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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
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One method of mitigating the damaging effects of earthquake-induced liquefaction is to provide rapid dissipation of excess pore pressures by the use of vertical drains through the liquefiable material. Drain systems are currently designed using a chart-based approach. Field experience suggests that the performance of these installations cannot yet be accurately predicted.
In this paper, high quality centrifuge testing is used to help clarify drain behaviour. It will be established, supported by centrifuge test data, that the pore water from a radially expanding zone of soil contributing to drainage through the drains is developed. Naturally, the geometry of this expanding zone changes with time. It will be shown that fluid from deeper strata is drained first, reducing the effectiveness of the drain for near-surface soil layers. It is concluded that these zones are useful in analysing more complicated drain system geometries. 相似文献
4.
Shaking table tests were performed to investigate the damage mechanisms of a subway structure in soft soil while experiencing strong ground motions. The seismic responses of the structure and soil were found to be more sensitive to input motions with richer low-frequency components. The excess pore pressure ratio of soil increased slightly, and the distribution of the excess pore pressure surrounding the structure showed clear spatial effects. The frequency spectrum characteristics of input ground motions clearly influenced the lateral displacement of the structure. In addition, the structure was most severely damaged at the top or the bottom of the interior columns. Finite element analyses were conducted by using the modified Martin–Seed–Davidenkov viscoelastic and the rate-independent plastic-damage constitutive models for soil and concrete, respectively. Satisfactory agreement was observed between the simulation and test results, the difference between these results was discussed in detail. The results provide insight into how the characteristics of strong ground motion might influence and present a simplified analysis method to quantitatively evaluate the damage of subway structures in soft soil. 相似文献
5.
将废弃橡胶轮胎内填充散体材料形成加筋土结构,已被应用于地基、挡土墙和边坡加固等工程,表现出较好的减震隔振效果,而轮胎加筋土的抗液化性能尚缺乏研究。开展3组小型振动台试验,通过改变轮胎垫层的排水条件,验证轮胎加筋砂垫层的抗液化效果。结果表明:轮胎加筋砂垫层具有良好的抗液化效果,与刚性垫层相比,超静孔压比峰值差值范围在0.01~0.19,残余超静孔压比差值范围在0.08~0.16,轮胎加筋砂垫层提供的排水通道具有抑制超静孔隙水压力发展和加速超静孔隙水消散的作用,孔隙水会沿着轮胎与下部土体的界面以及胎间的排水通道排出;采用量测侧向动土压力的方法,定义土体液化程度量化指标,进一步验证轮胎加筋砂垫层抗液化效果;振动过程中轮胎加筋垫层表面沉降范围为11.3~15.7 mm,表现出较好的变形协调性能。 相似文献
6.
Wen-Jong Chang Ellen M. Rathje Kenneth H. Stokoe II Brady R. Cox 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):723
A dynamic full scale testing program was performed to quantitatively assess the effectiveness of prefabricated vertical drains as a liquefaction countermeasure. The testing program involved a new in situ liquefaction testing technique, which uses a large hydraulic vibrator to generate waves propagating through an embedded instrumentation area to measure the coupled soil-pore water response. The effectiveness of prefabricated vertical drains is assessed experimentally by comparing the pore pressure generation, pore pressure dissipation, and settlement from two reconstituted soil specimens; one without a drain in place and the other with a single drain installed. Because the prefabricated drain was installed during the specimen preparation process, no accompanying densification during installation occurred. Therefore, the effect of drainage alone was evaluated. The testing results show that the drainage provided by prefabricated drains can significantly reduce pore pressure generation, accelerate post-shaking pore pressure dissipation, and limit associated settlement. The outcome also shows that the new developed in situ liquefaction testing technique can be an alternative to quantitatively evaluate the effects of various liquefaction remediation techniques. 相似文献
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In this paper, different formulations of a macro‐element model for non‐linear dynamic soil‐structure interaction analyses of structures lying on shallow foundations are first reviewed, and secondly, a novel formulation is introduced, which combines some of the characteristics of previous approaches with several additional features. This macro‐element allows one to model soil‐footing geometric (uplift) and material (soil plasticity) non‐linearities that are coupled through a stiffness degradation model. Footing uplift is introduced by a simple non‐linear elastic model based on the concept of effective foundation width, whereas soil plasticity is treated by means of a bounding surface approach in which a vertical load mapping rule is implemented. This mapping is particularly suited for the seismic loading case for which the proposed model has been conceived. The new macro‐element is subsequently validated using cyclic and dynamic large‐scale laboratory tests of shallow foundations on dense sand, namely: the TRISEE cyclic tests, the Public Works Research Institute and CAMUS IV shaking table tests. Based on this comprehensive validation process against a set of independent experimental results, a unique set of macro‐element parameters for shallow foundations on dense sand is proposed, which can be used to perform predictive analyses by means of the present model. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Khoshnoudian Faramarz Shahreza MehdiPaytam Farzane 《Soil Dynamics and Earthquake Engineering》2012,34(1):25-36
The earthquake responses of structures are usually analyzed under the assumption that the foundation is firmly bonded to the soil (fixed at their base). Such analyses often predict a base overturning moment that exceeds the available overturning resistance due to gravity loads, which implies that a portion of the foundation mat or some of the individual column footings, as the case may be, would intermittently uplift during the earthquake. In addition, p-delta phenomena are another valuable parameter that influence the response of structure with foundation uplift. Therefore it is a vital subject to investigate the influence of uplift on earthquake response of structures with including the p-delta effects. In the current paper, the investigation has been performed using finite element method with considering nonlinear material behavior. The computer program used already incorporates foundation uplift in a more realistic approach than structural models available in literature. The response of structures was compared in four cases: 1—with foundation uplift, 2—without foundation uplift, 3—with including the p-delta effects and 4—without including the p-delta effects. Some additional parametric studies have been conducted such as slender of structure, elastic modulus of soil and bi-directional input ground motion. These studies show the importance of uplift foundation on the seismic behavior of structures and the beneficial effects of foundation uplift in computing the earthquake response of structures are demonstrated. In addition, p-delta effects are the main reason to resonate the differences between the four cases. 相似文献
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Due to the increased need of storage, larger and higher structures are being built all over the world, thus requiring a more careful evaluation of the mechanical performance of their foundation deposits both in terms of bearing capacity and compressibility behaviour. The design of such structures and their serviceability and stability is largely governed by the effects of the dynamic loading conditions principally because of their significantly elevated risk in seismic prone zones. In this paper, numerical analyses using an advanced constitutive model, able to account for the initial soil structure and its progressive degradation, have been performed to investigate the seismic response of a silo foundation built on structured clays. The proposed analyses involve the use of a fully-coupled finite element approach. For the dynamic simulations, three different input motions have been selected form earthquake databases according to the seismic hazard study of the specific site. The results of the silo dynamic response are illustrated in terms of signal amplification, permanent excess pore water pressures, accumulated displacements and structure induced degradation during and after the seismic loading. The dynamic behaviour of the footing indicates that extreme earthquake events can induce large destructuration in natural clays, leading to ground settlements up to twice the observed ones under static loads, which need to be properly accounted for in the design. This suggests that there are significant advantages in using advanced models which recognise the existence of initial soil structure and its subsequent damage due to the applied dynamic loads. 相似文献
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地震作用下土体发生液化之后,由于超静孔隙水压力的产生和土体抗剪强度的降低,管道易发生上浮破坏。为研究管道上浮动力反应的影响因素,基于OpenSees有限元软件,通过目标反应谱和谱匹配等方法选取地震波,考虑不同管土特性和地震动特性,对地震作用下管道上浮动力反应进行了二维数值模拟。结果表明:土体相对密度、管径和管道埋深对管道上浮反应的影响较大,分别给出了土体相对密度、管径、管道埋深对管道上浮位移的影响规律及对应拟合公式;长持时地震动作用下,超静孔隙水压力消散较慢,管道上浮位移可达短持时地震动作用下管道上浮位移的2倍左右;近断层脉冲地震动作用下,管道上浮破坏和横向破坏两种破坏模式同时存在,且由于速度脉冲效应,管道横向破坏风险大于上浮破坏风险。 相似文献
11.
George D. Bouckovalas Achilleas G. Papadimitriou Dimitrios G. Niarchos Yannis Ζ. Tsiapas 《Soil Dynamics and Earthquake Engineering》2011
This paper revisits the seminal work of Seed and Booker (1977) [21] on the design of infinitely permeable drains for liquefaction mitigation. It is shown that their basic mathematical assumption for the rate of earthquake-induced excess pore pressure generation overlooks sand fabric evolution effects during cyclic loading and eventually leads to underestimation of the drain effectiveness. This is because such effects cause peak excess pore pressures to be attained at the early stages of partially drained shaking, followed by a gradual attenuation even if shaking continues undiminished, a response feature not predicted by the original formulation. In addition, special emphasis is given to the analytical relation describing the excess pore pressure build-up until liquefaction in undrained tests. This relation was considered unique in the original work, for reasons of simplicity, thus neglecting sand fabric evolution effects that may differentiate it for various sands, densities and loading conditions. Hence, a revised analytical formulation is proposed, which takes into account both above effects of sand fabric evolution. The paper provides a quantitative assessment of their influence on drain effectiveness and establishes a new set of charts for drain design. Experimental measurements from shaking table tests, as well as robust numerical simulations are shown, which underline the necessity for the revised solution and design charts. 相似文献
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It is well known that the generation of excess pore water pressure and/or liquefaction in foundation soils during an earthquake often cause structural failures.This paper describes the behavior of a small-scale braced wall embedded in saturated liquefiable sand under dynamic condition.Shake table tests are performed in the laboratory on embedded retaining walls with single bracing.The tests are conducted for different excavation depths and base motions.The influences of the peak magnitude of the ground motions and the excavation depth on the axial forces in the bracing,the lateral displacement and the bending moments in the braced walls are studied.The shake table tests are simulated numerically using FLAC 2D and the results are compared with the corresponding experimental results.The pore water pressures developed in the soil are found to influence the behavior of the braced wall structures during a dynamic event.It is found that the excess pore water pressure development in the soil below the excavation is higher compared to the soil beside the walls.Thus,the soil below the excavation level is more susceptible to the liquefaction compared to the soil beside the walls. 相似文献
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Pipelines buried in saturated sand deposits, during earthquake loading could damage from resulting uplift due to excess pore water pressure generation. Several studies have been made to better understand the uplift mechanism and evaluate the effectiveness of mitigating techniques through experiment, but little numerical works have been done to assess the influence of soil properties and field conditions in pipeline floatation. Especially for previously buried pipelines, in order to set the priority for seismic retrofit, evaluating the risk of floatation in each region could be a concern. In this paper, effects of several parameters including dilatancy angle and density ratio of natural soil, diameter and burial depth of pipe, underground water table and thickness of the saturated soil layer on uplift of pipe have been investigated. Results show the prominent role of burial depth in pipe response and that there exits an optimum level for drop of water table to reduce floatation. 相似文献
14.
Jingzhe Zheng Kiichi Suzuki Naoto Ohbo J.H. Prevost 《Soil Dynamics and Earthquake Engineering》1996,15(6):369-379
The evaluation of a countermeasure against liquefaction which uses a sheet pilering for oil tank sites is presented. The simulation of earthquake responses observed at tank sites with and without sheet pile-ring is first performed to validate the three-dimensional finite element numerical model. Using the numerical model, liquefaction analysis is performed and the excess pore water pressure generated in the soil and the settlement of tank are investigated. The comparison of two- and three-dimensional models is also conducted to assess the applicability of two-dimensional analysis. The results show that the numerical model could simulate the observed earthquake responses of tank-ring-soil system, and that the excess pore water pressure and the settlement of the tank could be significantly reduced using a sheet pile-ring. The two-dimensional analysis proves to be capable of representing the main features of the dynamic response of the three-dimensional tank-ring-soil system. 相似文献
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编制完全耦合的三维排水有效应力动力反应分析程序，对可液化地基进行三维地震响应分析，探讨了不同土性参数、不同土层构成和不同附加压重等因素对可液化地基抗液化性能的影响。结果表明：在地震荷载作用下，天然饱和砂土地基中的超孔隙水压力随深度的增大而增大；在不同深度处，超孔压峰值到达的时刻比地震加速度峰值到达的时刻要晚；随输入地震加速度的减弱，深层处的超孔压开始消散或基本保持不变，浅层处的超孔压保持不变或略有上升，这一现象与土性参数、输入地震荷载的情况等因素有关；土性参数对土体本身的抗液化性能有重要影响，初始孔隙比越小，相对密度越大，土体的抗液化能力越强；附加压重有利于地基抗液化能力的提高；随着附加压重的增大，超孔压比减小；附加压重对地基中超孔隙水压力的增长有明显的抑制作用。 相似文献
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Understanding the response of partially saturated earth structures under various static and dynamic loads is important for the design and construction of economical and safe geotechnical engineering structures. In this study, the numerical approach is used to understand the dynamics of partially saturated soils. The mathematical equations governing the dynamics of partially saturated soils are derived based on the theory of mixtures and implemented within a finite element framework. The stress–strain behavior of the soil is represented by an elasto-plastic constitutive model for unsaturated soil based on bounding surface concept and the moisture-suction behavior is modeled using van Genuchten model. Fully coupled finite element simulations are performed to study the response of partially saturated soil embankment under earthquake loading and validated with centrifuge test results available in the literature. The predicted displacement responses are in good agreement with the measured responses. The pore water pressure, pore air pressure, matric suction, the degree of saturation in various elements and the response of the embankment under different initial moisture content are also discussed. 相似文献
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A transient analytical model is worked out for predicting seepage from a ponded field of infinite extent to a network of equally spaced ditch drains in a homogeneous and anisotropic soil underlain by an impervious barrier at a finite distance from the surface of the soil. The solution can account for finite width and finite level of water in the ditches, finite penetration of the drains in the soil, and also a variable ponding field at the surface of the soil. The study highlights the fact that the transient state duration of a partially penetrating ponded drainage scenario may be considerable should the drains be dug in a lowly conductive soil with a high storage coefficient, particularly if the underlying impervious layer lies at a large distance from the bottom of the ditches and the separation between the adjacent ditches is also large at the same time. 相似文献
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Vertical earthquake response of megawatt‐sized wind turbine with soil‐structure interaction effects 
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下载免费PDF全文 The dynamic response of a wind turbine on monopile is studied under horizontal and vertical earthquake excitations. The analyses are carried out using the finite element program SAP2000. The finite element model of the structure is verified against the results of shake table tests, and the earthquake response of the soil model is verified against analytical solutions of the steady‐state response of homogeneous strata. The focus of the analyses in this paper is the vertical earthquake response of wind turbines including the soil‐structure interaction effects. The analyses are carried out for both a non‐homogeneous stratum and a deep soil using the three‐step method. In addition, a procedure is implemented which allows one to perform coupled soil‐structure interaction analyses by properly tuning the damping in the tower structure. The analyses show amplification of the ground surface acceleration to the top of the tower by a factor of two. These accelerations are capable of causing damage in the turbine and the tower structure, or malfunctioning of the turbine after the earthquake; therefore, vertical earthquake excitation is considered a potential critical loading in design of wind turbines even in low‐to‐moderate seismic areas. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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地下结构物抗震稳定性的研究具有重要实际意义。基于动态土工离心试验,应用有效应力法分析了不同水平地震作用下土层和地下RC结构物的最大水平位移、不同埋深的土层加速度和超孔隙水压力变化规律,以及结构物的破坏发展特征,并进一步与试验结果进行了相互验证和对比,取得了较好效果,为重要地下结构物的抗震设计提供了依据和参考。 相似文献
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为了研究水平地震作用下桥梁结构及地铁设施的相互影响,以山西省太原市解放路改造工程为依托工程,分别建立了高架桥、地铁站、高架桥及地铁设施组合结构的三维动力有限元模型,并考虑设置碎石隔震层,进行不同工况下结构的抗震性能分析。结果表明:由于碎石层的缓冲隔震作用,组合结构中高架桥的桥墩内力更小,且地震作用越大时,内力减小程度越大;另一方面,高架桥的建造对地铁结构的抗震性能影响较小。此外,对于桥梁结构而言,碎石层的厚度变化对桥墩内力有一定影响,但影响程度较小;而对于地铁结构而言,碎石层厚度越小,地铁柱剪力弯矩值往往会越大,但增加幅度有限。 相似文献