EFFECTS OF SOIL CRUSTING ON SOIL MOISTURE, RUNOFF AND EROSION: FIELD OBSERVATIONS     

Tongxin ZHU 《国际泥沙研究》2002,17(4)

1 INTRODUCTION Soil crusting, or soil sealing, is one of the common phenomena in agricultural lands or semi-arid and arid soils. Due to the breakdown of soil aggregates by raindrops, soil surface develops a very thin, often less than a few millimeters, dense layer. Many studies indicated that such a thin layer significantly reduces infiltration capacity and increases surface runoff (i.e. McIntyre, 1958; Edward and Larson, 1969; Agassi et al., 1985; Bradford et al., 1986; Romkens et al.,…  相似文献   

Fuzzy neural network models for liquefaction prediction   总被引：1，自引：0，他引：1  

M. S. Rahman  Jun Wang 《Soil Dynamics and Earthquake Engineering》2002,22(8)

Integrated fuzzy neural network models are developed for the assessment of liquefaction potential of a site. The models are trained with large databases of liquefaction case histories. A two-stage training algorithm is used to develop a fuzzy neural network model. In the preliminary training stage, the training case histories are used to determine initial network parameters. In the final training stage, the training case histories are processed one by one to develop membership functions for the network parameters. During the testing phase, input variables are described in linguistic terms such as ‘high’ and ‘low’. The prediction is made in terms of a liquefaction index representing the degree of liquefaction described in fuzzy terms such as ‘highly likely’, ‘likely’, or ‘unlikely’. The results from the model are compared with actual field observations and misclassified cases are identified. The models are found to have good predictive ability and are expected to be very useful for a preliminary evaluation of liquefaction potential of a site for which the input parameters are not well defined.  相似文献   

Development of site-specific design ground motions in Western and Eastern North America     

Walter Silva  Carl Costantino   《Soil Dynamics and Earthquake Engineering》2002,22(9-12):755-764

This paper presents results recently obtained for generating site-specific ground motions needed for design of critical facilities. The general approach followed in developing these ground motions using either deterministic or probabilistic criteria is specification of motions for rock outcrop or very firm soil conditions followed by adjustments for site-specific conditions. Central issues in this process include development of appropriate attenuation relations and their uncertainties, differences in expected motions between Western and Eastern North America, and incorporation of site-specific adjustments that maintain the same hazard level as the control motions, while incorporating uncertainties in local dynamic material properties. For tectonically active regions, such as the Western United States (WUS), sufficient strong motion data exist to constrain empirical attenuation relations for M up to about 7 and for distances greater than about 10–15 km. Motions for larger magnitudes and closer distances are largely driven by extrapolations of empirical relations and uncertainties need to be substantially increased for these cases.

For the Eastern United States (CEUS), due to the paucity of strong motion data for cratonic regions worldwide, estimation of strong ground motions for engineering design is based entirely on calibrated models. The models are usually calibrated and validated in the WUS where sufficient strong motion data are available and then recalibrated for applications to the CEUS. Recalibration generally entails revising parameters based on available CEUS ground motion data as well as indirect inferences through intensity observations. Known differences in model parameters such as crustal structure between WUS and CEUS are generally accommodated as well. These procedures are examined and discussed.  相似文献   

Screening model for volatile pollutants in dual porosity soils     

Mohamed M. Hantush  Rao. S. Govindaraju  Miguel A. Marioand Zhonglong Zhang 《Journal of Hydrology》2002,260(1-4):58-74

This paper develops mass fraction models for transport and fate of agricultural pollutants in structured two-region soils. Mass fraction index models, based on a semi-infinite domain solution, are derived that describe leaching at depth, vapor losses through soil surface, absorption, and degradation in the dynamic- and stagnant-water soil regions. The models predict that leaching is the result of the combined effect of the upward vapor-phase transport relative to downward advection, residence time relative to half-life, dispersion, and lateral diffusive mass transfer. Simulations show that leached fraction of volatile compounds does not always decrease monotonically with increased residence time relative to the pollutant half-life, as a result of complex interactions among the different physical and biochemical processes. The results show that leaching, volatilization, and degradation losses can be affected significantly by lateral diffusive mass transfer into immobile-water regions and advection relative to dispersion (i.e. Peclet number) in the mobile-water regions. It is shown that solute diffusion into the immobile phase and subsequent biochemical decay reduces leaching and vapor losses through soil surface. Potential use of the modified leaching index for the screening of selected pesticides is illustrated for different soil textures and infiltration rates. The analysis may be useful to the management of pesticides and the design of landfills.  相似文献   

红壤丘陵区农业开发中的生态环境效应及其调控   总被引：3，自引：0，他引：3  

周炳中  杨浩  周生路  张震宇  张红 《地域研究与开发》2002,21(4):14-19

文章以江西余江县为例。通过实验研究，历史资料对比分析及邻近参照等方法。研究红壤区农业开发中的生态环境效应。农业开发引起的微观环境效应在于改变土壤水分及其运动状况，加速土壤物质迁移及降低土壤肥力质量；区域性效应是植被减少，农业面源污染，水土流失扩大及气候异常；全球性影响除区域集聚效应外，则是农业活动中产生的温室气体对全球气候的影响等，采取的调控对策主要是：保持合理开发，适当减轻土地压力，优化农业开发模式，更新农业耕作技术。强化环境整治与生态建设。  相似文献   

西藏自治区的土壤理化特性探讨     

刘刚才  王小丹  刘淑珍 《山地学报》2003,21(Z1):54-57

通过对西藏自治区主要土壤类型的实地踏勘和采样分析,并结合全国土壤普查资料的结果进行分析,揭示了本区土壤具有4点特性:即多砾石性、砂质性、成土幼年性和低矿化的富有机质性。因此,在改良本区土壤时,应重视去石与防治沙漠化措施,加强矿质养分肥料的施用,稳定有机肥的投入。  相似文献   

Fire Severity,Water Repellency Characteristics and Hydrogeomorphological Changes Following the Christmas 2001 Sydney Forest Fires     

R. A. SHAKESBY  C. J. CHAFER  S. H. DOERR  W. H. BLAKE  P. WALLBRINK  G. S. HUMPHREYS 《The Australian geographer》2003,34(2):147-175

Soil water repellency can enhance overland flow and erosion and may be altered by fire. The Christmas 2001 bushfires near Sydney allowed investigation of the relationship between fire severity, water repellency and hydrogeomorphological changes. For two sub-catchments with differences in fire severities in Nattai National Park, south-west of Sydney, this paper considers: (1) the links between fire severity based on SPOT image analysis and ground observation of fire severity and repellency; (2) the textural and organic/minerogenic characteristics of eroded sediment; and (3) erodibility, erosion and deposition of soils in both catchments. Ground surveys show that image analysis reflects well the degree of vegetation consumption by fire, but cannot adequately predict the degree of ground litter consumption, associated soil heating and repellency effects. Fire had varying effects on repellency, leaving it unchanged, destroying it or enhancing it, depending on the soil temperature reached. The main post-fire hydrogeomorphological changes have been widespread erosion and colluvial and alluvial deposition of topsoil in foot-slope locations and river systems, but only localised redistribution of the highly erodible, repellent sandy subsurface layer. The fire did not trigger major geomorphological change in the study area, but fires probably cause important topsoil and nutrient depletion and may also affect water quality.  相似文献   

应县木塔地基工程地质勘测与分析   总被引：1，自引：0，他引：1  

魏剑伟  李铁英  张善元  李世温 《工程地质学报》2003,11(1):70-78

对山西应县木塔环境地质进行了研究,弄清了地层年代及存在的断层;通过样品分析、标准贯入及静探等方法试验、测试,得出了塔院区塔基土的工程物理性质和力学性质、承载力;用地学层析成像技术探测了木塔的基础结构及塔院地基的分层结构。  相似文献   

高速公路下伏某煤矿采空区地质特征及注浆充填法治理研究   总被引：1，自引：0，他引：1  

朱宜生  方磊  童立元  杜广印 《江苏地质》2003,27(1):37-40

煤矿采空区是工程建设中不良地质条件之一，其地质特征评价和如何治理是两个关键问题。笔者结合高速公路建设中某采空区的治理实践，对这两方面进行了探索，对工程建筑中所遇各类采空区的地质特征评价及其治理方法有一定借鉴意义。  相似文献   

覆盖区地球化学异常特征及甄别方法探讨     

薛水根  吴新民 《江苏地质》2003,27(4):199-202

覆盖区地球化学异常是由自然和人为因素引起的，在土壤垂直剖面上元素有多种分布类型，它反映了元素在土壤中迁移、演化及人为干扰的分布特征；通过对自然和人为污染的地球化学异常源追踪和评价，为环境污染治理和地区经济可持续发展提供决策依据。  相似文献