A deep excavation for the underground structure of St. Ignatius High School Station of the Taipei Mass Rapid Transit System has been chosen for case study. This project used the bottom-up construction techniques with an excavation depth of 31.65 m in 11 stages. At the final stage of excavation, an accident of water and soils burst-in occurred in one section and induced a very large diaphragm deflection, some ground settlement and some minor damages of adjacent buildings. The complete record of diaphragm deflection was retrieved herein and back analysis was performed to simulate the field situations. Results obtained showed the significant changes of soil properties due to the influence of various constructional works.