主应力轴旋转下小偏压固结密实粉土崩塌特性及孔压模型研究
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摘要
为研究主应力轴旋转复杂动应力对偏压固结粉土的性状演变影响,以空心圆柱试样为对象,开展具有不同初始固结比的密实粉土(Dr=70%)在不排水主应力轴循环旋转下的系列试验。结果表明:①初始固结比不大于1.5时,主应力轴旋转导致试样发生中低应变崩塌,进而液化的脆性破坏模式;而固结比大于1.5时,试样变为应变持续稳定开展至高应变,孔压最终进入动态平衡的延性破坏模式,且不同固结比下试样发生崩塌液化和稳态延性破坏的孔压峰值间不存在交叉。②小偏压固结试样的液化峰值孔压和崩塌孔压均随固结比增加而有规律地下降,但受动剪应力水平影响很小,这与等压固结试样的崩塌孔压值受控于剪应力水平有很大差异。③相同初始球应力水平下,崩塌振次反映的小偏压固结试样强度高于等压固结试样,但在偏压条件下强度与固结比不存在单调变化关系,表明小偏压固结试样崩塌除受制初始围压水平外,很大程度上还取决于偏压程度。④基于上述试验结果,提出了主应力轴循环旋转下小偏压固结粉土的孔压预测模型,该模型不仅突显了崩塌状态对相变及液化破坏的重要预测作用,还反映了固结比和动剪应力对孔压开展的综合影响。
In order to study the properties of anisotropically consolidated silt subjected undrained cyclic principal stress rotation,series of tests are performed.The tested hollow cylinder silt samples have the initial relative density of 70%,and are consolidated with different consolidation ratio(Kc) before cyclic principal stress rotation.The results show that for the samples with Kc≤1.5,they collapsed at low or medium strain and liquefied,but when Kc > 1.5,the samples' strain increases stably and the pore water pressure developed into dynamic equilibrium states;and the peak values of pore pressure in dynamic equilibrium states are lower than those in the liquefaction failure states.On the other hand,differing from the isotropically consolidated samples,the samples with Kc between 1.1 and 1.5 have the maximum pore water pressure at liquefaction lower than the initial effective spherical stress.Furthermore they decrease with the increase of Kc,but barely dependent of dynamic shear stress.So do the pore water pressure at collapse states.The collapse cycles of anisotropically consolidated samples are larger than that of the isotropically consolidated ones with the same shear stress level.But there are no monotonic relationship between collapse cycles and Kc.Finally,a model of pore water pressure development for the anisotropically consolidated silt under cyclic principal stress rotation is put forward,which could reflect the collapse characteristics as well as the effects of consolidation ratio and dynamic shear stress level.
In order to study the properties of anisotropically consolidated silt subjected undrained cyclic principal stress rotation,series of tests are performed.The tested hollow cylinder silt samples have the initial relative density of 70%,and are consolidated with different consolidation ratio(Kc) before cyclic principal stress rotation.The results show that for the samples with Kc≤1.5,they collapsed at low or medium strain and liquefied,but when Kc > 1.5,the samples' strain increases stably and the pore water pressure developed into dynamic equilibrium states;and the peak values of pore pressure in dynamic equilibrium states are lower than those in the liquefaction failure states.On the other hand,differing from the isotropically consolidated samples,the samples with Kc between 1.1 and 1.5 have the maximum pore water pressure at liquefaction lower than the initial effective spherical stress.Furthermore they decrease with the increase of Kc,but barely dependent of dynamic shear stress.So do the pore water pressure at collapse states.The collapse cycles of anisotropically consolidated samples are larger than that of the isotropically consolidated ones with the same shear stress level.But there are no monotonic relationship between collapse cycles and Kc.Finally,a model of pore water pressure development for the anisotropically consolidated silt under cyclic principal stress rotation is put forward,which could reflect the collapse characteristics as well as the effects of consolidation ratio and dynamic shear stress level.
引文
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[12]温晓贵,张勋,周建,等.复杂应力路径下杭州原状软黏土破坏标准研究[J].岩土力学,2010,31(9):2793-2798.WEN Xiao-gui,ZHANG Xun,ZHOU Jian,et al.Study offailure criterion for Hangzhou intact soft clay undercomplex stress path[J].Rock and Soil Mechanics,2010,31(9):2793-2798.
[13]ALARCON-GUZMAN A,LEONARDS G A,CHA-MEAU J L.Undrained monotonic and cyclic strength ofsands[J].Journal of Geotechnical Engineering,ASCE,1988,114(10):1089-1108.
[14]SASITHARAN S,ROBERTSON P K,SEGO D C,et al.Collapse behavior of sand[J].Canadian GeotechnicalJournal,1993,30(4):569-577.
[15]SKOPEK P,MORGENSTERN N R,ROBERTSON P K,et al.Collapse of dry sand[J].Canadian GeotechnicalJournal,1994,31(6):1008-1014.
[2]ISHIHARA K,TOWHATA I.Sand response to cyclicrotation of principal stress directions as induced by waveloads[J].Soils and foundations,1983,23(4):11-26.
[3]姚兆明.饱和软黏土循环累积变形与交通荷载引起的长期沉降[D].上海:同济大学,2011.
[4]SHAHNAZARI H,TOWHATA I.Torsion shear tests oncyclic stress-dilatancy relationship of sand[J].Soils andFoundations,2002,2(1):105-119.
[5]NAKATA Y,HYODO M,MURATA H.Flow deformationof sands subjected to principal stress rotation[J].Soilsand Foundations,1998,38(2):115-128.
[6]张晨明,董秀竹,郭莹.波浪荷载作用下砂土变形特性的模拟试验研究[J].地震工程与工程振动,2005,25(2):155-159.ZHANG Chen-ming,DONG Xiu-zhu,GUO Ying.Experimental study on dynamic deformation behavior ofsand under wave-induced loading[J].EarthquakeEngineering and Engineering Vibration,2005,25(2):155-159.
[7]TOWHATA I,ISHIHARA K.Undrained strength of sandundergoing cyclic rotation of principal stress axes[J].Soils and Foundations,1985,25(2):135-147.
[8]YANG Z X,LI X S,YANG J.Undrained anisotropy androtational shear in granular soil[J].Geotechnique,2007,57(4):371-384.
[9]钱寿易,杜金声,楼志刚,等.海洋土力学现状及发展[J].力学进展,1980,10(4):1-14.QIAN Shou-yi,DU Jin-sheng,LOU Zhi-gang,et al.Thestatus and development of ocean soil mechanics[J].Advances in Mechanics,1980,10(4):1-14.
[10]沈扬,闫俊,刘汉龙,等.主应力轴循环旋转下高密实粉土稳定性影响研究[J].岩土力学,2011,32(10):2957-2964.SHEN Yang,YAN Jun,LIU Han-long,et al.Stability ofhigh relative density silt under cyclic principal stressrotation[J].Rock and Soil Mechanics,2011,32(10):2957-2964.
[11]SHEN Y,YAN J,LIU H L,et al.Critical behavior ofhigh-density silt under cyclic principal stress rotation afterdifferent initial consolidation ratio[C]//InternationalSymposium on Geomechanics and Geotechnics:FromMicro to Macro.Boca Raton:CRC Press,2010:117-124.
[12]温晓贵,张勋,周建,等.复杂应力路径下杭州原状软黏土破坏标准研究[J].岩土力学,2010,31(9):2793-2798.WEN Xiao-gui,ZHANG Xun,ZHOU Jian,et al.Study offailure criterion for Hangzhou intact soft clay undercomplex stress path[J].Rock and Soil Mechanics,2010,31(9):2793-2798.
[13]ALARCON-GUZMAN A,LEONARDS G A,CHA-MEAU J L.Undrained monotonic and cyclic strength ofsands[J].Journal of Geotechnical Engineering,ASCE,1988,114(10):1089-1108.
[14]SASITHARAN S,ROBERTSON P K,SEGO D C,et al.Collapse behavior of sand[J].Canadian GeotechnicalJournal,1993,30(4):569-577.
[15]SKOPEK P,MORGENSTERN N R,ROBERTSON P K,et al.Collapse of dry sand[J].Canadian GeotechnicalJournal,1994,31(6):1008-1014.
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