Abstract: Using an expressway tunnel in large, loose deposits as an example, an indoor saturated consolidation drained shearing test was carried out to obtain the mechanical parameters of the loose deposits, focusing on the secondary lining cracks in the unsymmetrical loaded section of the left tube. The results were combined with actual measured data and a 3D numerical model was created to simulate the construction process and mechanically analyze the secondary lining cracking mechanism. The results show that: 1) because of the great difference between the stiffness of the retaining wall and deposits, an obvious stress concentration has emerged at the haunch of the retaining wall and the secondary lining after tunnel excavation, even though a 30 m-long pipe roof has been installed at the unsymmetrical loaded portal section; 2) the loose deposits are extremely sensitive to construction disturbance, which will cause major horizontal ground displacement towards the low-lying area; and 3) the stress concentration at the haunch of the retaining wall and the secondary lining, as well as the horizontal displacement of the secondary lining, will gradually increase with the buried depth, which constitutes the main cause of cracking of the secondary lining. This analysis may provide a reference for the design and construction of similar tunnels.