Crack propagation trajectories for rocks under mixed mode I-II fracture   总被引：4，自引：0，他引：4  

Naser A. Al-Shayea 《Engineering Geology》2005,81(1):84-97

Propagation of a crack in engineering materials including rocks can cause failure. Knowledge of the stress state under which a crack can propagate, and the trajectory it may follow during its growth are thus very important for the stability of rock masses/materials and for the safe design of structures in/on rocks. In this paper, the crack initiation angle and subsequent crack propagation path are experimentally investigated for limestone rock specimens. This investigation was conducted under various mixed mode I-II loading conditions, including pure mode-I and pure mode-II.This study includes conducting diametrical compression tests on notched Brazilian disk specimens. Moreover, the effect of confining pressure and temperature on crack initiation and propagation were also studied. The experimental results were compared with theoretical predictions of crack initiation angle. The results showed that limestone behaves in brittle fashion, and the effects of confining pressure and temperature on failure trajectories were not significant. Generally, the crack initiation angle can be predicted by the maximum tangential stress criterion. However, for notched Brazilian disk with high value of crack orientation with respect to loading direction, crack does not propagate from the tip of the crack. This important observation indicated that the tensile-strength failure can become more critical than the fracture-toughness failure.  相似文献   

Meteorological triggering of earthquake swarms at Mt. Hochstaufen, SE-Germany   总被引：3，自引：0，他引：3  

T. Kraft  J. Wassermann  E. Schmedes  H. Igel   《Tectonophysics》2006,424(3-4):245

A growing body of evidence suggests that fluids are intimately linked to a variety of faulting processes. Yet, the particular mechanisms through which fluids and associated parameters influence the stress regime and thus the seismicity of a particular area are not well understood.We carry out a study of the spatio-temporal behavior of earthquakes, fluid-related parameters (groundwater levels) and meteorological observables (precipitation) in the swarm earthquake area of Bad Reichenhall, southeastern Germany. The small volume in which the earthquakes take place, almost yearly occurring earthquake swarms and a permanent, seismo-meteorological monitoring network, provide nearly controlled experimental conditions to study the physics of earthquake swarms and to infer characteristic properties of the seismogenic crust.In this paper we (1) describe this fairly unique study area in terms of geology, seismicity and atmospheric conditions; (2) present two cases of earthquake swarms that seem to follow above-average rainfall events; and (3) examine the observed migration of hypocenters with a simple pore pressure diffusion model.We find significant correlation of seismicity with rainfall and groundwater level increase, and estimate an average hydraulic diffusivity of D = 0.75 ± 0.35 m²/s for Mt. Hochstaufen in 2002.  相似文献   

金坛石灰岩资源合理利用与供需保障分析     

倪嘉曾  宋云飞 《江苏地质》2006,30(1):77-79

金坛非金属矿产资源比较丰富,石灰岩是主要的优势矿产。石灰岩原探明的储量有2亿多吨,但因部分储量位于茅山风景名胜区禁采区内不能利用,加之20多年来的开采消耗了较多储量,资源形势日趋严峻。有限的资源,持续上升的需求,供需矛盾严峻的形势摆在面前,为促进经济社会的可持续发展,必须加强对石灰岩资源的保护,科学配置、合理利用资源,以提高石灰岩矿资源保障能力。  相似文献   

The application of rock mass classification systems to underground excavation in weak limestone, Atatürk dam, Turkey     

A. Tu rul 《Engineering Geology》1998,50(3-4):337-345

The Atatürk dam was built across the Firat River on clayey limestone. A grout curtain, providing impermeability in the left and right abutments, was done in grouting galleries. The well known rock mass classification systems for tunneling purposes [rock structure rating (RSR), rock mass rating (RMR) and rock mass quality index (Q)] were used to classify the rock mass along these galleries. Based on RSR, RMR and Q values, the rock masses in the galleries have been classified into three different classes. Correlation between the three classification systems is discussed and suggestions are made for using rockbolt, shotcrete with wiremesh and steel ribs for supporting the rock mass.  相似文献   

An overview of the geology of the Transvaal Supergroup dolomites (South Africa)   总被引：1，自引：0，他引：1  

P. G. Eriksson  W. Altermann 《Environmental Geology》1998,36(1-2):179-188

 In the Neoarchaean intracratonic basin of the Kaapvaal craton, between approximately 2640 Ma and 2516 Ma, two successive stromatolitic carbonate platforms developed. Deposition started with the Schmidtsdrif Subgroup, which is probably oldest in the southwestern part of the basin, and which contains stromatolitic carbonates, siliciclastic sediments and minor lava flows. Subsequently, the Nauga formation carbonates were deposited on peritidal flats located to the southwest and were drowned during a transgression of the Transvaal Supergroup epeiric sea, around 2550 Ma ago. This transgression led to the development of a carbonate platform in the areas of the preserved Transvaal and Griqualand West basins, which persisted for 30–50 Ma. During this time, shales were deposited over the Nauga Formation carbonates in the southwestern portion of the epeiric sea. A subsequent period of basin subsidence led to drowning of the stromatolitic platform and to sedimentation of chemical, iron-rich silica precipitates of the banded iron formations (BIF) over the entire basin. Carbonate precipitation in the Archaean was largely due to chemical and lesser biogenic processes, with stromatolites and ocean water composition playing an important role. The stromatolitic carbonates in the preserved Griqualand West and Transvaal basins are subdivided into several formations, based on the depositional facies, reflected by stromatolite morphology, and on intraformational unconformities; interbedded tuffs and available radiometric age data do not yet permit detailed correlation of units from the two basins. Thorough dolomitisation of most formations took place at different post-depositional stages, but mainly during early diagenesis. Partial silicification was the result of diagenetic and weathering processes. Karstification of the carbonate rocks was related to periods of exposure to subaerial conditions and to percolation of groundwater. Such periods occurred locally at the time of carbonate and BIF deposition. Main karstification, however, probably took place during an erosional period between approximately 2430 Ma and 2320 Ma. Received: 15 September 1996 · Accepted: 12 May 1998  相似文献   

Interaction of rock and atmosphere: patinas on Mediterranean monuments   总被引：2，自引：0，他引：2  

M. Garcia-Vallès  M. Vendrell-Saz  J. Molera  F. Blazquez 《Environmental Geology》1998,36(1-2):137-149

 This paper analyzes – chemically, mineralogically, and petrolographically – the patinas developed on several Mediterranean monuments made with different stones (siliceous and carbonatic) in order to establish their origin and their evolution under the present environmental conditions, and to evaluate the environmental parameters controling their development. Most of the patinas show a common sequence of layers, which, from the outer to the inner zone, are: (1) present bioactivity and/or biological remains, (2) gypsum-rich patina, and (3) calcitic brown to orange patina. Each one may exhibit different fabrics (from micritic to stromatolitic) and may be more or less continuous and homogeneous. The main mineral components are calcite and gypsum, but Ca-oxalates and Ca-phosphates have also been found associated to biological structures, as well as quartz and clays. The different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem to be related to the biological activity, facilitating the growth of different organisms and leading to the development of a deposit with distinct characteristics (fabric, texture, porosity, etc.). The gypsum-rich patina has been interpreted as a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the atmospheric dust. The mineralogy and texture of the patina is independent of the nature of the underlying rock and only in few cases a micritization process has been observed as interaction between patina and rock. Recently, the penetration of endolithic microflora produced drillings and the development of a fissuration system parallel to the surface, and thus the detachment of the crust from the rock and even flackening of the rock itself has been observed. Consequently, under the present climatic conditions in the Mediterranean basin, erosion is a more active process than deposition, and the crusts and patinas show a tendency to disappear from the surface of the monuments. Received: 3 November 1996 · Accepted: 10 September 1997  相似文献   

西秦岭铀成矿带中志留系硅岩灰岩的成因研究     

赵兵 《岩石学报》1997,13(2):233-244

通过大量的剖面测制和室内分析，从岩石的地质产状、岩石学及地球化学特别是稀土元素地球化学方面研究了西秦岭铀成矿带中硅、灰岩的成因。原始沉积的泥晶灰岩和球粒泥晶灰岩沉积于水下高地较低能环境，球粒主要为粪球粒及少量硅质生物体。硅岩具生物化学沉积（Ｉ类）和由灰岩硅化（交代）成因（Ｉ类）两种成因类型，它们在地质产状、结构构造、常量元素及稀土元素地球化学等方面都存在显著差异。在综合分析的基础上建立了西秦岭铀成矿带早志留世沉积环境模式  相似文献   

A quantitative scanning electron microscope study of evidence for lichen weathering of limestone,Mendip Hills,Somerset     

Heather Viles 《地球表面变化过程与地形》1987,12(5):467-473

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下扬子地区三迭系下统瘤状灰岩成因研究   总被引：2，自引：0，他引：2  

郭福生 《华东地质学院学报》1989,12(4):17-22

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石灰岩地区砼灌注桩抽芯检测实例     

孙云波 《云南地质》2003,22(3):326-328

以灰岩地区砼灌注桩两个抽芯工程为例，介绍灰岩地区砼灌注桩抽芯检查过程中应注意的问题，为砼灌注桩抽芯检查积累经验。  相似文献