Comparison of 24 h and Long-term pHstat Leaching Tests for Heavy Metal Mobilization from Solid Matrices

The dynamic leaching behaviour of environmentally relevant heavy metals makes it difficult to fix a suitable elution time of leaching tests. With ten different solid materials which were characterized by wavelength-dispersive X-ray fluorescence analysis and by the determination of aqua regia soluble amounts of heavy metals we performed 24 h and long-term leaching tests using the pH_stat procedure at pH 4 to be able to compare the resulting acid neutralization capacities (ANC) and heavy metal mobilization. This comparison demonstrates firstly the limitations in predicting the extent of heavy metal release after a longer (geological) time period only from the leached amounts after 24 hours and the ratio of the ANC values measured in the 24 h test and in a long-term experiment, respectively. Secondly, the effect of elution time on the leachability is not uniform but element specific and matrix dependent. Hence, the pH_stat leaching test performed in the usual manner does not seem to be suitable particularly for assessing long-term mobilization of heavy metals under acidic conditions. Additional experiments under variation of shaking frequency and time clearly demonstrate the dominant influence of the first parameter on the resulting ANC and support the necessity of further studies to optimize the pH_stat leaching procedure before the test can be recommended in regulations for environmental protection.     

Applicability of Single and Sequential Extractions for Assessing the Potential Mobility of Heavy Metals in Contaminated Soils

Heavy metal polluted sites are bearing an acute hazardous risk for the groundwater, but also a potential one. While the acute risk can be assessed directly via seepage water measurements, determination of the potential risk is much more complex. It results from the sum of all reactions that are capable to mobilize heavy metals under worst case environ-mental conditions. Using a fourfold sequential extraction (SE₄) such a worst case was simulated for four soils highly contaminated with Pb, Zn, and Cu. The resulting potential mobilizable amounts ϕ_pm have been compared with those derived from 6 single extractions. By means of variance analyses, it is shown that ϕ_pm of lead can be represented by a single extraction with NH₂OH. In contrary, ϕ_pm of zinc can be represented using the pH_stat test or an extraction with aqua regia, while ϕ_pm of copper can be represented only by aqua regia extraction. The water-soluble amounts deriving from the DEV-S4 test do not correlate with the potential mobilizable amounts of any metal. Therefore, an assessment of contaminated sites should include an aqua regia extraction additionally to the seepage water analysis.     

黄河流域降雨侵蚀力对全球变化的响应

分析土壤侵蚀力对全球变化的响应,有助于国家和区域未来水土保持宏观战略的决策.本文利用Had-CM3模型,在A2和B2情景下系统研究了未来不同时期（2020年、2050年和2080年）黄河流域降雨侵蚀力的潜在变化.结果表明在全球气候变化条件下,黄河流域的降雨侵蚀力有显著的增加;增加的幅度随着GCM情景和研究时期的不同而不同,从南向北逐渐增大;A2情景下,黄河流域的降雨侵蚀力分别增加11.5%（2020年）、24.8%（2050年）和40.6%（2080年）,B2情景下的相应变化分别为20.9%、12.5%和20.8%;加强中、长期土地利用规划、植被建设和水土保持是应对全球变化的基本方略.     

INFLUENCE OF BUILDING EXISTENCE ON SEISMIC LIQUEFACTION OF SUBSOILS

A new simplified method is presented to evaluate seismic liquefaction potential of subsoils of buildings. Based on a review of the limited number of publications so far available, dealing with the related theme, the authors have devised the method in such a way that it is simple to handle and has clear physical insight and sufficient engineering accuracy, by taking advantage of Seed's simplified method for free ground sites and of the cone model concept well developed by Meek and Wolf in dynamics in recent years as well as by some American and German scholars in soil statics early since the 1930s. A simple example showed the reasonableness and tendency in good accord with the results of small model tests and of finite element analyses. Therefore, it would have a broad prospect of engineering application. © 1997 by John Wiley & Sons, Ltd.     

土壤区划类型的参比与属地化研究

文章以详细的1981年土壤分区资料为基础,将以发生分类(GSCC)为基础的土壤类型名称分别参比成中国土壤系统分类(CST)名称和美国土壤系统分类(ST)名称。同时利用G IS空间分析技术,确定了中国8个土壤大区在地级市(盟)和各县、区、旗(市)的行政归属,并以江南低山丘陵和台湾北部地区为例,探讨了二级分区的行政归属。     

山西平陆黄河北岸第四纪软沉积物变形构造的古地震成因研究

为研究山西南部平陆地区黄河北岸一级阶地中软沉积物变形构造的触发机制,对观测剖面中发育的碟状构造、液化卷曲构造和球枕构造等3类软沉积物变形构造的特征进行描述,分析其形成机制,通过总结对比软沉积物变形的地震成因,推测剖面中的变形构造为地震成因,并依此建立山西南部平陆地区的地震成因地层沉积序列。光释光测年结果显示,该变形构造形成年龄为1.9±0.2 ka,通过影响烈度的计算并结合山西及邻近省的地震资料发现,2次历史地震可能与该软沉积物变形构造相关。     

Soil organic carbon mapping using remote sensing techniques and multivariate regression model

Soil organic carbon (SOC) is an important aspect of soil quality and plays an imperative role in soil productivity in the agriculture ecosystems. The present study was applied to estimate the SOC stock using space-borne satellite data (Landsat 4–5 Thematic Mapper [TM]) and ground verification in the Medinipur Block, Paschim Medinipur District and West Bengal in India. In total, 50 soil samples were collected randomly from the region according to field surveys using a hand-held Global Positioning System (GPS) unit to estimate the surface SOC concentrations in the laboratory. Bare soil index (BSI) and normalized difference vegetation ndex (NDVI) were explored from TM data. The satellite data-derived indices were used to estimate spatial distribution of SOC using multivariate regression model. The regression analysis was performed to determine the relationship between SOC and spectral indices (NDVI and BSI) and compared the observed SOC (field measure) to predict SOC (estimated from satellite images). Goodness fit test was performed to determine the significance of the relationship between observed and predicted SOC at p ≤ 0.05 level. The results of regression analysis between observed SOC and NDVI values showed significant relationship (R² = 0.54; p < 0.0075). A significant statistical relationship (r = ?0.72) was also observed between SOC and BSI. Finally, our model showed nearly 71% of the variance of SOC distribution could be explained by SOC and NDVI values. The information from this study has advanced our understanding of the ongoing ecological development that affects SOC dissemination and might be valuable for effective soil management.     

Experimental study on the soil thrust of underwater tracked vehicles moving on the clay seafloor

As the soil traction of the track system consisting of a track plate and protruded grousers is generally higher than that of a comparable wheel system, underwater tracked vehicles are the favored platforms for heavy-weight remotely operated vehicles (ROVs). When an underwater tracked vehicle moves on the seafloor, the track system laterally transmits an engine torque to the soil-track interface, resulting in slip displacement and an associated soil thrust acting as a traction force. Therefore, to evaluate the mobility of underwater tracked vehicle, it is critical to evaluate the soil thrust of the track system based on the soil-track interaction. Unlike the soil thrust of sandy soils, a reliable soil thrust assessment method accounting for the failure mechanism of clayey soil has yet to be developed in spite of its significance. An experimental study on the mechanism of the soil thrust of clayey soil was thus performed. Model track experiments were conducted on a model track system with clayey soil. Based on the experiment results, the mechanism of the soil thrust of clayey soil was investigated and was compared with the mechanism of soil thrust derived from the previous soil thrust assessment methods using sandy soil. Particular attention was given to the development of a new soil thrust prediction model for the track system on clayey soil using the limit equilibrium analysis technique.     

The role of submerged berms on the momentary liquefaction around conventional rubble mound breakwaters

Berms deployed at the toe of conventional rubble mound breakwaters can be very effective in improving the stability of the armor layer. Indeed, their design is commonly tackled by paying attention to armor elements dimensioning. Past research studies showed how submerged berms can increase the stability of the armor layer if compared to straight sloped conventional breakwaters without a berm. To fill the gap of knowledge related to the interaction between breakwaters with submerged berm, waves and soil, this research aims to evaluate how submerged berms configuration influences the seabed soil response and momentary liquefaction occurrences around and beneath breakwaters foundation, under dynamic wave loading. The effects of submerged berms on the incident waves transformation have been evaluated by means of a phase resolving numerical model for simulating non-hydrostatic, free-surface, rotational flows. The soil response to wave-induced seabed pressures has been evaluated by using an ad-hoc anisotropic poro-elastic soil solver. Once the evaluation of the seabed consolidation state due to the presence of the breakwater has been performed, the dynamic interaction among water waves, soil and structure has been analyzed by using a one-way coupling boundary condition. A parametric study has been carried out by varying the berm configuration (i.e. its height and its length), keeping constant the offshore regular wave condition, the berm and armor layer porosity values, the water depth and the elastic properties of the soil. Results indicate that the presence of submerged berms tends to mitigate the liquefaction probability if compared to straight sloped conventional breakwater without a berm. In addition, it appears that the momentary liquefaction phenomena are more influenced by changing the berm length rather than the berm height.     

Shear strength of soil berm during lateral buckling of subsea pipelines

The soil resistance developed during temperature- and pressure-induced large lateral movements of shallowly embedded subsea flowlines is an important input parameter for the structural design process. A major source of uncertainty in calculation of the soil resistance is the undrained shear strength of the soil berm produced as the flowline moves across the seabed, which is affected by the level of remoulding. To investigate the effect of pipeline embedment and displacement amplitude on the shear strength of the berm, a set of centrifuge model tests was conducted on kaolin clay, involving laterally moving pipelines with constant embedments in the range 5%–35% of the pipe diameter. Back-analysis of the test results, using finite element limit analysis, showed that the shear strength of the soil berm is a function of pipe displacement amplitude, pipe embedment, and soil sensitivity. On the basis of these results, we propose that the overall berm undrained shear strength may be determined as a convolution of the shear strengths of its constituent soil elements. Finally, a formula is presented for calculating the shear strength of soil elements within the soil berm, and this is used to back-analyse the overall soil berm resistance from the model tests.