库水升降条件下考虑饱和渗透系数空间变异性的白水河滑坡渗流变形分析     

薛阳  吴益平  苗发盛  李麟玮  廖康  张龙飞 《岩土力学》2020,41(5):1709-1720

堆积层滑坡的岩土体渗透系数具有一定的不确定性,且渗透系数是饱和-非饱和渗流分析的重要参数,开展考虑其空间变异性的库岸堆积层滑坡渗流变形分析具有重要意义。以三峡库区中的白水河滑坡为研究对象,基于地面核磁共振技术获取的岩土体渗透系数,分析滑坡体渗透系数的空间变异特征,采用半变异函数方法求得滑坡体渗透系数的竖直波动范围,在此基础上建立渗透系数的非平稳随机场模型。以非侵入式随机有限元的方式开展库水升降两种工况下不确定模型与确定模型的流固耦合模拟,分析两种模型的渗流场、位移变形特征及其差异。结果表明：相比于确定模型,不确定模型孔压改变的滞后性更为明显,且库水下降工况下整体的变形更大,若忽略滑体渗透系数的非平稳空间变异特征将会低估滑坡的实际变形。  相似文献   

现代土壤磁化率空间分布特征及成壤影响因素分析——以桑干河阳原段为例     

焦天  董进  汤文坤  迟振卿  王永  庞健锋  孙楠 《地质论评》2020,66(1):229-244

为了揭示影响成壤作用发生的主要因素,对河北省阳原县桑干河流域表层土壤开展常规土壤指标和环境磁学参数的地统计学分析,结果表明,土壤的频率磁化率(χ_(fd20))、Eh值、有机质、黏土—粉砂含量等参数的空间分布特征受控于研究区的高程,而土壤的含水量、铁游离度和活化度的空间分布特征受控于坡向。因此,在影响成壤作用的五大因素(母质、气候、地形、有机质、时间)中,地形(高程、坡向)是影响研究区成壤作用强弱的主要因素。此外,虽然前人发现频率磁化率和铁游离度都能反映铁氧化物含量和成壤作用强弱,但本次研究通过对比空间分布特征发现,频率磁化率与有机质、Eh值等土壤指标有较好的相似性,且与耕地类型分布一致,所以,相对于铁游离度,频率磁化率更能反映研究区土壤发育状况。  相似文献   

Stochastic finite element methods for the seismic response of soils     

C. H. Yeh  M. S. Rahman 《国际地质力学数值与分析法杂志》1998,22(10):819-850

Some of the available stochastic finite element methods are adapted and evaluated for the analyses of response of soils with uncertain properties subjected to earthquake induced random ground motion. In this study, the dynamic response of a soil mass, with finite element discretization, is formulated in the frequency domain. The spectral density function of the response variables are obtained from which the evaluation of the root-mean-squared and the most probable extreme values of the response are made. The material non-linearities are incorporated by using strain compatible moduli and damping of soils using an equivalent linear model for stress–strain behaviour of soils and an iterative solution of the response. The spatial variability of the shear modulus is described through a random field model and the earthquake included motion is treated as a stochastic process. The available formulations of direct Monte-Carlo simulation, first-order perturbation method, a spectral decomposition method with Neumann expansion and a spectral decomposition method with Polynomial Chaos are used to develop stochastic finite element analyses of the seismic response of soils. The numerical results from these approaches are compared with respect to their accuracy and computational efficiency. © 1998 John Wiley & Sons Ltd.  相似文献   

先验概率分布及似然函数模型的选择对边坡可靠度评价影响的定量评估     

蒋水华  刘源  章浩龙  黄发明  黄劲松 《岩土力学》2020,41(9):3087-3097

受工程勘察成本及试验场地限制,可获得的试验数据通常有限,基于有限的试验数据难以准确估计岩土参数统计特征和边坡可靠度。贝叶斯方法可以融合有限的场地信息降低对岩土参数不确定性的估计进而提高边坡可靠度水平。但是,目前的贝叶斯更新研究大多假定参数先验概率分布为正态、对数正态和均匀分布,似然函数为多维正态分布,这种做法的合理性有待进一步验证。总结了岩土工程贝叶斯分析常用的参数先验概率分布及似然函数模型,以一个不排水黏土边坡为例,采用自适应贝叶斯更新方法系统探讨了参数先验概率分布和似然函数对空间变异边坡参数后验概率分布推断及可靠度更新的影响。计算结果表明：参数先验概率分布对空间变异边坡参数后验概率分布推断及可靠度更新均有一定的影响,选用对数正态和极值I型分布作为先验概率分布推断的参数后验概率分布离散性较小。选用Beta分布和极值I型分布获得的边坡可靠度计算结果分别偏于保守和危险,选用对数正态分布获得的边坡可靠度计算结果居中。相比之下,似然函数的影响更加显著。与其他类型似然函数相比,由多维联合正态分布构建的似然函数可在降低对岩土参数不确定性估计的同时,获得与场地信息更为吻合的计算结果。另外,构建似然函数时不同位置处测量误差之间的自相关性对边坡后验失效概率也具有一定的影响。  相似文献   

青海高原太阳辐射时空分布特征   总被引：9，自引：3，他引：6  

陈芳马英芳  李维强 《气象科技》2005,33(3):231-234

对西宁莫家泉湾和玉树辐射观测站的资料分别进行了订正和插补,对青海省太阳辐射的空间分布、年际变化进行了系统研究。结果表明：青海省年总辐射量高,总的分布趋势西高东低;20世纪70年代是总辐射高值时期,而80年代处于明显的低值时期,80年代末期至90年代初期有所回升,但90年代中期后处于下降状态。70年代的高值期和80年代低值期的出现与该时段青海省云雨状况和全球重大火山喷发事件密切相关,火山喷发是导致80年代总辐射量减少的重要原因。  相似文献   

与北极涛动或北半球环状模相关的纬向对称的正规模态   总被引：6，自引：3，他引：3  

赵南  Masaaki Takahashi 《气象学报》2005,63(6):857-863

作为一个全球气候变率的重要模态,北极涛动或北半球环状模态(AO/NAM)一般由北半球海平面气压变率的EOF1来表示。但是通常认为EOF1仅有统计学意义而并不能够表明它是否是一种实际的物理模态。另一方面,现有的波-流相互作用理论也仅能给出纬向风的纬向平均状况,而不能够保证沿着某一纬圈的变化,所以它并不意味着一个具有半球尺度的纬向对称的相干结构能够组织起来。因此AO/NAM的形成机制仍然是一个具有争议的问题。文章提出纬向对称的或环状的正规模态与基本气候态附近的线性(进而非线性)动力学之间有着最直接的联系,因而可能在AO/NAM动力学的理解中扮演重要角色。为了深入探讨AO/NAM的动力学本质,使用p-坐标球面原始方程计算了冬季北半球及全球气候基本态附近的线性动力系统纬向对称的正规模态,发现在半球尺度上的纬向对称正规模态具有AO/NAM的经向偶极子及垂直方向近似正压的空间结构特征。而这些纬向对称正规模的时间变化尺度取决于与其他非纬向对称正规模间的相互作用。从而说明了AO/NAM可能是半球尺度上纬向对称正规模态的动力学行为的反映。  相似文献   

亚热带城市湖泊与河流CO₂气体通量特征及其影响因素     

刘纪明  赵优  肖启涛  屈琦  胡又心  李郑杰  易心钰  卢伟志 《湖泊科学》2024,36(2):499-511

湖泊、河流等内陆水体是连接陆地生态系统和海洋的“长程碳环路”的重要节点,也是温室气体二氧化碳(CO₂)排放源,在调节陆地、海洋间的碳迁移转换中发挥着重要作用。相对于自然水体,城市水体因面积小、水深浅且受监测方法限制,水-气界面碳通量经常被忽略。为探讨我国亚热带城市水体温室气体排放特征,本研究以湖南省长沙市典型城市水体,包括洋湖、西湖、松雅湖、月湖4个湖泊和湘江长沙段为研究对象,分别于2022年4和10月采用光化学反馈-腔增强吸收光谱法(OF-CEAS)和扩散模型法对水-气界面CO₂通量进行对比测定。结果表明,长沙城市湖泊与河流春季为CO₂排放源,秋季为吸收汇,河流水-气界面CO₂通量呈显著季节差异。河湖之间CO₂通量在春季表现为显著差异,秋季差异不显著。CO₂通量与水体溶解氧、水体总氮浓度等呈显著正相关。2种方法的CO₂通量对比测定在湖泊上显著相关,但对河流而言相关性不显著。研究揭示的城市湖泊与河流CO₂气体的排放特征有利于深入探究城市水体碳的迁移转化,可对全面了解全球气候变化过程和河湖湿地温室气体减排和调控提供科学支撑。  相似文献   

SPATIAL AND SEASONAL VARIABILITY IN THE COMPONENTS OF THE RIVER HEAT BUDGET     

B. W. WEBB  Y. ZHANG 《水文研究》1997,11(1):79-101

Detailed hydrometeorological measurements have been used to establish the components of the river heat budget for 495 days covering 18 study periods and 11 study reaches in the Exe Basin, Devon, UK. Averaging the results across the whole data-set indicates that net radiation, friction, sensible heat transfer, condensation and bed conduction contributed 56.0, 22.2, 13.2, 5.8 and 2.8%, respectively, to the non-advective energy gains, whereas net radiation, evaporation, sensible heat exchange and bed conduction accounted for 48.6, 30.4, 10.6 and 10.4%, respectively, of the non-advective heat losses. Precipitation falling on the river channel had little impact on the river heat budgets, but energy advected in groundwater accounted for an average 5% of the heat storage in the river. The magnitude and importance of the river heat budget components were found to be variable in space and time. The influence of channel morphology, valley topography, riparian vegetation, substratum nature and hydrological conditions, especially the effects of river regulation, promoted inter-reach variability in the make up of the heat budget and caused significant differences in energy fluxes at a local scale. Heat budget components also exhibited considerable differences between seasons and varied from day to day for individual reaches. © 1997 by John Wiley & Sons, Ltd.  相似文献   

The information content theory for the estimation of the topographic index distribution used in TOPMODEL     

GIUSEPPE MENDICINO  AURELIA SOLE 《水文研究》1997,11(9):1099-1114

This paper analyses the significance of the entropy concept in the topography parameterization within the model TOPMODEL proposed by Beven and Kirkby (1979), by means of the hydrological behaviour of an experimental basin in southern Italy. For a significant number of flood events recorded at the basin outlet, the performance of TOPMODEL for different spatial distributions of the topographic index, ln(a/tan β), has been observed. Performance is related to the information content estimated as an entropy measure, corresponding to each of the spatial distributions of the topographic index, with the aim of identifying the procedures most suitable to represent the hydrological process of rainfall–runoff. The results obtained have shown that for flood events corresponding to brief, heavy precipitation, some procedures provide better performances than others. Moreover, these improvements are justified by greater information content in the corresponding spatial distributions of the topographic index. Finally, TOPMODEL performances for some procedures have been analysed, varying the resolution scale of the topographic index. For analogous hydrological performances, scale change produced variations in some of the subsurface hydraulic parameters. These variations were proportional to a spatial variability measure of the topographic index distribution, derived from the corresponding information content. © 1997 John Wiley & Sons, Ltd.  相似文献   

The distribution of solute processes on an acid hillslope and the delivery of solutes to a stream: I. Exchangeable bases     

T. P. Burt  S. J. Park 《地球表面变化过程与地形》1999,24(9):781-797

This paper aims to identify the spatial distribution of exchangeable base cations in soils on an acid hillslope and to investigate possible cation release processes from slope soils to the stream. The basic assumption underlying this research is that the amount of exchangeable cations in soils reflects the nutrient stores and cation leaching processes across the slope where vegetation and parent materials are similar. The distribution of exchangeable Ca²⁺, Mg²⁺, K⁺ and Na⁺ has been investigated on a three-dimensional hillslope on the Quantock Hills, Somerset, UK. A two-way ANOVA shows that soil depth is predominant in explaining the total variance of exchangeable bases, despite the steep slope gradient and clear podzolic catena development. Major nutrient base cations, such as Ca²⁺, Mg²⁺ and K⁺, display homogeneous topsoil storage right across the slope. This spatial pattern may indicate that the spatial distribution of major nutrient cations is tightly controlled by the soil–vegetation system in nutrient-poor heathland environments. Na⁺ is an exception to this vegetation-controlled spatial distribution, because of its small involvement in the soil–vegetation and soil exchangeable systems. In subsurface soils, cations liberated from the soil–vegetation system are subject to redistribution over the slope according to the hydrological flowpaths operating on the slope, with some eventually released into the stream. The saturated wedge developed at the base of the slope plays a key role in the storage and release processes of base cations from slope soils to the stream. Ca²⁺, Mg²⁺ and Na⁺ carried by throughflow are stored in the saturated wedge and gradually released into the stream at times of high flow. K⁺, however, shows an apparently different spatial behaviour, being deficient in the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献