In the mechanized excavation of subway tunnels, the shield tunnel boring machine (TBM) has been developed in recent decades for managing the instability of the excavation profile in complicated geotechnical conditions in urban areas. The paper presents a 3D simulation procedure for the detailed description of TBM (via the finite element code Abaqus) and quantifies the influence of TBM face pressure on ground surface settlements. The model is used to calculate ground surface settlements for different values of TBM face pressure. An additional aspect of the investigation is the determination of the critical value of TBM face pressure, which controls face instability in very weak ground. During the advancement of shield tunnel boring machines, the face-stabilizing pressure is one of the most important factors of critical. In tunneling by shield tunnel boring machines, high face pressure often leads to surface upheaval, whereas low face pressure leads to sudden collapse of the face and ultimately settlement of the surface. For the model condition, the maximum value was quantity 250 kPa and the minimum value obtained quantity 150 KPa.