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381.
Summary A two dimensional finite element procedure is applied to simulate a coal mining excavation sequence. A procedure with linear solution steps is developed and applied to an idealized mountain cross-section with exceptionally thick coal seams and large dip angle. The results provide information on pillar pressure, floor and roof stability, displacement characteristics and surface subsidence.The results presented here were obtained in the course of research sponsored by the Department of Energy, Mines and Resources, Grant No. 69-2570. 相似文献
382.
斯匹次卑尔根岛是斯瓦尔巴特群岛中最大的岛屿,具有较全的地质时代记录、反映多次构造运动的构造现象。本文从构造组合的观点,对斯匹次卑尔根岛的构造划分为东西向、南北向、北北西向三组方向,它们反映了本区自元古代以来至少经历了三次不同方向的构造应力场作用。 相似文献
383.
The main characteristics of river flow and grainsize in a bend of the sand bedded meandering river Dommel, The Netherlands, are presented. Measurements were carried out at a relatively low discharge in a sharply curved bend following a long straight reach. In the studied bend, secondary circulation is restricted to the thalweg area; only in the downstream part of the bend it exists over the entire cross-section. Therefore, on the entire pointbar platform, which comprises the larger part of the bend, the median sedimentation diameter of the bedload material is governed by the distribution of the longitudinal components of the bed shear stress only. 相似文献
384.
385.
童家院锑矿床广泛发育地下空洞,影响矿山开采。本文根据矿田构造和矿化特征研究,认为本区至少经受过两期构造应力作用。成矿前,在左旋水平扭动作用下,形成NE向锡矿山复式背斜、纵向逆断层和矿化空洞,成矿后,在NE向挤压应力下,产生了NW向叠加褶皱以及正断层。同时,该应力场所控制的层间破碎带和背斜,大大影响了地下空洞的成生和分布。 相似文献
386.
大同盆地现今构造活动及地壳应力场特征 总被引:5,自引:1,他引:5
大量震源机制结果推断出大同分轩现代地壳应力场和主压应力方向为NE-NEE,仰角变化不定,主张应力方向为NW-NNW,仰角很小的结论。这与区域构造应力场NE-NEE向挤压作用的结果相符,另据大同一阳高6.1级、5.8级地震的震源机制结果得出,大同一阳高地震的孕震应力场与华北区域应力场相一致,而不是受本地局部小区域应力场的控制的结论。 相似文献
387.
Rifting dynamics at spreading axes is governed by two processes: the large-scale plate divergence and the local magma accumulation in the crust-mantle transition layer. Both evolve simultaneously. A model is developed particularly for the situation in Iceland where a well studied rifting episode occurred in the Krafla volcanic system 1975–1984. Both the divergence and the buoyant rise of magma create tensile deviatoric stress in the axial region, but while divergence generates an altogether extensional stress field, uprising of buoyant melt produces tension only near the axis but compression of the sides. The buoyant rise is driven by the differential pressure gradient in rock and melt. The processes are studied with a two-dimensional finite-element routine. Presently thermal effects are neglected. The model parameters are density difference, size of the buoyant body, externally applied stress field, mechanical properties of rock and melt. Relatively small amounts of divergence and small increases of buoyancy are shown to generate axial tension which can overcome the tensile strength. Axial tension produced by buoyant bodies can even overcome lateral compression. Observed long intervals of quiescence require either large rock strength, quasi-continuous stress relaxation, small buoyant bodies, and/or a compressive deviatoric stress normal to the axis during much of the time between rifting episodes. Buoyant rise and injection of melt must be important in generating compression. 相似文献
388.
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390.
A steady state model of the Somali current including forcing by both the curl and the divergence of the wind stress is discussed.
The model equations are linear, but the results presented are for the one nonlinear case. The grid resolution was 12 km in
the zonal and 24 km in the meridional direction. The streamfunction and velocity potential of the current are presented for
forcing by divergence and compared with a situation when only the curl is present. The results indicate that a two-gyre system
appears in July, a representative month for the summer monsoon, only when divergence is included. Computations with available
data indicate that the divergence is comparable in magnitude to the curl near the location of the Somali current. The model
produces three other important features: (i) strong upwelling off the east coast of Africa, (ii) downwelling over central
Arabian sea and (iii) a strong eastward current in the upper layer towards the interior of the Arabian sea near 12°N. 相似文献