Influence of a coarse interlayer on seawater intrusion and contaminant migration in coastal aquifers

Vertical 2D slice laboratory experiments were carried out in homogenous and layered sand tanks to elucidate the effects of a highly permeable (coarse‐grained sand) interlayer on seawater intrusion and transport of contaminants to a coastal sea. Tidal fluctuations produced oscillations in the seawater–freshwater transition zone, fluctuations of the contaminant infiltration rate and a zigzag contaminant plume outline. The seawater wedge became discontinuous at the (vertical) edges of the interlayer because of increased lateral movement of the seawater–freshwater interface within the interlayer. The contaminant plume formed a tail within the interlayer depending on the tidal stage, and similar to the wedge, its movement was accentuated. A simple analytical model that neglected vertical flow reliably predicted steady‐state seawater intrusion into the coastal aquifer. Numerical modeling was used to gain insight into the groundwater hydrodynamics and contaminant migration. The numerical results confirmed the experimental findings, i.e. that a highly permeable interlayer can provide a rapid transit path for contaminants to reach the seaward boundary and that the interlayer amplifies the effects of tidal fluctuations, resulting in wider transition zones for the seawater wedge and contaminant plume. Numerical simulations further showed that, with increasing interlayer hydraulic conductivity, the maximum seawater intrusion distance inside the interlayer increases approximately linearly. For the fixed‐head contaminant injection condition used, the model showed that contaminant infiltration increases approximately logarithmically with increasing interlayer hydraulic conductivity (other factors held fixed). Copyright © 2013 John Wiley & Sons, Ltd.     

Autogenic avulsion,channelization and backfilling dynamics of debris‐flow fans

Alluvial fans develop their semi‐conical shape by quasi‐cyclic avulsions of their geomorphologically active sector from a fixed fan apex. On debris‐flow fans, these quasi‐cyclic avulsions are poorly understood, partly because physical scale experiments on the formation of fans have been limited largely to turbidite and fluvial fans and deltas. In this study, debris‐flow fans were experimentally created under constant extrinsic forcing, and autogenic sequences of backfilling, avulsion and channelization were observed. Backfilling, avulsion and channelization were gradual processes that required multiple successive debris‐flow events. Debris flows avulsed along preferential flow paths given by the balance between steepest descent and flow inertia. In the channelization phase, debris flows became progressively longer and narrower because momentum increasingly focused on the flow front as flow narrowed, resulting in longer run‐out and deeper channels. Backfilling commenced when debris flows reached their maximum possible length and channel depth, as defined by channel slope and debris‐flow volume and composition, after which they progressively shortened and widened until the entire channel was filled and avulsion was initiated. The terminus of deposition moved upstream because the frontal lobe deposits of previous debris flows created a low‐gradient zone forcing deposition. Consequently, the next debris flow was shorter which led to more in‐channel sedimentation, causing more overbank flow in the next debris flow and resulting in reduced momentum to the flow front and shorter runout. This topographic feedback is similar to the interaction between flow and mouth bars forcing backfilling and transitions from channelized to sheet flow in turbidite and fluvial fans and deltas. Debris‐flow avulsion cycles are governed by the same large‐scale topographic compensation that drives avulsion cycles on fluvial and turbidite fans, although the detailed processes are unique to debris‐flow fans. This novel result provides a basis for modelling of debris‐flow fans with applications in hazards and stratigraphy.     

Investigation of directional hydraulic fracturing based on true tri-axial experiment and finite element modeling

The initiation and propagation of directional hydraulic fracturing (DHF) was investigated based on true tri-axial experiment and finite element modeling. The influences of notch angle, notch length and injection rate on the DHF were investigated. The initiation and propagation of DHF was modeled by a 3D nonlinear finite element method. A comparison between experimental investigation and numerical modeling results indicates that there is a good correlation between unbalanced force (UF) and fracturing. UF can be used to predict the hydraulic fracture initiation and propagation.     

飞机下投探空在台风探测中的应用

在海洋探测方面,利用飞机进行下投探空拥有巨大的潜力去弥补全球高空探测网的空白。台风形成后,飞机飞入台风中心或绕台风飞行,下投配有全球卫星定位(GPS)装置的"探空仪",探空仪上安装有温度、气压、湿度传感器,通过GPS定位测风,对台风实施立体观测。多年来,飞机下投探空能够充分掌握台风的整体气象要素分布结构,从而提高对台风强度和移动路径等预报的准确性,飞机下投探空在国际上已经从科学试验转变成业务应用,并且形成新型的探测技术——目标观测。本文主要总结了国际上利用飞机搭载下投式探空仪进行台风探测的发展历程,为我国开展下投探空,特别是台风监测提供可借鉴的经验。     

“GIS工程设计”的实验教学模式研究

"GIS工程设计"的教学目的是培养学生GIS设计的综合能力,因此,该课程的实践教学很重要。本文提出将"GIS工程设计"的实践教学体系分为基础实验和综合设计两部分,研究实践教学安排,改善实习的考核体系和辅助教学方法,形成一套高效的实践教学模式。     

岩石中的压力影形成的实验观测研究

野外地质观察发现,在大陆地壳变质岩中可以广泛观察到围绕一个大的单晶或者硬质点的两端区域填充低粘度相物质形成的压力影。为了定量研究岩石材料中压力影的形成条件,本文利用高精度Paterson气体介质变形装置,对含有刚性球的圣卡罗橄榄石和洋中脊玄武岩(MORB)的混合物圆柱型样品进行了高温高压扭转变形试验。变形实验前样品的初始熔融均匀分布,比例为φ≈0.05,变形试件尺寸为D8.9mm×L5.5mm,内含8粒直径约1mm的刚性球。扭转变形试验温度为1473K,围压为300MPa,应变率为γ≈1×10~(-4)s~(-1),最大剪切变形为γ≈4。实验结果表明,岩石受到扭转力的作用产生变形之后,当局部剪切应变达到γ≈1时,可以在刚性球周围形成熔融富集带和熔融贫乏带,即压力影构造,围绕刚性球对称分布。由于熔融分布的不均一性,富集带熔融比例上升,最高可以达到φ_(high)=0.1~0.3,熔融贫乏带熔融比例下降,含量为φ_(low)=0.01~0.02。由于刚性球对其周围的压力分布的扰动区域大约为刚性球的尺度范围,因此,在离开刚性球一定距离后,熔融趋于均匀分布。     

不同近岸河床组成情况下岸坡崩塌试验

在弯道水槽中开展6组试验,分别用非黏性土及黏性土填筑河床,研究相同水力作用下近岸河床组成对黏性岸坡崩塌的影响规律。研究发现,在试验给定的岸坡及河床组成情况下,非黏性河床凹冲凸淤且总体表现为淤积,近岸河床及凹岸岸坡冲刷强度大,凸岸附近床面上泥沙掺混较明显;黏性河床及凹岸岸坡均被冲刷,河床主流区冲刷强度比近岸河床及凹岸岸坡大。相较于黏性河床,非黏性河床近凹岸处较易冲刷,水流结构重新调整,凹岸坡脚处水流流速及紊动能可增至2倍左右,环流强度可增至11倍,加速了岸坡崩塌及崩塌体的分解输移;非黏性河床近凹岸坡脚处变形以及凹岸岸坡崩塌量均相对较大,岸坡崩塌强度为河床淤积强度的2~4倍,崩塌物质可充分补给河床的泥沙来源;经水力冲刷后非黏性河床组成情况下形成的河道滩槽高差相对较小,河道横断面相对宽浅。     

Different thermal preferences for brooding and larval dispersal of two neighboring shrimps in deep‐sea hydrothermal vent fields

Temperature is an important factor affecting the distributions and life‐history traits of marine animals. Deep‐sea hydrothermal vents are suitable environments to examine ecologic differences related to temperature, due to the steep temperature gradients around the vents. Rearing experiments under various temperature conditions (5–30 °C) at atmospheric pressure demonstrated a difference in thermal effects on egg hatching and larva in two co‐occurring, vent‐associated alvinocaridid shrimps – the peripherally distributed Alvinocaris longirostris and the centrally distributed Shinkaicaris leurokolos. The duration before hatching became shorter as temperature increased, while the maximum hatching rate occurred at higher temperatures in S. leurokolos (10–20 °C) than in A. longirostris (10 °C). Hatched larvae of both species were negatively buoyant, and larva with normal abdominal length could actively swim and stay suspended in the mid‐ or surface water layers of the culture plates under our experimental conditions. However, no larvae settled or metamorphosed into juveniles under the rearing conditions used in this study. Larvae with shortened abdomens occurred under most of the experimental conditions, although they were less frequent at 10 °C in A. longirostris and 20 °C in S. leurokolos. The maximum survival periods at these temperatures were 88 days in A. longirostris and 30 days in S. leurokolos. These characteristics may cause differences in the distributional ranges of the two species. The present results indicate that temperature is an important factor controlling life‐history traits of vent shrimps.     

基于五种油源的中重度风化溢油的常规鉴定指标的应用效果评估

本文利用采集于我国三大油田的五种原油样品开展了长达210天的溢油风化模拟实验,并依据相对偏差和重复性限数学分析法,进行溢油风化过程分析和诊断比值应用效果评估。研究结果表明:经过210天的风化,溢油鉴定诊断比值发生明显改变;其中来源于萜烷、甾烷和多环芳烃的诊断比值变化率要远低于正构烷烃,可用于中长期风化溢油鉴定。此外,研究发现,在这些有效诊断比值中有4个变化率较小,相对偏差低于5%,保持了较好的稳定性,更适合于重度风化溢油鉴定。     

锈蚀钢筋在疲劳荷载作用下压磁场分布研究

针对锈蚀钢筋的疲劳损伤与寿命评估中的难度大、精度低等问题,引入压磁检测技术,对锈蚀钢筋疲劳过程中的压磁场分布进行检测,从宏观与微观相结合的角度分析压磁场分布与疲劳损伤之间的联系。试验结果表明,锈蚀钢筋的压磁场分布能够反映疲劳损伤的演变规律,疲劳后期非线性特征加剧,锈蚀率及应力幅越大则变化越为明显,磁感强度值、磁场分布梯度、"反转"现象等均有助于进行疲劳损伤评价与寿命预测。研究结果可为压磁无损检测技术在钢筋混凝土结构中的应用提供依据。