SLOPE STABILITY ANALYSIS BY NUMERICAL METHODS USING PLAXIS2D AND SLIDE 6 SOFTWARE, IN THE CASE OF EDO- SEROFTA -WARKA ROAD PROJECT

Abstract

Slope failure, which causes serious losses and property damage, can be categorized into man-made and natural slope failures. This study focuses on analysis of slope stability, particularly along the Edo-Serofa-Warka road projects. In these areas, road construction often involves cut-and-fill techniques to create necessary space. The Edo-Serofta-Warka region experiences high rainfall and humidity, which is sensitive to slope failure. The main aim of this study is to evaluate the future stability of man-made slopes under varying rainfall intensities. For this investigation, undisturbed and disturbed soil samples were collected from ten test pits across five slopes. These samples underwent a series of field test and laboratory tests including moisture content determination, wet sieve analysis, hydrometer analysis, unit weight measurement, specific gravity assessment, Atterbargs limit, triaxial tests, and consolidation tests. Based on Atterberg limits and wet sieve analysis of failed slope, soils were found under A-7, sub of A-7-5, except TP 1 which was found under A-5 according to the AASHTO classification system. These tests provided parameters essential for modeling, the slope stability using software tools. Additional data on topography, geology, temperature, and rainfall were also incorporated. Two numerical methods were employed: the Finite Element Method (FEM) using plaxis2D software, and Limit Equilibrium Method (LEM) using slide 6 software. Laboratory and field test results indicated that the soil on these slopes consists mainly of residual soils with medium to high clay content. Engineering parameters, such as cohesion (C) and the angle of internal friction (𝝓), were found to decrease by more than 50% as moisture content increased. Finally, the calculated factor of safety (FoS) in both dry conditions and with varying moisture content was greater than the critical value of 1 for most slopes, except for slopes 1 and 2. The analysis identified rainfall as the primary cause of slope failures in the studied areas. Consequently, implementing mitigation measures that consider rainfall impact is crucial for ensuring the stability of these and surrounding slopes.