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971.
This paper presents a general solution to the consolidation system of viscoelastic soil by vertical drains incorporating a fractional-derivative model and arbitrary time-dependent loading. The fractional-derivative Merchant model is introduced to describe the viscoelastic behavior of saturated soil around the vertical drains. Based on this model, the governing partial differential equation of a consolidation system incorporating vertical and horizontal drainage is obtained for the equal strain condition. Then, a general solution to the consolidation system involving arbitrary time-dependent loading is derived using the Laplace transform technique and eigenfunction expansion method. Further, two comparisons are presented to verify the exactness of the proposed solution, and the consolidation behavior involving four time-dependent loadings is illustrated and discussed. 相似文献
972.
Throughfall enrichment and stream nutrient chemistry in small headwater catchments with different land cover in southern Chile 下载免费PDF全文
Land cover changes have a great impact on nitrogen (N) and phosphorous (P) fluxes catchments. In this study, we wanted to compare different land covers: deciduous (D), evergreen (E) (both native forests), and exotic Eucalyptus globulus plantation (EP), affected precipitation, and stream discharge on N and P species concentrations and fluxes, under a low deposition climate in south‐central Chile. For this, we collected bulk precipitation, throughfall, and stream water samples after 41 rainfall events in E and EP, during the period June 2009–March 2011, and 31 rainfall events in D, during the period October 2009–March 2011. The highest canopy enrichment of N and P species for throughfall was observed in deciduous forest, while E. globulus showed the minimum enrichment. Total nitrogen (total‐N) discharge in EP was about 8.6 times higher than that of E and D catchments. Total‐N annual retention was positive only in E and D catchments. However, EP catchment showed a net loss (?4.79 kg N ha/year). The biggest difference was observed in nitrate stream concentrations, which showed low values for E (3.4 ± 1.3 μg/L), while EP and D showed higher nitrate concentrations (84.9 ± 16.7 and 134.7 ± 36.7 μg/L, for EP and D, respectively). Total phosphorous (total‐P) discharge flux was low in EP (0.4 kg P ha/year), and negligible in E and D forests (<0.1 kg P ha/year). Total‐P annual retention was near to 1.0 kg N ha/year (on E and D), while a net loss (?1.5 kg N ha/year) was observed for EP. We attribute the observed differences in nutrient throughfall enrichment due to high multi‐stratified canopies in the native forests. Both deciduous and evergreen native forest‐covered catchments showed the highest retention of total‐N and total‐P, in contrast to Eucalyptus‐covered plantation. 相似文献
973.
Kurt Friese Gerald Schmidt Jorge Carvalho de Lena Dieter W. Zachmann 《Limnologica》2010,40(2):114-125
The artificial reservoir Lagoa da Pampulha in central Brazil has been increasingly affected by sediment deposition and pollution from urban and industrial sources. This study investigates water chemistry and heavy metal concentrations and their fractionation in the lake sediment using ICP-OES, ICP-MS, and XRD analyses. Fractionation analysis was done by sequential extraction under inert gas as well as after oxidation. The lake exhibits a permanent stratification with an oxygen-free hypolimnion below 2 m depth. Nutrient concentrations are enriched for phosphorous components (SRP, PO4). In the sediment it was not possible to detect oxygen. Carbon, sulfur, and most of the analyzed heavy metals are enriched in the top sediment layer with a pronounced downward decrease, indicating the presence of an anthropogenic influence. Statistical analysis, including correlations and a Principal Component Analysis (PCA) of depth-related total concentration data, helps to distinguish presumably anthropogenic heavy metals from geogenic components. Some samples with high element concentrations in the sediment also show elevated concentrations in their pore water. Analyses of element distribution between sediment and pore water suggest a strong bonding of heavy metals to the anoxic sediment. The trend towards elevated solubility in the pore water of oxidized samples is clear for most of the analyzed elements. Fractionation analysis reveals characteristic associations of selected elements to specific mineral bonding forms. In addition, it indicates that the behavior of heavy metals in the sediment is strongly influenced by organic substances. These substances provide buffering against oxidation, acidification, and metal release. The high nutrient loading causes reducing conditions in the lake sediment. These conditions trigger the accumulation of sediments rich in S2−, which stabilizes the fixation of heavy elements. In the future, care must be taken to reduce the supply of contaminants and to prevent the release of heavy metals from sediments dredged for remediation purposes. 相似文献
974.
田云锋 《大地测量与地球动力学》2010,30(5):64-67
??????????????????й??????????????GPS?????????,?????????????????????·?????????????????????????????ATML??????????????3????а?????????????????С????????????????????????????ATML????????????????????????????????????????ATML??????????????????????:?????????????????????????????С???????????????????????????????????????????С?? 相似文献
975.
Chronology and nutrients change in recent sediment of Taihu Lake,lower Changjiang River Basin,east China 总被引:1,自引:0,他引:1
Two short sediment cores named ZS and THS dated by the 210Pb or 137Cs method were collected from the northwest and southwest of Taihu Lake respectivly,and total organic carbon(TOC) and nutrients including total nitrogen(TN) and total phosphorus(TP) were determined to analyze the chronology and nutrients change in recent sediment.The results show that 137Cs activities are low(less than 15 Bq/kg) in the two cores,attributed to the 137Cs migration.Based on 210Pb constant rate of supply(CRS) model,the sedimentation accumulation rates range from 0.13 g/(cm2·yr) to 0.76 g/(cm2·yr) in the ZS core,and from 0.10 g/(cm2·yr) to 0.56 g/(cm2·yr) in the THS core.A remarkable increase in organic matter and nutrients has occurred in the two dated cores since the mid-1980s.The historical changes of organic matter and nutrients in the two cores are consisitent with the monitoring data for surface sediment after the 1960s.The TP accumulation rates after the early 1980s are 0.97 and 0.92 times higher than those from the 1950s to the 1980s in ZS and THS cores,respectively.Higher TP concentrations in the past two-decade deposits of Taihu Lake are due to both diagenetic factors and human activities. 相似文献
976.
以中国生态系统研究网络CERN长武王东沟实验站的坡耕地和塬耕地为供试土壤,研究了黄土高原沟壑塬区旱耕地原状土壤氮素迁移和时空变异。结果表明:耕作土壤NO3--N为23.1~33.8 mg/kg,NH4+-N为0.23~0.50mg/kg,DOC为9.17~13.38 mg/kg,P为0.18~0.23 mg/kg;坡耕地和塬耕地的NO3--N和NH4+-N主要集中在0~20 cm的上层土壤,中下层土壤NO3--N和NH4+-N起源于上层淋溶迁移和累积;高含量时养分淋溶溶出呈指数衰减型;NO3--N、NH4+-N、DOC向下层的迁移塬耕地慢于坡耕地。 相似文献
977.
动荷载作用下结构性软土微结构变化的分形研究 总被引:1,自引:0,他引:1
为探讨天津滨海新区典型结构性软土的动力特性,采用动三轴试验和压汞试验,对交通荷载作用下结构性软土微观结构变化进行了研究。取原状土和动荷载作用后的土样进行压汞测试,用分形理论对压汞测试数据进行分析,探讨孔隙分布特征,提出孔径划分的方法,给出了卓越频率与土体孔隙变化的规律。研究结果表明:在动荷载作用后,天津滨海新区典型软土的孔隙分布发生改变,可分为3种类型;利用Menger海绵模型研究交通荷载作用下结构性软土的孔隙分布特性是可行的;用孔隙分维数可实现对卓越频率的预测以及路基土体变形行为的机制分析。 相似文献
978.
考虑非Darcy渗流时循环荷载下饱和黏土一维固结分析 总被引:1,自引:0,他引:1
考虑到土体处于超固结状态下的压缩性一般要比正常固结状态下的低,引入描述非Darcy渗流的Hansbo方程,修正了Terzaghi饱和黏土一维固结方程,并将其推广到低频循环荷载作用的情况。采用有限体积法对该方程进行了求解,并讨论了非Darcy渗流参数、循环荷载周期以及超固结状态下土体压缩性对固结进程的影响。计算结果表明,在矩形波载作用下,按孔压定义和按变形定义的固结度都随时间增长而震荡增加,且按孔压定义的固结度的震荡幅度明显大于按变形定义的固结度。另外,非Darcy渗流减缓了地基的沉降速率,且循环荷载周期越短,或超固结状态下压缩性越高,地基的沉降速率就越慢。 相似文献
979.
980.
根据定位观测的数据,探讨了2代杉木人工林幼林造林后6—9年凋落物数量及其养分特征,结果表明,在4a中,杉木幼林向林地输入凋落物共为1408.67kg·hm^-2,年均凋落量352.17k·hm^-2,6~9年的各年凋落量占总凋落量的比例为:19.84%、21.93%、28.51%、30.99%;在年凋落量中枝叶占多数,6~9年枝叶凋落总量分别为:233.43kg·hm^-2、264.80kg·hm^-2、334.09kg·hm^-2、354.11kg.hm^-2,年总凋落量、年枝叶凋落量均随着年份的增加而增加.在2002年、2003年和2004年夏季和秋季杉木幼林内凋落物的总量较多,冬季和春季较少,而2005年春季凋落总量最多,冬季最少.在凋落物各组分养分归还量中,杉木叶和其他叶N、P、K和C归还量较多,且年变化较大,杉木枝、其他枝、虫粪和碎屑N、P、K和C归还量较少,年变化亦较小. 相似文献