基于状态曲面的非饱和土强度准则及其验证
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摘要
考虑体变对非饱和土土-水状态的影响,将状态曲面函数引入传统的Vanapalli强度公式得到与孔隙比相关的抗剪强度准则,新准则使用饱和土的强度参数和两条不同孔隙比对应的土-水特征曲线。选择一种尾矿砂和高岭土的混合土料为研究对象,进行一系列的土-水特征曲线试验、吸力控制的等向压缩和三轴剪切试验。试验结果表明,新准则能更准确地预测非饱和土的强度,证明了传统强度预测的误差主要来源于忽略了体变导致的土-水状态变化,并提出在不同应力空间内精确地获得抗剪强度包线的方法,合理地解释了强度包线斜率在净应力-强度平面内随吸力增大、强度包线形状在吸力-强度平面内随净应力发生变化的特性。
Considering the influence of the volumetric behavior on the soil state, a void-ratio-dependent shear strength criterion for unsaturated soils is proposed by introducing the state surface expression into the Vanapalli's shear strength equation. The saturated shear strength parameters and two series of soil water characteristic curve(SWCC) corresponding to different void ratios are employed in the proposed criterion. A series of SWCC tests, isotropic compression tests and suction-controlled triaxial tests are performed on a soil mixture of tailing sand and speswhite China kaolin. The testing results indicate that the proposed criterion can provide a more accurate prediction of shear strength for unsaturated soils than that of convention prediction using a unique SWCC. It is proved that the principal source of errors in the conventional estimation of shear strength is related to the evolution of soil state caused by the volume change. Moreover, a method for accurately identifying the failure envelopes in different stress spaces is developed. Several mechanical characteristics of unsaturated soils, including an increase in the slope of failure envelope with suction in net stress versus shear strength plane and the influence of the net stress on the shape of the failure envelope in the suction-strength plane, are reasonably interpreted by this method.
Considering the influence of the volumetric behavior on the soil state, a void-ratio-dependent shear strength criterion for unsaturated soils is proposed by introducing the state surface expression into the Vanapalli's shear strength equation. The saturated shear strength parameters and two series of soil water characteristic curve(SWCC) corresponding to different void ratios are employed in the proposed criterion. A series of SWCC tests, isotropic compression tests and suction-controlled triaxial tests are performed on a soil mixture of tailing sand and speswhite China kaolin. The testing results indicate that the proposed criterion can provide a more accurate prediction of shear strength for unsaturated soils than that of convention prediction using a unique SWCC. It is proved that the principal source of errors in the conventional estimation of shear strength is related to the evolution of soil state caused by the volume change. Moreover, a method for accurately identifying the failure envelopes in different stress spaces is developed. Several mechanical characteristics of unsaturated soils, including an increase in the slope of failure envelope with suction in net stress versus shear strength plane and the influence of the net stress on the shape of the failure envelope in the suction-strength plane, are reasonably interpreted by this method.
引文
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[17]GALLIPOLI D,WHEELER S,KARSTUNEN M.Modelling the variation of degree of saturation in a deformable unsaturated soil[J].Geotechnique,2003,53(1):105-112.
[18]胡冉,陈益峰,周创兵.基于孔隙分布的变形土土水特征曲线模型[J].岩土工程学报,2013,35(8):1451-1462.HU Ran,CHEN Yi-feng,ZHOU Chuang-bing.Soil-water characteristic curves for deformable soils based on the pore-size distributon[J].Chinese Journal of Geotechnical Engineering,2013,35(8):1451-1462.
[19]ZHOU AN-NAN,SHENG DAI-CHAO,CARTER J P.Modelling the effect of initial density on soil-water characteristic curves[J].Geotechnique,2012,62(8):669-680.
[20]陈伟,孔令伟,郭爱国,等.吸力对弱膨胀土强度贡献的试验研究与预测分析[J].岩土力学,2008,29(7):1783-1787.CHEN Wei,KONG Ling-wei,GUO Ai-guo,et al.Experimental study and prediction analysis on the contribution of suction to the shear strength of a weak expansive soil[J].Rock and Soil Mechanics,2008,29(7):1783-1787.
[21]FUTAI M M,ALMEIDA M S S.An experimental investigation of the mechanical behavior of an unsaturated gneiss residual soil[J].Geotechnique,2005,55(3):201-213.
[22]SHAO LONG-TAN,LIU GANG,ZENG FEI-TAO,et al.Recognition of the stress-strain curve based on the local deformation measurement of soil specimens in the triaxial test[J].Geotechnical Testing Journal,2016,39(4):658-672.
[23]孙德安.饱和度对非饱和土力学性质的影响[J].岩土力学,2009,30(2):13-16.SUN De-an.Influence of degree of saturation on the mechanical properties of the unsaturated soils[J].Rock and Soil Mechanics,2009,30(2):13-16.
[2]LU NING,JONATHAN W G,DAVID T W.Aclosed-form equation for effective stress in unsaturated soil[J].Water Resources Research,2010,46(5):567-573.
[3]ALONSO E E,PEREIRA J M,VAUNAT J,et al.Amicrostructurally based effective stress for unsaturated soils[J].Geotechnique,2010,60(12):913-925.
[4]FREDLUND D G,MORGENSTERN N R,WIDGER R S.The shear strength of unsaturated soils[J].Canadian Geotechnical Journal,1978,15(3):313-321.
[5]VANAPALLI S K,FREDLUND D G,PUFHAL D E,et al.Model for the prediction of shear strength with respect to soil suction[J].Canadian Geotechnical Journal,1996,33(3):379-392.
[6]MIAO L C,LIU S Y,LAI Y M.Research of soil-water characteristics and shear strength feature of Nanyang expansive soil[J].Engineering Geology,2002,65(4):261-267.
[7]XU YONG-FU.Fractal approach to unsaturated shear strength[J].Journal of Geotechnical and Geoenvironmental Engineering,2004,130(3):264-274.
[8]徐筱,赵成刚,蔡国庆.区分毛细和吸附作用的非饱和土抗剪强度模型[J].岩土力学,2018,39(6):2059-2064.XU Xiao,ZHAO Cheng-gang,CAI Guo-qing.Shear strength of unsaturated soils considering capillary and adsorptive mechanisms[J].Rock and Soil Mechanics,2018,39(6):2059-2064.
[9]孙德安.非饱和土的水力和力学特性及其弹塑性描述[J].岩土力学,2009,30(11):3217-3231.SUN De-an.Hydro-mechanical behaviors of unsaturated soils and their elasto-plastic modelling[J].Rock and Soil Mechanics,2009,30(11):3217-3231.
[10]刘艳,韦昌富,房倩.非饱和土水力本构模型及其隐式积分算法[J].岩土力学,2014,35(2):365-370.LIU Yan,WEI Chang-fu,FANG Qian.Implicit integration algorithm of a hydro mechanical coupling constitutive model for unsaturated soils[J].Rock and Soil Mechanics,2014,35(2):365-370.
[11]吴珺华,杨松.干湿循环下膨胀土基质吸力测定及其对抗剪强度影响试验研究[J].岩土力学,2017,38(3):678-684.WU Jun-hua,YANG Song.Experimental study of matric suction measurement and its impact on shear strength under drying-wetting cycles for expansive soils[J].Rock and Soil Mechanics,2017,38(3):678-684.
[12]张昭,刘奉银,赵旭光,等.考虑应力引起孔隙比变化的土-水特征曲线模型[J].水利学报,2013,44(5):578-585.ZHANG Zhao,LIU Feng-yin,ZHAO Xu-guang,et al.Asoil water characteristic curve model considering void ratio variation with stress[J].Journal of Hydraulic Engineering,2013,44(5):578-585.
[13]张雪东,赵成刚,蔡国庆,等.土体密实状态对土水特征曲线影响规律研究[J].岩土力学,2010,31(5):1463-1468.ZHANG Xue-dong,ZHAO Cheng-gang,CAI Guo-qing,et al.Research on the influence of soil density on soil-water characteristic curve[J].Rock and Soil Mechanics,2010,31(5):1463-1468.
[14]褚峰,邵生俊,陈存礼.干密度和竖向应力对原状非饱和黄土土水特征影响的试验研究[J].岩石力学与工程学报,2014,33(2):413-420.CHU Feng,SHAO Sheng-jun,CHEN Cun-li.Experimental research on influences of dry density and vertical stress on soil-water characteristic curves of intact unsaturated loess[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(2):413-420.
[15]孙德安.非饱和土的水力与力学性质及其模拟的关键点[C]//第二届全国岩土本构理论研讨会.上海:[出版社不详],2014:214-222.SUN De-an.Some issues in hydro-mechanical behavior of unsaturated soils and its modeling[C]//The Second Conference on Constitutive Theory for Geomaterials.Shanghai:[s.n.],2014:214-222.
[16]邹维列,王协群,罗方德,等.等应力和等孔隙比状态下的土水特征曲线[J].岩土工程学报,2017,39(9):1711-1717.ZOU Wei-lie,WANG Xie-qun,LUO Fang-de,et al.The soil-water characteristic curves under constant stress state and constant void ratio[J].Chinese Journal of Geotechnical Engineering,2017,39(9):1711-1717.
[17]GALLIPOLI D,WHEELER S,KARSTUNEN M.Modelling the variation of degree of saturation in a deformable unsaturated soil[J].Geotechnique,2003,53(1):105-112.
[18]胡冉,陈益峰,周创兵.基于孔隙分布的变形土土水特征曲线模型[J].岩土工程学报,2013,35(8):1451-1462.HU Ran,CHEN Yi-feng,ZHOU Chuang-bing.Soil-water characteristic curves for deformable soils based on the pore-size distributon[J].Chinese Journal of Geotechnical Engineering,2013,35(8):1451-1462.
[19]ZHOU AN-NAN,SHENG DAI-CHAO,CARTER J P.Modelling the effect of initial density on soil-water characteristic curves[J].Geotechnique,2012,62(8):669-680.
[20]陈伟,孔令伟,郭爱国,等.吸力对弱膨胀土强度贡献的试验研究与预测分析[J].岩土力学,2008,29(7):1783-1787.CHEN Wei,KONG Ling-wei,GUO Ai-guo,et al.Experimental study and prediction analysis on the contribution of suction to the shear strength of a weak expansive soil[J].Rock and Soil Mechanics,2008,29(7):1783-1787.
[21]FUTAI M M,ALMEIDA M S S.An experimental investigation of the mechanical behavior of an unsaturated gneiss residual soil[J].Geotechnique,2005,55(3):201-213.
[22]SHAO LONG-TAN,LIU GANG,ZENG FEI-TAO,et al.Recognition of the stress-strain curve based on the local deformation measurement of soil specimens in the triaxial test[J].Geotechnical Testing Journal,2016,39(4):658-672.
[23]孙德安.饱和度对非饱和土力学性质的影响[J].岩土力学,2009,30(2):13-16.SUN De-an.Influence of degree of saturation on the mechanical properties of the unsaturated soils[J].Rock and Soil Mechanics,2009,30(2):13-16.