆方案,选择合理的注浆材料、注浆压力以及注浆量,从浆液填充率、钻孔电视探测、分段注水、巷道检测4个方面进行注浆效果检验。结果表明,分层注浆工艺裂缝的浆液填充率可达90%以上,孔隙率低于10%,填充效果优于传统注浆工艺。