循环荷载下人工结构性土变形与强度特性试验研究

针对长期动载作用下天然沉积结构性黏土地基强度和刚度循环软化问题,分别以水泥和食糖为模拟粒间胶结和大孔隙的材料,制备了不同胶结强度和初始孔隙比的人工结构性土,开展了人工结构性土与相应重塑土的动三轴试验,分析了土体胶结强度、初始孔隙比、围压和动应力幅值对累积变形和动强度的影响规律。试验结果表明：累积应变-振动次数曲线以临界循环应力为界分为：塑性安定型、临界型和破坏型;临界循环应力随胶结强度增大、初始孔隙比减小而增大;土体胶结强度越高,脆性破坏越明显,累积应变曲线转折点对应的应变越小。动强度的应变破坏标准采用转折点应变值更符合土性变化规律;动强度随胶结强度增大、初始孔隙比减小而增大;动黏聚力cd随破坏振次增大而降低,而动内摩擦角?d基本不变。试验结果可为软弱土地基动力灾变控制提供有益参考。     

Accelerated initial stiffness schemes for elastoplasticity

Iterative methods for the solution of non‐linear finite element equations are generally based on variants of the Newton–Raphson method. When they are stable, full Newton–Raphson schemes usually converge rapidly but may be expensive for some types of problems (for example, when the tangent stiffness matrix is unsymmetric). Initial stiffness schemes, on the other hand, are extremely robust but may require large numbers of iterations for cases where the plastic zone is extensive. In most geomechanics applications it is generally preferable to use a tangent stiffness scheme, but there are situations in which initial stiffness schemes are very useful. These situations include problems where a nonassociated flow rule is used or where the zone of plastic yielding is highly localized. This paper surveys the performance of several single‐parameter techniques for accelerating the convergence of the initial stiffness scheme. Some simple but effective modifications to these procedures are also proposed. In particular, a modified version of Thomas' acceleration scheme is developed which has a good rate of convergence. Previously published results on the performance of various acceleration algorithms for initial stiffness iteration are rare and have been restricted to relatively simple yield criteria and simple problems. In this study, detailed numerical results are presented for the expansion of a thick cylinder, the collapse of a rigid strip footing, and the failure of a vertical cut. These analyses use the Mohr–Coulomb and Tresca yield criteria which are popular in soil mechanics. Copyright © 2000 John Wiley & Sons, Ltd.     

FWG2递减开发模型

本文提出了ＦＷＧ２递减开发模型,提出了开发速度,采出程度等开发指标的数学关系式,分析了参数对ＦＷＧ２递减开发模型的影响,提出了开发初期ＦＷＧ２递减开发模型的确定方法,便于开发初期决策,制作了ＦＷＧ２递减开发模型的ｌｏｇＶｄ－ｌｏｇＲｐ图版,ｌｏｇＶＤ～ｌｏｇ（ａｔ）图版,ｌｏｇＲｐ－ｌｏｇ（ａｔ）图版,提出了开发中晚期ＦＷＧ２递减开发模型的判断方法,三点抛物线法和三种图牌区配的拟合方法,为开发中晚期预测奠定了基础,ＦＷＧ２递减开发模型是一种高精度直线递减模型。     

岩体的加、卸载状态与能量的分配关系

岩体是流变体,在高地应力的长时间作用下其内部非均匀应力随着时间自我松弛,逐渐趋向于静水压力状态。在这样的状态下,虽然其体积仍维持弹性,但丧失了进一步抵抗剪切变形的能力,处于流动的状态,其能量储存具有体积的特征。采用平面压缩模型,研究岩石在不同应力水平长期作用下的变形性状及能量分配关系,给出在快速卸荷条件下发生自持续动力断裂破坏条件,以期揭示深部岩体初始地应力水平（能量在体变及形变上的分配关系）对卸荷条件下岩体运动过程中表现的惯性、黏性及弹塑性变形的影响规律,为建立深部岩体加卸荷本构关系打下基础。     

含初始缺陷地铁隧道的抗震动力学行为研究

针对含初始缺陷的既有地铁隧道受邻近穿越隧道施工影响的首都地铁隧道工程背景,基于有限差分方法,通过对既有地铁车站结构受邻近隧道穿越后的抗震性能研究,揭示其抗震动力响应机理。结果表明,在邻近隧道穿越影响下,含初始缺陷的既有隧道各薄弱控制点在地震作用下位移和应力动力时程的波动趋势具有相似性,说明衬砌结构是整体运动的,其位移、应力较穿越前均有所增加,边墙和仰拱在穿越后抗震性能影响最大,剪切破坏主要以车站结构周边土体为主,新线穿越后其剪切破坏分布范围有所增大,应进行注浆加固处理,与自身结构刚度相匹配,提高抗震能力。     

Stochastic analysis of bounded unsaturated flow in heterogeneous aquifers: Spectral/perturbation approach

This paper describes a stochastic analysis of steady state flow in a bounded, partially saturated heterogeneous porous medium subject to distributed infiltration. The presence of boundary conditions leads to non-uniformity in the mean unsaturated flow, which in turn causes non-stationarity in the statistics of velocity fields. Motivated by this, our aim is to investigate the impact of boundary conditions on the behavior of field-scale unsaturated flow. Within the framework of spectral theory based on Fourier–Stieltjes representations for the perturbed quantities, the general expressions for the pressure head variance, variance of log unsaturated hydraulic conductivity and variance of the specific discharge are presented in the wave number domain. Closed-form expressions are developed for the simplified case of statistical isotropy of the log hydraulic conductivity field with a constant soil pore-size distribution parameter. These expressions allow us to investigate the impact of the boundary conditions, namely the vertical infiltration from the soil surface and a prescribed pressure head at a certain depth below the soil surface. It is found that the boundary conditions are critical in predicting uncertainty in bounded unsaturated flow. Our analytical expression for the pressure head variance in a one-dimensional, heterogeneous flow domain, developed using a nonstationary spectral representation approach [Li S-G, McLaughlin D. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour Res 1991;27(7):1589–605; Li S-G, McLaughlin D. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour Res 1995; 31(3):541–51], is precisely equivalent to the published result of Lu et al. [Lu Z, Zhang D. Analytical solutions to steady state unsaturated flow in layered, randomly heterogeneous soils via Kirchhoff transformation. Adv Water Resour 2004;27:775–84].     

The solitary waves of the barotropic quasi-geostrophic model with the large-scale orography

Starting from a modified barotropic quasi-geostrophic model equation, considering the actual situation of the large-orography of the Tibetan Plateau, neglecting its slope in x direction, and using the reductive perturbation method, then the solitary waves are obtained. The results show that the orography is essential factor exciting solitary Rossby waves in a flow without shear.     

1991年夏季持续性异常环流的共轭敏感性分析

在共轭敏感性分析的基础上发展了最敏感扰动的概念。用共轭模式对江淮流域大水1991年东亚夏季环流的持续异常特征,包括乌拉尔阻塞高压、鄂霍次克海偶极子型阻塞以及副热带高压的变动过程进行了分析,分别得到了对这些过程影响最大的初始扰动。结果从新的角度揭示了这些系统最重要的影响因子,也显示了共轭敏感性分析方法在大气环流物理过程诊断中的有效性和应用前景。     

初值形成方法对降水数值预报的影响

北欧有限区域模式ＨＩＲＬＡＭ被应用于中国的暴雨个例以探讨初值形成方法对有限区域模式定量降水数值预报的影响,对两种初值形成方案进行了对比,一种是由ＨＩＲＬＡＭ自己的数值同化系统提供初值,另一种是直接内插ＥＣＭＷＦ全球模式的相应分析场,与这两种方案对应的数值试验分别是控制试验（ＣＯＮＬ）和对比试验（ＣＯＭＰ）,将ＣＯＮＬ和ＣＯＭＰ的降水预报与观测值比较,结果表明：（１）当为ＣＯＭＰ提供初值的ＥＣＭＷＦ     

Adjoint Sensitivity Analyses on the Anomalous Circulation Features in East Asian Summer Monsoon

ＡｄｊｏｉｎｔＳｅｎｓｉｔｉｖｉｔｙＡｎａｌｙｓｅｓｏｎｔｈｅＡｎｏｍａｌｏｕｓＣｉｒｃｕｌａｔｉｏｎＦｅａｔｕｒｅｓｉｎＥａｓｔＡｓｉａｎＳｕｍｍｅｒＭｏｎｓｏｏｎ①ＹａｎｇＹａｎ（杨燕），ＬｉＺｈｉｊｉｎ（李志锦）ａｎｄＪｉＬｉｒｅｎ（纪立人）Ｉ...