Above and belowground phenology of four Mediterranean sub-shrubs. Preliminary results on root–shoot competition     

S. Palacio  G. Montserrat-Martí 《Journal of Arid Environments》2007,68(4):522-533

Above and belowground phenology are critical aspects for plant life in areas of seasonal climate like Mediterranean regions. However, fine root growth phenology is rarely considered in most phenological studies. In this article we describe the above and belowground phenology of four species of Mediterranean sub-shrubs growing along a gradient of temperature and water availability, with special attention at the relationship between both processes. Observations were conducted monthly over a minimum of 12 months per species. Fine root growth varied significantly throughout the year, being higher in autumn than in spring and minimum in summer. In the species growing in cold areas, root growth was also reduced during winter. Shoot growth was maximum in spring for the four study species, buts its beginning was related to the site temperature, being earlier in those species growing in warmer sites. The species displaying a short vegetative period tended to separate root and shoot growth processes throughout the year. These results emphasize the importance of water availability and winter cold on fine root growth. A trade-off appears to exist between the duration of the vegetative period and the overlap between root and shoot growth processes.  相似文献   

深层搅拌桩在某住宅楼地基加固中的应用     

唐欣然 《矿产与地质》2007,21(5):580-584

以桂林某工地为例阐述了深层搅拌桩在深厚软弱地基中的设计、施工方法以及应用效果。  相似文献   

土性指标和地层性质对水泥搅拌桩成桩质量的影响     

符学兵 《江苏地质》2007,31(4):370-372

从水泥土的固化机理出发,结合水泥搅拌桩桩身标准贯入试验和水泥土配合比试验,分析讨论了土性指标、土质条件和地层性质对水泥搅拌桩成桩质量的影响。  相似文献   

Analysis of kinematic seismic response of tapered piles   总被引：2，自引：0，他引：2  

Mahmoud Ghazavi 《Geotechnical and Geological Engineering》2007,25(1):37-44

In the present work, a two-phase analysis is used to assess the lateral movement of a tapered pile due to kinematic seismic loading resulted from earthquakes. First, the free-field horizontal displacement of the ground due to earthquake is estimated using available theory of wave propagation. Second, these estimated soil movements are imposed on the taper pile in a closed-form solution to compute the pile response. The governing differential equation for an arbitrary pile segment is obtained, which includes the free-field horizontal movement estimated from the first phase. The equation is solved explicitly to obtain the horizontal deflection. Parametric studies show that tapered piles tend to be more flexible than uniform piles of the same volume and length under earthquake loading, which is soundly interesting.  相似文献   

森林地下碳分配(TBCA)研究进展     

陈光水  杨玉盛  刘乐中  李熙波  赵月彩  袁一丁 《福建地理》2007,(1)

森林地下碳分配(TBCA)是森林碳循环的重要通量,对森林碳吸存有十分重要作用.TBCA是森林生态系统GPP中一个最大的汇,可占GPP的21%～61%,土壤呼吸的2/3来自TBCA.目前国际上常用的TBCA测定方法为碳平衡法,在假定地下碳库处于稳定状态时,TB-CA可由土壤呼吸减去凋落物量获得,但该方法存在一系列问题.影响森林TBCA的因素有生产力、森林类型、树龄和森林演替阶段、土壤养分和水分有效性、林分密度和树种组成、气候变化因素等.TBCA中各个组成部分均较难以测定和量化,通常假定TBCA中根系呼吸与根系生产力各约占50%,而TBCA中菌根菌和根系分泌物的贡献则仍不清楚.有关TBCA各组分去向及影响机理的研究亦很少.TBCA未来的研究应致力于揭示TBCA的根本驱动因子和其对全球变化的响应机理,以及TBCA转化为土壤新碳的效率及控制因素;同时应提高TBCA测定方法的确定性,特别是应将碳同位素法、微根管法及碳平衡法三者相结合.  相似文献   

Impact of root architecture on the erosion‐reducing potential of roots during concentrated flow     

S. De Baets  J. Poesen  A. Knapen  P. Galindo 《地球表面变化过程与地形》2007,32(9):1323-1345

Many studies focus on the effects of vegetation cover on water erosion rates, whereas little attention has been paid to the effects of the below ground biomass. Recent research indicates that roots can reduce concentrated flow erosion rates significantly. In order to predict this root effect more accurately, this experimental study aims at gaining more insight into the importance of root architecture, soil and flow characteristics to the erosion‐reducing potential of roots during concentrated flow. Treatments were (1) bare, (2) grass (representing a fine‐branched root system), (3) carrots (representing a tap root system) and (4) carrots and fine‐branched weeds (representing both tap and fine‐branched roots). The soil types tested were a sandy loam and a silt loam. For each treatment, root density, root length density and mean root diameter (D) were assessed. Relative soil detachment rates and mean bottom flow shear stress were calculated. The results indicate that tap roots reduce the erosion rates to a lesser extent compared with fine‐branched roots. Different relationships linking relative soil detachment rate with root density could be established for different root diameter classes. Carrots with very fine roots (D < 5 mm) show a similar negative exponential relationship between root density and relative soil detachment rate to grass roots. With increasing root diameter (5 < D < 15 mm) the erosion‐reducing effect of carrot type roots becomes less pronounced. Additionally, an equation estimating the erosion‐reducing potential of root systems containing both tap roots and fine‐branched roots could be established. Moreover, the erosion‐reducing potential of grass roots is less pronounced for a sandy loam soil compared with a silt loam soil and a larger erosion‐reducing potential for both grass and carrot roots was found for initially wet soils. For carrots grown on a sandy loam soil, the erosion‐reducing effect of roots decreases with increasing flow shear stress. For grasses, grown on both soil types, no significant differences could be found according to flow shear stress. The erosion‐reducing effect of roots during concentrated flow is much more pronounced than suggested in previous studies dealing with interrill and rill erosion. Root density and root diameter explain the observed erosion rates during concentrated flow well for the different soil types tested. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

长螺旋钻孔泵压灌注CFG桩缩径与对策   总被引：1，自引：0，他引：1  

贺为民  尚红  孙铭心  刘明军  常河林 《水文地质工程地质》2002,29(2):62-63,65

CFG桩是水泥粉煤灰碎石桩的简称。长螺旋钻孔泵压灌注CFG桩在层状土层的软硬分界处及软土中出现缩径，通过降低提钻速率和设置降水井点，缩径问题有所缓解，采取复打技术后彻底解决了缩径问题。  相似文献   

抗滑桩间土拱力学特性与最大桩间距分析   总被引：40，自引：2，他引：40  

王成华  陈永波  林立相 《山地学报》2001,19(6):556-559

抗滑桩最大桩间距确定的基础理论至今未建立起来，工程实践中仍依赖专家经验。本文从方桩桩间土拱形成的原理、力学特性论证入手，较全面地分析了桩间土拱的受力、变形，力的传递和土拱破坏瞬间的最大桩间距。并建立了最大桩间距平面计算模型。  相似文献   

孵漂石地层大口径钻头与钻进工艺的选择   总被引：2，自引：1，他引：2  

荆和平  经明等 《地质与勘探》2001,37(4):79-80

根据工程实例，通过钻头和钻进工艺的对比试验，得出了利用大直径滚刀钻头，在致密卵漂石地层施工中大口径桩孔，能大幅度提高钻进效率。  相似文献   

夯扩桩成桩过程引起的挤土效应分析   总被引：3，自引：0，他引：3  

黄生根  曹辉 《岩土工程技术》2001,(1):53-56

夯扩桩在成桩过程中会产生挤土效应。通过采用柱形孔扩张理论，推导出砂土中形成扩大头时引起的挤土影响半径和土体位移，并对一工程实例进行了分析。  相似文献