Three-dimensional discontinuous deformation analysis (3-D DDA) using a new contact resolution algorithm     

S. Amir Reza Beyabanaki  Roozbeh Geraili Mikola  Kianoosh Hatami   《Computers and Geotechnics》2008,35(3):346-356

This paper presents a new contact calculating algorithm for contacts between two polyhedra with planar boundaries in the three-dimensional discontinuous deformation analysis (3-D DDA). In this algorithm, all six type contacts in 3-D (vertex-to-face, vertex-to-edge, vertex-to-vertex, face-to-face, edge-to-edge, and edge-to-face) are simply transformed into the form of point-to-face contacts. The presented algorithm is a simple and efficient method and it can be easily coded into a computer program. In this paper, formulations of normal contact, shear contact and frictional force submatrices based on the new method are derived and the algorithm has been programmed in VC⁺⁺. Examples are provided to demonstrate the new contact rule between two blocks.  相似文献   

Low-pressure,water-assisted anatexis of basic dykes in a contact metamorphic aureole,Fuerteventura (Canary Islands): oxygen isotope evidence for a meteoric fluid origin     

M. I. Holloway  F. Bussy  T. W. Vennemann 《Contributions to Mineralogy and Petrology》2008,155(1):111-121

Migmatites produced by low-pressure anatexis of basic dykes are found in a contact metamorphic aureole around a pyroxenite–gabbro intrusion (PX2), on Fuerteventura. Dykes outside and inside the aureole record interaction with meteoric water, with low or negative δ¹⁸O whole-rock values (+0.2 to −3.4‰), decreasing towards the contact. Recrystallised plagioclase, diopside, biotite and oxides, from within the aureole, show a similar evolution with lowest δ¹⁸O values (−2.8, −4.2, −4.4 and −7.6‰, respectively) in the migmatite zone, close to the intrusion. Relict clinopyroxene phenocrysts preserved in all dykes, retain typically magmatic δ¹⁸O values up to the anatectic zone, where the values are lower and more heterogeneous. Low δ¹⁸O values, decreasing towards the intrusion, can be ascribed to the advection of meteoric water during magma emplacement, with increasing fluid/rock ratios (higher dyke intensities towards the intrusion acting as fluid-pathways) and higher temperatures promoting increasing exchange during recrystallisation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Parameters affecting maximum fluid transport in large aperture fractures   总被引：1，自引：0，他引：1  

Maria Ines Dragila  Noam Weisbrod   《Advances in water resources》2003,26(12):1219-1228

We present results of laboratory experiments to study the behavior of liquids moving in unsaturated wide-aperture fractures. A 5-mm-thick glass plate cut with a 1.7-mm aperture was used as a fractured rock analog to study behavior of film and capillary droplet flow modes. Flow rates ranged between 0.6 and 6.0 ml/min. Variability in the ambient barometric pressure, resulting from weather conditions, seemed to play a role in the natural selection of flow mode. For droplet mode, constant input conditions resulted in highly variable transport properties within the fracture. The advancing meniscus exhibited a dynamic contact angle that was a function of the droplet speed and much larger than the static contact angle. Flow rate was reduced due to the larger contact angle. Analytical expressions for droplet velocity and flow capacity are presented as a function of the dynamic rather than the static contact angle.  相似文献   

Migmatites from Grenville, Quebec: metamorphic P-T-X conditions in transitional amphibolite/granulite-facies rocks     

J. V. Owen  J. D. Greenough 《Lithos》1997,39(3-4):195-208

Migmatitic rocks near Grenville, Quebec, preserve features indicative of reactions at the onset of granulite facies metamorphism. In this area, metapelites and metacarbonates of the classic Grenville Series are spatially associated with granitic gneiss and metabasite, and flank a Paleozoic, Fe-rich syenite stock. Near this intrusion, the metapelite is diatexitic and nearly devoid of biotite, indicating the involvement of biotite during melting in the contact aureole of this intrusion. Outside of the contact aureole, metapelites and associated rocks contain biotite and are metatexitic. These features suggest two episodes of migmatization, the earlier predating the syenite, the later, synchronous with this intrusion.

Hornblende-rich metabasites near the syenite contain a two-part neosome consisting of coarse-grained leucosome veins and patches that are enclosed by fine-grained, pyroxene-rich envelopes. Migmatization is attributed to dehydration melting in the presence of CO₂-rich fluids possibly derived from nearby carbonate rocks prior to and/or during emplacement of the syenite. The occurrence of isolated mafic clots in the mesosome and rarity of melanosome seams on leucosomes suggest that some melts were mobile on an outcrop scale. These observations suggest that the leucosomes formed by the segregation of melts, which, coupled with CO₂ flux, dehydrated the wallrock along narrow margins, forming the pyroxene-rich neosomes. Back-reaction with residual fluids led to the local scapolitization of plagioclase and the concomitant formation of coronal garnet on pyroxene in neosomes. Thermobarometry of corona structures within the contact aureole generates diffusional Mg-Fe blocking temperatures ( 550 °C at 5.5 kbar). Extrapolated up-temperature, P-sensitive equilibria for the coronas yield similar pressures (8–9 kbar) as texturally-equilibrated assemblages for which high temperatures ( 750 ± 50 °C; X_CO2 = 0.90−0.95) were determined for rocks sampled inside and outside of the contact aureole. This suggests that the Grenville migmatites had not been substantially decompressed by the time that the syenite was emplaced.  相似文献   

Mechanical transitional behavior of binary mixtures via DEM: Effect of differences in contact-type friction coefficients     

《Computers and Geotechnics》2017

This report presents a numerical investigation of the shear behavior of binary mixtures via a two-dimensional discrete element method. The effect of the coarse particle content on the peak shear strength of mixtures is investigated for different contact-type friction coefficients. A detailed analysis on the anisotropies enables us to understand the microscopic mechanisms that result in the dependency of the peak shear strengths on the coarse particle content. The contributions of different contact types to the peak shear strength are quantified. Lastly, the inter-particles structures are examined when the binary mixtures become coarse-particle-supported structures.  相似文献   

关于巴罗式变质带的最新研究及其对研究秦岭杂岩的意义   总被引：1，自引：1，他引：0  

任留东  李崇  王彦斌  李淼 《岩石学报》2018,34(4):913-924

本文对苏格兰高地Grampian造山运动中产生的经典巴罗变质带进行了讨论,重点介绍了近年来关于其变质作用的特征及发生机制认识方面的重大变化。强调巴罗变质作用仅发生在整个造山运动过程中的部分时段,纪录了短暂的加热过程,时空上与区域内大规模的双峰式岩浆活动有关。经典的巴罗变质系列并非形成于地壳增厚及其热弛豫,而是代表了中地壳内大规模的接触变质作用。参考经典地区的变质特征,对发育巴罗式变质作用的秦岭杂岩进行了初步对比分析,指出其中与夕线石有关的变质P-T-t轨迹可能是等压冷却过程,而不是等温降压的顺时针演化模式。秦岭杂岩的变质作用时间仍需要进一步准确厘定。结合其它相关地质特征的分析和对比,得出如下推论:巴罗式变质带发育地区的变质作用、混合岩与花岗岩均属于同一动力系统作用的结果,花岗质岩体不是变质作用的原因;基性岩浆可能提供了巴罗式变质作用发生所需要的热能,但不是必要条件;巴罗式变质作用可以发生在正常地壳厚度情况下,不是碰撞构造的标志;伴随热异常的变形过程中产生了变质带的梯度分布(巴罗式变质带)和一些花岗岩,形成类似于底辟的冲起构造。  相似文献   

易门赵普新沟白钨矿矿床地质及控制因素     

邹春林  周仕雄  张红英  许建文 《云南地质》2007,26(4):421-427

新沟白钨矿属典型的接触交代(矽卡岩)变质矿床。晋宁晚期的岩浆活动强烈,黑云二长花岗岩是矿区主要成矿岩体。钨矿体赋存在花岗岩体两侧与昆阳群大龙口组灰岩接触带矽卡岩中,地层、岩石、构造对矽卡岩及矿体都有控制作用。  相似文献   

Nonlinear seismic response analysis of arch dam-foundation systems- part II opening and closing contact joints     

Xiuli Du  Jin Tu 《Bulletin of Earthquake Engineering》2007,5(1):121-133

A time-domain method for the analysis of arch dam-foundation rock dynamic interaction during earthquake was proposed, and the dynamic relaxation technique was adopted to obtain the initial static response for dynamic analysis by [Du et al. (2005). The paper has been contributed to Bulletin of earthquake engineering]. In this paper, a nonlinear explicit method in time domain considering the opening and closing effect of contact joints on arch dam during earthquake is further proposed by introducing the dynamic contact force model into the method. The simulation accuracy of dynamic contact force model is verified by comparing its calculation result and test result of scale model on shaking table. Finally, the influence of joints on the seismic response of Xiaowan arch dam is studied by the proposed method and some conclusions are given.  相似文献   

潞西团坡厂铁锌多金属矿成因     

曾培林 《云南地质》2010,29(3):283-285,282

矿体产于印支期黑云角闪花岗闪长岩与寒武系(未分,∈?)变质岩接触带,F1压扭性断裂控制矿体的形态和展布。成因类型为热液接触交代一矽卡岩型铁锌矿。  相似文献   

Large deformation dynamic analysis of saturated porous media with applications to penetration problems     

《Computers and Geotechnics》2014

This paper outlines the development as well as implementation of a numerical procedure for coupled finite element analysis of dynamic problems in geomechanics, particularly those involving large deformations and soil-structure interaction. The procedure is based on Biot’s theory for the dynamic behaviour of saturated porous media. The nonlinear behaviour of the solid phase of the soil is represented by either the Mohr Coulomb or Modified Cam Clay material model. The interface between soil and structure is modelled by the so-called node-to-segment contact method. The contact algorithm uses a penalty approach to enforce constraints and to prevent rigid body interpenetration. Moreover, the contact algorithm utilises a smooth discretisation of the contact surfaces to decrease numerical oscillations. An Arbitrary Lagrangian–Eulerian (ALE) scheme preserves the quality and topology of the finite element mesh throughout the numerical simulation. The generalised-α method is used to integrate the governing equations of motion in the time domain. Some aspects of the numerical procedure are validated by solving two benchmark problems. Subsequently, dynamic soil behaviour including the development of excess pore-water pressure due to the fast installation of a single pile and the penetration of a free falling torpedo anchor are studied. The numerical results indicate the robustness and applicability of the proposed method. Typical distributions of the predicted excess pore-water pressures generated due to the dynamic penetration of an object into a saturated soil are presented, revealing higher magnitudes of pore pressure at the face of the penetrometer and lower values along the shaft. A smooth discretisation of the contact interface between soil and structure is found to be a crucial factor to avoid severe oscillations in the predicted dynamic response of the soil.  相似文献