Taiwan is located along a segment of the convergent boundary between the Eurasian and Philippine Sea plates , and has long been known as a geologically complicated and tectonically unstable area. Due to the ongoing plate-arc collision, two-thirds of the island is hilly and mountainous. With such topographical constrains, underground excavations such as power caverns , tunnels, etc. are featured in many major infrastructures projects. Presently over 105 km of tunnels are under construction and aditional 480 km or so are under planning, which form part of the development projects including highways, railways, subways, high speed railway, sewer systems, among others.
As Taiwan's geological structure is rife with shear and fault zones, tunnelling can easily cause high convergence of the surrounding rock, and the situation may become worse when encountering high groundwater ingress bursting out from the fragmented rock zones. Construction of long rock tunnels with high overburden poses especially great challenges in many highway projects, like the 12.9 km long Pinglin tunnel under construction in the Taipei-Ilan Expressway project ,and the tunnels under planning in the Central Cross-Island Expressway and Southern Cross-Island Expressway projects , in which the length of the longest tunnel may exceed 15 and 17 km respectively. Aside from difficult ground conditions such as fault zones , squeezing ground and high water inflow, difficulties resulting from high rock cover and high geothermal gradient, and ventilation and maintenance problems during operation, etc. are also awaiting to be solved. Tunnelling in unconsolidated soft deposits for metropolitan MRT projects as well as in gravel formations is another tough challenge.
For exchange knowlege and experience, and for upgrading tunnelling techniques, tunnelling related organizations and individuals co-founded the Chinese Taipei Tunnelling Association in Taipei Taiwan in June 1996. AS a nonprofit society, there are currently 45 corporate members and 923 individual members. The aims of the Association are to raise the domestic level of tunnelling technology through research and extension, and to promote contact and cooperation with international tunnel organizations. It is our hope that by means of interchanges, we would be able to learn from our foreign counterparts and also to share with them the engineering experience we have gained under the unique tectonic conditions of Taiwan, in the interest of the world tunnelling profession.