Soil grouting is generally adopted to enhance engineering properties of soil deposits by introducing cohesive agents into the ground. The effectiveness of the technique, however, is influenced by various factors, and relies upon a substantial portion of on-site experience and engineering judgment. Major uncertainties in grouting appear to be the actual mechanism of injection and the performance of the grouted ground. Although several attempts have been made in the past, results of related studies on the injection mechanism are generally not conclusive and the improvement of grouting on engineering properties of soils can not be practically quantified. The study herein discusses an examination on the injection mechanism, through an in-situ grouting program and the subsequent excavation. Various types of grout were introduced into different soil layers of the ground, with controlled injection pressure and volume. Field mapping and laboratory testing of the grouted soils were carried out. A numerical simulation of the grouting process was also performed and discussed for clarification of the observed mechanism.