The emplacement of intermediate volume ignimbrites: A case study from Roccamonfina Volcano,Southern Italy     

P. D. Cole  J. E. Guest  A. M. Duncan 《Bulletin of Volcanology》1993,55(7):467-480

A model is presented for the emplacement of intermediate volume ignimbrites based on a study of two 6 km³ volume ignimbrites on Roccamonfina Volcano, Italy. The model considers that the flows were slow moving, and quickly deflated from turbulent to non-turbulent conditions. Yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows. In proximal locations, on the caldera rim, heterogeneous exposures including discontinuous lithic breccias, stratified and cross-stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows. In medial locations thick, massive ignimbrite occurs associated with three types of co-ignimbrite lithic breccia which we interpret as being emplaced by non-turbulent flows. Multiple grading of different breccia/lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower-moving front part. This overriding of different parts of non-turbulent pyroclastic flows could be caused by at least two different mechanisms: (1) changes in flow regime, such as hydraulic jumps that may occur at breaks in slope; and (2) periods of increased discharge rate, possibly associated with caldera collapse, producing fresh pulses of lithic-rich material that sheared onto the slower-moving part of the flow in front.We propose that ground surge deposits enriched in pumice compared with their associated ignimbrite probably formed by a flow separation mechanism from the top and front of the pyroclastic flow. These turbulent clouds moved ahead of the non-turbulent lower part of the flow to form stratified pumice-rich deposits. In distal regions well-developed coarse, often clast-supported, pumice concentrations zones and coarse intra-flow-unit lithic concentrations occur within the massive ignimbrite. We suggest that the flows were non-turbulent, possessed a relatively high yield strength and may have moved by plug flow prior to emplacement.  相似文献   

顶管施工中顶力与顶程关系及其影响因素分析     

向安田丁文其  朱合华 《探矿工程》2006,33(10):29-31,34

以上海某长距离急曲线顶管工程为例，通过现场实测4节管段顶进过程中的顶力，研究了顶力随顶程的变化规律，系统分析了顶进过程中顶力的主要影响因素，得到了一些有用的结论。  相似文献   

Effect of a submerged bay-mouth breakwater on tsunami behavior analyzed by 2D/3D hybrid model simulation     

Koji Fujima 《Natural Hazards》2006,39(2):179-193

The hybrid numerical model had been developed to simulate a complicated 3D flow around structures generated by tsunami. In the model, the conventional 2D model is adopted for the wide region far from structures and the 3D non-hydrostatic pressure model is used in the limited region adjacent to structures. The applicability of the model is shown by comparisons of the numerical results with the experimental results of the laboratory model tests and the numerical analysis results of the conventional whole 2D simulation. In addition, the effect of a submerged structure at the opening of a breakwater is discussed from the numerical simulations by the hybrid model. The submerged structure improves the stability of the rubble mound and reduces the tsunami inflow into the bay, while it increases the water surface velocity around the opening of the breakwater. The increase of surface velocity causes the increases of impulsive forces by collision with drafts and so on.  相似文献   

企业内部会计控制弱化及其对策     

宋建新 《中国煤田地质》2005,17(3):68-70

列举了企业内邵会计控制存在的内部会计系统控制机制不健全，监督、考核机制乏力，财务控制存在漏洞、公司企业治理结构不完善等目前企业内部会计控制现状及重点存在问题。提出了完善企业的内部会计控制环境．不相容职务必须分离，强化监督，督促实施，加强会计基础工作，完善会计电算化管理，规范业务处理程序等具体改进建议。  相似文献   

三峡库区滑坡治理工程设计中推力荷载计算方法初探     

潘伟  赵欣  谭建民 《地质灾害与环境保护》2002,13(4):70-72

随着三峡水利工程的逐步实施，淹没区移民及新城镇建设等人类工程活动的加剧，以滑坡为主的环境地质问题日益突出。本文从稳定系数、安全系数入手，对铁道、公路等部门常用的设计计算原理进行了研究，并由此类比分析研究了三峡区回水后或库水位正常运行条件下，滑坡治理工程设计计算方法。  相似文献   

钉土相互作用的剪滞力理论分析   总被引：6，自引：2，他引：6  

贾洪 《工程地质学报》2002,10(2):156-159

在深基坝支护设计中 ,对钉土作用机理存在着许多模糊认识。为此 ,本文在一定假设条件下 ,建立了钉土相互作用的剪滞力模型 ;结合实例分析对模型进行了验证 ,并对钉土相互作用机理进行了分析.  相似文献   

多年冻土地区L型挡土墙土压力(冻胀力)的分析与试验   总被引：6，自引：0，他引：6  

梁波  王家东  严松宏  黄志军  杨泉 《冰川冻土》2002,24(5):628-633

为适应多年冻土区土体冻胀过程所产生的较大变形的特性, 缩短施工进程, 减少扰动时间, 在青藏铁路格拉段选择了一个试验工点进行了L型悬臂挡墙的初步验证性试验研究. 通过对L型挡墙的受力模式分析, 确定了对粗颗粒填料不考虑冻胀力的土压力设计控制值. 通过与现场实测土压力分布规律的对比, 探讨了土压力与冻胀力的关系.  相似文献   

农牧交错带典型区农业与牧业用地互动关系研究   总被引：13，自引：0，他引：13  

高清竹  何立环  江源  王家骥 《地球科学进展》2002,17(2):209-214

利用1989年和2000年的两期Landsat-TM数据和相关的统计资料以及气候数据，应用转移距阵和多元回归分析等研究方法，对地处典型农牧交错带地区的兴和县土地利用变化进行研究，结果表明：农田和草地是研究区域中最主要的土地利用类型，Landsat-TM卫星影像数据和统计数据比较一致地反映农田和草地面积的变化；农田和草地的相互转换率在各种用地相互转化中非常剧烈；农业与牧业用地的互动特征具有明显的区域差异；农业和牧业用地的互动特点是自然因素和社会经济因素同时影响的结果。  相似文献   

影响地下应力状态的构造作用   总被引：4，自引：0，他引：4  

刘瑞珣  吕古贤 《地球学报》2002,23(2):103-106

成岩成矿的外部条件中压力是很重要的因素。地下岩石所受的压力不仅来自上覆岩石的重力，而且来自构造力和热力及其它力。这些力合成一个三轴不等的应力状态，相当一个以最短轴为半径的球状应力迭加一个差应力。前者影响成岩成矿和变质作用，后者控制岩石变形和组构的变化。通过三维应变应力测量，这两部分力通过计算是可以区分开的，因而这将是建立地下深度测算新方法的一个基础。  相似文献   

可调滞回模型的磁流变阻尼器及其试验   总被引：5，自引：0，他引：5  

杨飓  关新春  欧进萍 《地震工程与工程振动》2002,22(2):115-120

本文在现在磁流变阴尼器性能研究的基础上，提出了可调滞回模型的磁流变阻尼器及其试验方法，并进行理论、试验及算例分析。首先，根据恒定电流下磁流变阻尼器的阻尼力滞力特性，利用磁流变材料特性的电流（即磁场）可控特点，建立了变电流下的阻尼力滞回模型；其次，在中通过电路板控制外加电流与装置变形间的函数关系，实现了变电流调节的阻尼力滞回模型；最后，将磁流变阻尼器与橡胶隔震装置结合，形成智能磁流变隔夺装置，并对一个单自由度隔震结构进行了数值仿真分析。  相似文献