Construction Problems on the Karstified Limestone Tuffs of Condeixa, Central Portugal: A Case Study     

M. Quinta Ferreira  J. L. Velho 《Geotechnical and Geological Engineering》2006,24(1):101-116

During the excavations for the foundations of a three storey building on the limestone tuffs of Condeixa, Central Portugal, a large dissolution fissure and smaller dissolution voids were found. Since the area has never been the subject of engineering geology investigation, it was decided to evaluate the risk associated with the construction of the building. These limestone tuffs were formed in a continental environment by the precipitation of calcite carried by the water coming from the large limestone body in the east. The precipitated calcite mixed with the terrigenous materials and around trunks and leaves of plants, originating a very heterogeneous and porous ground, which is characteristic of limestone tuffs. The study started with a detailed geological survey followed by a large number of destructive drillings, located essentially under the pad foundations. The results revealed several karstic cavities with serious problems for the building foundations and the structure, and many smaller dissolution cavities, often filled with clayey soils. The ground treatment solutions used included, dental cleaning, filling with concrete or granular material the dissolution structures accessible at the level of the foundation, reinforcement of the footing and the structure of the building and adding a continuous foundation beam to hold the foundations together. The cost of the engineering geology study, site investigation, ground treatment, and the reinforcement of the foundation and building, increased the total construction cost from 2%, at the design stage, to 4.8%.  相似文献   

鄂西火烧坪地区岩溶生态环境系统及生态农业模式初探     

万军伟  杨俊  王增银  潘欢迎 《地质科技情报》2002,21(1):71-74,82

通过对鄂西火烧坪地区的自然地理、地质构造、水文地质、土壤、植被及社会经济等方面的初步研究表明，在岩溶化作用十分强烈的岩溶山区，当气候、地形地貌、地质构造等条件匹配较好时，同样存在着一些极其有利于农业、林业发展的特殊生态环境。在这些地区，结合当地植物资源特点和市场需求，通过农作物类型的调整，能够在短时间内使当地摆脱贫穷的面貌。但在发展经济的同时必须特别关注当地土地资源相对缺乏、水资源时空分布不均、生态环境脆弱等不利因素，做到适度开发，稳步发展，才能从根本上实现小康目标。  相似文献   

渤海湾盆地北部奥陶纪岩相古地理   总被引：8，自引：0，他引：8  

金振奎  邹元荣  由伟丰  蒋春雷 《沉积学报》2002,20(1):13-19

渤海湾盆地北部主要包括黄骅坳陷、沧县隆起、冀中坳陷和下辽河坳陷,区内奥陶系厚 6 0 0～ 80 0m,主要由石灰岩和白云岩组成。下奥陶统分为冶里组和亮甲山组,中奥陶统分为下马家沟组、上马家沟组和峰峰组,上统缺失。其中下马家沟组、上马家沟组和峰峰组又进一步划分为下段和上段。早奥陶世冶里期和亮甲山期,本区以局限海环境为主,其内散布着一些潮坪和滩。中奥陶世,本区岩相古地理面貌变化旋回极为明显,下马家沟期早期潮坪广布,晚期以局限海为主;上马家沟期早期又是潮坪广布,晚期以开阔海为主;峰峰期早期潮坪广布,晚期又以开阔海为主。在奥陶纪,本区经历了 4个大的海侵-海退旋回,其中上马家沟期晚期是本区乃至整个华北地台的最大海侵期。  相似文献   

贵州喀斯特地区生态环境恶化的人为因素分析   总被引：18，自引：2，他引：18  

李瑞玲  王世杰  张殿发 《矿物岩石地球化学通报》2002,21(1):43-47

贵州是喀斯特强烈发育的省区。由于人类活动的影响，近年来贵州喀斯特地区的生态环境出现了日益恶化的趋势，严重影响可持续发展甚至西部大开发战略的顺利实施。本阐述了喀斯地区生态环境恶化的现状，深入探讨了人为因素对喀斯特地区生态环境恶化的影响，为防止喀斯特地区生态环境进一步恶化提供科学依据。  相似文献   

鲁中南岩溶水资源综合类型及合理调蓄研究   总被引：6，自引：1，他引：6  

贺可强  刘炜金  邵长飞 《地球学报》2002,23(4):369-374

鲁中南岩溶区是中国北方半干旱温带岩溶区中具有代表性的地区之一。该区岩水资源分布具有明显的不均匀性和大面积分散补给而局部富集等特征。岩溶形态以溶蚀裂隙洞穴为主，地下水类型多为裂隙溶洞型。在对该区岩溶水补给，富集，径流及排泄特征的研究基础上，初步将本区地表水和地下水资源划分为两大类型，即地下岩溶水径带变化带水资源类型和排泄带水资源及地下岩溶水资源类型。对该地区地表水和地下水的合理调蓄问题进行了系统的分析和总结，并提出了相关的对策。  相似文献   

地震次生毒气泄漏与扩散的数值模拟与动态仿真   总被引：16，自引：1，他引：16  

赵振东  余世舟  钟江荣 《地震工程与工程振动》2002,22(5):137-142

文章对破坏性地震中可能发生的次生毒气泄漏与扩散灾害进行了数值模拟与动态仿真研究，设定了几种有实际意义的数值分析模型，分别进行了结构地震破坏，有毒有害气体泄漏，在一定泄漏和气象条件下的向周围空间扩散的动态仿真研究，给出了典型毒气扩散过程中可致人员死亡，严重危险和有感区域的范围的动态变化结果，作者认为地震次生毒气泄漏与扩散研究对大地震应急、城市和大型企业防灾都有重要的意义和广阔的应用前景。  相似文献   

Phénomènes karstiques fossiles et actuels au sein des formations métamorphiques silico-alumineuses de la nappe pan-africaine de Yaoundé (Sud-Cameroun)Fossil and present-time karstic phenomena in silico-aluminous metamorphic formations of the Pan-African nappe of Yaoundé (South-Cameroon)     

Jean-Paul Vicat  Hubert Mvondo  Luc Willems  André Pouclet 《Comptes Rendus Geoscience》2002,334(8):545-550

Numerous karstic features have been recognised in the non-carbonaceous micaschists and gneisses of the Yaoundé Pan-African nappe, south of Cameroon. It is shown that their formation was controlled by the structural features of the rocks. The wells and the pipes in the bedrock outcrops point out a current karstification process, resulting from the plagioclase dissolution by the acid rain waters. Hill wall alveoli and caves, of pre-Miocene age, are exhumed features that were done by dissolution in the aquiferous underground. To cite this article: J.-P. Vicat et al., C. R. Geoscience 334 (2002) 545–550.  相似文献   

八宝喀斯特山区生态环境问题与治理措施   总被引：3，自引：1，他引：3  

郭芳  姜光辉  裴建国 《云南地理环境研究》2003,15(1):80-85

喀斯特峰丛山区生态系统特征有：结构简单，稳定性差，恢复困难等。其生态系统脆弱性表现为：（1）裸露型喀斯特山地坡度陡峻，土壤贫脊，耕地少而分散，水土保持能力差；（2）地下水文网发育导致地表水大量漏失，地下水位埋藏深，难以开采利用；（3）植被树种单一，生长缓慢，资源开发过程中易产生耕作粗放，水土流失，石漠化等环境问题，对其治理和恢复过程应是渐进式的：水－土－林，即首先要科学开发利用各种水资源，同时合理规划利用土地资源，其次要加速生态系统重建，使其形成良性循环发展方式。  相似文献   

Implementing spectral leakage corrections in global surface wave tomography     

Jesper Spetzler  Jeannot Trampert 《Geophysical Journal International》2003,155(2):532-538

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Microclimate, freezing tolerance, and cold acclimation along an elevation gradient for seedlings of the Great Basin Desert shrub, Artemisia tridentata     

Michael E. Loik  Sean P.Redar 《Journal of Arid Environments》2003,54(4):769-782

Vegetation, microclimate, seedling frequency, freezing tolerance, and cold acclimation were compared for seedlings of Artemisia tridentata collected from 1775, 2175, and 2575 m elevation in the eastern Sierra Nevada, California. Data were used to test the hypothesis that ecotypic differences in stress physiology are important for seedling survival along gradients from desert to montane ecosystems. The vegetation canopy cover and A. tridentata seedling frequency were greatest at 2575 m, compared to 1775 and 2175 m. Snow cover ameliorated temperatures near the soil surface for part of the winter and depth varied across elevations. Freezing tolerance was compared for seedlings maintained in growth chambers at day/night air temperatures of 25°C/15°C. The temperature at which electrolyte leakage and Photosystem II function (F_V/F_M) from leaves were half-maximum was approximately −13·5°C for leaves of seedlings from all three elevations. Shifting day/night air temperatures from 25°C/15°C to 15°C/5°C initiated about 1·5° of acclimation by plants from all three altitudes, with seedlings from the highest elevation exhibiting the greatest acclimation change. Measurements of ambient air and canopy temperatures at the three elevations indicated that wintertime average low temperatures were consistent with the measured degree of freezing tolerance. At small spatial scales used in this study, pollen and seed dispersal between study sites may have precluded resolution of ecotypic differences. Patterns of freezing tolerance and cold acclimation may depend on a combination of mesoclimate and microclimate temperatures, canopy cover, snow depth, and snow melt patterns.  相似文献