ABSTRACT
Underground construction in the Middle East presents some unique conditions that Design & Build contracts have to overcome in order to avoid the cumbersome and time-consuming iterations of short-term changes implied by the contractor during execution of the works. Extremely variable ground conditions of the sedimentary rock in the Middle East, the shallow groundwater table and tight construction schedules are a few of the challenges that have to be coped with. An efficient solution, particularly for large open cuts and shaft excavations, is the Variable Support Method. It defines a series of excavation classes and associated support systems based on variable rock mass conditions in the design phase. The excavation classes are presented in a matrix form, based on the expected ground conditions. The contractor is then allowed, with the assistance of the Designer, to choose and apply the most suitable support class within the defined design framework.
