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1.
Development of new drain method for protection of existing pile foundations from liquefaction effects 总被引：1，自引：0，他引：1
Naoyuki Harada Ikuo Towhata Tadashi Takatsu Shinsuke Tsunoda Vlatko Sesov 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):297-312
Pile foundation as well as other underground structures could be seriously affected by soil liquefaction during strong earthquakes. Damages on pile foundation due to liquefaction can be reduced by implementation of some soil improvement method. Main objective of present study is developing of drain method that can improve the soil in order to mitigate the destructiveness of liquefaction on superstructure supported by pile foundation. Series of shaking table tests were conducted on 2×2 pile foundation and soil model was improved by drains. Configurations of drains around piles, intensity of shaking were one of the parameters that were changing during the tests in order to investigate the response of pile foundation in improved soil condition.Shaking table tests and performed On-site experiment showed the following effects of the new drain method. (1) When the intensity of earthquake motion is 200 gal or less, generation of excess pore water pressure is reduced and the pile bending moment is decreased, (2) when the intensity of earthquake motion is stronger (300 gal or more), drainage effect prevents disappearance of subgrade reaction, and (3) proposed new type of drain can control excess pore water pressure without clogging. 相似文献
2.
The objectives of this paper are to show practically: (1) the validation of a proposed three-dimensional effective stress analysis for the pile foundations, and (2) the effectiveness of remedial deposits on pile stresses under liquefaction by making comparisons between the results of centrifuge tests and those of the proposed analysis. Two foundation models supported by end-bending piles were studied with improved and unimproved deposits. There exists a good consistency between the numerical and experimental results for excess pore water-pressure ratios ranging from 0 to about 0·9. From the numerical results, the bending moment at the pile top with the improved deposit is about 50 per cent lower than that with the unimproved deposit. However, it was found that the smaller the bending moment develops in the pile with the improved deposit, the larger the compressive and/or tensional axial stresses in the pile. This is due to the predominant excitation of rocking vibration of the foundation. From the analytical and experimental results, it has been found that the remedial method can be a variable means to protect piles from soil liquefaction hazards. However, both axial stress and bending moment produced in piles should be considered in assessing the liquefied seismic capacity of group pile-foundation–structural systems with improved soil deposits. © 1998 John Wiley & Sons, Ltd. 相似文献
3.
To investigate the seismic response of a pile group during liquefaction, shaking table tests on a 1/25 scale model of a 2 × 2 pile group were conducted, which were pilot tests of a test project of a scale-model offshore wind turbine with jacket foundation. A large laminar shear box was utilized as the soil container to prepare a liquefiable sandy ground specimen. The pile group model comprising four slender aluminum piles with their pile heads connected by a rigid frame was designed with similitude considerations focusing on soil–pile interaction. The input motions were 2-Hz sinusoids with various acceleration amplitudes. The excess pore water pressure generation indicated that the upper half of the ground specimen reached initial liquefaction under the 50-gal-amplitude excitation, whereas in the 75-gal-amplitude test, almost entire ground was liquefied. Accelerations in soil, on the movable frames composing the laminar boundary of the shear box, and along the pile showed limited difference at the same elevation before liquefaction. After liquefaction, the soil and the movable-frame accelerations that represented the ground response considerably reduced, whereas both the movable frames and the piles exhibited high-frequency jitters other than 2-Hz sinusoid, and meantime, remarkable phase difference between the responses of the pile group and the ground was observed, all probably due to the substantial degradation of liquefied soil. Axial strains along the pile implied its double-curvature bending behavior, and the accordingly calculated moment declined significantly after liquefaction. These observations demonstrated the interaction between soil and piles during liquefaction. 相似文献
4.
Numerical analysis of an infinite pile group in a liquefiable soil was considered in order to investigate the influence of pile spacing on excess pore pressure distribution and liquefaction potential. It was found that an optimal pile spacing exists resulting in minimal excess pore pressure. It was also found that certain pile group configurations might reduce liquefaction potential, compared to free field conditions. It was observed that for closely spaced piles and low frequency of loading, pile spacing has little influence on the response of the superstructure. 相似文献
5.
Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns (SDCM). This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity. 相似文献
6.
Flora A. Bilotta E. Chiaradonna A. Lirer S. Mele L. Pingue L. 《Bulletin of Earthquake Engineering》2021,19(10):3835-3864
Within the European project LIQUEFACT some activities have been devoted to the experimental verification of the effectiveness of two techniques in the mitigation of soil liquefaction susceptibility: induced partial saturation (IPS) and horizontal drains. After a preliminary check of their efficiency via centrifuge tests, the two techniques have been studied by means of some large scale shaking tests carried out in a field trial located in the Emilia-Romagna Region (Italy). A preliminary extensive in situ and laboratory investigation was necessary to identify the shallow liquefiable soil layer in which the mitigation techniques and the monitoring instrumentations (pore pressure transducers and geophones) had to be installed. Both techniques required the installation of horizontal well screens via a directional controlled drilling technique: the pipes were used as drainage systems (linear HDL and rhomboidal configurations HDR) or for the air injection in the area treated with IPS technique. The in situ experimental evidences showed that both techniques are able to avoid liquefaction triggering, that on the contrary was attained during the tests in the untreated testing area. The processing of in situ data highlighted that the efficiency of the two techniques is strictly related to chosen arrangement of the horizontal drains and the induced degree of saturation.
相似文献7.
A large number of houses suffered from liquefaction-induced damages in recent large earthquakes due to lack of economical countermeasures. In this study, the shallow ground improvement, up to several meters deep, was proposed as an economical liquefaction countermeasure for houses. Based on the case studies, the design criteria of allowable tilt angles and penetration settlements of houses were proposed for the required level of serviceability against moderate and large earthquakes. The results of questionnaire survey, airborne LiDAR survey and centrifuge model tests demonstrated that even a few meters of non-liquefiable layers in shallow ground could greatly reduce settlements and tilting of houses. A series of numerical analyses indicated that non-liquefiable layer of three meters thick below ground water table improved by solidification methods can prevent significant damages of houses. Furthermore, cost analyses were carried out for different ground improvement methods for both new and existing houses. 相似文献
8.
地基液化导致沉箱码头破坏及地基加固方法的非线性数值分析 总被引：2，自引：0，他引：2
地震作用引发的地基液化,往往导致沉箱基础的破坏。本文基于Biot两相饱和多孔介质动力耦合理论,采用FE-FD耦合数值分析方法,对液化海床沉箱基础的地震反应进行非线性有效应力分析。在数值分析过程中,建立了以土骨架位移和超静孔隙水压力表达的us-pw动力固结方程和循环弹塑性本构模型,该方法能够很好地模拟地震作用下沉箱码头的动力特性及液化破坏的影响。通过数值模拟计算,分析了采用碎石桩进行置换砂区域的防液化加固方法,并就碎石桩处理区域的选择提出了建议。 相似文献
9.
The purpose of this paper is to investigate the effects of liquefaction on modal parameters (frequency and damping) of pile‐supported structures. Four physical models, consisting of two single piles and two 2 × 2 pile groups, were tested in a shaking table where the soil surrounding the pile liquefied because of seismic shaking. The experimental results showed that the natural frequency of pile‐supported structures may decrease considerably owing to the loss of lateral support offered by the soil to the pile. On the other hand, the damping ratio of structure may increase to values in excess of 20%. These findings have important design consequences: (a) for low‐period structures, substantial reduction of spectral acceleration is expected; (b) during and after liquefaction, the response of the system may be dictated by the interactions of multiple loadings, that is, horizontal, axial and overturning moment, which were negligible prior to liquefaction; and (c) with the onset of liquefaction due to increased flexibility of pile‐supported structure, larger spectral displacement may be expected, which in turn may enhance P‐delta effects and consequently amplification of overturning moment. Practical implications for pile design are discussed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
10.
The present study aims at investigating the nonlinear behavior of single hollow pile in layered soil subjected to varying levels of horizontal dynamic load. A finite element model has been developed using commercially available FEM based software. Mohr–Coulomb plasticity model is used to simulate the soil plasticity whereas the pile-material is idealized as elastic. Numerical results are validated comparing with the experimental results. The experimental investigations were carried out in the field located at IIT Kharagpur. Two types of motion: horizontal and rocking are studied. The effects of various influencing parameters, namely, exciting moment, length and diameter of the pile etc. on the nonlinear dynamic response of piles are investigated. It is found that separation of pile from the surrounding soil considerably affects the resonance frequency and amplitude of the pile foundations. 相似文献
11.
为研究倾斜场地中桩基的动力响应,以2011年新西兰地震中受损的Dallington桥为原型,设计并完成可液化倾斜场地桥梁桩-土相互作用的振动台模型试验。试验再现了喷砂、冒水、地裂缝、场地流滑等宏观现象。试验结果表明,土层足够的液化势及惯性是造成倾斜场地侧向流滑的必要条件;浅层土相比深层土更易液化,液化层中的加速度由下至上呈现逐渐衰减的趋势,而未液化砂土层却表现为逐渐增大的特征;深部测点的桩侧土压力明显大于浅部测点,且土体的液化会弱化土对结构的压力;结构应变最大值位于上部桥台,而结构弯矩在桩身中部及土层分界面附近出现两个较大值,桩端嵌固及倾斜场地流滑是造成出现两个弯矩较大值的主要原因。 相似文献
12.
Ryota Kusakabe Kohei Fujita Tsuyoshi Ichimura Takuma Yamaguchi Muneo Hori Lalith Wijerathne 《地震工程与结构动力学》2021,50(1):197-213
Much research has been conducted for physics‐based ground‐motion simulation to reproduce seismic response of soil and structures precisely and to mitigate damages caused by earthquakes. We aimed at enabling physics‐based ground‐motion simulations of complex three‐dimensional (3D) models with multiple materials, such as a digital twin (high‐fidelity 3D model of the physical world that is constructed in cyberspace). To perform one case of such simulation requires high computational cost and it is necessary to perform a number of simulations for the estimation of parameters or consideration of the uncertainty of underground soil structure data. To overcome this problem, we proposed a fast simulation method using graphics processing unit computing that enables a simulation with small computational resources. We developed a finite‐element‐based method for large‐scale 3D seismic response analysis with small programming effort and high maintainability by using OpenACC, a directive‐based parallel programming model. A lower precision variable format was introduced to achieve further speeding up of the simulation. For an example usage of the developed method, we applied the developed method to soil liquefaction analysis and conducted two sets of simulations that compared the effect of countermeasures against soil liquefaction: grid‐form ground improvement to strengthen the earthquake resistance of existing houses and replacement of liquefiable backfill soil of river wharves for seismic reinforcement of the wharf structure. The developed method accelerates the simulation and enables us to quantitatively estimate the effect of countermeasures using the high‐fidelity 3D soil‐structure models on a small cluster of computers. 相似文献
13.
The present paper deals with the influence of soil non-linearity, introduced by soil liquefaction, on the soil-foundation–structure interaction phenomena. Numerical simulations are carried out so as to study an improvement method to reduce the liquefaction potential in a sandy soil profile subjected to a shaking. The efficiency of the preloading in both the mitigation of a liquefiable soil and the reduction of induced structure relative settlements is showed. However, the intervention at the foundation soil modifies the dynamic characteristics of soil–structure system and it seems to increase the induced seismic forces during earthquake. In addition, a numerical parametric analysis is performed so as to quantify the impact of the uncertainties associated with the input signal on both the ground motion and the apparition of liquefaction phenomena. 相似文献
14.
汶川大地震中德阳地区液化特点分析 总被引：1，自引：0，他引：1
汶川大地震中八个主要地区均有液化现象出现,其中德阳地区液化现象及其震害最为显著.通过现场调查和工程地质资料分析,德阳地区的液化特点为:液化带主要集中在绵竹市、什邡市和德阳市,绵竹市最为严重;液化在烈度Ⅶ、Ⅷ、Ⅸ度区均有出现,但Ⅷ度区最为集中;液化喷水高度多在几公分到2m之间,最高一处超过10 m;液化场地喷出物基本涵盖... 相似文献
15.
The influence of inclined piles on the dynamic response of deep foundations and superstructures is still not well understood and needs further research. For this reason, impedance functions of deep foundations with inclined piles, obtained numerically from a boundary element–finite element coupling model, are provided in this paper. More precisely, vertical, horizontal, rocking and horizontal–rocking crossed dynamic stiffness and damping functions of single inclined piles and 2 × 2 and 3 × 3 pile groups with battered elements are presented in a set of plots. The soil is assumed to be a homogeneous viscoelastic isotropic half‐space and the piles are modeled as elastic compressible Euler–Bernoulli beams. The results for different pile group configurations, pile–soil stiffness ratios and rake angles are presented. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
16.
为研究液化场地变截面桩的动力响应,依托翔安大桥实体工程,采用有限元软件,建立变截面桩－土和等截面桩－土相互作用模型,模拟液化场地变截面桩及等截面桩在地震作用下的振动反应,分析在地震作用下变截面位置不同的变截面桩及等截面桩的动力响应特征。结果表明:地震作用下,液化土层不同深度处的孔压比变化规律基本相同,均从0逐渐增大最后趋于稳定;变截面桩的桩身加速度和桩身位移均大于等截面桩,且桩顶加速度峰值出现的时刻均滞后于桩底;在饱和砂土层处,桩身位移变化趋势均较陡;变截面桩的桩身弯矩峰值和桩身剪力峰值均大于等截面桩,且其峰值出现的位置较等截面桩深;地震作用下,变截面桩及等截面桩的弯矩与剪力均在安全范围之内;液化场地变截面梁桥桩基础抗震设计时,应着重分析液化土层与非液化土层分界面以下的抗弯能力设计及液化土层中抗剪能力设计。 相似文献
17.
The seismic performance of four pile‐supported models is studied for two conditions: (i) transient to full liquefaction condition, i.e. the phase when excess pore pressure gradually increases during the shaking; (ii) full liquefaction condition, i.e. defined as the state where the seismically induced excess pore pressure equalises to the overburden stress. The paper describes two complementary analyses consisting of an experimental investigation, carried out at normal gravity on a shaking table, and a simplified numerical analysis, whereby the soil–structure interaction (SSI) is modelled through non‐linear Winkler springs (commonly known as p–y curves). The effects of liquefaction on the SSI are taken into account by reducing strength and stiffness of the non‐liquefied p–y curves by a factor widely known as p‐multiplier and by using a new set of p–y curves. The seismic performance of each of the four models is evaluated by considering two different criteria: (i) strength criterion expressed in terms of bending moment envelopes along the piles; (ii) damage criterion expressed in terms of maximum global displacement. Comparison between experimental results and numerical predictions shows that the proposed p–y curves have the advantage of better predicting the redistribution of bending moments at deeper elevations as the soil liquefies. Furthermore, the proposed method predicts with reasonable accuracy the displacement demand exhibited by the models at the full liquefaction condition. However, disparities between computed and experimental maximum bending moments (in both transient and full liquefaction conditions) and displacement demands (during transient to liquefaction condition) highlight the need for further studies. Copyright © 2016 The Authors Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd. 相似文献
18.
Sand boiling and liquefaction-induced damage to houses and infrastructures occurred in Minami-Kurihashi, Kuki City, during the 2011 off the Pacific Coast of Tohoku Earthquake, Japan. After the earthquake, extensive site investigations were conducted in the affected areas, including 14 borehole surveys and 43 sounding tests, where Piezo Drive Cone penetrometer, a newly developed test method, was used which could be effectively employed in detecting local change of soil profiles. A filled sandy soil layer existed near the ground surface in the affected areas, which originated from reclamation works using dredged materials to construct housing lots. In addition, a Holocene sandy soil layer existed partly at a depth of about 10–13 m. Though these two layers were evaluated to be potentially liquefiable, the liquefaction-induced damage was observed to concentrate in the areas where the reclamation works had been executed, suggesting that the liquefaction of the reclaimed layer caused such damage. It was deduced that possible liquefaction of the Holocene layer did not contribute to the damage and to the occurrence of sand boiling at the ground surface. As countermeasure against future liquefaction, ground water lowering method has been selected, and in-situ tests and numerical analyses were executed to predict the long-term ground settlement. A subsequent study on detailed design of the selected countermeasure is underway as of June 1, 2015. 相似文献
19.
桥台在桥梁系统中占据重要位置,桥台的稳定性直接影响到桥梁的抗震性能。在国内外大量震害中发现大量由桥台破坏引起的桥梁损坏,而且这些破坏常常伴随着由于液化引起的地面大变形。为研究液化场地中桥台滑坡机理,采用完全耦合的有效应力分析方法,利用修正的PasterZienkiewicz Mark-Ⅲ模型来模拟砂土在地震荷载作用下的液化特性。研究台顶梁重和液化层位置对桥台位移的影响,并分析夯实作用对砂土液化的影响。结果表明:模拟得出结果与振动台试验结果基本一致,而且简单的夯实不能降低砂土液化的风险。 相似文献
20.
Suresh R. Dash Subhamoy Bhattacharya Anthony Blakeborough 《Soil Dynamics and Earthquake Engineering》2010,30(1-2):32-39
This paper investigates the importance of bending–buckling interaction in seismic design of piles in liquefiable soils using numerical techniques. A pseudo-static analysis has been performed using a well documented case history, where the pile–soil interaction is modelled as a beam on nonlinear winkler foundation (BNWF). Six possible analytical methods, three force based and three displacement based, are performed in which the pile is subjected to both lateral and axial load. Three out of six analysis cases did not predict the failure of the piles when analysed only for bending (i.e., lateral loads only). The buckling analysis showed that the pile was also safe against pure buckling during full liquefaction. Further, two out of those three cases which did not predict failure in bending were reanalysed for bending–buckling interaction (i.e., lateral and axial loads acting simultaneously). These combined analyses showed a more realistic behaviour of pile response and did predict the pile failure. Hence, it can be concluded that if a pile is designed for bending and buckling criteria separately and safe for these individual design criteria, it may fail due to their combined effect. 相似文献