Stress path of the surrounding soil during tunnel excavation: An experimental study br

Many analytical and numerical studies have been performed to investigate the stress path of the surrounding soil during tunnel excavation, but experimental researches on this problem are very limited. In this paper, a tunnel excavation model test is carried out in a 2000 mm x1000 mm x1500 mm soil box using a shield machine with a cutterhead diameter of 285 mm. The three-dimensional stress states of the surrounding soil are measured with custom earth pressure cells. The measurement results indicate that the major principal stress Sigma 1 at the crown becomes horizontal when the cutterhead reaches the monitoring section, and the mean stress p decreases while the deviatoric stress q exhibits an increase-decrease-increase trend until soil collapses. The principal stress di-rections at the upper shoulder gradually rotate due to the soil arching effect. At the springline, the stress path develops under a constant p value but is far from the zero tension line. At the bottom, the stress path is similar to the conventional triaxial compression stress path, due to the self-weight of the shield machine. Therefore, to accurately predict the ground settlement after tunnel excavation, the soil deformation under the above stress paths should be reasonably described.