Soil–pile–structure interaction: experimental outcomes from shaking table tests

An effective way to study the complex seismic soil‐structure interaction phenomena is to investigate the response of physical scaled models in 1‐g or n‐g laboratory devices. The outcomes of an extensive experimental campaign carried out on scaled models by means of the shaking table of the Bristol Laboratory for Advanced Dynamics Engineering, University of Bristol, UK, are discussed in the present paper. The experimental model comprises an oscillator connected to a single or a group of piles embedded in a bi‐layer deposit. Different pile head conditions, that is free head and fixed head, several dynamic properties of the structure, including different masses at the top of the single degree of freedom system, excited by various input motions, e.g. white noise, sinedwells and natural earthquake strong motions recorded in Italy, have been tested. In the present work, the modal dynamic response of the soil–pile–structure system is assessed in terms of period elongation and system damping ratio. Furthermore, the effects of oscillator mass and pile head conditions on soil–pile response have been highlighted, when the harmonic input motions are considered. Copyright © 2015 John Wiley & Sons, Ltd.     

Permanent earthquake‐induced actions in buried pipelines: Numerical modeling and experimental verification

Buried pipelines are often constructed in seismic and other geohazard areas, where severe ground deformations may induce severe strains in the pipeline. Calculation of those strains is essential for assessing pipeline integrity, and therefore, the development of efficient models accounting for soil‐pipe interaction is required. The present paper is aiming at developing efficient tools for calculating ground‐induced deformation on buried pipelines, often triggered by earthquake action, in the form of fault rupture, liquefaction‐induced lateral spreading, soil subsidence, or landslide. Soil‐pipe interaction is investigated by using advanced numerical tools, which employ solid elements for the soil, shell elements for the pipe, and account for soil‐pipe interaction, supported by large‐scale experiments. Soil‐pipe interaction in axial and transverse directions is evaluated first, using results from special‐purpose experiments and finite element simulations. The comparison between experimental and numerical results offers valuable information on key material parameters, necessary for accurate simulation of soil‐pipe interaction. Furthermore, reference is made to relevant provisions of design recommendations. Using the finite element models, calibrated from these experiments, pipeline performance at seismic‐fault crossings is analyzed, emphasizing on soil‐pipe interaction effects in the axial direction. The second part refers to full‐scale experiments, performed on a unique testing device. These experiments are modeled with the finite element tools to verify their efficiency in simulating soil‐pipe response under landslide or strike‐slip fault movement. The large‐scale experimental results compare very well with the numerical predictions, verifying the capability of the finite element models for accurate prediction of pipeline response under permanent earthquake‐induced ground deformations.     

5•12汶川地震中山区公路桥梁震害及启示

桥梁结构的振动特性受场地条件及土—结相互作用影响显著,为提高桥梁结构的抗震性能,减少因结构破坏而产生的经济损失,进一步开展考虑场地土体非线性以及土—结相互作用对桥梁结构地震反应影响的研究工作十分必要。本文以一典型桥梁结构为例,着重介绍了美国太平洋地震工程研究中心基于性能的桥梁有限元模拟平台BridgePBEE应用中所涉及的地震动选取、桥梁结构建模、土体本构选择以及基于构件的桩—土—桥梁结构体系损伤评估方法,为研究震后桥梁结构经济损失分析方法提供可行性方案。     

庐枞火山盆地深部岩石与成矿过程

黄铁矿-硬石膏-磁铁矿矿石为典型矿石的金属矿床产于长江中下游中生代火山盆地,庐枞火山岩盆地。丰富的铁矿和黄铁矿床,主要分布在火山岩和潜火山岩里,同时也分布于盆地周边。火山岩石主要是钾玄岩-粗安岩-粗面岩组合。在深部,与它们的成分对应的岩浆岩石是碱性辉长岩-辉石二长岩-正长岩组合,如缺口辉长岩,杨山地区的辉石正长岩。火山岩和深部的辉长岩-二长岩-正长岩都经历了多次水热活动。黄铁矿-硬石膏-磁铁矿矿床主要伴随两套蚀变,即,火山岩石的大面积深色蚀变(硬石膏-辉石-长石蚀变岩)和浅色蚀变(硅化泥化)。在二长-正长岩与火山岩石的接触带,有强烈的类云英岩石(电气石-石英-云母组合)。在缺口辉长岩里,曾经发现大量磁铁矿脉(磁铁矿-方柱石-方钠石-石榴石组合)。在杨山和马口地区,正长岩里的铁矿是辉石钾长石磁铁矿组合及阳起石-磷灰石-磁铁矿组合。二长-正长岩体在盆地里广泛分布,在大范围内是几乎是层状的。调查研究表明:火山盆地底部辉长岩-二长岩-正长岩组合与铁矿有关。盆地里深部岩石和成矿作用存在有垂直分布特性。上面是喷发岩石,及潜火山岩石,下面是深部的碱性辉长岩-二长岩-正长岩杂岩体。中间有过渡带,岩墙岩席带。上面是与钾玄岩-粗安岩层和潜火山岩石里赋存的磁铁矿和黄铁矿床,下面有产于碱性辉长岩-二长岩-正长岩里也有铁矿化。蚀变岩石地质年代的初步研究发现:罗河铁矿的深部钠长石化岩石,与马口铁矿附近的正长岩石的地质年代接近(110～119Ma)。事实说明,在火山岩和潜水火山岩石里成矿作用和深部岩浆岩里成矿作用可能是同时发生的。20～435℃条件下正长岩石与水的反应动力学实验表明,在400℃左右时正长岩最容易被溶解。正长岩与水反应后,也会形成一个携带金属的流体。水岩相互作用实验提供了认识深部岩石性质的依据,有利于理解对深部的地球物理探测结果。     

剪切带的流体－岩石相互作用

作为大陆岩石圈中的应变局部化带，剪切带中一般都渗透着大量流体。流体的来源与剪切带所处的构造背景、流变域和水文条件有关，而剪切带中流体的流动则受岩石的渗透率、孔隙度、孔隙性质、流体的扩散和渗透能力、环境的温压条件、应力或载荷的梯度等因素所制约。剪切带中流体的成分、通量及赋存状态或流动方式，直接影响着岩石的流变。由应变局部化及力学失稳所引起的化学不平衡和由流体与岩石的相互作用，使剪切带岩石的矿物成分和化学成分发生调整，其变异程度取决于原岩的性质、剪切的温压条件和流体的成分及通量等。由于流体的渗透流动和流体与岩石的相互作用使剪切带的体积有所变化，体积变化过程是一种自组织行为。较大的体积亏损，意味着剪切带中渗透过大量的流体，这对剪切带的流变行为、化学行为和成矿作用都有深刻的影响。     

First results from the North Iceland experiment

Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system.     

Nonlinear Dynamic Behaviors of A Floating Structure in Focused Waves

Floating structures are commonly seen in coastal and offshore engineering. They are often subjected to extreme waves and, therefore, their nonlinear dynamic behaviors are of great concern. In this paper, an in-house CFD code is developed to investigate the accurate prediction of nonlinear dynamic behaviors of a two-dimensional (2-D) box-shaped floating structure in focused waves. Computations are performed by an enhanced Constrained Interpolation Profile (CIP)-based Cartesian grid model, in which a more accurate VOF (Volume of Fluid) method, the THINC/SW scheme (THINC: tangent of hyperbola for interface capturing; SW: Slope Weighting), is used for interface capturing. A focusing wave theory is used for the focused wave generation. The wave component of constant steepness is chosen. Comparisons between predictions and physical measurements show good agreement including body motions and free surface profiles. Although the overall agreement is good, some discrepancies are observed for impact pressure on the superstructure due to water on deck. The effect of grid resolution on the results is checked. With a fine grid, no obvious improvement is seen in the global body motions and impact pressures due to water on deck. It is concluded that highly nonlinear phenomena, such as distorted free surface, large-amplitude body motions, and violent impact flow, have been predicted successfully.     

Effects of backfill on seismic behavior of rectangular tanks

The reliability and/or stability of the lifeline structures against failure under seismic loads are of critical concern, and must be studied carefully. Therefore, the main objective of this paper is to demonstrate the commonly encountered backfill effects on the dynamic response of rectangular tanks. However, only the exterior wall of the tank which interacts with both the backfill and fluid is tackled, as each part of the structure shows considerable differences in terms of both the load bearing mechanisms and the geometrical and positional differences. Finite element analyses are employed, taking into consideration the fluid-wall-backfill interaction. The analyses are conducted to observe whether or not both backfill and wall behavior can be affected by variation of the internal friction angle. For that purpose, some comparisons are made on vertical displacements of the backfill, roof displacements, stress responses, etc., by means of internal friction angle variations of the backfill from 25° to 40°. Consequently, it is observed that the variations on maximum vertical displacements are affected considerably. In contrast, the maximum stress responses are affected partially. However, the inertial effects of the backfill show that pseudo-static approximations may be insufficient to understand the dynamic behavior of the backfill-wall-fluid system.     

Analysis and prediction of vortex-induced vibrations of variable-tension vertical risers in linearly sheared currents

Many studies have tackled the problem of vortex-induced vibrations (VIV) of a vertical riser with a constant tension and placed in uniform currents. In this study, attention is focused on the cross-flow VIV modelling, time-domain analysis and prediction of variable-tension vertical risers in linearly sheared currents. The partial-differential equation governing the riser transverse motion is based on a flexural tensioned-beam model with typical pinned-pinned supports. The hydrodynamic excitation model describing the modulation of lift force is based on a distributed van der Pol wake oscillator whose nonlinear equation is also partial-differential due to the implementation of a diffusion term. The variation of empirical wake coefficients with system parameters and the water depth-dependent Reynolds number is introduced. Based on the assumed Fourier mode shape functions obtained by accounting for the effect of non-uniform tension, the Galerkin technique is utilized to construct a low-dimensional multi-mode model governing the coupled fluid-riser interaction system due to VIV. Numerical simulations in the case of varying sheared flow profiles are carried out to systematically evaluate riser nonlinear dynamics and highlight the influence of fluid-structure parameters along with associated VIV aspects. In particular, the effects of shear and tensioned-beam (tension versus bending) parameters are underlined. Some comparisons with published experimental results and observations are qualitatively and quantitatively discussed. Overall parametric analysis and prediction results may be worthwhile for being a new benchmark against future experimental testing and/or numerical results predicted by an alternative model and methodology.