The failure modes of geocell-reinforced retaining walls differ from those of rigid retaining walls, for which only limited information is available in the literature. In the present study, a series of centrifuge model tests was carried out to investigate the performances of geocell-reinforced retaining walls at limit equilibrium under various conditions. Digital image analysis was employed to determine the displacement vectors of soil and geocell-reinforced soil, which were used to obtain the failure surface and $g$ -level at limit equilibrium. The effects of the geocell pocket size, geocell layer height, geocell membrane tensile stiffness, and backfill surface loading location on the stability and failure mode were investigated. In addition, the preferred layout of geocell-reinforced sections, additional reinforcement layers, and two-tiered geocell retaining walls were studied. The test results indicate that the stability of geocell-reinforced retaining walls could be improved by reducing the spans between the welded spots of geocells, increasing geocell-membrane stiffness, and connecting additional geogrid layers to geocell walls. Two-tiered geocell retaining walls performed better than single-tiered ones at the same height. It was also found that the limit equilibrium method for slope stability analysis may be employed to predict the stability and critical failure surfaces of geocell-reinforced retaining walls. Some limitations of the present study are also discussed.

Since the 1980s, flexible geocell-reinforced retaining walls have been used more frequently for slope protection as an alternative to conventional retaining structures. The benefits of these geocell structures include light weight, rapid construction, cost-effectiveness, ecological protection and landscape enhancement. However, the deformation mechanisms and failure modes of geocell-reinforced retaining walls are often complicated, thereby restricting their use in engineering practice. The differences in failure behaviour between geocell-reinforced and rigid-facing retaining walls need to be identified. In the present study, a series of centrifuge model tests on retaining walls reinforced by geocells were performed. The tests varied with respect to aspect ratio (the reinforcement length to the height of the wall) and the slope inclination (horizontal to vertical). The experimental results indicate that the critical failure surface is a non-linear shape that passes through the toe of the wall and intersects with the back of the wall. As the aspect ratio decreased, the horizontal distance between the top of the critical failure surface and the wall increased, whereas the location of the critical failure surface intersecting with the wall moved downward. In the case of a smaller inclination angle, the critical failure plane had a compound shape that included part of the backfill material near the top portion of the wall. In the case of a larger inclination angle, the size of the sliding zone was small and the failure was mainly due to sliding of the wall along the slope. The internal displacement distributions in the sliding zone were measured using digital image analysis and indicated that the locations of the maximum lateral face displacement in geocell retaining walls differs from those in conventional rigid retaining walls.

Geocell-reinforced retaining walls are widely used in engineering practice due to their advantages of light weight, simple construction, low environmental impact and aesthetics. However, limited studies can be found on the failure mechanisms and method of stability analysis for this type of earth structure. In this study, limit equilibrium analysis to predict the global stability of geocell-reinforced retaining walls is conducted. The results indicate that the classical Rankine and Coulomb theories of earth pressure are not suitable for analyzing the stability of geocell-reinforced retaining walls. Instead, the failure mechanisms of geocell-reinforced retaining walls are similar to those of slopes. The general limit equilibrium method, with an assumption of a polygonal failure surface and assisted by the improved Monte Carlo searching technique, may reproduce the critical failure surface. The analyzed factor of safety along the critical failure surface may be somewhat higher than the actual one; this difference is related to the soil density and progressive failure of soil along the critical failure surface. The effectiveness of the analytical approach is validated by two sets of model tests. It is shown that the stability of geocell-reinforced retaining walls may be analyzed by the general limit equilibrium method, provided that the apparent cohesion of geocell-reinforced soil is accurately estimated and the shape of the critical failure surface is properly assumed.

A series of triaxial compression tests with different confining pressures were conducted for gravels, road surface milling materials, and surface–base milling mixtures to investigate the stress–strain relationships of these three kinds of materials. On the basis of the analysis of the test results, the strength and the deformation of the geocell-reinforced surface milling materials and the geocell-encased surface–base milling mixtures were predicted and compared with those of the gravels via the constitutive model of geocell–soil composites. The effects of the geocell pocket size, tensile stiffness, and the peak internal frictional angle on the stress–strain responses of the geocell-reinforced surface–base milling mixtures were examined. Moreover, by employing the finite element strength reduction technique, stability analysis was conducted on the geocell-reinforced retaining wall with the surface–base milling mixtures to investigate the factor of safety and the failure mechanism of the structure. The study results indicated that the surface milling materials exhibited strain hardening, while the gravels and the surface–base milling mixtures exhibited strain softening. The surface milling materials displayed evident shear contraction characteristics, whereas the gravels and surface–base milling mixtures first displayed shear contraction and later dilatancy features. In addition, the strength of the geocell-reinforced surface milling materials is smaller than that of the gravels, but the strength of the geocell-encased surface–base milling mixtures is larger than that of the gravels. Thus, the geocell-reinforced surface–base milling mixtures can be used to replace the gravels in engineering practices. Additionally, the size of the sliding wedge and the factor of safety of the retaining walls increase significantly with reductions in the geocell pocket size.

Reinforced soil structures are widely used in civil engineering for the slope protection because of their unique advantages. However, the failure mechanism of such structures has not been fully studied. In this paper, the stability analysis of reinforced slopes is carried out based on the limit equilibrium method. Furthermore, the effects of the location, the length and the tensile strength of the reinforcement layers on the safety factor and the critical failure surface are investigated. The research results indicate that the above parameters have great effects on the safety factor and the critical failure surface of the reinforced slope. However, the effects of the length and the tensile strength of the reinforcement on the location where the failure surface starts are not significant. Based on the analysis of computation results, the failure mechanism is analyzed and the optimum design scheme of the reinforced slope is recommended.