Influence of the Geosynthetic Type and Compaction Conditions on the Pullout Behaviour of Geosynthetics Embedded in Recycled Construction and Demolition Materials

The effects of the climate change that the planet has been experiencing, and the growing awareness of citizens that natural resources are finite, highlight the inevitability of making society more sustainable. Since the construction industry is responsible for a high consumption of natural resources and it simultaneously produces high volumes of waste, it is of great importance to investigate the feasibility of using construction and demolition (C&D) wastes as alternatives to common natural materials. This paper investigates the feasibility of using fine-grain recycled C&D wastes as backfill material of geosynthetic reinforced steep slopes, through a laboratory study focused mainly on the pullout behaviour of two geosynthetics embedded in these alternative materials. The influence of the geosynthetic type, moisture content and compaction degree of the recycled C&D material on the pullout behaviour is assessed and discussed. The physical and mechanical characterization of the filling material is also presented. The pullout test results have pointed out that, although the two geosynthetics have similar tensile strength, the pullout resistance of the geogrid is higher than that of the geotextile and is achieved at lower frontal displacements. While the reduction of the compaction moisture content below the optimum value induced a slight decrease in the geogrid pullout resistance (ranging from 5% to 7%), conversely the pullout capacity of the geotextile increased up to 22%. The compaction degree of the recycled C&D material had the expected effect on the geotextile pullout resistance, reflected in an increase of about 20% when the degree of compaction rose from 80% to 90%. However, the expected trend was not observed on the geogrid pullout behaviour. The pullout interaction coefficient tended to decrease with the variation of the compaction moisture content around the optimum value (maximum decrease of 33% and 16% for the geogrid and the geotextile, respectively) and with an increase in the vertical confining pressure from 10 kPa up to 50 kPa (decrease around 25%). The average value of the pullout interaction coefficient, fb, ranged from 0.61 to 1.09 for the geogrid and from 0.67 to 1.25 for the geotextile. From all these findings it can be concluded that recycled C&D materials can be seen as an environmentally friendly alternatives to the natural resources commonly used in the construction of geosynthetic-reinforced embankments.