Three-dimensional structure of inclined sheet swarms: Implications for crustal thickening and subsidence in the volcanic rift zones of Iceland

Inward-dipping (cone) sheet swarms and an associated central volcano are well-exposed in the deeply-eroded Tertiary crust of Vatnsdalur, Skagi Peninsula region, northern Iceland. Spatially registered orientations of 389 mafic sheets, mapped in three distinct sheet swarms define both the overall shape and magmatic source of each swarm. The Vatnsdalur sheet swarms consist of planar inward-dipping sheets that collectively define a conical shape rather than a bowl- or trumpet-shape as have been found in swarms in other locations. In the best exposed swarm, three-dimensional projection of mafic sheets into the subsurface defines two distinct foci, which are interpreted as the magmatic sources of two temporally distinct sub-swarms. These results help to establish the influence of inclined sheet intrusion on crustal accretion at central volcanoes. The geometry of the swarm constrains the thickness of material that was added to the crust during sheet intrusion. When combined with estimates of surface relief, we calculate that 2.2 to 4.1 km of subsidence were required beneath the central volcano in order to accommodate the intrusion of the sheet swarm. Similar processes of crustal thickening and subsidence likely occur in a wide variety of both continental rift and mid-ocean ridge systems where magmatic activity is focused at central volcanoes.     

粉细砂的室内无填料振冲试验研究

在室内严格控制的边界条件下,通过室内模型试验研究了粉细砂无填料在振冲中孔隙水压力增长与消散的规律、孔隙水压力空间分布规律、相对密度和静力触探指标与振冲次数之间的关系等。定性地验证了无填料振冲对于规范中未推荐使用的粉细砂土的适应性,并为后来某工程大面积地基处理成功地提供了参考。     

地基承载力经验公式的变异性分析

应用随机场理论,研究了地基承载力表、CPT等地基承载力经验公式的变异性分析方法,提出经验公式确定地基承载力的变异性是由经验公式本身的不确定性和土性参数的不确定性组成,提出了考虑土性参数自相关性的地基承载力经验公式的变异性分析方法,通过对编制CPT确定地基承载力经验公式资料的计算分析,得出CPT确定地基承载力的变异系数在0.1~0.135之间。     

Dimensionless and unbiased CPT interpretation in sand

The cone penetration test (CPT) is widely used, and although initially developed as a stratigraphic logging tool its excellent repeatability and accuracy offers a benchmark quantitative test for sand in particular. A continuing difficulty, however, is that the CPT does not measure any soil property directly, so that parameters of interest must be recovered from solution of an inverse boundary value problem, which is difficult. To date most CPT interpretations in sand have been based on very limited calibration testing carried out in large chambers on a few sands from which mappings are developed. But there are differences in the CPT response from one sand to another leaving the interpretation imprecise (and arguably even speculative) because these differences remain poorly understood. In this paper we use the familiar spherical cavity expansion analogy to the CPT including large strains and a good, critical-state-based, soil model to develop a pattern of behaviour which we then compare to some of the reference chamber test data. We find that one of the issues of dispute in the empirical interpretation methods, the so-called stress-level effect, is caused by neglect of elasticity and that there are several additional parameters of first-order significance to cavity expansion in sands. More generally, we show that the difference in CPT response between various chamber sands in predicted. Our results are cast in dimensionless form and the inversion illustrates that extreme care is required in interpreting CPT data if the in situ sand state is to be determined with precision approaching that suggested as achievable by the repeatability of the CPT data itself. Aspects requiring particular care in interpreting CPT data in sand are discussed. © 1998 John Wiley & Sons, Ltd.     

地下水降落漏斗分类研究

地下水降落漏斗是抽水井开采地下水必然产生的物理现象,在其不同的发展阶段与不同的工程地质和水文地质条件结合,会产生截然不同的环境地质问题或是地质灾害.从地下水降落漏斗发生、发展及产生的地质灾害可能性分析出发,按照形成时间、开采井数量、危害程度和发展趋势对地下水降落漏斗进行了分类,旨在帮助人们加深对地下水降落漏斗本质的认识和理解,有助于对地下水资源的科学管理.     

基于二阶锥规划有限元增量加载法的条形浅基础极限承载力分析

地基极限承载力分析是土力学研究中的一个经典课题。基于Hellinger-Reissner混合变分原理和有限元方法,将岩土体弹塑性问题构造成基于有限元框架的二阶锥规划（second-order cone programming,SOCP）问题,进而提出一种基于二阶锥规划理论的增量有限元法,即FEM-SOCP法。将岩土体弹塑性问题构造成二阶锥规划的数学优化问题,可以避免采用传统弹塑性计算中复杂的应力点积分等算法和屈服面棱角的平滑处理。此外,对于二阶锥规划问题,可以采用具有原始?对偶内点求解法的标准数学规划求解器MOSEK进行求解。将增量加载FEM-SOCP法应用于经典的基底粗糙的条形浅基础地基极限承载力分析中,分别考虑了关联和非关联塑性条件下的Mohr-Coulomb屈服准则。数值结果表明：所提出的增量加载FEM-SOCP法获得的地基承载力系数及地基承载力与传统FEM计算结果基本一致,而与常规有限元计算结果相比,基于增量加载的FEM-SOCP法所获得的屈服区更加平滑。     

一种静力触探模型箱试验装置的研制及其试验研究

设计了一套静力触探模型箱试验装置,该装置可以在模型箱水平面内任意位置进行贯入试验,贯入速率在一定范围可控,贯入倾角可调节。将该装置用于TJ-1模拟月壤静力触探力学特性的研究,试验结果表明：地基表层模拟月壤发生刺入剪切破坏;贯入阻力随贯入深度的增加而增加;探杆周围同一深度处土体的水平土压力表现出轴对称特征,其值在探头靠近土压力盒过程中逐渐增大至最大值,后随探头远离土压力盒又逐渐减小至0,且不同深度土体水平土压力峰值随贯入深度增加而增大;贯入点正下方土体的垂直土压力随贯入深度的增加而增加,主要影响范围约为距探头200 mm处。基于以上试验研究,表明该模型箱的设计是合理的,且TJ-1模拟月壤力学特性的研究成果能够为将来涉及到TJ-1模拟月壤的航天试验提供必要的技术参考。     

基于孔压静力触探确定土体的渗透系数

近年来许多研究者致力于通过孔压静力触探(CPTU)确定土体的渗透系数,但是存在偏差大,而且不能从机制上清楚地解释孔压静力触探确定土体渗透系数的原因。为了应用孔压静力触探现场快速地确定土体的渗透系数,在总结前人对孔压静力触探确定土体渗透系数方法的研究基础上,提出孔压静力触探时锥头处呈球冠形孔隙水流动的计算模型,假定锥头处初始超孔隙水压力为负指数型分布,推导出土体渗透系数的表达式,并且结合现场实测数据,将所提出的方法与已有的方法进行对比分析。研究发现：所提出的方法扩大了现有方法的应用范围;渗透系数计算结果受锥头角度的影响较大,随着锥头角度的增大而增大;针对国际上通用的60°角的标准锥头,所提出的方法计算的渗透系数大于前人的方法,而且更接近室内外试验结果。     

新疆阿什库勒火山群野外地质科学考察

2011年5月4日至5月30日,由中国地震局地质研究所和新疆维吾尔自治区地震局组成的科考队,完成了2010年度地震行业专项“新疆于田7.3级地震与阿什库勒火山综合科学考察”的野外综合科学考察。火山地质组通过对阿什库勒火山群的野外地质、地貌实地考察,初步查明了阿什库勒盆地新生代火山类型、数量、结构参数和火山活动历史,并且对该地区存在的一些有争议的问题, 如阿什火山1951年5月27日喷发事件的报道、大黑山火山的喷发方式、高台山火山的存在与否等问题提供了野外证据。