路堤边坡稳定可靠度计算中的模型不确定性分析

基于均质路堤边坡Monte Carlo法的稳定可靠度计算,分析了临界滑面搜索策略和稳定分析方法两类模型不确定性对边坡可靠度的影响特性,讨论了边坡失效概率随土工参数变异性的变化规律。研究表明,选用不同的临界滑面搜索策略所得可靠度结果差异不大,参数滑面法（overall slope）的失效概率略大于均值滑面法（global minimum）,但差别对边坡稳定性分析没有实质性影响;土性参数变异水平是影响边坡可靠度的最重要因素,边坡在相同设计参数安全系数下的可靠度指标随参数变异性增大而急剧降低;不同稳定性分析方法对应的安全系数概率密度函数曲线形态基本一致,但失效概率差异明显,因此目标可靠度指标取值应与稳定性分析方法相适应。提出的考虑土工参数变异水平的安全系数取值修正原则,对改进确定性设计的边坡稳定分析技术有积极意义。     

花岗岩残积土冲击损伤与损伤演化特性试验研究

选取东南沿海某建筑工程地基浅层残积土为试样,运用超声波岩土损伤检测技术,测试计算在不同冲击荷载作用下试样纵波波速。选用纵波波速为损伤变量进行损伤度计算,分析了冲击荷载冲击频率、冲量等参数对试样损伤度的影响关系。同时结合试样试验破坏实际情况,分析了冲击荷载作用下试样损伤演化破坏特性。结果表明,随着冲击频率和冲量的增大,残积土试样损伤度都有增大上升趋势;随着损伤度的增加,残积土冲击损伤演化过程可分为小变形、端部出现裂纹、前端1/3处鼓胀或出现裂纹、前端裂纹扩展与表面剥落等几个不同破坏阶段。研究结论为揭示动荷载作用下残积土动力损伤演化规律提供科学依据和量化参数。     

内蒙古宝昌台地电阻率长期观测数据研究

分析了内蒙古宝昌台地电阻率长期观测数据的可靠性,应用归一化变化速率方法和傅氏滑动方法处理了1985年以来的地电阻率观测数据,研究了该台在地震前中期、短期阶段的监测效能,结果显示：该台两个正交测道的地电阻率观测对台站周围的中等以上地震有一定的监测能力,表现出了与地震有关的震前持续性的中期、短期异常,且在中国大陆及周边发生的数次远距离8级以上大震前也记录到持续1年尺度时间的下降/上升异常。     

Identifying spatio-temporal variation and controlling factors of chemistry in groundwater and river water recharged by reclaimed water at Huai River,North China

Reclaimed water is efficiently used to recover the dry river, but river water and groundwater may be impacted considering the water quality. Thus, it is critical to study the factors controlling water chemistry. Samples of reclaimed water, river and groundwater were collected monthly from January to September in 2010, in Huai River (North China). And samples were analyzed for major 15 physio-chemical parameters. Using hierarchical cluster analysis, 9 months are divided into two distinct groups, which show the clear temporal variation. In reclaimed water and river water, one group includes February, while the other includes other months. In shallow and deep groundwater, one group includes months from January to April, while the other encompasses others. Monitoring stations are classified into three groups. Group A with high value of ions and nitrogen (order: NH₄-N > NO₃-N > NO₂-N) includes reclaimed water and river water. Group B with moderate concentration and nitrogen (order: NO₃-N > NH₄-N > NO₂-N) includes all shallow groundwater and one deep groundwater. Group C with the low value and nitrogen (order: NO₃-N > NO₂-N > NH₄-N), includes two deep groundwater. Using multivariate analysis and ionic relationships, river water chemistry is found to be controlled by reclaimed water and evaporation process; chemistry in shallow groundwater and one deep groundwater, with type of Na–Ca(Mg)–HCO₃–Cl, is controlled by dissolution of calcite, carbonate weathering. Additionally, reactions of nitrification, denitrification and cation exchange occur in the infiltration of reclaimed water; chemistry in the other deep groundwater, with type of Ca–Mg–HCO₃–Cl, is controlled by dissolution of calcite, carbonate weathering and denitrification.     

陆态网络GNSS基准站阶跃偏移量的精确估计

通过对发生阶跃的GNSS基准站坐标序列谱指数的求解,表明了其具有有色噪声的特性,并对三分量分别建立了最优噪声模型,以此对GNSS基准站坐标的阶跃偏移量进行了精确估计,探明了地震和仪器更换对测站产生的精细影响。同时利用求解的阶跃偏移量对坐标序列进行修正,对获取连续性变化的测站坐标序列和获取精确的测站三维运动参数具有重要意义。     

Upper mantle seismic anisotropy beneath a convergent boundary: SKS waveform modeling in central Tibet

This study used SKS waveforms from the International Deep Profiling of Tibet and the Himalayas (INDEPTH) III dataset and a new 2D method for modeling seismic waves in anisotropic media to construct an image of anisotropic structures beneath central Tibet. A preferred model revealed three-segment anisotropic structures in the upper mantle beneath the study region. Waveform modeling demonstrated that the anisotropy was mainly generated by the lithosphere but not the asthenosphere, and that an anisotropic model with a flatter axis of symmetry provides a more consistent interpretation of the observations than models having steeply dipping symmetry axes. A relatively low velocity zone may underlie or intermingle with the anisotropic structures in the northern portion of the region. Synthetic tests also indicate that variations in the elastic constants and depth extent of the anisotropy assumed by the calculations do not affect the general conclusions, although trade-offs exist among certain model parameters. The modeling results suggest that the complex seismic structures in central Tibet were associated with underthrusting of the Indian lithosphere beneath the Asian lithosphere; the inferred flat symmetry axis of the anisotropy was likely generated during this collision process. If this were not the case, the inherited anisotropy would exhibit a steeply dipping axis of symmetry, parallel to the direction of underthrusting.     

Soil phosphorus bioavailability assessed by XANES and Hedley sequential fractionation technique in a glacier foreland chronosequence in Gongga Mountain,Southwestern China

The primary productivity of terrestrial ecosystems is influenced by soil phosphorus bioavailability, which depends largely on chemical fractions of phosphorus. The sequential fractionation technique developed by Hedley et al. or its subsequent modification is a well-known method to determine soil phosphorus forms. Hedley sequential fractionation technique separates the phosphorus into fractions based on their different chemical solubilities in extractants with certain chemical properties. Recently, synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy has been employed to measure soil phosphorus species directly and non-invasively. The XANES method provides information concerning local structure and chemical information of target elements at a molecular level. Thus, it can distinguish phosphorus fractions bound by metal oxides or hydroxides (such as Fe, Al, and Ca). In this present work, the phosphorus speciation of topsoil along a glacial foreland chronosequence in Gongga Mountain is determined using these two methods. The changes in soil phosphorus bioavailability along the 120-year-old chronosequence are assessed based on comparisons of the results obtained by these two methods. The results indicate that Hedley sequential fractionation technique shows a greater ability to determine soil bioavailable phosphorus (Resin-P and NaCHO₃-P), while XANES is effective in distinguishing phosphorus bound by metal compounds. In the chronosequence, Ca- and Al-bound phosphorus were derived mainly from primary minerals, whose phosphorus contents decreased within 120 years of moraine weathering and soil development. The content of soil bioavailable phosphorus increased rapidly after 30 years since deglaciation. The increasing phosphorus bioavailability promoted the colonizing and primary succession vegetation.     

The provenance of Gansu Group in Longxi region and implications for tectonics and paleoclimate

The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.     

A three-scale cracking criterion for drying soils

Cracking is a most unwanted development in soil structures undergoing periodic drying and wetting. Desiccation cracks arise in an apparent absence of external forces. Hence, either an internal, self-equilibrated stress pattern resulting from kinematic incompatibilities, or a stress resulting from reaction forces at the constraints appear as a cracking cause, when reaching tensile strength. At a meso-scale, tubular drying pores are considered in the vicinity of a random imperfection, inducing a stress concentration in the presence of significant pore suction. This approach allows one to use the effective stress analysis, which otherwise, away from the stress concentration, usually yields compressive effective stress and hence a physically incompatible criterion for a tensile crack. Recent experiments on idealized configurations of clusters of grains provide geometrical data suggesting that an imperfection as a result of air entry deep into the granular medium penetrates over 4 to 8 internal radii of a typical pore could yield a tensile effective stress sufficient for crack propagation.