Keller has worked on several stations on the Gold and Red line.
The Doha metro network covers 85km and is part of Qatar Integrated Rail Project (QIRP) that will include the east coast link, high-speed link, freight link and a light rail system. The railway will serve the suburbs of Doha and developments such as Lusail, Education City and West Bay. Approximately 37 stations and 60 further excavations are planned for the entire Doha Metro Network to be completed in 2020.
Subway stations require deep excavations of 25 to 40m. Shallow water tables and presence of weathered and highly fissured limestone rocks allow large volumes ground water to seep at high discharge rate that requires intensive dewatering costs. The objective given to Keller was to reduce the rate of water seepage and subsequently reduce dewatering costs by grouting solutions.
In addition to this, as the deep excavations are adjacent to existing structures and roads. The shoring system that was adopted needed to be anchored by Keller to restrict movement and increase stability. In many locations, anchors were required to be removed after their serviceable life and in other locations, where the TBM would cut them, GRP strand anchors were used. Drilling anchor holes under hydrostatic pressure was a major challenge and required special skills and technique during execution.
Keller mitigated this geotechnical challenge by applying the bottom up permeation grouting process using Tube-a-manchette (TAM) tubes to pressure grout in stages ensuring optimal closure of fissures in rock or occasional cavities. The grout injection was done in a regular grid along periphery of the excavations and following some trials the design of grout mixes were adjusted. The grout curtains were successfully installed, in accordance with the design requirements.
For the anchors, fully cased holes and particular techniques to prevent grout washout under hydrostatic pressures were drilled and place with single bond multiple anchors. All anchors were pre-stressed and locked at the desired capacity.