Experimental study on seismic deformation modes of reinforced-soil walls

A series of 1-g shaking table tests were conducted on 1 m high reinforced-soil wall models. The physical models were subjected to harmonic sinusoidal-like time history input motions at frequencies of 2, 5, 8 and 10 Hz. The effects of parameters such as soil density, reinforcement length, spacing and stiffness on the seismic response of the model walls were studied. Free-sliding toe boundary and wrap-around wall facing were selected to reveal all potential deformation modes of the wall and different deformation shapes of the facing. Different deformation modes (overturning and bulging) of the facing as well as base sliding were observed. Determinant parameters in the formation of each mode were identified by introducing internal failure indexes. A bulging index was introduced to measure the bulging intensity of the wall facing. Additionally, the distribution of the shear stiffness modulus (G) and damping ratio (D) of the reinforced soil along the wall height were assessed. The effect of the confining pressure (σv) and shear strain on variations of G and D were traced. G proved to be dependent on σv and, as expected, to be incremental with depth below the crest of the wall. Based on measurements and relevant approximations, no incremental or decremental patterns for D were detected along the wall height. Moreover, at large strains of about 10−3, an average D of about 20% was observed. Overall, based on the results of physical model testing in this study, which confirm similar findings of previous research, it was concluded that reinforcement stiffness is a key parameter dominating the seismic response and deformation mode of a wall and not reinforcement ultimate tensile strength, which is currently used as the main parameter for wall design in existing codes.