Critical cyclic stress ratio of undisturbed saturated soft clay in the yangtze estuary under complex stress conditions

Abstract

There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index distinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus developed by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio were investigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic coupling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does.

Keywords

complex stress condition / undisturbed saturated soft clay / critical cyclic stress ratio / three-directional anisotropic consolidation / cyclic coupling shear / cyclic torsional shear

References

[1] Larew H G, Leonards G A. A repeated load strength criterion[C]. In: Proceedings, 41, Highway Research Board. Washington DC, USA, 1962. 529–556.

[2] Sangrey D A, Castro G, Poulos S J et al. Cyclic loading of sands, silts and clays[C]. In: Proceedings of the Specialty Conference on Earthquake Engineering and Soil Dynamics. Pasadena, California, USA, 1978. 836–851.

[3] Zhou J., Gong X., Li Jianqiang. Experimental study of saturated soft clay under cyclic loading[J]. Industrial Construction, 2000, 30(11): 43-47.

[4] Zhou J., Gong Xiaonan. Strain degradation of saturated clay under cyclic loading[J]. Canadian Geotechnical Journal, 2001, 38(1): 208-212.

[5] Wang J., Cai Y., Xu C., et al. Study on strain softening model of saturated soft clay under cyclic loading[J]. Chinese Journal of Rock Mechanics and Engineering, 2007, 26(8): 1713-1719.

[6] Wang J., Chen Z., Cai Y., et al. Study on dynamic stress-strain relationship of soft clay considering degradation of stiffness under cyclic loading[J]. Journal of Zhejiang University, 2007, 41(1): 23-28.

[7] Nnadi G. N., Mitchell R. J. Behaviour of cemented sandfills under repeated loadings[J]. Canadian Geotechnical Journal, 1991, 28(5): 746-752.

[8] Wang S., Gao Y., Mahfouz A. H. Experimental study on the critical cyclic stress ratio of lightweight sand-EPS beads soil (LSES)[J]. Journal of Disaster Prevention and Mitigation Engineering, 2007, 27(2): 171-176.

[9] Luan M., Nie Y., Yang Q., et al. Coupling cyclic tests on saturated clay under different waveforms[J]. Chinese Journal of Geotechnical Engineering, 2008, 30(9): 1276-1281.

[10] Erken A., Can Ulker B. M. Effect of cyclic loading on monotonic shear strength of fine-grained soils[J]. Engineering Geology, 2007, 89(3/4): 243-257.

[11] Luan M., Guo Y., Li M., et al. Development and application of soil static and dynamic universal triaxial and torsional shear apparatus[J]. Journal of Dalian University of Technology, 2003, 43(5): 670-675.

[12] Luan Maotian, Jin Dan, Zhang Zhendong et al. Liquefaction of sand under bi-directional cyclic loading[C]. In: Proceedings of Geotechnical Engineering for Disaster Mitigation and Rehabilitation, the 2nd International Conference for Disaster Mitigation and Rehabilitation. Nanjing, China, 2008. 387–397.

[13] Luan Maotian, Xu Chengshun, He Yang et al. Experimental study on behavior of saturated loose sands under complex shear loading[C]. In: Proceedings of the Fifteenth International Offshore and Polar Engineering Conference. Seoul, Korea, 2005. 491–497.

[14] Luan M., He Y., Xu C., et al. Experimental study on cyclic pore water pressure and volumetric changes of saturated loose sands under complex stress condition[J]. Earthquake Engineering and Engineering Vibration, 2005, 25(6): 127-134.

[15] Qi J., Luan M., Feng X., et al. Cyclic shearing deformation behavior of saturated clays[J]. Journal of Ocean University of China, 2007, 6(4): 413-420.

[16] Luan Maotian, Nie Ying, Tang Xiaowei et al. Experimental investigation on multidirectional loading under different initial stress states in clay[C]. In: Proceedings of the International Young Scholar’ Symposium on Rock Mechanics. Beijing, China, 2008. 133–137.