Centrifuge Model Studies on Performance of Hybrid Geosynthetic–Reinforced Slopes with Poorly Draining Soil Subjected to Rainfall

This study explored a suitable technique of reducing pore-water pressures and deformations in poorly draining soil slopes subjected to rainfall. The reinforcing function of woven geogrid was coupled with the drainage property of nonwoven geotextile in the form of a hybrid geosynthetic material. A series of centrifuge tests was conducted with an in-flight rainfall simulator on silty-sand slopes representing 7.2 m height and $2\mathrm{V}:1\mathrm{H}$ inclination at $30\mathit{g}$ using the 4.5-m-radius beam centrifuge at the Indian Institute of Technology (IIT) Bombay, India. The surface settlements, displacement contours, strains experienced by geosynthetics, and pore-water pressures developed during a heavy rainfall event of $20\mathrm{mm}/\mathrm{h}$ were investigated. The unreinforced slope underwent toe failure with rainwater infiltration due to absence of either drainage or reinforcing elements. The geogrid-reinforced slopes experienced considerable deformations and increasing phreatic levels with rainfall due to insufficient drainage, accompanied by geogrid straining in the range of 38%–48%. Although the increase in phreatic levels decreased substantially in the geotextile-reinforced slope, an eventual slope failure was induced by rainfall due to inadequate reinforcement. In comparison, the crest settlements and slope face movements were 86% and 82% lower, respectively, in the hybrid geosynthetic–reinforced slopes, and phreatic levels at the slope base decreased 40%. Moreover, negligible peak strains on the order of 3%–8% were registered along hybrid geosynthetics throughout the rainfall event. A seepage-stability analysis was further conducted to investigate the reinforcing effects of geogrids, geotextiles, and hybrid geosynthetics separately in controlling the slope factor of safety with rainfall.