Dynamic behavior of wrap-faced reinforced soil retaining wall on soft clay

Abstract

This research aimed to understand the dynamic behavior (acceleration amplification, displacement, strain, and pore water pressure) of wrap-faced reinforced soil retaining wall resting on soft clayey soil. It also investigated the response of wrap faced reinforced soil retaining wall with respect to sand types (Sylhet and Local), surcharge loads, and relative densities under dynamic loading. For these purposes, experimental study and numerical simulations were carried out.

The experimental study was basically a model study using a shake table. The test scheme included a succession of 1D Shake Table Tests (STT) with 0.05g to 0.2g base acceleration on 0.4 m high wrap faced reinforced-soil wall model, which was placed over 0.3 m high soft clayey soil foundation. To assess the seismic behavior, the model was subjected to harmonic sinusoidal input motions at frequencies of 1 Hz, 2 Hz, 3 Hz, and 5 Hz. The model was also subjected to earthquake loadings (1995 Kobe earthquake, Japan and 1989 Loma Prieta earthquake, USA). In order to incorporate the influences of soil, a laminar box was used to contain the soil during the experiments. The base excitations, frequencies, and surcharge pressures were varied in several shake table tests with different relative densities (48%, 64%, and 80% for Sylhet sand and 27%, 41%, and 55% for local sand). A total of 576 (Five hundred and seventy-six) shaking table tests for harmonic sinusoidal wave and 144 (One hundred and forty-four) for earthquake wave (Kobe and Loma Prieta) were carried out on this model embankment. The levels of base acceleration, intensities of frequency and magnitude of surcharge loads had a significant influence on the model wall and varied along the elevation. The acceleration amplification, faced displacement, pore water pressure, and strain were also influenced by the base excitation, frequency, surcharge pressure and relative density.

The response of wrap faced reinforced soil retaining wall was also compared with a similar model developed by a numerical model using PLAXIS3D software. After defining soil stratigraphy, the embankment and wrap faced retaining wall was defined. In the next step, the mesh was generated. After assigning the loadings, the calculation was performed. The results obtained from PLAXIS 3D were compared with the results obtained from model shake table tests. The results of this study revealed that input accelerations, frequency, and surcharge load had significantly influenced the acceleration amplification, faced displacement, excess pore water pressure, and strain changes along the elevation. Acceleration response was increased with the increase in base acceleration, the difference being more perceptible at higher elevations. The displacement, pore water pressures, and strain were found to be high for high base shaking and low surcharge pressures at higher elevations. The strains of the bottom-layer were the smallest, and the strains of the top-layer were the largest, which indicated that the geotextiles located in the top layers play important roles in the seismic stability of the wrap faced reinforced retaining walls. The walls constructed with higher backfill relative density had shown lesser face displacements, strain and acceleration amplification compared to the walls constructed with lower densities when tested at higher base excitation. The experimental result was found to be lower than the numerical result, the deviation was less than 15%. These results are helpful to observe the dynamic behavior of the wrap faced soil retaining wall on the soft clay layer, which is useful for the design process of this type of retaining wall considering the dynamic loading conditions in Bangladesh.