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Results of full-scale field impact load tests on HDPE pipes with geogrid protective layer

Considering the limitations due to scale issues with laboratory experiments, field impact load tests were conducted on 600 mm diameter instrumented HDPE pipes of 2000 mm length, protected with geogrid layers of varying properties. The impact load was obtained by the free fall of a 3125 N con-crete block from a height of 3 m. The behavior under impact loads was investigated considering both the efficiency in terms of reducing the impact load transmitted to the pipe and the pressure adsorption capaci-ty. The protective layers considered in this study are a granular soil layer of constant relative density, i.e., the reference case, and sand backfill reinforced with geogrid, strip geogrid, and strip composite geogrid layers. In addition, a geotextile layer with a density of 600 g/m2 was also used. The magnitudes of accel-erations on the pipe and pressure in the soil at various depths were measured during the experiments with two sets of accelerometers and pressure cells. The results demonstrate the efficiency of geosynthetics-based protection systems under impact loading conditions, with significant reductions both in the acceler-ations and the loads transmitted to the pipes compared to the reference case. It was observed that geotex-tile in general performed superior to geogrids under impact loads for the specific types employed in this study. The reductions in the measured acceleration values on the pipes range between 50% and 60% for the load tests that involve geogrids, whereas a reduction of more than 80% was measured for those that employed geotextile. However, the use of geotextile and non-strip geogrid resulted in similar efficiencies when the cost was also taken into consideration.