CPⅢ技术在变形监测中的应用

CPⅢ控制网是直接控制无碴轨道施工的最后一级平面、高程控制网,已经在高速铁路建设中大量采用,其数据采集和数据处理技术已日趋成熟。文中结合重庆市某桥墩变形监测项目,介绍将CPⅢ技术应用于变形监测工程的操作流程。监测结果表明,CPⅢ后方交会测量精度达毫米级,能够满足大部分变形监测工程的精度要求。     

The Use of Polyphenolic Compounds from Black Tea for the Solid Phase Extraction and Determination of Trace Iron in Drinking Water

A simple and selective solid phase extraction procedure for the trace analysis of iron(III) in water samples has been developed. Sodium dodecyl sulfate coated alumina, modified with polyphenolic compounds (extracted from black tea) was used for the extraction and preconcentration of iron(III) from water samples before determination by flame atomic absorption spectrometry. Due to the complexation reaction between iron(III) and polyphenol compounds, iron(III) was quantitatively extracted on the proposed sorbent and then eluted by 2.0 mL of HCl (1.0 mol/L). The effects of extraction parameters, such as pH and volume of sample solution, amount of polyphenolic compounds, type of eluting agent and the effect of interfering ions on the extraction of iron(III), were investigated. It was found that the proposed method had a good linear range (15.0–100.0 μg/L) and a low detection limit (10.0 μg/L). The procedure was successfully applied for iron determination in drinking water samples.     

北极III区海冰面积低频变化对北半球冬季大气环流异常的作用

北极III区海冰面积的低频变化所引起的热力强迫作用，可以激发出EA和类似于WP的大气遥相关型。冰气系统之间存在着3～4年的不规则振荡，在振荡过程中，它们是相互作用的。对比表明，北极III区的重冰年和轻冰年，北半球冬季中纬度地区大气环流以及我国的天气气候特征有十分明显的差异。     

缺氧酸性条件下三价铁对锑释放的作用机制

辉锑矿（Sb2S3）的氧化溶解是控制锑（Sb）从岩矿中释放进入水土环境并影响其迁移转化的首要过程。酸性矿山废水中的三价铁[Fe（III）]是矿区环境中广泛存在的天然氧化剂,然而Fe（III）对Sb2S3的氧化溶解与Sb的释放作用机制尚不明确。通过模拟黑暗缺氧酸性的矿山地下水环境,开展Fe（III）浓度与Sb2S3表面积比值（I）控制的Sb2S3氧化溶解动力学实验,结合S-Sb-Fe氧化还原作用产物的溶解态组成与固相表征手段,揭示Fe（III）对Sb释放的作用机制。结果显示：Fe（III）作用下Sb2S3的氧化溶解是一个产酸的过程,I值越大,Fe（III）对Sb释放的促进作用越明显。缺氧条件下,Fe（III）与Sb2S3发生氧化还原作用,主要产物是五价锑[Sb（V）]、硫单质[S（0）]和二价铁[Fe(Ⅱ)],反应后矿物表面有S（0）和Fe2O3检出,阻碍了Sb2S3氧化溶解反应的持续进行。 I值一定时,低浓度的Fe（III）和溶解氧（DO）质量浓度的增加均会减少矿物表面S（0）的附着量,促进Sb释放量的增加;溶液中的Cl−通过配位络合效应会促进Sb2S3的溶解释放。缺氧酸性条件下Fe（III）与Sb2S3的作用控制着Sb的释放。研究结果可为矿山闭坑后地下水Sb污染防治提供重要的理论依据。     

砂岩的I/III复合型断裂试验研究

为了了解砂岩的I/III复合型断裂力学性能,采用含有裂纹面垂直于底面但倾斜于正背面的三点弯曲（TPB）试件实现面外断裂。使用Abaqus通过有限元法研究了不同裂纹面倾斜角下沿着试件厚度的I型、II型与III型无量纲应力强度因子。通过讨论可知,在靠近试件厚度中点处I型与III型无量纲应力强度因子取得较大值,而II型无量纲应力强度因子取得接近于0的可以忽略的极小值,且靠近自由面处的应力强度因子不作考虑。故该种试件可用于测量材料的I/III复合型断裂性能。数值计算结果与常规TPB试件的解析公式及倾斜裂纹面TPB试件的近似计算公式的结果进行对比,证明了数值模拟结果的准确性并讨论了近似公式存在的问题。使用7组共28个该种三点弯曲试件,研究砂岩的I/III复合型断裂特性,结果表明：砂岩的I型与III型临界应力强度因子随着裂纹面倾斜角的增大先增大后减小,但其变化趋势不同;砂岩的I/III复合型等效断裂韧度随着裂纹面倾斜角的增大先增大后减小,在倾斜角接近20°时取得最大值。裂纹扩展时裂纹面将发生扭转,倾斜角θ越大则扭转角度越大。     

Gas-generation potential of shales in small and medium-sized basins: a case study from the Xuanhua Basin,north China

Abstract

Small- and medium-sized basins are widely distributed, and some contain commercial gas reservoirs demonstrating their gas-generation potential. The Xuanhua Basin, which is a small-sized coal-bearing basin in north China, includes a promising target for shale-gas exploration in the Xiahuayuan Formation. In this study, we used this basin as a case study to assess the critical geochemical features for small or medium-sized basins to form commercial gas reservoirs. Total organic carbon (TOC) analysis, Rock-Eval pyrolysis, microscopic observation of macerals, vitrinite reflectance measurement and kerogen stable carbon isotope analysis were performed to characterise the organic geochemistry of the Xiahuayuan shales. The original total organic carbon (TOC_o) content and hydrocarbon-generative potential (S_2o) were reconstructed to further evaluate the gas-generation potential of these shales. In addition, geochemical data of shales from other similar-sized basins with gas discoveries were compared. The results showed that the kerogen from the Xiahuayuan Formation is Type III (gas-prone), and macerals are dominated by vitrinite. TOC values showed a strong heterogeneity in the vertical profiles, with most higher than 1.5?wt%. The measured R_o values ranged from 1.4 to 2.0%. However, thermal maturity was not correlated with the present-day burial depth with higher maturity in the wells closest to the diabase intrusion centre. The remaining generation potential (S₂) averaged 0.91?mg HC/g rock, equal to 1.4?cm³ CH₄/g rock, and the average amount of hydrocarbon generated was 4.33?cm³ CH₄/g rock. In small and medium-sized basins, the TOC content of commercially developed gas shales ranged from 0.5 to 2.5?wt%, organic matter was mainly humic (gas-prone), and the burial depth was generally shallow. Biogenic gas reservoirs for commercial exploitation tend to have larger shale thicknesses (120–800?m) than thermogenic gas reservoirs (60–90?m).

1. The Xiahuayuan Formation is a good gas-source rock with gas-prone kerogen type, relatively high TOC values and moderate thermal maturity.

2. The average amount of hydrocarbon generated from the Xiahuayuan shales is about 4.33?cm³ CH₄/g rock, indicating a potential to form a shale gas reservoir.

3. Owing to the influence of diabase intrusions, the Xiahuayuan shales have entered the dry gas window at relatively shallow-buried depths.

4. Small- and medium-sized basins have the potential to generate commercial gas reservoirs with the generated volume mainly a product of the thickness and maturity of black shales.

     

Environmental flow requirements assessment in the Halda River,Bangladesh

Abstract

Environmental flows have scarcely been considered in river water management in Bangladesh. This study attempts to assess the environmental flow requirements in the Halda River, Bangladesh. Thus, the objectives are to estimate the Halda River flow with different return periods/probabilities, which was done using the log-Pearson Type III distribution (LPIII), and to mitigate the environmental problems in the Halda River using the building block method. The LPIII distribution was used to estimate the expected extreme and satisfactory flows for fish habitat at Panchpukuria station and the expected extreme water levels at Panchpukuria, Narayanhat, Telpari and Enayethat stations. It was found that floods are likely to occur at least once in 2.1, 1.02, 1.75 and 1.25 years at Panchpukuria, Narayanhat, Telpari and Enayethat stations, respectively. The results of flow and water quality analyses suggest that environmental flow requirements cannot be achieved in this river throughout the year. The environmental flow requirements and conservation of fish resources can be achieved by implementing the suggestions provided in conjunction with a comprehensive awareness programme, investigations and trade-off analyses being among the suggestions.

Editor Z.W. Kundzewicz; Associate editor B. Sivakumar

Citation Akter, A. and Ali, Md. H., 2012. Environmental flow requirements assessment in the Halda River, Bangladesh. Hydrological Sciences Journal, 57 (2), 326–343.     

Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing

Results of drag coefficient(CD) from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH Ⅲ has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input,numerical experiments under idealized wind field and tropical cyclone Bonnie(1998) were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced CD significantly decrease wind energy input into the wave model and then simulate lower significant wave height(SWH) than the original model. However,the effects on spatial distribution of SWH,mean wavelength,mean wave direction,and directional wave spectra are insignificant. Due to the reduced wind energy input,the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants;it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of CD in high winds creates a simulation that agrees best with scanning radar altimeter observations.