Abstract: Due to the characteristics of large scale and special geological conditions, as well as a couple of tough construction situations and incidents of groundwater inrush during the span of 15 years, the issue of structural safety on Hsuehshan Tunnel has been attracting the public's attention. To make sure longterm tunnel stability, a monitoring system was therefore set up after the completion of Hsuehshan Tunnel. This longterm monitoring project was started from 2009 and completed for the first phase in March, 2011. The monitoring system consists of five items, including "control survey", "3D optical monitoring system (36 crosssections)", "crack displacement gauges (4 spots)", "piezometers (43 spots)" and "flow meters (6 stations)". This article is aimed to analyze and evaluate the collected monitoring results so far for future operation and maintenance purpose.

Key words: Hsuehshan Tunnel, monitoring system, expressway tunnel