中坝隧道地下分水岭演化的数值模拟分析

由于铁路隧道的施工,地下水进入隧道,形成了新的排泄基准面,对区域地下水环境产生较大影响,故对该类问题进行深入研究具有重要的工程实践意义。以中坝岩溶隧道为例,采用Visual modflow对中坝隧道进行三维数值模拟,模拟中坝隧道开挖建设后,地下分水岭的演化过程,以此来探讨分析其对地下水环境的影响。     

内蒙古科右中旗地区梅勒图组安山岩年代学特征及其地质意义

对内蒙古科右中旗地区梅勒图组安山岩锆石LA--ICP--MS U--Pb年代学、锆石Hf同位素和岩石地球化学测试分析结果表明,梅勒图组安山岩形成时代约为早白垩世中期(123~125 Ma)。锆石εHf(t)=(+5.84~+9.34),一阶段Hf模式年龄为412~553 Ma。岩石地球化学分析表明,安山岩K2O含量较高,SiO2含量和Mg#值中等,富集大离子亲石元素,高场强元素Nb、Ta、Ti等明显亏损。这些特征反映出梅勒图组安山岩的源区为新形成的富集地幔。结合地球化学特征和区域大地构造背景,研究区梅勒图组安山岩的形成可能与太平洋板块俯冲作用后的陆内伸展环境有关。     

萃取分离—石墨炉原子吸收光谱法测定铅锌矿中的铟

样品经硝酸、氢氟酸分解除硅,加热硫酸冒烟除尽硝酸、氢氟酸,利用铟与氢溴酸能生成稳定的络合物并被乙酸丁酯萃取的性质,将铟与其它干扰离子分离并富集.使用MOLAARM6（Thermo Electron Corporation）石墨炉原子吸收分光光度计,以钒为机体改进剂,测定铅锌矿中的铟.方法检出限为LD=0.012ug/ml.实验结果令人满意.     

全球二叠系顶部白云岩与沉积相关系统计及其白云石化机制的意义

本文对全球范围内23个典型的研究程度较高的晚长兴期露头进行了研究,逐一检查了晚长兴期白云岩前身沉积的沉积相,结果发现所有白云岩的前身都是浅水相的(除汉中梁山一个剖面外)。相反,目前已经研究的深水相上二叠统碳酸盐沉积物都没有发生白云岩化。这一结果表明,世界范围内上二叠统顶部白云岩的形成机制可能都与海平面下降有关,很可能是蒸发成因的浓缩卤水使沉积物发生白云岩化。据此推断,四川盆地东北部长兴组白云岩也应当是此种成因。     

Variation of albedo to soil moisture for sand dunes and biological soil crusts in arid desert ecosystems

Surface albedo plays a crucial role in the energy balance of soils. The surface albedo and surface soil moisture of bare sand and biological soil crusts (BSCs) were concurrently observed on field plots of shifting sand dune and in revegetated desert ecosystems at Shapotou, northwestern China, to study relationships between surface albedo, solar elevation angle, and surface soil moisture. Results indicated that rainfall exerted a remarkable lowering effect on the variation of surface albedo by increasing surface soil moisture. Surface albedo was an exponential function of solar elevation angle, and the normalized surface albedo (solar elevation angle effect was removed) decreased exponentially with the increase of surface soil moisture. Sand surface had a higher albedo (0.266) than BSCs (0.226) when the surfaces were very dry. However, sand surface albedo became increasingly lower than that of BSCs when the surfaces were in wet conditions and when the soil moisture exceeded a critical value. The changes in soil surface albedo from sand dune to BSCs after revegetation in shallow soil profiles associated with the variation of the surface soil moisture can be seen as an indicator of the degree of sand dune stabilization when compared with the original shifting sand dune soil.     

Anisotropic shear strength characteristics of a tailings sand

The deposition process of tailings in a tailings dam may lead to the anisotropy of mechanical properties of tailings. To investigate the anisotropic shear strength characteristics of a tailings sand, samples deposited under gravity were sheared in a modified direct shear apparatus along different orientations of the shear planes relative to the bedding plane. The experimental results reveal that the anisotropy has a substantial effect on the peak shear strength of the tailings sand, leading to a variation in peak friction angle of 10°. It is found that the effect of anisotropy on the peak shear strength of the tailings sand is mainly attributed to the effect of anisotropy on soil dilatancy. On the other hand, the effect of anisotropy on the residual friction angle of the tailing sand is relatively smaller, likely due to the partial erasure of anisotropy at large shear deformation. The degree of anisotropy is reduced by an increase in normal stress. To achieve more accurate stability analysis of tailings dams, it is suggested to take into account the shear strength anisotropy of tailings soils.     

Modeling the risk of nitrate leaching and nitrate runoff loss from intensive farmland in the Baiyangdian Basin of the North China Plain

The water movement and soil nitrogen cycle of the Baiyangdian Basin were simulated, and the risk of nitrate leaching and nitrate runoff loss from intensive farmland was assessed by using the distributed hydrological soil and water assessment tool (SWAT) in this study. The model assessment showed that SWAT was able to simulate water and nitrate movement in the region with satisfactory results. The modeling analysis indicated that fertilizer application was the overriding source of soil nitrogen and might result in a large amount of nitrate accumulation in soils; this nitrate might be lost by leaching or runoff driven by water movement. In 2009, nitrate nitrogen leaching represented 19.5 % of the total amount of nitrogen fertilizer application, while nitrate nitrogen runoff represented 1.7 % only. Thus, it showed that the nitrate leaching was the main approach of soil nitrogen movement in farmland because of strong percolation. It also showed a significant variation of nitrate leaching from different soil depths, with the largest amount leached from surface soil layers and the smallest amount leached from lower soil layers. Therefore, it could be further revealed that the nitrate concentration was very low at soil layers lower than the root zone of crops (1.2 m). Validated by groundwater observations, groundwater pollution by nitrate derived from fertilizers was not serious because of the deep groundwater level in the study plain. However, the risk of groundwater pollution would increase significantly if precipitation increased.     

基于地层结构组合的第四纪地质单元划分研究——以皖江经济带沿江丘陵平原区为例

为支撑地质条件复杂地区的水文地质、工程地质和环境地质调查研究,在皖江经济带沿江丘陵平原区通过系统分析第四纪地层的岩性、结构、构造等组合,以地貌以及第四系成因、沉积相和沉积物物源为指标,结合已有区域第四纪研究成果以及年代地层和岩石地层划分标准,进行皖江沿江丘陵平原区“第四纪地质单元”划分,共划分出冲积-湖积平原地质单元、洪积-坡积岗地地质单元和残积-剥蚀丘陵地质单元3个一级地质单元,总结了7种类型第四纪地层结构组合及其特征,为区域水文地质和工程地质调查与研究奠定了基础。     

Characteristics of shallow geothermal fields in major cities of Tibet Autonomous Region

Based on the project titled “Investigation and evaluation of shallow geothermal energy in major cities of Tibet Autonomous Region”, the distribution characteristics and occurrence conditions of shallow geothermal fields in these cities were introduced in this paper. To this end, relevant data in Lhasa, Shigatse and Nyingchi Cities through vertical thermometry was a focus, so as to analyze groundwater temperature and the distribution law of strata with constant temperature. Then through comprehensive comparisons and analysis of the relationship between groundwater temperature and climate, differences in this aspect of Nagqu City were taken as a typical case to clarify formation of geothermal field and corresponding influence on groundwater temperature, furthermore providing basic data for rational development and utilization of shallow geothermal energy in Tibet Autonomous Region.