Abstract:
This study focuses on enhancing the understanding of the effectiveness of sub-horizontal drainage as a slope rectification
method and assessing the effectiveness of the shear strength reduction method in practical applications. It compares the
results with the limit equilibrium method. Based on the analysis result on the homogeneous slope, sub-horizontal drains are
most effective when positioned at the toe of a slope. Furthermore, the research finds that extending drains beyond a 15 m
length in the homogeneous slope gradually reduces the rate of increase in the safety factor. Theoretical suggestions indicate
that sub-horizontal drains are most efficient when installed at a 0-degree angle. Modeling sub-horizontal drains using these
maximum effective drain parameters can increase the factor of safety to 1.394 in the limit equilibrium method and 1.325 in
the shear strength reduction method, respectively. The analysis of drain performance has revealed that sub-horizontal drains
can effectively improve the stability of the slope during rainfall. The analysis results for the case study on Pinnawala slope
indicate a factor of safety of 1.058 and a shear strength reduction factor of 1.04 before installing the sub-horizontal drain.
After improving the sub-horizontal drain, the factor of safety increases to 1.202 and the strength reduction factor to 1.2,
respectively.
