Stress‐dependent hardening and failure surfaces of dry sand

During several triaxial compression experiments on plastic hardening, softening, and failure properties of dense sand specimens, it was found on various stress paths that the size of the failure surface was not constant. Instead, it changed depending on the current state of hydrostatic pressure. This finding is in contrast to the standard opinion consisting of the fact that the failure surface remains constant, once it has been reached during an experiment or in situ. In general, the behaviour of cohesionless granular‐material‐like sand is somehow characterised in between fluid and solid, where the solid behaviour results from the angle of internal friction and the confining pressure. Although the friction angle is an intrinsic material property, the confining pressure varies with the boundary conditions, thus defining different solid properties like plastic hardening, softening, and also failure. Based on our findings, it was the goal of the present contribution to introduce an improved setting for the plastic strain hardening and softening behaviour including the newly found yield properties at the limit state. For the identification of the material parameters, a complete triaxial experimental analysis of the tested sand is given. The overall elasto‐plasticity concept is validated by numerical computations of several laboratory foundation‐ and slope‐failure experiments. The performance of the proposed approach is compared with the standard concept of a constant failure surface, where the corresponding yield surfaces are understood as contours of equivalent plastic work or plastic strain. Copyright © 2012 John Wiley & Sons, Ltd.     

Estimating the crush zone size under a cutting tool in coal

Summary As part of an effort to understand the mechanics of fine fragment formation in coal, which is important in studies of respirable dust due to mining, fracture toughness measurements and the strain energy density (SED) theory were applied to calculate the crush zone size under a cutting tool in coal. This zone is the major source of fine fragments in the 1 to 10 µm size range. The model used in these calculations is a boundary element program containing a failure criterion based on the SED theory. The boundary element program calculates linear elastic stresses at numerous points in the coal material ahead of a cutting bit. These stresses are then input to a subroutine called critical flaw length and orientation (CFLO) which uses the SED theory to determine the CFLO for a small crack at the boundary element stress computation point. The extent of crushing is based on earlier postulates about the role of inherent flaws in a fragmentation process. To form 1 to 10 µm fragments requires firstly a local stress strong enough to activate flaws with a characteristic length less than 1 to 10 µm and secondly, a flaw density sufficient to provide an average spacing between flaws also on the order of 1 to 10 µm. The locus of active 10 µm flaws represents the maximum possible extent of fine fragmentation in the 10 µm or less size range assuming that a sufficient inherent flaw density exists. The approach offers a first order approximation to the extent of crushing under a tool tip. The size and shape of the crush zone volume is affected by the attack angle and geometry of the tool.     

岩浆包裹体化学成分研究

岩浆包裹体化学成分研究难度较大,为了获得可信的数据,应当注意:1.非演化型岩浆包裹体的化学成分可以代表其初始成分。演化型岩浆包裹体应先均一、淬火后再行测定。2.均一演化型岩浆包裹体应严格遵守加热规则,否则过热作用会使包裹体壁部分熔化,造成淬火后所测包裹体成分与其真正的初始成分并不相当。3.实测资料证明,“边界层效应”对于岩浆包裹体化学成分影响微不足道。4.岩浆包裹体的化学成分只能代表其主矿物结晶时周围岩浆的成分,即仅相当于岩浆液相线上的一个点。5。把显微冷热台测温、激光喇曼探针和电子探针分析技术结合使用,对查明单个包裹体中挥发组分的性状和浓度具有很大的潜力和前途。     

边界单元法在电法勘探中的应用

本文用加权剩余法导出点源二维地电断面的边界单元法积分方程。通过付氏反变换,可获得三维空间的电位。若干模型上正演计算结果与解析解完全一致。对实测的ρ_s曲线进行了地形攻正及选择法反演拟合,解释结果与实际地质断面符合得很好。     

Active tectonics of the Himalaya

The Himalayan mountains are a product of the collision between India and Eurasia which began in the Eocene. In the early stage of continental collision the development of a suture zone between two colliding plates took place. The continued convergence is accommodated along the suture zone and in the back-arc region. Further convergence results in intracrustal megathrust within the leading edge of the advancing Indian plate. In the Himalaya this stage is characterized by the intense uplift of the High Himalaya, the development of the Tibetan Plateau and the breaking-up of the central and eastern Asian continent. Although numerous models for the evolution of the Himalaya have been proposed, the available geological and geophysical data are consistent with an underthrusting model in which the Indian continental lithosphere underthrusts beneath the Himalaya and southern Tibet. Reflection profiles across the entire Himalaya and Tibet are needed to prove the existence of such underthrusting. Geodetic surveys across the High Himalaya are needed to determine the present state of the MCT as well as the rate of uplift and shortening within the Himalaya. Paleoseismicity studies are necessary to resolve the temporal and spatial patterns of major earthquake faulting along the segmented Himalayan mountains.     

Relative sea-level fluctuations and brown coal formation around the Early-Middle Miocene boundary in the Lusatian Brown Coal District

The Tertiary sedimentary sequence in the Lusatian Brown Coal District is the result of several transgressive pulses with intercalated regressive phases. Regression repeatedly resulted in the formation of large littoral bogs at the transition between brackish and terrestrial palaeoenvironments. In the lithofacies changes of the Lower-Middle Miocene strata (high energy sands, low energy intertidal silts, paralic peats) long-term changes as well as short-term oscillations of sea level are recorded. The rise of sea level in the upper Lower Miocene (Hemmoorian transgression) is proved in numerous localities of the investigation area. After a regression phase with major peat formation events around the Lower-Middle Miocene boundary, a renewed sea-level rise resulted in the widest extension of marine-brackish beds over pre-Tertiary basement in the south of the region (higher Reinbekian transgression, Middle Miocene). Very differentiated, fine-scaled, probably sea-level induced coastline oscillations could probably be traced even into the coal seams by the recognition of successive bogfacial types possibly showing a groundwater level change in the ancient peat bog (change of topogeneous and ombrogeneous bog types). A biostratigraphic calibration of the decalcified Lower-Middle Miocene sequence with its alternating transgressive and regressive trends to the fully marine sediments of the basinal centre, which are dated by calcareous microfossils, is possible by means of dinoflagellate cysts and pollen and spores. Correspondence to: C. Strauss     

贵州长顺代化石炭系中间界线的沉积相研究

在碳酸盐微相的详细研究基础上，贵州长顺代化下、上石炭统剖面由下至上可分出５个主要沉积相：盆地相、开阔海陆架相、下斜坡相、中斜坡相和上斜坡相，下、上石炭统界线处于连续沉积的中斜坡相内。     

Age Assignment of the Lycoptera- bearing Bed

In the Yanliao area, the occurrence of the Nestoria-Keratestheria fauna and the Eoparacypris- Luanpingella-Darwinula assemblage in the Dabeigou Formation s.s., a Rb-Sr isochron age of 145.2 Ma for the Baiqi Formation and a complete stratigraphic sequence-all this proves that the Lycoptera-bearing bed overlies the Upper Jurassic. The Jehol fauna comprises the primitive Trigonioidids fauna, Eosestheria fauna, Lycoptera fauna et al., and their own laws of evolution expound that they belong to Cretaceous faunas. The associations of Eosestheria with Yanjiestheria, Lycoptera with Eosestheria, and Kuntulunia with Yanjiestheria as well as the occurrence of early angiosperms and sporo - pollen in the Fuxin Formation and its equivalents also demonstrate that the Lycoptera-bearing, bed should be assigned to the Cretaceous. The confirmation of the existence of Aucellina in the Jixi Group and the correlation of Trigonioidids and Cypridids with those in the equivalent strata of Japan and Western Europe have also been     

Dynamic faulting under rate-dependent friction

We discuss the effects of rate-dependent friction on the propagation of seismic rupture on active faults. Several physicists using Burridge and Knopoff's box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self-similar stress distribution on the fault plane. If this model proves to be correct, it has important consequences for the origin of the complexity of seismic sources. In order to test these ideas on a more realistic earthquake model, we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate-dependent friction. We study rupture dynamics of models with single and twin asperities. In our models, asperities are places on the fault with a higher value of prestress. Othewise all fault parameters are homogeneous. We show that for models with such asperities, a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough. For models with asperities, we can also observe narrow slip velocity pulses, qualitatively similar to the so-called Heaton pulses observed in some earthquake accelerograms. We also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law.