Determining the optimal pumping duration of transient pumping tests for estimating hydraulic properties of leaky aquifers using global curve-fitting method: a simulation approach

Global curve-fitting method (GCFM) is regarded as an effective approach in hydrogeological parameter estimation, as it integrates and uses pumping data and water recovery data of a transient pumping test for parameter estimation. The impacts of pumping duration on hydrogeological parameter estimation by GCFM were investigated in the present study using 2 in situ pumping tests and 24 simulated transient pumping tests. Empirical formulas for determining the optimal pumping duration were derived. The study results suggest that pumping duration will have impacts on the accuracy of hydrogeological parameter estimation. When pumping duration is longer than a certain period, relative errors of hydrogeological parameter estimation keep relatively stable within an acceptable limit. Therefore, it is unnecessary to continue the pumping for a very long time after the groundwater level has become stable. When the change rate of drawdown over time (γ) in an observation well located within a distance of 100 m to the pumping well reaches 0.134, the pumping can be stopped. If there are more than one observation wells in a pumping test, the smallest γ value should be selected to determine the optimal pumping duration. This research is meaningful in the instruction of pumping tests, and will reduce test costs greatly.     

Assessment of soil salinization based on a low-cost method and its influencing factors in a semi-arid agricultural area,northwest China

An investigation of soil salinization was carried out in the Nanshantaizi area (Northwest China) with WET Sensor. This device can measure such soil parameters as bulk soil electrical conductivity, water content, and the pore water electrical conductivity that are important for soil salinization assessments. A distribution map of soil salinization was produced, and the factors influencing soil salinization and its processes were discussed in detail. The study shows that moderately salinized to salt soils are mainly observed in the alluvial plain, where groundwater level is high and lateral recharge water contains high salinity. Nanshantaizi is covered by slightly salinized soils. The soil salinization distribution estimated by WET Sensor is generally consistent with the actual levels of salinization. Soil salinity in Nanshantaizi is mostly of natural origin and accumulated salts could leach to deeper soils or aquifers by water percolation during irrigation. Groundwater evaporation, groundwater level depth and quality of recharge water are important factors influencing soil salinization in the alluvial plain.     

Magnetic properties of airborne particulate matter in Shanghai during dust storm events and the implications for heavy metal contaminant sources

Airborne particulate samples (including dust storm period samples) were collected from the Putuo, Qingpu and Minhang districts of Shanghai city from October, 2009 to October, 2010, and also tracked the dust transporting pathways from NW (Northwest) to SE (Southeast) including the cities of Xi’an, Beijing, Zhengzhou and Nantong, as a means of sampling the dust storm particulate matter in the spring of 2010. After measuring the magnetic parameters and the concentrations of particles and heavy metals, their magnetic properties were analyzed to track the source locations of heavy metal pollution during dust storm events, and then combined for backward trajectory analysis. It was found that the slightly polluted dust particles carried many contaminants during dust storm periods when the dust palls were transported by winter monsoon winds from the NW desert region towards the SE. The contaminants were further increased by contributions of fine SP&SD grains derived from local automobile exhausts in Shanghai as well as being enriched also in Northern cities during non-dust storm periods. A significantly positive linear relation was found between the χ_lf and SIRM of loess and the storm dust, indicating a similar material source for these two kinds of samples. A higher χ_lf and SIRM in storm dust content compared to loess suggests that storm dust contains not only materials from natural sources, but also those from partly anthropogenic sources. Backward trajectory analysis indicates intuitively the source region of the Shanghai storm dust. These conclusions have important scientific significance for research on long-distance transportation of contaminants (such as heavy metals) adsorbed onto airborne particulate matter during dust storm events.     

应用响应曲面法优化凯氏定氮法的消解条件

经典凯氏定氮法是通过观察消解反应现象来控制温度和时间,对于数量较多的样品同时消解会耗费大量的人力及时间,因此需要采用合理的试验设计方法确定最佳消解温度和时间,以实现批量消解样品,提高分析效率。本文利用响应曲面法对凯氏定氮法中的消解条件进行了优化分析,选择料液比、消解温度和消解时间作为优化因素,研究三因素的不同水平对氮含量测定的影响。通过响应曲面分析得到最优的消解条件为:料液比(g/mL)=0.3∶5,消解温度260℃,消解时间60 min。重复实验结果表明,样品在优化的条件下能够很好地消解,重现性较好;标准物质的氮含量的实验测定值(1310×10-6)与标准值(1300×10-6)基本一致,两者的对数误差绝对值为0.003,方法的准确性高。应用响应曲面试验设计方法,对于评价凯氏定氮法中三个消解条件对氮含量的非线性影响起到了很好的优选作用,能更好地预测实验因素对分析结果的影响趋势,可以准确控制消解温度和消解时间,对于提高分析效率具有实用意义。     

On improving tropical cyclone track forecasts using a scale-selective data assimilation approach: a case study

A dynamical downscaling approach based on scale-selective data assimilation (SSDA) is applied to tropical cyclone (TC) track forecasts. The results from a case study of super Typhoon Megi (2010) show that the SSDA approach is very effective in improving the TC track forecasts by fitting the large-scale wind field from the regional model to that from the global forecast system (GFS) forecasts while allowing the small-scale circulation to develop freely in the regional model. A comparison to the conventional spectral-nudging four-dimensional data assimilation (FDDA) indicates that the SSDA approach outperforms the FDDA in TC track forecasts because the former allows the small-scale features in a regional model to develop more freely than the latter due to different techniques used. In addition, a number of numerical experiments are performed to investigate the sensitivity of SSDA’s effect in TC track forecasts to some parameters in SSDA, including the cutoff wave number, the vertical layers of the atmosphere being adjusted, and the interval of SSDA implementation. The results show that the improvements are sensitive in different extent to the above three parameters.     

基于试验的模拟月壤表层取样理论修正及其应用

月球探测对于我国各方面综合实力的提升均具有巨大的推动作用。当前我国各研发机构对月球采样的研发重点集中于采样机具的设计制造上,对采样机具和月壤之间相互作用却研究较少。与地球土壤相比,月壤的形成环境与条件完全不同,从而造就了其较为特殊的物理力学性质。在利用与真实月壤类似的模拟月壤进行的薄壁圆筒贯入试验中,发现存在月壤滞留和月壤附壁现象,从而分析得出在采样机具表面与月壤相互作用的理论分析中,除了传统的摩擦力理论外,还可通过最大抗剪强度进行分析。通过对试验现象和数据对比摩擦力理论和最大抗剪强度理论发现,最大抗剪强度理论更加符合实际情况。故将最大抗剪强度理论引入已有的月球螺旋钻进采样的理论模型中,通过计算得出基于最大抗剪强度理论计算的螺旋临界转速低于基于摩擦力理论计算的临界转速,在一定程度上能够降低采样机具的能耗。     

新疆二红洼镁铁—超镁铁岩体橄榄石成因及其对硫化物熔离的指示

二红洼岩体位于新疆东天山黄山镁铁—超镁铁岩带的西段,地表由南、北两个小岩体组成,北岩体出露面积约1.42km2,呈北东—南西向展布;南岩体在呈椭圆形,出露面积约为6.25km2。岩体可分为两个侵入期次:第一侵入期次岩性为(含长)二辉橄榄岩和橄榄辉长岩,第二侵入期次岩性为辉长苏长岩和淡色辉长岩,辉长苏长岩侵入于第一期次形成的含长二辉橄榄岩和橄榄辉长岩中。岩体橄榄石Fo值在80.9~89.7之间,为贵橄榄石;Ni含量变化范围较大,主要集中在102.19×10-6~4319.66×10-6之间。岩体母岩浆MgO含量为10.3%,FeO含量为10.8%;回归计算结果显示二红洼岩体的原始岩浆中MgO含量为15.73%,FeO含量为10.71%。在橄榄石的结晶过程中母岩浆达到硫饱和,并发生有硫化物的熔离作用;橄榄石与硫化物的晶出质量比(橄榄石:硫化物)为50~100∶1。通过岩石学、矿物学特征以及模拟计算结果表明,二红洼岩体具有形成铜镍矿床的基本条件,但是岩体在深部岩浆房已经达到硫饱和并发生了硫化物的熔离作用,导致母岩浆中亏损Ni、Cu等成矿元素,未能形成工业矿体;在以后找矿勘探中,需要寻找早期硫化物熔离所形成的那部分硫化物熔体,并进一步寻找成矿富集的有利地段。     

Cold–wet spells in mainland China during 1951–2011

Two types of persistent extreme weather events, the cold–wet spell (CWS) and the persistent wet-freezing event (PWFE), are defined by considering the persistence of both extreme low temperature (ELT) and precipitation. Regional CWS and PWFE are identified based on temporal persistence and spatial contiguity of single-station-based CWS event and PWFE, respectively. Relevant factors are further discussed to reveal the features of spatial distribution and temporal variability of such events. The results indicate that: (1) station-based CWSs are mostly observed in southern China, especially in eastern part of southwest China and south China. PWFEs are relatively frequently observed immediate south of middle reach of the Yangtze River. Both CWS and PWFE of longer duration are frequently observed in the northern part of the Yunnan–Guizhou Plateau. Further analyses indicate that the occurrence of these events in southern China is positively related to elevation. (2) A total of 48 regional CWSs and 21 regional PWFEs are identified during cold season over 1951–2011 in China. The long-lasting ELT and rainy (snowy)/freezing condition render the event in southern China in 2008, the most severe one in the last five decades. (3) Precipitation is the limitation condition for the occurrence of CWS and PWFE in northern China, while ELT is the dominant factor for CWS and PWFE in southern China.     

黄土陡坡降雨冲刷试验及其三维颗粒流流-固耦合模拟

针对坡角为70°的黄土边坡,进行2.7 mm/min降雨强度下的室内坡面冲刷试验。根据边坡冲刷破坏的过程特征,将边坡侵蚀方式演变过程归纳为试验初期的片蚀、中期的细沟侵蚀、到后期的切沟侵蚀和坍塌。试验中坡顶处侵蚀强度大于其他部位,当坡面形成上下贯通的切沟之后,水流开始掏蚀沟槽底部土体,随着冲刷的持续,切沟两侧土体强度降低,坡顶土体发生坍塌。以此为基础利用三维颗粒流软件PFC3D对边坡降雨冲刷过程进行流-固耦合模拟,在模拟颗粒大变形的同时得到颗粒运动轨迹、孔隙率、流体单元内流速等重要参数,这些参数的定量变化过程反映了降雨过程中边坡遭受侵蚀程度及水流侵蚀能力的分布规律:坡顶处侵蚀最为强烈、水流侵蚀能力最强,且两者随高度降低呈减小趋势,与室内试验结果一致。     

考虑桩-土体系渐进破坏的单桩承载特性研究

针对目前桩基承载特性确定时未考虑桩-土体系渐进变形过程的现状,采用现场试验和理论分析等手段对考虑桩-土体系渐进破坏的单桩承载特性展开研究。首先,利用现场试验数据对侧阻和端阻的软化特性展开深入探讨,提出了侧阻和端阻软化模型,明确了模型中各参数取值方法,并验证了其合理性。同时,根据提出的侧阻和端阻软化模型,建立了一种可考虑桩-土体系渐进破坏的单桩承载特性的迭代算法。算例分析表明,计算获得的破坏性单桩承载特性与实测值有较好的一致性,且可反映侧阻和端阻的破坏特性。实际工程中,结合单桩承载特性分析算法,可根据单桩的实际受力特点灵活选用不同形式的侧阻和端阻荷载传递函数来分析不同桩顶荷载水平下的单桩受力特性。