Experimental and Numerical Study on California Bearing Ratio for Two-Layer Soil Systems

Abstract

Design of pavement is performed based on effective California bearing ratio (CBR) of subgrade soil. It is important to investigate quality of subgrade soil by means of CBR test to ensure quality of pavement. Pavement must be designed to avoid excessive and differential settlement. It is very challenging when the subgrade comprises of multiple soil layers having both good and poor quality soils. In the present study, experimental and numerical studies have been carried out to estimate the CBR of two-layer subgrades. Locally available clay and sand are used to prepare two-layer soil system with different thickness and combinations for CBR test in laboratory. 3D numerical model has been developed in finite element software package ABAQUS 2018 to simulate California bearing ratio (CBR) test for two-layer system of subgrade soils for further parametric study. The soils are simulated with Mohr-Coulomb constitutive model in numerical study. The results obtained from numerical model are compared with the CBR obtained from laboratory testing of single-layer and two-layer samples using conventional CBR testing machine. The laboratory tests and numerical studies are performed for unsoaked as well as soaked samples. It is observed that the CBR of two-layer soil system is governed by the soil in top layer. It is also observed that CBR of two-layer soil, with clay at top and sand at bottom, is higher than CBR of only clay sample.KeywordsCBRTwo-layer soilSubgrade3D numerical modelingABAQUS