核安全相关边坡与一般边坡挡土墙抗震稳定性验算对比分析     

陈立伟 《地质力学学报》2015,21(4):527-535

在挡土墙稳定性计算基本原理基础上, 引入《核电厂抗震设计规范》(GB 50267-97) 关于地震系数的规定, 重新建立了安全相关边坡挡土墙土压力和地震角计算公式, 并应用到实际工程中。对比分析显示, 挡土墙按核安全边坡和一般边坡进行抗震验算时, 地震系数、地震角的取值相差较大; 由于按核安全边坡计算时地震力远大于一般边坡, 因此稳定系数远小于一般边坡。   相似文献   

基于点稳定系数法的斜坡稳定性分析     

马建全  王念秦  张新社 《吉林大学学报(地球科学版)》2015,45(2):533-540

基于莫尔-库伦强度理论构架,界定了点稳定系数的概念,并推导其计算公式。利用Geostudio软件建立了均质斜坡模型及计算其应力分布,并在此基础上结合MATLAB软件计算斜坡模型中各点的点稳定系数,勾绘出斜坡体内不同稳定度区域,探析了斜坡稳定性,并与传统极限平衡法进行了对比。对比结果表明:对直立斜坡,两种方法的计算结果均为不稳定,但点稳定性系数法勾绘出坡脚及坡脚底部存在两处不稳定区域;对60°斜坡,点稳定系数法的计算结果表明坡脚处存在潜在不稳定区域,而极限平衡法的计算结果表明坡体处于稳定状态;对45°斜坡,两种方法的计算结果均为稳定,计算结果一致。进一步分析得到结论:点稳定系数法不需要假设或指定某一形状滑面进行斜坡稳定性评价,且可考虑应力集中对坡体稳定性的影响;极限平衡法以稳定系数表达计算结果,而点稳定系数法以不稳定区域表达计算结果。在分析了应力和岩土体力学参数因素对点稳定系数法计算结果的敏感性后发现:相对于极限平衡法,岩土体力学参数对点稳定系数法影响更为敏感,存在黏聚力界限点和内摩擦角界限点,且对均质斜坡破坏形式(局部滑动变形破坏或整体压缩变形破坏)起着非常重要的作用。  相似文献   

地震和煤矿采动耦合作用下露天矿边坡及采空区稳定性研究     

李海军  魏晓刚  孙琦  卫星  母倩雯 《地震研究》2015,38(1)

为了探讨地震和煤矿采动耦合作用下的露天矿边坡及采空区的稳定性,以辽宁排山楼金矿露天转井工开采为研究对象,基于FLAC3D有限元分析平台,采用强度折减法研究了未进行煤炭开采时和煤矿采动单独作用下露天矿边坡的安全系数,重点探讨了煤矿采动和地震耦合作用下露天矿边坡及采空区应力场、位移场及塑性区的分布规律。结果表明:未经采动时,露天矿边坡的安全系数为1.21,边坡处于稳定状态;煤矿采动后露天矿边坡安全系数降为1.12,仍处于稳定状态,单独的煤矿采动作用不会导致露天矿边坡失稳;在地震和煤矿采动耦合作用下,露天矿边坡坡体内出现了较大的拉应力,采空区顶板出现冒落现象,底板出现底鼓现象;在地震和采动耦合作用下,边坡将出现失稳破坏,破坏形式主要为采动区顶板的大面积冒落和边坡的崩塌。  相似文献   

含泥化夹层反倾岩质边坡动力响应的大型振动台试验   总被引：1，自引：0，他引：1       下载免费PDF全文

范刚  张建经  付晓 《地震工程学报》2015,37(2):422-427

针对含泥化夹层反倾岩质边坡制作相似比为1∶30的试验模型进行大型振动台试验,研究泥化夹层饱水前(天然含水状态)和饱水状态下边坡的加速度和位移响应规律,探讨边坡的破坏模式。试验结果表明:泥化夹层饱水后坡面水平向加速度放大系数小于饱水前;泥化夹层饱水前和饱水后随着相对高度的增加,坡面水平向加速度放大系数呈现非线性增加的趋势,其整体上大于坡体内部的加速度放大系数;坡面位移从下至上在泥化夹层饱水前,呈现出非线性增长特性;饱水后位移呈先增大后减小,临近坡肩处坡面最大,坡面呈现鼓出形态。泥化夹层饱水前,在幅值为0.3g的地震波作用下坡体仅出现坡肩局部掉块;饱水后,输入地震动幅值≥0.4g时,坡体先出现坡肩的局部掉块,随后坡体沿中上部的饱和泥化夹层滑动剪出,与此同时,坡体中上部出现纵向裂隙并与水平裂隙贯通,坡顶被震碎。  相似文献   

相对密实度对随机波与定次数波作用下土体变形关系的影响          下载免费PDF全文

孟凡超  袁晓铭  卢滔 《地震工程学报》2015,37(2):476-480

通过砂土的一系列动三轴实验,研究不规则地震荷载作用下与定次数等幅荷载作用下土体变形间的关系,给出砂土相对密实度对二者间关系的影响规律。结果表明:真实地震荷载下土的变形发展与等幅正弦荷载明显不同,应变发展时程的形态主要受地震动的形态控制;应变比C与砂土相对密度间关系具有规律性,随相对密度增大而降低,若采用以20周作为标准作用次数、0.65倍地震波峰值为等幅荷载代替不规则的地震荷载,修正真实地震应力下的残余变形,其应变比C随砂土密实度的增大而减小。同时,冲击型荷载的应变比C`要远大于振动型荷载。  相似文献   

汶川地区震后钢筋混凝土框架结构的地震易损性研究          下载免费PDF全文

郑山锁  马德龙  刘洪珠 《地震工程学报》2015,37(1):131-137

以汶川地震为研究背景,针对震后典型钢筋混凝土框架结构进行地震易损性研究。基于Cornell理论框架结合汶川地质资料,拟合出考虑场地特点的地震危险性模型,同时定义损伤水平状态及限值指标,以概率解析易损性研究方法为基础,运用考虑地震动参数的解析易损性评估方法绘制汶川地区钢筋混凝土框架建筑的地震易损性曲线。研究结果表明:考虑地震动参数的概率解析易损性研究方法是一种有效的地震易损性评估方法;以PGA作为地震强度输入指标的结构反应,随自振周期的增大体系最大响应的相关性降低,结构各个损伤状态的失效概率均随之增大。  相似文献   

一种启发式有环河系自动分级算法   总被引：2，自引：0，他引：2  

郝志伟  李成名  殷勇  武鹏达  吴伟 《测绘通报》2017,(10):68-73

在地图综合中,河流分级是对水系要素表达的重点也是技术难点,对精确性和计算速度都有较高的要求。目前对河系分级的研究中,已有分级算法的效率较低,且鲜有针对有环河系的分级。基于此,本文建立了河系分级的属性规则、几何规则、环规则,对河系中存在的不同环类型进行了分类处理,且在求取河流最长路径时,运用启发式算法迭代计算,实现了河系的自动分级。实际河系数据试验表明,该算法能在对有环河系的处理中取得良好的效果,提高了河系分级的计算效率和准确度。  相似文献   

Transition from storm wave‐dominated outer shelf to gullied upper slope: The mid‐Pliocene Orinoco shelf margin,South Trinidad          下载免费PDF全文

Yang Peng  Ronald J. Steel  Cornel Olariu 《Sedimentology》2017,64(6):1511-1539

Shelf‐edge deltas are a key depositional environment for accreting sediment onto shelf‐margin clinoforms. The Moruga Formation, part of the palaeo‐Orinoco shelf‐margin sedimentary prism of south‐east Trinidad, provides new insight into the incremental growth of a Pliocene, storm wave‐dominated shelf margin. Relatively little is known about the mechanisms of sand bypass from the shelf‐break area of margins, and in particular from storm wave‐dominated margins which are generally characterized by drifting of sand along strike until meeting a canyon or channel. The studied St. Hilaire Siltstone and Trinity Hill Sandstone succession is 260 m thick and demonstrates a continuous transition from gullied (with turbidites) uppermost slope upward to storm wave‐dominated delta front on the outermost shelf. The basal upper‐slope deposits are dominantly mass‐transport deposited blocks, as well as associated turbidites and debrites with common soft‐sediment‐deformed strata. The overlying uppermost slope succession exhibits a spectacular set of gullies, which are separated by abundant slump‐scar unconformities (tops of rotational slides), then filled with debris‐flow conglomerates and sandy turbidite beds with interbedded mudstones. The top of the study succession, on the outer‐shelf area, contains repeated upward‐coarsening, sandstone‐rich parasequences (2 to 15 m thick) with abundant hummocky and swaley cross‐stratification, clear evidence of storm‐swell and storm wave‐dominated conditions. The observations suggest reconstruction of the unstable shelf margin as follows: (i) the aggradational storm wave‐dominated, shelf‐edge delta front became unstable and collapsed down the slope; (ii) the excavated scars of the shelf margin became gullied, but gradually healed (aggraded) by repeated infilling by debris flows and turbidites, and then new gullying and further infilling; and (iii) a renewed storm wave‐dominated delta‐front prograded out across the healed outer shelf, re‐establishing the newly stabilized shelf margin. The Moruga Formation study, along with only a few others in the literature, confirms the sediment bypass ability of storm wave‐dominated reaches of shelf edges, despite river‐dominated deltas being, by far, the most efficient shelf‐edge regime for sediment bypass at the shelf break.  相似文献   

Response of unconfined turbidity current to normal‐fault topography          下载免费PDF全文

Zhiyuan Ge  Wojciech Nemec  Rob L. Gawthorpe  Ernst W.M. Hansen 《Sedimentology》2017,64(4):932-959

Turbidity currents descending the slopes of deep‐water extensional basins or passive continental margins commonly encounter normal‐fault escarpments, but such large‐magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory. This study uses advanced computational fluid dynamics numerical simulations to monitor the response of large, natural‐scale unconfined turbidity currents (100 m thick and 2000 m wide at the inlet gate) to normal‐fault topography with a maximum relief of nearly 300 m. For comparative purposes, the turbidity current is first released on a non‐faulted pristine slope of 1·5° (simulation model 1). The expanding and waxing flow bypasses the slope without recognizable deposition within the visibility limit of 8 vol.% sand grain packing. Similar flow is then released towards the tip (model 2) and towards the centre (model 3) of a normal‐fault escarpment. In both of these latter models, the sand carried by flow tends to be entrapped in four distinct depozones: an upslope near‐gate zone of flow abrupt expansion and self‐regulation; a flow‐transverse zone at the fault footwall edge; a flow‐transverse zone at the immediate hangingwall; and a similar transverse zone near the crest of the hangingwall counter‐slope, where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow. The near‐bottom reverse flow appears to be generated on a counter‐slope of 1·1°, increased to 2·0° by deposition. The Kelvin–Helmholtz interface instability plays an important role by causing three‐dimensional fluctuations in the flow velocity magnitude and sediment concentration. The thick deposits of large single‐surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows. The study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope‐fan conceptual models when it comes to the spatial prediction of main sand depozones.  相似文献   

Flow dynamics at the origin of thin clayey sand lacustrine turbidites: Examples from Lake Hazar,Turkey          下载免费PDF全文

Sophie Hage  Aurélia Hubert‐Ferrari  Laura Lamair  Ulaş Avşar  Meriam El Ouahabi  Maarten Van Daele  Frédéric Boulvain  Mohamed Ali Bahri  Alain Seret  Alain Plenevaux 《Sedimentology》2017,64(7):1929-1956

Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focused on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X‐ray, thin sections and CT scan imagery combined with grain‐size, geochemical and mineralogical measurements on the cores allow characterization of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence‐dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence‐dominated mechanism despite their high clay content. This divergence may in part relate to input variables, such as water chemistry and clay mineralogy, that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field‐scale basin made of a complex physiography that cannot be tackled by flume experiments.  相似文献