Studies are lacking in establishing the quantitative relationship between the mechanical response and the rock and soil mechanical parameters by digital rotary penetration. In this study, based on the custom-built rock and soil strength parameter test device and the three-dimensional flexible boundary loading device, we conducted an experimental study of the manufactured sand-soil model with moisture contents of 5%, 10%, and 15% under different confining pressures (0, 0.12, 0.18, 0.24, and 0.42 MPa). Analysis was conducted on the influencing factors and laws of water content on the experimental results, and a quantitative relationship model (W-T-BC model) between the drilling torque and the bearing capacity of manufactured sand-soil under the condition of different water contents was established. Through failure detection verification on the manufactured sand-soil-filled subgrade of the Taihang Mountains Expressway in Beijing, the average conformity between the calculated value of the bearing capacity of the W-T-BC model and the standard experimental bearing capacity was 93.23%, which proved the validity and accuracy of the model. Finally, the rigid-soft interface grid body of sand-soil particles was analyzed. The reason why the manufactured sand-soil exhibited better stability than homogeneous soil under the action of external force in microcosmic aspect was expounded. The establishment of the W-T-BC model provided a scientific basis and important reference for further study of the relationship between mechanical response and force parameters under different conditions of different materials.