循环荷载作用下桩周土体强度弱化特性试验研究
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摘要
软黏土地基在循环周期荷载的连续作用下不会发生液化现象,但是随着循环荷载的周期、振幅、应力的不断增加,土体的有效强度会不断降低,从而引起土体破坏。特别是桩结构在工作期间除了要承受竖向的荷载外,还将受到波浪、冰荷载以及船的撞击荷载。这些荷载一般都具有往复作用的性质,这种往复荷载作用期间会使桩周土体产生疲劳效应,土体结构发生破坏,引起桩周土体的弱化。通过室内动三轴模拟天津码头区域桩周土承受的静(结构荷载)、动(波浪荷载)组合作用,对振动前后桩周土体的强度弱化情况进行研究,试验获得该区域桩周土体在周期荷载作用下,土体土体强度的变化关系。同时提出一个相对较简单且符合试验规律的天津地区桩周土的强度弱化公式,为该地区土体弱化的评估提供参考依据。
Liquefaction does not occur in a soft foundation under the action of wave cyclic loading;however,increases in period,amplitude and stress decrease the effective strength of soil.As a result,soil foundations lose bearing capacity.In addition to vertical load,a wharf structure also bears loads of waves,ice,and ship impact.Because these loads are generally cyclic,the soil around a pile will experience a fatigue effect.As a result of cyclic loading,the soil will incur structural damage and weakening.In this study,we use indoor dynamic triaxial testing to simulate the combined stress of cycle wave loading and vertical loading,and we apply these loads to the soil of Tianjin port to study the relationship among soil strength,combined stress,and soil depth.The laws of soil under combined stress loads at various depths are then obtained by the dynamic tri-axial test research.Moreover,a simple formula to determine soil strength weakening is presented to provide scientific data for further evaluation of the soil strength weakening in engineering applications.
Liquefaction does not occur in a soft foundation under the action of wave cyclic loading;however,increases in period,amplitude and stress decrease the effective strength of soil.As a result,soil foundations lose bearing capacity.In addition to vertical load,a wharf structure also bears loads of waves,ice,and ship impact.Because these loads are generally cyclic,the soil around a pile will experience a fatigue effect.As a result of cyclic loading,the soil will incur structural damage and weakening.In this study,we use indoor dynamic triaxial testing to simulate the combined stress of cycle wave loading and vertical loading,and we apply these loads to the soil of Tianjin port to study the relationship among soil strength,combined stress,and soil depth.The laws of soil under combined stress loads at various depths are then obtained by the dynamic tri-axial test research.Moreover,a simple formula to determine soil strength weakening is presented to provide scientific data for further evaluation of the soil strength weakening in engineering applications.
引文
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[10]张建民,宋飞.考虑填土侧向变形的地震土压力计算方法[J].地震工程学报,2013,35(1):9-20.ZHANG Jian-min,SONG Fei.Evaluation of Seismic Earth Pressure Considering Lateral Deformation[J].China Earthquake Engineering Journal,2013,35(1):9-20.(in Chinese)
[2]Andersen K H,Kleven A,Heien D.Cyclic Soil Data for Design of Gravity Structures[J].ASCE,1988,114(GT5):517-539.
[3]Azzouz A S,Malek A M,Baligh M M.Cyclic Behavior of Clays in Undrained Simple Shear[J].J Geotech Engrg,1989,115(5):637-657.
[4]冯军,闫澍旺.长江口软粘土在波浪循环荷载作用下的弱化分析[J].中国海洋平台,2005,20(1):18-21.FEING Jun,YAN Shu-wang.Degradation of Soft Clay in the Entrance to Sea of the Changjiang River Under Wave Cycle Loading[J].China Offshore Platform,2005,20(1):18-21.(in Chinese)
[5]张德文,张建民.桩基础抗震性能的简易评价方法[J].地震工程学报,2013,35(1):69-83.ZHANGDe-wen,ZHANG Jian-min.Simplified Method for Evaluating Seismic Performance of Pile Foundation[J].China Earthquake Engineering Journal,2013,35(1):69-83.(in Chinese)
[6]刘晶波,王文晖,赵冬冬,等.地下结构抗震分析的整体式反应位移法[J].岩石力学与工程学报,2013,32(8):1618-1624.LIU Jing-bo,WANG Wen-hui,ZHAO Dong-dong,et al.Integral Response Deformation Method for Seismic Analysis of Underground Structure[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(8):1618-1624.(in Chinese)
[7]黄茂松,李进军,李兴照.饱和软粘土的不排水循环累积变形特性[J].岩土工程学报,2006,28(7):891-895.HUANG Mao-song,LI Jin-jun,LI Xing-zhao.Cumulative Deformation Behaviour of Soft Clay in Cyclic Undrained Tests[J].Chinese Journal of Geotechnical Engineering,2006,28(7):891-895.(in Chinese)
[8]周建,龚晓南.循环荷载作用下饱和软粘土应变软化研究[J].土木工程学报,2000,33(5):75-78,82.ZHOU Jian,GONG Xiao-nan.Study on Strain Soften in Saturated Soft Clay under Cyclic Loading[J].China Civil Engineering Journal,2000,33(5):75-78,82.(in Chinese)
[9]邓津,王兰民,张振中,等.我国黄土的微结构类型与震陷区域划分[J].地震工程学报,2013,35(3):664-670.DENG Jin,WANG Lan-min,ZHANG Zhen-zhong,et al.The China Loess Microstructure Types and Its Seismic Subsidence Zones Divided[J].China Earthquake Engineering Journal,2013,35(3):664-670.(in Chinese)
[10]张建民,宋飞.考虑填土侧向变形的地震土压力计算方法[J].地震工程学报,2013,35(1):9-20.ZHANG Jian-min,SONG Fei.Evaluation of Seismic Earth Pressure Considering Lateral Deformation[J].China Earthquake Engineering Journal,2013,35(1):9-20.(in Chinese)
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