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991.
992.
Marco Loia Paola La Valle Loretta Lattanzi Barbara La Porta Monica Targusi Luisa Nicoletti 《Marine Ecology》2020,41(6):e12615
Recolonization patterns of benthic assemblages after relict sand dredging were investigated in an area offshore of Capo d’Anzio (central Tyrrhenian Sea). Surveys were performed before, during, and after dredging in 2007. Sampling stations were located within and outside the dredging site in water depths between 40 and 56 m. Defaunation due to sand extraction was the main impact observed in the inner stations and in stations located in proximity of the dredging site. At the inner stations, 9 months after dredging, a significant increase in species richness and diversity was observed: the sediment removal led to an increase of the sandy sediment fraction, favouring the settlement of sabulicolous species. A decrease in number of individuals and species was also observed in most of the outer stations, probably due to fine sediment redeposition. Recolonization of macrobenthic assemblages was essentially achieved at inner stations both in terms of abundance and species richness, while at outer stations it was still in progress. Results of this study, providing a picture of recovery times and processes in the Tyrrhenian Sea, could be used to develop predictions of the effects of future offshore sand dredging projects in comparable areas. Monitoring programs and research have a key role to provide a more detailed overview of biological recovery processes and times in different regions and with different dredging intensity. 相似文献
993.
994.
在热带地区开展水运工程设计施工项目,经常会遇到珊瑚砂地质,其力学特性较为特别,强度低、易碎、黏性低,力学指标变异性较大,国内现有设计规范对珊瑚砂地质条件特殊性考虑不足,设计人员在相关设计参数选取时经常忽略采用可靠度理论进行结构安全复核。以马尔代夫机场扩建项目为案例,运用可靠度理论分析了珊瑚砂力学指标的高变异性对钢板桩结构稳定可靠度的影响。根据分析,在珊瑚砂地质条件下,按照《码头结构设计规范》(JTS167-2018)进行稳定性计算,得出的结果偏于危险,应引起结构设计人员的重视。在进行结构设计时,应同时按照《港口工程结构可靠性设计统一标准》(GB50158-2010)复核板桩结构可靠度。同时,珊瑚砂较小的黏性,在进行结构可靠度计算时可以忽略。 相似文献
995.
AbstractHollow cylinder torsional shear tests on loose isotropically and anisotropically consolidated calcareous sand were conducted to investigate the cyclic behavior under three different linear stress paths, including horizontal line, oblique line, and vertical line stress paths, in a coordinate system of the normal stress difference and the horizontal shear stress. The dominant strain components of the isotropically consolidated specimens are affected by the stress paths. With increasing consolidation stress ratio, axial strain gradually becomes the dominant strain component under the three different stress paths. The cyclic strength of the isotropically consolidated specimens under the three different stress paths are almost the same, while for the anisotropically consolidated specimens, the cyclic strengths are strongly affected by the stress paths. These results indicate that conventional cyclic triaxial tests may overestimate cyclic strength in some cases. Irrespective of the stress paths and cyclic stress ratios, the terminal residual excess pore pressure ratio decreases with increasing consolidation stress ratio. Moreover, an empirical equation is proposed to describe the relationship between the normalized shear work and the normalized residual excess pore pressure ratio. The comparative study reveals that the relationship proposed for silica sand is not suitable for the dynamic analyses of calcareous sand. 相似文献
996.
997.
南海珊瑚礁人工岛淡水透镜体形成过程及影响因素 总被引:1,自引:0,他引:1
中国目前在珊瑚礁上建设人工岛的目标是建成生态宜居岛屿,人工岛地下海水在降雨入渗驱替作用下逐渐淡化,形成的淡水透镜体是支撑岛屿生态系统的重要水源。本文针对南海珊瑚礁普遍存在的上土下岩的二元地质结构,考虑不同测量方法得到的南海人工岛填筑所用珊瑚砂渗透系数存在较大差异,建立了珊瑚礁人工岛淡水驱替海水形成淡水透镜体的动态模拟模型,对南海某珊瑚礁人工岛开展了系列数值模拟研究。结果表明,人工岛礁二元地质结构不同的渗透性对人工岛淡水开始形成时间无明显影响,填岛完成2年左右的时间可观测到淡水,估计(或理论计算)在10~20年内可形成相对稳定的淡水透镜体;在人工岛面积达到一定规模的前提下,全新世珊瑚砂沉积物渗透性是控制人工岛礁淡水透镜体的主要因素,能够形成的淡水透镜体体积随渗透系数增大而呈对数减小,并且淡水透镜体体积随全新世沉积物渗透性增大而减小的速率较淡水透镜体厚度更加显著;淡水透镜体越过不整合面进入更新世礁灰岩后,由于含水层渗透系数突然增大,淡水透镜体向水平方向扩展,在礁灰岩顶界形成“髭”状淡水体。 相似文献
998.
分析三峡水库与葛洲坝水库蓄水、泄洪、冲沙的非固体潮时、空、强、频特征,研究其对宜昌台地形变观测的影响。 相似文献
999.
Sediment segregation by biodiffusing bivalves 总被引:1,自引:0,他引:1
F. Montserrat C. Van Colen P. Provoost M. Milla M. Ponti K. Van den Meersche T. Ysebaert P.M.J. Herman 《Estuarine, Coastal and Shelf Science》2009,83(4):379-391
The selective processing of sediment fractions (sand and mud; >63 μm and ≤63 μm median grain size) by macrofauna was assessed using two size classes of inert, UV-fluorescent sediment fraction tracers (luminophores). The luminophores were applied to the sediment surface in 16 m2 replicated plots, defaunated and control, and left to be reworked by infauna for 32 days. As the macrofaunal assemblage in the ambient sediment and the control plots was dominated by the common cockle Cerastoderma edule, this species was used in an additional mesocosm experiment. The diversity, abundance and biomass of the defaunated macrobenthic assemblage did not return to control values within the experimental period. Both erosion threshold and bed elevation increased in the defaunated plots as a response to the absence of macrofauna and an increase in microphytobenthos growth. In the absence of macrobenthos, we observed an accretion of 7 mm sediment, containing ca. 60% mud. Image analysis of the vertical distribution of the different luminophore size classes showed that the cockles preferentially mobilised fine material from the sediment, thereby rendering it less muddy and effectively increasing the sand:mud ratio. Luminophore profiles and budgets of the mesocosm experiment under “no waves–no current” conditions support the field data very well. 相似文献
1000.
Processes affecting the hydraulic stability of coastal revetments made of geotextile sand containers
Softer and flexible protection alternatives, such as structures made of geotextile sand containers (GSC) are often used instead of hard coastal structures made of concrete or rubble material. 相似文献