地表水入渗引起工程抗浮问题及对策     

李健生  张洒 《岩土工程技术》2020,(2):97-101

城市地下空间利用日趋受到重视,工程抗浮问题成为岩土工程领域的一个重要部分。对于建筑物整个使用期的抗浮研究相对深入,但往往对于由工程施工本身引起的、改变水文地质条件后可能存在的抗浮问题不够重视。近年来,信阳市垄岗地貌分布区高层建筑及整体地下车库建设规模较大。由于垄岗地形地貌的岩土体渗透性较差,同时该地区5—8月份暴雨较为集中,地表水通过肥槽等薄弱环节进入基础底板以下,易造成地下结构破坏。结合具体案例,研究地表水入渗引起工程抗浮问题并提出相应措施,工程实践效果良好。  相似文献   

Late Quaternary evolution of the Çanakkale Strait region (Dardanelles, NW Turkey): implications of a major erosional event for the postglacial Mediterranean-Marmara Sea connection   总被引：2，自引：2，他引：0  

Erkan Gökaşan  Hüseyin Tur  Mustafa Ergin  Tolga Görüm  Fatma Gül Batuk  Nurcan Sağcı  Timur Ustaömer  Ozan Emem  Hakan Alp 《Geo-Marine Letters》2010,30(2):113-131

Seismic and bathymetric data from the Çanakkale Strait and its extensions onto the shelves of the Marmara and Aegean seas indicate that the strait was formed mainly by an erosional event. Four seismic units are observed on seismic profiles. The lower two of these (units 4 and 3) constitute the basement of a regionally widespread erosional unconformity (ravinement), which developed during marine isotope stage 2 (MIS 2). The two upper units (units 2 and 1), which overlie the ravinement surface, form a higher-order sequence. Sequence stratigraphic analysis indicates that units 2 and 1 deposited as lowstand and highstand systems tracts respectively, since the end of MIS 2. The transgressive systems tract is represented by a major erosional event which occurred throughout the Çanakkale sill area when the Mediterranean-Marmara Sea connection and, hence, the Çanakkale Strait was formed. The existence of the erosive ?arköy Canyon along the shelf edge of the southern Marmara Sea demonstrates that the flow direction causing the erosion was from south to north, thus proving that it was produced by Mediterranean water flowing over the sill into the Marmara Sea basin.  相似文献   

New evidence of sea‐level lowstands and paleoenvironment during MIS 6 and 4 in the Cantabrian coastal karst: the Cobiheru cave (North Iberia)          下载免费PDF全文

Daniel Ballesteros  Laura Rodríguez‐Rodríguez  Saúl González‐Lemos  Santiago Giralt  Diego Jaime Álvarez‐Lao  Luna Adrados  Montserrat Jiménez‐Sánchez 《地球表面变化过程与地形》2017,42(11):1704-1716

The geomorphological evolution of the Cobiheru Cave shows the influence of the non‐carbonate coastal mountain ranges on coastal karst evolution, as well as the temporal distribution of the cold‐adapted fauna sites in the Cantabrian Coast. Geomorphological observation and uranium/thorium (U/Th) dating lead to the construction of an evolution model. The model comprises two episodes of cave deposition occurring at c. 60–70 and 130–150 ka, linked to cold climate conditions, global sea‐level lowstands and the erosion of alluvial fans that covered the karst. Moreover, the comparison between the Cobiheru record and some raised beaches identified in previous studies sets the beginning of the sea‐level lowering in the Cantabrian Sea during the marine isotope stages (MIS) 5–4 transition. Two palaeoenvironments are inferred based on finding Equus ferus and Elona quimperiana. A wet deciduous forest would have developed on the emerged marine terrace of the Cobiheru Cave since at least the Middle Pleistocene, and an open landscape with scarce vegetation would have been present at c. 65 ka. The erosional event identified in the Cobiheru Cave helps to understand the temporal distribution of cold‐adapted mammals located in the Asturias region. The probable sites of cold‐adapted fauna developed in caves and alluvial fans would have disappeared after 65 ka. Therefore, palaeontological and palaeoclimate research based on cold‐adapted mammals suggests the occurrence of an hiatus in the palaeontological record prior to 50 ka. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Uniform fragility spectra for the performance‐based seismic design of structures considering variabilities in structural properties          下载免费PDF全文

Mauro Niño  Gustavo Ayala  Saúl López 《地震工程与结构动力学》2018,47(8):1742-1754

This paper presents a new methodology based on structural performance to determine uniform fragility design spectra, i.e., spectra with the same probability of exceedance of a performance level for a given seismic intensity. The design spectra calculated with this methodology provide directly the lateral strength, in terms of yield‐ pseudo‐accelerations, associated with the rate of exceedance of a specific ductility characterizing the performance level for which the structures will be designed. This procedure involves the assessment of the seismic hazard using a large enough number of seismic records of several magnitudes; these records are simulated with an improved empirical Green function method. The statistics of the performance of a single degree of freedom system are obtained using Monte Carlo simulation considering the seismic demand, the fundamental period, and the strength of the structure as uncertain variables. With these results, the conditional probability that a structure exceeds a specific performance level is obtained. The authors consider that the proposed procedure is a significant improvement to others considered in the literature and a useful research tool for the further development of uniform fragility spectra that can be used for the performance‐based seismic design and retrofit of structures.  相似文献   

Tropical Cyclone Impacts on Coastal Regions: the Case of the Yucatán and the Baja California Peninsulas,Mexico     

Luis M. Farfán  Eurico J. D’Sa  Kam-biu Liu  Victor H. Rivera-Monroy 《Estuaries and Coasts》2014,37(6):1388-1402

Tropical cyclones (TCs) are large-scale natural disturbances that generate strong winds and heavy rainfall, impacting coastal and inland environments. TCs also influence biogeochemical and hydrological cycles controlling aquatic primary productivity in tropical and subtropical coastal ecosystems. We assessed TC landfall activity and identified sites along the Mexican east and west coasts with high frequency in the period 1970–2010 and evaluated TCs with significant precipitation. Changes in chlorophyll-a (Chl-a) concentrations before and after storm impacts were estimated using remotely sensed ocean color. There were 1,065 named TCs with a wide diversity in tracks. Three states with the highest number of landfalls were identified: Baja California Sur and Sinaloa on the west coast and Quintana Roo on the east coast. While a relative increase in Chl-a values following TC landfalls in the Baja California and Yucatán Peninsula regions appeared to be strongly linked to TC strength, the intensity of precipitation, the spatial scales of the two peninsulas, and the relative movement of TCs appeared to have contributed to Chl-a variability. Satellite estimates of Chl-a in the nearshore coastal waters following TC passage were likely enhanced by coastal morphology and water discharge along with constituents such as suspended particulate, colored dissolved organic matter and nutrients from rivers, tributaries, and groundwater.  相似文献   

Selective Separation and Preconcentration of Fe(III) and Zn(II) Ions by Solvent Extraction Using a New Triketone Reagent     

Şerife Saçmacı  Şenol Kartal  Mustafa Saçmacı 《洁净——土壤、空气、水》2011,39(6):584-590

A simple, rapid, and accurate method was developed for separation and preconcentration of trace levels of iron(III) and zinc(II) ions in environmental samples. Methyl‐2‐(4‐methoxy‐benzoyl)‐3‐(4‐methoxyphenyl)‐3‐oxopropanoylcarbamate (MMPC) has been proposed as a new complexing agent for Fe(III) and Zn(II) ions using solvent extraction prior to their determination by flame atomic absorption spectrometry (FAAS). Fe(III) and Zn(II) ions can be selectively separated from Fe(II), Pb(II), Co(II), Cu(II), Mn(II), Cr(III), Ni(II), Cd(II), Ag(I), Au(III), Pd(II), Cr(VI), and Al(III) ions in the solution by using the MMPC reagent. The analytical parameters such as pH, sample volume, shaking time, amount of MMPC reagent, volume of methyl isobutyl ketone (MIBK), effect of ionic strength, and type of back extractant were investigated. The recovery values for Fe(III) and Zn(II) ions were greater than 95% and the detection limits for Fe(III) and Zn(II) ions were 0.26 and 0.32 µg L^?1, respectively. The precision of the method as the relative standard deviation changed between 1.8 and 2.1%. Calibration curves have a determination coefficient (r²) of at least 0.997 or higher. The preconcentration factor was found to be 100. Accuracy of the method was checked by analyzing of a certified reference material and spiked samples. The developed method was applied to several matrices such as water, hair, and food samples.  相似文献   

Pigments in sediments beneath recently collapsed ice shelves: The case of Larsen A and B shelves,Antarctic Peninsula     

E. Sañé  E. Isla  A. Grémare  J. Gutt  G. Vétion  D.J. DeMaster 《Journal of Sea Research》2011,65(1):94-102

In March 2002, 3200 km² of the Larsen B ice shelf collapsed off the Eastern Antarctic Peninsula (EAP). In the austral summer of 2006, sea floor sediment was recovered beneath the extinct Larsen B ice shelf and in a region off the Northern Antarctic Peninsula (NAP), which has been free of ice shelves for more than 1000 yr. To assess changes in the chemical composition of the sediment after ice shelf collapses, chlorophylls and pheophytins were measured in sediment cores at six stations. This is the first time that chlorophyll pigments have been analysed in sediment samples from regions under recently collapsed ice shelves. Five years after the ice shelf collapse, Chla and Chlc concentrations were similar in the interfacial sediment (upper 1 cm) of NAP and EAP regions. However, in EAP Chla and Chlc concentrations decreased more rapidly with depth in the sediment column and were negligible below 2 cm depth. The high Chla to Pheoa ratios indicated that sedimentary pigments found in EAP had undergone limited degradation suggesting that they were locally produced rather than laterally advected. Complementary information from excess ²¹⁰Pb activity and diatom valve distributions provided further evidence that the pigment fluxes to the seabed in EAP took place only after the ice shelf collapse.  相似文献   

Isotopic and Chemical Constraints on the Biogeochemistry of Dissolved Inorganic Carbon and Chemical Weathering in the Karst Watershed of Krka River (Slovenia)   总被引：1，自引：0，他引：1  

Saša Zavadlav  Tjaša Kanduč  Jennifer McIntosh  Sonja Lojen 《Aquatic Geochemistry》2013,19(3):209-230

The hydrogeochemical and carbon isotope characteristics of the Krka River, Slovenia, were investigated to estimate the carbon transfer from the land ecosystem in the watershed. During the 3-year sampling period (2008–2010), temperature, pH, electrical conductivity, major ion content, dissolved inorganic carbon (DIC) and dissolved organic carbon content, and the isotopic composition of DIC (δ¹³C_DIC) were monitored in the main stream of the Krka River and its tributaries. The major solute composition of analysed waters is dominated by an input of HCO₃ ^?, Ca²⁺ and Mg²⁺ originating from carbonate dissolution. The Mg²⁺/Ca²⁺ and Mg²⁺/HCO₃ ^? molar ratio values ranging from 0.24 to 0.71 and 0.05 to 0.30, respectively, indicate a high degree of dolomite dissolution relative to calcite. Dissolved CO₂ concentrations in the river were up to tenfold supersaturated relative to the atmosphere, resulting in supersaturation with respect to calcite and degassing of CO₂ downstream. The δ¹³C values in river water range from ?15.6 to ?9.4 ‰ and are controlled by the input of tributaries, exchange with atmospheric CO₂, degradation of organic matter, and dissolution of carbonates. The mass balance calculations for riverine DIC suggest that the contribution from carbonate dissolution and degradation of organic matter have major influence, whereas the exchange with atmospheric CO₂ has minor influence on the inorganic carbon pool in the Krka River.  相似文献   

Comment     

Antonio A. G. Sa da Costa  John L. Wilson 《水文科学杂志》2013,58(2):267-268

Résumé

Les observations tensiométriques et piézométriques au voisinage du ruisseau des Maurets, dans le bassin du Réal Collobrier, fournissent des informations intéressantes sur les mécanismes hydrologiques en cas de crue. Des mesures au pas de temps hebdomadaire montrent une bonne corrélation entre le débit dans la rivière et le niveau piézométrique au voisinage de celle-ci. D'autre part, on observe que ce niveau ne peut monter que si la pression d'eau dans le sol avant la crue est voisines de zéro. D'autres observations tensiométriques plus détaillées ont été effectuées au pas de temps de la demi-heure. Elles montrent que seules les pluies de fortes intensités peuvent provoquer une montée rapide de la pression positive d'eau du sol (saturation), à condition que cette pression soit très voisine de zéro avant la pluie. Dans ce cas, le gradient vertical de la charge hydraulique est quasi-nul, et des zones saturées contributives apparaissent et se développent, accompagnées de forts débits de crue dans la rivière. Ainsi, même dans des conditions méditerranéennes, les crues peuvent être provoquées par le développement des surfaces saturées contributives au voisinage des rivières. Dans ce cas, sur le bassin étudié, ces surfaces saturées ont une durée de vie très courte.  相似文献   

Distributional changes in rainfall and river flow in Sarawak,Malaysia     

Zulfaqar Sa’adi  Shamsuddin Shahid  Tarmizi Ismail  Eun-Sung Chung  Xiao-Jun Wang 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(4):489-500

Climate change may not change the rainfall mean, but the variability and extremes. Therefore, it is required to explore the possible distributional changes of rainfall characteristics over time. The objective of present study is to assess the distributional changes in annual and northeast monsoon rainfall (November-January) and river flow in Sarawak where small changes in rainfall or river flow variability/distribution may have severe implications on ecology and agriculture. A quantile regression-based approach was used to assess the changes of scale and location of empirical probability density function over the period 1980-2014 at 31 observational stations. The results indicate that diverse variation patterns exist at all stations for annual rainfall but mainly increasing quantile trend at the lowers, and higher quantiles for the month of January and December. The significant increase in annual rainfall is found mostly in the north and central-coastal region and monsoon month rainfalls in the interior and north of Sarawak. Trends in river flow data show that changes in rainfall distribution have affected higher quantiles of river flow in monsoon months at some of the basins and therefore more flooding. The study reveals that quantile trend can provide more information of rainfall change which may be useful for climate change mitigation and adaptation planning.  相似文献