Evaluation of impacts on existing structures induced by deep excavations in Bangkok MWA project

The Metropolitan Waterworks Authority involves the construction of several shafts and a tunnel for the Water Transmission Tunnel Project in Bangkok, Thailand. In this project, numerous existing structures are located in close proximity to the underground construction areas. Consequently, these structures are susceptible to potential impacts due to the construction activities, particularly deep excavation of the shafts associated with excessive ground movements. This paper presents the evaluation of effects on the adjacent existing infrastructure resulting from the construction of two shafts with opening sizes of 12 m x 8 m and 10 m x 6 m, and the depth of excavation is around 30 m. A three-dimensional numerical analysis using PLAXIS 3D is carried out to investigate the responses, movements and imposed loads on the structures and piled foundations induced by the excavation in soft ground conditions. Extensive instrumentation and monitoring programs are implemented to observe such movements and to evaluate the serviceability of the existing structures. The monitoring results are in agreement with the analysis results and the construction has been successfully completed.