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Recent decades have witnessed the increasing usage of deep cement mixing (DCM) mixers in the field of marine infrastructure construction. The mixing performance, including the torque history, can be helpful for structural safety evaluation, design, and the optimization of agitators, which is of engineering significance. However, to the best of the authors' knowledge, there are no related publications that have reported the mixing behaviors of deep cement mixing agitators. In light of this, the present work conducts experimental and numerical investigations of the mixing behaviors of a DCM ship mixing agitator. To achieve this end, a model test device is established, and mixing experiments using two- and three-blade mixers are respectively conducted. Silt and clay soils are considered in the experiments with a three-blade mixer, while clay soils are used for those with a two-blade mixer. In addition, this work designs a torque transducer placed inside the rotating rod to accurately measure the torque history of the agitator during model test experiments. The experimental results show that, when mixing clay using agitators with different blades, the average torque value required for a two-blade agitator is slightly larger than that for a three-blade one. This study also presents a computational framework based on the arbitrary Lagrangian–Eulerian (ALE) method for an efficient and accurate modeling of the soil-mixing behaviors of the agitator. The numerical results are found to be in good agreement with the experimental data from model tests in terms of torque history, which demonstrates the effectiveness and capacity of our presented computational framework. The numerical results show that the average torque value is smaller at a higher rotational speed during the mixing of clay using a two-bladed agitator, but the effect of rotational speed on the torque history is small. The experimental and numerical methods introduced in the present work can act as a useful tool for investigations of mixing behaviors of DCM agitators. [ABSTRACT FROM AUTHOR]