Model test study on mechanical behavior of extremely shallow double-arch tunnel during excavation

Based on the construction of Changchengling double-arch tunnel with heavily jointed soft rock mass,a model test was carried out to analyze the stress characteristics during the excavation.With the help of monitoring instruments,the datas of stress,strain and pressure were collected and analyzed.Then a numberical simulation was carried out with FLAC3D,and its results verify the conclusions of model test.Combining with numerical analysis,the results of the model test reveals the variation laws of the tunnel surrounding rock stress and the change trends of pressure above and below the middle wall.