适用于斜坡降雨入渗分析的修正Green-Ampt模型

降雨入渗分析是预测降雨诱发滑坡的关键因素之一。Green-Ampt模型原理简单、使用方便,在浅层滑坡的降雨入渗分析中有很大的应用潜力,但该方法主要适用于初始含水率为均匀分布的情况。基于这一不足,推导了初始含水率为非均匀分布条件下降雨入渗深度和时间的关系,并给出了基于Runge-Kutta原理的数值解法。当初始含水率为均匀分布时,提出的方法可简化为文献中已有的Green-Ampt模型。当初始含水率为非均匀分布时, Richards方程预测所得的孔隙水压力分布图中土体饱和区和未受降雨影响的非饱和区之间存在一个较窄的过渡段,由新模型计算所得的湿润锋穿过这一过渡段,且靠近饱和部区的底部。总体而言,新方法计算所得的孔隙水压力分布与Richards方程求解结果类似。     

考虑初始含水率分布的覆盖层边坡非饱和入渗过程与稳定性计算方法

根据覆盖层边坡特性设计室内降雨试验模型,提出初始含水率分布沿高程呈反比例分布。根据边坡表面未饱和时降雨入渗受总降雨量控制的基本假设,建立了不排水状态下覆盖层边坡降雨入渗的解析计算方法。基于上述降雨入渗理论,考虑非饱和土抗剪强度变化规律,建立适用于非饱和覆盖层边坡的边坡稳定性计算方法。分析了覆盖层厚度、初始含水率分布参数以及覆盖层边坡角度对边坡稳定性的影响规律。具体结论如下:(1)覆盖层边坡内部初始含水率分布可采用反比例分布近似表示,基于总降雨量控制假设,得到可考虑初始含水率分布的覆盖层边坡降雨入渗解析计算方法。(2)基于半无限空间体边坡假设,给出覆盖层边坡在降雨入渗条件下不同位置滑动面的稳定系数计算方法。(3)在相同降雨量条件下,边坡初始稳定性随覆盖层土体厚度的增加而下降。降雨入渗对覆盖层边坡稳定性的影响随着上覆土层厚度的增加而减小。(4)当降雨量相同时边坡稳定性随着覆盖层土体初始含水率分布参数的增加而下降,降雨时间越长,初始含水率分布对边坡稳定的影响越明显。(5)不同角度的覆盖层边坡稳定性均随降雨量增加而逐渐减小。在初始状态下边坡角度增加所引起的最小稳定系数下降幅度最大,随着降雨量的增加,边坡稳定性受角度影响逐渐减小。     

降雨入渗条件下土质边坡含水率分布与浅层稳定性研究

设计一种可以测量土体体积含水率的降雨入渗试验模型,通过试验得到土体初始含水率分布状态以及降雨入渗条件下土体含水率变化规律。在此基础之上,结合非饱和土抗剪强度理论与极限平衡理论,得到降雨入渗条件下土质边坡浅层稳定性计算方法。对杭新景高速公路七里连接线工程沿线土质边坡稳定性进行分析,具体结论如下:可采用含水率分布参数A、修正系数λ、μ表征的反比例函数表示自然状态下土体的初始含水率分布规律。含水率分布参数对边坡稳定性影响表现为随着A值的增大,边坡初始稳定性逐渐下降,边坡受降雨影响的敏感程度也随之下降。降雨强度相同时,初始表面含水率越大引起边坡失稳所需的降雨时间越短;降雨时间相同时,初始表面含水率越大引起边坡失稳所需的降雨强度越小。在相同地下水位条件下,边坡降雨强度与导致边坡失稳所需的降雨时间成反比。     

考虑降雨入渗参数空间变异性的浅层滑坡时效风险分析

降雨条件下边坡所处的滑坡风险状态与土体参数空间分布密切相关,为高效评估降雨诱发滑坡所处的风险等级,应用Python计算平台进行编码,采用修正Green-Ampt入渗模型推导出无限长边坡（infinite slope）的极限状态函数,结合岩土参数随机场理论及一阶可靠度分析方法,得到了降雨诱发滑坡的概率分析结果,并建立了算例边坡的易损性曲线。研究结果表明：相比于传统的边坡稳定性定值分析方法,可靠度分析结果可以较为全面地反映边坡在不同降雨强度以及降雨持时条件下所处的风险状态;当降雨强度超过一定等级后,在相同的降雨持时条件下其强度大小对边坡失效概率的影响不大;在特定研究区域内,当降雨强度已知时,可以通过易损性明确边坡在容许风险等级下的失效时间,为滑坡防控领域的防灾减灾工作提供重要参考。     

降雨入渗条件下土质边坡含水率分布与浅层稳定性研究

设计一种可以测量土体体积含水率的降雨入渗试验模型,通过试验得到土体初始含水率分布状态以及降雨入渗条件下土体含水率变化规律。在此基础之上,结合非饱和土抗剪强度理论与极限平衡理论,得到降雨入渗条件下土质边坡浅层稳定性计算方法。对杭新景高速公路七里连接线工程沿线土质边坡稳定性进行分析,具体结论如下：（1）可采用含水率分布参数A、修正系数α、β表征的反比例函数表示自然状态下土体的初始含水率分布规律。（2）含水率分布参数对边坡稳定性影响表现为随着A值的增大,边坡初始稳定性逐渐下降,边坡受降雨影响的敏感程度也随之下降。（3）降雨强度相同时,初始表面含水率越大引起边坡失稳所需的降雨时间越短;降雨时间相同时,初始表面含水率越大引起边坡失稳所需的降雨强度越小。（4）在相同地下水位条件下,边坡降雨强度与导致边坡失稳所需的降雨时间成反比。     

基于Green-Ampt模型的饱和-非饱和黄土入渗改进模型及其参数研究

黄土中水分入渗理论分析对预测土体附加变形及强度弱化十分重要,但现有针对均质地基的Green-Ampt入渗分析模型运用于黄土区还有较多不足。基于黄土入渗饱和-非饱和分层假定,考虑入渗过程中土体实际渗透系数随深度的变化,对Green-Ampt模型进行修正,并用实例进行了验证;通过测量累积入渗量和含水率的时变规律,并结合Philip模型与Green-Ampt模型的相关关系及实际渗透系数随时间的变化关系获取模型参数。结果表明,相比于WGAM和Kostiakov模型,修正模型在黄土区的应用效果更好。在修正模型基础上,分析了饱和渗透系数、饱和含水率、初始含水率以及基质吸力对水分入渗深度的影响规律,并对参数的敏感指数进行了分析与对比。发现土体初始和饱和含水率变化对模型计算结果产生较大影响。该模型的建立对黄土地区水分入渗规律相关研究有一定的积极作用。     

考虑非饱和浸润层厚度和累积入渗量的改进Green-Ampt模型

矿山内排土场因其储量大、结构松散和强度低等特点,在降雨条件下极易产生侵蚀或整体失稳破坏,因此降雨入渗分析对预测内排土场稳定性至关重要。以元宝山露天煤矿内排土场为原型,按相似试验理论进行物理模型试验,研究降雨入渗特征,根据试验结果对经典Green-Ampt入渗模型进行改进。结果表明:雨水入渗过程中,随着浸润锋的向下运移,坡面侵蚀由溅蚀凹槽开始,逐渐过渡为径流侵蚀,最后呈现为溯源侵蚀破坏,整体呈现平行于坡表面的浅层滑坡特征;浸润锋之上非饱和浸润层的存在,导致经典Green-Ampt模型计算结果不准确;在考虑浸润层厚度和累积入渗量基础上,推导出改进的Green-Ampt模型;改进后的Green-Ampt模型为分段函数,能够反映降雨入渗使坡面由非饱和向饱和过渡的实际特征。验证结果显示,使用改进模型,浸润锋入渗深度和累积入渗量的预测精度显著提升,虽然冲蚀破坏和初始含水率的差异导致降雨入渗后期的预测精度有所下降,但相关结果对煤矿内排土场降雨初期稳定性分析具有重要意义。改进后的Green-Ampt模型的计算结果与实测数据更为接近,能为分析露天煤矿内排土场降雨入渗规律及边坡稳定性研究提供参考。     

斜坡降雨入渗的改进Mein-Larson模型

土壤初始含水率分布是影响湿润锋下移的重要因素之一.传统的降雨入渗模型仅假定初始含水率均匀分布,并没有考虑非均匀分布的情况.以Mein-Larson降雨入渗模型为基础,假定初始含水率随垂直于坡面方向深度呈线性分布,推导了一种新的滑坡降雨入渗函数,弥补了原模型只能用于初始含水率均匀分布情况下的不足.研究结果表明:初始含水率分布对湿润锋下移有较大影响,在初始含水率呈线性分布的情况下,坡体表面含水率越大,含水率随垂直于坡面方向深度的变化率k值越接近零,湿润锋下渗速度越快,当k=0时,新模型退化为Mein-Larson降雨入渗模型,证明Mein-Larson降雨入渗模型是新模型的一个特例.与有限元法得到的结果对比表明,提出的降雨入渗新模型计算的湿润锋下渗深度与数值解结果相接近,证明了该方法的可靠性.      

前期含水率对浅层滑坡降雨入渗及稳定性影响研究

降雨是诱发滑坡的主要因素之一。目前普遍认为,湿润锋下移导致的土体基质吸力减少是降雨影响滑坡失稳的主要原因,而土壤前期含水率是影响湿润锋下移过程的重要因素之一。基于Green-Ampt模型,推导了考虑坡角影响下的滑坡体降雨入渗表达式,同时,结合无限斜坡模型分析了持续稳定的降雨条件下滑坡体稳定性的变化情况,探讨了前期含水率对于降雨过程中浅层滑坡稳定性的影响规律。结果表明:随着降雨的持续进行,浅层滑坡稳定性开始下降较快,之后趋于平缓。前期含水率会影响湿润锋的下移速度,当前期含水率分别为0.32,0.36,0.40时,湿润锋下移速度分别为0.109,0.173,0.42m/h,说明前期含水率越大,湿润锋下移的速度越快;而前期含水率对于浅层滑坡稳定性的影响主要在降雨初期。     

基于改进Green-Ampt模型的花岗岩残积土边坡降雨入渗规律研究

花岗岩残积土广泛分布于我国南方地区,具有许多不良物理力学性质。该类型土边坡在降雨作用下极易发生变形破坏,因此,对花岗岩残积土边坡的降雨入渗规律进行深入研究具有重要意义。在Green-Ampt模型的基础上综合考虑了坡体的初始含水率、地下水位、非饱和特性,建立了一种适用于不同降雨工况的入渗模型,并采用数值模拟及前人经典模型计算结果对该模型进行了验证。运用该模型对赣南3种典型降雨工况下的花岗岩残积土边坡进行了分析,结果表明:在距离地下水位线较远时初始含水率对湿润锋的迁移速率影响不大,但在接近地下水位线附近时湿润锋的迁移速率逐渐增大,呈现出指数形式的变化趋势;相同降雨时间内、不考虑坡面冲刷的情况下,降雨强度略大于土体饱和渗透系数的工况下湿润锋迁移深度最大、边坡稳定性系数降低最多,在实际情况中尤其需要加强防范。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

Définition d'une limite multicritère ; stratigraphie du passage Campanien–Maastrichtien du site géologique de Tercis (Landes,SW France)Definition of a multi-criteria boundary; stratigraphy of the Campanian–Maastrichtian interval of the geological site at Tercis (Landes,SW France)

Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

正~~     

GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)