| Forepoling—the use of a pipe umbrella—during conventional tunneling is widely used in poor ground conditions to stabilize the tunnel face. Recently, numerical analysis has been more widely used in the design of forepoling. In 2D numerical, it is often said that tunnel displacement or stress generated in tunnel supports may be reduced with forepoling. However, such effects have been fully understood in the field measure-ments. Therefore, we examined the 3D effects of forepoling and considered methods to evaluate it. Here we measured the 3D effect of forepol-ing form measurement results and conducted 3D numerical analysis to reproduce the results. Major conclusions include that forepoling is not affect to the final deformations of tunnel and stress generated in supports, though front loads are supported by forepoling. |
