珊瑚岛礁场地非线性地震反应特征分析
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摘要
南海珊瑚岛礁的地震安全问题是一个亟需解决的基础性科学问题。以某南海珊瑚岛礁为研究对象,开展了16组饱和珊瑚砂试样的动三轴试验,发现采用修正Matasovic本构模型描述珊瑚砂的动剪切模量折减和阻尼比增长特性是适宜的,并给出了相应的模型参数。详细考虑岛礁场地的工程地质特性和珊瑚砂的动力非线性特性、自由场非均匀网格划分和人工边界条件,尤其强调了土体应力–应变滞回曲线的不规则加卸载准则,建立珊瑚砂岛礁场地的二维非线性地震反应分析模型,分析了珊瑚岛礁场地峰值加速度放大系数的空间变异特征、地表加速度反应谱的谱形与持时特征。结果表明:①峰值加速度随场地高程的增加总体上呈增大的趋势,10 m以浅放大效应显著,灰沙岛和港池区域尤为显著;②基岩输入地震动频谱特性对珊瑚岛礁地表谱加速度的谱形影响显著,地表谱加速度在周期小于0.7 s部分的反应非常显著。③地表地震动持时较之输入地震动持时均有所减小,地形地貌特征对地表地震动持时有一定程度的影响。该研究结果对南海类似珊瑚砂岛礁军事和民事功能设施的抗震分析具有借鉴意义。
The seismic safety evaluation of the coral islands in the South China Sea is an urgent and fundamental scientific issue.For a coral island in the South China Sea, the cyclic triaxial tests on 16 sets of saturated coral sand samples are performed. The test results show that the modified Matasovic constitutive model is suitable to characterize the shear modulus ratio reduction and damping ratio increase of coral sand, and the parameters of the Matasovic model are also proposed. Considering the engineering geology characteristics of the coral island, nonlinear dynamic behaviors of the coral sand, layout of nonuniform mesh of the free-field site and artificial boundary conditions as well as the special emphasis given to the irregular unloading-reloading rules for the stress-strain hysteresis loop, a two-dimensional nonlinear seismic response analysis model for the coral island is established. The spatial variation characteristics of the peak acceleration amplification factors, shapes of ground surface acceleration response spectra and durations of the coral island are analyzed. The results show that:(1) The peak accelerations of the coral sand site tend to increase as the elevation increases, the peak acceleration amplifications are obvious for the shallow depth less than 10 m, and the amplification effects are especially strong in lime-sand island and harbor basin regions.(2) The shapes of ground surface acceleration response spectra are closely related to the characteristics of the input bedrock motions. The ground surface spectral acceleration is very significant in the period less than 0.7 s.(3) The ground motion durations are shortened to different degrees, which are closely related to the characteristics of seismic bedrock motions,and to some extent related to the topographical and geomorphic characteristics of the coral island. The results will be of use in the construction of future coral islands in the South China Sea.
The seismic safety evaluation of the coral islands in the South China Sea is an urgent and fundamental scientific issue.For a coral island in the South China Sea, the cyclic triaxial tests on 16 sets of saturated coral sand samples are performed. The test results show that the modified Matasovic constitutive model is suitable to characterize the shear modulus ratio reduction and damping ratio increase of coral sand, and the parameters of the Matasovic model are also proposed. Considering the engineering geology characteristics of the coral island, nonlinear dynamic behaviors of the coral sand, layout of nonuniform mesh of the free-field site and artificial boundary conditions as well as the special emphasis given to the irregular unloading-reloading rules for the stress-strain hysteresis loop, a two-dimensional nonlinear seismic response analysis model for the coral island is established. The spatial variation characteristics of the peak acceleration amplification factors, shapes of ground surface acceleration response spectra and durations of the coral island are analyzed. The results show that:(1) The peak accelerations of the coral sand site tend to increase as the elevation increases, the peak acceleration amplifications are obvious for the shallow depth less than 10 m, and the amplification effects are especially strong in lime-sand island and harbor basin regions.(2) The shapes of ground surface acceleration response spectra are closely related to the characteristics of the input bedrock motions. The ground surface spectral acceleration is very significant in the period less than 0.7 s.(3) The ground motion durations are shortened to different degrees, which are closely related to the characteristics of seismic bedrock motions,and to some extent related to the topographical and geomorphic characteristics of the coral island. The results will be of use in the construction of future coral islands in the South China Sea.
引文
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[16]陈国兴.岩土地震工程学[M].北京:科学出版社,2007.(CHEN Guo-xing.Geotechnical earthquake engineering[M].Beijing:Science Press,2007.(in Chinese))
[17]刘晶波,谷音,杜义欣.一致黏弹性人工边界及黏弹性边界单元[J].岩土工程学报,2006,28(9):1070-1075.(LIU Jing-bo,GU Yin,DU Yi-xin.Consistent viscous-spring artificial boundaries and viscous-spring boundary elements[J].Chinese Journal of Geotechnical Engineering,2006,28(9):1070-1075.(in Chinese))
[18]中国地震台网中心.中国及邻区地震震中分布图[Z].北京:地震出版社,2015.(China Earthquake Networks Center.Map of earthquake epicentre in China and adjacent areas[Z].Beijing:Seismological Press,2015.(in Chinese))
[19]TRIFUNAC M D,BRADY A G.A study on the duration of strong earthquake ground motion[J].Bulletin of the Seismological Society of America,1975,65(3):581-626.
[20]CHEN G X,JIN D D,ZHU J,et al.Nonlinear analysis on seismic site response of Fuzhou Basin,China[J].Bulletin of the Seismological Society of America,2015,105(2A):928-949.
[2]BRANDES H G,NICHOLSON P G,ROBERTSON I N.Liquefaction of Kawaihae Harbor and other effects of 2006Hawaii earthquakes[C]//Proceedings of the 17th International Offshore and Polar Engineering Conference.International Society of Offshore and Polar Engineers,2007:1169-1176.
[3]GREEN R A,OLSON S M,COX B R,et al.Geotechnical aspects of failures at Port-au-Prince seaport during the 12January 2010 Haiti earthquake[J].Earthquake Spectra,2011,27(S1):S43-S65.
[4]CELESTINO T B,MITCHELL J K.Behavior of carbonate sands for foundations of offshore structures[C]//Proceedings,Brazil Offshore.Rio de Janeiro,1983:85-102.
[5]崔永圣.珊瑚岛礁岩土工程特性研究[J].工程勘察,2014,42(9):40-44.(CUI Yong-sheng.Study on geotechnical characteristics of coral island[J].Geotechnical Investigation and Surveying,2014,42(9):40-44.(in Chinese))
[6]SALEM M,ELMAMLOUK H,AGAIBY S.Static and cyclic behavior of North Coast calcareous sand in Egypt[J].Soil Dynamics and Earthquake Engineering,2013(55):83-91.
[7]PANDO M A,SANDOVAL E A,CATANO J.Liquefaction susceptibility and dynamic properties of calcareous sands from Cabo Rojo,Puerto Rico[C]//Proceedings of the 15th World Conference on Earthquake Engineering.Lisbon,2012.
[8]CARRARO J A H,BORTOLOTTO M S.Stiffness degradation and damping of carbonate and silica sands[J].Frontiers in Offshore Geotechnics III.Meyer,ed.London,2015:1179-1183.
[9]HASHASH Y M A,PARK D.Non-linear one-dimensional seismic ground motion propagation in the Mississippi embayment[J].Engineering Geology,2001,62(S1/2/3):185-206.
[10]YEE E,STEWART J P.Elastic and large-strain nonlinear seismic site response from analysis of vertical array recordings[J].Journal of Geotechnical and Geoenvironmental Engineering,2013,139(10):1789-1801.
[11]陈国兴,金丹丹,朱姣,等.河口盆地非线性地震效应及设计地震动参数[J].岩土力学,2015,36(6):1721-1736.(CHEN Guo-xing,JIN Dan-dan,ZHU Jiao,et al.Nonlinear seismic response of estuarine basin and design parameters of ground motion[J].Rock and Soil Mechanics,2015,36(6):1721-1736.(in Chinese))
[12]战吉艳,陈国兴,杨伟林,等.远场大地震作用下大尺度深软场地的非线性地震效应分[J].岩土力学,2013,11(11):3229-3238.(ZHAN Ji-yan,CHEN Guo-xing,YANGWei-lin,et al.Seismic response characteristics analysis of deep soft site under far-field ground motion of great earthquake[J].Rock and Soil Mechanics,2013,11(11):3229-3238.(in Chinese))
[13]王新志.南沙群岛珊瑚礁工程地质特性及大型工程建设可行性研究[D].武汉:中国科学院武汉岩土力学研究所,2008.(WANG Xin-zhi.Study on engineering geological properties of coral islands and feasibility of large project construction on Nansha Islands[D].Wuhan:Institute of Rock and Soil Mechanics,2008.(in Chinese))
[14]MATASOVIC N,VUCETIC M.Cyclic characterization of liquefiable sands[J].Journal of Geotechnical Engineering,1993,119(11):1805-1822.
[15]赵丁凤,阮滨,陈国兴,等.基于Davidenkov骨架曲线模型的修正不规则加卸载准则与等效剪应变算法及其验证[J].岩土工程学报,2017,39(5):888-895.(ZHAODing-feng,RUAN Bin,CHEN Guo-xing,et al.Validation of the modified irregular loading-reloading rules based on Davidenkov skeleton curve and its equivalent shear strain algorithm implemented in ABAQUS[J].Chinese Journal of Geotechnical Engineering,2017,39(5):888-895.(in Chinese))
[16]陈国兴.岩土地震工程学[M].北京:科学出版社,2007.(CHEN Guo-xing.Geotechnical earthquake engineering[M].Beijing:Science Press,2007.(in Chinese))
[17]刘晶波,谷音,杜义欣.一致黏弹性人工边界及黏弹性边界单元[J].岩土工程学报,2006,28(9):1070-1075.(LIU Jing-bo,GU Yin,DU Yi-xin.Consistent viscous-spring artificial boundaries and viscous-spring boundary elements[J].Chinese Journal of Geotechnical Engineering,2006,28(9):1070-1075.(in Chinese))
[18]中国地震台网中心.中国及邻区地震震中分布图[Z].北京:地震出版社,2015.(China Earthquake Networks Center.Map of earthquake epicentre in China and adjacent areas[Z].Beijing:Seismological Press,2015.(in Chinese))
[19]TRIFUNAC M D,BRADY A G.A study on the duration of strong earthquake ground motion[J].Bulletin of the Seismological Society of America,1975,65(3):581-626.
[20]CHEN G X,JIN D D,ZHU J,et al.Nonlinear analysis on seismic site response of Fuzhou Basin,China[J].Bulletin of the Seismological Society of America,2015,105(2A):928-949.