平面应变加、卸荷条件下考虑初始应力的原状黄土强度与变形特性试验研究
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摘要
针对黄土工程中的众多平面应变加、卸载问题,利用平面应变改造后的西安理工大学真三轴仪,模拟黄土原位沉积方向及不同初始应力状态,在不同围压下对不同初始应力状态原状黄土进行竖向加载和侧向卸载平面应变试验,揭示不同初始应力状态原状黄土在加、卸载不同应力路径条件下的强度和变形特性。研究结果表明:两种应力路径条件下的应力应变曲线均呈硬化型,加载曲线均高于卸载,加载强度大于卸载强度,但卸载时,土的强度发挥较快。剪切过程中,黄土的侧向变形与竖向变形均呈非线性关系。竖向加载时,土的初始应力状态k值对土强度和变形的影响与固结围压的大小关系紧密;侧向卸载时,k值的增大可以限制侧向变形的发展。竖向加载条件下的体积应变均为剪缩,侧向卸载时均为剪胀。加、卸载条件下p-q平面内的破坏强度线基本一致,近似呈线性关系。侧向卸载条件下土体破坏时的应变远小于竖向加载和常规三轴试验。随着k值的增大,加、卸载应力路径时,黏聚力均线性减小,内摩擦角均线性增大。
Aiming at the loading and unloading plane strain problems in loess engineering, the loess was simulated in the in-situ deposit direction and initial stress state. The vertical loading and lateral unloading plain strain tests of intact loess with different initial stress state and different confining pressures were carried out by using the modified triaxial apparatus of Xi'an University of Technology. The strength and deformation characteristics of the intact loess under different stress path are revealed. The study results show that the stress-strain relationship curve is harden type under the two stress paths, the loading curves are higher than the unloaded ones and the loading strength is greater than the unloading strength, but the strength of the soil grows faster when unloading,. The result also reveals that the lateral deformation of loess has a non-linear relationship with the vertical one. The effect of the initial stress state on the soil strength and deformation is closely related to the confining pressure under vertical loading condition. The increase of the k value can limit the development of lateral deformation under lateral unloading condition. The volume deformation under vertical loading conditions is shear shrinkage, and the lateral unloading is dilatancy. Under the loading and unloading conditions, the failure strength lines in the p-q plane are basically the same with approximate linear relation. Under the condition of lateral unloading, the failure strain of the soil is much less than that of the vertical loading and the conventional triaxial test. With the increase of k value, the cohesive force decreases linearly and the internal friction angle increases linearly under the loading and unloading stress path.
Aiming at the loading and unloading plane strain problems in loess engineering, the loess was simulated in the in-situ deposit direction and initial stress state. The vertical loading and lateral unloading plain strain tests of intact loess with different initial stress state and different confining pressures were carried out by using the modified triaxial apparatus of Xi'an University of Technology. The strength and deformation characteristics of the intact loess under different stress path are revealed. The study results show that the stress-strain relationship curve is harden type under the two stress paths, the loading curves are higher than the unloaded ones and the loading strength is greater than the unloading strength, but the strength of the soil grows faster when unloading,. The result also reveals that the lateral deformation of loess has a non-linear relationship with the vertical one. The effect of the initial stress state on the soil strength and deformation is closely related to the confining pressure under vertical loading condition. The increase of the k value can limit the development of lateral deformation under lateral unloading condition. The volume deformation under vertical loading conditions is shear shrinkage, and the lateral unloading is dilatancy. Under the loading and unloading conditions, the failure strength lines in the p-q plane are basically the same with approximate linear relation. Under the condition of lateral unloading, the failure strain of the soil is much less than that of the vertical loading and the conventional triaxial test. With the increase of k value, the cohesive force decreases linearly and the internal friction angle increases linearly under the loading and unloading stress path.
引文
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[11]高帅,骆亚生,胡海军,等.非饱和原状黄土增湿条件下力学特性试验研究[J].岩土工程学报,2015,37(7):1313-1318(Gao Shuai,Luo Yasheng,Hu Haijun,et al.Triaxial tests on water immersion of unsaturated and undisturbed loess[J].Chinese Journal of Geotechnical Engineering,2015,37(7):1313-1318(in Chinese))
[12]张玉,邵生俊.平面应变加?卸荷条件下黄土的非线性变形特性的研究[J].岩土工程学报,2015,37(增1):185-190(Zhang Yu,Shao Shengjun.Non-linear stress-strain behaviors of loess under plane strain state of vertical loading and lateral unloading[J].Chinese Journal of Geotechnical Engineering,2015,37(S1):185-190(in Chinese))
[13]张玉,邵生俊.平面应变条件下黄土的竖向加载变形与强度特性分析[J].土木工程学报,2016,49(3):112-121(Zhang Yu,Shao Shengjun.An analysis of vertical loading deformation and strength characteristics of loess under plain strain condition[J].China Civil Engineering Journal,2016,49(3):112-121(in Chinese))
[14]张玉,何晖,赵敏,等.平面应变条件下原状黄土侧向卸载变形与强度特性分析[J].岩土力学,2017,38(5):1233-1242(Zhang Yu,He Hui,Zhao Min,et al.Analysis of lateral unloading deformation and strength characteristics of intact loess under plain strain condition[J].Rock and Soil Mechanics,2017,38(5):1233-1242(in Chinese))
[2]邵生俊,邓国华.原状黄土的结构性强度特性及其在黄土隧道围岩压力分析中的应用[J].土木工程学报,2008,41(11):93-98(Shao Shengjun,Deng Guohua.The strength characteristics of loess with different structures and its application in analyzing the earth pressure on loess tunnel[J].China Civil Engineering Journal,2008,41(11):93-98(in Chinese))
[3]陈昌禄,邵生俊,罗爱忠,等.结构性对原状黄土强度影响规律的真三轴试验研究[J].岩土工程学报,2013,35(12):2322-2327(Chen Changlu,Shao Shengjun,Luo Aizhong,et al.True triaxial tests on structural effects on strength of intact loess[J].Chinese Journal of Geotechnical Engineering,2013,35(12):2322-2327(in Chinese))
[4]张常光,胡云世,赵均海.平面应变条件下非饱和土抗剪强度统一解及应用[J].岩土工程学报,2011,33(1):32-37(Zhang Changguang,Hu Yunshi,Zhao Junhai.Unified solution of shear strength for unsaturated soil under plane strain condition and its application[J].Chinese Journal of Geotechnical Engineering,2011,33(1):32-37(in Chinese))
[5]钱建固,吕玺琳,黄茂松.平面应变状态下土体的软化特性与本构模拟[J].岩土力学,2009,30(3):617-622(Qian Jiangu,Lv Xilin,Huang Maosong.Softening characteristics of soils and constitutive modeling under plane strain condition[J].Rock and Soil Mechanics,2009,30(3):617-622(in Chinese))
[6]王炜,骆亚生.陕西子洲原状黄土平面应变试验研究[J].人民黄河,2014(3):123-125(Wang Wei,Luo Yasheng.Study on the plane strain test of Shaanxi Zizhou undisturbed loess[J].Yellow River,2014(3):123-125(in Chinese))
[7]张玉,邵生俊,王丽琴,等.平面应变条件下土的强度准则分析及验证[J].岩土力学,2015,36(9):2501-2509(Zhang Yu,Shao Shengjun,Wang Liqin,et al.Analysis and verification of soil strength criterion in plain strain state[J].Rock and Soil Mechanics,2015,36(9):2501-2509(in Chinese))
[8]郑刚,颜志雄,雷华阳,等.天津市区第一海相层粉质黏土卸荷变形特性的试验研究[J].岩土力学,2008,29(5):1237-1242(Zheng Gang,Yan Zhixiong,Lei Huayang,et al.Experimental studies of unloading deformation properties of silty clay of first marine layer in Tianjin urban area[J].Rock and Soil Mechanics,2008,29(5):1237-1242(in Chinese))
[9]梅国雄,陈浩,卢廷浩,等.坑侧土体卸荷的侧向应力-应变关系研究[J].岩石力学与工程学报,2010,29(增1):3108-3112(Mei Guoxiong,Chen Hao,Lu Tinghao,et al.Reach on lateral stress-strain relation on side of foundation pit with lateral unloading[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(S1):3108-3112(in Chinese))
[10]李家贵,陈正汉,黄雪峰,等.Q3黄土侧向卸荷时的细观结构演化及强度特性[J].岩土力学,2010,31(4):1084-1091(Li Jiagui,Chen Zhenghan,Huang Xuefeng,et al.CT-triaxial shear tests on the meso-structure evolution and strength of unsaturated loess Q3 during unloading confining pressure[J].Rock and Soil Mechanics,2010,31(4):1084-1091(in Chinese))
[11]高帅,骆亚生,胡海军,等.非饱和原状黄土增湿条件下力学特性试验研究[J].岩土工程学报,2015,37(7):1313-1318(Gao Shuai,Luo Yasheng,Hu Haijun,et al.Triaxial tests on water immersion of unsaturated and undisturbed loess[J].Chinese Journal of Geotechnical Engineering,2015,37(7):1313-1318(in Chinese))
[12]张玉,邵生俊.平面应变加?卸荷条件下黄土的非线性变形特性的研究[J].岩土工程学报,2015,37(增1):185-190(Zhang Yu,Shao Shengjun.Non-linear stress-strain behaviors of loess under plane strain state of vertical loading and lateral unloading[J].Chinese Journal of Geotechnical Engineering,2015,37(S1):185-190(in Chinese))
[13]张玉,邵生俊.平面应变条件下黄土的竖向加载变形与强度特性分析[J].土木工程学报,2016,49(3):112-121(Zhang Yu,Shao Shengjun.An analysis of vertical loading deformation and strength characteristics of loess under plain strain condition[J].China Civil Engineering Journal,2016,49(3):112-121(in Chinese))
[14]张玉,何晖,赵敏,等.平面应变条件下原状黄土侧向卸载变形与强度特性分析[J].岩土力学,2017,38(5):1233-1242(Zhang Yu,He Hui,Zhao Min,et al.Analysis of lateral unloading deformation and strength characteristics of intact loess under plain strain condition[J].Rock and Soil Mechanics,2017,38(5):1233-1242(in Chinese))