Fabric evolution within shear bands of granular materials and its relation to critical state theory

In an effort to study the relation of fabrics to the critical states of granular aggregates, the discrete element method (DEM) is used to investigate the evolution of fabrics of virtual granular materials consisting of 2D elongated particles. Specimens with a great variety of initial fabrics in terms of void ratios, preferred particle orientations, and intensities of fabric anisotropy were fabricated and tested with direct shear and biaxial compression tests. During loading of a typical specimen, deformation naturally localizes within shear bands while the remaining of the sample stops deforming. Thus, studying the evolution of fabric requires performing continuous local fabric measurements inside these bands, a suitable task for the proposed DEM methodology. It is found that a common ultimate/critical state is eventually reached by all specimens regardless of their initial states. The ultimate/critical state is characterized by a critical void ratio e which depends on the mean stress p, while the other critical state fabric variables related to particle orientations are largely independent of p. These findings confirm the uniqueness of the critical state line in the e ? p space, and show that the critical state itself is necessarily anisotropic. Additional findings include the following: (1) shear bands are highly heterogeneous and critical states exist only in a statistical sense; (2) critical states can only be reached at very large local shear deformations, which are not always obtained by biaxial compression tests (both physical and numerical); (3) the fabric evolution processes are very complex and highly dependent on the initial fabrics. Copyright © 2010 John Wiley & Sons, Ltd.     

亚洲季风年代际振荡及与天文因子的相关

主要通过滑动ｔ－检验方法和相关统计,分析了近５０年来南亚季风、东亚季风以及高原季风的相互关系,并对其与太阳黑子周期长度（ＳＣＬ）和地球自转速度（Δω）的关系进行了讨论。结果表明：三种亚洲季风虽然在年际变化上相关不好,但在年代变化上具有很好一致性;亚洲季风的年代际变化与ＳＣＬ和Δω均相关很好,其中以与Δω关系最好,且Δω的变化超前亚洲季风的变化。对日地因子的短期变化如何影响亚洲季风年代际振荡提出了初     

厄尔尼诺事件和拉尼娜事件的成因与预测

通过对南极气温资料、环南极海冰资料、臭氧变化资料、太平洋海温资料、地球自转速度变化资料、厄尔尼诺和拉尼娜资料的综合验证,发现了构造运动与厄尔尼诺因果关系。大气、海洋与岩石圈的角动量交换在南半球和北半球有不同的形式,这是由陆海分布的差异决定的。南极上空臭氧变化和环南极海冰变化是赤道海温和全球气候准两年振荡的原因。其中,德雷克海峡的海冰变化起主要作用。这个结论给出了作者提出的“海洋锅炉效应”、“臭氧洞漏能效应”、“德雷克海冰气候开关效应”和“大洋地壳跷跷板运动”的相互关系,证明构造运动对厄尔尼诺的重要影响。强潮汐准4a周期的发现,表明南极海冰变化、东太平洋海温变化、地球自转变化和厄尔尼诺都具有4a准周期变化的原因。海温和海冰开关的准2a周期和日食-厄尔尼诺系数理论有较好的预测效果。     

热幔柱的启动动力

科氏力是地球各圈层差异旋转的原因。在重力分异过程中，随着地球质量不断向地心集中，地球自转动能也不断向地核集中，从而产生圈层分化和差异旋转。     

横向载荷作用下刚性桩变位规律研究

目前对横向受载刚性桩的研究主要集中在其承载力方面,对变化规律研究很少。为此提出了利用刚性桩上两点位移求桩上任意一点位移、桩回转中心位置及转角的方法。通过对粉质黏土中的刚性桩进行模型试验与数值计算发现,回转中心位置随位移和载荷的增大,先是急剧下降,然后变缓,最后基本趋于稳定,而且桩埋置参数与土力学参数对回转中心位置的变化规律影响很小;而桩的转角随位移增大近似线性变化。比较发现,由试验和数值计算得到的回转中心极限位置与由极限地基反力法得到的结果相差不大     

Porphyroblast rotation during crenulation cleavage development: an example from the aureole of the Mooselookmeguntic pluton, Maine, USA

In the low‐pressure, high‐temperature metamorphic rocks of western Maine, USA, staurolite porphyroblasts grew at c. 400 Ma, very late during the regional orogenesis. These porphyroblasts, which preserve straight inclusion trails with small thin‐section‐scale variation in pitch, were subsequently involved in the strain and metamorphic aureole of the c. 370 Ma Mooselookmeguntic pluton. The aureole shows a progressive fabric intensity gradient from effectively zero emplacement‐related deformation at the outer edge of the aureole ～2900 m (map distance) from the pluton margin to the development of a pervasive emplacement‐related foliation adjacent to the pluton. The development of this pervasive foliation spanned all stages of crenulation cleavage development, which are preserved at different distances from the pluton. The spread of inclusion‐trail pitches in the staurolite porphyroblasts, as measured in two‐dimensional (2‐D) thin sections, increases nonlinearly from ～16° to 75° with increasing strain in the aureole. These data provide clear evidence for rotation of the staurolite porphyroblasts relative to one another and to the developing crenulation cleavage. The data spread is qualitatively modelled for both pure and simple shear, and both solutions match the data reasonably well. The spread of inclusion‐trail orientations (40–75°) in the moderately to highly strained rocks is similar to the spread reported in several previous studies. We consider it likely that the sample‐scale spread in these previous studies is also the result of porphyroblast rotation relative to one another. However, the average inclusion‐trail orientation for a single sample may, in at least some instances, reflect the original orientation of the overgrown foliation.     

重塑黏土空心圆柱试样制备技术改进及应用

受大体积制样降低土体均衡性及取芯扰动试样的影响,目前在包括主应力轴旋转等复杂应力路径下所开展的重塑软黏土力学特性试验研究的可靠性有待进一步提高。基于真空预压技术设计了制备重塑样的新型装置及方法,具有渗透排水与内壁成型双重作用的竖向排水体、分级施加真空负压以及多个试样同时制作等部件和技术,可快速制备大量空心圆柱试样,所制试样含水率具有较好的均匀性和一致性,减小了后期取芯对试样造成的扰动。开展了主应力轴旋转路径下的相关验证试验,从土体力学性能方面证明了所制试样用于研究复杂应力路径条件下土体性态演变规律的可靠性,为系统研究软黏土静动力学特性与长期稳定性提供了前提。     

小波变换应用于日长变化的研究进展

随着空间测地技术的发展,日长变化的观测资料已经达到了空前高的程度,迫切需要合适的数学工具和方法从这些高精度的观测资料中提取有价值的信息.近些年,小波变换被应用于天文学和地球科学的资料分析中,它通过伸缩和平移等运算对时间信号进行多尺度的细化分析,从中提取有效的信息.本文主要介绍了小波变换应用于日长变化的研究进展,并初步探讨该领域以后的研究方向.     

旋转椭球面上的应变与转动张量表达

以旋转椭球体面上某点为原点建立一个大地坐标单位活动坐标架. 通过平移, 使活动坐标架的原点与以椭球中心为原点的笛卡尔单位标架的原点相重合. 然后再通过两次标架旋转, 使活动坐标架与笛卡尔单位标架完全重合. 本文给出了使两个单位标架相重合的转换关系式, 以及该点位移在两个单位标架中的坐标转换式; 在此基础上, 考虑该点的位移及活动坐标架皆为该点大地坐标的函数, 经复杂推导, 分别给出了该点位移向量的微分在大地坐标系中的分量以及该点分别沿坐标曲线的弧微分表达式, 继而导出了该点的位移梯度矩阵; 最后推导出了椭球坐标系的应变张量与转动张量表达式, 并对转动张量的几何含义进行了较详细的解释, 且采用曲面理论对球面与椭球面的应变张量间的内在关系进行了讨论.