土层剪切波速不确定性对场地刚性判断的影响
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摘要
岩土工程中的不确定性是工程风险的重要来源。在我国7个主要地区的20个工程场地上开展了国内外首次大范围现场剪切波速不确定性专项试验,共由47家单位用11种工程常用仪器采用单孔法完成,获取了600组土层剪切波速V_s实测数据。依据实测结果拟合了场地时间平均剪切波速V_(s, z)的变异系数COV与计算深度Z的对应公式,揭示了土层剪切波速不确定性对场地刚性判断的影响,进而分析了我国场地分类的可能潜在误判区域。结论如下:在目前我国现场剪切波速测试水平下,V_(s, z)的变异系数与深度负相关——在近地表处达到极大值15%,并随着深度增加明显减小;地表至10 m深度区间内,V_(s, z)的变异系数迅速减小;10～20 m深度区间内,V_(s, z)的变异系数减小趋势变缓;超过20 m深度后,V_(s, z)的变异系数小于5%且基本不变;我国Ⅲ、Ⅳ类场地分类采用的等效剪切波速V_(se)和欧美场地分类指标V_(s, 30)的变异系数基本相等;依据我国建筑抗震设计规范GB50011-2010,对Ⅰ类场地以及覆盖层厚度小于5 m或等效剪切波速接近500 m/s的Ⅱ类场地分类时需考虑剪切波速不确定性的潜在影响,其他类型的Ⅱ类场地、Ⅲ类和Ⅳ类场地在分类时基本可忽略其影响。
Uncertainty in geotechnical engineering greatly results in engineering risk. In this study, the first large-scale uncertainty experiment on the in-situ shear-wave velocity(V_s) was carried out on 20 typical sites in 7 major regions of China. A total of 11 kinds of common engineering instruments were completed by using single hole method in 47 units, and 600 groups of V_s were obtained finally. According to this in-situ database, the corresponding formula between Coefficient of variation(COV) of time-average shear-wave velocity(V_(s, z)) and the calculated depth(Z) was fitted. We revealed the impact of in-situ V_s uncertainty on the judgement of site stiffness and pointed out the possible potential misjudging area of site classification in China. At the current level of in-situ V_s test in China, COV of V_(s, z) is negatively correlated with depth, which indicates that it reaches the max value of 15% near the site surface and then decreases significantly with the increasing of the depth. In the depth range from 0 m to 10 m, the COV of V_(s, z)decreases rapidly; in the depth range of 10-20 m, the COV of V_(s, z) decreases slowly; after the depth of 20 m, the COV of V_(s, z) is less than 5% and basically unchanged; the COV of equivalent shear wave velocity(V_(se)) used for site classification of Class Ⅲ and Ⅳ sites in China is basically the same as that of the field classification index V_(s, 30) used in Europe and America. Based on China building code GB50011-2010, Class Ⅰ and Class Ⅱ sites with the soil thickness less than 5 m or V_(se) close to 500 m/s should consider the potential impact of V_s uncertainty, while other types of Class Ⅱ and Class Ⅲ and Class Ⅳ sites could ignore the uncertainty.
Uncertainty in geotechnical engineering greatly results in engineering risk. In this study, the first large-scale uncertainty experiment on the in-situ shear-wave velocity(V_s) was carried out on 20 typical sites in 7 major regions of China. A total of 11 kinds of common engineering instruments were completed by using single hole method in 47 units, and 600 groups of V_s were obtained finally. According to this in-situ database, the corresponding formula between Coefficient of variation(COV) of time-average shear-wave velocity(V_(s, z)) and the calculated depth(Z) was fitted. We revealed the impact of in-situ V_s uncertainty on the judgement of site stiffness and pointed out the possible potential misjudging area of site classification in China. At the current level of in-situ V_s test in China, COV of V_(s, z) is negatively correlated with depth, which indicates that it reaches the max value of 15% near the site surface and then decreases significantly with the increasing of the depth. In the depth range from 0 m to 10 m, the COV of V_(s, z)decreases rapidly; in the depth range of 10-20 m, the COV of V_(s, z) decreases slowly; after the depth of 20 m, the COV of V_(s, z) is less than 5% and basically unchanged; the COV of equivalent shear wave velocity(V_(se)) used for site classification of Class Ⅲ and Ⅳ sites in China is basically the same as that of the field classification index V_(s, 30) used in Europe and America. Based on China building code GB50011-2010, Class Ⅰ and Class Ⅱ sites with the soil thickness less than 5 m or V_(se) close to 500 m/s should consider the potential impact of V_s uncertainty, while other types of Class Ⅱ and Class Ⅲ and Class Ⅳ sites could ignore the uncertainty.
引文
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[18]张小平,马顺,金源,等.大连地区工程场地各类岩土剪切波速的变化特征分析[J].防灾减灾学报,2012,28(4):7-11.ZHANG Xiao-ping,MA Shun,JIN Yuan,et al.Variation characteristic analysis of shear wave velocity by various types of soil on sites in Dalian region[J].Journal of Disaster Prevention and Reduction,2012,28(4):7-11.
[19]张驰,许汉刚,陈国兴,等.苏州深厚场地等效剪切波速与计算深度分析[J].防灾减灾工程学报,2017,37(5):718-724.ZHANG Chi,XU Han-gang,CHEN Guo-xing,et al.Analysis of equivalent shear wave velocity and its calculation depth of deep sediment layers in Suzhou region[J].Journal of Disaster Prevention and Mitigation Engineering,2017,37(5):718-724.
[20]WANG S Y,WANG H Y,LI Q.An alternative method for estimating Vs(30)from a shallow shear-wave velocity profile(depth<30 m)[J].Soil Dynamics and Earthquake Engineering,2017,99:68-73.
[21]WANG H Y,WANG S Y.A new method for estimating VS(30)from a shallow shear wave velocity profile(depth<30 m)[J].Bull Seismic.Society Am.,2015,105(3):1359-1370.
[22]REAL C R.Turkey Flat-USA site effects test area:report 2,site characterization[R].California:California Bureau of Geological Survey,1988.
[23]GAROFALO F,FOTI S,HOLLENDER F,et al.Comparison of invasive and non-invasive methods for seismic site characterization.Part II:Inter-comparison between surface-wave and borehole methods[J].Soil Dynamics and Earthquake Engineering,2016,82(3):241-254.
[24]BOORE D M.Determining subsurface shear-wave velocities:a review[R].Grenoble,France:[s.n.],2006.
[25]XIA J,MILLER R D,PARK C B,et al.Comparing shear-wave velocity profiles inverted from multichannel surface wave with borehole measurements[J].Soil Dyn.Earthq.Eng.,2002,22:181-190.
[26]ASTEN M W,BOORE D M.Comparison of shear-velocity profiles of unconsolidated sediments near the Coyote borehole(CCOC)measured with fourteen invasive and non-invasive methods[R].U.S.:[s.n.],2005.
[27]THOMPSON E M,BAISE L G,KAYEN R E.Spatial correlationof shear-wave velocity in the San Francisco Bay area sediments[J].Soil Dyn.Earthq.2007,27:144-152.
[28]THELEN W A,CLARK M,LOPEZ C T,et al.A transect of 200 shallow shear-velocity profiles across the Los Angeles Basin[J].Bull.Seismol.Soc.Am.,2006,96:1055-1067.
[29]陈卓识.现场剪切波速测试误差及其对地震动影响研究[D].哈尔滨:中国地震局工程力学研究所,2015.CHEN Zhuo-shi.The study of situ shear wave velocity test error and its effects on ground motion[D].Harbin:Institute of Engineering Mechanics,China Earthquake Administration,2015.
[30]中华人民共和国国家标准.GB/T50269-2015地基动力特性测试规范[S].北京:中国计划出版社,2015.State Standard of the People’s Republic of China.GB/T50269-2015 Code for measurement methods of dynamic properties of subsoil[S].Beijing:China Planning Press,2015.
[2]CASAGRANDE A.Role of the“calculated risk”in earthwork and foundation engineering[J].Journal of the Soil Mechanics and Foundations Division,1965,91(4):1-40.
[3]TERZAGHI K.Theoretical soil mechanics[M].New York:Wiley,1943.
[4]FELL R.Land slide risk management concepts and guidelines-Australian geomechanics society subcommittee on landslide risk management[Z].Christchurch,NZ,2000,51-93.
[5]WHITMAN R V.Evaluating calculated risk in geotechnical engineering[J].Journal of Geotechnical Engineering,1984,110(2):143-188.
[6]王永志,袁晓铭,王海.动力离心试验常规点位式量测技术改进方法[J].岩土力学,2015,36(增刊2):722-728.WANG Yong-zhi,YUAN Xiao-ming,WANG Hai.Improvement method of node-oriented measurement technique for dynamic centrifuge modeling[J].Rock and Soil Mechanics,2015,36(Suppl.2):722-728.
[7]董林,王兰民,夏坤,等.基于台湾集集地震数据的CPT与SPT液化判别方法比较[J].岩土力学,2017,38(12):3643-3648.DONG Lin,WANG Lan-min,XIA Kun,et al.Comparison of CPT-based and SPT-based liquefaction discrimination methods by Taiwan Chi-Chi earthquake data[J].Rock and Soil Mechanics,2017,38(12):3643-3648.
[8]付海清,袁晓铭,王淼.基于现场液化试验的饱和砂土孔压增量计算模型[J].岩土力学,2018,39(5):1611-1618.FU Hai-qing,YUAN Xiao-ming,WANG Miao.An incremental model of pore pressure for saturated sand based on in-situ liquefaction test[J].Rock and Soil Mechanics,2018,39(5):1611-1618.
[9]中华人民共和国国家标准.GB50011-2010建筑抗震设计规范[S].北京:中国建筑工业出版社,2010.State Standard of the People’s Republic of China.GB50011-2010 Code for seismic design of buildings[S].Beijing:China Architecture and Building Press,2010.
[10]ASCE7-10,Minimum Design loads for buildings and other structures[S].Reston:ASCE,2010.
[11]Eurocode 8:Design of structures for earthquake resistance-Part 1:General rules,seismic actions and rules for buildings[S].London:[s.n.],2004.
[12]The Ministry of Land,Infrastructure,Transport and Tourism(MLIT).Building standard law of japan[S].Tokyo:[s.n.],2007.
[13]高玉峰,刘汉龙.合肥膨胀土剪切波速的特征分析[J].岩土工程学报,2003,25(3):371-373.GAO Yu-feng,LIU Han-long.Study on shear wave velocities in expansive soils of Hefei[J].Chinese Journal of Geotechnical Engineering,2003,25(3):371-373.
[14]刘红帅,郑桐,齐文浩,等.常规土类剪切波速与埋深的关系分析[J].岩土工程学报,2010,32(7):1142-1149.LIU Hong-shuai,ZHENG Tong,QI Wen-hao,et al.Relationship between shear wave velocity and depth of conventional soils[J].Chinese Journal of Geotechnical Engineering,2010,32(7):1142-1149.
[15]邱志刚,薄景山,罗奇峰.土壤剪切波速与埋深关系的统计分析[J].世界地震工程,2011,27(3):81-88.QIU Zhi-gang,BO Jing-shan,LUO Qi-feng.Statistical analysis of relationship between shear wave velocity and depth of soil[J].World Earthquake Engineering,2011,27(3):81-88.
[16]张忠利.建设场地剪切波速的统计分析[D].哈尔滨:中国地震局工程力学研究所,2008.ZHANG Zhong-li.Statistical analysis of shear wave velocity in construction sites[D].Harbin:Institute of Engineering Mechanics,China Earthquake Administration,2008.
[17]董菲蕃,陈国兴,金丹丹.福建沿海3个盆地的土层剪切波速与深度的统计关系[J].岩土工程学报,2013,35(增刊2):145-151.DONG Fei-fan,CHEN Guo-xing,JIN Dan-dan,Statistical relation between shear wave velocity and depth of soils in three basins in coastal area of Fujian province[J].Chinese Journal of Geotechnical Engineering,2013,35(Suppl.2):145-151.
[18]张小平,马顺,金源,等.大连地区工程场地各类岩土剪切波速的变化特征分析[J].防灾减灾学报,2012,28(4):7-11.ZHANG Xiao-ping,MA Shun,JIN Yuan,et al.Variation characteristic analysis of shear wave velocity by various types of soil on sites in Dalian region[J].Journal of Disaster Prevention and Reduction,2012,28(4):7-11.
[19]张驰,许汉刚,陈国兴,等.苏州深厚场地等效剪切波速与计算深度分析[J].防灾减灾工程学报,2017,37(5):718-724.ZHANG Chi,XU Han-gang,CHEN Guo-xing,et al.Analysis of equivalent shear wave velocity and its calculation depth of deep sediment layers in Suzhou region[J].Journal of Disaster Prevention and Mitigation Engineering,2017,37(5):718-724.
[20]WANG S Y,WANG H Y,LI Q.An alternative method for estimating Vs(30)from a shallow shear-wave velocity profile(depth<30 m)[J].Soil Dynamics and Earthquake Engineering,2017,99:68-73.
[21]WANG H Y,WANG S Y.A new method for estimating VS(30)from a shallow shear wave velocity profile(depth<30 m)[J].Bull Seismic.Society Am.,2015,105(3):1359-1370.
[22]REAL C R.Turkey Flat-USA site effects test area:report 2,site characterization[R].California:California Bureau of Geological Survey,1988.
[23]GAROFALO F,FOTI S,HOLLENDER F,et al.Comparison of invasive and non-invasive methods for seismic site characterization.Part II:Inter-comparison between surface-wave and borehole methods[J].Soil Dynamics and Earthquake Engineering,2016,82(3):241-254.
[24]BOORE D M.Determining subsurface shear-wave velocities:a review[R].Grenoble,France:[s.n.],2006.
[25]XIA J,MILLER R D,PARK C B,et al.Comparing shear-wave velocity profiles inverted from multichannel surface wave with borehole measurements[J].Soil Dyn.Earthq.Eng.,2002,22:181-190.
[26]ASTEN M W,BOORE D M.Comparison of shear-velocity profiles of unconsolidated sediments near the Coyote borehole(CCOC)measured with fourteen invasive and non-invasive methods[R].U.S.:[s.n.],2005.
[27]THOMPSON E M,BAISE L G,KAYEN R E.Spatial correlationof shear-wave velocity in the San Francisco Bay area sediments[J].Soil Dyn.Earthq.2007,27:144-152.
[28]THELEN W A,CLARK M,LOPEZ C T,et al.A transect of 200 shallow shear-velocity profiles across the Los Angeles Basin[J].Bull.Seismol.Soc.Am.,2006,96:1055-1067.
[29]陈卓识.现场剪切波速测试误差及其对地震动影响研究[D].哈尔滨:中国地震局工程力学研究所,2015.CHEN Zhuo-shi.The study of situ shear wave velocity test error and its effects on ground motion[D].Harbin:Institute of Engineering Mechanics,China Earthquake Administration,2015.
[30]中华人民共和国国家标准.GB/T50269-2015地基动力特性测试规范[S].北京:中国计划出版社,2015.State Standard of the People’s Republic of China.GB/T50269-2015 Code for measurement methods of dynamic properties of subsoil[S].Beijing:China Planning Press,2015.