Experimental Study On Dynamic Shear Modulus And Damping Ratio Of Loess Under Complex Initial Stress States

As a kind of regional special soil, loess is widely distributed in middle and western areas of China, where earthquake often happens and the seismic intensity is high. In recent years, with the increment of engineering constructions, the load effect of cyclic traffic, earthquake and waves puts forward new challenges to the engineering anti-earthquake design in loess area. Therefore, it is of great practical significance to obtain reasonable loess dynamic characteristic parameters and provide more accurate reference for the engineering anti-earthquake design in loess area.It is hard to simulate the complex initial stress state of soil in practical projects by using the conventional triaxial test apparatus. Therefore, based on the improved DTC-199 type electro-hydraulic servo cyclic torsional dynamic triaxial apparatus, the effects of dry densityρd, moisture content w, initial angles of principal stressα0, initial coefficient of intermediate principal stress b0, initial deviator stress ratioη0 and initial average principal stress pm0 on dynamic stress ~ strain (τd ~γd) relations, dynamic shear modulus Gd and damping ratioλof loess under complex initial stress states are investigated. The conclusions are as follows:(1) Dynamic stress ~ strain (τd ~γd) relations of loessOther conditions being the same, the same dynamic shear stressτd produces less dynamic shear strainγd on undisturbed loess than on remodeled loess. Other conditions being the same, the biggerρd, or the lower w, or the smallerα0, or the smallerη0, or the bigger pm0, the biggerτd which generates the sameγd. The effect law of b0 on theτd ~γd relations of loess is not obvious.(2) Dynamic shear modulus Gd of loessOther conditions being the same, Gd, G0 andτdmax of undisturbed loess are greater than them of remodeled loess.w, pm0 andη0 have some influence to different degree on the Gd, G0 andτdmax of loess. Other conditions being the same, the lower w or the bigger pm0, the bigger Gd, G0 andτdmax. The biggerη0, the quicker of the attenuation rate of Gd with the increment ofγd. Other conditions being the same,ρd andα0 have little effects on Gd of loess. The biggerρd or the smallerα0, the bigger G0 andτdmax. The effect law of b0 on Gd, G0 andτdmax of loess is not obvious.(3) Damping ratioλof loess The damping ratiosλof loess first decrease with the increase ofγd, and then increase gradually under the condition of initial pre-shearing stresses. The existing method of using semilogarithmic coordinates to fit the line equation is no longer applicable to the calculation ofλof loess under that condition. The value ofλunder complex initial stress states is 0.15 to 0.4.Under the condition of high pm0 and high w, the effects of structural state onλof loess show a trend thatλof remodeled loess is greater than that of undisturbed loess. Other conditions being the same, the effects of w,α0 andη0 onλ~γd of loess show a trend that the higher w, the biggerα0 or the biggerη0, the biggerλ. The effects ofρd, b0 and pm0 onλ~γd of loess is not obvious.