粉粒含量对砂土强度特性的影响
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摘要
对含无塑性粉粒的砂土进行了三轴固结不排水试验,结果显示:粉粒含量通过颗粒组成和结构对粉砂强度和变形产生重要影响。在粉粒含量为6%,9%和12%时,松散试样在100 kPa围压下出现了静态液化现象,而粉粒含量增至15%时该现象消失,且随着围压的增大该现象也消失;在同一粉粒含量下,粉砂土残余内摩擦角高于峰值内摩擦角,但残余偏应力值很小,这是由于孔压增长很大,抵消了内摩擦角由?p′提高到?r′的有利影响;稳态线也受粉粒含量的影响,表现在随着粉粒含量的增加,稳态线逐渐向下移动;各粉细砂强度和变形对围压的敏感性强于纯净砂;粉粒含量对孔隙比的影响是含量超出一定值后才变得显著的,这说明粉粒加入到砂骨架中时,并未全部充填至砂粒孔隙中,而是以砂粒间接触点或面上为主,这样的接触结构导致了粉砂具有高体缩性,由此使得粉砂样表现出典型的应变软化特征。
An experimental study on sands with different content of nonplastic fines(particles smaller than 0.075 mm in diameter) was performed.It was shown that the strength and strain of the silty sands were affected by fines content.Silty sands with fines content of 6%,9% and 12% exhibited static liquefaction under the confining pressure of 100 kPa,but samples with fines content of 0%,3% and 15% did not.And the static liquefaction disappeared under the confining pressure of 200 kPa.For a kind of silty sands with certain fines content,the friction angle which was relevant to the residual stress difference was higher than that to the peak stress difference,but the residual stress difference was quite low,because the increase of pore water was fast,and counterbalanced the advantage of the increase from ?p′ to ?r′.The steady state line moved downward with the increase of fines content.The strength of samples with different fines content was more sensitive to the confining pressure than that of clean sand.The influence of fines content on void ratio was remarkable when the fines content was more than 12%.It was shown that the void between load-bearing grains was not entirely filled with fines of low content and might be only filled with the fines were on the contact of the sand grains.Silty sands with the sand-silt fabric were highly compressible and exhibited typical strain-soften characteristics and instability under low confining pressure.
An experimental study on sands with different content of nonplastic fines(particles smaller than 0.075 mm in diameter) was performed.It was shown that the strength and strain of the silty sands were affected by fines content.Silty sands with fines content of 6%,9% and 12% exhibited static liquefaction under the confining pressure of 100 kPa,but samples with fines content of 0%,3% and 15% did not.And the static liquefaction disappeared under the confining pressure of 200 kPa.For a kind of silty sands with certain fines content,the friction angle which was relevant to the residual stress difference was higher than that to the peak stress difference,but the residual stress difference was quite low,because the increase of pore water was fast,and counterbalanced the advantage of the increase from ?p′ to ?r′.The steady state line moved downward with the increase of fines content.The strength of samples with different fines content was more sensitive to the confining pressure than that of clean sand.The influence of fines content on void ratio was remarkable when the fines content was more than 12%.It was shown that the void between load-bearing grains was not entirely filled with fines of low content and might be only filled with the fines were on the contact of the sand grains.Silty sands with the sand-silt fabric were highly compressible and exhibited typical strain-soften characteristics and instability under low confining pressure.
引文
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[9]PITMAN T D,ROBERTSON P K,SEGO D C.Influence of fines on the collapse of loose sands[J].Canadian Geotechnical Journal,1994,31:728–739.
[10]POULOS S J,et al.Liquefaction evaluation procedure[J].J Geotechnical Engineering Division,ASCE,1985,111(GT6):772–792.
[11]赵成刚,尤昌龙.饱和砂土液化与稳态强度[J].土木工程学报,2001,34(3):90–96.(ZHAO Cheng-gang,YOU Chang-long.Liquefaction and steady state strength[J].China Civil Engineering Journal,2001,34(3):90–96.(in Chinese))
[12]李广信.高等土力学[M].北京:清华大学出版社,2004.(LI Guang-xin.Advanced soil mechanics[M].Beijing.Tsinghua University Press,2004.(in Chinese))
[2]THEVANAYAGAM S,MOHAN S.Intergranular state variable and stress-strain behaviour of silty sands[J].Geotechnique,2000,50(1):1–23.
[3]POLITO C P,MARTIN II J R.Effects of nonplastic fines on the liquefaction resistance of sands[J].Journal of Geotechnical and Geoenvironmental Engineering,2001,127(5):408–415.
[4]GEORGIANNOU V N,BURLAND J B,HIGHT D W.The undrained behaviour of clayey sands in triaxial compression and extension[J].Geotechnique,1990,40(3):431–449.
[5]刘雪珠,陈国兴.黏粒含量对南京粉细砂液化影响的试验研究[J].地震工程与工程振动,2003,23(6):150–155.(LIU Xue-zhu,CEHN Guo-xing.Experimental study on influence of clay particle content on liquefaction of Nanjing fine sand[J].Earthquake Engineering and Engineering Vibration,2003,23(6):150–155.(in Chinese))
[6]衡朝阳,何满潮,裘以惠.含黏粒砂土抗液化性能的试验研究[J].工程地质学报,2001,9(4):339–344.(HENG Chao-yang,HE Man-chao,QIU Yi-hui.Experimental study of liquefaction-resistant characteristics clayey sand[J].Journal of Engineering Geology,2001,9(4):339–344.(in Chinese))
[7]YAMAMURO J A,LADE P V.Steady-state concepts and static liquefaction of silty sands[J].Journal of Geotechnical and Geoenvironmental Engineering,1998,124(9):868–877.
[8]YAMAMURO J A,LADE P V.Static liquefaction of very loose sands[J].Canadian Geotechnical Journal,1997,34:905–917.
[9]PITMAN T D,ROBERTSON P K,SEGO D C.Influence of fines on the collapse of loose sands[J].Canadian Geotechnical Journal,1994,31:728–739.
[10]POULOS S J,et al.Liquefaction evaluation procedure[J].J Geotechnical Engineering Division,ASCE,1985,111(GT6):772–792.
[11]赵成刚,尤昌龙.饱和砂土液化与稳态强度[J].土木工程学报,2001,34(3):90–96.(ZHAO Cheng-gang,YOU Chang-long.Liquefaction and steady state strength[J].China Civil Engineering Journal,2001,34(3):90–96.(in Chinese))
[12]李广信.高等土力学[M].北京:清华大学出版社,2004.(LI Guang-xin.Advanced soil mechanics[M].Beijing.Tsinghua University Press,2004.(in Chinese))
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