Design of reinforcement geosynthetics in landfill piggyback expansion Roll placement The PVA reinforcement geosynthetic is unrolled on a base that has been graded and compacted (Figure 7). The product is placed with the woven geotextile on top to protect the high-tenacity yarns during the backfilling. Two layers of geosynthetics were installed, perpendicular to each other, with a soil layer in between. Overlaps Side-by-side (longitudinal) connections are achieved with a minimum overlap of 12 inches (300 mm) following the direction of the backfill placement. FIGURE 7 Installation of reinforcement geosynthetic Bottom ash material placement The incinerator bottom ash material is free of foreign matter that could damage the geosynthetic. A 1-foot (300-mm) thick layer has been placed between the two geosynthetic layers to improve the interface friction properties (Figure 8). Monitoring The implementation of a monitoring system to record the settlements of the reinforcement geosynthetic aims to validate and refine the calculation and assumptions considered in the geotechnical model and to better understand the reality and dynamics of the settlements. The settlement-monitoring system includes hydraulic settlement gauges connected to a reference tank. They are arranged as required, in line every 98 feet (30 m). Each gauge has been placed on the reinforcement geosynthetic on a rectangular plate and protected with sand to limit unexpected settlements (Figure 9). The gauges are connected to a referFIGURE 8 Placement of bottom ash soil over geosynthetic 30 Geosynthetics | June July 2021 ence tank, and a data logger is mounted on a concrete base outside the cell. The concrete base must not settle and is under a topographical survey. The data acquisition is made manually by connecting a reading device to the data logger.