The Bangkok MRT Orange Line East Project consists of 6 km long twin tunnels and seven stations. The tunnel alignment runs along one of the most congested road corridors of the city. Due to adverse conditions of limited road right of way, obstructions from existing structures such as buildings, infrastructure, tunnels, and other utilities, the design and construction of the tunnel require careful consideration and implementation of excavation works to limit excessive ground movements and mitigate the potential impacts on existing structures. This article presents the concepts and procedures in detail on assessing the impact on each type of adjacent structure due to tunnel construction which contribute to the successful completion of the MRT Orange Line Project. Additionally, some mitigation measures for critical cases are highlighted.