Seismic behavior of geosynthetic reinforced retaining structures with cohesive backfills

In this study, seismic performance of geosynthetic-reinforced modular block retaining walls backfilled with cohesive, fine grained clay-sand soil mixture was investigated. Four model walls were constructed and shaking table tests performed for three ½ scaled (wall height 190 cm) and ¼ scaled model walls were evaluated to investigate the effects of backfill type, the influence of reinforcement length and the scaling effects. Scaled versions of the recorded El Centro and Kobe earthquakes were applied to the model walls. Polyester geogrids were used in the tests with a vertical spacing of 20 cm. Reinforcement length to wall height ratio was 0.8 (for one model 0.6 was used). A 12.5° battered facing was constructed with modular hollow concrete blocks. Model walls were instrumented by 8 accelerometers, located on facing and on backfill surface. 8 laser displacement transducers were used and 15 strain gages were located on three geogrid layers at top, mid and bottom heights of wall. Maximum and permanent displacements on front wall, acceleration amplification ratios on front wall and inside the backfill, strain values to calculate tensile loads on reinforcements and visual observations for facing and backfill surface were the results of this test to evaluate the performance of cohesive backfilled model wall. No stability problem was occurred under extreme seismic loading. Any indication of failure was not observed except minimal residual deformations on the facing during base excitations. And acceptable tension cracks were observed on the backfill surface after final seismic motions. As a result it can be said that; the model walls with cohesive backfill performed well under seismic loading conditions when compared with granular backfills and checked with the limit design values described in previous studies.