Abstract: This study proposes a model for optimizing the California Bearing Ratio (CBR) of loose lateritic soil mixed with quarry dust and water using Scheffe’s experimental design techniques on simplex lattice. The developed model uses a polynomial of second degree to express the behavior of the components of the mixture in a simplex lattice. Weights of different components of the mixture generated from Scheffe’s theory were used in arriving at the resulting model. A computer program for optimization based on the model is also developed. The optimal mix proportion obtained by the model is 1:2.75:0.135 (Lateritic soil: quarry dust: water) with a CBR value of 18.2%. This represents an increase of about 56.9% in the CBR value of the original lateritic soil. The model predictions were compared with the experimental results and found to be adequate at 5% significance level.