Stability improvement of laterite soil slopes using bottom ash and coir fiber

Laterite Soil (LS) is a common construction material in tropical countries due to its excellent engineering properties. However, with the increase in climate change, slope instabilities have become more frequent in these areas, resulting in significant loss of life and property worth millions of dollars. To address this issue, this study recommends a stabilization method that uses inexpensive and locally available materials such as Bottom Ash (BA) and Coir Fiber (CF) to stabilize highway embankments. This study aimed to enhance the erosion resistance and stability of laterite soil slopes while facilitating reuse options for industrial waste products. Laboratory tests included basic tests of raw materials, compaction, direct shear, tensile strength, and permeability tests. Chemical tests included X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), and Electron Dispersive X-ray Spectroscopy (EDS). Finally, rainfall simulation tests were conducted to evaluate the resistance of the embankments to surface erosion. The findings indicated that adding BA to the LS increased its frictional angle due to the angular shape of its particles. This addition also significantly improved the soil's permeability. On the other hand, lime-treated mixtures had better cohesion and tensile strength, and lower hydraulic conductivity because of cementation and pozzolanic products' voids-filling effect. Moreover, the inclusion of CF in mixtures enhanced the soil's ductility and slowed down soil failure in both tension and shear. In addition, it significantly improved the permeability of the mixtures when added in substantial amounts. Based on these tests, it was determined that the optimum mixture for both lime- and lime-free compositions was 70LS30BA1CF. This mixture was selected for the rainfall simulation test, which was conducted on embankments (treated and untreated) with 45-degree slope angles and 70% Dr compaction. Heavy rainfall with an intensity of 250 mm/h was applied to the embankments to evaluate their erosion resistance. The results showed that BA and CF can help reduce the rate of erosion of embankment slopes subjected to heavy rainfall. However, subsequent rainfall events of similar intensities can cause excessive erosion. Nonetheless, it was found that treating the top embankment layer with lime could significantly improve its stability.