温度对CPTU在海底泥中测试结果的影响及修正方法
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摘要
温度改变会影响孔压静力触探(CPTU)的测量结果.利用CPTU调查了海底泥的特性,由于海底泥的锥尖阻力(qc)和侧壁摩阻力(fs)较小而且调查时海底泥和海水中的温差较大,fs大多数是负值且随深度逐渐减小.据此提出了在没有安装温度传感器的情况下考虑温度对CPTU在海底泥中测试结果影响的修正方法:首先通过室内温度校正试验获得qc和fs的温度校正系数;然后假设浅层海底泥的fs随深度线性增加,根据相关测量结果或经验估计"实际"的fs剖面;再根据测量和"实际"的fs剖面的区别估计地基中的温度剖面;最后根据温度剖面和温度校正系数对CPTU的测量结果进行温度修正.对本文CPTU测试数据的温度修正结果表明,如果不考虑温度的影响,CPTU在海底泥中的fs会被低估,其值会随深度减小甚至变为负值;在约3.5 m深度处,海底泥的qt(考虑孔压修正的锥尖阻力)可能会被高估50%以上;海底泥的不排水抗剪强度(su)将会被高估,温度修正后CPTU所得su更接近于室内试验所得的su.在本文所建议的修正方法中,唯一不确定的参数是正常固结海底沉积物的fs随深度的增加率(α).本文通过反分析得出的α=0.2 kPa/m,黏土矿物类型和沉积环境等因素可能会影响α的大小.实际中应该根据相关的测量数据确定α的大小,如果没有相关的测量数据,可以采用本文建议的α值.
The measurement results of the piezocone penetration test(CPTU)are influenced by temperature.In this study,we used the CPTU to investigate the properties of seabed sediments.We found that the values of sleeve friction(fs)were generally negative and decreased with increasing depth owing to the lower values of the cone resistance(qc)and fs in seabed sediments and the greater temperature difference between the seabed sediments and seawater.We propose a correction method for considering the temperature effect on CPTU measurements in seabed sediments for cases in which there is no temperature sensor in the CPTU probe.First,we obtain the temperature correction factors of fs and qc through laboratory temperature calibration testing. Then,we estimate the "actual" fs profile according to the local experience or measured data based on the assumption that the fs value of shallow seabed sediments linearly increases with depth.Then,we estimate the ground temperature profile based on the difference between the measured and "actual" fs profiles. Finally,we correct the CPTU measurements based on the ground temperature profile and temperature correction factors.The temperature correction results for the CPTU measurements in this study show that if temperature correction had not been performed,the fsvalues of seabed sediments might have been underestimated.Further,we found that the values of fsgenerally decreased with increasing depth and became negative.In addition,the qt values might have been overestimated by more than 50% at a depth of approximately 3.5 m,the undrained shear strength(su)values might have been overestimated,and the corrected CPTUmeasured su values were comparable with those measured in the laboratory.In the proposed method,the only uncertain key parameter is the rate of increase of fs with depth(α)of normally consolidated young seabed deposits.For this case study,we back-calculated α=0.2 k Pa/m.The value of α may change with the deposit environment and type of clay mineral.The value of α should be determined based on the available measured data,but if there are no directly measured data for determining the value of α,the proposed value of α in this study can be adopted.
The measurement results of the piezocone penetration test(CPTU)are influenced by temperature.In this study,we used the CPTU to investigate the properties of seabed sediments.We found that the values of sleeve friction(fs)were generally negative and decreased with increasing depth owing to the lower values of the cone resistance(qc)and fs in seabed sediments and the greater temperature difference between the seabed sediments and seawater.We propose a correction method for considering the temperature effect on CPTU measurements in seabed sediments for cases in which there is no temperature sensor in the CPTU probe.First,we obtain the temperature correction factors of fs and qc through laboratory temperature calibration testing. Then,we estimate the "actual" fs profile according to the local experience or measured data based on the assumption that the fs value of shallow seabed sediments linearly increases with depth.Then,we estimate the ground temperature profile based on the difference between the measured and "actual" fs profiles. Finally,we correct the CPTU measurements based on the ground temperature profile and temperature correction factors.The temperature correction results for the CPTU measurements in this study show that if temperature correction had not been performed,the fsvalues of seabed sediments might have been underestimated.Further,we found that the values of fsgenerally decreased with increasing depth and became negative.In addition,the qt values might have been overestimated by more than 50% at a depth of approximately 3.5 m,the undrained shear strength(su)values might have been overestimated,and the corrected CPTUmeasured su values were comparable with those measured in the laboratory.In the proposed method,the only uncertain key parameter is the rate of increase of fs with depth(α)of normally consolidated young seabed deposits.For this case study,we back-calculated α=0.2 k Pa/m.The value of α may change with the deposit environment and type of clay mineral.The value of α should be determined based on the available measured data,but if there are no directly measured data for determining the value of α,the proposed value of α in this study can be adopted.
引文
[1]Lunne T,Robertson P K,Powell J J M.Cone Penetration Testing in Geotechnical Practice[M].New York:Blackie Academic,EF Spon/Routledge,1997.
[2]刘松玉,蔡国军,童立元.现代多功能CPTU技术理论与工程应用[M].北京:科学出版社,2013.Liu Songyu,Cai Guojun,Tong Liyuan.Research and Engineering Application of the Digital Multifunctional Piezocone Penetration Test System[M].Beijing:Science Press,2013(in Chinese).
[3]International Society for Soil Mechanics and Geotechnical Engineering.International Reference Test Procedure for Cone Penetration Test(CPT)[S].Swedish:Swedish Geotechnical Institute,Linkoping,Information,1989.
[4]Robertson P K.Soil classification using the cone penetration test[J].Can Geotech J,1990,27(1):151-158.
[5]Cai G J,Liu S Y,Tong L Y,et al.Field evaluation of undrained shear strength from piezocone penetration tests in soft marine clay[J].Marine Georesources and Geotechnology,2010,28:143-153.
[6]Chanmee N,Chai J C,Hino T,et al.Methods for evaluating overconsolidation ratio from piezocone sounding results[J].Underground Space,2017,2(2).doi:10.1016/j.undsp.2017.05.004.
[7]Chai J C,Agung P M A,Hino T,et al.Estimating hydraulic conductivity from piezocone soundings[J].Géotechnique,2011,61(8):699-708.
[8]American Society for Testing and Materials.ASTMD5778 Standard Test Method for Electronic Friction Cone and Piezocone Penetration Testing of Soils[S].Pennsylvania:West Conshohocken,2012.
[9]Peuchen J,Terwindt J.Introduction to CPT accuracy[C]//Proceedings of 3rd International Symposium on Cone Penetration Testing.Las Vegas,USA,2014:1-45.
[10]Lunne T,Eidsmoen T,Gillespie D,et al.Laboratory and field evaluation of cone penetrometers[C]//Proceedings of ASCE Specialty Conference In Situ’86:Use of In Situ Tests in Geotechnical Engineering.Blacksburg,USA,1986:714-729.
[11]Nader A,Fall M,Hache R.Characterization of sensitive marine clays by using cone and ball penetrometers:Example of clays in Eastern Canada[J].Geotech Geol Eng,2015,33(4):841-864.
[12]Konrad J M.Piezo-friction-cone penetrometer testing in soft clays[J].Can Geotech J,1987,24(4):645-652.
[13]Lee C,Kim R,Lee J S,et al.Quantitative assessment of temperature effect on cone resistance[J].B Eng Geol Environ,2013,72(1):3-13.
[14]International Organization for Standardization.BSENISO 22476-1 Geotechnical Investigation and TestingField Testing(Part 1):Electrical Cone and Piezocone Penetration Test[S].BSI Standards Publication,2012.
[15]Sandven R.Influence of test equipment and procedures on obtained accuracy in CPTU[C]//Proceedings of 2 nd International Symposium on Cone Penetration Testing,CPT’10.Huntington Beach,CA,USA,2010:1-26.
[16]Jia R,Hino T,Hamada T,et al.Density and undrained shear strength of bed sediment from ND-CPT[J].Ocean Dynam,2013,63(5):507-517.
[17]Japanese Geotechnical Society.Japanese Standards for Geotechnical and Geoenvironmental Investigation Methods-Standards and Explanations[S].Tokyo,Japan,2004(in Japanese).
[18]丁红岩,贾楠,张浦阳,等.海上风电复合筒型基础粉质黏土下沉试验分析[J].天津大学学报:自然科学与工程技术版,2017,50(9):893-899.Ding Hongyan,Jia Nan,Zhang Puyang,et al.Analysis of penetration test of composite bucket foundations for offshore wind turbines in silty clay[J].Journal of Tianjin University:Science and Technology,2017,50(9):893-899(in Chinese).
[19]Mimura M,Yoshimura M.Development of new radio isotope density cone penetrometer and progress in accuracy of measurement[J].Journal of JSCE,2007,63(2):649-661(in Japanese).
[20]Moqsud M A,Hayashi S,Suetsugu D,et al.Thermal environment of tidal mud of Ariake Sea[J].Lowland Technology International,2010,12(2):34-41.
[21]郑刚,王凡俊,孙宏宾,等.软土地区CFG桩群孔效应引发的地表沉降[J].天津大学学报:自然科学与工程技术版,2017,50(8):796-805.Zheng Gang,Wang Fanjun,Sun Hongbin,et al.Surface settlement caused by borehole group effect of CFGpiles in soft soil[J].Journal of Tianjin University:Science and Technology,2017,50(8):796-805(in Chinese).
[2]刘松玉,蔡国军,童立元.现代多功能CPTU技术理论与工程应用[M].北京:科学出版社,2013.Liu Songyu,Cai Guojun,Tong Liyuan.Research and Engineering Application of the Digital Multifunctional Piezocone Penetration Test System[M].Beijing:Science Press,2013(in Chinese).
[3]International Society for Soil Mechanics and Geotechnical Engineering.International Reference Test Procedure for Cone Penetration Test(CPT)[S].Swedish:Swedish Geotechnical Institute,Linkoping,Information,1989.
[4]Robertson P K.Soil classification using the cone penetration test[J].Can Geotech J,1990,27(1):151-158.
[5]Cai G J,Liu S Y,Tong L Y,et al.Field evaluation of undrained shear strength from piezocone penetration tests in soft marine clay[J].Marine Georesources and Geotechnology,2010,28:143-153.
[6]Chanmee N,Chai J C,Hino T,et al.Methods for evaluating overconsolidation ratio from piezocone sounding results[J].Underground Space,2017,2(2).doi:10.1016/j.undsp.2017.05.004.
[7]Chai J C,Agung P M A,Hino T,et al.Estimating hydraulic conductivity from piezocone soundings[J].Géotechnique,2011,61(8):699-708.
[8]American Society for Testing and Materials.ASTMD5778 Standard Test Method for Electronic Friction Cone and Piezocone Penetration Testing of Soils[S].Pennsylvania:West Conshohocken,2012.
[9]Peuchen J,Terwindt J.Introduction to CPT accuracy[C]//Proceedings of 3rd International Symposium on Cone Penetration Testing.Las Vegas,USA,2014:1-45.
[10]Lunne T,Eidsmoen T,Gillespie D,et al.Laboratory and field evaluation of cone penetrometers[C]//Proceedings of ASCE Specialty Conference In Situ’86:Use of In Situ Tests in Geotechnical Engineering.Blacksburg,USA,1986:714-729.
[11]Nader A,Fall M,Hache R.Characterization of sensitive marine clays by using cone and ball penetrometers:Example of clays in Eastern Canada[J].Geotech Geol Eng,2015,33(4):841-864.
[12]Konrad J M.Piezo-friction-cone penetrometer testing in soft clays[J].Can Geotech J,1987,24(4):645-652.
[13]Lee C,Kim R,Lee J S,et al.Quantitative assessment of temperature effect on cone resistance[J].B Eng Geol Environ,2013,72(1):3-13.
[14]International Organization for Standardization.BSENISO 22476-1 Geotechnical Investigation and TestingField Testing(Part 1):Electrical Cone and Piezocone Penetration Test[S].BSI Standards Publication,2012.
[15]Sandven R.Influence of test equipment and procedures on obtained accuracy in CPTU[C]//Proceedings of 2 nd International Symposium on Cone Penetration Testing,CPT’10.Huntington Beach,CA,USA,2010:1-26.
[16]Jia R,Hino T,Hamada T,et al.Density and undrained shear strength of bed sediment from ND-CPT[J].Ocean Dynam,2013,63(5):507-517.
[17]Japanese Geotechnical Society.Japanese Standards for Geotechnical and Geoenvironmental Investigation Methods-Standards and Explanations[S].Tokyo,Japan,2004(in Japanese).
[18]丁红岩,贾楠,张浦阳,等.海上风电复合筒型基础粉质黏土下沉试验分析[J].天津大学学报:自然科学与工程技术版,2017,50(9):893-899.Ding Hongyan,Jia Nan,Zhang Puyang,et al.Analysis of penetration test of composite bucket foundations for offshore wind turbines in silty clay[J].Journal of Tianjin University:Science and Technology,2017,50(9):893-899(in Chinese).
[19]Mimura M,Yoshimura M.Development of new radio isotope density cone penetrometer and progress in accuracy of measurement[J].Journal of JSCE,2007,63(2):649-661(in Japanese).
[20]Moqsud M A,Hayashi S,Suetsugu D,et al.Thermal environment of tidal mud of Ariake Sea[J].Lowland Technology International,2010,12(2):34-41.
[21]郑刚,王凡俊,孙宏宾,等.软土地区CFG桩群孔效应引发的地表沉降[J].天津大学学报:自然科学与工程技术版,2017,50(8):796-805.Zheng Gang,Wang Fanjun,Sun Hongbin,et al.Surface settlement caused by borehole group effect of CFGpiles in soft soil[J].Journal of Tianjin University:Science and Technology,2017,50(8):796-805(in Chinese).