Response of circular flexible foundations subjected to horizontal and rocking motions

A methodology using modal analysis is developed to evaluate dynamic vertical displacements of a circular flexible foundation resting on soil media subjected to horizontal and rocking motions. The influence of the soil reaction forces on the foundation is considered by introducing modal impedance functions, which can be determined by an efficient procedure with ring elements. The displacements of the foundation can then be easily solved by modal superposition. Parametric studies for modal responses of the flexible foundation indicate that the coupled response of the foundation is significantly influenced by relative stiffness among the foundation and the soil medium, vibration frequency range, foundation mass, and boundary contact conditions. The welded boundary condition should be considered to predict the coupling response while the relaxed boundary condition may be used to predict approximately the vertical displacements. As a foundation with a relative stiffness ratio more than three, it is found that the foundation can be considered as rigid to calculate coupling displacements. For a slightly flexible foundation, considerations of three modes are sufficient enough to obtain accurate foundation responses. Moreover, at low frequencies, the coupling effect due to higher mode can be neglected.     

基于格林函数的相邻条形基础摇摆动力相互作用

基于弹性半空间理论,研究两个相邻明置条形基础的摇摆动力相互作用,将各条形基础与地基的接触面分割成若干个子单元,各单元的位移由基础的刚体位移决定。推导了非对称简谐条形均布载荷作用下弹性地基位移的格林函数,通过分段积分及Cauchy主值积分处理多值广义函数的积分问题。运用所得格林函数求解各单元上的接触力,根据叠加原理得到土与相邻明置条形基础的摇摆动力耦合阻抗函数,详细分析了基础和地基参数对摇摆动力相互作用的影响。计算表明,当两明置条形基础距宽比S/L≤4.0时,应考虑其摇摆动力相互作用效应。所提方法具有计算简便和精度高的特点,对全频段阻抗函数的计算均适用,研究结果为结构抗震设计中考虑土体与多基础的动力相互作用提供了理论依据。     

深层软基加固处理方案试验研究

在软土地区既有铁路线旁修建复线时,为控制施工期沉降与工后沉降,保证既有线路与新建线路的稳定性,对新建复线的深层软基加固区,通过现场试验采用6种方法分7个观察项目进行了对比研究。试验结果表明：无论是沉降分析、稳定分析或是对既有线的影响分析,用粉喷桩加固地基比用砂井、插塑板及土工布加固地基均有着显而易见的优越性,相对来说短而密的粉喷桩较长而疏的粉喷桩加固效果更好。     

Seismic behaviour of shallow foundations: Shaking table experiments vs numerical modelling

The capability of a simplified approach to model the behaviour of shallow foundations during earthquakes is explored by numerical simulation of a series of shaking table tests performed at the Public Works Research Institute, Tsukuba, Japan. After a summary of the experimental work, the numerical model is introduced, where the whole soil–foundation system is represented by a multi‐degrees‐of‐freedom elasto‐plastic macro‐element, supporting a single degree‐of‐freedom superstructure. In spite of its simplicity and of the large intensity of the excitation involving a high degree of nonlinearity in the foundation response, the proposed approach is found to provide very satisfactory results in predicting the rocking behaviour of the system and the seismic actions transmitted to the superstructure. The agreement is further improved by introducing a simple degradation rule of the foundation stiffness parameters, suitable to capture even some minor details of the observed rocking response. On the other hand, the performance of the model is not fully satisfactory in predicting vertical settlements. Copyright © 2007 John Wiley & Sons, Ltd.     

海上平台桶形基础负压沉贯技术的模拟试验研究方案

对海上平台桶形基础负压沉贯技术的模拟试验研究提出了初步方案,可作为本单位此项技术训端性研究工作的参考。     

常时微动在地基勘察工程中的应用

本文讨论了利用常时微动的卓越周期和振幅对地基进行分类,并求取软弱层地基的横波平均速度及软弱层厚度,进而对工程地基进行评价.     

An experimental,analytical and numerical study on the thermal efficiency of energy piles in unsaturated soils

Energy piles are bi-functional foundation elements used as structural support as well as ground heat exchangers for shallow geothermal energy systems. Because they are relatively short, energy piles may be partially embedded in unsaturated soils. Saturation conditions influence the thermal properties of the ground and therefore the heat exchange rate, which in turn affects the efficiency of energy piles. This paper combines analytical, experimental and numerical investigations to evaluate the heat exchange rate of energy piles partially or fully embedded in unsaturated soils. The proposed analytical solution is based on the cylindrical heat source theory that treats the soil as a semi-infinite, homogeneous, and isotropic medium. The solution from this theory is multiplied by a function developed analytically in this paper and the outcome is the heat exchange rate for energy piles in unsaturated soils. The proposed function depends on soil saturation, soil and pile thermal properties, and pile geometry. The analytical solution was compared against a finite element solution; which was in turn validated against results from laboratory experiments. Very satisfactory agreements between the analytical, numerical and experimental outputs were observed. The proposed method can be used for a quick and simple evaluation of the efficiency of energy piles in unsaturated conditions. The proposed analytical solution can also be a useful tool for the verification of numerical codes developed for the design of energy piles in unsaturated soils.     

Neoliberal development through technical assistance: Constructing communities of entrepreneurial subjects in Oaxaca, Mexico

Technical assistance (TA) has a long and varied history as a development practice. It initially emerged as a set of ‘hard’ programs, tools, and technologies delivered to developing countries by imported First World experts, typically in the agricultural and resource sectors. Later, in response to critical and antidevelopment theories, TA morphed into its ‘soft’ version, attempting to empower marginalized people in the Global South by delivering the know-how - often collaboratively generated - sufficient to produce forms of development ‘from below’. In spite of this shift in the politics and practices of TA, it remains susceptible to neoliberal styles of development that have proceeded apace with withdrawal of state institutions in the funding and operation of social and economic development programs, and with the concomitant rise of nongovernmental organizations (NGOs).In this paper, we follow the operation of one TA program operated by an intermediary NGO in Oaxaca, Mexico. We find that the program intersects with neoliberalization in two prominent ways, relying on a form of governmentality that codifies and prescribes: (a) the social spaces of action and need, and (b) learning subjects deficient in entrepreneurial initiative and know-how. We conclude by commenting on the political economic conditions that continue to underwrite TA as a development practice in spite of a decade or more of criticism directed at it and we consider the possibilities for its subversion.     

液化地基中桩的破坏机理研究进展

地震诱发的地基液化对桩基础的破坏极大,液化地基中桩的破坏机理是岩土地震工程中的一个重要研究课题。目前地基液化时桩土结构系统的地震性态尚没有认识充分,已有的研究内容较多局限于桩身材料的强度破坏方面,难以考虑液化土体侧向流动、基桩屈曲失稳、以及土与结构动力相互作用等复杂因素的影响。本文重点加强以下3个方面的深入探讨和研究:(1)液化地基中桩的屈曲失稳;(2)液化地基中桩基破坏的数值模拟新方法;(3)液化地基中桩-土-结构的动力相互作用分析。     

A macroelement formulation for shallow foundations on cohesive and frictional soils

The scope of this paper is to present a macroelement model for shallow foundations encompassing the majority of combinations of soil and foundation–soil interface conditions that are interesting for practical applications. The basic idea of the formulation is to raise the common assumption that the surface of ultimate loads of the foundation is identified as a yield surface in the space of force parameters which the footing is subjected to. Instead, each non‐linear mechanism participating in the global response of the system is modelled independently and the surface of ultimate loads is retrieved as the combined result of all active mechanisms. This allows formulating each mechanism by respecting its particular characteristics and offers the possibility of activating, modifying or deactivating each mechanism according to the context of application. The model comprises three non‐linear mechanisms: (a) the mechanism of sliding at the soil–footing interface, (b) the mechanism of soil yielding in the vicinity of the footing and (c) the mechanism of uplift as the footing may get detached from the soil. The first two are irreversible and dissipative and are combined within a multi‐mechanism plasticity formulation. The third mechanism is reversible and non‐dissipative. It is reproduced with a phenomenological non‐linear hyperelastic model. The model is validated with respect to the existing results for shallow foundations under quasi‐static loading tests. It is shown that although the ultimate surface of the foundation is not explicitly used in the formulation of the model, the obtained force states by the model are always contained within it. Copyright © 2010 John Wiley & Sons, Ltd.