Rock magnetic properties of Nihewan sediments at Xujiayao

Rock magnetic measurements of Nihewan sediments from Xujiayao section demonstrate that magnetite, hematite and maghemite are dominant remanent magnetization carriers. Monitoring the variations of magnetic susceptibility (MS) and saturating isothermal remanent magnetization (SIRM) at low temperature are the attractive ways of detecting the presence of magnetite, maghemitization and superparamagnetic grain sizes. Low-temperature MS investigations suggest that susceptibility enhancement for Xujiayao samples is mainly due to the remarkable presence of SD/MD magnetite to some degree though some magnetite grains have been partially oxidized at some depths. It is tentatively concluded that both SD/MD magnetite and hematite are of detrital origin and carry a characteristic remanent magnetization (ChRM), whereas maghemite can be attributed to be chemical origin, overprinting a reversed polarity component of Matuyama age.     

基于滞回曲线以及结构动力方程的混凝土结构抗震稳定性分析

为准确全面地量化分析研究土木工程建筑中混凝土结构抗震稳定性,提出基于滞回曲线以及结构动力方程的混凝土结构抗震稳定性分析方法。首先采用滞回曲线描述混凝土结构在地震作用下的损伤情况,对滞回曲线模型拐点进行有效操作,确保动力方程对混凝土结构抗震稳定性进行有效分析。其次采用基于混凝土结构动力方程的抗震稳定性分析方法,对地震地面运动模型以及结构分析模型来分析混凝土结构的随机地震反应情况,得到混凝土结构随机反应的汇总量,在此基础上通过双参数的结构破坏模型,基于结构稳定性原理,获取运算混凝土结构抗震稳定性的概率表达式,再基于该表达式分析混凝土结构的抗震稳定性情况。实验结果说明,所提方法能够对土木工程建筑中不同类型混凝土构件抗震稳定性进行有效分析,分析结果准确且全面。     

Modelling of R/C members accounting for shear failure localisation: Hysteretic shear model

Reinforced concrete (R/C) frame buildings designed according to older seismic codes represent a large part of the existing building stock worldwide. Their structural elements are often vulnerable to shear or flexure‐shear failure, which can eventually lead to loss of axial load resistance of vertical elements and initiate vertical progressive collapse of a building. In this study, a hysteretic model capturing the local shear response of shear‐deficient R/C elements is described in detail, with emphasis on post‐peak behaviour; it differs from existing models in that it considers the localisation of shear strains after the onset of shear failure in a critical length defined by the diagonal failure planes. Additionally, an effort is made to improve the state of the art in post‐peak shear response modelling, by compiling the largest database of experimental results for shear and flexure‐shear critical R/C columns cycled well beyond the onset of shear failure and/or up to the onset of axial failure, and developing empirical relationships for the key parameters defining the local backbone post‐peak shear response of such elements. The implementation of the derived local hysteretic shear model in a computationally efficient beam‐column finite element model with distributed shear flexibility, which accounts for all deformation types, will be presented in a companion paper.     

砂-锯末混合模型土的动力特性试验研究

为研究砂-锯末混合模型土的动力参数规律特性,采用动三轴试验,研究了此类土的滞回圈特性以及其动剪切模量和阻尼比随循环加载次数的变化规律.试验结果表明:分级循环加载过程中,随着荷载级别的增加,滞回圈的面积逐渐增大,形状从柳叶形向新月形发展;模型土的动剪切模量在各循环下基本为常量而阻尼比呈上下波动;而随荷载级别的增大,动剪切...     

Remanent hysteresis study of dolerite dykes

Saturation remanent hysteresis studies were carried out on numerous dolerite dyke samples from the peninsular India. These studies result in four types of remanent hysteresis curves which indicate that the magnetic material is magnetite or titanomagnetite with variable grain-size having remanent coercive forces (H _cr ) of 8 to 30 mT, requiring saturating fields (H _s ) up to 250 mT. Two extreme types of samples with (1) low coercive forces requiring high saturating fields and (2) high coercive forces requiring low saturating fields are noticed along with the generally observed ones. The Granulometric and Lowrie-Fuller Tests on these samples indicated that the magnetic material i.e., magnetite or titanomagnetite in these rocks is in the form of Multi-Domain (MD), Cation Deficient (CD) and a mixture of these two forms (MD+CD) within.     

Field‐scale phosphorus losses from a drained clay soil in Sweden

The objective of this study was to determine and discuss field‐scale phosphorus losses via subsurface tile drains. A total phosphorous (Tot‐P) export, which averaged 0·29 kg ha⁻¹ year⁻¹, was measured over a six‐year period from the 4·43 ha drainage system of a Eutric Cambisol in Central Sweden. The main part (63%) was in particulate form (PP) while the remainder was either in phosphate form (PO₄‐P) or in other dissolved or colloidal forms. A very small area, less than 1% of the soil surface, was demonstrated to be hydraulically active by using a staining technique in soil monoliths taken from the field. The stained macropores were few, but were continuous downward, and were relatively evenly distributed among the eight 7 dm² areas that were investigated. The transport from the field mainly occurred in episodes during which the relationship between phosphorus concentration and discharge was characterized by hysteresis loops. On average, half of the yearly P transport occurred in 140 hours. Compared with flow‐proportional and frequent sampling, manual and fortnightly sampling underestimated the transport of Tot‐P and suspended solids (SS) by 59 and 42%, respectively, during the six years studied. Amounts of different phosphorus forms exported through the tile drains were very similar to those reported from other clay soils in Northern Europe and North America. Copyright © 1999 John Wiley & Sons, Ltd.     

Estimating the deep seepage component of the hillslope and catchment water balance within a measurement uncertainty framework

Deep seepage is a term in the hillslope and catchment water balance that is rarely measured and usually relegated to a residual in the water balance equation. While recent studies have begun to quantify this important component, we still lack understanding of how deep seepage varies from hillslope to catchment scales and how much uncertainty surrounds its quantification within the overall water balance. Here, we report on a hillslope water balance study from the H. J. Andrews Experimental Forest in Oregon aimed at quantifying the deep seepage component where we irrigated a 172‐m² section of hillslope for 24·4 days at 3·6 ± 3 mm/h. The objective of this experiment was to close the water balance, identifying the relative partitioning of, and uncertainties around deep seepage and the other measured water balance components of evaporation, transpiration, lateral subsurface flow, bedrock return flow and fluxes into and out of soil profile storage. We then used this information to determine how the quantification of individual water balance components improves our understanding of key hillslope processes and how uncertainties in individual measurements propagate through the functional uses of the measurements into water balance components (i.e. meteorological measurements propagated through potential evapotranspiration estimates). Our results show that hillslope scale deep seepage composed of 27 ± 17% of applied water. During and immediately after the irrigation experiment, a significant amount of the irrigation water could not be accounted for. This amount decreased as the measurement time increased, declining from 28 ± 16% at the end of the irrigation to 20 ± 21% after 10 days drainage. This water is attributed to deep seepage at the catchment scale. Copyright © 2010 John Wiley & Sons, Ltd.     

高空观测球炸后的探空记录可用性分析

通过对射阳高空气象观测站采集的球炸后探空仪下降过程中的感应资料进行分析,发现探空仪上升和下降过程中同气压层温度差是由摩擦增温、滞后误差、仪器故障、温度空间变化、温度时间变化等原因造成,并就采集的下降资料因仪器快速下降造成的摩擦增温误差、滞后误差测算方法进行了研究,探讨了一些获取球炸后探空仪下降过程中周边环境准确气象资料的途径和努力方向,提出了高空观测球炸后继续观测和使用降落伞减缓下降速度的建议,以利获取更多的气象资料。     

土体冻融特征研究现状与展望

冻土中水分迁移是导致土体冻胀的关键因素,而研究水分迁移及其驱动力的核心问题是要充分理解未冻水含量与温度、基质吸力等变量之间的关系,这些关系可充分体现土体在冻融过程中土水变化特征。长期以来,对土体冻融特征的研究采取的是与非饱和土力学中的土水特征类比的方法进行,结果也证明了二者存在一定的相似性。但是冻土中因冰-水相界面作用产生基质吸力与融土中水-气相界面作用产生基质吸力的机理并不完全相同,而由于相变等其他作用产生的冻融滞后效应与融土中孔隙“墨水瓶效应”等引起的滞后效应机理也有区别。针对这些机理性的不同,还需要做大量的研究工作才能真正揭示土体的冻融特征。通过对目前土体冻融特征方面研究进展和存在问题的归纳总结,笔者认为今后在这方面还需深入开展如下研究：建立适合各类土壤冻融特征的一般预测模型,使得在缺少数据条件下能快速获取所需土样的冻融特征;研究土体在冻融和干湿变化过程中存在的类似性及区别,对冻融过程中存在的滞后效应机理给出合理的解释;提升冻融特征变量的测试技术水平,研发高精度的相关仪器设备。     

非饱和土毛细滞回内变量模型的修正

土-水特征关系是基质吸力和含水率之间关系。在反复干湿循环路径下土-水特征曲线呈现出毛细滞回特性。基于毛细滞回内变量理论和传统的土-水特征关系经验模型,提出了能模拟在任意干湿循环路径下土-水特征关系的修正模型。该模型比原模型增加了一个可逆参数,考虑了含水率的可逆变化,使扫描线在靠近边界线的时候斜率不会无限大,同时保留了原模型精度。通过与文献中的试验结果进行比较,修正模型可以更好地模拟非饱和土的土-水特征关系的循环滞回特性,并讨论了可逆参数的确定方法。