刚性桩复合地基抗震计算的一种简化方法

应用广泛的刚性桩复合地基目前其抗震设计还没有足够简便的计算方法,工程设计中对其抗震设计往往予以回避。本文首先介绍了笔者之前的一种对刚性桩复合地基进行抗震分析的拟静力方法,进而对其中有关上部结构惯性作用对桩身内力影响的计算部分进行了进一步简化,之后通过多种设计工况及实际土层条件下的计算对比,验证了改进方法的可行性。还对上部结构惯性作用的影响深度、地基分层对桩身内力的影响等进行了讨论。     

Nonlinear bend stiffener analysis using a simple formulation and finite element method

Flexible marine risers are commonly used in deepwater floating systems.Bend stiffeners are designed to protect flexible risers against excessive bending at the connection with the hull.The structure is usually analyzed as a cantilever beam subjected to an inclined point load.As deflections are large and the bend stiffener material exhibits nonlinear stress-strain characteristics,geometric and material nonlinearities are important considerations.A new approach has been developed to solve this nonlinear problem.Its main advantage is its simplicity;in fact the present method can be easily implemented on a spreadsheet.Finite element analysis using ABAQUS is performed to validate the method.Solid elements are used for the bend stiffener and flexible pipe.To simulate the near inextensibility of flexible risers,a simple and original idea of using truss elements is proposed.Through a set of validation studies,the present method is found to be in a good agreement with the finite element analysis.Further,parametric studies are performed by using both methods to identify the key parameters and phenomena that are most critical in design.The most important finding is that the common practice of neglecting the internal steel sleeve in the bend stiffener analysis is non-conservative and therefore needs to be reassessed.     

双重眼壁台风大风降水对比分析

通过利用多普勒雷达图、OLR日平均场、环境场和比湿场等资料对7514(ELSIE)、7908(HOPE)、0313(Dujuan)号台风进行对比诊断分析。结果表明3个双重眼壁台风都有规则和紧凑的螺旋云带，外围的云带范围小、副高强盛、登陆前850hPa西南风没加强等等，都是造成台风风大而且影响范围广，降水量偏少的原因；OLR场分布与降水场分布的同时对应关系很好，OLR低中心最终没移至陆上，因此陆上降水偏少；台风OLR低中心移向陆地的地点与强降水中心基本相符；登陆时台风中心比湿值、等值线的梯度越大、移速的越慢，则降水时间越长、雨强越大。降水越集中。     

Confidence level-based robust design of cantilever retaining walls in sand

Reliability-based geotechnical design entails accurate sample statistics (i.e., mean and standard deviation or coefficient of variation, denoted herein as cov) of soil parameters. However, the cov values of soil parameters are difficult to determine with confidence due to the limited availability of high-quality data and inherent spatial variability. As a result, estimated cov values of soil parameters can vary within a wide range, which can result in overdesign or underdesign. In this paper, a confidence level (CL)-based method is proposed to address the problem of geotechnical design in the face of uncertainty. Here, CL is a measure of confidence that the target reliability index will be satisfied in the face of uncertainty in the estimated cov. The proposed method is demonstrated through the design of a cantilever retaining wall in sand. To ensure the practicality of the proposed method, a simplified approach was developed, which requires little extra effort over that required for traditional reliability-based design. To develop the CL-based method further, a metric called the “true reliability index” is proposed, which is the actual reliability index in the face of the uncertainty in the estimated parameter statistics (mainly cov).     

On Plane Symmetric Domain Walls and Cosmic Strings in Bimetric Theory

Plane symmetric thick domain walls and cosmic strings are considered in Rosen's (General Relativity and Gravitation 4, 435, 1973) bimetric theory of gravitation. It is shown that, in this theory, thick domain walls and cosmic strings do not exist. Hence, the vacuum solutions in both the cases are presented. PACS No.:98.80     

机载LiDAR数据大区域城墙自动提取

针对传统测量耗时耗力且难以获取古城墙精确侧面信息的缺点,该文提出将LiDAR技术应用于古城墙数字存档工作。提出基于城墙断面的"横向探测—纵向探测"城墙顶部和侧面点云提取算法,以及"城墙待选区提取—断面格网构建—顶部侧面点云提取"技术方案,有效地克服城墙特殊的空间形态和复杂的点云结构所带来的点云分割困难,实现大区域机载LiDAR数据城墙点云自动提取,解决了利用机载LiDAR进行古城墙数字存档的关键技术问题。基于南京明城墙的实验结果表明,该算法对于大区域古城墙提取切实可行有效。     

新疆伊犁某移民新区黄土滑坡成因分析及防治对策

移民新区东坡滑坡发育于小吉尔格朗河东岸二级残留阶地,坡面中部,坡体平均坡度35°,均为小型土质滑坡。因滑坡剪出口位置较高,滑动后,多为快速滑动,极易成灾,对沙尕村移民新区构成较大威胁。通过研究发现,滑坡主要受地形地貌、地层岩性、地质构造等原生地质条件控制,受大气降水、地下水、地震、人类工程活动等外界条件影响,其中大气降水和地下水为滑坡成因的主要影响因素。结合滑坡成因及影响因素,提出抗滑桩板墙和挡土墙相结合并辅以排水措施的防治方案,对该地区的滑坡防治具有较好的指导意义。     

On numerical computation of impedance functions for rigid soil-structure interfaces embedded in heterogeneous half-spaces

We present fully-discrete procedures for computing the impedance functions of rigid massless soil-structure interfaces that are embedded in arbitrarily heterogeneous half-spaces. The finite element method (FEM) is used for obtaining the wave responses of (visco-)elastic half-spaces truncated by Perfectly Matched Layers (PMLs), which provide the wave absorbing boundary conditions. The devised FEM-PML approach is verified in both time and frequency domains by using various benchmark solutions. Requirements on the prescribed input excitations for obtaining accurate impedances in the time domain as well as the relative computational cost of time- and frequency domain solutions are investigated. Accuracy of the implemented PMLs in extracting the impedance functions is also examined in comparison to Lysmer–Kuhlemeyer dashpots; and it was found that this simplified boundary treatment is generally inadequate. The utility of the proposed method is demonstrated by extracting the impedance matrix of rectangular and circular voids embedded in a linearly stiffening half-space. Impedance functions for such complex soil-structure systems are shown to be highly coupled and frequency-dependent due to wave reflections and interference caused by the soil heterogeneity and interface geometry. Fully discrete approaches, such as those proposed herein, are necessary to adequately capture these effects.     

A new excavation analysis method for slope design using discrete fracture network based polyhedral modelling

A method to analyse potential excavation geometries, termed excavation isoplethogram, has previously been proposed for use in civil or mining engineering. The results are typically presented in the form of a contour plot identifying orientations of proposed excavation planes that may lead to large volumes (or masses) of unstable blocks and wedges. In this paper, a novel algorithm is proposed to utilise the probabilistic discrete fracture network approach to quantify the risk associated with various slope designs. The method is applied using open cut mine data in order to demonstrate its potential for decision making in mine design and operations.     

山东邹城雨山村西南滑坡灾害特征与防治方案

山东邹城雨山村西南滑坡在20世纪50年代发生过滑动,导致部分农田被毁。该滑坡为浅层土质滑坡,滑体成分主要为含碎石粉质粘土,滑带位于含碎石粉质粘土层与基岩接触带,由于人工切坡,滑带在滑坡前缘局部已揭露,滑床为下伏强风化闪长岩。近年来,频繁的人类工程活动导致该滑坡存在重新滑动的可能,为消除该地质灾害隐患,采取了悬臂式挡墙支挡和截排水结合的防治方案,达到了治理效果。