Exploring some relationships between biological soil crusts, soil aggregation and wind erosion

A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r²=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm⁻¹s⁻¹ for a 65kmh⁻¹ wind at 10m height, a crust cover of approximately 20% is required. When a multiple regression model which sequentially fitted biological crust cover and dry aggregation greater than 0·85mm was applied to the data, dry aggregation accounted for more of the variation in sediment transport rate than biological crust cover. These data were used to develop a conceptual model which integrates crust cover and dry aggregation, and provides a useful framework within which to predict the likely impacts of changes in soil crust cover and aggregation.     

自重固结与土层的固结状态初探

介绍了沉积厚度与时问平方根和沉积厚度与时间呈直线关系、底面不排水时沉积过程中固结的Gibson理论解答以及不考虑沉积时固结作用、底面不排水时沉积后自重固结的Terzaphi理论解答，据此分析了上述两种沉积模式不同沉积速率时目前仍处于沉积过程的土层的固结状态，求算出了停止沉积后土层固结所需的最长时问，指出业已停止沉积数百年以上的土层一般不应处于欠固结状态。     

地裂缝灾害研究现状与展望

1927年美国首先发现地裂缝以来，各国学者对地裂缝的发生、发展进行了细致的研究。美国学者首先从地震研究入手，认为地裂缝的形成受构造因素影响。后逐渐加强研究地下水超采对地裂缝的影响，形成了构造与地下水开采复合成因观点。我国学者重点对汾渭地堑地裂缝成因问题进行了较系统的研究，提出几种成因机理模型，并用GIS技术建立简单的预测预报系统。文章在详细介绍国内、外对地裂缝成因机理和水文特性的研究以及预测、预报工作的同时，对今后研究趋势进行了展望。目前，地裂缝的研究正从以往的定性静态描述转向以过程为目标的精确定量动力学研究。利用相似材料模拟地裂缝的形成与发展，以非线性理论（如分形）对地裂缝系统进行定量的数学描述，建立准确的预测、预报模型（如人工神经网络模型），并与GIS相结合，建立完善的预测、预报系统，减少地裂缝灾害对环境的影响，进而对它加以利用，是今后地裂缝研究的主要方向。     

陇东地区水土流失与地质作用初步分析

陇东地区是黄河上游水土流失严重区 ,也是国家重点治理的地区之一。由于特殊的岩土体的存在 ,加重了这一地区水土流失作用的危害性。本文通过水土流失现象与地质作用的关系进行偿试性探讨 ,旨在从中找到防治水土流失的有效措施 ,开展治理工作     

A critical state interpretation for the cyclic liquefaction resistance of silty sands

Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in (e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses (p₀<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress.     

Lithology and palynology of Neogene sediments on the narrow edge of the Kitakami Massif (basement rocks), northeast Japan: Significant change for depositional environments as a result of plate tectonics

Abstract A controversial stratigraphic section, the Taneichi Formation, is exposed along the Pacific Coast of northeastern Honshu, the main island of the Japanese Archipelago. Although most sediments of the formation have long been dated as late Cretaceous, the northern section of it has been assigned to (i) the Upper Cretaceous; (ii) the Paleogene; or (iii) the Neogene. In the present report, we present the data of palynological and sedimentological studies, showing that the northern section should be assigned to the Neogene. A more important point in the present study is that we invoke some basic principles of fluvial sedimentology to resolve this stratigraphic subject. The lignite layers full of Paleogene–Miocene dinoflagellate cysts and pollen assemblages drape over the boulder‐sized (>40 cm in diameter) clasts in the northern section. However, the layers totally consist of aggregates of small lignite chips, indicating that the lignites are allochthonous materials. The mega‐clasts with derived microfossils in the lignites are thought to have been deposited as Neogene fluvial (flood) sediments in the newly formed Japanese Archipelago. Prior to the Miocene, the northern Honshu was part of the Eurasian Plate, thus the boulder‐sized clasts cannot be envisaged as long river flood deposits along the continental Paleogene Pacific Coast. Instead, the mega‐clasts with the draping lignites were probably derived from nearby Miocene highlands in the newly born island arc.     

The importance of plant root characteristics in controlling concentrated flow erosion rates

While it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross‐sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley & Sons, Ltd.     

Short‐term erosion rates from a 7Be inventory balance

Detailed soil erosion studies bene?t from the ability to quantify the magnitude of erosion over time scales appropriate to the process. An inventory balance for ⁷Be was used to calculate sediment erosion in a 30·73 m² plot during a series of runoff‐producing thunderstorms occurring over three days at the Deep Loess Research Station in Treynor, Iowa, USA. The inventory balance included determination of the pre‐ and post‐storm ⁷Be inventories in the soil, the atmospheric in?ux of ⁷Be during the event, and pro?les of the ⁷Be activity in the soil following the atmospheric deposition. The erosion calculated in the plot using the ⁷Be inventory balance was 0·058 g cm^?2, which is 23 per cent of the annual average erosion determined using ¹³⁷Cs inventories. The calculated erosion from the mass balance is similar to the 0·059 g cm^?2 of erosion estimated from the amount of sediment collected at the outlet of the 6 ha ?eld during the study period and the delivery ratio (0·64). The inventory balance of ⁷Be provides a new means for evaluating soil erosion over the time period most relevant to quantifying the prediction of erosion from runoff. Copyright © 2003 John Wiley & Sons, Ltd.     

多因素复杂系统最佳因素权重确定的一种新思路——以深港西部通道工程深圳湾公路大桥为例

为了客观地反映各因素对目标问题的影响程度,本文首次提出了最佳因素权重概念。定义最佳因素权重为研究区域内系统质量处于极限状态时的各因素权重之组合。结合深港西部通道工程深圳湾公路大桥桥址比选方案,详细说明了本方法的研究思路及其确定方法。通过最佳因素权重方法,能客观地、定量地确定出多因素复杂系统中的最优场址。     

Flexure of the Indian plate and intraplate earthquakes

The flexural bulge in central India resulting from India's collision with Tibet has a wavelength of approximately 670 km. It is manifest topographically and in the free-air gravity anomaly and the geoid. Calculations of the stress distribution within a flexed Indian plate reveal spatial variations throughout the depth of the plate and also a function of distance from the Himalaya. The wavelength (and therefore local gradient) of stress variation is a function of the effective elastic thickness of the plate, estimates of which have been proposed to lie in the range 40–120 km. The imposition of this stress field on the northward moving Indian plate appears fundamental to explaining the current distribution of intraplate earthquakes and their mechanisms. The current study highlights an outer trough south of the flexural bulge in central India where surface stresses are double the contiguous compressional stresses to the north and south. The Bhuj, Latur and Koyna earthquakes and numerous other recent reverse faulting events occurred in this compressional setting. The N/S spatial gradient of stress exceeds 2 bars/km near the flexural bulge. The overall flexural stress distribution provides a physical basis for earthquake hazard mapping and suggests that areas of central India where no historic earthquakes are recorded may yet be the locus of future damaging events.