Large-scale dynamic triaxial tests on saturated gravel soil in Nanning metro area

The gravel soil in Nanning metro area is taken as the research object, and a series of large-scale drained dynamic triaxial tests are conducted on saturated gravel. The effects of the relative density, dynamic stress amplitude and number of loading cycles on the accumulation strain, stress-strain hysteresis loops and pore pressure of saturated round gravel are analyzed. The experimental results show that when the dynamic stress amplitudes are small, the curves of accumulated axial strain with number of loading cycles are stable with the increasing rule of hyperbolic function. A linear relation between the parameter α in the hyperbolic function and the relative density D_r is found. However, the curves exhibit failure type and the increasing rule conforms to power function under a large dynamic stress amplitude. The stress-strain hysteresis loops of saturated round gravel exhibit double-lined type. When the dynamic stress amplitude is small, with the increasing number of loading cycles, the area of hysteresis loops firstly increases and then decreases, the secant modulus firstly decreases and then increases, and the pore pressure firstly increases and then decreases. In the later period of cyclic loading, the pore pressure is high when D_r=0.5 in comparison to the situation D_r=0.3 or 0.7, and this result relates to the gravel breaking characteristics at different initial relative densities.