中龄和老龄杉木人工林细根序级形态和呼吸特征     

熊德成  黄锦学  杨智杰  陈光水  杨玉盛 《福建地理》2014,(2):45-51

以福建省南平市王台镇溪后村安曹下19年生和91年生杉木人工林为研究对象,对其1~5级细根的形态及呼吸特征进行了比较研究。结果表明:2个林分细根直径、根长、组织密度随序级升高逐渐增大,比根长及比根呼吸随序级升高则减小;2个林分细根仅在4级根之间和5级根之间的直径以及5级根之间的比根呼吸具有显著差异(P0.05)。方差分析表明林龄仅对细根直径有极显著影响(P0.01),对根长、比根长、组织密度及比根呼吸的影响均不显著;林龄和序级的交互作用对细根直径,比根长及比根呼吸有显著影响(P0.05,P0.01),对根长和组织密度的影响不显著;序级对两个林分细根直径、根长、比根长、组织密度及比根呼吸的影响均达到极显著水平(P0.01)。回归分析表明2个林分细根直径、根长、比根长、组织密度及比根呼吸与序级之间具有三次函数,指数函数,或者幂函数关系。  相似文献   

Assessment of soil–pile–structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations     

《Computers and Geotechnics》2014

The role of the seismic soil–pile–structure interaction (SSPSI) is usually considered beneficial to the structural system under seismic loading since it lengthens the lateral fundamental period and leads to higher damping of the system in comparison with the fixed-base assumption. Lessons learned from recent earthquakes show that fixed-base assumption could be misleading, and neglecting the influence of SSPSI could lead to unsafe design particularly for structures founded on soft soils. In this study, in order to better understand the SSPSI phenomena, a series of shaking table tests have been conducted for three different cases, namely: (i) fixed-base structure representing the situation excluding the soil–structure interaction; (ii) structure supported by shallow foundation on soft soil; and (iii) structure supported by floating (frictional) pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free field soil response by minimising boundary effects during shaking table tests. In addition, a fully nonlinear three dimensional numerical model employing FLAC3D has been adopted to perform time-history analysis on the mentioned three cases. The numerical model adopts hysteretic damping algorithm representing the variation of the shear modulus and damping ratio of the soil with the cyclic shear strain capturing the energy absorbing characteristics of the soil. Results are presented in terms of the structural response parameters most significant for the damage such as foundation rocking, base shear, floor deformation, and inter-storey drifts. Comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil–structure interaction amplifies the lateral deflections and inter-storey drifts of the structures supported by floating pile foundations in comparison to the fixed base structures. However, the floating pile foundations contribute to the reduction in the lateral displacements in comparison to the shallow foundation case, due to the reduced rocking components.  相似文献   

排桩内支撑基坑典型失稳原因及处理对策分析          下载免费PDF全文

虞利军  王茸  陈敏军 《探矿工程》2014,41(6):77-79

排桩内支撑支护结构是软土地区建筑工程中常用的一种基坑支护结构型式。从设计和施工2方面对影响排桩内支撑支护结构稳定的因素进行了分析,并结合某基坑工程破坏实例,对排桩内支撑支护结构典型失稳原因进行了分析探讨,提出了处理对策。开挖结果表明处理措施安全有效。  相似文献   

青藏高原东北部观赏地被植物马蔺根系固土护坡效应研究          下载免费PDF全文

刘亚斌  李湘  余冬梅  马政  吉海龙  王芃  胡夏嵩  朱海丽  李国荣 《盐湖研究》2022,30(3)

为了进一步丰富青藏高原东北部地区植被护坡工程植物选择,推动区内植被护坡工程实用性和观赏性兼顾发展。该项研究以青藏高原东北部观赏地被植物马蔺为研究对象,以青海省大通县朔北藏族乡至东峡镇之间区域为研究区,在野外植物分布特征和生长特征调查的基础上,结合单根拉伸试验和重塑根-土复合体三轴压缩试验,定量评价了野生马蔺植株和根系生长特征、单根抗拉特性以及根系对土体抗剪强度的增强效应。试验结果表明：马蔺主要分布在研究区内洪积扇、坡积裙和河漫滩等地貌单元,立地条件包括上述地貌单元内的林下坡地、田间、道旁、湿地、荒地等;通过选取两处试验区开展调查可知,马蔺平均株高、冠幅和植株密度分别为75.22±11.40 cm、106.09±25.62 cm和1.51±0.55 株/m2;马蔺标准株根系分布深度可达50 cm,主要分布在0~30 cm深度范围内,根幅约40~50 cm;马蔺根径为0.20～0.70 mm,单根抗拉力、抗拉强度和延伸率平均值分别为7.94±2.91 N,46.30± 11.06 MPa和54.17%±17.08%,随着根径的增大,单根抗拉力和单根抗拉强度分别呈幂函数增大和幂函数降低关系,单根极限延伸率随着根径的增大呈逐渐增大变化趋势,但二者之间未表现出相对显著性的关系;马蔺根系对土体黏聚力和内摩擦角均有增强作用,可分别显著增强0~30 cm和0~10 cm深度范围内土体黏聚力和内摩擦角,且对土体黏聚力的增强作用较为显著。该项研究成果对于选用观赏地被植物马蔺进行研究区坡面水土流失、浅层滑坡等地质灾害现象的生态防护工作,具有理论研究价值和实际指导意义。  相似文献   

Spatio‐temporal distribution of near‐surface and root zone soil moisture at the catchment scale     

C. Martinez  G. R. Hancock  J. D. Kalma  T. Wells 《水文研究》2008,22(14):2699-2714

Soil moisture is highly variable both spatially and temporally. It is widely recognized that improving the knowledge and understanding of soil moisture and the processes underpinning its spatial and temporal distribution is critical. This paper addresses the relationship between near‐surface and root zone soil moisture, the way in which they vary spatially and temporally, and the effect of sampling design for determining catchment scale soil moisture dynamics. In this study, catchment scale near‐surface (0–50 mm) and root zone (0–300 mm) soil moisture were monitored over a four‐week period. Measurements of near‐surface soil moisture were recorded at various resolutions, and near‐surface and root zone soil moisture data were also monitored continuously within a network of recording sensors. Catchment average near‐surface soil moisture derived from detailed spatial measurements and continuous observations at fixed points were found to be significantly correlated (r² = 0·96; P = 0·0063; n = 4). Root zone soil moisture was also found to be highly correlated with catchment average near‐surface, continuously monitored (r² = 0·81; P < 0·0001; n = 26) and with detailed spatial measurements of near‐surface soil moisture (r² = 0·84). The weaker relationship observed between near‐surface and root zone soil moisture is considered to be caused by the different responses to rainfall and the different factors controlling soil moisture for the soil depths of 0–50 mm and 0–300 mm. Aspect is considered to be the main factor influencing the spatial and temporal distribution of near‐surface soil moisture, while topography and soil type are considered important for root zone soil moisture. The ability of a limited number of monitoring stations to provide accurate estimates of catchment scale average soil moisture for both near‐surface and root zone is thus demonstrated, as opposed to high resolution spatial measurements. Similarly, the use of near‐surface soil moisture measurements to obtain a reliable estimate of deeper soil moisture levels at the small catchment scale was demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Axial kinematic response of end‐bearing piles to P waves     

George Anoyatis  Raffaele Di Laora  George Mylonakis 《国际地质力学数值与分析法杂志》2013,37(17):2877-2896

Kinematic pile–soil interaction under vertically impinging seismic P waves is revisited through a novel continuum elastodynamic solution of the Tajimi type. The proposed model simulates the steady‐state kinematic response of a cylindrical end‐bearing pile embedded in a homogeneous viscoelastic soil stratum over a rigid base, subjected to vertically propagating harmonic compressional waves. Closed‐form solutions are obtained for the following: (i) the displacement field in the soil and along the pile; (ii) the kinematic Winkler moduli (i.e., distributed springs and dashpots) along the pile; (iii) equivalent, depth‐independent, Winkler moduli to match the motion at the pile head. The solution for displacements is expressed in terms of dimensionless transfer functions relating the motion of the pile head to the free‐field surface motion and the rock motion. It is shown that (i) a pile foundation may significantly alter (possibly amplify) the vertical seismic excitation transmitted to the base of a structure and (ii) Winkler moduli pertaining to kinematic loading differ from those for inertial loading. Simple approximate expressions for kinematic Winkler moduli are derived for use in applications. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Using a H∞ filter assimilation procedure to estimate root zone soil water content     

Haishen Lü  Xiaoli Li  Zhongbo Yu  Robert Horton  Yonghua Zhu  Zhenchun Hao  Long Xiang 《水文研究》2010,24(25):3648-3660

Root zone soil water content impacts plant water availability, land energy and water balances. Because of unknown hydrological model error, observation errors and the statistical characteristics of the errors, the widely used Kalman filter (KF) and its extensions are challenged to retrieve the root zone soil water content using the surface soil water content. If the soil hydraulic parameters are poorly estimated, the KF and its extensions fail to accurately estimate the root zone soil water. The H‐infinity filter (HF) represents a robust version of the KF. The HF is widely used in data assimilation and is superior to the KF, especially when the performance of the model is not well understood. The objective of this study is to study the impact of uncertain soil hydraulic parameters, initial soil moisture content and observation period on the ability of HF assimilation to predict in situ soil water content. In this article, we study seven cases. The results show that the soil hydraulic parameters hold a critical role in the course of assimilation. When the soil hydraulic parameters are poorly estimated, an accurate estimation of root soil water content cannot be retrieved by the HF assimilation approach. When the estimated soil hydraulic parameters are similar to actual values, the soil water content at various depths can be accurately retrieved by the HF assimilation. The HF assimilation is not very sensitive to the initial soil water content, and the impact of the initial soil water content on the assimilation scheme can be eliminated after about 5–7 days. The observation interval is important for soil water profile distribution retrieval with the HF, and the shorter the observation interval, the shorter the time required to achieve actual soil water content. However, the retrieval results are not very accurate at a depth of 100 cm. Also it is complex to determine the weighting coefficient and the error attenuation parameter in the HF assimilation. In this article, the trial‐and‐error method was used to determine the weighting coefficient and the error attenuation parameter. After the first establishment of limited range of the parameters, ‘the best parameter set’ was selected from the range of values. For the soil conditions investigated, the HF assimilation results are better than the open‐loop results. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Calibration of an evapotranspiration model to simulate soil water dynamics in a semiarid rangeland     

M. P. Maneta  S. Schnabel  W. W. Wallender  S. Panday  V. Jetten 《水文研究》2008,22(24):4655-4669

  相似文献   

Three‐dimensional finite element analysis of the interaction between tunneling and pile foundations     

H. Mroueh  I. Shahrour 《国际地质力学数值与分析法杂志》2002,26(3):217-230

This paper concerns analysis of the impact of construction of urban tunnels on adjacent pile foundations. It is carried out using an elastoplastic three‐dimensional finite element modelling. Numerical simulations are performed in two stages, which concern, respectively, the application of the pile axial loading and the construction of the tunnel in presence of the pile foundations. Analysis is carried out for both single piles and groups of piles. Results of numerical simulations show that tunneling induces significant internal forces in adjacent piles. The distribution of internal forces depends mainly on the position of the pile tip regarding the tunnel horizontal axis and the distance of the pile axis from the centre of the tunnel. Analysis of the interaction between tunneling and a group of piles reveals a positive group effect with a high reduction of the internal forces in rear piles. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

浅议岩溶发育区施工勘察对桩基施工的指导作用     

檀集满  朱怀高  沈高平 《安徽地质》2007,17(2):140-142

某水泥厂生料均化库桩基工程施工中,通过施工勘察顺利地解决了岩溶发育区冲孔灌注桩施工中持力层选择、全断面入岩判断、溶洞处理及桩基施工顺序等一系列问题.措施行之有效,工程质量良好.  相似文献