True triaxial tests on unsaturated soils with suction-controlled condition
ZHENG Fang1, SHAO Sheng-jun1, 2, ZHANG Bo1, SHE Fang-tao1
1. Institute of Geotechnical Engineering, Xi’an University of Technology, Xi’an 710048, China; 2. Shaanxi Key Laboratory of Loess Mechanics and Engineering, Xi'an 710048, China
Abstract:Based on the new true triaxial apparatus of Xi’an University of Technology, the pedestal of the pressure chamber is installed with a high-air-entry-value ceramic disk and porous plate is placed on the top of the specimens. Thereby, the pore-gas pressure and pore-water pressure can be independently controlled and measured. Thus the axial translation technique is used to control the matric suction. In addition, the true triaxial apparatus is newly equipped with a water-air control panel unit and the pneumatic duplex pieces, which makes the true triaxial apparatus further improvement to control suction. On this basis, the consolidation drainage true triaxial tests are firstly conducted on the remolded loess with suction and net mean stress controlled condition. During the tests, the matric suction (s=100 kPa) and the net mean stress (p= 300 kPa) are kept constant. The measured curves of variation of deviatoric stress (q) versus major, intermediate and minor principal strains (,,) are analyzed under different intermediate stress parameters (b=0,0.25,0.5,0.75,1). In addition, the failure loci of the remolded loess on -plane are given, and the comparision is made between the experimental results and the predicted failure loci of Lade-Duncan failure criterion and Mohr-Coulomb failure criterion.
[1] 詹良通, 吴宏伟. 非饱和膨胀土变形和强度特性的三轴试验研究[J]. 岩土工程学报, 2006, 28(2): 196-201. (ZHAN Liang-tong, NG C W W . Experimental study on mechanical behavior of recompacted unsaturated expansive clay[J]. Chinese Journal of Geotechnical Engineering, 2006, 28(2): 196-201. (in Chinese)) [2] 方祥位, 陈正汉, 申春妮, 等. 原状Q2 黄土三轴剪切特性[J]. 岩石力学与工程学报, 2008, 27(2): 383-389. (FANG Xiang-wei, CHEN Zheng-han, SHEN Chun-ni, et al.Triaxial shear properties of undisturbed loess Q2 [J]. Chinese Journal of Rock Mechanics and Engineering, 2008, 27(2): 383-389. (in Chinese)) [3] SAFFARI P, NOOR M J M, HADI B A, et al. Laboratory Test methods for shear strength behavior of unsaturated soils under suction control, using triaxial apparatus[M]// In CIEC 2014, Springer Singapore, 2015. [4] 申春妮, 方祥位, 陈正汉. 非饱和重塑Q2黄土的三轴试验研究[J]. 地下空间与工程学报, 2010, 6(3): 503-508. (SHEN Chun-ni, FANG Xiang-wei, CHEN Zheng-han.Triaxial tests of unsaturated remolded Q2 loess[J]. Chinese Journal of Underground Space and Engineering, 2010, 6(3): 503-508. (in Chinese)) [5] 陈存礼, 张登飞, 董玉柱, 等. 常含水率三轴条件下非饱和原状黄土的吸力和力学特性[J]. 岩土工程学报, 2014, 36(7): 1195-1202. (CHEN Cun-li, ZHANG Deng-fei, DONG Yu-zhu, et al.Suction and mechanical behaviours of unsaturated intact loess from constant water content triaxial tests[J]. Chinese Journal of Geotechnical Engineering, 2014, 36(7): 1195-1202. (in Chinese)) [6] MATSUOKA H, SUN D, KOGANE A, et al.Stress-strain behaviour of unsaturated soil in true triaxial tests[J]. Canadian Geotechnical Journal, 2002, 39(3): 608-619. [7] HOYOS L R, PÉREZ-RUIZ, DIEGO D, PUPPALA A J. Refined true triaxial apparatus for testing unsaturated soils under suction-controlled stress paths[J]. International Journal of Geomechanics, 2012, 12(3): 281-291. [8] 石建刚, 邵生俊, 陶虎, 等. 非饱和土的真三轴试验及强度变形特性分析[J]. 岩土工程学报, 2011, 33(增刊1): 85-90. (SHI Jian-gang, SHAO Sheng-jun, TAO Hu, et al.True triaxial tests and strength deformation behaviors of unsaturated soils[J]. Chinese Journal of Geotechnical Engineering, 2011, 33(S1): 85-90. (in Chinese))