A multi‐asperity plastic‐contact crack plane model for geomaterials     

I. C. Mihai  A. D. Jefferson 《国际地质力学数值与分析法杂志》2013,37(11):1492-1509

A mechanistic constitutive model for fully formed cracks in geomaterials, such as concrete and rock, is presented. A three‐dimensional characterisation of the crack morphology is employed in which the crack surface is idealised as a series of conical teeth and corresponding recesses of variable height and slope. Based on this geometrical characterisation, an effective contact function is derived to relate the contact stresses that develop on the sides of the teeth to the net stresses on a crack plane. Plastic embedment and frictional sliding are simulated using a local plasticity model in which the plastic surfaces are expressed in terms of the contact surface function in cylindrical relative displacement space. Finally, the performance of the model is assessed against several sets of experimental data from direct shear tests, and it is concluded that the model is able to capture key characteristics of the behaviour of fully formed cracks in geomaterials. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Benthic control upon the morphology of transported fine sediments in a low‐gradient stream          下载免费PDF全文

James Fox  William Ford  Kyle Strom  Gabriele Villarini  Michelle Meehan 《水文研究》2014,28(11):3776-3788

The structure of fluvial sediments in streams has environmental implications to contaminant fate, nutrient budgeting and the carbon flux associated with fine particulate organic matter (FPOM). However, the influence of sediment structure is lacking in environmental predictive models. To this end, the present study links field‐based results of sediment aggregate structure to seasonal biological functions in the surface fine‐grained laminae (SFGL) of a low‐gradient stream. Fluvial sediment collection, microscopy and image analysis are used to show that aggregates collected over a 20 month time period support the concept that aggregate structure can vary seasonally in low‐gradient streams where temporarily stored sediment is prominent. Results show that the structure of the transported aggregates is more irregular in the summer with the structure being elongated about the long axes. In the winter, the aggregate structure is compacted and more spherical. Statistical analysis and results suggest that heterotrophic and autotrophic biological activity within the SFGL exhibits seasonal control upon the morphology of transported sediments. Implications of this research are highlighted through calculations of the reactive surface area of the transported suspended sediment load. The surface area of transported sediment is estimated to be 40% greater in the summer as compared to the winter time period, which implies that (i) the affinity of sediments to sorb contaminants is higher in summer months and (ii) the downstream reactivity of FPOM in large rivers, lakes and estuaries is not just a function of microbial drivers but also the seasonally dependent structure of transported FPOM derived from low‐order streams. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

利用海洋疏浚泥生产轻质陶粒的研究     

谢健  林鑫城  石萍  万德荣  陈炜 《广东海洋大学学报》2004,24(6):32-36

为将疏浚泥转化为可再利用的材料,以减少疏浚泥海洋倾倒量,利用烧结技术将疏浚泥转 化为建筑材料———轻质陶粒进行再利用,把掺疏浚泥的混合料投入应用性试生产。结果表明,当 混合料中疏浚泥与黏土的比例达到1∶2或1∶3时,烧结温度1160℃,焙烧效果较好,所得陶粒的 颗粒密度较低;陶粒产品的表观密度<450kg/m3,筒压强度>1.2MPa,产品性能符合国家标准;生 产成本基本上没有增加,并可节约耕地,产生一定的环境效益和社会效益。  相似文献   

Gravel seeding – A suitable technique for restoring the seabed following marine aggregate dredging?     

Keith Cooper  Suzanne WareKoen Vanstaen  Jon Barry 《Estuarine, Coastal and Shelf Science》2011

Restoration of offshore marine habitats is a relatively new concept, with attempts in the European Union being largely instigated by requirements of various strategic directives. In this experiment, we investigate the practicality and effectiveness of gravel seeding, using a commercial aggregate dredging vessel, in order to recreate a gravel habitat. The experimental design consisted of a Treatment and Control site, both within an area of historic dredging characterised by an overburden of sand, and a gravel dominated Reference site. All sites were surveyed, using a combination of acoustic, camera and grab techniques, 2 months before, and then at 0, 12 and 22 months after the deposition of 4444 m³ of gravel dominated sediments within the Treatment site. Although financial and practical constraints limited replication of the Treatment to one area, and so precluded strong statistical conclusions, our results suggested that the technique was both practically feasible, and successful in terms of returning the physical and biological attributes at the Treatment site to a state more representative of gravelly substrata in the wider, un-impacted environment.  相似文献   

Implications of dredging induced changes in sediment particle size composition for the structure and function of marine benthic macrofaunal communities     

Cooper KM  Curtis M  Wan Hussin WM  Barrio Froján CR  Defew EC  Nye V  Paterson DM 《Marine pollution bulletin》2011,62(10):2087-2094

A meta-analysis approach was used to assess the effect of dredging induced changes in sediment composition, under different conditions of natural physical disturbance, for the structure and function of marine benthic macrofaunal communities. Results showed the sensitivity of macrofaunal communities increased as both the proportion of gravel increased and the level of natural physical disturbance decreased. These findings may be explained by the close association of certain taxa with the gravel fraction, and the influence of natural physical disturbance which, as it increases, tends to restrict the colonisation by these species. We conclude that maintaining the gravel content of surface sediments after dredging and, where practicable, locating extraction sites in areas of higher natural disturbance will minimise the potential for long-term negative impacts on the macrofauna.  相似文献   

宁津甲子山地区正长岩体作为混凝土骨料的适宜性评价     

汪子杰  王群  王晓光 《山东国土资源》2015,31(6)

砂石骨料在混凝土中起着极其重要的作用,其质量关系工程寿命的大计。该文选择山东省荣成市宁津甲子山地区正长岩体作为研究对象,对该地区正长岩体作为混凝土骨料的适宜性进行了评价研究。通过野外实地调查及大量的分析测试数据对该地区三叠纪宁津所序列甲子山单元、东山单元、朝阳洞单元岩石进行了分析研究,确定其用作粗细骨料的适宜性,并提出了开采的建议。  相似文献   

Setting limits for acceptable change in sediment particle size composition: Testing a new approach to managing marine aggregate dredging     

Keith M. Cooper 《Marine pollution bulletin》2013

A baseline dataset from 2005 was used to identify the spatial distribution of macrofaunal assemblages across the eastern English Channel. The range of sediment composition found in association with each assemblage was used to define limits for acceptable change at ten licensed marine aggregate extraction areas. Sediment data acquired in 2010, 4 years after the onset of dredging, were used to assess whether conditions remained within the acceptable limits. Despite the observed changes in sediment composition, the composition of sediments in and around nine extraction areas remained within pre-defined acceptable limits. At the tenth site, some of the observed changes within the licence area were judged to have gone beyond the acceptable limits. Implications of the changes are discussed, and appropriate management measures identified. The approach taken in this study offers a simple, objective and cost-effective method for assessing the significance of change, and could simplify the existing monitoring regime.  相似文献   

喀斯特山地土地利用方式对土壤团粒的影响——以重庆黔江为例   总被引：3，自引：1，他引：2  

严宁珍  白仲才  徐卫红  李阳兵 《中国岩溶》2011,30(1):72-77

土壤结构恶化是土壤侵蚀性退化的普遍现象和结果,在喀斯特地区表现尤为突出。本文以重庆黔江区为例,分析了四种不同的土地利用方式下,土壤团聚体的组成、稳定性及其影响因素。结果表明:研究区土壤颗粒组成主要集中在<0.05mm的范围内,土壤粘粒(<0.001mm)含量普遍较高;土壤经人为开垦利用转变为耕地后,表层土壤颗粒砂化明显;土地利用方式不同,风干团聚体含量相差不大,而水稳性团聚体组成和稳定性差异较大,＞5mm和＞1mm水稳性团聚体含量由大到小为:灌草坡＞林地＞退耕地＞耕地,＞0.25mm团聚体含量由大到小为:灌草坡＞退耕地＞林地＞耕地。灌草坡的水稳性团聚体含量最大,稳定性最强,耕地最差。有机质是影响水稳性团聚体的主要因素,因此,增加有机质的含量是恢复和改良喀斯特山地土壤结构状况的关键   相似文献   

压力溶解对颗粒聚集岩体中热-水-应力耦合作用的弹塑性有限元分析     

周英博  张玉军 《岩土力学》2016,37(6):1781-1790

将Taron等提出的颗粒聚集体的压力溶解模型引入笔者所研制的孔隙介质热-水-应力耦合有限元程序中,并使用摩尔-库仑准则,针对一个假设的实验室尺度且位于饱和石英颗粒聚集岩体中的高放废物地质处置库模型,拟定弹性分析和弹塑性分析两种计算工况,进行4 a处置时段的数值模拟,考察了岩体中的温度、颗粒界面水膜及孔隙中的溶质浓度、迁移和沉淀质量、孔隙率及渗透系数、孔隙水压力、地下水流速和应力及塑性区的变化、分布情况。结果主要显示：弹塑性分析中由于应力调整和增大了分子扩散系数,使得塑性区的颗粒介质的溶解、迁移和沉淀有明显的变化,并对渗流场（孔隙水压力及流速）和应力场产生显著的影响。但两种工况弹性区中的颗粒介质的溶解、迁移和沉淀差别较小。  相似文献   

混合充填骨料胶结充填强度试验与最优配比决策研究     

杨啸  杨志强  高谦  陈得信 《岩土力学》2016,37(Z2):635-641

将全尾砂作为充填料进行充填法采矿,不仅可以降低采矿成本,而且还能够实现固体废弃物资源化利用,同时将固体废弃物充填地下保护环境,维护生态平衡。由于尾砂粒径较细,需要与棒磨砂、戈壁砂混合作为充填料应用于充填采矿,有必要开展混合充填骨料的配比优化研究。首先,分别测试了棒磨砂、戈壁砂和尾砂3种骨料的粒径级配和不均匀系数。然后进行了9组配比的胶结充填体强度试验,在该基础上对试验样本进行训练,建立了神经网络预测模型。最后采用该预测模型,进行混合充填骨料正交设计方案的充填体强度预测,并分别采用极差分析和回归分析,揭示了充填体强度与混合充填骨料特征值之间的关系。研究发现,混合骨料平均粒径和不均匀系数不同,充填体早期和后期强度存在显著差异;平均粒径较小的混合骨料早期强度较高,而平均粒径较大者则更利于提高充填体的后期强度。  相似文献