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91.
The strength of frozen soils has been one of the most extensively studied aspects in frozen soil mechanics. When carrying
out deep excavations using freezing methods, high stress states are often encountered. Therefore, the strength of frozen soils
under high confining pressures is of major concern. This paper first reviews the present failure criteria for frozen soils,
especially with regard to the effect of confining pressure on the strength. It is suggested that the strength consists of
two components, cohesion and friction, and can be expressed by the Mohr–Coulomb criterion and in the framework of the Drucker–Prager
criterion. However, these two components are both dependent on the stress state. Duncan’s equation for the friction angle
is extended to frozen soils. A frozen Lanzhou fine sand is taken as study subject. The frozen sand is compressed at a high
strain rate under three different temperatures and under a wide range of confining pressure. Experimental results have confirmed
the generally recognized principle that the strength increases with the confining pressure up to certain value. Thereafter,
it decreases with continued increase in confining pressure. Experimental data from our own tests and literature are fitted
to the new criterion, which shows its validity. 相似文献
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93.
Bihong Fu Xinglin Lei Khaled Hessami Yoshiki Ninomiya Takashi Azuma Hisao Kondo 《Journal of Geodynamics》2007,44(3-5):160-172
The December 26, 2003 Mw 6.6 Bam earthquake is one of the most disastrous earthquakes in Iran. QuickBird panchromatic and multispectral satellite imagery with 61 cm and 2.4 m ground resolution, respectively provide new insights into the surface rupturing process associated with this earthquake. The results indicate that this earthquake produced a 2–5 km-wide surface rupture zone with a complex geometric pattern. A 10-km-long surface rupture zone developed along the pre-existing Bam fault trace. Two additional surface rupture zones, each 2–5 km long, are oblique to the pre-existing Bam fault in angles of 20–35°. An analysis of geometric and geomorphic features also shows that movement on the Bam fault is mainly right-lateral motion with some compressional component. This interpretation is consistent with field investigations, analysis of aftershocks as well as teleseismic inversion. Therefore, we suggest that the 2003 Bam earthquake occurred on the Bam fault, and that the surface ruptures oblique to the Bam fault are caused by secondary faulting such as synthetic shears (Reidel shears). Our fault model for the Bam earthquake provides a new tectonic scenario for explaining complex surface deformations associated with the Bam earthquake. 相似文献
94.
HE Keqiang Department of Civil Engineering Qingdao Institute of Architecture & Engineering Qingdao Shandong ChinaLIU ChangliInstitute of Hydrogeology Engineering Geology Chinese Academy of Geological Sciences Zhengding Hebei Chinaand WANG Sijing Institute of Geology Chinese Academy of Sciences Beijing China 《《地质学报》英文版》2001,75(3):330-335
Karst collapse, caused by natural or artificial abstraction of groundwater, has been a focus of environmentalgeological problems for its ever-increasing hazardousness. The potential erosion theory and vacuum suction erosion theory, which reveal the origin of karst collapse macroscopically, are popularly accepted. However, a mathematic prediction criterion for karst collapse cannot be established only by these two theories. From a new perspective, this paper attempts to explain the microcosmic mechanism of karst collapse on the basis of these two theories. When the shear stress surpasses the shear strength of soil, a certain point or a certain plane in the unconsolidated soil covering karst caves will fail under the mechanical effects of water and air as well as its load-pressure, and with the increase of damaged points, a breaking plane appears and the soil on karst caves is completely damaged; as a result, the karst ground collapses. On the basis of the Mohr-Coulomb failure theory and previous studies, 相似文献
95.
简要介绍了近年来一些国家地震灾害造成的经济损失占这些国家国内生产总值的比例;主要介绍了多震地区开展地震断层探测研究的概况以断层活动为基础的地震保险试验的内容及研究进展。 相似文献
96.
Fault-controlled dolomitization at Swan Hills Simonette oil field (Devonian), deep basin west-central Alberta, Canada 总被引:6,自引:0,他引:6
The partly dolomitized Swan Hills Formation (Middle‐Upper Devonian) in the Simonette oil field of west‐central Alberta underwent a complex diagenetic history, which occurred in environments ranging from near surface to deep (>2500 m) burial. Five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post‐date stylolites in limestones (depths >500 m). These include early planar varieties and later saddle dolomites. Fluid inclusion data from saddle dolomite cements (Th=137–190 °C) suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data (Tpeak=160 °C). Thus, at least some dolomitizing fluids were ‘hydrothermal’. Fluorescence microscopy identified three populations of primary hydrocarbon‐bearing fluid inclusions and confirms that saddle dolomitization overlapped with Upper Cretaceous oil migration. The source of early dolomitizing fluids probably was Devonian or Mississippian seawater that was mixed with a more 87Sr‐rich fluid. Fabric‐destructive and fabric‐preserving dolostones are over 35 m thick in the Swan Hills buildup and basal platform adjacent to faults, thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults. This ‘plume‐like’ geometry suggests that early and late dolomitization events were fault controlled. Late diagenetic fluids were, in part, derived from the crystalline basement or Palaeozoic siliciclastic aquifers, based on 87Sr/86Sr values up to 0·7370 from saddle dolomite, calcite and sphalerite cements, and 206Pb/204Pb of 22·86 from galena samples. Flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m, both vertically along reactivated faults and laterally in the buildup along units that retained primary and/or secondary porosity. 相似文献
97.
The breakdown and foundation of geostrophic balance is one of the important movements inthe mid-and high-latitude atmosphere and oceans.In the tropical area,the value of Coriolis pa-rameter is so small that it is difficult to satisfy the bi-geostrophic equilibrium between the pressureand velocity fields.However,in the tropical area,the zonal velocity of some motions in the atmo-sphere and oceans is large,so the Coriolis force is not small,geostrophic balance can exist in zonaldirection,i.e.semi-geostrophic balance.Furthermore,in the dominant area of Hadley circulationin the atmosphere or the area near the ocean meridional boundary,the meridional velocity is large,so geostrophic balance can also exist in meridional direction.In this paper,the process of the dis-persion of inertial gravity wave and the foundation of semi-geostrophic balance are first discussed.Second,the adjustment process between the velocity and pressure fields after adaptation is alsoviewed,and the scale criterion of the semi-geostrophic adaptation is discussed,i.e.for the motionwith meridional scale greater than the equatorial Rossby radius of deformation,the velocity andpressure fields after adaptation change to fit the initial pressure field;on the contrary,the fieldschange to fit the initial zonal velocity field,and the strength of the fields after adaptation dependson the zonal scale. 相似文献
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