Analysis Of Dynamic Shear Modulus And Damping Ratio For West Sichuan Unsaturated Mixed Soil

The west mountainous area of Sichuan Basin is located on the Longmen Mountain Fracture Zone, which belongs to Mediterranean-Himalayas Earthquake Belt—one of the main earthquake belts around the earthcrust. This area is famous for its complicated geological structure and frequent earthquakes. In this area, colluvium mixed soil is distributed widely, most of which is of unsaturated under natural condition. This thesis mainly deals with the dynamic shear modulus and damping ratio of West Sichuan unsaturated mixed soil. During the research period, the main jobs and achievements showed on the thesis are as follows:Firstly, ordinary physical and mechanical tests for five kinds of mixed soil from different landslides on West Sichuan were carried out. The tests include: XRD mineral composition analysis, natural water content and density test, specific density test of solid particles, particle size distribution of soil test, Atterberg limits water content test, etc. According to the result of XRD composition analysis, particles gradation, and plasticity index, three kinds of soil, which differ apparently in physical property and represent West Sichuan mixed soil typically, were selected to take the dynamic tri-axial test.Secondly, dynamic tri-axial test were carried out. Depending on the tri-axial test apparatus and the software Wolfram Mathematica, the dynamic deformation characteristic under equivalent seismic load and in narrow strain range was researched, while the dynamic test data was fitted by Hardin-Drnevich hyperbolic model, and the curves for dynamic shear modulus ratio function Gd/Gmax=Gd/Gmax(yd) and damping ratio function λ=λ(yd)were figured out. With the fitted curves, the influential factors for dynamic shear modulus and damping ratio, such as degree of saturation, particle size range, dry density, consolidation ratio, cyclic vibration times and frequency were analyzed, especially concentrating on the influence of degree of saturation and particle size range. The results proves that with the increase of degree of saturation, the dynamic shear modulus decreases while the damping ratio increase s and with the increase of particle size, the dynamic shear modulus and damping ratio increase together.Additionally, the experimental value of was compared to the reported value and the result shows that experimental value of maximum soil particle size 2mm in saturation approximates the reported value, while the others deviate to it.Finally, recommendation value of dynamic shear modulus and damping ratio for typical kinds of West Sichuan mixed soil was provided. Synthetically considering different influence factor, test data from specified soil and different degree of saturation was put together to be fitted as the recommendation dynamic shear modulus ratio and damping ratio functions. The recommendation value was calculated through the functions. The recommendation value can be used as reference value during seismic engineering design and earthquake engineering safety evaluation.