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111.
现浇薄壁管桩是处理大面积软土地基的一项新技术,目前已在沿海软土地区高速公路建设中得到了一定的应用,但其产生的时间较短,开展的研究相对较少,利用Plaxis岩土工程有限元软件对现浇薄壁管桩(PCC桩)的工作特性、荷载传递规律及其影响因素、加固机理等方面进行了详细的分析,结果表明,桩外壁摩阻力随桩深近乎呈线性分布,桩内壁摩擦力只在桩下端一定长度内有所发挥,桩芯土体具有较好的闭塞效应,研究成果具有较大的指导意义. 相似文献
112.
Elastic lateral dynamic impedance functions are defined as the ratio of the lateral dynamic force/moment to the corresponding lateral displacement/rotation at the top ending of a foundation at very small strains. Elastic lateral dynamic impedance functions have a defining influence on the natural frequencies of offshore wind turbines supported on cylindrical shell type foundations, such as suction caissons, bucket foundations, and monopiles. This paper considers the coupled horizontal and rocking vibration of a cylindrical shell type foundation embedded in a fully saturated poroelastic seabed in contact with a seawater half‐space. The formulation of the coupled seawater–shell–seabed vibration problem is simplified by treating the shell as a rigid one. The rigid shell vibration problem is approached by the integral equation method using ring‐load Green's functions for a layered seawater‐seabed half‐space. By considering the boundary conditions at the shell–soil interface, the shell vibration problem is reduced to Fredholm integral equations. Through an analysis of the corresponding Cauchy singular equations, the intrinsic singular characteristics of the problem are rendered explicit. With the singularities incorporated into the solution representation, an effective numerical method involving Gauss–Chebyshev method is developed for the governing Fredholm equations. Selected numerical results for the dynamic contact load distributions, displacements of the shell, and lateral dynamic impedance functions are examined for different shell length–radius ratio, poroelastic materials, and frequencies of excitation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
113.
This paper presents an analytical method for modeling the dynamic response of a rigid strip footing subjected to vertical-only loads. The footing is assumed to rest on the surface of a viscoelastic half-space; therefore, effects of hysteretic soil damping on the impedance of the foundation and the generated ground vibrations are considered in the solution. To solve the mixed boundary value problem, we use the Fourier transform to cast a pair of dual integral equations providing contact stresses, which are solved by means of Jacobi orthogonal polynomials. The resulting soil and footing displacements and stresses are obtained by means of the Fourier inverse transform. The solution provides more realistic estimates of footing impedance, compared to existing solutions for elastic soil, as well as of the attenuation of ground vibrations with distance of the footing. The latter is important for the estimation of machine vibration effects on nearby structures and installations. 相似文献
114.
Tensionless–frictionless interaction of flexible annular foundation with a transversely isotropic multi‐layered half‐space
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Morteza Eskandari‐Ghadi Ghasem Gorji‐Bandpey Azizollah Ardeshir‐Behrestaghi Seyed Masoud Nabizadeh 《国际地质力学数值与分析法杂志》2015,39(2):155-174
A transversely isotropic multi‐layered half‐space, with axis of material symmetry perpendicular to the free surface, supports a flexible either annular or solid circle foundation. The contact area of the foundation and the half‐space is considered to be both frictionless and tensionless. The foundation is assumed to be affected by a vertical static axisymmetric load. Detailed analysis of the interaction of these two systems with different thickness of layers is the target of this paper. With the use of ring load Green's functions for both the foundation and the continuum half‐space, an integral equation accompanied with some inequalities is introduced to model the complex BVP. With the incorporation of ring‐shape FEM, we are capable of capturing both regular and singular solution smoothly. The validity of the combination of the analytical and numerical method is proved with comparing the results of this paper with a number of benchmark cases of both linear and nonlinear interaction of circular and annular foundation with half‐space. Some new illustrations are presented to portray the aspect of the anisotropy and layering of the half‐space. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
115.
深基坑工程是地下工程施工中内容比较丰富且富有变化的领域。为了确保基坑工程施工安全顺利进行,在复杂的地质条件下进行变形监测,及时发现和预报异常现象。对有效控制基坑变形、指导施工、保证施工质量具有重要意义。 相似文献
116.
The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM. 相似文献
117.
在短期基坑沉降监测中,由于数据量少且呈非线性变化,沉降模型很难准确建立。灰色GM(1,1)对数据少、趋势性强、波动小的数据有较高的预测精度,但不能模拟复杂的非线性函数;BP神经网络可以对非线性数据进行学习训练,具有自学习、自适应能力;通过将GM(1,1)与BP神经网络组合,并优化网络部分的学习率、权值和阈值等,建立一种改进的灰色神经网络模型,该模型具有对非线性数据自学习、自适应能力和预测精度更高等优点。通过某基坑沉降监测分析,验证改进的灰色神经网络模型预测精度更高,适合短期建模,具有很好的实用性。 相似文献
118.
为探寻全吸力范围内土壤水分特征曲线的可靠测定方法,采用沙箱排水法、Hyprop仪蒸发法、压力膜仪排水法和露点水势仪蒸发法分吸力段测定盐亭紫色土耕地表层2~7 cm和亚表层7~12 cm土壤的水分特征曲线,对比测定结果的方法间差异,并分析其原因。结果表明:对于表层和亚表层土壤,低吸力段(h >-100 cm)水分特征曲线的沙箱法和Hyprop仪法的均方根误差ERMS (θ)均较小,在0.026~0.082 cm3/cm3范围内,确定系数R2均大于0.962,说明这两种方法测定结果之间差异不大。高吸力段(h <-330 cm)的压力膜仪法与露点仪法测定结果之间的差异较大,ERMS (θ)为0.062~0.097 cm3/cm3,R2较低,为0.775~0.952。因此,全吸力范围内水分特征曲线测定方法的选择与组合应考虑土壤孔径分布特征和研究目的。 相似文献
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120.