Unified numerical study of shallow foundation on structured soft clay under unconsolidated and consolidated-undrained loadings

Abstract

Based on a new elasto-plastic constitutive model, this paper presents a soil–water coupled numerical prediction of the bearing capacity for shallow foundation constructed on Ballina soft clay for unconsolidated undrained (UU) and consolidated undrained (CU) conditions. This elasto-plastic constitutive Shanghai model has an advantage of describing the mechanical behaviour of over-consolidated and structured soil under different loading and drainage conditions, by using one set of material parameter. In this paper, the Shanghai model used for both UU and CU conditions has the same initial parameters obtained from laboratory test results. The loading conditions and consolidation stages vary based on construction details. The predicted bearing pressure-settlement responses for UU and CU, approves the field observation. The phenomenon of gaining the bearing capacity due to consolidation is captured and explained by the use of soil–water coupled numerical analysis with a new elasto-plastic model. The stress strain behaviour, stress paths and the decay of the structure of elements at different depths presented in this study, reveal the mechanism for the difference between UU and CU conditions to understand the foundation behaviour. Effect of the initial degree of soil structure on the bearing capacity is also addressed. Overall, this approach provides the integrated solution for the shallow foundation design problems under short and long-term loadings.     

发展地理学研究进展与展望

本文回顾和总结了20世纪以来发展地理学的研究进展,涉及发展地理学内涵和理论、领域和方法及其发展趋势。系统梳理了发展地理学在欠发达国家或地区发展收敛、发达地区或国家生活品质提升过程中的收敛及其路径等研究内容。通过分析国外研究进展,指出了发展地理学在中国的发展条件与学科优势,并着眼于国际学术前沿最新动向与国家宏观战略需求,提出了今后中国发展地理学研究需重点关注的领域。未来发展地理学研究应以可持续发展理论为指引,以提升欠发达地区可持续生计能力与区域绿色发展水平为核心,以构建发展地理学理论和跨学科综合集成研究体系为目标,聚焦区域发展的空间格局、扩散特征与收敛研究,探索出服务于区域经济建设与产业发展的调控政策与科学路径。     

南海风暴潮对风场和外围海水敏感性研究

为探索来自西北太平洋台风风暴潮与南海局地生成台风风暴潮不同,本研究在假设两种台风气象条件相同情况下,研究随台风而来外围海水所形成增水对南海沿岸的影响。以0814"黑格比"强台风风暴潮为基础,使用ROMS(regional ocean modeling system)模式进行数值模拟并通过设计对比试验方法进行研究,研究发现在台风登陆时引起的增水最大,最大增水出现在台风路径右侧,其中在沿岸区域,外围海水形成增水约占总增水10%,且大约3 h后出现增水回震现象。同时,设计对比试验,研究来自西北太平洋台风风暴潮对台风路径、台风强度、台风移动速度和流入角等气象条件敏感性,并获得与前人一致的结果。     

An assessment of Arctic cloud water paths in atmospheric reanalyses

The role of Arctic clouds in the recent rapid Arctic warming has attracted much attention. However, Arctic cloud water paths(CWPs) from reanalysis datasets have not been well evaluated. This study evaluated the CWPs as well as LWPs(cloud liquid water paths) and IWPs(cloud ice water paths) from five reanalysis datasets(MERRA-2,MERRA, ERA-Interim, JRA-55, and ERA5) against the COSP(Cloud Feedback Model Intercomparison Project Observations Simulator Package) output for MODIS from the MERRA-2 CSP(COSP satellite simulator) collection(defined as M2 Modis in short). Averaged over 1980–2015 and over the Arctic region(north of 60°N), the mean CWPs of these five datasets range from 49.5 g/m~2(MERRA) to 82.7 g/m~2(ERA-Interim), much smaller than that from M2 Modis(140.0 g/m~2). However, the spatial distributions of CWPs, show similar patterns among these reanalyses, with relatively small values over Greenland and large values over the North Atlantic. Consistent with M2 Modis, these reanalyses show larger LWPs than IWPs, except for ERA-Interim. However, MERRA-2 and MERRA underestimate the ratio of IWPs to CWPs over the entire Arctic, while ERA-Interim and JRA-55 overestimate this ratio. ERA5 shows the best performance in terms of the ratio of IWPs to CWPs. All datasets exhibit larger CWPs and LWPs in summer than in winter. For M2 Modis, IWPs hold seasonal variation similar with LWPs over the land but opposite over the ocean. Following the Arctic warming, the trends in LWPs and IWPs during 1980～2015 show that LWPs increase and IWPs decrease across all datasets, although not statistically significant. Correlation analysis suggests that all datasets have similar interannual variability. The study further found that the inclusion of re-evaporation processes increases the humidity in the atmosphere over the land and that a more realistic liquid/ice phase can be obtained by independently treating the liquid and ice water contents.     

Metamorphic P–T Paths from pelitic schists and greenstones from the south-west Tauern Window, Eastern Alps

Abstract Petrological data from intercalated pelitic schists and greenstones are used to construct a pressure–temperature path followed by the Upper Schieferhülle (USH) series during progressive metamorphism and uplift in the south-west Tauern Window, Italy. Pseudomorphs of Al–epidote + Fe-epidote + albite + oligoclase + chlorite after lawsonite and data on amphibole crystal chemistry indicate early metamorphism in the lawsonite-albite-chlorite subfacies of the blueschist facies at P ± 7–8 kbar. Geothermometry and geobarometry yield conditions of final equilibration of the matrix assemblage of 475±25°C, 5–6 kbar; calculations with plagioclase and phengite inclusions in garnet indicate early garnet growth at pressures of ∼ 7.5 kbar. Garnet zoning patterns are complex and reversals in zoning can be correlated between samples. Thermodynamic modelling of these zoning profiles implies garnet growth in response to four distinct phases of tectonic activity. Fluid inclusion data from coexisting immiscible H₂O–CO₂–NaCl fluids constrain the uplift path to have passed through temperatures of 380 + 30°C at 1.3 + 0.2 kbar.
There is no evidence for metamorphism of USH at pressures greater than ∼ 7.5 kbar in this area of the Tauern Window. This is in contrast to pressures of ± 10 kbar recorded in the Lower Schieferhülle only 2–3 km across strike. A history of differential uplift and thinning of the intervening section during metamorphism is necessary to reconcile the P–T data obtained from these adjacent tectonic units.     

A spatial and statistical analysis of the impact of transformation of raster cost surfaces on the variation of least-cost paths

Planners who are involved in locational decision-making often use raster-based geographic information systems to quantify the value of land in terms of suitability or cost for a certain use. From a computational point of view, this process can be seen as a transformation of one or more sets of values associated with a grid of cells into another set of such values through a function reflecting one or more criteria. While it is generally anticipated that different transformations lead to different ‘best’ locations, little has been known on how such differences arise (or do not arise). The paper attempts to answer this question in the context of path planning through a series of computational experiments using a number of random landscape grids with a variety of spatial and nonspatial structures. In the experiments, we generated least-cost paths on a number of cost grids transformed from the landscape grids using a variety of transformation parameters and analyzed the locations and (weighted) lengths of those paths. Results show that the same pair of terminal cells may well be connected by different least-cost paths on different cost grids though derived from the same landscape grid and that the variation among those paths is affected by how given values are distributed in the landscape grid as well as by how derived values are distributed in the cost grids. Most significantly, the variation tends to be smaller when the landscape grid contains more distinct patches of cells potentially attracting or distracting cost-saving passage or when the cost grid contains a smaller number of low-cost cells.     

走时反演的一种非迭代算法

本文给出了用剥皮法反演地下介质速度的思想,并将某些特定路径的直射线用于反演井间速度,并在此基础上对算法进行了探讨,避开了一般的迭代算法而用消元法,这种方法具有简捷、直观的特点,也指出了该方法的不足:误差的传递积累。在文章的最后,讨论了该方法的实际应用价值及理论试算,得到了比较好的效果,每个模型的处理时间不超过五分钟.     

用于图像重建的波前法射线追踪

本文给出一种基于Huygens-Fresnel原理的射线追踪方法--波前法.该方法精度高、计算速度快,不仅可给出波从源点传播到接收点的透射走时和射线路径,而且可给出任何时刻的波阵面,为层析成像提供了一种有效的射线追踪方法.     

麻粒岩地体构造模型及其PTt轨迹研究中应注意的问题

近年来的研究表明,麻粒岩地体形成的地球动力学过程是多样的,并提出多种构造模型来解释麻粒岩相条件出现的原因。本文评述了几种主要构造模型及其PTt轨迹,并就进一步研究中应注意的某些问题作了探讨。     

造山带的伸展作用及其地壳演化意义

造山带的伸展作用大致可以分为两种类型:(1)喜马拉雅型伸展,伸展限于上地壳,表现为规模有限的伸展断层,发生于俯冲—碰撞阶段;(2)科迪勒拉型伸展,整个地壳发生伸展,涉及拆离断层、沉积盆地、变质核杂岩的形成,发生于碰撞后阶段。对加厚地壳的热力学模拟,可以解释造山带挤压终止到伸展开始的时序与岩浆活动的关系。喜马拉雅型伸展伴随高压变质作用,并使变质岩系近等温减压;科迪勒拉型伸展与高温变质作用关系密切,伴随花岗质岩体的侵位,并使变质岩系近等温减压之后近等压冷却。