Evaluation of undercut depth for flexible pavement on unsuitable tropical red soils using finite element method

Abstract

Due to the lack of a reliable classification system and inadequate evaluation of their engineering properties, undercut depth is recommended for tropical red soils when used in flexible pavement construction. The aim of this study is to determine the ideal depth for subgrade undercutting, which is the process of removing and replacing unsuitable soil under flexible pavement. In order to estimate the proper undercut depth, the study used numerical modeling with PLAXIS 2D software to evaluate tropical red soils. In this study, three different categories of subgrade were selected. The test programs included determination of index properties, subgrade strength properties, geochemical properties, and X-ray diffraction analysis. The numerical analysis program was conducted using cyclic (dynamic) pulse loading on top of flexible pavement and the Hardening-Soil Model with Small-Stiffness Material Model was used for simulating the behavior of unsuitable subgrade soils. The subgrade soils were classified as silty soil with high plasticity, and high clay content that are inactive and have a non-expansive nature. The numerical deformation analysis revealed that 50 cm and 100 cm undercut depth treatments are adequate for unsuitable soils having properties of categories 2 and 3, respectively. The effectiveness of undercut treatment in relation to deformation resulting from numerical simulation and the comparison of this study’s findings with the current practice in Ethiopia are also presented in this paper. Furthermore, conducting additional geotechnical investigations and numerical analysis on a large number of unsuitable tropical red subgrade soils is recommended in order to obtain reliable and comprehensive results.