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At the end of May 2012, the Po plain region in northern Italy was shaken by a long sequence of seismic events. The 2012 Northern Italy earthquake sequence counted two mainshocks, about 1,600 aftershocks and lasted for several weeks. Although the mainshocks, which occurred on May 20 and May 29, 2012, registered a moment magnitude of 5.9 and 5.8, respectively, these two events caused widespread soil liquefaction and substantial damages to the built environment. This paper reports lessons learnt from a field investigation conducted in the areas affected by the earthquake sequence. Based on the field observations, it was concluded that despite the relatively low magnitudes of the shocks, most of the damages occurred as a consequence of liquefaction phenomena and/or absence of retrofitting of historical structures. The latter comprise churches, tower bells, towers, castles and fortresses. It was found that the occurrence of liquefaction was mainly associated with the presence of saturated alluvial soil deposits which were characterised by high liquefaction susceptibility. It was noted that these highly liquefiable soils were mainly located in proximity of ancient river courses that were artificially diverted in the eighteenth century to mitigate flooding and other hydrological risks. 相似文献
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Bridges are a part of vital infrastructure,which should operate even after a disaster to keep emergency services running.There have been numerous bridge failures during major past earthquakes due to liquefaction.Among other categories of failures,mid span collapse(without the failure of abutments)of pile supported bridges founded in liquefiable deposits are still observed even in most recent earthquakes.This mechanism of collapse is attributed to the effects related to the differential elongation of natural period of the individual piers during liquefaction.A shake table investigation has been carried out in this study to verify mechanisms behind midspan collapse of pile supported bridges in liquefiable deposits.In this investigation,a typical pile supported bridge is scaled down,and its foundations pass through the liquefiable loose sandy soil and rest in a dense gravel layer.White noise motions of increasing acceleration magnitude have been applied to initiate progressive liquefaction and to characterize the dynamic features of the bridge.It has been found that as the liquefaction of the soil sets in,the natural frequency of individual bridge support is reduced,with the highest reduction occurring near the central spans.As a result,there is differential lateral displacement and bending moment demand on the piles.It has also been observed that for the central pile,the maximum bending moment in the pile will occur at a higher elevation,as compared to that of the interface of soils of varied stiffness,unlike the abutment piles.The practical implications of this research are also highlighted. 相似文献
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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
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The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction) for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil. The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile. The p-y curves were obtained for two ground conditions:(a) lateral spreading of liquefied soil, and(b) liquefied soil in level ground. These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries, which are modelled as quay walls. The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier). The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed. Based on the results of these model tests, guidance for the construction of p-y curves for use in engineering practice is also provided. 相似文献
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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
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Natural Hazards - An earthquake of magnitude 6.9 hit the city of Izmir (Turkey) on 30 October 2020, resulting in 117 deaths (in Turkey) and considerable economic losses. The earthquake also... 相似文献
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Ashis Biswas Santanu MajumderHarald Neidhardt Dipti Halder Subhamoy BhowmickAishwarya Mukherjee-Goswami Amit KunduDebasree Saha Zsolt BernerDebashis Chatterjee 《Applied Geochemistry》2011,26(4):516-525
Patchy occurrences of elevated As are often encountered in groundwater from the shallow aquifers (<50 m) of the Bengal Delta Plain (BDP). A clear understanding of various biogeochemical processes, responsible for As mobilization, is very important to explain this patchy occurrence and thus to mitigate the problem. The present study deals with the periodical monitoring of groundwater quality of five nested piezometeric wells between December 2008 and July 2009 to investigate the temporal changes in groundwater chemistry vis-a-vis the prevalent redox processes in the aquifer. Geochemical modeling has been carried out to identify key phases present in groundwater. A correlation study among different aqueous redox parameters has also been performed to evaluate prevailing redox processes in the aquifer. The long term monitoring of hydrochemical parameters in the multilevel wells together with hydrogeochemical equilibrium modeling has shown more subtle differences in the geochemical environment of the aquifer, which control the occurrence of high dissolved As in BDP groundwater. The groundwater is generally of Ca-HCO3 type. The dissolved As concentration in groundwater exceeded both WHO and National drinking water standard (Bureau of Indian Standards; BIS, 10 μg L−1) throughout the sampling period. The speciation of As and Fe indicate persistent reducing conditions within the aquifer [As(III): 87-97% of AsT and Fe(II): 76-96% of FeT]. The concentration of major aqueous solutes is relatively high in the shallow aquifer (wells A and B) and gradually decreases with increasing depth in most cases. The calculation of SI indicates that groundwater in the shallow aquifer is also relatively more saturated with carbonate minerals. This suggests that carbonate mineral dissolution is possibly influencing the groundwater chemistry and thereby controlling the mobilization of As in the monitored shallow aquifer. Hydrogeochemical investigation further suggests that Fe and/or Mn oxyhydroxide reduction is the principal process of As release in groundwater from deeper screened piezometric wells. The positive correlations of U and V with As, Fe and Mn indicate redox processes responsible for mobilization of As in the deeper screened piezometric wells are possibly microbially mediated. Thus, the study advocates that mobilization of As is depth dependent and concentrations of As in groundwater depends on single/combined release mechanisms. 相似文献
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A case study is presented of the interaction between the bending due to laterally spreading forces and axial-load induced settlement on the piled foundations of the Kandla Port and Customs Tower located in Kandla Port, India, during the 2001 Bhuj earthquake. The 22 m tall tower had an eccentric mass at the roof and was supported on a piled-raft foundation that considerably tilted away as was observed in the aftermath of the earthquake. The soil at the site consists of 10 m of clay overlaid by a 12 m deep sandy soil layer. Post-earthquake investigation revealed the following: (a) liquefaction of the deep sandy soil strata below the clay layer; (b) settlement of the ground in the vicinity of the building; (c) lateral spreading of the nearby ground towards the sea front. The foundation of the tower consists of 0.5 m thick concrete mat and 32 piles. The piles are 18 m long and therefore passes through 10 m of clayey soil and rested on liquefiable soils. Conventional analysis of a single pile or a pile group, without considering the raft foundation would predict a severe tilting and/or settlement of the tower eventually leading to a complete collapse. It has been concluded that the foundation mat over the non-liquefied crust shared a considerable amount of load of the superstructure and resisted the complete collapse of the building. 相似文献
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海上风机是一种高柔性海洋结构物,其支撑结构动力响应受风、浪、流等环境因素,风机荷载及基础刚度的影响异常敏感。本文在结构动力特性试验平台上,建立了以基础-塔架-顶部集中质量为一体的风机简化分析模型,并利用新型循环加载装置,在砂土中开展了4组针对风机模型长期动力特性变化规律的试验。主要研究在一定的加载频率下,支撑结构一阶自振频率在不同幅值的循环荷载作用下的变化规律,并从土体力学行为特性及循环荷载下土颗粒运移规律角度对试验现象进行分析。通过该模型试验所获得的结论,并基于一系列的相似性准则,在一定程度上可以揭示长期循环荷载下,海上风机支撑结构动力特性的变化规律,并对今后实际工程中有关基础选型及支撑结构设计上给出了相关建议。 相似文献
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Puri Nitish Jain Ashwani Nikitas George Dammala Pradeep Kumar Bhattacharya Subhamoy 《Natural Hazards》2020,103(1):447-478
The paper highlights the importance of using site-specific shear modulus reduction (G/Gmax versus shear strain, γ) curves and damping ratio (D versus shear strain, γ) curves for ground response analysis. In order to develop comprehensive G/Gmax–γ and D–γ curves (i.e. over a wide range of strain level), two types of apparatus, viz. resonant column and cyclic simple shear, have been used. The case study considered the geological deposits from the river beds of Yamuna River originating from the Himalayan seismic zone of North India. The tests results have been analysed to develop G/Gmax–γ and D–γ curves and compared with standard curves. It has been observed that upper and lower boundaries for the standard curves are remarkably different for the geological deposit under consideration. In order to assess the impact of using standard curves rather than site-specific curves, ground response analysis has been carried out at five sites along the Yamuna River using two types of curves (standard and site-specific developed in this study). The study showed that the amplification of shear waves at these sites based on the experimentally derived curves is much higher as compared to the standard curves. The proposed curves better represent dynamic behaviour of the soil deposits of the region and will provide a realistic response as far as practically possible, for the structures constructed in the states of Haryana and Delhi and nearby areas. It is anticipated that the data presented in this paper will have wide application and usage.
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