A free-fall impact apparatus was used to examine the behavior of 160 mm diameter HDPE pipe systems with geocell-based protective layers, considering both the efficiency and the energy adsorption capacity under impact loading. The protective layers considered in this study are a granular soil layer of constant relative density, i.e., the reference case, and sand layers reinforced with a geocell layer with different sheet thicknesses and placement depths. In addition, the effect of the addition of a single layer of geotextile, geogrid, and geonet as an additional protection under the geocell was considered. The magnitudes of impact load as well as the resultant accelerations on the pipes were measured as a function of time during the experiments. Time histories of accelerations recorded in each test were used to calculate the displacements, which in turn led to the estimation of the level of energy absorbed by the protective layer systems. This enabled a fair comparison of the relative performance of each protective layer-pipe system under impact loading conditions. Thus, the results are indicative of the significance of the sheet thickness and placement depth of the geocell, as well as the collaboration potential of other geosynthetics with geocell when used as a protective layer. It was observed that all of the geocell-based protective systems contributed significantly to the pipe safety. When compared with the reference case, the reductions in the measured acceleration values on the pipes range between about 40% and 60% with the use of geocell protective layers only. On the other hand, the experimental results indicate that the most successful pipe protection performance under impact loading was achieved through the use of an additional 4 mm thick geotextile reinforced soil layer under a shallow geocell. A reduction of more than 90% in the measured accelerations was obtained for this system compared to the reference case.
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