This paper is based upon the investigation and design stages for two of the 30 metre deep underground stations constructed in water-bearing sands and very weak rock as part of the initial development for the Red line of the Dubai Metro, United Arab Emirates (UAE). The paper firstly outlines the geological and hydro-geological conditions encountered at the City Centre and Burjuman underground stations designed by Hyder, with specific details of the geotechnical design parameters and groundwater data. The design criteria and constraints for the structures are subsequently discussed from a geotechnical perspective, in particular the issues of dewatering during construction and the impact of the long term uplift pressure after completion on the design solution. Two critical geotechnical design issues are the use of the tension piles/barrettes against uplift for the station box and load bearing barrettes for the viaducts immediately above the underground station structures. This paper also describes the progression from concept to detail designs and how the uplift issues were resolved and the lessons learnt.
Both empirical design methods and numerical modelling for the design of tension piles/barrettes are presented in the paper to emphasize the complexity of what at face value appears straightforward. The load transfer mechanism of the viaduct load through the barrette panels and their displacement compatibility with the station box slabs were analysed using both 2D analysis and 3 dimensional methods.
The permanent underground station box structures have now been completed and are in operation. The design assumptions were validated through the construction stage using an observational approach/monitoring, reflecting the effective and successful application of the design and decision making process.