Abstract
This paper describes seismic isolation effects of soft layers installed directly around a rectangular shape tunnel and placed beside the tunnel as vertical walls. 2D-FEM analyses with different properties and arrangements of the soft layers and the ground were conducted. The results show that the soft layers can restrict propagation of shear forces effectively; the layer directly around the tunnel with shear modulus of 1/100-1/1, 000 of the ground can decrease the section forces due to earthquakes to half of the case without the layer. In cases with the 10cm and 30cm thick soft layers installed besides the tunnel as vertical walls. the section forces due to earthquakes can be reduced to 60-70% and 40-50%, respectively, of the case without the layers.
