Effect of Geocomposite Layers on Slope Stability Under Rainfall Condition

Abstract

Slope instability and associated loss of matric suction under rainfall condition is a serious global issue, and deserves special attention. The objective of the present paper is to investigate the effect of inclusion of a special variety of geosynthetic material, referred to as geocomposite (or dual-function hybrid geosynthetic) within slopes subjected to rainfall. In this regard, centrifuge based physical modelling was performed on a model silty-sand slope having 7.2 m height (prototype scale) and 2V:1H inclination at 30 gravities using the 4.5 m radius centrifuge facility available at IIT Bombay, India. A rainfall simulating assembly was designed and developed for the above study, capable of producing fine mist at a uniform rate during in-flight testing using specially designed pneumatic nozzles (intensity range: 2 mm/h to as high as 80 mm/h). The surface settlements, displacement profile, strain experienced by reinforcement layers, and pore water pressure profiles developed during rainfall were investigated in the unreinforced and reinforced slope models. It was observed that, the unreinforced slope model experienced excessive settlement and increasing phreatic levels with rainfall, leading to catastrophic failure. On the contrary, the geocomposite reinforced slope was stable under rainfall condition, and experienced negligible deformation with progress of rainfall, the maximum peak strain value being as low as 8.01%. Further, the inclusion of geocomposite layers provided preferential drainage channels within the slope, and resulted in reduction of pore water pressure values by almost 47%, thereby indicating the importance of coupling the functions of reinforcement and drainage simultaneously within low-permeability slopes subjected to rainfall. The above finding facilitates the use of locally available low-permeable soils in construction of reinforced soil walls/slopes, thereby economizing the project. Further, use of marginal soils in combination with geocomposites (or hybrid geosynthetics) can prevent the unsustainable mining of natural sand deposits for construction purposes, while catering to the problem of scarcity of good quality permeable granular materials in recent times.