Abstract: Enhancing the boring efficiency of full-face rock tunnel boring machines (TBM) in hard or highly abrasive rock formations represents a critical challenge in modern tunnelling engineering. Empirical evidence from field applications has substantiated that free surface assisted rock breaking is an effective method to enhance the boring efficiency of TBMs. A high-pressure water jet is used to create a circular free surface to better simulate the actual engineering scenario. Vertical penetration experiments and rotary cutting experiments are used to study the load change, rock breaking efficiency, and unit rock chip mass of different rock breaking modes. In the vertical penetration experiment, the centre rock breaking mode and overlapping rock breaking mode were set up, and the experiments at two radii were carried out, and the conventional rock breaking mode experiment without free surface assistance was also carried out. In the rotary cutting experiement, the conventional rock-breaking mode experiment under three radii was carried out, and the load (normal force and torque) and rock-breaking effect of the centre rock-breaking mode were studied. The main conclusions are as follows: In vertical penetration rock breaking, the load of the conventional rock breaking mode has a ‘leap forward’ phenomenon, and the centre rock breaking mode has a ‘double peak’ phenomenon, and the rock breaking efficiency of the overlapping rock breaking mode is higher than that of the centre rock breaking mode. In the centre rock breaking mode, after the large rock chips are dislodged, the load shows a continuous ‘leap forward’ phenomenon similar to that of the conventional rock breaking mode. The installation radius affects the rock-breaking characteristics of the disc cutter. In rotary cutting rock breaking, the peak load and average load of the conventional rock-breaking mode show an increasing trend with the increase of installation radius, while the unit work and unit rock chip mass gradually decrease with the increase of installation radius. In rotary cutting rock breaking, the specific energy of the two experiments of the centre mode is smaller than that of the conventional rock breaking mode, while the unit rock chip mass is negatively correlated with the rock breaking efficiency, and the rock breaking efficiency of the disc cutter can be measured by the unit rock chip mass. Moreover, the deeper the free surface, the higher the rock-breaking efficiency of the disc cutter.