地下洞室围岩顶拱承载力学机制及稳定拱设计方法

 受枢纽布置和地形地质条件的限制,三峡工程地下厂房布置于右岸白岩尖山体中,主厂房洞室上覆岩体最薄处仅1倍厂房跨度,显然不满足现行规范关于上覆岩体厚度不小于2倍开挖宽度的要求。对于这类浅埋式的大跨度高边墙地下厂房,在上覆岩体厚度有限及一定初始应力条件下,洞室顶拱的稳定性是必须解决的首要技术问题。从岩体结构、岩体强度和地应力水平对围岩稳定性控制的角度出发,通过对地下厂房洞室围岩顶拱承载力学机制的研究,提出地下洞室岩体稳定拱的定义及其存在的力学条件,给出地下洞室岩体稳定拱的确定方法,分析采用地下洞室岩体稳定拱确定上覆岩体厚度的可行性,形成一套确定浅埋式地下厂房洞室埋置深度的稳定拱设计方法。研究结果表明,三峡工程地下厂房顶拱围岩具备形成稳定拱的埋深条件和水平应力等条件,形成稳定拱的最小埋深约为2/3倍洞跨,在上覆岩体中形成稳定拱的最小水平侧压系数应大于1.5,而最大水平侧压系数不宜高于3.0。据此进行主厂房顶拱设计,多年的应用成效显示,地下厂房顶拱围岩是稳定安全的,表明三峡工程地下厂房顶拱在既定的围岩强度、岩体结构以及初始地应力水平等条件下,采用稳定拱设计方法确定洞室上覆岩体厚度是合适、可靠的,能够保障洞室围岩稳定,满足工程安全的要求,可为解决大型浅埋洞室的设计提供理论基础和科学依据。     

溪洛渡水电站地下厂房岩体工程实践

 溪洛渡超大型地下洞室群玄武岩组内层间与层内错动带使得围岩非连续性和各向异性损伤问题突出,采用损伤弹塑性理论对围岩稳定性进行分析,以良好的施工组织与工艺水平对潜在的不稳定区域和地质缺陷部位实施精细化光面爆破,严格控制围岩的开挖损伤并保证岩梁等的优良成型。针对关键部位和地质缺陷部位进行补强加固并实施安全监测,利用现阶段监测成果对围岩稳定性预测进行检验,并对实际围岩安全性进行评价。针对典型复杂地下洞室的地质条件、稳定性分析、开挖与支护程序、安全监测成果分析等岩体工程实践环节的回顾,在设计理念和工程实施方面提出一些见解,可为类似超大地下工程实际提供直接借鉴。     

三峡右岸地下电站窑洞口围岩稳定性三维断裂损伤分析

三峡地下电站厂房窑洞口围岩属于一种断续节理裂隙切割的节理岩体,对主厂房与窑洞口相接处围岩的稳定情况,应用三维国国节理裂隙岩体的本构关系、损伤演比方程来评价此类岩体稳定性和变形行为。结果表明所建模型是有效的。     

三峡工程永久船闸陡高边坡各向异性卸荷岩体力学研究

岩体工程具有加载和卸荷两类不同性质的力学状态,在此力学状态各异的情况下,节理岩体的力学特性有本质的区别。岩体高边坡工程的力学状态主要为卸荷。在三峡工程永久船闸高边坡的研究中,作者提出了“各向异性卸荷岩体力学的新概念”,得出了与目前常规岩体力学研究不同的结论。该研究成果已被多项边坡工程和地下工程实例所验证。以前应用该理论对三峡永久船闸陡高边坡的研究成果,也日益为监测资料所验证。     

Advances in statistical mechanics of rock masses and its engineering applications

To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.     

Use of the equivalent continuum approach to model the behavior of a rock mass containing an interlayer shear weakness zone in an underground cavern excavation

An interlayer shear weakness zone (ISWZ) is a weak zonal geotechnical system of variable thickness that occurs between different rock strata (e.g., tuff and basalt). At the site of the future Baihetan hydropower station, Sichuan Province, China, because of the relatively poor ISWZ mechanical properties, the overall stability of the underground powerhouse is potentially at risk. In this study, to evaluate the effects of ISWZs on the stability of the future underground powerhouse by means of three-dimensional continuum modeling (3-D continuum modeling), the concept of a virtual rock mass composed of ISWZ and host rock is proposed. An equivalent continuum approach, including a rock–soil composite material (RSCM) model, is elaborated, with corresponding expressions for the input parameters. Comparisons were made between the predictions from the RSCM model, the results obtained by an analytic method, and existing data from physical model tests. The comparison showed that all three types of information showed good consistency in terms of failure mode and strength. This indicates the suitability of the RSCM model for describing the behavior of a rock mass containing discontinuities. Furthermore, comparison between the predictions of the proposed equivalent continuum approach, the joint element approach, and the solid element approach for a deformation of a test tunnel section containing an ISWZ show that the results produced by the first two approaches are similar, but much smaller than that using the third approach. Further comparison of the actual state of the ISWZ-containing rock mass in the test tunnel section confirmed the applicability of the proposed equivalent continuum approach to prediction of deformation of the rock masses containing ISWZs at the future Baihetan underground powerhouse site.     

三峡地下厂房顶拱典型块体研究

 岩石块体稳定性问题是三峡工程地下电站洞室工程的主要地质问题之一。电站主厂房洞室跨度大、边墙高，形成的临空边界宽大。本文介绍块体软件GeneralBlock的基本分析过程，并采用GeneralBlock软件建立三维岩石块体模型，对顶拱进行块体识别和稳定性分析。根据块体识别及分析结果，并考虑各块体内的组合形式，设计、施工了相应的预应力锚索或锚杆加固处理，并对锚杆、锚索和块体进行系统监测。监测结果表明，块体变形控制在2 mm以内，锚杆应力和锚索损失率保持稳定，锚固效果较好。     

地下厂房围岩稳定分析若干问题探讨

地下厂房稳定分析首先要确定围岩变形破坏运动类型。本文按照四种岩石力学条件从工程实践中归纳了五种变形破坏运动类型,以便在设计阶段进行初步判断和选择岩体力学模型,并以三峡工程地下厂房为实例,着重研究了块体结构的围岩稳定分析方法。在建立围岩力学模型时,要结合地下洞室的尺寸处理不同规模的不连续面。三个方向的应力对块体稳定性的响影同样重要,在没有条件使用三维有限单元法时,可用全空间赤平投影法与二维有限单元法结合计算。研究结果表明,在设计地下洞室方向时,不仅要考虑初始应力的方位,同时还应考虑软弱结构面的方向。     

三峡地下厂房岩体结构及围岩稳定性控制

长江三峡工程右岸地下厂房共安装6台700MW水轮发电机组,主厂房为直墙曲顶拱型断面,高度大,跨度长,浅埋于白云尖山体坚硬的混合花岗岩体内,其岩体结构特征控制围岩稳定状态。通过岩体结构的构造演化,结构面分布及工程地质特性研究,并结合主厂房开挖变形监测、三维数值模拟及结构面组合效应分析,较详细地探讨了岩体结构对主厂房围岩变形及块体稳定性的控制作用。成果可供三峡地下厂房及类似大型地下洞室围岩稳定及支护设计参考。     

高应力硬岩地区岩体结构对地下洞室围岩稳定的控制效应研究

官地水电站地下厂房属典型的硬岩地区深埋大型地下洞室群,其重要特点是同时面临高地应力和结构面发育这2个不利条件,实测最大主应力为25～35 MPa,厂区无大的断层和软弱结构面,但错动带和裂隙十分发育。通过对地下洞室群施工过程中出现的围岩局部失稳破坏现象进行全面的分析整理,对三大洞室的岩体结构特征和围岩变形破坏模式进行系统的分析、比较和总结,从而对影响围岩稳定的两大控制因素——地应力和岩体结构对官地地下厂房洞室群围岩稳定的影响程度和方式进行分析和对比。研究表明,由于三大洞室围岩类别以II类为主,岩体结构以块状～次块状结构为主,围岩具有较高的力学强度和强度应力比,从而具有较强的抵抗应力破坏的能力;岩体结构对地下厂房围岩变形与稳定的控制作用较地应力则更为明显,地下洞室群开挖过程中出现的局部失稳或较大变形多与不利方位的结构面直接相关。三大洞室围岩岩体结构特征总体上的相似性非常明确,反映在三大洞室围岩的变形特征和破坏模式上具有很好的统一性。然而,三大洞室的岩体结构特征也存在一定的差异,导致岩体结构影响围岩稳定的方式和程度有所不同。结构面发育造成的另一个不利影响是为坚硬岩体在高地应力条件下产生卸荷时效变形提供了内部条件。因此,在强度应力比较高的硬岩地区,应充分重视岩体结构及其演化对围岩变形和稳定的控制效应。     

岩体开挖过程中初始应力的动态卸荷效应研究

提出了边坡、地下洞室开挖施工过程中岩体初始应力动态卸荷的概念。以龙滩水电站地下厂房开挖为例，比较了爆破荷载和岩体初始应力动态卸荷对岩体的动态影响。计算结果表明：（1）在中高地应力区，岩体开挖过程中初始应力场的动态卸荷可能是引起岩体松动的重要因素之一；（2）虽然炮孔近区的损伤主要是由爆破荷载引起的，而远区的忪，力则可能由岩体初始应力的动态卸荷引起；（3）初始应力卸荷越快，其引起的松动范围越大。     

Simulation of cracking near a large underground cavern in a discontinuous rock mass using the expanded distinct element method

The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. A number of experimental and numerical investigations have demonstrated the significant influences of discontinuities on the mechanical, thermal and hydraulic behaviors of discontinuous rock masses, indicating that the deformation mechanism and stability of rock structures in the discontinuous rock masses depend not only on the existing discontinuities but also on the new cracks generated and thereafter keep propagating due mainly to the stress redistribution induced by excavation.In this study, an expanded distinct element method (EDEM) was developed for simulating the crack generation and propagation due to the shear and tension failures in the matrix rock blocks. Using this method, excavation simulations of deep underground caverns have been carried out on the models with differing depths of cavern and differing geometrical distributions of the existing discontinuities. Model experiments by using the base friction test apparatus were conducted to verify the proposed numerical approach. Furthermore, the support effects of rock bolts on controlling the deformations of the rock mass surrounding a cavern and movements of key blocks were evaluated by means of the EDEM approach.     

大型地下洞室位移量级预测初步探讨

 位移是岩体最容易测量与控制的参数,其量级与速率是隧道工程围岩稳定评判或位移监控的基本参数。但对于大型地下洞室而言,目前尚未建立相应的标准。以我国西南地区已建或开挖完毕的6个水电站大型地下厂房的位移监测成果为基础,总结影响地下厂房围岩位移量级的因素,提炼出主要影响因素,即围岩初始地应力水平和岩体性状,分别用最大主应力 与岩块饱和单轴抗压强度 表征。引入围岩应力强度比 代表2个主要因素,建立其与边墙最大和平均位移量级的2个经验关系式,取得了较好的研究结果,该成果可为地下洞室位移监测设计、预警与监控标准的建立提供参考。最后,对经验公式的适用性与改进途径进行分析。     

喷锚支护与隧道自承拱的机理

为了使岩石隧洞拱部稳定,喷锚支护被广泛用于地下隧洞的支撑设计中。正确的喷锚支护设计应该基于对喷锚支护加固的特性和洞顶岩石拱结构的机理两方面都有一个清楚的认识。为此,以三峡工程地下厂房拱顶设计为例,研究洞顶岩石拱结构形成及加固机理。     

地下厂房岩锚梁裂缝成因分析

针对水电站地下厂房开挖过程中出现的岩锚梁与围岩结合部位的纵向裂缝,结合地质资料、监测成果和施工过程,对岩锚梁裂缝产生的原因进行较为详细的分析,认为裂缝形成的时间在2006年10月底至11月初,即地下厂房进行第Ⅴ层开挖施工期间;裂缝段围岩的差异变形是裂缝产生的主要原因;导致围岩差异变形的地质原因是存在岩脉断层,施工原因是支护措施不能有效地节制围岩变形.因此,考虑岩体的非连续性,加强施工期地质工作,及时预测侧墙可能出现的差异变形,并采取有力的支护措施对确保岩锚梁安全十分重要.     

向家坝水电站地下厂房缓倾角层状围岩稳定分析

 向家坝水电站地下厂房跨度33.4 m、高85.2 m,为国内最大跨度与高度的地下厂房。缓倾角岩层中大跨度地下洞室群的开挖致使顶拱围岩稳定问题突出,为典型结构面控制型地下岩体工程。采取三维离散单元法与应力位移监测相结合的研究对策,对围岩稳定进行综合分析,实施对穿锚索和系统锚杆的加固对策,并基于监测成果说明厂房顶拱围岩在开挖加固后的稳定性。研究表明,浅至中等埋深结构面控制型围岩稳定问题必须加强工程地质分析,重视岩体的非连续性和各向异性,宜采用非连续介质力学分析方法进行分析,以实施针对性加固措施。     

溪洛渡水电站超大型地下厂房洞室群岩体工程控制与监测

 金沙江溪洛渡水电站地下厂房洞室群规模巨大,结构复杂,玄武岩组内层间与层内错动带致使岩体非连续性是主要地质问题。采用损伤弹塑性数值方法对围岩稳定性进行分析,确定洞室开挖顺序和支护参数。精细化施工组织,严格控制开挖对岩体的损伤范围,并保证洞室轮廓的良好成型。及时对监测数据进行分析和反演分析,对支护工作量进行动态设计。开挖过程中,位移和应力变化规律较好;开挖完成后,位移和应力总量值较小,洞室围岩稳定性良好。溪洛渡地下厂房洞室群规模为我国已建和在建工程之首,总结其设计、开挖与支护,监测与反演等岩体工程控制措施,对类似工程具有指导和借鉴作用。     

锦屏一级水电站地下厂房围岩开裂变形机制研究

针对锦屏一级水电站地下厂房高应力、低强度应力比条件下开挖施工引起的围岩变形开裂及相关力学问题,从全空间赤平投影解析、平面投影应力特征等多角度全方位研究地下厂房区地应力场分布特征及规律;并结合力学定性分析和三维数值模拟等手段对地下洞室群围岩变形开裂机制进行深入分析,研究洞室群围岩开挖损伤演化规律。研究表明,锦屏一级地下厂房区域出现的围岩、喷层较大变形乃至破坏现象本质上是由高地应力和相对较低的岩体强度形成的不利组合所造成的,在主厂房、主变室的拱腰、拱座和边墙以及母线洞侧墙等部位出现的开裂破坏,属于典型的高应力、低强度应力比条件下围岩的卸荷变形与破坏。提出锦屏地下厂房围岩变形开裂概化模型,为地应力场反演和施工过程的数值仿真分析提供重要参考和定性依据;最后针对开挖维护围岩稳定性问题提出相应的建议,为锦屏一级地下厂房的开挖施工及动态支护设计提供技术支持。     

岩锚吊车梁破坏机制的计算模拟分析

采用非线性有限元方法研究了钢筋混凝土岩锚吊车梁和围岩的力学特性。结合某水电站三期扩建工程实践，假定地下厂房围岩和混凝土材料满足Drucke-Prager弹塑性本构关系，采用三维有限元方法计算模拟了岩锚吊车梁的破坏机制，并进行了相应的稳定性分析。数值模拟结果表明，地下厂房围岩与岩锚吊车梁交界面的粘聚力和摩擦系数大小对岩锚吊车梁的稳定性有着重要的影响。随着围岩与混凝土岩锚吊车梁粘聚力的降低，岩锚吊车梁的抗滑安全系数减小。而当围岩与岩锚梁交界面出现破坏时，岩锚吊车梁的安全系数为3．7。地下厂房的继续开挖对于吊车梁系统锚杆和周围岩体的应力分布有较大影响。有效控制地下厂房爆破开挖对围岩的损伤，对于改善岩锚吊车梁的受力状态和提高吊车梁的稳定性具有实际意义。     

Modeling mechanical layering effects on stability of underground openings in jointed sedimentary rocks

This paper examines the significance of mechanical layering for “blocky” rock mass deformation around underground openings excavated through sedimentary rocks. The analysis is based on an integration of geologically based discrete fracture models (“geoDFN”), which incorporate “mechanical layering”, with the numerical discrete element method—the discontinuous deformation analysis (DDA). We begin with addressing limitations of classical solutions for mine roof stability in layered and jointed rock masses via the analysis of the free standing, unsupported, 2000-year-old underground quarry known as Zedekiah's cave below the old city of Jerusalem, Israel. We show that both the “clamped beam” model and the “Voussoir beam analogue” fail to predict the observed roof stability. Only application of discrete element modeling, which allows for interactions between multiple blocks in the rock mass, can capture correctly the arching mechanism which takes place in the roof and which properly explains the long-term stability of this underground opening.We continue with examining the effect of joint trace geometries on “blocky” rock mass deformation using the hybrid geoDFN-DDA approach. We show that with increasing joint length and decreasing bridge length vertical deformations in the rock mass are enhanced. We explain this by the greater number of distinct blocks in the rock mass due to the greater joint intersection probability in such geometries. We find that rock bridge length is particularly important when considering the stability of the immediate roof. With increasing rock bridge length the number of blocks in immediate roof decreases and consequently individual block width is increased. Increased block width in immediate roof layers enhances stable arching development, thus improving their load carrying capacity and overall stability of the underground structure.