Creation of an opening in the rock mass results in redistribution of in-situ stresses, potentially causing overstressing in the vicinity of the excavation. This can sometimes result in excessive deformation if not designed appropriately, ultimately leading to the failure of the tunnel. Despite numerous studies on the shapes and sizes of a tunnel opening, there have been incidents of tunnel collapse under rock burst, spalling, or squeezing ground conditions. Hence, a comprehensive study is performed in the present study to numerically investigate the stress distribution around a tunnel with varied shapes, sizes, and loading conditions. The tunnel shapes considered in the present study are circular, square, and horseshoe-shaped configurations, with tunnel sizes ranging from 5 m to 10 m. A linear strain rate-dependent Drucker–Prager constitutive model is used to perform the stability analysis of the tunnel under different loading conditions using finite element software, ABAQUS. The effects of gravitational, train, and blast loads are applied systematically to develop a finite element numerical model, and the simulation results are studied thereof. A comparison of the optimized tunnel shapes with different sizes at a constant overburden depth of 15 m is analyzed for combined static and dynamic loading conditions and stated herein. The outcome of this study will provide valuable insights into the influence of shapes and sizes on the stress distribution around an underground opening, facilitating the development of optimized designs under various loading scenarios.