颗粒体系中的骨架及力链网络   总被引：4，自引：0，他引：4  

孙其诚  辛海丽  刘建国  金峰 《岩土力学》2009,30(Z1):83-87

颗粒物质是大量离散的固体颗粒相互作用而组成的复杂体系,具有非连续和接触耗散等基本特征,其物理机制研究是近20年科学前沿之一。砂土就是典型的颗粒物质,土体中的有效应力是作用在土体骨架上的平均应力,土体变形主要来源于骨架上的颗粒位置,但对土体骨架并没有一个清晰的物理描述。近期颗粒物质力学研究认为,体系中颗粒相互接触形成的网络结构是外荷载传递路径的物理基础,可能就是土力学所指的骨架。同时还发现,较大的力通常沿着准直线的路径传递,人们常把传递较大力、与该准直线路径对应的若干颗粒组成的链状结构,称为强力链;弱力链则传递较小力。力链结构及其演变规律的描述是颗粒物质研究的核心之一。以单轴侧限压缩数值模拟为例,对比说明了土体颗粒骨架与力链结构的关系,明确提出强力链网络决定颗粒体系的宏观力学行为。  相似文献   

颗粒物质在微剪切振动下的能量耗散研究     

汪盼盼  王万景  刘长松  朱震刚 《岩土力学》2009,30(Z1):129-134

采用改进的低频内耗仪研究了几种常见颗粒体系（沙子、玻璃珠）的相对能量耗散性质：能量耗散的振幅谱和频率谱。实验发现,振幅谱中随振幅增大形成一个能量耗散峰,而频率谱线中则观察到随着频率的增加依次出现四个能量耗散峰,对应着体系模量的四个衰减。随探针插入深度的增加相对能耗先增加后减小,出现一个能耗峰值,该峰值对应的深度为体系的临界深度。基于对颗粒体系的介观分析,提出一个流变模型来阐述流变耗散机制,结果表明摩擦在颗粒力学响应中除耗散能量外还起到增加体系弹性的作用。频率谱的分析表明颗粒中还存在另一种耗散机制：颗粒链的共振耗散。  相似文献   

Dust emission by off-road driving: Experiments on 17 arid soil types, Nevada, USA   总被引：2，自引：0，他引：2  

Dirk Goossens  Brenda Buck 《Geomorphology》2009,107(3-4):118-138

Field experiments were conducted in Nellis Dunes Recreational Area (Clark County, Nevada, USA) to investigate emission of dust produced by off-road driving. Experiments were carried out with three types of vehicles: 4-wheelers (quads), dirt bikes (motorcycles) and dune buggies, on 17 soil types characteristic for a desert environment. Tests were done at various driving speeds, and emissions were measured for a large number of grain size fractions. This paper reports the results for two size fractions of emissions: PM10 (particles < 10 μm) and PM60 (particles < 60 μm). The latter was considered in this study to be sufficiently representative of the total suspendable fraction (TSP). Off-road driving was found to be a significant source of dust. However, the amounts varied greatly with the type of soil and the characteristics of the top layer. Models predicting emission of dust by off-road driving should thus consider a number of soil parameters and not just one key parameter. Vehicle type and driving speed are additional parameters that affect emission. In general, 4-wheelers produce more dust than dune buggies, and dune buggies, more than dirt bikes. Higher speeds also result in higher emissions. Dust emitted by off-road driving is less coarse than the parent sediment on the road surface. Off-road driving thus results in a progressive coarsening of the top layer. Exceptions to this are silty surfaces with no, or almost no, vegetation. For such surfaces no substantial differences were observed between the grain size distribution of road dust and emitted dust. Typical emission values for off-road driving on dry desert soils are: for sandy areas, 30–40 g km^− 1 (PM10) and 150–250 g km^− 1 (TSP); for silty areas, 100–200 g km^− 1 (PM10) and 600–2000 g km^− 1 (TSP); for drainages, 30–40 g km^− 1 (PM10) and 100–400 g km^− 1 (TSP); and for mixed terrain, 60–100 g km^− 1 (PM10) and 300–800 g km^− 1 (TSP). These values are for the types of vehicles tested in this study and do not refer to cars or trucks, which produce significantly more dust.  相似文献   

A new framework for evaluating along-wind responses of a transmission tower     

Guohuan Liu  Hongnan Li 《地震工程与工程振动(英文版)》2009,8(1):87-93

In this paper, an analytical framework to evaluate the along-wind-induced dynamic responses of a transmission tower is presented. Two analytical models and a new method are developed: (1) a higher mode generalized force spectrum (GFS) model of the transmission tower is deduced; (2) an analytical model that includes the contributions of the higher modes is further derived as a rational algebraic formula to estimate the structural displacement response; and (3) a new approach, applying load with displacement (ALD) instead of force, to solve the internal force of transmission tower is given. Unlike conventional methods, the ALD method can avoid calculating equivalent static wind loads (ESWLs). Finally, a transmission tower structure is used as a numerical example to verify the feasibility and accuracy of the ALD method.  相似文献   

基于球孔扩张理论和侧阻力退化效应的压桩力计算模拟   总被引：2，自引：0，他引：2  

刘俊伟  张明义  赵洪福  王静静 《岩土力学》2009,30(4):1181-1185

根据静压桩的贯入机制,将沉桩过程模拟为半无限土体中一系列球形孔的连续扩张,土体假定为Mohr-Coulomb材料。利用球孔扩张和源-源假设理论,并采用Boussinesq解进行地面应力的修正,在此基础上分别计算出桩侧极限摩阻力和桩端阻力。通过现场试验研究发现,沉桩过程中侧摩阻力退化效应带来的影响是明显的,提出了相应的侧阻力退化公式。在充分考虑以上因素的基础上推导出了静压桩压桩力的模拟计算公式。使用Matlab6.5软件进行理论计算,并与山西太原某试验进行对比分析,一定深度以下理论值与实测数据基本吻合,证明该计算模拟是可行的。  相似文献   

桩锚结构变形协调方法的改进研究     

晏鄂川  刘焕斌  李相依  吴益平 《岩土力学》2009,30(5):1446-1450

桩锚结构变形协调条件是桩锚结构设计中内力计算的关键点。现行桩锚结构变形协调条件是在锚索施加预应力后桩身向坡内变形十分微小而忽略不计的条件下推导得到的,只适用于锚索预应力微小或为0的情况。但在许多工程实例中,锚索的预应力较大,导致的桩身变形不能被忽略。因此,现行的变形协调条件假设与桩锚结构的实际工作状态不一致。利用结构力学理论,在研究桩锚结构体系的两阶段变形过程的基础上,对变形协调方程从2个方面改进,其一是改变原有方法中抗滑桩滑面处位移和转角的计算方法;其二是改变第j排锚索对桩身 点处位移贡献的计算形式。算例分析表明,改进桩锚结构变形协调条件,可以更好地为工程设计服务。  相似文献   

关于用科氏力预测最大余震问题的讨论   总被引：1，自引：0，他引：1  

郭增建  郭安宁 《中国地震》2009,25(4)

对用科里奥利力效应预测余震最大强度的某些问题进行了讨论.并介绍了用该效应对2008年汶川8级地震的最大余震所作的正确预测.  相似文献   

Axisymmetric transient waves in transversely isotropic half-space     

Morteza Eskandari-Ghadi  Siamak Sattar 《Soil Dynamics and Earthquake Engineering》2009

A transversely isotropic material in the sense of Green is considered. Using a series of potential functions proposed in [Eskandari-Ghadi M. A complete solution of the wave equations for transversely isotropic media. J Elasticity 2005; 81:1–19], the solutions of the transient wave equations within a half-space under surface load are obtained in the Laplace–Hankel domain for axisymmetric problems. The solutions are investigated in detail in the special case of a surface point force pulse varying with time as Heaviside function. Using Cagniard–De Hoop method, the inverse Laplace transform and inverse Hankel transform of the solutions are then obtained in the form of integrals with finite limits. For validity of the analytical results, the final formulations for surface waves are degenerated for an isotropic material and compared with the existing formulation obtained by Pekeris [The seismic surface pulse. Proc Natl Acad Sci USA 1955;41:469–80], to show that they are exactly the same. The numerical evaluations of the integrals for some transversely isotropic materials as well as an isotropic one are obtained. The present approach is then numerically verified by comparing a particular case of displacements for the surface of an isotropic half-space subjected to a point load of Heaviside function with the solutions obtained by Pekeris [The seismic surface pulse. Proc Natl Acad Sci USA 1955;41:469–80]. In addition, the wave equations for the mentioned medium are obtained on the vertical line directly under the applied surface load. The final formulations are degenerated for an isotropic material and compared with the existing formulation given in Graff [Wave motion in elastic solids. New York: Dover Publications Inc; 1975 [New Ed edition, November 1991]], to show that they are also exactly the same. Then equations are presented in graphical forms using an appropriate numerical evaluation.  相似文献   

Depth–energy and depth–force relationships in open channel flows. II: Analytical findings for power-law cross-sections     

A. Valiani  V. Caleffi 《Advances in water resources》2009

In a recent work [Valiani A, Caleffi V. Depth–energy and depth–force relationships in open channel flows: analytical findings. Adv Water Resour 2008;31(3):447–54], the authors analytically inverted the depth–specific energy and depth–total force relationships for flows in open channels with wide rectangular cross-sections.  相似文献   

干旱区盐渍地遥感动态监测及其驱动力研究——以渭干河-库车河三角洲绿洲为例   总被引：3，自引：1，他引：2  

王宏卫  塔两甫拉提·特依拜 《干旱区地理》2009,32(3)

土壤盐渍化作为主要的土地退化形式之一,已成为一个全球性问题.盐渍地的时空动态变化特征分析研究,是发展研究盐渍地动态监测与预报技术的重要基础工作之一,对于及时掌握盐渍化程度与分布,合理制定土地利用政策与生态改良措施,实现区域可持续发展等方面具有重要作用.针对目前塔里木盆地北缘地区广泛存在的土壤盐渍化问题,基于GIS和遥感变化检测方法,对渭-库绿洲1989、2001、2007年三个时期的盐渍地时空动态变化特征及其驱动力进行了分析.研究结果表明:1989-2007年间重度盐渍地的变化程度剧烈,呈剧烈增加态势;中轻度盐渍地面积减少,主要向重度盐渍地和非盐渍地转化;非盐渍地有所减少,主要向中轻度盐渍地和重度盐渍地转化;绿洲内部盐渍化程度有所降低,而绿洲外围盐渍化程度加剧;盐渍地重心具有向绿洲外围东南方向转移的趋势;通过分析盐渍地时空动态变化特征,表明盐渍地时空变化是一个极其复杂的过程,同时受到自然和人文两大系统的驱动,人为不合理的灌溉是促使土壤盐渍化的主要驱动力.研究为盐渍地时空动态分析与评价提供了普适性较强的实现方法,为构建盐渍地定量监测模型提供了一定科学依据.  相似文献