Abstract: To speed up construction of mass transit subway and the popularity rate of sewage, Taiwan's underground excavation works, especially for mechanical cutting cases, show an ascendant tendency. This study presents a generalized solution for underground geological-mechanical interaction. By using dimensional analysis, this model generalizes geological characteristics grouped into three categories, brittle (rocklike), the ductile (soillike) and brittleductile (gravellike) type, with respect to two cutting forces (thrust and torque) to evaluate their excavation/penetration rate. Furthermore, the leading cuttability indices can be obtained to be enable to assess the underground excavation. Meanwhile, insitu experimental results from shield tunneling and pipe jacking construction were used to examine this model and it shows a nice agreement between both. From this analytical approach, a proposed “ovalshaped cutting ellipsoid”, including its center (O), area (A) and long/short axis (ax/by, or ay/bx), can be used not only to estimate the functionality and efficiency of cutting machine adopted for tunnel project, but also to offer a warning information for inadequate cutting strategy.

Key words: tunnel boring machine(TBM), shield tunnel(ST), pipe jacking(PJ), generalized cutting mechanism, dimensional analysis(DA), cuttability indices(CI)