上海地区软黏土的OCR及地质成因
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摘要
通过覆盖上海地区两种沉积相(滨海平原和湖沼平原)19个工程的原位十字板强度Su FV,结合国内外研究成果,对上海3个软黏土层的超固结比OCR及其地质成因进行了分析。根据强度比S_(uFV)/σ'_(v0)(σ'_(v0)为有效上覆压力)计算OCR,给出了OCR随深度的变化规律。上海软土整体上处于超固结状态,浅部具有较大的OCR且较为离散(在1.3~5.0),随深度的增加OCR迅速减小,超过约13 m后维持在一稳定的数值(平均为1.6)。过去采用室内压缩试验给出的结果显著低估了上海软黏土的OCR。结合Hanzawa和Tanaka给出的模型对上海软黏土的强度及超固结地质成因进行了分析,认为基本符合浅部以胶结作用为主、深部以次压缩为主的特征。浅部的胶结作用变化范围较大而深部的次压缩作用则相对稳定,并初步给出了正常压缩、胶结作用和次压缩作用对总强度的贡献。
Through the field vane strengths Su FV of 19 projects involving two sedimentary facies of coastal plain and lacustrine plain in Shanghai and combined with the worldwide research findings, the overconsolidation ratio(OCR) and its geological causes of three Shanghai soft clay layers are analyzed. The OCR is calculated according to strength ratio S_(uFV)/σ'_(v0)(σ'_(v0) is the effective overburden pressure), and then its variation with depth is given. The results show that the Shanghai soft clay is overconsolidated in general. The OCR of shallow layers is larger and more discrete(from 1.3 to 5.0). The OCR decreases rapidly with the increase of depth and almost maintains a stable value(1.6 in averages) after 13 m deep. The OCR of Shanghai soft clay is significantly underestimated according to the laboratory compression tests in the past. Based on the model given by Hanzawa and Tanaka, the strength and geological causes of overconsolidation of Shanghai soft clay are analyzed. It is conformed that for the shallow layers of the clay the main cause is the cement effect varying in a wide range, and for deep layers the main cause is the secondary compression effect being in a relatively stable range. The contribution of normal compression, cement effect and secondary compression effect to the total strength of the soft clay is also given.
Through the field vane strengths Su FV of 19 projects involving two sedimentary facies of coastal plain and lacustrine plain in Shanghai and combined with the worldwide research findings, the overconsolidation ratio(OCR) and its geological causes of three Shanghai soft clay layers are analyzed. The OCR is calculated according to strength ratio S_(uFV)/σ'_(v0)(σ'_(v0) is the effective overburden pressure), and then its variation with depth is given. The results show that the Shanghai soft clay is overconsolidated in general. The OCR of shallow layers is larger and more discrete(from 1.3 to 5.0). The OCR decreases rapidly with the increase of depth and almost maintains a stable value(1.6 in averages) after 13 m deep. The OCR of Shanghai soft clay is significantly underestimated according to the laboratory compression tests in the past. Based on the model given by Hanzawa and Tanaka, the strength and geological causes of overconsolidation of Shanghai soft clay are analyzed. It is conformed that for the shallow layers of the clay the main cause is the cement effect varying in a wide range, and for deep layers the main cause is the secondary compression effect being in a relatively stable range. The contribution of normal compression, cement effect and secondary compression effect to the total strength of the soft clay is also given.
引文
[1]CHANG M F.Interpretation of overconsolidation ratio from in situ tests in Recent clay deposits in Singapore and Malaysia[J].Can Geotech J,1991,28:210-225.
[2]魏道垛,胡中雄.上海浅层地基土的前期固结压力及有关压缩性参数的试验研究[J].岩土工程学报,1980,2(4):13-22.(WEI Dao-duo,HU Zhong-xiong.Experimental study of preconsolidation pressure and compressibility of Shanghai subsoil[J].Chinese Journal of Geotechnical Engineering,1980,2(4):13-22.(in Chinese))
[3]张诚厚,王伯衍,汪兆京.上海黄浦江岸边淤泥质黏土的固结状态及强度特性[J].水利水运科学研究,1981,3(1):12-33.(ZHANG C H,WANG B H,WAN Z J.The consolidated condition and shear strength behavior of soft clay at the bank of Huangpu River,Shanghai[J].Hydro-science and Engineering,1981,3(1):12-33.(in Chinese))
[4]张诚厚.上海黏土的准超压密特性[J].岩土工程学报,1982,4(3):62-69.(ZHANG Cheng-hou.The apparent over consolidated behavior of Shanghai clay[J].Chinese Journal of Geotechnical Engineering,1982,4(3):62-69.(in Chinese))
[5]冯铭璋.软土压缩曲线特征[J].岩土工程学报,1992,14(5):95-100.(FENG Ming-zhang.Compression curve of soft cohesive soil[J].Chinese Journal of Geotechnical Engineering,1992,14(5):95-100.(in Chinese))
[6]JAMIOLKOWSKI M,LADD C C,GERMAINE J T,et al.New developments in field and laboratory testing of soils[C]//Proceedings of the 11th International Conference on Soil Mechanics and Foundation Engineering.San Francisco,1985:57-153.
[7]CHANDLER R J.The in-situ measurement of the undrained shear strength of clays using the field vane[C]//Field and Laboratory Studies,ASTM STP 1014,American Society for Testing and Materials.Philadelphia,1988:13-44.
[8]SKEMPTON A W.Vane tests in the alluvial plain of the River Forth near Grangemouth[J].Géotechnique,1948,1:111-124.
[9]MAYNE P W,MITCHELL J K.Profiling of overconsolidation ratio in clays by field vane[J].Canadian Geotechnical Journal,1988,25(4):150-157.
[10]SCHMERTMANN J H.The mechanical aging of soils[J].JGeotech Engineering Div,ASCE,1991,117(9):1288-1329.
[11]BJERRUM L.Problems of soils mechanics and construction on soft clays and structurally unstable soils collapsible,expensive and others[J].Proceedings of the 8th International Conference on Soil Mechanics and Foundation Engineering,1973,17(2):83-119.
[12]胡中雄.土力学与环境土工学[M].上海:同济大学出版社,1997.(HU Zhong-xiong.Soil mechanics and environmental geotechnique[M].Shanghai:Tongji University Press,1997.(in Chinese))
[13]HANZAWA H,TANAKA H.Normalized undrained strength of clay in the normally consolidated state and in the field[J].Soils and Foundations,1992,32(1):132-148.
[2]魏道垛,胡中雄.上海浅层地基土的前期固结压力及有关压缩性参数的试验研究[J].岩土工程学报,1980,2(4):13-22.(WEI Dao-duo,HU Zhong-xiong.Experimental study of preconsolidation pressure and compressibility of Shanghai subsoil[J].Chinese Journal of Geotechnical Engineering,1980,2(4):13-22.(in Chinese))
[3]张诚厚,王伯衍,汪兆京.上海黄浦江岸边淤泥质黏土的固结状态及强度特性[J].水利水运科学研究,1981,3(1):12-33.(ZHANG C H,WANG B H,WAN Z J.The consolidated condition and shear strength behavior of soft clay at the bank of Huangpu River,Shanghai[J].Hydro-science and Engineering,1981,3(1):12-33.(in Chinese))
[4]张诚厚.上海黏土的准超压密特性[J].岩土工程学报,1982,4(3):62-69.(ZHANG Cheng-hou.The apparent over consolidated behavior of Shanghai clay[J].Chinese Journal of Geotechnical Engineering,1982,4(3):62-69.(in Chinese))
[5]冯铭璋.软土压缩曲线特征[J].岩土工程学报,1992,14(5):95-100.(FENG Ming-zhang.Compression curve of soft cohesive soil[J].Chinese Journal of Geotechnical Engineering,1992,14(5):95-100.(in Chinese))
[6]JAMIOLKOWSKI M,LADD C C,GERMAINE J T,et al.New developments in field and laboratory testing of soils[C]//Proceedings of the 11th International Conference on Soil Mechanics and Foundation Engineering.San Francisco,1985:57-153.
[7]CHANDLER R J.The in-situ measurement of the undrained shear strength of clays using the field vane[C]//Field and Laboratory Studies,ASTM STP 1014,American Society for Testing and Materials.Philadelphia,1988:13-44.
[8]SKEMPTON A W.Vane tests in the alluvial plain of the River Forth near Grangemouth[J].Géotechnique,1948,1:111-124.
[9]MAYNE P W,MITCHELL J K.Profiling of overconsolidation ratio in clays by field vane[J].Canadian Geotechnical Journal,1988,25(4):150-157.
[10]SCHMERTMANN J H.The mechanical aging of soils[J].JGeotech Engineering Div,ASCE,1991,117(9):1288-1329.
[11]BJERRUM L.Problems of soils mechanics and construction on soft clays and structurally unstable soils collapsible,expensive and others[J].Proceedings of the 8th International Conference on Soil Mechanics and Foundation Engineering,1973,17(2):83-119.
[12]胡中雄.土力学与环境土工学[M].上海:同济大学出版社,1997.(HU Zhong-xiong.Soil mechanics and environmental geotechnique[M].Shanghai:Tongji University Press,1997.(in Chinese))
[13]HANZAWA H,TANAKA H.Normalized undrained strength of clay in the normally consolidated state and in the field[J].Soils and Foundations,1992,32(1):132-148.