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1、第30卷第3期岩土工程学报Vol.30No.32008年3月ChineseJournalofGeotechnicalEngineeringMar.,2008黄土场地震陷时桩基负摩阻力的现场试验研究1121,31王兰民,孙军杰,黄雪峰,徐舜华,石玉成(1.中国地震局兰州地震研究所,甘肃兰州730000;2.兰州理工大学,甘肃兰州730050;3.兰州大学土木工程与力学学院,甘肃兰州730000)摘要:有关强震诱发黄土震陷时桩基负摩阻力的研究资料极少,其影响尚未能引入桩基设计之中。通过开展爆破模拟地震动诱发黄土震陷
2、条件下桩基负摩阻力的现场观测试验,分析研究了强震引发黄土震陷时桩基负摩阻力的基本特征。本次现场试验在选定的黄土场地内布置试桩两根,每根试桩内按2m间距对称植入钢筋应力计20个;地震动由15组炸药微差延时爆破模拟生成,试验场地布设地震计17个。现场试验期间,整个场地所有沉降观测点都产生了不同程度的震陷,最大震陷量达33mm;桩基负摩阻力量值显著,桩身负摩阻力平均值达54kPa,桩身总的负摩阻力约1654kN。试验的观测结果表明,地震诱发黄土震陷时的桩基负摩阻力不容忽视,应当在桩基设计时加以考虑。关键词:负摩阻力;
3、桩基础;黄土;震陷;爆破中图分类号:TU444文献标识码:A文章编号:1000–4548(2008)03–0341–08作者简介:王兰民(1960–),男,陕西蒲城人,博士,研究员,主要从事岩土地震工程及防震减灾等方面的研究工作。E-mail:wanglm@gssb.gov.cn。Fieldtestsonnegativeskinfrictionalongpilescausedbyseismicsettlementofloess1121,21WANGLan-min,SUNJun-jie,HUANGXue-feng
4、,XUShun-hua,SHIYu-cheng(1.LanzhouInstituteofSeismology,ChinaEarthquakeAdministration,Lanzhou730000,China;2.LanzhouUniversityofScience&Engineering,Lanzhou730050,China;3.DepartmentofCivilEngineering&Mechanics,LanzhouUniversity,Lanzhou730000,China)Abstract:Pile
5、foundationhasbeenwidelyusedintheearthquake-proneloessareaofChina.However,thenegativeskinfriction(NSF)alongpilescausedbyasuddensettlementofloessduringstrongearthquakeshavenotbeentakenaccountintothedesignofpilefoundationduetothelackofNSFdatafromfieldtests.Inor
6、dertoinvestigateNSFalongpilesinloessduringtheseismicsettlementandtodevelopamethodtoestimateit,fieldtestswereperformedbymeansofaseriesofexplosions(shortdelayblasting)ataloesssitewheretwopilesweregrouted.Thegroundmotioncreatedbytheexplosionswasstrongenoughtoin
7、duceanobvioussettlementinthesite.Therewere40stressgagesamountedonthetwopileswithanintervalof2mtocollectthedataofNSFalongdepthduringthetests.Atthesametime,thegroundmotionandsettlementofloesssitecreatedbytheexplosionswererespectivelyobservedbyaccelerographesan
8、dalevelgauge.Duringfieldtests,themaximumseismicsettlementofloessfieldreached33mmwhiletheaverageNSFalongpilesattained54kPaandthecorrespondingtotalNSFwasabout1654kN.Itwasshownbythesetestdatathatth