公路膨胀土路堑边坡防护方案探讨

针对膨胀土路堑边坡的公路工程特点，总结以往膨胀土路堑边坡的防护措施，根据以往膨胀土路堑边坡的防护成败资料和经验。以保持边坡土体天然含水量状态的相对稳定，保持边坡土体结构的相对完整性。保持边坡土体足够的抗剪强度和防护工程应能适应边坡膨胀土体可能产生的膨胀变形与膨胀力不遭破坏。首先用DAH混合溶液改良膨胀土边坡的表层土，使DAH混合溶液与膨胀土产生离子交换发生化学反应，从而使表层膨胀土体改变性能，成为正常土，然后结合以往路堑边坡处理方法进行综合处理。实践证明，此方法不但充分利用了膨胀土．节约了工程投资，而且又绿化、美观了边坡，使其与周围环境相协调，从而为膨胀土地区公路路堑边坡处理提供了一种切实可行的防护措施。     

Ocean surface hidden structures in the Lofoten area of the Norwegian Sea

We investigate the structure of surface lateral mixing in the Lofoten area in the Norwegian Sea using surface velocity field derived from a 1/12^o reanalysis data. We compute a Lagrangian diagnostic based on the evolution of Finite Time Lyapunov Exponents (FTLEs) by advecting (backward in time) a large number of particles to quantify the hidden skeleton of different dynamical regions in the study area. By constructing maps of deterministic Lagrangian Coherent Structures (LCSs), four dynamical regions are generally identified: (i) regions of maximal dynamical attraction along the west coast of Norway and Barents Sea Opening; (ii) area of quasi-prominent anticyclonic eddy located at the centre of Lofoten Basin (LB); (iii) mid-ocean system of the Mohn Ridge which separates the Atlantic and Arctic waters: (iv) areas expanded between shallow continental shelf and deep basins populated with multiscale structures. We further construct a climatology of LCSs and FTLE statistical distributions with 11-year of reanalysis data to investigate the seasonal variability of Lagrangian circulations and to classify further their dynamical properties. The FTLE and LCS analyses in the present study can contribute to better understand the key transport barriers to the fate of larval dispersion and ocean contaminants, and marine population connectivity.     

A Review of Some Environmental Issues Affecting Marine Mining

Abstract

This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be site-specific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of “marine snow” (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested.     

Physical Modeling of a Footing on Soft Soil Ground with Deep Cement Mixed Soil Columns under Vertical Loading

Deep cement mixing (DCM) technique is a deep in-situ stabilization technique by mixing cement powder or slurry with soft soils below the ground surface to improve their properties and behavior. Some of DCM treated soft soil grounds are approximately in a plane-strain condition; for example, a fill embankment on DCM improved ground. In this study, a plane-strain physical model was created with instrumentation and used to investigate the bearing capacity and failure mode of a soft soil improved by an end-bearing DCM column group. This study focuses on the observed wedge-shaped shear failure of the model ground and attempts to give an account of the failure. Two different methods are used to calculate the bearing capacity of the model ground, and the computed values are compared with the measured ones. It is found that the simple Brom's method gives a better estimate of the bearing capacity of the present model ground. It is also found that measured data of pore water pressures at different locations in the soft soil indicate coupling between failure of columns and consolidation of the soft soil. This study has presented the first time that a wedge-shaped block failure was observed for pattern of DCM treated soil ground.     

Phosphorus and nitrate run‐off in hill pasture and forest catchments,Taita, New Zealand

Abstract

Phosphorus and nitrogen were measured in stream run‐off from the four catchments of the Taita Experimental Basin (41° 11′ S, 174° 58′ E). The land is used as exotic conifer forest, native forest, and hill pasture. Multiple regression analysis was used to estimate chemical losses per unit area in floods and at low flows.

At low flows, the hill pasture (fertilised with lime at 630 kg·ba^?1·y^?1, and superphosphate at 380 kg·ha^?1·y^?1) tended to lose more phosphorus and nitrate than the forested land, but differences were small, and not always significant. During large floods, the hill pasture (No. 5 Catchment) lost about 3 times as much reactive phosphate and 2–5 times as much total phosphorus as the forested land, and 130–190 times as much nitrate as land in the Exotic Forest and Native Forest 2 Catchments. Nitrate losses from land in the No. 4 Catchment (mainly native forest) were as high as those from the hill pasture, so high nitrate loss is not associated solely with agriculture.

Losses of total phosphorus via the catchment streams were estimated as: No. 5 Catchment (hill pasture), 293 g·ha^?1·y^?1; Native Forest 2 Catchment, 201 g·ha^?1·y^?1; No. 4 Catchment, 124 g·ha^?1·y^?1; Exotic Forest Catchment, 71 g·ha^?1.y^?1. Nitrate‐N losses were estimated to have been 1356 g·ha^?1·y^?1, 11.5 g·ha^?1·y^?1, 1436 g·ha^?1·y^?1, and 44 g·ha^?1·y^?1 respectively. Phosphorus and nitrate concentrations were similar in the Exotic Forest and Native Forest 2 streams, but the Exotic Forest tended to lose smaller amounts because it yielded about 50% less water per unit area.

Over the 2‐y study, an estimated 47–70% of phosphorus losses and up to 83% nitrate losses occurred in large floods; 31% and 48% respectively were apparently lost from the hill pasture catchment in a single flood. Less than 20% of estimated phosphorus losses and as little as 1% of nitrate losses occurred at low flows.

Run‐off of phosphorus and nitrate was spasmodic, and this should be considered in assessing the impact of surface run‐off on the biology and chemistry of receiving waters.     

Mixing processes relevant to phytoplankton dynamics in lakes

Active turbulence in lakes is confined to the surface mixed layer, to boundary layers on the lake sides and bottom, and to turbulent patches in the interior. The density stratification present in most lakes fundamentally alters the pathways connecting external mechanical energy inputs, for example by wind, with its ultimate fate as dissipation to heat; the density stratification supports internal waves and intrusions that distribute the input energy throughout the lake. Intrusions may be viewed as internal waves with zero horizontal wavenumber and are formed each time localised mixing occurs in a stratified fluid. Intrusions are also formed in the epilimnion by differential heating or cooling and by differential deepening. The fraction of lake volume below the diurnal mixed layer that is subject to active turbulence is very small, probably of the order of 1% or less in small to medium‐sized lakes. By contrast, in the surface mixed layer, turbulence is less intermittent and maintains phytoplankton in suspension and controls their exposure to the underwater solar flux. Nutrient transport to individual cells depends not only on the cell Reynolds number but also on the Peclet number, which, if large, implies enhanced mass transfer above purely diffusive values.     

A comparison of two global ocean-ice coupled models with different horizontal resolutions

A global eddy-permitting ocean-ice coupled model with a horizontal resolution of 0.25 by 0.25 is established on the basis of Modular Ocean Model version 4 (MOM4) and Sea Ice Simulator (SIS). Simulation results are compared with those of an intermediate resolution ocean-ice coupled model with a horizontal resolution of about 1 by 1 . The results show that the simulated ocean temperature, ocean current and sea ice concentration from the eddy-permitting model are better than those from the intermediate resolution model. However, both the two models have the common problem of ocean general circulation models (OGCMs) that the majority of the simulated summer sea surface temperature (SST) is too warm while the majority of the simulated subsurface summer temperature is too cold. Further numerical experiments show that this problem can be alleviated by incorporating the non-breaking surface wave-induced vertical mixing into the vertical mixing scheme for both eddy-permitting and intermediate resolution models.     

西南黄海M2分潮的数值模拟

本文采用普林斯顿大学海洋模式(POM)结合中国海军司令部发布的海图地形资料, 对西南黄海M2分潮进行了三维数值模拟。利用近岸4个验潮站水位资料和一组2008年夏季鲁南海槽中30m水深处潜标测流资料, 对模拟的潮汐和潮流结果进行了对比。模式模拟的M2分潮振幅与青岛、石臼所和吕泗这三个验潮站的实测资料符合良好; 但与连云港验潮站的实测振幅相比, 模拟振幅明显偏小, 推断主要原因是连云港港口实际水深值与海图地形中的水深值相差较大, 造成模拟结果的偏差。模拟的潮流结果与潜标测流资料在上层和中层较接近, 模拟的近底层潮流结构与实测资料相比存在较大偏差, 推断是由于模式的垂直混合系数误差造成的。使用该模式研究了西南黄海M2分潮对模式地形的敏感性, 发现采用海图地形数据和ETOPO5地形数据所模拟的西南黄海潮汐和潮流有显著不同。使用较平滑的ETOPO5地形数据所模拟的结果中, 西南黄海近岸海区M2分潮振幅偏小、相位偏大、潮流偏弱。研究表明, 鲁南海槽的存在增大了海州湾的潮汐振幅, 苏北浅滩对向南传播的潮波起到了阻挡作用。以上两个西南黄海近岸海区地形的重要特征在ETOPO5地形数据中没有被体现出来, 因此造成模拟误差。     

复合土钉墙技术在陕西国土资源大厦深基坑工程中的应用

在陕西国土资源大厦深基坑支护工程中,采用水泥土搅拌桩-土钉墙和预应力锚杆的复合土钉墙技术。介绍了施工技术要点及实际施工效果。