基于强度折减的土质边坡破坏及稳定分析

边坡的破坏过程是由土体局部破坏向整体失稳发展的过程,其塑性区的开展及其水平位移增量的变化较完美地展现了这个过程。根据边坡的实际破坏和有限元数值模拟情况,提出了以特征点位移增量的突变及塑性区贯通作为边坡的失稳判断准则;并以此为判据,采用基于强度折减的大变形有限元方法分析了土质边坡的破坏及稳定性。研究表明,采用强度折减有限元法可有效分析边坡的破坏及其稳定性;此外还分析了带有软弱夹层黏土边坡的破坏性状及其稳定性,并比较了大、小变形有限元的计算结果,结果表明,带有软弱夹层黏土边坡的破坏性状随软弱夹层土体性质的变化而变化,由大小变形有限元分析得到的边坡稳定安全系数较为一致,但边坡的破坏机制随软弱夹层土体性质变化的转变点不同。     

岩质高边坡开挖优化及稳定性分析的复合方法

以一最终开采境界为180 m的岩质边坡为工程背景,建立了基于极限平衡法和强度折减法的稳定性复合分析方法,探讨边坡开挖优化方案及其宏观力学变形响应.建立简化Bishop极限平衡模型,分析边坡在不同工况下,安全系数随开挖坡度的变化情况,确定优化开挖方案;利用数值分析方法,建立数值计算模型,计算边坡在最优台阶开挖方案下的破坏模式、应力应变响应以及安全系数.结果表明,所确定的开挖方案下,边坡稳定性和经济性达到较好组合; 数值分析方法能够直观反映出应力和变形在完整岩体和断层裂隙间的传递规律,验证符合实践情况;开挖完毕后,边坡处于稳定状态,其潜在破坏形式为局部滑坡;复合方法能够同时发挥极限平衡法快速计算安全系数的优点和数值分析方法动态监测开挖进程的优点.     

物质点强度折减法及其在边坡中的应用

物质点法适用于模拟连续介质大变形,如边坡失稳全过程。在物质点法中应用强度折减法,用于边坡稳定性评价。与极限平衡法相比,二者安全系数计算值、滑动面位置结果基本一致;与有限元强度折减法相比,物质点法失稳评价标准的物理意义明确。利用物质点法大变形计算优势,评价边坡失稳后的破坏后果,通过算例说明其评价不同安全系数下的滑坡堆积形态及滑移距离的能力,尤其是评价滑坡对临近建筑物的影响程度的能力。物质点强度折减法可用于边坡稳定性评价及边坡破坏后果评价。     

露采矿山台阶边坡结构面特性与破坏机制分析

基于四川峨胜露天矿山台阶边坡的结构面特征,结合离散单元软件3DEC对台阶边坡进行模拟,研究台阶边坡破坏机制。结果表明:(1)受区域地质构造影响,研究区域的优势结构面倾角较陡,且产状与构造迹线相关;(2)矿区台阶边坡变形破坏模式主要为平面滑动和楔形体破坏,发生倾倒破坏的可能性小;(3)边坡整体变形小,在结构面贯穿的位置有位移突变和增大的现象,临空面的楔形体出露后发生崩塌掉块,局部稳定性降低;(4)台阶边坡破坏机制为拉裂-滑移-崩塌,可分为三个阶段:弹性变形阶段,渐进变形阶段和变形破坏阶段。     

层状岩质边坡破坏模式及稳定性的数值分析

运用FLAC3D模拟层状岩质边坡的破坏模式,并采用强度折减法分析结构面倾角与稳定性之间的关系。结果表明:①水平层状边坡坡顶变形破坏早于坡面和坡脚,形成拉破坏区。当结构面倾角较小时,顺倾向层状边坡主要发生滑移破坏;当结构面倾角较大时,发生弯折-溃曲破坏。直立层状边坡主要发生弯曲-板间拉裂-塌落破坏。逆倾向层状边坡的破坏形式为对于小倾角为滑移破坏,对于陡倾角为倾倒破坏。②对于顺倾向边坡,整体安全系数随结构面倾角先减小后增大,呈现两头高、中间低的形态,在倾角为30°时安全系数最小;对于逆倾向边坡,曲线呈现增大-减小-增大的态势,并且大部分高于顺倾向边坡曲线,符合实际情况。③所采用的低强度弹塑性单元能够比较真实地模拟软弱结构面的变形。     

基于局部强度折减法的边坡多滑面分析方法及应用研究

边坡最危险滑动面的搜索方法一直是研究的热点,但边坡内部次级滑动面也可能不满足安全设计要求,因此,考虑边坡多条滑动面的分析方法亦应得到关注。在传统强度折减法中,对边坡整个区域的抗剪强度参数进行折减,此方法仅可得到一个临界滑动面和最小安全系数。提出了一种基于局部强度折减法的多滑面分析方法,即首先定义单元安全系数的概念,并且计算边坡每个单元的安全系数,然后自动搜索出单元安全系数处于不同范围内的单元集合,对各个单元集合的强度参数进行折减计算,即可得到不同安全系数对应的滑动面。通过单台阶和双台阶边坡算例验证了该方法的可行性,结果表明,随着安全系数的增大,潜在滑面的深度和潜在滑动区域亦增大。最后把该方法应用到某隧道进口仰坡的稳定性评价中, 通过该方法得到的多级滑动面与现场监测数据吻合较好。     

基于改进极限平衡法的多级均质黄土边坡稳定性分析

针对多级均质黄土边坡稳定性分析这一工程问题,给出了一种系统的分析方法。建立了多级黄土边坡整体破坏模式下与局部破坏模式下坡脚圆、中点圆等可能的破坏机构;基于改进极限平衡法,推导出各破坏机构对应的边坡安全系数解析式,进一步采用最优化方法来确定整体破坏模式下与局部破坏模式下各破坏机构所对应的边坡稳定安全系数极小值;给出了系统地进行多级黄土边坡稳定性分析的流程来确定边坡的最小安全系数及临界滑移面。通过算例验证表明:该方法边坡稳定性分析结果与传统条分法极为接近,两者最小安全系数相对偏差不超过-5%,确定的临界滑移面基本一致。该方法可广泛适用各类多级均质黄土边坡乃至单级边坡,可对边坡稳定性分析达到全面精准的效果提供一定的参考。     

基于ABAQUS仿真分析的高填粗粒土路基边坡稳定性研究

高填方粘性土边坡的稳定性以往研究较多,为了研究变形特性与强度都不同于粘性土的高填方粗粒土边坡,运用ABAQUS软件,采用强度折减法对多级加筋粗粒土边坡工程做了有限元数值模拟,分析了整个边坡的稳定性.研究结果表明,加筋不仅提高了各个台阶的局部稳定性,也加强了边坡的整体稳定;边坡中都存在水平位移,最大值出现在边坡底部坡脚附近,在坡脚处出现小部分沿x轴正向的负位移;水平位移随着填土高度的增加而减小,第一台阶的水平位移最大;越靠近边坡,土工格栅和土体的位移均越大,变大的趋势近似一致,但土体的水平位移明显大于土工格栅的水平位移.     

露井联采逆倾边坡破坏模式及稳定性评价方法研究

首先分析了单一露天开采逆倾边坡的变形破坏模式、地下开采覆岩变形破坏机理和露井联采逆倾边坡的变形机理,在此基础上,对露井联采逆倾边坡的破坏模式及稳定性定量评价方法进行了研究。研究表明,露井联采逆倾边坡的破坏模式可分为3种类型：滑移型破坏、塌陷型破坏和滑移-塌陷复合型破坏,地下开采的空间位置对边坡的破坏模式及稳定性影响显著,其影响程度受进入塌陷范围内的边坡潜在滑面长度和岩体强度参数弱化程度的控制,据此提出了露井联采逆倾边坡稳定性的极限平衡法,并结合工程实例进行了数值模拟验证。     

多层软弱夹层边坡岩体破坏机制与稳定性研究

以大量的实际工程为基础,基于Sarma极限平衡法和有限元强度折减法探讨层状岩质边坡在不同岩层倾角θ、边坡坡角β、结构面间距h条件下的安全系数与破坏面位置的变化规律,揭示复杂多层软弱夹层边坡岩体的破坏机制及稳定性特征。结果表明：不同θ条件下边坡岩体失稳机制和破坏面位置不同,随着θ的增大,破坏机制表现为滑移破坏→滑劈破坏→崩塌破坏→倾倒破坏→滑移破坏;当β、h一定时,直立层状边坡的稳定性略大于水平层状边坡,反倾向边坡的稳定性明显大于顺层边坡;β直接影响边坡岩体破坏特征,当β由30°增大至60°时,顺层边坡的安全系数约降低53%;反倾向层状边坡的安全系数约降低40%;h对边坡岩体破坏机制的影响较小,但对稳定性的影响较大,建议工程实践中加强密集结构面岩质边坡的监测和加固工作。     

平台分级对加筋土边坡稳定性的影响研究

对于分级修建的边坡,如何选择合适的平台宽度还有待研究。利用离心模型试验和有限元强度折减法对加筋土边坡进行分析,探讨平台分级的影响。试验表明,设置平台可以使边坡分解成若干个次级边坡,边坡分级后,其整体破坏向各个次级边坡集中,失稳部分的规模有所减少;加筋增强了边坡的整体性,能够强化次级边坡之间的独立性;合适的宽度可以使滑动面只发生在次级边坡中,对整体安全是有利的。有限元计算表明,边坡高度较大时,土的黏聚力的作用就会削弱,通过将高大的边坡变成高度较小的次级边坡,能够充分发挥黏聚力对边坡稳定的作用。而加筋的主要效果就是给土体提供一个似黏聚力。也就是说,合适的边坡高度分级能够充分发挥筋材的加筋效果。另外,对加筋高边坡来说,筋材的模量和延伸率是更为关键的材料参数。延伸率不足,在其他筋材的强度还没有发挥时被拉断,就达不到共同承载的目的。     

基于数字图像处理的裂缝测量系统——以北京108国道宝水段公路监测为例

传统的人工裂缝测量方法具有耗时,耗力.危险、花费高等缺点,为改进传统监测方法,研发了基于数字图像处理的裂缝测量系统。该系统解算过程包括像素标定,图像分割.灰度转换、阈值分割、滤波除噪等,通过以上步骤提取出裂缝的相关数字特征,进而计算得到裂缝的最大宽度、最小宽度,平均宽度和长度。将该测量系统应用于108国道宝水段公路监测,结果表明该裂缝测量系统操作方便,测量结果精度较高,具有一定的创新意义和实用价值。     

前置掺气坎阶梯溢洪道近壁掺气特性

为更清楚地认识前置掺气坎阶梯溢洪道近壁面沿程掺气规律,对其掺气特性进行了研究,得到了在不同坡度、单宽流量、台阶体型条件下阶梯竖直面和水平面近壁处掺气浓度沿程分布规律,并与不设前置掺气坎但设置过渡阶梯溢洪道的掺气规律进行了对比分析。研究表明:前置掺气坎式阶梯溢洪道中阶梯水平面与竖直面掺气浓度沿程的分布规律相似,受前置掺气坎的帮助,掺气浓度很高,沿程逐渐减小,达到一定距离后趋于稳定;掺气浓度随单宽流量的增大而减小,随坡度的减缓而减小;前置掺气坎克服了过渡阶梯存在前几级的底部清水区的缺陷,能够用于更大单宽流量。     

Channel formation by flow stripping: large-scale scour features along the Monterey East Channel and their relation to sediment waves

The Monterey East system is formed by large‐scale sediment waves deposited as a result of flows stripped from the deeply incised Monterey fan valley (Monterey Channel) at the apex of the Shepard Meander. The system is dissected by a linear series of steps that take the form of scour‐shaped depressions ranging from 3·5 to 4·5 km in width, 3 to 6 km in length and from 80 to 200 m in depth. These giant scours are aligned downstream from a breech in the levee on the southern side of the Shepard Meander. The floor of the breech is only 150 m above the floor of the Monterey fan valley but more than 100 m below the levee crests resulting in significant flow stripping. Numerical modeling suggests that the steps in the Monterey East system were created by Froude‐supercritical turbidity currents stripped from the main flow in the Monterey channel itself. Froude‐supercritical flow over an erodible bed can be subject to an instability that gives rise to the formation of cyclic steps, i.e. trains of upstream‐migrating steps bounded upstream and downstream by hydraulic jumps in the flow above them. The flow that creates these steps may be net‐erosional or net‐depositional. In the former case it gives rise to trains of scours such as those in the Monterey East system, and in the latter case it gives rise to the familiar trains of upstream‐migrating sediment waves commonly seen on submarine levees. The Monterey East system provides a unique opportunity to introduce the concept of cyclic steps in the submarine environment to study processes that might result in channel initiation on modern submarine fans.     

The replacement of anthophyllite by jimthompsonite: a model for hydration reactions in biopyriboles

Anthophyllite crystals found in ultramafic lenses of the Lepontine Alps (Switzerland) contain coherent, submicroscopic intergrowths of ordered and disordered biopyribole polysomes. The chain width distributions of disordered polysomes were analyzed using high resolution transmission electron microscopy (HRTEM). Chains wider than triple were interpreted as intermediate products in the transformation of anthophyllite to the triple chain silicate jimthompsonite. The concentration of individual chain types is strongly correlated with the reaction progress. Based on observed zipper terminations and the transformation rules given by Veblen and Buseck (1980) a scheme of possible reaction paths leading from anthophyllite to jimthomp sonite is proposed. The reaction scheme and a simple kinetic model for elementary reactions allow modeling of the observed chain width distributions. The model suggests that the complex reaction paths involving steps with increasing and decreasing chain width are more important in the formation of jimthompsonite than the direct transformation from anthophyllite. The wide chains (>triple) occurring as intermediate products of the multi-step paths are structurally closer to talc than jimthompsonite. The back-transformation of these wide chains to triple chains is, therefore, a strong argument that jimthompsonite is a stable phase and not only a metastable intermediate product in the transformation of anthophyllite to talc. Received: 8 July 1996 / Accepted: 13 December 1996     

储层建模中几种原型模型的建立

储层地质知识库的建立是储层建模过程中极为重要的一步，它为建模提供基本的条件数据及各种统计参数。本文总结了建立地质知识库的主要步骤及基本内容。在资料较少的情况下，需要借助原型模型来提供一些无法直接获得但对建模十分重要的参数，如砂体宽厚比、水平方向变差函数等。文中用3个实例较详细的介绍了建立原型模型的3种主要方法，分别是利用露头、成熟油田和沉积模拟实验建立原型模型，并比较了各自的优缺点。     

Dissolution kinetics of calcite at 50-70 °C: An atomic force microscopic study under near-equilibrium conditions

Direct measurements of calcite faces were performed using in situ atomic force microscopy (AFM) to reveal the dissolution processes as a function of solution saturation state and temperature. Time-sequential AFM images demonstrated that step velocities at constant temperature increased with increasing undersaturation. The anisotropy of obtuse and acute step velocities appeared to become more significant as solutions approached equilibrium and temperature increased. At saturation state Ω > 0.02, a curvilinear boundary was formed at the intersection of two acute steps and the initially rhombohedral etch pit exhibited a nearly triangular shape. This suggests that the and steps may not belong to the calcite-aqueous solution equilibrium system. Further increase in the saturation state (Ω ? 0.3) led to a lack of etch pit formation and dissolution primarily occurred at existing steps, in accordance with Teng (2004). Analysis of step kinetics at different temperatures yielded activation energies of 25 ± 6 kJ/mol and 14 ± 13 kJ/mol for obtuse and acute steps, respectively. The inconsistencies in etch pit morphology, step anisotropy, and step activation energies from the present study with those of studies far-from-equilibrium can be explained by increased influence of the backward reaction, or growth, near-equilibrium. We propose that the backward reaction occurs preferentially at the acute-acute kink sites. The kinetics and effective activation energies of near-equilibrium calcite dissolution presented in this work provide accurate experimental data under likely CO₂ sequestration conditions, and thus are crucial to the development of robust geochemical models that predict the long-term performance of mineral-trapped CO₂.     

2D finite-element elastic models of transtensional pull-apart basins

A set of two-dimensional finite-element elastic models are presented to provide insights on the evolution of transtensional pull-apart basins between two right-stepping, right-lateral fault segments. Three representative fault segment interaction geometries are modelled, showing underlapping, neutral and overlapping segments. Despite the simplifications of the 2D model, overall results are obtained that might help understanding the formation of pull-apart basins. Firstly, the orientations of the local σ₁ and σ₃ tensional stress directions markedly depend on the segment's position. Secondly, the mean normal stress is extensional in a transtensional basin between segments, while the region outside the step is characterized by more compressive mean normal stresses. Thirdly, the angle of offset between the fault segments is one of the most important parameters controlling the geometries of the transtensional pull-apart basins: connected depocenters with basin high and lozenge shape in the case of underlapping steps, spindle shape or lazy S or Z shape in the case of neutral steps, and broadly elongate rhomboidal to sigmoidal basins in the case of overlapping steps. Generally, en-échelon basin margin system, dual opposing asymmetric depocenter, intrabasin relative structural high, and wide basin width can be used as indicators that a pull-apart basin is developing in transtension zones.     

Structural Attributes of Travertine-Filled Extensional Fissures in the Pamukkale Plateau,Western Turkey

Numerous active and inactive fissure-ridge travertines are located in the hanging wall of the Pamukkale range-front fault, a large normal fault bounding the northeast side of the Denizli Basin. A typical principal fissure-ridge comprises flanking bedded travertines dipping gently away from a nearly vertical, irregular central fissure, partially filled by vertically banded travertine. More complex ridges bear parasitic fissures and associated ridges on their flanks. Fissures roughly follow the long axes of ridge crests, some of them being divided into angular segments and others anastomosing. The traces of fissures are commonly parallel but some are oblique to one another. Fissures vary in width from a few millimeters to 5 m, and range in length from a few meters to a few kilometers.

The widths of central fissures are at a maximum near the midpoints of ridges, but decrease toward both ends, suggesting that they grew in length over time. Lateral fissure development involved the opening of both new and old cracks, some of which propagated into former process zones at crack tips. Fissures increase in width with depth either gradually or in a series of steps, depending on whether there was a uniform rate of fissure dilation during travertine deposition or episodic dilation during fracture propagation. The characteristic irregular morphology of fractures probably reflects extension-fracture propagation in differential stress fields that were weak as a consequence of location near the earth's surface. The fissures probably express a set of subsidiary extension fractures splaying from the Pamukkale range-front fault into its hanging wall.