Shaking table tests on gravel slopes reinforced by concrete canvas

Abstract

The behaviour and performance of different reinforced slopes during earthquake loading were investigated through a series of shaking table tests. Concrete-canvas and composite reinforcement (geogrid attached to concrete-canvas) were proposed for reinforcing slopes. By considering the effects of different reinforcement methods, the seismic responses of the reinforced slopes were analysed, along with the accelerations, crest settlements, and lateral displacements. The failure patterns of different model slopes were compared using white coral sand marks placed at designated elevations to monitor the internal slide of the reinforced slopes. Both the concrete-canvas and composite reinforcement could increase the safety distance, which ranged from the slide-out point to the back of the model box. The composite reinforcement decreased the volume of the landslide and increased the failure surface angle as a result of the larger global stiffness in the reinforced zone. These results indicate that the recently developed concrete canvas has a better effect on restricting the slope deformation during seismic loading than the nonwoven geotextile reinforcement, and that the use of composite reinforcement could improve the seismic resistance of slopes.

Introduction

In seismic active regions, earthquake induced collapses constitute a part of devastating natural disasters. However, reinforced slopes and retaining walls can be used to reduce the damage. These should show satisfactory seismic performance and cost effectiveness. Reinforcement materials can be characterized as inextensible and extensible ones. Extensible geosynthetic reinforcement is often used in slopes and can enhance the performance of slopes by decreasing deformation. Building steep reinforced slopes in less space has been an interesting topic to geotechnical engineers over the years.

Geosynthetic reinforced walls have been widely used in the past few decades given their good performance in terms of the ductility of structures (EI-Emam and Bathurst, 2007; Murali Krishna and Madhavi Latha, 2007; Panah et al., 2015; Yazdandoust, 2017; Song et al., 2018; Huang, 2019; Fan et al., 2020; Xu et al., 2020). To examine the influence of reinforcement parameters (i.e., the length, stiffness, and vertical spacing) on wall design, El-Emam and Bathurst (2007) performed model tests with rigid facing slabs. Furthermore, Panah et al. (2015) conducted massive experiments on 80-cm-high walls reinforced by polymers. Those researchers also discussed the influence of the reinforcement material arrangement on the model response. However, compared with reinforced walls, studies on the dynamic responses of reinforced slopes with gentle slopes are relatively limited, particularly studies on gravel slopes (Lin et al., 2015; Edinçliler and Toksoy, 2016; Srilatha et al., 2016; Xu and Yang, 2019; Wang et al., 2019). Meanwhile, for reinforced slopes, most studies have focused on the reinforcing effect of geotextile. For example, Huang et al. (2011) conducted shaking table tests on geotextile reinforced slopes with a stepwise intensified sine load. The results showed that the acceleration amplification factor is a function of the base frequency and that a change from an amplification state to a de-amplification state occurred when the input ground acceleration reached a certain level. Srilatha et al. (2013) investigated the influence of seismic frequency on the dynamic responses of geotextile reinforced slopes. They found that the displacement increased proportionately with the seismic frequency, whereas frequency had little effect on the acceleration amplifications. Furthermore, Srilatha et al. (2016) investigated the effects of different reinforcement materials (geotextiles and geogrids) on the response of a model slope. Their results showed that a geotextile-reinforced slope better reduced lateral deformation compared to a geogrid-reinforced slope, and that varying the reinforcement quantity had no effect on the acceleration amplification. As the strength between the geotextile and backfill interface is relatively low, particularly in multi-layered interfaces, sliding problems of reinforced soils are often caused by the weakening of the interaction between the reinforcement and the soil. Fortunately, a recently developed concrete canvas has demonstrated good tensile strength and bond force, which could significantly increase the friction between the backfill and reinforcement. Therefore, it would be worthwhile to investigate the seismic performance of the concrete canvas in reinforced slopes.

This study evaluates the performance of a proposed concrete-canvas reinforcement and composite reinforcement (geogrid attached to concrete-canvas) in reinforcing slopes. By considering the effects of different reinforcement methods, the behaviour and performance of the reinforced slopes during seismic excitation were analysed, along with the accelerations, crest settlements, and lateral displacements. The failure patterns of different model slopes were compared by monitoring the residual length of white coral sand marks placed at designated elevations. Furthermore, the safety distance from the slide-out point to the back of the model box was calculated under the conditions of concrete-canvas and composite reinforcements.