基坑降水引起地面沉降的实时预测

由于基坑降水引起周围土体应力的重新调整,造成基坑相邻建筑物地基不均匀沉降,情况严重则造成相邻建筑物破坏,因此对不均匀沉降量的预测具有现实意义。利用地下水动力学的非稳定流原理及土力学基本理论,介绍了基坑降水设计中引起周围地面沉降的实时预测方法,探讨了不同土层在降水过程中孔隙水压力消散对土层固结的影响,通过实例分析了公式中不同参数的取值合理性,编制了相关程序。该方法对分析、预测由于基坑降水所引起的周围地面沉降有一定参考价值。     

考虑隧道降水和开挖施工过程的三维地面沉降模拟

明挖法是隧道施工中常用的一种方法,但其降水和开挖施工不可避免地会引起周围地面沉降.为了防止隧道施工对周围环境及建筑物产生严重的不良影响,地面沉降控制是检验施工支护设计合理性的关键.隧道施工造成地面沉降的主要原因有降水、开挖和支护作业,以往研究大多集中于单一因素的影响分析,为使分析结果更接近于工程实际,需将三者综合考虑,...     

基坑开挖及降水引起周围建筑物不均匀沉降的实例

在建筑物较近处,放坡开挖８．０ｍ的基坑,由于降水、开挖及雨后土体强度的降低,引起建筑物不均匀沉降,通过实测发现,降水引起的地面沉降影响范围约为井深的１．５倍;放坡开挖引起的地面沉降影响范围的为坑深的３￣４倍,以及雨后土体强度降低会进一步加强土体变形等结论。     

深基坑降水对邻近建筑物的影响

深基坑降水对邻近建筑物的影响周天红（电力部西北电力设计院勘测处，西安，７１００３２）１前言基坑降水工程是一项复杂的施工系统工程，它既要考虑降水引起的基坑底板的稳定性，又要考虑降水引起的周围地面沉降使邻近建筑物受到的威胁。因而对于基坑降水工程来说，就要...     

富水粉土基坑装配式可回收支护开挖响应分析

装配式可回收支护结构为地下空间开发提供了一种经济安全、功能协同、可持续发展的新型绿色支护体系。以郑州市某顶管工作井基坑为背景,基于相似比理论开展了缩尺基坑模型试验,并采用ABAQUS建立能够区分支护系统中刚性构件与柔性构件变形差异的三维流固耦合模型,研究降水开挖过程中支护结构受力和变形特性,分析了降水和开挖对基坑变形发展的影响规律。研究表明：降水开挖过程中,支护结构受力及变形整体均小于设计值,但是钢面板在与支撑连接的位置易出现局部屈服现象;支护结构水平位移增量模式随降水施工和开挖施工的情况不同而差异较大,随着基坑降水开挖的进行,影响支护结构变形的主要因素由基坑降水逐渐向基坑开挖转变;基坑降水对地表沉降的影响较基坑开挖更大,第1级降水期间地表沉降快速增长,沉降增量占比最大达44.6%。     

天津中心城区基坑降水对地面沉降的影响范围研究

依托天津地区5个典型工程案例,对基坑降水引起的地面沉降规律进行了基本分析。由于基坑降水引起地面沉降的范围较远,往往能达到墙后5~10倍基坑开挖深度的距离,而实际基坑工程坑外沉降的测点往往布置在墙后1~4倍基坑开挖深度的距离,因此难以全面的获得不同类型基坑(如基坑深度不一)降水对地面沉降的影响范围。本文利用有限差分软件Modflow建立三维地下水渗流模型,并利用文化中心站的工程实测数据对该模型进行验证,最后利用该模型研究不同开挖深度的基坑(5~25m)降水对地面沉降的影响范围,并探讨5种不同止水帷幕截断方式的工况下坑内降水后坑外水位及地面沉降随时间发展关系。     

软土本构模型在深基坑环境影响分析中的适用性探讨

基坑降水开挖的环境影响常采用顺序耦合法和全耦合法两种方法进行数值分析,其计算结果的可靠性主要受土本构模型和计算参数选取的影响,对于全耦合分析尤其突出。针对该问题,在系统地比较分析几类常用土体本构模型优缺点的基础上,对某基坑实例在降水开挖作用下引起的基坑周边地面沉降等规律进行分析;通过对比数值计算结果和实测结果,评价了不同本构模型在基坑降水开挖耦合分析中的全耦合数值模拟,分析降水开挖引起的地面沉降、围护结构水平位移适用性。分析结果表明:降水开挖耦合分析中,在重点关注地表沉降值时,应根据关注位置与开挖区边缘的相对距离而选用不同本构模型;关注地面沉降时采用修正剑桥模型较合适,而关注围护结构侧移时采用摩尔—库伦模型更合理。     

济南西客站站房基坑降水对京沪高铁路基沉降影响分析

工程上通常用降水的方法来保证基坑开挖的顺利进行,但是基坑降水会改变基坑周围土的工程性质,所以基坑周围的建筑物必然会受到很大影响,如出现不均匀沉降、建筑物开裂等。济南西客站站房基坑施工降水对其附近的京沪高速铁路路基的沉降产生了很大影响。本文针对此问题,基于在宽大站场条件下基坑降水对其周围的桩板复合地基沉降影响的理论尚未成熟,对基坑降水对复合地基沉降的影响进行了研究。本文选取济南西客站断面DIK419+250作为研究对象,现场采用沉降板进行路基表面的沉降变化监测,采用分层沉降仪进行路基深层土层的沉降变化监测,采用剖面沉降管进行路基横断面的沉降变化监测,并将各监测结果整理得出站房基坑降水对高铁路基表面沉降的影响、对路基深度方向土层沉降的影响、对路基横断面方向沉降的影响; 又根据现场的工况采用有限元软件进行数值模拟计算分析; 最终将数值模拟计算结果与现场监测所得结果进行对比,总结了基坑降水对复合地基沉降的影响。通过对比分析结果得出以下结论:(1)复合地基的加固会使路基沉降受基坑降水的影响减小; (2)复合地基的变桩长区域受基坑降水影响较大; (3)基坑降水对路基加固区沉降的影响大于对下卧层沉降的影响。     

软土地区基坑工程环境影响及其保护实例分析

以基坑工程为背景,针对上海外环隧道浦西暗埋段的大型超深基坑工程的主要环境保护问题,对基坑开挖引起的主要管线和建筑物的沉降、跟踪注浆保护措施及其效果进行了分析.实测数据表明,基坑开挖使周围建筑物和管线会产生较大的沉降速率和沉降量,尤其是降低深层承压水使远处的建筑物产生了不容忽视的均匀下沉.实践证明,采取预注浆与跟踪注浆相结合的保护措施,可以有效地减小基坑开挖对周围环境的影响.     

深圳宝安填海区地面沉降特征探讨

深圳市宝安中心区为大规模填海形成,发生了多处地面沉降。通过野外地质调查和收集大量资料,在填海区建立地面沉降监测点,查明了填海范围的地质环境特征,分析了填海区地面沉降的机理和特征。产生沉降的主要因素有两个:一是土层在建筑物等外部荷载作用下产生的固结沉降,主要发生在建筑物施工期间及使用期间,作用时间相对较长;二是由于基坑降水引起附加沉降,这部分沉降主要发生在基坑开挖期间,作用的时间相对较短,一般随着基坑的回填及地下水位的恢复,沉降便基本完成。通过数学方法研究了软土的欠固结、固结和次固结沉降,其中次固结沉降为填海区软土固结过程中贡献最大。抽取地下水和大规模密集高层建筑群也是产生地面沉降的影响因素之一,但影响范围有限。     

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.     

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

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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.)     

GEOCHEMISTRY

正20142002 Wei Hualing(Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang065000,China);Zhou Guohua Element Content and Mineral Compositions in Different Sizes of Soil in Tongling Area,Anhui Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(11),2013,p.1861