循环荷载作用下泥炭质土动力累积特性试验研究
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摘要
工程实践中,泥炭质土由于富含有机质,具有高含水量、低密度、超高压缩性以及低强度的异常力学特性,往往被视为问题土。针对昆明地区交通荷载作用下泥炭质土的动力响应特征,选取滇池草海附近典型泥炭质土,开展考虑围压水平、动应力幅值以及静偏应力影响的不排水循环三轴试验,研究该土的长期累积变形特性。研究表明:研究土样具有典型泥炭质土特征,表现为含水量181.5%~259.3%,密度1.10~1.22 g/cm~3、有机质含量29.9%~53.0%,有机物质分解度较高;动应力幅值和静偏应力对昆明泥炭质土的长期动力特性影响显著,大动应力幅值和静偏应力加剧累积变形和孔压的发展,同时,当动应力水平小而静偏应力大时,累积塑性变形的发展速度反而大;虽然初始围压对累积变形影响较小,但对残余孔压的影响显著。此外,基于双对数坐标下累积应变速率与循环周次关系以及前人研究方法,建立了泥炭质土累积塑性应变与动荷载循环周次间的经验关系。
Peaty soils are generally viewed as"problematic"soils for their high organic matter content,high water contents,low bulk density,high compressibility and low strength characteristics. The long-term accumulative behaviour of peaty soils subjected to traffic loads was studied through a series of cyclic triaxial compression tests on the samples retrieved from the site nearby Caohai on the northern side of Lake Dian. The variables including the confining stress level,the amplitude of dynamic stress and the static deviatoric stress were taken into account in this study. It was found that the tested samples were typical peaty soil,which had the initial water contents of 181.5%–259.3%,the initial densities of 1.10–1.22 g/cm~3,the organic contents of 34.7%–44.2%. The organic matters were highly decomposed. Both the amplitude of dynamic stress and static deviatoric stress had the distinct influences on the developments of permanent axial strain and pore water pressure. The larger amplitude of dynamic stress or the static deviatoric stress accelerated the developments of the permanent axial strain and pore water pressure. The development of permanent axial strain was faster when a lower dynamic stress and a larger static deviatoric stress were applied,in contrast to the case that a larger dynamic stress and a lower static stress were applied. The initial confining stress level appeared to have a little effect on the development of permanent axial strain,while it had a significant impact on the accumulation of pore water pressure. In addition, an empirical relation between the accumulative plastic strain and loading cycles was presented based on the relationships between the permanent axial strain rate and loading cycles under dual logarithmic coordinates as well as the previous studies.
Peaty soils are generally viewed as"problematic"soils for their high organic matter content,high water contents,low bulk density,high compressibility and low strength characteristics. The long-term accumulative behaviour of peaty soils subjected to traffic loads was studied through a series of cyclic triaxial compression tests on the samples retrieved from the site nearby Caohai on the northern side of Lake Dian. The variables including the confining stress level,the amplitude of dynamic stress and the static deviatoric stress were taken into account in this study. It was found that the tested samples were typical peaty soil,which had the initial water contents of 181.5%–259.3%,the initial densities of 1.10–1.22 g/cm~3,the organic contents of 34.7%–44.2%. The organic matters were highly decomposed. Both the amplitude of dynamic stress and static deviatoric stress had the distinct influences on the developments of permanent axial strain and pore water pressure. The larger amplitude of dynamic stress or the static deviatoric stress accelerated the developments of the permanent axial strain and pore water pressure. The development of permanent axial strain was faster when a lower dynamic stress and a larger static deviatoric stress were applied,in contrast to the case that a larger dynamic stress and a lower static stress were applied. The initial confining stress level appeared to have a little effect on the development of permanent axial strain,while it had a significant impact on the accumulation of pore water pressure. In addition, an empirical relation between the accumulative plastic strain and loading cycles was presented based on the relationships between the permanent axial strain rate and loading cycles under dual logarithmic coordinates as well as the previous studies.
引文
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[2]MADASCHI A,GAJO A.One-dimensional response of peaty soils subjected to a wide range of oedometric conditions[J].Geotechnique,2015,65(4):274–286.
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[13]陈颖平,黄博,陈云敏.循环荷载作用下结构性软黏土的变形和强度特性[J].岩土工程学报,2005,27(9):1 065–1 071.(CHEN Yingping,HUANG Bo,CHEN Yunmin.Deformation and strength of structural soft clay under cyclic loading[J].Chinese Journal of Geotechnical Engineering,2005,27(9):1 065–1 071.(in Chinese))
[14]王常晶,陈云敏.交通荷载引起的静偏应力对饱和软黏土不排水循环性状影响的试验研究[J].岩土工程学报,2007,29(11):1 742–1 747.(WANG Changjing,CHEN Yunmin.Study on effect of traffic loading induced static deviator stress on undrained cyclic properties of saturated soft clay[J].Chinese Journal of Geotechnical Engineering,2007,29(11):1 742–1 747.(in Chinese))
[15]PARR G B.Some aspects of the behaviour of London clay under repeated loading[Ph.D.Thesis][D].UK:UK University of Nottingham,1972.
[16]黄茂松,李进军,李兴照.饱和软黏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 Maosong,LI Jinjun,LI Xingzhao.Cumulative deformation behaviour of soft clay in cyclic undrained tests[J].Chinese Journal of Geotechnical Engineering,2006,28(7):891–895.(in Chinese))
[17]黄茂松,姚兆明.循环荷载下饱和软黏土的累积变形显式模型[J].岩土工程学报,2011,33(3):325–331.(HUANG Maosong,YAO Zhaoming.Explicit model for cumulative strain of saturated clay subjected to cyclic loading[J].Chinese Journal of Geotechnical Engineering,2011,33(3):325–331.(in Chinese))
[18]唐益群,张曦,赵书凯,等.地铁振动荷载下隧道周围饱和软黏土的孔压发展模型[J].土木工程学报,2007,40(4):82–86.(TANG Yiqun,ZHANG Xi,ZHAO Shukai,et al.Model of pore water pressure development in saturated soft clay around a subway tunnel under vibration load[J].China Civil Engineering Journal,2007,40(4):82–86.(in Chinese))
[19]王军,蔡袁强,徐长节.循环荷载作用下软黏土刚度软化特征试验研究[J].岩土力学,2007,28(10):2 138–2 144.(WANG Jun,CAI Yuanqiang,XU Changjie.Experimental study on degradation of stiffness of saturated soft clay under undrained cyclic loading[J].Chinese Journal of Geotechnical Engineering,2007,28(10):2 138–2 144.(in Chinese))
[20]ASTM D2974-14.Standard test methods for moisture,ash,and organic matter of peat and other organic soils[S].West Conshohocken,PA,USA:ASTM International,2014.
[21]LANDVA A O,KORPIJAAKKO E O,PHEENEY P E.Geotechnical classification of peats and organic soils[S].Testing of peats and organic soils,ASTM STP 820,American Society of Testing and Materials,1983:37–51.
[22]HYODO M,YAMAMOTO Y,SUGIYAMA M.Undrained cyclic shear behaviour of normally consolidated clay subjected to initial static shear stress[J].Soils and Foundations,1994,34(4):1–11.
[23]HSU C C,VUCETIC M.Threshold shear strain for cyclic pore-water pressure in cohesive soils[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(10):1 325–1 335.
[24]闫澍旺,封晓伟,田俊峰.循环荷载下滨海软黏土孔压发展规律及强度弱化特性[J].中国港湾建设,2010,169(增1):86–89.(YAN Shuwang,FENG Xiaowei,TIAN Junfeng.Pore pressure development and strength softening character of littoral soft clay under cyclic loading[J].China Harbour Engineering,2010,169(Supp.1):86–89.(in Chinese))
[25]MONISMITH C L,OGAWA N,FREEME C R.Permanent deformation characteristics of subgrade soils due to repeated loading[J].Transport Research Record,1975,537:1–17.
[26]LI D,SELIG E T.Cumulative plastic deformation for fine-grained subgrade soils[J].Journal of Geotechnical Engineering,1996,122(12):1 006–1 013.
[27]CHAI J C,MIURA N.Traffic-load-induced permanent deformation of road on soft subsoil[J].Journal of Geotechnical and Geoenvironmental Engineering,ASCE,2002,128(11):907–916
[28]中华人民共和国国家标准编写组.GB/T 50123—1999土工试验方法标准[S].北京:中国建筑工业出版社,1999.(The National Standards Compilation Group of People?s Republic of China.GB/T50123—1999 Standard for soil test method[S].Beijing:China Architecture and Building Press,1999.(in Chinese))
[2]MADASCHI A,GAJO A.One-dimensional response of peaty soils subjected to a wide range of oedometric conditions[J].Geotechnique,2015,65(4):274–286.
[3]MESRI G,STARK T D,AJLOUNI,M.et al.Secondary compression of peat with or without surcharging[J].Journal of Geotechnical and Geoenviromental Engineering,1997,123(5):411–421.
[4]MESRI G,AJLOUNI M.Engineering properties of fibrous peats[J].Journal of Geotechnical and Geoenviromental Engineering,2007,133(7):850–866.
[5]O?KELLY B C.Effective stress strength testing of peat[J].Proceedings of the ICE,Environmental Geotechnics,2015,2(1):34–44.
[6]刘伟,赵福玉,杨文辉,等.安嵩线草海段泥炭质土的特征及性质[J].岩土工程学报,2013,35(增2):671–674.(LIU Wei,ZHAO Fuyu,YANG Wenhui,et al.Features and properties of peaty soil in Caohai section of Anning-Sonming line[J].Chinese Journal of Geotechnical Engineering,2013,35(Supp.2):671–674.(in Chinese))
[7]桂跃,余志华,刘海明,等.高原湖相泥炭土固结系数变化规律试验研究[J].岩石力学与工程学报,2015,35(增1):3 259–3 267.(GUI Yue,YU Zhihua,LIU Haiming,et al.Experimental study of the change law of consolidation coefficient of the plateau lacustrine peaty soil[J].Chinese Journal of Rock Mechanics and Engineering,2015,35(Supp.1):3 259–3 267.(in Chinese))
[8]吕岩,佴磊,徐燕,等.有机质对草炭土物理力学性质影响的机理分析[J].岩土工程学报,2011,33(4):655–660.(LU Yan,NIE Lei,XU Yan,et al.The mechanism of organic matter effect on physical and mechanical properties of turfy soil[J].Chinese Journal of Geotechnical Engineering,2011,33(4):655–660.(in Chinese))
[9]柳雁玲.草炭土路基沉降与变形特性研究[博士学位论文][D].长春:吉林大学,2006.(LIU Yanling.Research on settlement and deformation characteristics of peat soil roadbed[Ph.D.Thesis][D].Changchun:Jilin University,2006.(in Chinese))
[10]蒋忠信,黄俊,陈国芳.南昆线七甸泥炭土路基加固的沉降控制[J].铁道工程学报,1998,(4):79–89.(JIANG Zhongxin,HUANG Jun,CHEN Guofang.Subsidence control for reinforcing peat soil roadbed in the Qidian worksite of Nanning-Kunming railway[J].Journal of Railway Engineering Society,1998,(4):79–89.(in Chinese))
[11]TSB.Railway investigation report R99Q0019[R].[S.l.]:The Transportation Safety Board of Canada,1999.
[12]TSB.Railway investigation report R04Q0040[R].[S.l.]:The Transportation Safety Board of Canada,2004.
[13]陈颖平,黄博,陈云敏.循环荷载作用下结构性软黏土的变形和强度特性[J].岩土工程学报,2005,27(9):1 065–1 071.(CHEN Yingping,HUANG Bo,CHEN Yunmin.Deformation and strength of structural soft clay under cyclic loading[J].Chinese Journal of Geotechnical Engineering,2005,27(9):1 065–1 071.(in Chinese))
[14]王常晶,陈云敏.交通荷载引起的静偏应力对饱和软黏土不排水循环性状影响的试验研究[J].岩土工程学报,2007,29(11):1 742–1 747.(WANG Changjing,CHEN Yunmin.Study on effect of traffic loading induced static deviator stress on undrained cyclic properties of saturated soft clay[J].Chinese Journal of Geotechnical Engineering,2007,29(11):1 742–1 747.(in Chinese))
[15]PARR G B.Some aspects of the behaviour of London clay under repeated loading[Ph.D.Thesis][D].UK:UK University of Nottingham,1972.
[16]黄茂松,李进军,李兴照.饱和软黏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 Maosong,LI Jinjun,LI Xingzhao.Cumulative deformation behaviour of soft clay in cyclic undrained tests[J].Chinese Journal of Geotechnical Engineering,2006,28(7):891–895.(in Chinese))
[17]黄茂松,姚兆明.循环荷载下饱和软黏土的累积变形显式模型[J].岩土工程学报,2011,33(3):325–331.(HUANG Maosong,YAO Zhaoming.Explicit model for cumulative strain of saturated clay subjected to cyclic loading[J].Chinese Journal of Geotechnical Engineering,2011,33(3):325–331.(in Chinese))
[18]唐益群,张曦,赵书凯,等.地铁振动荷载下隧道周围饱和软黏土的孔压发展模型[J].土木工程学报,2007,40(4):82–86.(TANG Yiqun,ZHANG Xi,ZHAO Shukai,et al.Model of pore water pressure development in saturated soft clay around a subway tunnel under vibration load[J].China Civil Engineering Journal,2007,40(4):82–86.(in Chinese))
[19]王军,蔡袁强,徐长节.循环荷载作用下软黏土刚度软化特征试验研究[J].岩土力学,2007,28(10):2 138–2 144.(WANG Jun,CAI Yuanqiang,XU Changjie.Experimental study on degradation of stiffness of saturated soft clay under undrained cyclic loading[J].Chinese Journal of Geotechnical Engineering,2007,28(10):2 138–2 144.(in Chinese))
[20]ASTM D2974-14.Standard test methods for moisture,ash,and organic matter of peat and other organic soils[S].West Conshohocken,PA,USA:ASTM International,2014.
[21]LANDVA A O,KORPIJAAKKO E O,PHEENEY P E.Geotechnical classification of peats and organic soils[S].Testing of peats and organic soils,ASTM STP 820,American Society of Testing and Materials,1983:37–51.
[22]HYODO M,YAMAMOTO Y,SUGIYAMA M.Undrained cyclic shear behaviour of normally consolidated clay subjected to initial static shear stress[J].Soils and Foundations,1994,34(4):1–11.
[23]HSU C C,VUCETIC M.Threshold shear strain for cyclic pore-water pressure in cohesive soils[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(10):1 325–1 335.
[24]闫澍旺,封晓伟,田俊峰.循环荷载下滨海软黏土孔压发展规律及强度弱化特性[J].中国港湾建设,2010,169(增1):86–89.(YAN Shuwang,FENG Xiaowei,TIAN Junfeng.Pore pressure development and strength softening character of littoral soft clay under cyclic loading[J].China Harbour Engineering,2010,169(Supp.1):86–89.(in Chinese))
[25]MONISMITH C L,OGAWA N,FREEME C R.Permanent deformation characteristics of subgrade soils due to repeated loading[J].Transport Research Record,1975,537:1–17.
[26]LI D,SELIG E T.Cumulative plastic deformation for fine-grained subgrade soils[J].Journal of Geotechnical Engineering,1996,122(12):1 006–1 013.
[27]CHAI J C,MIURA N.Traffic-load-induced permanent deformation of road on soft subsoil[J].Journal of Geotechnical and Geoenvironmental Engineering,ASCE,2002,128(11):907–916
[28]中华人民共和国国家标准编写组.GB/T 50123—1999土工试验方法标准[S].北京:中国建筑工业出版社,1999.(The National Standards Compilation Group of People?s Republic of China.GB/T50123—1999 Standard for soil test method[S].Beijing:China Architecture and Building Press,1999.(in Chinese))