Large-scale shaking table tests on the seismic responses of soil slopes with various natural densities

To distinguish how the natural density of soil affects the seismic response of a soil slope, three large-scale shaking table tests are conducted on slopes of different densities under seismic excitations. The natural density of the homogeneous dense slope (HDS, case #1) is 1.65 g/cm(3); that of the heterogeneous graded slope (HGS, case #2) increases from 1.35 g/cm(3) to 1.65 g/cm(3) with depth; that of the homogeneous loose slope (HLS, case #3) is 1.35 g/cm(3). The failure processes, acceleration response laws, spectral characteristics, dynamic strain responses and shear stress-strain behaviours observed during the three tests are compared. The results show that the soil density distribution has a significant effect on the seismic response of a slope. The HGS and HLS fail suddenly under peak ground accelerations (PGAs) of 0.6 g and 0.5 g, respectively. The failure zone in the upper HLS is larger than that in the HGS. The acceleration amplification effect of the HDS is weak, while those of the HGS and HLS gradually increase with the PGA. The position and energy required to produce a nonlinear acceleration amplification factor effect are closely related to the natural density of the slope. The acceleration amplification factors of the HGS and HLS show nonlinear effects at 0.50 times and 0.357 times the slope height, respectively, and the corresponding PGAs are 0.4 g and 0.3 g. With an increasing natural density, the acceleration amplification factor decreases gradually, and more energy is required for the slope to fail under earthquake activity. The acceleration response law is related to the shape and amplitude of the peak in the fast Fourier transform (FFT) spectrum. The dominant frequency differences among the FFT spectra show that the lower the natural density of the slope is, the lower the location of damage in the slope. Combining the results of the peak micro-strain and shear stress-strain behaviour of the three slopes, the shear modulus of the HDS is the highest, and that of the HLS is the lowest.