Peridotites from the southern Mariana forearc: Heterogeneous fluid supply in mantle wedge

Detailed petrological work was carried out on serpentinized peridotite dredged and sampled by submersible from the southern part of the Mariana Trench to reveal the nature of the mantle wedge in the southern Mariana forearc. The southern part of the Mariana Trench is important in that we should expect to find a transect of a typical island arc structure; that is, from east to west, the Mariana forearc, the Mariana arc proper, the Mariana Trough (active back-arc spreading center), and the West Mariana Ridge (remnant arc). The most striking feature of peridotites from the southern part of the trench is that primary hornblende is a major constituent mineral in many specimens. Thus, the peridotite samples are divided into anhydrous (A-type), hydrous (H-type) and intermediate (I-type) groups. Petrological data suggest that each type of peridotite is a residue of extensive partial melting in the upper mantle. It is argued here that the I- and H-type peridotites were modified from `proto-A-type peridotite' by fluid infiltration. The fluid was enriched in Al, Ti, Fe, and alkalis, and may have caused changes in mineral and bulk chemical compositions of the peridotites. A-type peridotite derives from the `proto-A-type peridotite' directly, without any fluid contamination. After the formation of the `proto-A-, I-, and H-type peridotites', lower-temperature fluids, probably of seawater origin, produced retrograde metamorphism and alteration including serpentinization. The mantle wedge in the southern Mariana forearc was heterogeneous in fluid supply.     

轻型井点结合明排降水新工艺

研究了在渗入水和层间滞水作为补给的水文地质条件下的基坑降水方法,设计了轻型井点结合明排降水的施工方案,创新地应用了滤水管间隔增减长度法、横插滤水管集水法的工艺措施.实践表明,这些方法成功地解决了上述条件下基坑降水的难题.     

土坡降雨入渗影响因子模拟实验

综合模拟实验土坡降雨入渗的各种常见影响因子,实验结果表明:土质对降雨入渗能力的影响明显,土中粘粒含量越高,颗粒越细微,粒间孔隙越小,吸、保水性能越强,开始入渗速度较快,在一定时间后入渗趋于平缓,浸润线前锋位置与雨水之间存在滞后现象;土体结构都对土体入渗能力产生较大影响,随着土体密实程度的增加,土体水力传导度减小,其水分入渗能力明显降低,开始入渗速度较快,在30min过后入渗趋于平缓;在临界含水量内,渗透系数与饱和度成反比;在正常温度范围内,对渗透影响不明显;坡度与累积入渗深度基本呈凸形曲线关系;随着植被覆盖度增加,累积入渗量成直线增加。     

利用泉水长观资料计算降水入渗系数——以务川自治县大竹园铝土矿区岩溶充水矿床为例

务川自治县大竹园铝土矿区为高山台地向斜正地形,岩溶充水矿床,水位埋藏较深,大气降水是地下水的唯一补给源,北、东、西为陡崖或陡坡,崖脚为矿系和隔水层,沿陡崖上部边缘分布一条开口向西的地表分水岭,形成完整的水文地质单元,地下水在向斜内由东向西汇集于梅古洞排泄。铝土矿层直接顶板梁山组(P_2l)页岩,厚度小,不连续,其上部茅口栖霞组(P_2m+q)灰岩强含水层与矿层直接接触,并且岩溶管道发育。因此,计算矿坑涌水量的方法用水均衡法较为恰当,即利用泉水观测资料计算入渗系数,从而达到预测矿坑涌水量、评价含水层富水性的目的。     

潼关高程的变化及其对渭河下游洪水的影响探讨

三门峡水库1960年投入使用之后,经过两次改建和三次运行方式调整,不仅发挥了较大的防洪效益,也为多沙河流上修建水库长期保持兴利库容积累了丰富经验。但水库运用也给库区造成一系列问题。通过分析潼关高程的变化及其对渭河下游河道及下游洪水特征值的影响,提出了防治渭河下游洪灾的对策。     

河北雨洪模型中下渗公式的一种改进方法

下渗强度的计算是干旱半干旱地区超渗产流计算的关键环节。河北雨洪模型中的流域下渗强度计算公式由两部分组成,一部分为由张力引起的下渗强度,另一部分为由重力引起的下渗强度(稳定下渗能力)。计算以上两部分下渗强度时,公式所用的雨量有重复,致使总下渗强度普遍偏大,从而导致模型模拟的洪水过程的洪量及洪峰偏小。提出一个改进的流域下渗强度计算公式,计算张力引起的下渗时所用雨强为总雨强与稳定下渗能力的差值。利用改进前后的计算公式,分别对2mm/h到10mm/h雨强及0mm到140mm表层土湿条件下的下渗强度进行计算,并对结果进行对比分析。大阁流域的实例应用结果表明,改进后的下渗强度计算公式,对模拟洪水过程的洪量和洪峰流量的增加效果明显,增加值分别为实测值的14.14%和10.08%。     

关于我国金刚石钻头生产技术的分析研究

我国金刚石钻进取得了很大的成绩,但是其技术经济指标尚不理想,与国外相比尚有差距,特别是其中关键的金刚石钻头性能指标更是如此。我国目前主要使用热压烧结技术生产金刚石钻头。但是,热压烧结有“短板”,国外冷压浸渍烧结有强项,微波加热烧结有优点。建议试验研究冷压浸渍、微波烧结金刚石钻头,以便把我国的金刚石钻探技术经济指标提高到一个新水平。     

Laboratory study of infiltration into two frozen engineered (sandy) soils recommended for bioretention

Infiltration of water into two frozen engineered soils of different gradation was studied in laboratory soil columns 1.2 m long and 0.1 m in diameter. Prior to testing, the soil moisture was adjusted to two levels, described by the gravimetric water content of 5% or 10%, and soils were compacted to about 80–90% of the maximum dry density and refrigerated to temperatures ranging from ?8 to ?2 °C. Water with temperatures 8–9 °C was thereafter fed on the top of columns at a constant head, and the times of water breakthrough in the column and reaching a steady percolation rate, as well as the percolation rate, were recorded. The soil water content was a critical factor affecting the thawing process; during freezing, soil moisture was converted into ice, which blocked pores, and its melting required high amounts of energy supplied by infiltrating water. Hence, the thawing of soils with higher initial water content was much slower than in lower moisture soils, and water breakthrough and the attainment of steady percolation required much longer times in higher moisture soils. Heat transfer between infiltrating water, soil ice, and frozen soil particles was well described by the energy budget equations, which constitute a parsimonious model of the observed processes. The finer grained soil and more compacted soil columns exhibited reduced porosity and required longer times for soil thawing. Practical implications of study results for design of bioretention facilities (BFs) in cold climate include the use of coarse engineered soils and fitting bioretention facilities with a drain facilitating soil drainage before the onset of freezing weather. Copyright © 2015 John Wiley & Sons, Ltd.     

Snow and frost: implications for spatiotemporal infiltration patterns – a review

Vast regions of the northern hemisphere are exposed to snowfall and seasonal frost. This has large effects on spatiotemporal distribution of infiltration and groundwater recharge processes as well as on the fate of pollutants. Therefore, snow and frost need to be central inherent elements of risk assessment and management schemes. However, snow and frost are often neglected or treated summarily or in a simplistic way by groundwater modellers. Snow deposition is uneven, and the snow is likely to sublimate, be redistributed and partly melt during the winter influencing the mass and spatial distribution of snow storage available for infiltration, the presence of ice layers within and under the snowpack and, therefore, also the spatial distribution of depths and permeability of the soil frost. In steep terrain, snowmelt may travel downhill tens of metres in hours along snow layers. The permeability of frozen soil is mainly influenced by soil type, its water and organic matter content, and the timing of the first snow in relation to the timing of sub‐zero temperatures. The aim with this paper is to review the literature on snow and frost processes, modelling approaches with the purpose to visualize and emphasize the need to include these processes when modelling, managing and predicting groundwater recharge for areas exposed to seasonal snow and frost. Copyright © 2015 John Wiley & Sons, Ltd.