Wave characteristics past a flexible fishnet

The scattering of surface waves by a flexible fishnet is studied analytically. The fishnet is modelled as a porous flexible barrier displaced solely by hydrodynamic force like a catenary. The objective is to investigate how a flexible permeable barrier affects the passing waves in the way they are transmitted and reflected, as observed by the fact that the water inside a fishfarm surrounded by fishnets is significantly calmer than that outside. The boundary value problems are solved by defining the reflection coefficient in terms of velocity potential and then the full solutions are obtained by suitable application of the eigenfunction expansion method and the least squares approximation method. The variations of the reflection coefficient, hydrodynamic pressure, barrier deformation and surface wave elevation are determined with respect to the barrier length, porosity and stiffness. It is observed that as the fishnet gets more flexible, its deformation increases and the reflection coefficient decreases, whereas as the fishnet gets more porous, more water can pass through it and thus the reflection coefficient, barrier deformation and the hydrodynamic force are reduced. The flexibility of the barrier behaves like its porosity by allowing more wave energy to act on it through its deformation and hence reduce the reflection and hydrodynamic force of the incident waves acting on the barrier.     

Benthic foraminifera of the Holocene transgressive west-central Florida inner shelf: paleoenvironmental implications

The sedimentology, stratigraphic position, and benthic foraminiferal biostratigraphy of early- to mid-Holocene deposits from the west-central Florida shelf suggest that barrier islands developed along this coast as early as 8.3 ka, in an environment that was more arid than today. Predominant foraminifera of three paralic sedimentary facies deposited between 5.3 and 8.3 ka include miliolids, Elphidium spp., and Ammonia spp., all of which are common in back-barrier environments. Foraminiferal assemblages also suggest that early back-barrier sediments were deposited in a hypersaline environment, similar to that of the arid Laguna Madre of the western Gulf of Mexico. Modern back-barrier foraminifera in the Tampa Bay region are indicative of the humid subtropical climate of today. Thus, the climate of west-central Florida at approximately 8 ka was more arid than today, which is consistent with recent studies showing that climate in the Gulf of Mexico was dryer and cooler during this time period.     

Experimental Study of Factors Controlling Sorption of Heavy Metals on Ariake Clay and Implication for Practice

A series of batch tests have been presented to investigate the effects of solid-solution contact time, solid:solution ratio, and pH of solution on sorption of Cd²⁺ and Pb²⁺ on Ariake clay from Kyushu region of Japan. The results show that, among the three investigated factors, solid:solution ratio (SD/SN) seems to be the crucial controlling factor. The Freundlich sorption parameters determined from the batch tests were applied to a typical field landfill in which the Ariake clay was used as soil barrier. The impacts of the landfill were assessed by numerical analysis. Based on the analysis result, the significance of selecting proper solid:solution ratio for determining sorption parameters from batch test has been discussed.     

Wave interaction with partially immersed twin vertical barriers

The wave transmission, reflection and energy dissipation characteristics of partially immersed twin vertical barriers and the water surface fluctuations in between the barriers were studied using physical models. Regular and random waves of wide ranges of wave heights and periods, nine different immersions of the barriers and a constant water depth were used for the investigation. The coefficient of transmission, and the coefficient of reflection were obtained from the measurements and coefficient of energy dissipation is estimated using the law of conservation of energy. It is found in general that the twin barrier is better in reducing the coefficient of transmission and increasing the coefficient of dissipation in random waves than with the regular waves, especially for increasing incident wave energy levels. The coefficient of transmission reduces significantly with the increased relative water depth. Increase of relative water depth from 0.09 to 0.45 resulted in reduction of transmission coefficient from 0.65 to 0.05. It is possible to achieve a transmission coefficient less than 0.20 for six immersion configurations with relative depth of immersions of the barrier less than (0.28, 0.43), especially in the region closer to deep water conditions. Coefficient of dissipation ranging from 0.65 to 0.85 can be obtained due to random wave interaction.     

Wave interaction with ‘’-type breakwaters

The wave transmission, reflection and energy dissipation characteristics of ‘’-type breakwaters were studied using physical models. Regular and random waves in a wide range of wave heights and periods and a constant water depth were used. Five different depths of immersion (two emerged, one surface flushing and two submerged conditions) of this breakwater were selected. The coefficient of transmission, K_t, and coefficient of reflection, K_r, were obtained from the measurements, and the coefficient of energy loss, K_l was calculated using the law of balance of energy. It was found that the wave transmission is significantly reduced with increased relative water depth, d/L, whether the vertical barrier of the breakwater is surface piercing or submerged, where ‘d’ is the water depth and ‘L’ is the wave length. The wave reflection decreases and energy loss increases with increased wave steepness, especially when the top tip of the vertical barrier of this breakwater is kept at still water level (SWL). For any incident wave climate (moderate or storm waves), the wave transmission consistently decreases and the reflection increases with increased relative depth of immersion, Δ/d from −0.142 to 0.142. K_t values less than 0.3 can be easily obtained for the case of Δ/d=+0.071 and 0.142, where Δ is the height of exposure (+ve) or depth of immersion (−ve) of the top tip of the vertical barrier. This breakwater is capable of dissipating wave energy to an extent of 50–80%. The overall performance of this breakwater was found to be better in the random wave fields than in the regular waves. A comparison of the hydrodynamic performance of ‘’-type and ‘T’-type shows that ‘T’-type breakwater is better than ‘’-type by about 20–30% under identical conditions.     

沙坝—泻湖海岸动力地貌学研究进展

国内外对沙坝－泻湖海岸的研究主要采取动力地貌学的方法，本文评述了近一个半世纪以来在这一领域所取得的重要成果。波浪、潮汐、径流等特殊的动力场决定了泥沙输运的方式和路径，从而形成了与其相应的沙坝、泻湖、潮汐通道三大地貌体系。     

THM analysis of a large‐scale heating test incorporating material fabric changes

Engineered barriers are basic elements in the design of repositories for the isolation of high‐level radioactive waste. This paper presents the thermo‐hydro‐mechanical (THM) analysis of a clay barrier subjected to heating and hydration. The study focuses on an ongoing large‐scale heating test, at almost full scale, which is being carried out at the CIEMAT laboratory under well‐controlled boundary conditions. The test is intensely instrumented and it has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. Comprehensive laboratory tests carried out in the context of the FEBEX and NF‐PRO projects have allowed the identification of the model parameters to describe the THM behaviour of the compacted expansive clay. A conventional THM approach that assumes the swelling clay as a single porosity medium has been initially adopted to analyse the evolution of the test. The model was able to predict correctly the global THM behaviour of the clay barrier in the short term (i.e. for times shorter than three years), but some model limitations were detected concerning the prediction of the long‐term hydration rate. An additional analysis of the test has been carried out using a double structure model to describe the actual behaviour of expansive clays. The double structure model explicitly considers the two dominant pore levels that actually exist in the FEBEX bentonite and it is able to account for the evolution of the material fabric. The simulation of the experiment using this enhanced model provides a more satisfactory reproduction of the long‐term experimental results. It also contributes to a better understanding of the observed test behaviour and it provides a physically based explanation for the very slow hydration of the barrier. Copyright © 2011 John Wiley & Sons, Ltd.     

雅鲁藏布江色东普沟冰崩—堵江—溃决灾害数值模拟

为了揭示雅鲁藏布江色东普沟2018年10月17日冰崩—堵江—溃决灾害链的动力演化过程,基于Massflow数值模拟仿真平台,使用Fortran编程语言,根据研究区域地质条件特征对程序进行二次开发以优化Voellmy模型,模拟冰崩—泥石流动力过程;将模拟泥石流得到的堰塞坝体嵌入地形中,运用ArcGIS计算堰塞湖范围及体积,通过Manning模型模拟堰塞湖溃决洪水动力过程。采用分段模拟法再现冰崩—泥石流—堵江—堰塞湖—溃坝的完整动力过程,对泥石流运动过程中的流速、流深,坝体高度,溃决洪水的流深、流速等参数进行定量化研究,为色东普流域的防灾减灾工作提供有效支撑。为了揭示雅鲁藏布江色东普沟2018年10月17日冰崩-堵江-溃决灾害链的动力演化过程,采用Massflow数值模拟仿真平台,以Fortran语言为编程手段,根据研究区域地质条件特征对程序进行二次开发优化Voellmy模型,模拟冰崩-泥石流动力过程;将模拟泥石流所得到的堰塞坝体嵌入地形中,采用ArcGIS计算堰塞湖范围及体积,通过曼宁模型模拟堰塞湖溃决洪水动力过程。采用分段模拟法再现冰崩-泥石流-堵江-堰塞湖-溃坝的完整动力过程,对泥石流运动过程中的流速、流深,坝体高度,溃决洪水的流深、流速等参数进行定量化研究,为色东普流域的防灾减工作提供有效支撑。     

砂岩型铀矿床层间氧化带前锋区稀有元素富集机制

在深入研究砂岩型铀矿床层间氧化带各地球化学分带中铀及其伴生元素的分布规律时,发现一些单价态(不变价)元素也常常富集在层间氧化带前锋区,其典型代表是钪(Sc)、钇(Y)和稀土元素(REE)等。作者在综合分析前苏联众多砂岩型铀矿床各地球化学分带中各种元素大量测试数据的基础上,论述了层间氧化带前锋区Eh值和pH值的变化规律以及它们所导致的变价元素(U、Se、Mo和V)和不变价元素(Sc、Y和REE)的分布规律和富集机制。实际上,层间氧化带前锋区既是氧化-还原电位(Eh值)又是酸碱度(pH值)的急剧变化区,两者大致同步消长。层间氧化带前锋区有两类地球化学障:单纯的还原障和还原-碱性综合障。两种地球化学障的发育与强度取决于原始未氧化岩石中硫化物、有机质和碳酸盐的含量。     

Pozzolanic fly ash as a hydraulic barrier in land fills

The liner plays an important role in controlling migration of contaminants present in the leachate in waste containment systems such as land fills and impoundments. Although questions have been raised about the performance of clay liners, they are increasingly used singly or as double liners in disposal sites. Though the clay liners possess many advantages such as low permeability and large attenuative capacity, they also possess high shrinkage potential and hence can crack under unsaturated conditions causing instability and increase in leakage rates. Further, the permeability of the clay linear can increase due to clay–pollutant interaction. This study examines the potential of pozzolanic fly ash as a hydraulic barrier in land fill. The behaviour of three different types of fly ashes, showing a range of physical properties and chemical composition from three different sources are reported in the study. Geotechnical properties, needed to evaluate the use of fly ashes as barriers, such as shrinkage, compaction, permeability, consolidation and strength characteristics are reported. The results show that fly ashes possess low shrinkage and hence do not crack. Compacted fly ashes undergo very little volume changes. They also show that pozzolanic fly ashes develop good strength properties with time. Pozzolanic fly ashes containing sufficient lime develop strength even without addition of lime. Non-pozzolanic fly ashes do not develop strength even on addition of lime. Fly ashes generally consist of silt size particles and consequently possess high permeability. However, pozzolanic fly ashes with lime exhibit low permeability on curing because of the formation of gelatinous compounds which block the pores. Thus, pozzolanic fly ashes appear to be promising for construction of liners to contain alkaline leachate.