Centrifuge testing of dual row retaining walls in dry sand: The influence of earthquake sequence and multiple flights

Abstract

Multi-hazard threats from tsunami events preceded by large earthquakes have been put into sharp focus in recent times. Dual row retaining walls are soil-structure systems that can have large lateral capacity with a small horizontal extent, making them ideal for the next generation of coastal protection. However, the dynamics of their behaviour is a complex interaction problem. Centrifuge tests, with multiple earthquakes within a single flight as well as multiple flights with varied embedment ratio were conducted to elucidate the mechanics of these systems when founded in dry sand. The structural response shows permanent, plastic deformations during the early cycles dependent mainly on the PGA superposed with more elastic vibrations during prolonged shaking. The development of the soil stresses and stiffnesses mobilised is used to explain the overall system response. Finally, the recorded structural and soil behaviour during swing up and down are combined to show that the soil stress and strain state is effectively reset between flights. Overall, useful methods for judging the progressive response of a complex soil-structure system are presented which can help justify future comparisons between experimental datasets and understand the implications of practical dynamic design.

Dual row retaining walls in dry sand: influence of wall stiffness on seismic response

“…4b, where the experiment featured a slightly larger input motion (PGA of 0.4 g vs. 0.35 g) which was applied after a sine sweep (PGA of ≈ 0.4 g at 1.7Hz), the match suggests the peak dynamic displacement was insensitive to the small variation in the input motion and motion order. The latter observation is in agreement with Madabhushi and Haigh (2019), where the effect of multiple shaking events could be understood through permanent plastic deformations accrued proportional to the PGA superposed with elastic vibrations during prolonged shaking.…”

“…The sequence of earthquake loadings applied to the centrifuge models is described by Madabhushi and Haigh (2019). The benefits of an initial, small (< 0.05 g) sine motion that may remove unstable soil arches present from the model construction process were shown.…”

“…Figure 3b shows that for system DS666 that the dynamic bending moments also cycle about the static distribution, with greater inward and outward bending induced every half cycle. The contrasting static distributions between the stiff and flexible walls is touched upon in Madabhushi and Haigh (2019), in the context of justifying the greater tie force for the stiffer systems, and is attributed to the tendency of the flexible walls to bow out between the tie and wall toe versus a stiffer wall which more rigidly rotates about the tie. Figure 3b substantiates this theory.…”

“…The terms relatively flexible and relatively stiff refer to the wall stiffness with respect the soil stiffness for the geometries investigated. The wall's flexural stiffness to soil stiffness ratio cannot be straightforwardly normalized by wall height as the soil stiffness is stress and strain dependent (Li, 1990;Madabhushi and Haigh, 2019).…”

“…In this paper the dynamic response of dual row retaining walls founded in dry sand is further examined, with the contrasting cases of systems with relatively flexible and stiff wall elements being presented. Madabhushi and Haigh (2019) previously showed experimental results from these cases, focussing on the effect of the earthquake sequence and multiple centrifuge flights. Measured temporal variations of the wall displacement, bending moment, tie force and soil stresses illustrated how the wall stiffness influences both the dynamic loads attracted and the resulting dynamic response.…”