Problems in the design of highway and airfield pavements in the arid or semi-arid countries of the Middle East are concerned more with the detrimental effects of the environment on the completed pavement than with the capacity of the subgrade soil to carry the traffic loads. These problems occur even when pavements are constructed on soils which would be regarded as providing an excellent subgrade by Western European standards. In most Middle Eastern countries the soil conditions are such that the graded soil when compacted by traffic provides a good running surface for road vehicles or taxi-ing aircraft without any need for paving. Until quite recently many inter-city roads were unpaved, and propeller-driven and even jet aircraft operated successfully from unsurfaced runways (Fig. 1). Paving was required only when the intensity of road traffic reached the stage when ravelling of the road surface commenced with the consequent unpleasant ‘washboard’ effect. Similarly heavy trafficking on unsurfaced runways and taxiways resulted in ingestion of stones into aircraft engines and damage to wing surfaces.
The silty and clayey soils of parts of Jordan, Iraq and Iran, and the silty sabkha soils fringing the Trucial Coast undergo appreciable softening during rainy weather. Hence pavings are provided where all-weather serviceability is required from highways or airfields. Also run-off from the semi-impervious crust on the desert surface during heavy rain causes washouts of unpaved roads, requiring the attention of a grader to backfill the erosion gullies and restore the running surface. However, when a decision is
- © The Geological Society, London 1978