Centrifuge Modelling of Marginal Soil Slopes Under Rainfall with Hybrid Geosynthetic Inclusions

The present study focuses on investigating the effect of inclusion of an innovative hybrid geosynthetic on the seepage, deformation and stability aspects of marginal soil slopes subjected to rainfall. Model hybrid geosynthetics were prepared in the study by integrating the drainage potential of nonwoven geotextile with the reinforcement function of woven geogrid. The model soil was a blend of fine sand and kaolin in the ratio of 4:1 by dry weight. The silty sand exhibited a percentage of fines equal to 20% and a saturated permeability of 1.54 × 10^–6 m/s, thereby representing the properties of marginal soils found in major portions of India and other parts of the world. Centrifuge-based physical modelling was adopted at 30 gravities on slopes of 7.2 m height and crest width of 7.5 m using the 4.5 m radius beam centrifuge facility available at IIT Bombay, India. Rainfall was simulated using a custom-designed rainfall simulating assembly for a prototype rainfall intensity of 20 mm/h. It was observed that the unreinforced slope model experienced a catastrophic failure, while the hybrid geosynthetic reinforced slope experienced negligible deformation throughout the rainfall event. The surface settlements and slope face movements decreased substantially by about 94% and 71%, respectively, owing to the geogrid component. Further, the inclusion of geotextile component of hybrid geosynthetics resulted in a reduction of pore water pressures by almost 66%, thereby indicating the importance of hybrid geosynthetics in alleviating the instability of marginal soil slopes subjected to rainfall. Use of hybrid geosynthetics thus facilitate the use of marginal soils in reinforced earth construction, thereby economizing the project.