The New Doha international airport terminal station box in Qatar was constructed within the weathered Simsima Limestone where geotechnical properties relating to retaining wall design were not well understood. In order to reduce the construction programme to meet the scheduled airport opening, conservative geotechnical parameters, derived from available site investigation data within the region, were adopted for the preliminary design and subsequently revised as more comprehensive site investigation data became available. Accordingly, the structural instrumentation and monitoring programme was implemented to facilitate the design and construction verification process. This paper describes the performance of the instrumented diaphragm walls and props in the central section of the box. Permanent large-diameter reinforced concrete props were adopted at roof and mezzanine levels. An additional level of temporary strutting was required between mezzanine and base levels owing to the significant vertical span between these levels. Design predictions are compared with field measurements. Back-analyses have also been undertaken to permit a better understanding of the geotechnical properties and assist future design in similar ground conditions. These analyses demonstrated that wall deflections are sensitive to the assumed pore-water pressure conditions. Moreover, a Mohr–Coulomb model, with small strain stiffness for limestone/mudstone, is sufficient to capture the wall behaviour.

Most Irish earthworks fills consist of glacially derived soils with some excavated rock. Excavated rock and granular glacial soils will nearly always provide acceptable fill. Cohesive glacial soils are generally well-graded tills, characterized by low plasticity and relatively high undrained strength. These cohesive tills provide acceptable fills providing they can be placed and compacted to provide sufficient strength and stiffness, and achieve low air voids.In standard earthworks specifications, acceptability limits for cohesive fills may be specified by moisture content, moisture condition value or undrained shear strength. The lower limit of strength or moisture content adopted ensures acceptable trafficability, compressibility and stability. Laboratory relationship testing is carried out to establish the relationship between the various test properties.Experience has shown that simple measurements and descriptions of strength derived from data collected routinely during ground investigations are adequate for estimation at tender. For construction control, moisture condition value testing has been widely adopted, is suitable for the range of soils encountered and provides quick results allowing timely decision-making. Irish tills are moisture susceptible and on-site results allow marginal materials to be processed on site for re-use, providing care is taken to work only in dry weather and protect placed fill.

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