Dynamic Response of Pile Reinforced Soils and Piled Foundations

The rigid-pile soil-improvement technique aims to increase the bearing capacity of the soil and decrease the settlement of the surface structure. The most remarkable difference of this technique from the deep-foundation system is the soil layer between the pile heads and the structure. This soil layer, called the mattress, is made of compacted granular materials and participates in the load transfer through arching and shear mechanisms. In order to understand the dynamic behavior of rigid-pile reinforced soils, tri-dimensional finite-element analyses of a soil-pile-slab system, a soil-pile-mattress-slab system, and a soil-pile-mattress-embankment system are presented in this paper. Different geometric configurations are studied in terms of dynamic impedances. The soil, piles, mattress, and embankment are represented as continuum solids, and the slab is represented by structural plate-type elements. The horizontal and vertical impedances of pile foundations are presented and the results are compared with studies in the literature. This study shows the influence of the mattress stiffness, the geometrical configuration, and head/tip fixity conditions on the dynamic response of the foundation system. A comparison between rigid piles and pile foundations is then presented.     

Pseudostatic Seismic Response Analysis of a Pile Group in a Soil Slope

This paper presents a simple approximate pseudostatic method for estimating the maximum internal forces and horizontal displacements of a pile group located in a soil slope. The method is extension of an existing similar method developed by the authors for the case of a horizontal ground surface. The method employed for horizontal ground case involves two main steps: first, the free-field soil movements caused by the earthquake are computed; Then, the response of the pile group is analyzed based on the maximum free-field soil movements as static movements, as well as a static loading at the pile head, which depends on the computed spectral acceleration of the structure being supported. This newly developed methodology takes into account the effects of group interaction and soil yielding. Simple modifications are applied to take into account the effect of slope on seismic deformations of the pile group, making use of the Newmark sliding block method. The applicability of the approach and the developed program is verified by comparisons made with both experimental shaking table tests and the results of a more refined analysis of a pile-supported wharf. It is demonstrated that the proposed method yields reasonable estimates of the pile maximum moment and horizontal displacement for many practical cases, despite its relative simplicity. The simplifying assumptions and the limitations as well as reliability of the methodology are discussed, and some practical conclusions on the performance of the proposed approach are suggested.     

富含油储层地震响应特征分析

针对油层与水层的地震响应特征较为接近,常规的流体检测手段预测油层效果不理想的问题,通过测井、地质、地球物理的综合研究以及理论模型和实际资料的统计分析,由振幅和甜点属性的相对变化量对富含油储层的地震响应特征进行分析,并定量地总结了规律。研究结果表明:当油层厚度较小时,振幅和甜点的相对变化量也较小,且与油层厚度没有明显关系;随着油层厚度的增大,振幅相对变化量线性增大,甜点相对变化量指数增大,增大的速度更快。甜点属性能够放大油层和水层之间的差异。     

3D Seismic Stability Analysis of Bench Slope with Pile Reinforcement

Geotechnical and Geological Engineering - Pile reinforcement has been widely applied to ensure the stability of slopes. However, few investigations have been conducted on multi-stage or bench...     

Analysis of Construction Impact of a Large Diameter Shield Tunneling Side-Crossing Viaduct Pile Foundations in Short Distance

Geotechnical and Geological Engineering - The construction of shield tunneling through pile foundation will cause additional deformation and internal force of pile foundation, which will affect the...     

Equivalent-Linear Seismic Ground Response Analysis of Some Typical Sites in Mumbai

Any earthquake event is associated with a rupture mechanism at the source, propagation of seismic waves through underlying rock and finally these waves travel through the soil layers to the particular site of interest. The bedrock motion is significantly modified at the ground surface due to the presence of local soil layers above the bedrock beneath the site of interest. The estimation of the amplifications in ground response due to the local soil sites is a complex problem to the designers and the problem is more important for mega cities like Mumbai in India, where huge population may get affected due to devastations of earthquake. In the present study, the effect of local soil sites in modifying ground response is studied by performing one dimensional equivalent-linear ground response analysis for some of the typical Mumbai soil sites. Field borelog data of some typical sites in Mumbai city viz. Mangalwadi site, Walkeswar site, BJ Marg near Pandhari Chawl site are considered in this study. The ground responses are observed for range of input motions and the results are presented in terms of surface acceleration time history, ratio of shear stress to vertical effective stress versus time, acceleration response spectrum, Fourier amplitude ratio versus frequency etc. The typical amplifications of ground accelerations considering four strong ground motions with wide variation of low to high MHA, frequency contents and durations are obtained. Results show that MHA, bracketed duration, frequency content have significant effects on the amplification of seismic accelerations for typical 2001 Bhuj motion. The peak ground acceleration amplification factors are found to be about 2.50 for Mangalwadi site, 2.60 for Walkeswar site and 3.45 for BJ Marg site using 2001 Bhuj input motion. The response spectrum along various soil layers are obtained which will be useful for designers for earthquake resistant design of geotechnical structures in Mumbai for similar sites in the absence of site specific data.     

三峡链子崖危岩体非线性动力响应分析

采用非线性有限元法研究岩质边坡的动力响应问题，模拟了软弱夹层的材料非线性及断层或裂缝的接触问题，假定岩块弹性体，推导了非线性动力响应迭代格式并编制了适于岩质边坡动力响应分析的三维非线性有限元程序，利用该程序对三峡链子崖危岩体进行了动力响应分析，得出了一些有价值的结论，计算结果与模型试验结果基本相符，证明本文数值计算的正确性。     

薄层地震响应分析及识别技术

对薄层地震响应的振幅,频谱等特征进行了详细的分析,并分析了影响该地震的应波形特征的因素。同时,利用积分能谱技术对其进行处理,可以识别出薄层的厚度变化及透镜体的存在。实际应用表明,该项技术较常规的时频分析方法有更高的分辨能力。     

Multi-dimensional Seismic Response Analysis of Base-Isolated Frame Structure with 3D Isolator

INTRODUCTIONAs a new and effective method for withstandingthe horizontal component of earthquake motion on abuilding structure, the base isolation technique hascome to the engineering application phase ( Hu,1988). However, for some important buildings andfoundation facilities in an earthquake region, it is im portant to consider the effects of 3D aseismatic analy sis, including the vertical component, due to themulti dimensional characteristics of earthquakes (Suand …     

自重湿陷性黄土地区桩基设计探讨

根据自重湿陷性黄土的特点、《湿陷性黄土地区建筑规范》（GB50025—2004）和《建筑桩基技术规范》（JGJ94—94）中关于桩基设计的对比分析，通过自重湿陷性黄土场地工程实例分析计算，依据负摩擦产生的机理——中性点理论，论述了自重湿陷性黄土场地中桩基设计应考虑中性点，而不应全部计入负摩阻的观点。     

Nonlinear Site Response and Liquefaction Analysis in the New Madrid Seismic Zone

Many existing highway bridges in the New Madrid Seismic Zone are located in the Mississippi Embayment, consisting of deep soil deposits and liquefaction susceptible near surface soils. It is important to understand the comprehensive impact of deep soil deposits and liquefaction on the response of the bridge foundations under seismic loading. A nonlinear soil model is then presented to study the impacts of the deep soil deposit and liquefaction on response analysis. The soil model has the advantage of using input parameters that can be obtained from conventional field and laboratory testing methods, which makes it attractive to engineering practice. The model calibrations used field recorded motions and laboratory test data, which indicate that the model provides an acceptable outcome based on simple input parameters. The model is implemented into the site response analysis for a typical Missouri highway bridge site in this seismic zone. The effect of the deep soil deposit and liquefaction on the site response analyses is discussed.     

软土地基上静压预制桩承载力的工后增大效应

分析了软土地基上预制桩承载力的时效性机理，介绍了几种研究承载力时效性的经验回归公式，结合工程说明应充分认识承载力时效性的科学性和利用这种规律潜在的巨大经济效益。     

Pseudo-static Seismic Bearing Capacity of Shallow Foundations in Unsaturated Soils Employing Limit Equilibrium Method

There exist many structures founded on unsaturated soil deposits. Shear strength augmentation due to the evolution of the matric suction within the unsaturated porous media enhances the bearing capacity of the overlying foundation. This paper presents the evaluation of the pseudo-static seismic bearing capacity of the shallow foundations resting on unsaturated soil deposits using limit equilibrium method. Adopting the Coulomb failure mechanism and Bishop effective stress concept, the bearing capacity equations are solved. The distribution of the matric suction beneath the footing is assumed to be linear. The results of the bearing capacity evaluation are validated against some experimental data found in literature for the static condition. For the seismic loading consideration, the pseudo-static method is utilized. The dual effect of the earthquake acceleration vertical component is thoroughly discussed and a suction transition point is introduced in which the minimum bearing capacity is observed to bear the same value for both upward and downward directions. The increase in the matric suction throughout the soil deposit leads to the increase in the soil shear strength, thus posing more resisting forces as well as higher ultimate bearing capacity. The offered solution is deemed a consistent and useful tool for the accurate prediction of the seismic bearing capacity of shallow footings resting on unsaturated soil deposits.

     

Nonlinear Analysis of Local Site Effects on Seismic Ground Response in the Bam Earthquake

The influence of local geologic and soil conditions on the intensity of ground shaking is addressed in this study. The amplification of the ground motion due to local site effects resulted in severe damage to dwellings in the Bam area during the 2003 Bam Earthquake. A unique set of strong motion acceleration recordings was obtained at the Bam accelerograph station. Although the highest peak ground acceleration recorded was the vertical component (nearly 1 g), the longitudinal component (fault-parallel motion) clearly had the largest maximum velocity as well as maximum ground displacement. Subsurface geotechnical and geophysical (down-hole) data in two different sites have been obtained and used to estimate the local site condition on earthquake ground motion in the area. The ground response analyses have been conducted considering the nonlinear behavior of the soil deposits using both equivalent linear and nonlinear approaches. The fully nonlinear method embodied in FLAC was used to evaluate the nonlinear soil properties on earthquake wave propagation through the soil layer, and compare with the response from the equivalent linear approach. It is shown that thick alluvium deposits amplified the ground motion and resulted in significant damage in residential buildings in the earthquake stricken region. The comparison of results indicated similar response spectra of the motions for both equivalent and nonlinear analyses, showing peaks in the period range of 0.3–1.5 s. However, the amplification levels of nonlinear analysis were less than the equivalent linear method especially in long periods. The observed response spectra are shown to be above the NEHRP building code design requirements, especially at high frequencies.     

单孔折射波法在基桩完整性检测中的应用

单孔折射法在美国、以色列等国家的基桩检测中得到了广泛地应用,相应的检测仪器以及配套软件等已步入商业化阶段。对于单孔折射法,国内亦有少量文献及工程实例的报道,但是内容略显粗浅,对于指导工程实践仍不够充分。介绍了该法的基本原理、仪器设备、现场检测等内容,以期能为相关工程技术人员提供参考,推动该项技术在国内的发展。     

Multilinear Regression Analysis for Seismic Response and Engineering Properties of Liquefiable Coromandel Coastal Soil Deposits

This paper investigates the seismic characteristics and geotechnical properties with respect to the liquefaction potential of the deposits in the Coromandel coastal line of Nagapattinam town, Tamilnadu, India. A series of field tests were conducted using standard penetration test, cone penetration test and plate load test. Laboratory tests were conducted on the collected samples. From the results, a microzonation map was developed for the liquefaction potential and settlements. Some multilinear regression models between permeability, fines content, relative density, coefficient of curvature, coefficient of uniformity, mean particle size, factor of safety, settlement, standard penetration test values and cone penetration test values were developed. The shear wave velocity and shear modulus were calculated from the field penetration tests and correlations between the normalized values of peak ground accelerations, velocities and displacements, which were obtained from the equivalent linear ground motion analysis using SHAKE software, with other parameters of soil. From the results, it was found that at some of the areas are vulnerable to high amplification of waves even for small earthquake.     

地下综合管廊边界条件对地震动力响应影响数值分析

为研究综合管廊动力边界条件对地震动力响应的影响,以厦门地区的代表性土层为例,建立动力有限元数值模型,土体本构采用小应变硬化模型,分别设定固定边界、黏性边界和自由场3种人工边界条件,进行Rayleigh波和地震底部剪切波作用下的场地响应研究;并根据变形特征及拟绝对加速度反应谱（PSA）评价3种边界的有效性,提出综合管廊地震动力分析的优化动力边界组合方法。研究表明：在地震波（底部水平加速度时程）及Rayleigh波的作用下,由于考虑了黏性边界对外行波的吸收,但未考虑地震动的输入问题及边界外半无限介质的弹性恢复性能,边界会对模型内部土体的水平位移产生限制作用,使得场地内水平位移响应偏小,而采用自由场边界则基本不存在这种限制作用,表现出强烈的振荡;采用激励侧固定边界、远离激励侧黏性边界、其余侧自由场边界的优化组合动力边界,在Rayleigh波和底部加速度时程共同作用下,二者引起的动力响应交叉干扰较少,可按线性叠加处理;同时,黏性边界对地震波引起的动力响应有一定范围的吸收,自由场边界对Rayleigh波引起的动力响应也有一定范围的变形限制影响。研究成果可供地下综合管廊结构地震响应精细化数值模拟及抗震设计参考。     

低应变反射波法检测基桩完整性

运用低应变反射波的时频综合分析法，对桩基的完整性和缺陷性质进行了系统分析，并结合波速的区间分析，论证了强度与波速的关系。结合工程实例检分析了基桩的完整性及缺陷类型，对桩基进行了质量评价。     

银川地区软土及灰砂桩处理软土地基的研究

本文概述银川地区区域地质及软土成因、分布范围和特征,简要介绍银川地区主要土层。灰砂桩处理软土地基原理及施工方法,成桩桩体分析、桩形和桩质量的影响因素。