<p>Soil-rock mixed fill foundations, characterized by significant heterogeneity and high post-construction settlement risks, pose a major challenge to urban renewal and sustainable development. This study conducted field tests using 3000 kN·m dynamic compaction to treat such foundations, focusing on improvement effects, ground vibration response, and dynamic stress distribution characteristics. Results show that the cumulative settlement decreases with successive blows, with the first 10 blows contributing most to compression. The average settlement of the final two blows meets design standards. Post-compaction, the effective improvement depth reaches 5.0–5.5 m. The bearing capacity achieves 150–175 kPa, meeting design requirements. Peak vibration velocity decays exponentially with horizontal distance from the compaction point. A brief decrease occurs after the fifth blow, signaling a shift from shallow plastic compression to deep elastic wave propagation due to gravel skeleton reconstruction. Regulatory standards set safe construction distances at 26.3 m for industrial/public buildings and 32.6 m for residential buildings. Dynamic stress showed nonlinear decay with depth, with significant attenuation between 2 and 4 m. The subsequent six blows enhanced the dynamic response in the 4–6 m soil layer, suggesting that the reconstruction of gravel particles created new energy transmission paths, gradually shifting the energy towards deep compression as the dominant factor. Dynamic stress calculations using Boussinesq’s theory deviate by less than 20% from measured values, especially in shallow heterogeneous layers. An elastoplastic model with heterogeneity correction is recommended to improve prediction accuracy. The findings provide valuable references for the design optimization, construction parameter selection, and environmental vibration control in dynamic compaction reinforcement of large-area, deep soil-rock mixed fill foundations.</p>