Earthquake, vehicles passing, mechanical vibration etc. dynamic load affect the shear strength and stability of soil-body, and it will induce hazard project accident such as foundation settlement and slippage, incline of construction, building collapse. Dynamic load cause easily serious cataclysm of geological environment such as landslide, dilapidation of embankment, ground subsidence. So the dynamic load has become the main external dynamic power that lead to geotechnical Engineering and geological disasters. Tri-axial shear tests are done before and after vibratory load acting, and testing samples are the red clay in Xiamen. The effects of vibratory loading on sample's cohesive force, internal friction angle, shear strength equation and the ability to resist side distortion etc. are studied by analyzing test data. After vibratory load acting, the cohesive strength index and internal friction angle of the sample are decreased by 51.72%and 50% respectively; and the shear strength curve shifts down obviously under same testing conditions, and the results show that vibratory load acting is disadvantage to stabilization and bearing capacity of red clay. The research conclusions have theoretic and practical significance for us to prevent geotechnical engineering disasters and geologic disasters.
Xiamen is located in the southeast coast, subtropical monsoon climate here; under the impact of ocean air masses, the local climate is hot and humidity. Typhoons, heavy rain, and large precipitation always raid here in summer; mountains and hills occupy large areas, topography and geological condition are complex and changeable, mountain erosion and weathering effect are quite strong, red clay develops well.[1] Xiamen city is experiencing a new upsurge in building, to achieve development by leaps and bounds as a Gulf City. A large number of projects, such as Xiamen Sea bottom Tunnel, High-speed Urban Road, CIGFE(China International Gardening & Flower Expo), Dongdu International Tourism Dock, Renovating and Developing Rounding East Sea Area, Coast reinforcement & Dike, Transformation of old city and new area development, etc, have been built, most of these projects are built on the soil ground; the foundation bearing capacity, the shoring of deep foundation ditch projects and so on, are closely related to the characteristic of the shear strength of soil.[2] However, the dynamic loads, such as Earthquake, vehicles passing, mechanical vibration etc, directly affect the shear strength and overall stability of soil, and may induce hazard project accident and geological disaster, such as destroy of foundation, the incline and collapse of projects, the instability and landslide of soil. So, it has important theoretical and practical significance for us to improve the design of foundation in Xiamen, to eliminate the construction security risks, and to reduce geotechnical geological disasters by studying the variety characteristics of shear strength of red clay under the dynamic loads.
