Structural Internal Force of Shield Tunnel in Expansive Soil Underlying Sandy Pebble Layer

The Chengdu metro line 2 partly passes through the complex strata of sandy pebble and expansive soil. In order to obtain the influence law of expansive force resulted from partial expansion on shield tunnel lining structure load in complex layers, the influence of partial expansion with various ranges and expansion forces on the contact pressure of tunnel lining structure was analyzed with a numerical method. Load distribution and internal forces of tunnel lining structure at the stage of grouting and after tunnel transfixion were obtained by field tests and compared with the calculated structural internal forces under different expansion loads. The research show that the expansion thickness and range have a little effect on the increment of pressure on the lining structure, but the expansion force has a great influence on the increment. The existence of partial expansion will increase the bending moment of segment and is harmful to the lining structure. The negative bending moment becomes the control factor of tunnel structure design in the complex layers. When structure internal forces in complex layers of sandy pebble and expansive soil are calculated, the influence of expansion load should be considered and it is better to use a numerical method to determine its value.