利用重力场模型对中国陆地和岛礁GNSS水准沉降进行分析

利用现势性很强的EGM2008,EIGEN-6C,EIGEN-6C2,GO_CONS_GCF_2_DIR_R4共四个地球重力场模型,对中国沿海近岸陆地和岛礁上16个区域的1 053个GNSS水准点进行了沉降分析,最后发现中国沿海浙江省、辽宁省、上海市、天津市、广西、琼州北(琼州海峡北)、琼州南(琼州海峡南)7个区域存在沉降。     

基于神经网络的大连东北海岸带碎石土地基强夯加固研究

以大连某实际工程作为研究场地,室内试验与原位测试所得碎石土地基物理力学参数与实测所得强夯处理沉降量作为样本,通过BP神经网络对样本的训练、学习,建立地基土力学参数与强夯处理的沉降量之间的映射关系,利用所得映射关系对场地实测的沉降量进行物理力学参数的反演分析。结果表明:经过训练的神经网络模型可快速得出所需参数,利用flac3d以反演所得参数进行计算,模拟沉降量与实测沉降量的误差为4.87%,在可接受的范围之内;基于神经网络的位移反分析方法可以省去繁琐的测试工作,但该方法的实现需要有充足的样本数据作为支撑。     

延安新区大厚度压实填土地基均匀性评价

延安新区大厚度压实填土由于其形成过程的特殊性,现行规范对其地基均匀性评价无具体的评价依据和判定准则。在研究了压实填土的工程性质和差异沉降影响因素的基础上,创新性地提出压实填土地基差异沉降敏感度概念,并给出了具体的地基均匀性判定方法,便于进行压实填土地基均匀性评价,为建筑物总平面布置、地基处理及基础设计提供依据。大厚度压实填土不均匀地基不仅应进行针对性的地基处理,还应采取必要的结构措施,并加强建筑物沉降观测,以进行长期深入研究。     

Changing Contributions of Suspended Sediment Sources in Small Basins Resulting from European Settlement on the Canadian Prairies

Lake sediments provide an integrated record of the sediment yields and sources in the contributing basin. In the research area on the prairies of western Canada, the earliest sediments deposited in the larger lakes predate European settlement, allowing direct evaluation of basin response to settlement. Lake sediment cores were collected from an unnamed lake in the Stony Creek drainage basin in the aspen parkland region of eastern Saskatchewan. Pre- and post-settlement sediments in a central core were separated on the basis of an increase in Populus pollen associated with the southward advance of the aspen parkland ecotone caused by fire suppression following settlement. A wet chemical extraction procedure was used to separate the operationally defined organic fraction, the acid-soluble authigenic fraction, and biogenic silica from the clastic, non-carbonate, allogenic fraction of the lake sediment. Changes in the mineralogy and geochemistry of the clastic, allogenic fraction indicate that settlement resulted in an increased contribution of topsoil to the sediment load of Stony Creek. Elemental ratios, however, show that topsoil did contribute to the allogenic lake sediment fraction prior to settlement. Post-settlement changes in deposition rates of the allogenic fraction resulted from changes in land use rather than from climatic variability. Allogenic deposition rates reached a maximum in the 1950s and 1960s owing to an increase in the area under field crops and the increased use of high-powered agricultural machinery. Allogenic deposition rates decreased in more recent years because of a more extensive application of soil conservation measures. Post-settlement changes in deposition rates of individual elements within the allogenic fraction indicate that various sediment sources respond differently to changes in land use. Over the most recent 100 years, since the onset of European settlement, the erosional response of the basin appears to be controlled by land use changes rather than by climatic variability. © 1997 John Wiley & Sons, Ltd.     

CS2: A PIECEWISE-LINEAR MODEL FOR LARGE STRAIN CONSOLIDATION

This paper presents a piecewise-linear finite-difference model for one-dimensional large strain consolidation called CS2. CS2 is developed using a fixed Eulerian co-ordinate system and constitutive relationships which are defined by discrete data points. The model is dimensionless such that solutions are independent of the initial height of the compressible layer and the absolute magnitude of the hydraulic conductivity of the soil. The capability of CS2 is illustrated using four example problems involving small strain, large strain, self-weight, and non-linear constitutive relationships. In each case, the performance of the model is comparable to other available analytical and numerical solutions. Using CS2, correction factors are developed for the conventional Terzaghi theory which account for the effect of vertical strain on computed values by elapsed time and maximum excess pore pressure during consolidation. © 1997 John Wiley & Sons, Ltd.     

沉降监测基准网稳定性分析的应用

结合工程实例介绍平均间隙法和单点位移分量法在沉降监测基准网稳定性分析中的具体应用,并根据分析结果比较了这两种方法的准确性和优缺点。     

多层软土地基中单桩沉降与内力位移分析

根据深厚多层软土地区地基土的物理力学性质,考虑桩侧土低荷载水平下的初始极限剪应力和高荷载水平下的应力软化特性以及桩端土承载力分段发挥特性,采用一种新的桩侧和桩端模型模拟单桩荷载传递机制。基于上述模型,利用递推迭代方法可计算单桩桩顶沉降、桩身轴力以及桩侧摩阻力。采取土工参数易于获取且适用于软土地区的经验p-y曲线描述桩-土界面力和位移的非线性关系。基于欧拉-伯努利梁和中心差分理论,考虑桩尖边界条件,采用数值计算方法对桩沿长度方向的转角、剪力、弯矩进行计算,以获取在特定荷载下这些变量的变化特征。最后,结合工程案例,对上述方法进行了验证,其计算简洁且与实际测试结果吻合良好。     

基于LSSVM与MCS的路基沉降可靠度分析

提出了一种计算路基沉降可靠度的新方法。基于FLAC中的修正剑桥模型,以最小二乘支持向量机为核心技术,结合蒙特卡罗法构建计算模型。由于修正剑桥模型参数较多,对模型参数进行了敏感性分析,将对沉降影响较大的参数确定为随机变量。选取训练样本对支持向量机进行训练,按照随机变量的概率分布进行抽样,馈送到最小二乘支持向量机得到相应的响应值,用Matlab编制程序完成可靠度计算,并进行了算例分析。计算结果表明,蒙特卡罗法结合支持向量机的沉降可靠度计算方法应用于公路软基沉降可靠度计算是可行的。     

浆固碎石桩单桩轴向荷载传递分析

浆固碎石柱是一种新型的桩基技术,已成功应用于铁路、高速公路等工程中。但由于浆固区的存在,浆固碎石桩荷载传递机理的复杂性制约了其发展和工程应用。荷载传递分析法是桩荷载传递机理分析的重要方法之一。本文采用线性弹塑性和双折线传递函数,分别模拟桩侧土体的非线性和桩端土的硬化特性,同时考虑浆固区存在对桩荷载传递的影响,推导出一种浆固碎石桩单桩荷载传递分析方法。最后,通过对工程实例进行计算,验证了本文计算方法的实用性。结果表明,浆固碎石桩除具有一般刚性桩的桩体置换作用外,浆固区的存在对提高浆固碎石柱承载力、减小沉降量也有着重要作用。