排序方式： 共有35条查询结果，搜索用时 140 毫秒
11.
Summary. We attempted to gain some insight into the mechanical properties of poorly consolidated granular rock by preparing and testing synthetic rock specimens in which different cement content and bimodal grain-size distributions were used. We mixed various proportions of fine and coarse sand, Portland cement, and water. The mixture was cast in a mold and left pressure-free during curing, thus ensuring that the final material was poorly consolidated. The specimens were tested in a uniaxial press. During these tests, the static Youngs modulus was measured by performing small stress excursions at discrete intervals along the stress-strain curve. We observed significant non-linear elasticity (i.e., Youngs modulus increased with stress) in all the specimens. As expected, the uniaxial compressive strength increased with increasing cement content. Furthermore, we observed a transition from grain-size sensitivity of strength at cement contents less than 20–30% to grain-size independence above this value. At high cement content, the measured values of Youngs modulus are relatively well explained by a model based on rigid inclusions embedded in a soft matrix. At low cement content, we suggest that modelling the individual cemented grain-to-grain contacts becomes necessary. But this could not be done here for lack of microstructural information. 相似文献
12.
2001-2015年天山山区积雪时空变化及其与温度和降水的关系 总被引：12，自引：9，他引：3
采用2001-2015年MODIS积雪和陆表温度数据、中国高时空分辨率降水数据,基于趋势分析和相关分析方法,分析了天山山区积雪时空变化及其与温度和降水的关系。结果表明：（1）年内积雪面积变化受海拔影响,海拔≤4 000 m,呈单峰型分布,积雪面积冬季大,夏季小;海拔介于4 000~≤5 000 m,积雪面积分别在春季和秋季出现两次峰值;海拔>5 000 m,积雪面积变化与低海拔相反,在夏季达到最大,冬季最小。就年际变化而言,全区积雪面积呈略微减少趋势,其中秋季略微增加,春季变化不大,冬季和夏季明显减少。（2）积雪覆盖频率受水汽来向和地形影响,呈西高东低、北高南低分布格局,与海拔呈正相关。山区大部分区域积雪覆盖频率呈减少趋势,其中海拔介于3 600~≤4 600 m的积雪覆盖频率减少最为显著。（3）在春、夏季,温度是决定积雪面积变化的主要因素,与积雪面积呈负相关;在秋、冬季,降水对积雪面积变化的贡献大于温度,与积雪面积呈正相关。（4）积雪覆盖频率整体上与年均温度呈负相关,与降水呈低度正相关,相关程度及显著性水平在空间分布上存在差异,温度对积雪覆盖频率变化的贡献大于降水。 相似文献
13.
Salwa Saidi 《水文科学杂志》2013,58(2):288-304
Abstract The assessment of groundwater vulnerability to pollution has proved to be an effective tool for water resource management, especially in arid and semi-arid regions like Mahdia and Ksour Essaf. The main objective of this study is to assess the aquifer vulnerability by applying the DRASTIC method as well as using sensitivity analysis to evaluate the effect of each DRASTIC parameter on the final vulnerability map. An additional objective is to demonstrate the role of the GIS techniques in the vulnerability assessment. The DRASTIC method assigns a high vulnerability to the coast of the Mahdia-Ksour Essaf. The lowest values are observed in the southern part of the study area. A sensitivity analysis applied in this study suggests that net recharge, aquifer media and depth of groundwater are the key factors determining vulnerability. The model is validated with groundwater quality data and the results have shown strong relationships between modified DRASTIC Vulnerability Index and nitrate and chloride concentrations. Citation Saidi, S., Bouri, S. & Ben Dhia, H. (2011) Sensitivity analysis in groundwater vulnerability assessment based on GIS in the Mahdia-Ksour Essaf aquifer, Tunisia: a validation study. Hydrol. Sci. J. 56(2), 288–304. 相似文献
14.
Ikram Jmal Bachaer Ayed Emna Boughariou Nabila Allouche Salwa Saidi Monji Hamdi Salem Bouri 《Arabian Journal of Geosciences》2017,10(16):364
The study region comprises the Sidi Bouzid shallow aquifer, which is located in the western part of Central Tunisia. It is mainly occupied by agricultural land with intensive use of chemical fertilizers especially nitrates. For this reason, nitrate measurement was performed in 38 water samples to evaluate and calibrate the obtained models. Several environmental parameters were analyzed using groundwater nitrate concentrations, and different statistical approaches were applied to assess and validate the groundwater vulnerability to nitrate pollution in the Sidi Bouzid shallow aquifer. Multiple linear regression (MLR), analyses of covariance (ANCOVA), and logistic regression (LR) were carried out for studying the nitrate effects on groundwater pollution. Statistical analyses were used to identify major environmental factors that control the groundwater nitrate concentration in this region. Correlation and statistical analyses were conducted to examine the relationship between the nitrate (dependent variable) and various environmental variables (independent variables). All methods show that “groundwater depth” and “land use” parameters are statistically significant at 95% level of confidence. Groundwater vulnerability map was obtained by overlaying these two thematic layers which were obtained in the GIS environment. It shows that the high vulnerability area coincides with the likelihood that nitrate concentration exceeds 24.5 mg/l in groundwater. The relationship between the groundwater vulnerability classes and the nitrate concentrations provides satisfactory results; it showed an Eta-squared correlation coefficient of 64%. So, the groundwater vulnerability map can be used as a synthetic document for realistic management of groundwater quality. 相似文献
15.
In this part we find out the 24 equations of secular perturbation equations for the subsystem J-S-U-N. The solution of these equations by the Lagrange-Laplace procedure and the Eigen value Eigen vector is analysed. Also we refer to Hurwitz theorem to test stability. 相似文献
16.
利用NCEP 1°×1°格点再分析、FY-2E相当黑体亮温TBB和地面加密自动气象站等资料,分析了辽宁3次典型长历时强降水TBB值与降水强度的关系、中尺度环境场特征及维持机制,并初步建立了辽宁长历时强降水概念预报模型。结果表明:在副热带高压的形态、位置和强度有利于辽宁产生强降水的大尺度形势下,副热带高压西侧低空急流持续输送的充沛暖湿空气与高空干冷空气在同一地点长时间相互作用,为强降水的发生和维持提供了有利的环境背景条件。强降水持续时间与其上空的强垂直速度持续时间有很好的对应关系,强降水持续时高空一般为弱的不稳定或中性层结。强降水不仅可出现在对流云团发展旺盛的冷云区内部或边缘,也可发生在TBB值较小的暖云区内。TBB值的大小与降水强度没有必然的关系,但TBB值的快速减小都预示强降水即将发生。这些结论有利于深化认识辽宁地区长历时强降水的成因并为预报提供线索。 相似文献
17.
In this research, we have focused on the geometrical characteristics of young faults in North Tehran tectonic wedge which is confined with the Mosha and North Tehran faults, the most outstanding active faults in Alborz fold-thrust belt. The statistical, genetic, and kinematic relationships between internal faults, boundary faults, and the stress regime in the area (at the finite state of deformation path) are considered in detail with the help of rose diagrams and Riedel??s model. On this basis, all faults with diverse mechanisms have been classified into different Riedel fractures and their orders of formation are identified. Pattern of faults implies a more or less N?CS compression at the period of faulting. Consideration of geometry and tectonic setting of abundant normal faults have led to propose folding and listric faulting model to explain the origin of normal faults in a compressional tectonic region. These structural models represent the mechanism of normal faulting in response to compression in crustal and upper crustal scales, respectively. 相似文献
18.
Helmi Saidi Marzia Ciampittiello Claudia Dresti Laura Turconi 《Environmental Earth Sciences》2014,72(11):4607-4616
With regard to extreme events, it is well documented that an intensity of about 1 mm/min already represents an extreme intensity. Under alpine conditions, a precipitation event with an intensity of 3 mm/min has occurred. Therefore, the rain gauges in this region have to be able to measure in this and even in higher intensity ranges. This study deals with basic automated tipping-bucket rain (TBR) gauge and Bulk precipitation samplers, which are able to hold more than 95 % of the cumulative rainfall, that are verified within the space of the week without losses during the extreme events and with minimal evaporation loss. Bulk samplers collected more rainfall than TBR gauges in 110 of 221 extreme events analysed over the past 10 years. In 17 extreme events, an underestimation greater than 10 % was evaluated. The objective was to single out the counting errors associated with TBR gauge, during extreme events, so as to help the understanding of the measured differences between instruments in the field. We want to determine whether the automated precipitation gauge can provide a reliable and precise measurement of precipitation with particular interest regarding heavy and extreme events. 相似文献
19.
Groundwater vulnerability and risk mapping of the Hajeb-jelma aquifer (Central Tunisia) using a GIS-based DRASTIC model 总被引：7，自引：2，他引：5
The aim of this study is to elaborate a synthetic document for the assessment of groundwater vulnerability to pollution in the Hajeb-Jelma aquifer. The specific object is to incorporate the Geographical Information System (GIS) to generate groundwater vulnerability and risk maps with DRASTIC model. Indeed, GIS could help to make the results of a complicated model more clear through visual representation, providing an applicable tool for decision makers. The vulnerability map of Hajeb-Jelma watershed shows three classes: moderate, high and very high depending on the intrinsic properties. The risk map shows a very high risk dependant on hydrogeological characteristics, land use and human impacts in major part of the Hajeb-Jelma region. These maps could serve as a scientific basis for sustainable land use planning and groundwater management in the Hajeb-Jelma region. 相似文献
20.