The effectiveness of UAM is generally accepted, but there has not been much rigorous study on UAM and its mechanical support mechanism is yet to be established. Also, most of UAM installations depend on empirical judgement rather than on engineering knowledge. In this study, an attempt to confirm the support effects and to understand the support mechanism of UAM has been made by analyzing the mechanical behavior of umbrella pipes installed in various ground conditions. The effects of overburden thickness, pipe size, overlap length and the placement of steel arch are studied using a three-dimensional finite element method. From the numerical parametric study, the support mechanism of UAM has been confirmed by analyzing the structural forces in the umbrella pipes due to the excavation.