The Pinglin tunnel of Taipei-Ilan expressway, including two main tubes and one pilot tube, is approximately 12.9km in length. The diameter of the main tubes and pilot tube are approximately 13m and 5m respectively. The Pinglin tunnel was excavated approximately 850m with drilling and blasting method from the Tou-Cheng portal firstly. Tunnel boring machine method will be adopted to complete the remaining section of the tunnel. The Chinyin fault with 60m wide is
the most important geological structure in the drilling and blasting section. The dialation behavior of the fault gouge material is very sensitive to the water, therefore the excavation sequence and support systems should be carefully studied. Some reinforced measures and more anticipated rock deformation also have been considered in order to avoid the excavated section intruding into the designed section. Systematic monitoring is also a very important task during the excavation. According to the monitoring results, the placing of the invert shotcrete to close the support system is the most effective and economic method to reduce the deformation of the rock mass after excavation.
