TRIAXIAL TESTS FOR DYNAMIC CHARACTERISTICS OF THE BEDDING FAULT MATERIAL WITHIN BASAL LAYER OF DAGUANGBAO LANDSLIDE

Daguangbao landslide is the largest landslide triggered by the 2008 Wenchuan earthquake.The sliding zone formed in a bedding fault which was composed of the material of mylonite and mud.The groundwater could be found flowing out.To analyze the process of earthquake dynamic characteristics of the saturated fault material, a series of dynamic triaxial tests were conducted on the three samples C₁, C₂ and C₃ which were taken from an exploratory tunnel in the fault.The results show that:(1)Under dynamic load(40 kPa, 60 kPa, and 80 kPa), C₁ and C₂ pore pressure shows slow growth, dynamic pore pressure is still far less than the confining pressure when achieving strain 5%, and the samples have no liquefactive.C₃ dynamic pore pressure is growing rapidly.When strain achieves 5%, dynamic pore pressure is equal to the confining pressure, and the sample is liquefied.(2)The dynamic strength and strain relations of sample are close.With the increase of strain, under the same cycles C₃ dynamic shear stress decreases obviously, while C₁ and C₂ have modest increase.(3)When the dynamic strain is certain, C₃ dynamic stress and the elastic modulus are the biggest, and its dynamic damping ratio is the least.C₂ dynamic stress and the elastic modulus are the least, and its dynamic damping ratio is the largest.It can be concluded that the fault material might be liquefied during the 2008 Wenchuan earthquake resulted in rapidly decreasing of the shear strength of the bedding fault.The Daguangbao landslide might be initiated suddenly.