ABSTRACT
This paper presents a case study of a close proximity spaced cut-and-cover tunnel (CCTN) constructed beneath the existing depot access (EDA) tunnels in Bangkok soft ground conditions. The new CCTN of the MRT Orange Line is constructed at an incline beneath the EDA tunnels of the MRT Blue Line with approximately 5.0 m of clearance. It is noteworthy that during the construction of the CCTN, the MRT Blue Line was in operation. The construction process of CCTN included deep excavation with a top-down supporting technique and a bottom-up construction method. The underpinning technique was performed to efficiently support and minimize the major effects on the existing EDA tunnels. To assure stability and serviceability, instrumentation and monitoring were implemented during the construction. According to aforementioned process, the construction was completed successfully. The monitoring results demonstrated good agreement with the design and construction specification of the project.
