Experimental Study On Dynamic Characteristics Of Expansive Soil

Expansive soil is widely distributed in China and many other countries and regions allover the world. With the typical properties of water swelling and drying shrinkage, expansivesoil has great damage effects to buildings especially lightweight buildings, roadbeds, airports,slope sides of the channel, dams, etc, and the harm is growing as construction developsrapidly. Currently, soil dynamics has become an important research topic of soil mechanicsdue to the nature geological disasters, such as earthquakes, occur frequently. For its particularmicrostructure, during dynamic loading the response of expansive soil is unique andcomplicate, and it is easy to cause disasters. The study on dynamic characteristics ofexpansive soil is very important and necessary.The paper based on the improved DTC-199type electro-hydraulic serve cyclic torsionaldynamic triaxial apparatus, studied the dynamic characteristics of expansive soil underdifferent initial angles of principal stress, dry density, moisture content and confining pressure,and the conclusions are follows:(1) Dynamic strength of expansive soilOther conditions being the same, the bigger α0, the higher w, the lower σc, the smallerdynamic strength of expansive soil, and the influence becomes more obviously when the w isover plastic limit.The normalization trend of τd/σ3～lgN curve is poor under the same α0, and the bigger α0,the poorer normalization trend. The normalization trend of τd/σ3～lgN curve is not obviousunder the same w, and the higher w, more obvious the normalization trend of τd/σ3～lgNcurve.With the vibration times increase, the dynamic strength indexes of expansive soil cdandφddecrease, and are stabilized gradually. The dynamic strength indexes of expansive cdand φddecrease as the increases of α0, and the influence on φdis stronger than that on cd. Thedynamic strength indexes of expansive cdand φddecrease as the increases of w, and theinfluence on cdis stronger than that on φd.(2) Dynamic deformation of expansive soilOther conditions being the same, the smaller α0, or the bigger ρd, or the lower w, or thebigger σc, the bigger τdwhich generates the same γd, and the influence of w on τd~γdis less obvious with high moisture content.With the γdincrease, the Gdof expansive soil decrease, and is stabilized gradually. Whenthe γdis small, the Gdof expansive soil drops severely.Other conditions being the same, the higher α0, the bigger Gd, G0and τdmax. The value ofλ under different α0states is0.2-0.4, and α0has some influence to degree on the λ, otherconditions being the same, the bigger α0, the higher value of λ.Other conditions being the same, the higher σc, or the bigger ρd, or the lower w, thebigger Gd, G0and τdmaxof expansive soil. The slower of the attenuation rate of Gdwith theincrement of γdwhen w is over plastic limit. The influence of w on the Gdof expansive soil ismore obvious with higher σcand ρd, and the influence of σcand ρdon the Gdof expansive soilis less obvious with higher w. The value of λ under simple initial stress states is0.15-0.35.Other conditions being the same, the effects of w and σcon λ~γdof expansive soil show atrend that the higher w or the bigger σc, the smaller λ. The effects of ρdonλ~γdof expansivesoil is not obvious.