Consultant’s view of durable and sustainable concrete tunnel constructions in the Middle East)
This paper presents the latest developments in concrete technology achieved on recent tunnel projects in the Middle East region. Strenuous requirements have been defined on recent underground concreting works in terms of strength, durability, workability and associated construction cost. COWI’s concrete technology and design teams worked closely with international contractors to implement the requirements given by the Employers in combination with recommendations of different design codes, among others the fib Model Code 2010, ITA guidelines, and Ciria Guideline CS 163. The efforts resulted in a highly durable and high strength concrete mix designs that can be used in various permanent structural lining of tunnels, shafts and underground cavities. Recent experience covers a wide range of applications from metro, drainage (stormwater and groundwater) and sewage tunnels constructed with tunnel boring machines as well as shafts and tunnels realized with conventional excavation.Steel fibre reinforced concrete (SFRC) is often used for concrete structures subject to severe exposure conditions e.g. bored tunnels exposed to saline ground water containing high levels of sulphates. In lieu of international, harmonised standards, the structural design of SFRC is covered by a number of national and international guidelines which describe considerations required for the SFRC in structural design along with classification of the mechanical properties of SFRC from standard tests. However, the durability design of SFRC is not sufficiently addressed by existing standards/guidelines, and consequently careful and thorough design processes need to be undertaken.In order to assess the durability of SFRC a number of parameters such as the exposure conditions and concrete quality, have to be considered , in particular with regard to chlorides. This paper details selected deterioration mechanisms which affect the concrete durability design. In addition, specific structural design aspects of SFRC are presented through case studies from recent projects successfully carried out by COWI in collaboration with international contractors in the Middle East.: Durability Design, Reinforced Concrete, Steel Fibre Reinforced Concrete, Bored Tunnels, Sustainability.