Pile Capacity Reduction due to Wetting in Saharan Deserts and Its Effect on the Serviceability of Cairo Monorail

Cairo Monorail is a high-speed driverless transit system under construction in Cairo, Egypt. The typical structure consists of four span guideway beams with expansion joints at approximately 120 m in length. This structural system makes the structure sensitive to differential settlement as well as rotation angles of the pier caps. The viaduct will be founded mainly on large diameter bored piles with diameters ranging from 1.8 to 2.4 m. The general geology of the New Administrative Capital city can be described within the geology of Cairo-Suez District (Saharan deserts). Thus, long-term changing of subsurface water conditions is expected. It has also been witnessed in similar projects within the same area due to the geological nature. Therefore, California Bearing Ratio (CBR) tests were performed on silty sand samples collected from different locations along the monorail path in dry and wet conditions. Results show that there is a loss in the soil stiffness ranging from 15% to 40% due to wetting. To consider the wetting effect on piles, pile load tests were conducted in dry and wet conditions. Pile load test results show that pile capacity reduction due to wetting was about 20%.