Probabilistic analysis of responses of cantilever wall-supported excavations in sands considering vertical spatial variability

The influence of vertical spatial variability of sands on the excavation-induced lateral wall deflection and bending moment of excavations supported by cantilever retaining walls is investigated in this paper. Herein, the random finite element method (RFEM) is adopted to explicitly study the effect of one-dimensional spatial variability of internal friction angle of sands on the predicted wall and ground responses. The RFEM analysis consists of three components: (1) finite element method for analyzing lateral wall deflection and bending moment, (2) random field theory implemented with Monte Carlo simulation (MCS), and (3) statistical interpretation of MCS results through confidence intervals. This study reveals the importance of random field modeling in coping with the spatial variability of sands in the problem of supported excavations: (1) neglecting spatial variability of soil property will cause an overestimation of the variation in the predicted wall deflection and bending moment; (2) the estimated probability of failure based on a well-established serviceability limit state may be overestimated or underestimated depending on the chosen limiting lateral wall deflection. This study further investigates the effect of the number of MCS on the confidence intervals of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment. The results also demonstrate that the confidence interval analysis of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment provides a rational tool for interpreting the statistical data from RFEM.     

一类抛物型方程反问题的数值解法

讨论了一类二阶抛物型方程反问题的数值解法。应用拟解法的思想,把原问题分解为一系列适定的正问题和一个不适定的线性代数方程组。对于相应的正问题,证明了解连续依赖于初始分布,由此得到了在时刻的稳定性估计。使用古典欧拉差分格式求解正问题和用截断奇异值分解法求解病态方程组。数值结果显示数值解与理论解吻合很好。     

Effect of interface characteristics on the influence coefficients of an embedded circular footing under horizontal and moment loading

By means of a semi-analytical FE approach an embedded circular footing under monotonic horizontal and moment loading is studied. In a non-homogeneous soil whose shear modulus is characterized by a power law variation with depth, horizontal, rocking and coupled modes of displacement, expressed in terms of influence factors are thoroughly examined. The exponent α that controls the shape of the stiffness variation with depth is termed shear modulus factor. Surface influence coefficients are considered for the situations where the interface between the soil and the footing is either perfectly rough or perfectly smooth. First, results of semi-analytical FE analysis in the case of rough footing are established and compared with those of another numerical method. Results of comparison show good agreement. Then, for different values of α the surface influence coefficients are presented for an embedded footing in perfect smooth contact with soil. The metacentre is referred to as the depth at which there is no coupling between the sliding and the rocking modes of footing deformations. Expressions for location and horizontal influence coefficient corresponding to this particular depth are developed and their variations with α examined. The paper finishes by showing the effect of interface conditions on the soil normal stresses developed beneath the embedded circular footing for the case of loading applied at the footing top.     

柴达木盆地油气资源战略调查成果与下步工作重点

柴达木盆地是中国七大含油气陆相盆地之一,油气资源总量丰富,勘探潜力巨大.柴达木盆地油气资源战略调查及评价项目研究工作开展2年以来,取得了重要的成果和认识:德令哈断陷内大面积分布中-下侏罗统烃源岩;盆地东部石炭系具有生烃能力;盆地北缘东段红山地区地震勘探采集到较好品质的资料;狮子沟地区天然地震勘探得到初步成果;综合应用地震、钻井等资料,确定了狮子沟构造的深层构造.下一步工作的重点是进一步加强盆地东部石炭系评价的力度,深化狮子沟、红山、德令哈等地区深层构造的研究及圈闭资源量评价工作.     

Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition

Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness, joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under constant normal load conditions. Shear stress–shear displacement and normal displacement–shear displacement of artificial joint specimens are simulated using the proposed numerical model at constant normal load condition (CNL). The results indicate the capability of the model for simulating rock joints behavior in both strength and deformation field. Although the numerical model has been developed for simulating the behavior of artificial joints, the concept of the method can also be used for natural rock joints.     

梁桥搁置长度的计算方法比较

梁桥的搁置长度是在桥梁上下部结构之间产生大的相对变位时，为防止上部结构脱落而需要确保的梁端到下部结构边缘的距离。通过修改桥梁参数，对计算梁桥搁置长度的反应谱法和静力法进行对比，分析2种方法产生差异的原因。研究表明，静力法不需考虑桥墩延性系数的变化和阻尼系数的影响，计算简单，适合于设计使用。     

Seismic Hazard Assessment for the Taiwan Region on the Basis of Recent Strong-Motion Data and Prognostic Zonation of Future Earthquakes

The paper describes an integrated approach to seismic hazard assessment, which was applied for the Taiwan region. First, empirical modelsfor ground motion estimation in the region were obtained on the basisof records from recent (1993-1999) earthquakes. The databaseincludes strong-motion data collected during the recent Chi-Chiearthquake (M=7.6, 21 September 1999) and large (M=6.8)aftershocks. The ground-motion database was also used for evaluationof generalised site amplification functions for typical soil classes(B, C and D). Second, the theoretical seismic catalogue (2001–2050)for the Taiwan region had been calculated using the 4D-model(location, depth, time) for dynamic deformation of the Earth' crustand 5D-model (location, depth, time, magnitude) for seismic process.The models were developed on the basis of available geophysical andgeodynamic data that include regional seismic catalogue. Third, theregion & site & time-dependent seismic analysis, which is basedon schemes of probable earthquake zones evaluated from the theoreticalcatalogue, regional ground motion models, and local site responsecharacteristics, has been performed. The seismic hazard maps arecompiled in terms of Peak Ground Acceleration (PGA) and ResponseSpectra (RS) amplitudes. The maps show distribution of amplitudesthat will not be exceeded with certain probability in condition oftypical soil classes during all possible earthquakes that may occur inthe region during time period of 2003–2025. The approach allowsintroducing new parameter that describes dependency of seismichazard on time, so-called 'period of maximum hazard'. Theparameter shows the period, during which every considered sitewill be subjected by the maximum value of ground motioncharacteristic (PGA or RS).     

我院近景摄影测量的回顾与展望

本文在全面阐述我院十多年来开展近景摄影测量应用研究和主要成果的基础上，提出了今后主要工作内容和发展方向。