关键块体概率分析在复杂构造条件下大型地下工程开挖中的应用

锦屏一级水电站泄洪洞位于雅砻江右岸埋深大于100m的大理岩中,构造条件复杂,确定隧洞开挖面是否可能产生关键块体对工程安全具有重要意义。本文在对泄洪洞中导洞地质调查和研究基础上,将随机概率模型引入关键块体理论,分析关键块体的生成概率、体积大小与安全系数,得出关键块体形成概率服从负指数分布,主要取决于J②、J④组裂隙迹长的分布情况; 关键块体的体积与主要结构面迹长成正比,最终收敛于结构面对关键块体完全切割时的关键块体体积; 关键块体的安全系数随主要结构面迹长的增加而降低,但是同样收敛于结构面对关键块体的完全切割情况。为设计有效的加固方案提供了依据,具有积极的工程应用价值。     

岩体三维裂隙网络地质熵与渗透特性关系研究

裂隙网络是岩体地下水的主要流动通道,而工程岩体中裂隙网络错综复杂,裂隙网络的几何特征和连通性对其渗透性有着重要影响.为了综合量化裂隙迹长、间距、倾角、开度对裂隙网络连通性和渗透性的影响,基于信息熵原理,提出了三维裂隙网络地质熵理论和连通性指标-熵尺度,对比熵尺度与其他传统三维裂隙网络连通性指标,验证了熵尺度评价三维裂隙网络连通性和渗透性的合理性.结合锦屏一级水电站左岸边坡裂隙统计分布,建立三维裂隙网络渗流数值计算方法,分析不同裂隙迹长、倾角、间距、开度条件下三维裂隙面密度、无量纲逾渗密度、熵尺度和渗透系数的变化关系.结果表明:当体积率一定,考虑开度影响时,三维裂隙面密度和无量纲逾渗密度无法定量表征迹长和间距对裂隙网络连通性的影响;裂隙迹长与熵尺度和渗透系数呈负相关关系,裂隙间距和开度与熵尺度和渗透系数呈正相关关系,裂隙倾角变化对熵尺度和渗透系数影响较小;熵尺度与渗透系数的非线性关系近似满足二次多项式.     

不连续面平均速长概率估值法及其应用

在进行不连续面3-D网络模拟过程中, 不连续面的大小是一个重要的参数, 该数据主要来源是在现场露头上测量不连续面出露的迹长。由于取样中不可避免的偏差而使结果有误差, 在进行平均迹长估计时取样的误差必须予以校正, 本文介绍一种用概率的方法考虑取样误差通过有限2-D露头上测量的不连续面数据求算无限2-D空间平均迹长的技术。该方法可以借助计算机进行处理。     

估计迹长概率分布函数的新方法及其应用

本文提出一种估计迹长概率分布函数的新方法。该方法的优点是不需要有节理在测窗上出露长度的数据, 有效的减少了野外工作量。     

非高斯风压的极值计算方法

以经典极值理论为基础,发展了一种基于单个标准样本的非高斯风压的极值计算方法. 首先介绍了风洞试验及试验数据处理的基本概况;然后在阐述经典Gumbel极值理论的基础上,根据观察极值的相互独立性推导了短时距下极值分布参数和长时距下极值分布参数的关系式,给出了一种由短时距样本推算长时距下的极值估算方法; 最后基于风洞试验数据,将常用极值估算方法(峰值因子法、改进峰值因子法和Sadek-Simiu法)和该方法的计算结果进行了比较. 得到如下结论:将一个标准长度的非高斯风压时程数据划分成若干等长的子段,可以通过子段的极值分布规律准确地估算出母段的极值期望值,子段的最佳分段长度可以通过自相关分析给出;与常用的极值估算方法相比,该方法更能准确估计非高斯风压的极值.      

复杂地质条件下顶拱大型不稳定块体分析与预测

锦屏一级水电站2#尾水调压室所处位置地质条件复杂,在桩号0+320°~0+360°和0+0°~0+120°之间开挖时局部掉块严重。本文综合分析后,提出了2#尾调室顶拱未开挖域产生大型不稳定块体的必要条件是：(1)由节理①④F183组结构面和开挖临空面切割产生;(2)块体大小主要取决于节理组①和④的延伸长度;(3)较大不稳定块体的产生区域,必然位于F18断层带下盘。对2#尾调室顶拱进行搜索预测,预测结果表明该潜在块体位于未开挖区域桩号0+180°～0+260°之间,规模约为50m3,重达133.5t。根据块体理论分析,其稳定性系数为1.052,处于临界状态,应采取相应的应急支护补强措施。     

结构模糊区间可靠性分析方法

在结构模糊可靠性分析模型的基础上,充分考虑了状态变量分布密度函数的相关参数的不确定性。这些参数的取值范围可以被确定在相应的区间内,并将这些区间引入到结构模糊可靠性的分析中,基于区间数学理论,提出了一种可以预测结构模糊可靠度所在范围的求解方法,并讨论了当状态变量服从正态分布时,结构的模糊区间可靠性的分析过程。算例表明该方法比传统的模糊可靠性方法能提供更多的关于结构安全程度的有用信息,也更具有工程实用价值。     

岩爆预测评估方法的动力数值分析

精准的预测评估是制定岩爆防治策略的重要前提.采用FISH语言编程对FLAC3D数值模拟软件进行二次开发,基于动力数值分析,将6种岩爆预测评价指标引用到锦屏Ⅱ级水电站4#引水隧洞数值模拟岩爆案例中,对岩爆的孕育过程和形成机制进行深入剖析.研究结果表明:隧洞掌子面右侧边墙及拱腰部位发生了以剪切破坏为主的突发性破坏,洞室周围...     

凹坑形表面在空气介质中的减阻性能研究

采用标准k-ε湍流模型对一种新型的非光滑表面———凹坑形表面在空气介质中不同条件下的流动进行了数值模拟,可以得到光滑表面和半径0.4mm的半球状凹坑分布的非光滑表面在4~48m/s范围内的来流速度下的阻力系数.计算结果表明该凹坑形非光滑表面在这个速度区间内均能产生一定的减阻效果.在速度为24m/s时,它的减阻率达到最大的7.2%.最后本文对该非光滑表面的减阻机理进行了研究.     

青藏高原东北缘黄河黑山峡出口段阶地特征与断层活动

青藏高原东北缘黄河黑山峡出口地段夜明山 -长流水沟一带 ,黄河的河流阶地发育和保存的较好。阶地的形成不仅记录了青藏高原北部第四纪以来地壳的 7次隆升过程的特点 ,而且阶地的空间展布及其特征反映了断层F8(7) 和F2 0 1活动的特点。详细的观测研究表明F8(7) 以南发育并保存有 7级阶地 ,而F8(7) 和F2 0 1之间及F2 0 1以北仅保存有 5级阶地。所有的阶地都为基座阶地。其中Ⅰ和Ⅱ级阶地前缘在区内连续展布 ,横跨断层F8(7) 两侧的Ⅲ级阶地前缘仍保持连续 ,但阶地宽度陡然变宽 ,Ⅳ级阶地前缘即Ⅲ级阶地后缘左旋位移 15 0m左右。横跨断层F2 0 1两侧 ,Ⅱ级阶地宽度由 2 0 0m急剧变宽为 710m ,Ⅱ级以上阶地前缘左旋位移均在 4 0 0m左右。断层F8(7) 和F2 0 1两侧阶地宽度的变化和阶地前缘的左旋位移记录了断层F8(7) 和F2 0 1第四纪晚期活动的时空规律 ,为断层的活动性评价提供了良好的依据     

Application of Fractional Differential Equations for Modeling the Anomalous Diffusion of Contaminant from Fracture into Porous Rock Matrix with Bordering Alteration Zone

Solute diffusion from a fracture into a porous rock with an altered zone bordering the fracture is modeled by a system of two diffusion equations (one for the altered zone and another for the intact porous matrix) with different coefficients of effective diffusivity. Since experimental studies of diffusion into rock samples with altered zones indicate that mathematical models of diffusion based on Fick’s law do not adequately describe the concentration field in a sample, fractional order diffusion equations are chosen in this study for modeling the anomalous mass transport in the rocks. In the case of significantly higher porosity of the altered zone (e.g., this is typical for carbonates) the effective diffusivity here can be much higher than the effective diffusivity of non-altered rocks. By introducing a small parameter that is the ratio of effective diffusivities in the non-altered and altered regions and applying the technique of perturbations, approximate analytical solutions for concentrations in the altered zone bordering the fracture and in the intact surrounding rocks are obtained. Based on these solutions, different regimes of diffusion into the rocks with different physical properties are modeled and analyzed. It is shown that, using experimentally obtained data, the orders of the fractional derivatives in the differential equations can be readily calibrated for the every specific rock.     

FINITE ELEMENT SURFACE MODEL FOR FLOW AROUND VERTICAL WALL ABUTMENTS

A two-dimensional finite element surface model is developed to determine velocities, depths, and turning angles around vertical wall abutments. The model solves the Reynolds-averaged turbulent flow equations along a horizontal plane passing through the average water surface. This approach is an improvement over the depth-averaged flow models where dispersion terms reflecting vertical effects are neglected. In the model, vertical gradient effects are accounted for through the use of power law for the vertical distribution of the longitudinal velocity; a similar treatment is applied to lateral turbulent shear stresses. The model is capable of computing the dynamic pressure distribution, which in turn is converted to water elevation values. The model, being two dimensional, is computationally efficient and practical to use. The numerical model was successfully verified using experimental data from vertical wall abutments and groins with protrusion ratios (ratio of protrusion length perpendicular to direction of flow to total channel width) of 0·1, 0·2 and 0·3. The results show the occurrence of a high intensity velocity zone close to the upstream abutment nose similar to those observed experimentally. The effects of roughness, depth, and energy slope on the intensity of flow field is investigated and an analytical expression is developed. Numerical experiments indicate that grain roughness affects flow field around the abutment nose by controlling the magnitude of the lateral velocity component and by controlling the lateral extent of the affected zone. Velocity amplification at the abutment nose is found to be mainly related to the protrusion ratio and to the friction factor, and can be up to 1·75 times the approach velocities for protrusion ratios of 0·3. For a protrusion ratio of 0·3, for a typical range of roughness values the increase in nose velocities due to friction factor alone was found to be up to 20 percent.     

Modeling the microstructural evolution of metallic polycrystalline materials under localization conditions

In general, the shear localization process involves initiation and growth. Initiation is expected to be a stochastic process in material space where anisotropy in the elastic-plastic behavior of single crystals and inter-crystalline interactions serve to form natural perturbations to the material's local stability. A hat-shaped sample geometry was used to study shear localization growth. It is an axi-symmetric sample with an upper “hat” portion and a lower “brim” portion with the shear zone located between the hat and brim. The shear zone length was 870-890 μm with deformation imposed through a Split-Hopkinson Pressure Bar system at maximum top-to-bottom velocity in the range of 8-25 m/s. The deformation behavior of tantalum tophat samples is modeled through direct polycrystal simulations. An embedded Voronoï-tessellated two-dimensional microstructure is used to represent the material within the shear zone of the sample. A thermo-mechanically coupled elasto-viscoplastic single crystal model is presented and used to represent the response of the grains within the aggregate shear zone. In the shoulder regions away from the shear zone where strain levels remain on the order of 0.05, the material is represented by an isotropic J₂ flow theory based upon the elasto-viscoplastic Mechanical Threshold Stress (MTS) model for flow strength. The top surface stress versus displacement results were compared to those of the experiments and over-all the simulated stress magnitude is over-predicted. It is believed that the reason for this is that the simulations are two-dimensional. A region within the numerical shear zone was isolated for statistical examination. The vonMises stress state within this isolated shear zone region suggests an approximate normal distribution with a factor of two difference between the minimum and maximum points in the distribution. The equivalent plastic strain distribution within this same region has values ranging between 0.4 and 1.5 and is not symmetric. Other material state distributions are also given. The crystallographic texture within this isolated shear zone is also compared to the experimental texture and found to match reasonably well considering the simulations are two-dimensional.     

Rotational asymmetry of reactant concentration and its evolution in a circulating fluidized bed riser

Rotational asymmetric distribution of reactant (ozone) concentration and its evolution along with the gas-solid reactive flow were studied in a 76 mm i.d., 10.2 m high circulating fluidized bed (CFB) riser reactor. The superficial gas velocity ranged from 3 to 5 m/s and the solids circulation rates were 50 and 100 kg/(m² s). Experimental results show that the asymmetry of reactant distribution can extend to a height close to the length of flow developing zone of the CFB riser reactor and then disappears. Based on the hydrodynamics of the gas and solid phases in the solids entrance region, this asymmetry can be attributed to the effect of the solids entrance structure.     

An experimental and numerical study of the localization behavior of tantalum and stainless steel

In general, the shear localization process involves initiation and growth. Initiation is expected to be a stochastic process in material space where anisotropy in the elastic–plastic behavior of single crystals and inter-crystalline interactions serve to form natural perturbations to the material’s local stability. A hat-shaped sample geometry was used to study shear localization growth. It is an axi-symmetric sample with an upper “hat” portion and a lower “brim” portion with the shear zone located between the hat and brim. The shear zone length is 870–890 μm with deformation imposed through a split-Hopkinson pressure bar system at maximum top-to-bottom velocity in the range of 8–25 m/s. We present experimental results of the deformation response of tantalum and 316L stainless steel samples. The tantalum samples did not form shear bands but the stainless steel sample formed a late stage shear band. We have also modeled these experiments using both conductive and adiabatic continuum models. An anisotropic elasto-viscoplastic constitutive model with damage evolution was used within the finite element code EPIC. A Mie-Gruneisen equation of state and the rate and temperature sensitive MTS flow stress model together with a Gurson flow surface were employed. The models performed well in predicting the experimental data. The numerical results for tantalum suggested a maximum equivalent strain rate on the order of 7 × 10⁴ s⁻¹ in the gage section for an imposed top surface displacement rate of 17.5 m/s. The models also suggested that for an initial temperature of 298 K a temperature in the neighborhood of 900 K was reached within the shear section. The numerical results for stainless steel suggest that melting temperature was reached throughout the shear band shortly after peak load. Due to sample geometry, the stress state in the shear zone was not pure shear; a significant normal stress relative to the shear zone basis line was developed.     

地质雷达在风火山隧道病害检测中的应用与结果分析

青藏铁路全线开通运营以来,对处于高寒地区的永久冻土隧道之一的风火山隧道的质量状态首次进行了无损检测。风火山隧道处于高寒永久冻土区,隧道全部处于冻岩中,两端洞口主要为砂岩与泥岩,并且为富冰冻土。受到季节性冻融的影响,隧道病害比较突出,主要表现为衬砌裂缝,漏水涌水,衬砌酥松剥落。为了准确地掌握风火山隧道衬砌结构质量状态,本文首次应用于风火山隧道衬砌结构的质量检测。该检测设备一改传统破坏式的检测方法,具有快速、简捷、无损、灵活的特点。通过对现场数据处理分析,可以精确探测衬砌厚度,查明衬砌背后存在的空洞和回填不密实区域。检测结果表明,隧道在高寒恶劣环境中,衬砌总体外观质量尚好,但是在两端洞口段有渗水现象; 衬砌背后空洞缺陷等级为严重地段测线长度为20m,等级为极严重地段测线长度为98m; 衬砌背后回填不密实缺陷等级为严重地段测线长度为41m,等级为极严重地段测线长度为33m。检测结果与实际病害情况基本相符。     

西气东输管道工程中卫黄河穿越隧道场地工程地质条件评价

西气东输工程中卫黄河穿越隧道长1197.77m,高4.3m,宽5.6m。隧道入口高于黄河水位28m,出口高于黄河水位45m。隧道顶板高程为1130m。位于黄河水下100m。隧道场地围岩为寒武系磨盘井组灰绿色、银灰色浅变质中厚层细粒长石石英砂岩、千枚状板岩、绢云母化千枚岩。围岩为弱风化Ⅲ～Ⅳ类岩石。透水率为4～67Lu,纵波波速为500～3300m.s^-1。BQ为300～400。变形模量为6.11～9.22GPa。泊松比（μ）0.14～0.24。内摩擦角（ψ）为42.1°～44.7°。地下水为基岩裂隙水。含水层为寒武系浅变质岩,受大气降水渗入补给,单井涌水量为1.0～50m³.d^-1。隧道轴线穿越区岩体较完整—较破碎,未有全新活动断层。隧道位置选择和开挖深度设计是可行的。施工和长期运营是安全的。     

秦山三期核电工程反应堆地段节理裂隙模拟

以秦山三期核电工程反应堆地段作为研究对象 ,针对节理裂隙在岩体中的分布具有随机性的特点 ,运用随机方法对其分布规律进行了研究。根据实测的节理裂隙产状、间距及迹线长度 ,推断节理裂隙概率分布特征。同时充分考虑到节理裂隙分布的不均匀性和方向性等特点 ,采用非平稳态随机过程模拟节理裂隙间距 ,通过 Monte- Carlo方法得到等效的节理裂隙网络。根据统计和拟合的结果 ,对反应堆地段岩体的节理裂隙进行了评价。