Alpine ocean seafloor spreading and onset of pelagic sedimentation: new radiolarian data from the Chenaillet-Montgenèvre ophiolite (French-Italian Alps)

Radiolarians of Middle Jurassic age (tentatively middle Bathonian) provide the first direct age determination from oceanic sediments associated with the Chenaillet-Montgenèvre ophiolite (Piemonte zone, French-Italian Alps). This datum obtained from radiolarites of the Lago Nero- Replatte thrust sheet is older than those previously established on ophiolite sedimentary covers from this segment of the western Alps. It also shows that Lago Nero-Replatte basal radiolarites are anterior to the youngest intrusives from the overlying Chenaillet s.s. thrust sheet. This chronological relationship implies either a late seafloor spreading-related magmatic activity in places younger than adjacent initial pelagic sedimentation, or more likely that the Lago Nero-Replatte and the Chenaillet s.s. thrust sheets are distinct and distant pieces of lithosphere that were eventually stacked together: the Lago Nero-Replatte unit was trapped within the accretionary wedge while the Chenaillet s.s., of a younger age and in a more distal position with regards to the European margin, was obducted. Regionally, the Lago Nero-Replatte sediments appear to be coeval to other Bathonian supraophiolitic radiolarites exposed in the western Alps. These results strengthen the Bathonian correlation of widespread seafloor spreading in both western Tethys and the central Atlantic ocean.     

Validation of Practice Oriented Models and Influence of Soil Stiffness on Lateral Pile Response Due to Kinematic Loading

Earthquakes usually cause both inertial and kinematic loading of pile foundations. Inertial loading and lateral pile response can be predicted to a certain extent by lateral pile load tests for important engineering projects. However, there is no accepted in situ assessment method for pile behavior due to kinematic loading. Therefore, it is important for geotechnical engineering practice to validate the practice oriented models and examine the influence of soil strength parameters on the performance of kinematically loaded piles due to lateral spreading. For this purpose, a well-documented case of full-scale lateral spreading test conducted at Port of Tokachi in Japan by Ashford et al. (2006 Ashford , S. A. , T. Juirnarongrit , T. Sugano , and M. Hamada . 2006 . Soil-pile response to blast-induced lateral spreading. I: Field test . Journal of Geotechnical and Geoenvironmental Engineering 132 ( 2 ): 152 – 162 . [Google Scholar]) is selected as a primary reference in terms of test data and site conditions. Four p-y analyses are performed using a special purpose software based on finite difference technique. The first two investigate the employment of different p-y curves suggested in the literature. The third one investigates the influence of variations in internal friction angle and undrained shear strength. In the fourth analysis, liquefied shear strength and residual shear strength approaches are utilized for the liquefiable layers and their effects are investigated. In all analyses, mobilized lateral pressures in non-liquefied layers are also scrutinized. The results of the analyses are discussed and compared with the measured values in the field. Finally, conclusions are given based on the analyses and discussions.     

Characterization of mixing and spreading in a bounded stratified medium

Matheron and de Marsily [Matheron M, de Marsily G. Is the transport in porous media always diffusive? A counter-example. Water Resour Res 1980;16:901–17] studied transport in a perfectly stratified infinite medium as an idealized aquifer model. They observed superdiffusive solute spreading quantified by anomalous increase of the apparent longitudinal dispersion coefficient with the square root of time. Here, we investigate solute transport in a vertically bounded stratified random medium. Unlike for the infinite medium at asymptotically long times, disorder-induced mixing and spreading is uniquely quantified by a constant Taylor dispersion coefficient. Using a stochastic modeling approach we study the effective mixing and spreading dynamics at pre-asymptotic times in terms of effective average transport coefficients. The latter are defined on the basis of local moments, i.e., moments of the transport Green function. We investigate the impact of the position of the initial plume and the initial plume size on the (highly anomalous) pre-asymptotic effective spreading and mixing dynamics for single realizations and in average. Effectively, the system “remembers” its initial state, the effective transport coefficients show so-called memory effects, which disappear after the solute has sampled the full vertical extent of the medium. We study the impact of the intrinsic non-ergodicity of the confined medium on the validity of the stochastic modeling approach and study in this context the transition from the finite to the infinite medium.     

几何缺陷对拱结构动力稳定性的影响

分析了外激励下几何缺陷对拱结构动力稳定性的影响。推导了拱结构边界确定而结构本身节点坐标偏差随机且指数相关时的条件相关矩阵,分解得到几何缺陷的分布方式和大小。从非线性运动方程出发,分别得出了周期荷载作用下非线性刚度矩阵可线性化,非周期荷载作用下同时考虑几何、材料非线性的Lyapunov指数计算方法。最后以一圆弧拱为例分别对周期荷载、阶跃荷载、脉冲荷载及地震荷载作用下几何缺陷的影响进行了数值分析。结果表明周期激励作用下拱结构存在动力失稳频域;在不同分布方式几何缺陷中动力稳定性对与屈曲模态相似的缺陷最为敏感。     

Major advances in liquefaction research by laboratory tests compared with in situ behavior

Major advances in liquefaction research in the laboratory to understand the basic mechanisms in comparison with in situ behavior during previous earthquakes are reviewed. Then, several issues related to liquefaction triggering and post-liquefaction deformation are selected for further discussion in the author's perspective. These include effects of fines associated with aging, effects of gravels, effects of initial shear stress, and lateral spreading and lateral flow due to void redistribution. It has been disclosed that a quite a few issues still remain to be settled in evaluating liquefaction onset and post-liquefaction deformations for improving engineering design, particularly for Performance-Based Design (PBD).     

Response of a pile group behind quay wall to liquefaction-induced lateral spreading:a shake-table investigation

The response of pile foundations near a quay wall under liquefaction-induced lateral spreading remains a complex problem. This study presents the results of a shake-table test on a 2×2 pile group behind a sheet-pile quay wall that was subjected to lateral spreading. The quay wall was employed to trigger liquefaction-induced large lateral ground deformation. The discussions focus on the behavior of the pile and the soil and on the bending moment distributions within the group pile and the restoring force characteristics at the superstructure. Overall, the piles exhibited apparent pinning effects that reduced soil deformation. In addition, the rear-row piles near the quay wall experienced larger bending moments than did the front-row piles, indicating significant pile group effects. The tests showed that lateral spreading could be a primary cause of larger monotonic deformations and bending moments. It can also be concluded that the monotonic bending moments were significantly decreased due to the presence of slow soil flow. The stiffness at the superstructure was reduced because of accumulated excess pore pressure before liquefaction, and it was recovered during lateral spreading. The present study further enhances current understanding of the behavior of low-cap pile foundations under lateral spreading.     

一种改进的林火蔓延模型及其实现

为了研究林火蔓延的动态模拟问题,结合元胞自动机原理,对现有的林火蔓延数学模型进行改进,提出一种新的模拟林火蔓延模型。该模型充分表达了可燃物类型、温度、湿度、坡度、风速和风向等林火蔓延影响因子在元胞空间中的作用形式,通过求解出燃烧元胞向摩尔(Moore)型邻域中八个方向元胞的林火蔓延速度,来确定元胞状态演变规则函数。最后,利用地理信息系统二次开发技术将该模型表达成计算机算法,实现了不同条件下的林火行为的仿真模拟。     

滑模摊铺机在混凝土路面施工中的应用

泰曲路(泰安-曲阜)改造工程三合同段的混凝土路面采用滑模摊铺机进行施工,滑摸摊铺机在不用固定模板的情况下可以连续完成摊铺、振动、刮平、成形、抹光以及打设传力杆等工序,工艺先进,具有一定的推广价值。     

A Numerical Model for Edge Waves on A Compound Slope

An edge wave is a kind of surface gravity wave basically travelling along a shoaling beach. Based on the periodic assumption in the longshore direction, a second order ordinary differential equation is obtained for numerical simulation of the cross-shore surface elevation. Given parameters at the shoreline, a cross-shore elevation profile is obtained through integration with fourth-order Runge-Kutta technique. For a compound slope, a longshore wavenumber is obtained by following a geometrical approach and solving a transcendental equation with an asymptotic method. Numerical results on uniform and compound sloping beaches with different wave periods, slope angles, modes and turning point positions are presented. Some special scenarios, which cannot be predicted by analytical models are also discussed.     

基于球体几何关系的球标靶特征提取算法

利用“球面上任意3点确定的平面与球的相交曲线为圆,该截面圆心与球心的连线(球截面圆心法线)垂直于圆平面”的几何关系,提出一种基于球体几何关系的球标靶特征提取算法。通过对球标靶点云构建多组截面圆,对截面圆设定约束条件,构造球心到球截面圆心法线距离平方和的目标函数,以此目标函数最小为条件求解球标靶的球心坐标。通过实验比较本文方法、最小二乘方法、整体最小二乘方法、加权整体最小二乘方法和稳健加权整体最小二乘方法对球标靶的处理效果,结果表明本文方法具有较高的准确性和稳健性。