The promoted advantages of implementing stiffness-based compaction specifications include that they enhance the efficiency and accuracy of compaction practices in earthworks projects, as they have the potential to improve project outcomes and cost-effectiveness. But reliably achieving the traditionally desired compaction targets, such as dry density, through correlation with stiffness indexes has remained a challenge for earthworks practitioners. In this study, we investigate two stiffness and compaction field trials. The presented results include in-situ stiffness parameters that can be easily determined during the production phase of earthworks Compaction Measurement Value (CMV) and Light Weight Falling Deflectometer (LWD)—and typical compaction assessment data from nuclear density gauge, plate load test, and particle size analysis. A novel empirical framework that links stiffness to density and degree of saturation is applied to the datasets. The analysis of the field trials encompasses an evaluation of the successes and challenges encountered in each case and discusses the potential areas of improvement for future trials and the potential for the creation of stiffness-based compaction specifications.