Physical weathering of marbles caused by anisotropic thermal expansion

 Marbles as building stones as well as in their natural environments show complex weathering phenomena. The most important damage scenario is based on the highly anisotropic thermal expansion coefficient α of calcite, i.e. extreme expansion parallel and contraction normal to the crystallographic c-axis. Therefore, the rock fabric and especially the lattice-preferred orientation (texture) of calcite and/or dolomite as the predominant mineral phases in marbles have a significant influence on the mechanical weathering. The textures of marbles from five different locations vary from a more or less perfect prolate to moderate oblate shape of the [006] pole figure tensor. Accordingly, the texture-derived bulk thermal dilatation anisotropy covers a broad range from –0.048 to 0.680. The modelled thermal dilatations correlate with those obtained from experimental measurements. The difference in magnitude is basically explained by the microcrack fabrics which was not considered in the computations. All samples show a deterioration due to thermal treatment regardless of the strength of texture. The directional dependence of (a) the total magnitude of the thermal dilatation coefficient and (b) of the residual strain is highest in marbles with a strong texture, whereas the Carrara marble with a weak texture exhibits a uniform crack formation. The progressive loss of cohesion along grain boundaries due to dilatancy may serve as an example for the initial stage of physical weathering. Received: 10 February 1999 / Accepted: 16 October 1999     

橄榄石集合体的简单剪切形变实验研究

本文利用高精度Paterson气体介质变形装置对富铁橄榄石集合体(Mg_(0.5),Fe_(0.5))_2SiO_4进行了高温简单剪切变形试验.试验在温度1473K和围压300MPa的条件下进行,差应力为64～153MPa,应变率为10~-5～10~-3s~-1.一共进行了三组试验,试件的剪切变形量分别为89%,131%和200%,通过对变形后试件的反射光学显微结构分析,得到富铁橄榄石集合体动态重结晶的微观机制,由结晶各向异性分析给出晶格最优取向和波速各向异性的分布及随应变的增加而表现出的演化特征.     

A lattice Boltzmann-finite element model for two-dimensional fluid–structure interaction problems involving shallow waters

In this paper, a numerical method for the modeling of shallow waters interacting with slender elastic structures is presented. The fluid domain is modeled through the lattice Boltzmann method, while the solid domain is idealized by corotational beam finite elements undergoing large displacements. Structure dynamics is predicted by using the time discontinuous Galerkin method and the fluid–structure interface conditions are handled by the Immersed Boundary method. An explicit coupling strategy to combine the adopted numerical methods is proposed and its effectiveness is tested by computing the error in terms of the energy that is artificially introduced at the fluid–solid interface.     

Mesoscale modeling of water penetration into concrete by capillary absorption

Water penetration into concrete by capillary absorption plays a very important role in the ingress of contaminative substances when the structures are built in aggressive environments. In the present paper the lattice network model is proposed based on the unsaturated flow theory to predict the water penetration into concrete. On the mesocale level, concrete is treated as a three-phase composite. By means of the Voronoi diagram meshing strategy, the lattice network model of concrete with different types of lattice elements is developed. The corresponding transport properties are assigned to the lattice elements in the network falling in different phases. As a result, the lattice elements are idealized as conductive “pipes” in which uni-directional flow can be realized between the two nodes of the elements. Parameters in the lattice network model, such as the sorptivity and porosity of the mortar and the ITZs are quantitatively determined. With help of the approach, the water content distribution within a concrete sample after any elapsed time, especially the penetration depth of water frontier, can be easily predicted. The cumulative water absorption calculated by the lattice network model is shown to be well agreed with the experimental results.     

Simulating flows in multi-layered and spatially-variable permeability media via a new Gray Lattice Boltzmann model

The simulation of flow in porous and fibrous permeable media is of high importance in many scientific and industrial applications. Although the finite element models at the representative elementary volume scales are used to solve a huge amount of scientific and engineering problems, they are hardly used to efficiently simulate pore-fluid flow problems at the particle scales. This encourages the development of numerical models to match the needs of such studies. In this paper, we propose a new Gray Lattice Boltzmann numerical model for simulating fluid flow in permeable media. Unlike most previous models, our proposed model has the ability to simulate multi-layers and space-variable permeability while preserving the continuity of the macroscopic velocity field. The model is verified with the available analytical solutions and a derived analytical expression for the case of variable porosity. In addition, we examine the importance of introducing a transition layer with a defined porosity function near the boundaries and interfaces. If this layer exists in practice, then the numerical results reveal that it cannot be neglected, and its impact is significant on the obtained velocity distribution. Finally, in the light of the obtained results, we can state that the proposed model has great potential to simulate complex and heterogeneous media with smoothness and accuracy, so that it may enrich the research content of the emerging computational geosciences.     

Dynamic Evolution of Precursory Field and Its Relation With the Group of Strong Earthquakes

Spatial scanning is done for two regions in Chinese Mainland,where displayed a denseprecursory network during 1994～1998.The two regions are the mid-southern segment of theNorth-south seismic belt(20°～35°N,95°～110°E)and North China(36°～42°N,110°～120°E).We took 0.5°×0.5°as a spatial window with a step of 0.25°and 4 months as atemporal window with a step of 1 month.For the two regions,the anomaly density is scannedfrom 1994 and 1995 respectively in the two regions.The precursory anomalies are all fromthe Division of Seismic Trend in China and the Division of Seismic Trend in the Capital Area,Center for Analysis and Prediction,China Seismological Bureau.A seismogenic tectonicmodel is introduced to explain the scanning results.In the model,the frictional strength ofthe focal sources is distributed randomly.After the boundary plate motion rate and all othergeological parameters are given,the stress of the sources in the system changesinhomogenously due to the variation of the frictional streng     

图形软件中矢量汉字的生成与应用

在研制岩土工程制图软件时，摸索出两种矢量汉字的生成技术，现作一介绍，以便为有同样问题的读者提供参考，避免不必要的重要工作。     

格子玻耳兹曼方法计算混合物整体电导率

本文采用格子玻耳兹曼方法计算混合物的整体电导率．整体电导率与各组分的电导率、体积分数和混合物结构有关．数值计算方法的有效性通过两相混合物并联或串联模型的解析解加以验证．对随机分布模型的计算发现格子玻耳兹曼方法得到的电导率落在H S理论边界内．对Al Bi合金整体电导率的数值模拟结果和实验结果非常相近．对饱和水岩石的介电常数的计算与实验结果相比误差较小．格子玻耳兹曼方法为混合物的整体电导率的计算提供了一个有效的途径.     

Dynamic Rupture in a 3-D Particle-based Simulation of a Rough Planar Fault

An appreciation of the physical mechanisms which cause observed seismicity complexity is fundamental to the understanding of the temporal behaviour of faults and single slip events. Numerical simulation of fault slip can provide insights into fault processes by allowing exploration of parameter spaces which influence microscopic and macroscopic physics of processes which may lead towards an answer to those questions. Particle-based models such as the Lattice Solid Model have been used previously for the simulation of stick-slip dynamics of faults, although mainly in two dimensions. Recent increases in the power of computers and the ability to use the power of parallel computer systems have made it possible to extend particle-based fault simulations to three dimensions. In this paper a particle-based numerical model of a rough planar fault embedded between two elastic blocks in three dimensions is presented. A very simple friction law without any rate dependency and no spatial heterogeneity in the intrinsic coefficient of friction is used in the model. To simulate earthquake dynamics the model is sheared in a direction parallel to the fault plane with a constant velocity at the driving edges. Spontaneous slip occurs on the fault when the shear stress is large enough to overcome the frictional forces on the fault. Slip events with a wide range of event sizes are observed. Investigation of the temporal evolution and spatial distribution of slip during each event shows a high degree of variability between the events. In some of the larger events highly complex slip patterns are observed.