Experimental Study on Creep Characteristics of Structural Soft Clay under Lateral Unloading Condition
JIA Mincai1,2, ZHAO Shun1, ZHANG Zhen1
1. School of Civil Engineering，Tongji University，Shanghai 200092，China; 2. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education，Tongji University，Shanghai 200092，China
Abstract：Triaxial undrained creep tests under lateral unloading condition were carried out on the soft clay obtained from Ruian，Wenzhou，China to study the influence of lateral unloading path and structural properties on time-strain curves，isochronous curves and other typical creep properties. A creep stabilization time model of soft clay under lateral unloading condition was built to analyze the relationship between strain rate and creep failure criterion of soil，and then applied to structural soft clay soils with different stress paths from different regions to verify its applicability. The results show that creep failure occurred as the ratio of unloading to initial consolidation stress reached 0.2–0.3，and that the deformation of the soft clay can be divided into four stages，i.e.，instantaneous deformation，decaying creep，isokinetic creep and accelerated creep. When soil samples under different confining pressures are in the accelerated creep stage，there is a linear relationship between logarithm of strain rate and creep time；the critical line of accelerated creep can be used as a criterion for the unloading creep failure of structural soft clay. The creep stabilization time of structural soft clay is dictated by its structural properties. The axial strain of Wenzhou soft clay increased with an increase in the consolidation confining pressure when the lateral unloading creep failure occurred. Influenced by creep，the cohesion of structural soft clay under unloading condition declined more than 50%，while the internal friction angle remained basically unchanged，resulting in severe attenuation of the long-term strength of shallow structural soft clays and small strains of creep failure，which should be paid more attention to during construction and monitoring.
LIN H D, WANG C C. Stress-strain-time function of clay[J]. Journal of Geotechnical & Geoenvironmental Engineering, 1998, 124(4): 289-296
[2]
周秋娟,陈晓平. 典型基坑开挖卸荷路径下软土三轴流变特性研究[J]. 岩土力学,2013,34(5): 1299-1305ZHOU Qiujuan, CHEN Xiaoping. Research on rheological properties of soft clay under typical pit unloading paths[J]. Rock and Soil Mechanics, 2013, 34(5): 1299-1305
[3]
闫澍旺，张京京，陶琳，等. 等向固结饱和黏土卸载特性影响因素研究[J]. 岩土工程学报，2016，38（增刊2）： 42-47.YAN Shuwang，ZHANG Jingjing，TAO Lin，et al. Influencing factors for unloading characteristics in saturated clay[J]. Chinese Journal of Geotechnical Engineering，2016，38(S2)： 42-47.
[4]
付艳斌，朱合华，杨骏. 软土卸荷时效性及其孔隙水压力变化试验研究[J]. 岩石力学与工程学报，2009，28（增刊1）： 3244-3249.FU Yanbin，ZHU Hehua，YANG Jun. Experimental study of timedependent properties and pore water pressure of soft soil under unloading[J]. Chinese Journal of Rock Mechanics and Engineering，2009，28(S1)： 3244-3249.
[5]
NASH D F T, SILLS G C, DAVISON L R. One-dimensional consolidation testing for soft clay from Bothkennar[J]. Géotechnique, 1992, 42(2): 241-256
[6]
LEONI M, KARSTUNEN M, VERMEER P A. Anisotropic creep model for soft soils[J]. Géotechnique, 2008, 58(3): 215-226
[7]
谭儒蛟,焦宇杰,徐文杰. 天津滨海软土固结-蠕变特性及微观结构分析[J]. 工程勘察,2015,43(5): 14-17TAN Rujiao, JIAO Yujie, XU Wenjie. Study on the consolidation-creep characteristics and microstructure of the soft soil in Tianjin Binhai Area[J]. Geotechnical Investigation & Surveying, 2015, 43(5): 14-17
[8]
朱鸿鹄,陈晓平,程小俊,等. 考虑排水条件的软土蠕变特性及模型研究[J]. 岩土力学,2006,27(5): 694-698ZHU Honghu, CHEN Xiaoping, CHENG Xiaojun, et al. Study on creep characteristics and model of soft soil considering drainage condition[J]. Rock and Soil Mechanics, 2006, 27(5): 694-698
[9]
孔令伟,张先伟,郭爱国,等. 湛江强结构性黏土的三轴排水蠕变特征[J]. 岩石力学与工程学报,2011,30(2): 365-372KONG Lingwei, ZHANG Xianwei, GUO Aiguo, et al. Creep behavior of Zhanjiang strong structured clay by drained triaxial test[J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30(2): 365-372
[10]
何利军,孔令伟,张先伟,等. 湛江软黏土蠕变特性及经验模型[J]. 水文地质工程地质,2011,38(1): 59-64HE Lijun, KONG Lingwei, ZHANG Xianwei, et al. Creep properties and empirical model of soft clay in Zhanjiang[J]. Hydrogeology and Engineering Geology, 2011, 38(1): 59-64
[11]
王国欣,周旺高. 原状结构性土先期固结压力与结构强度的确定[J]. 岩土工程学报,2003,25(2): 249-251WANG Guoxin, ZHOU Wanggao. Determination of preconsolidation pressure and structural strength of undisturbed stryctual soils[J]. Chinese Journal of Geotechnical and Engineering, 2003, 25(2): 249-251
[12]
张震. 温州软黏土卸荷条件下工程特性研究[D]. 上海：同济大学，2017.
[13]
但汉波. 天然软粘土的流变特性[D]. 杭州：浙江大学，2009.
[14]
张先伟. 结构性软土蠕变特性及扰动状态模型[D]. 吉林：吉林大学，2010.
[15]
陈宗基. 地下巷道长期稳定性的力学问题[J]. 岩石力学与工程学报,1982(1): 7-26CHEN Zongji. Mechanical problems of long-term stability of underground tunnels[J]. Chinese Journal of Rock Mechanics and Engineering, 1982(1): 7-26
[16]
杨爱武,吴磊. 结构性海积软土强度与变形时效特性试验研究[J]. 地下空间与工程学报,2015,11(4): 919-925YANG Aiwu, WU Lei. Experimental study on time-dependent strength and deformation of structured marine soft soil[J]. Chinese Journal of Underground Space and Engineering, 2015, 11(4): 919-925
[17]
杨爱武，张兆杰，孔令伟. 不同应力状态下软黏土蠕变特性试验研究[J]. 岩土力学，2014，35（增刊2）： 53-60.YANG Aiwu，ZHANG Zhaojie，KONG Lingwei. Experimental study of creep property of soft clay under different stress conditions[J]. Rock and Soil Mechanics，2014，35(S2)： 53-60.
