In 1958–59, 25 loading tests were made at Khorramshahr on concrete friction piles driven in connection with extensions to the port, where the ground consists of deep deposits of soft to medium estuarine silty clays. Thirteen of the piles tested had been coated with a thin layer of bitumen as a protection against attack by soil acids: the remaining twelve piles were uncoated.
The loading tests showed that the shaft bearing capacities of the coated piles were between 30 and 80 percent lower than those of equivalent uncoated piles. A further, most interesting, finding was that the bearing capacity of the coated piles fluctuated seasonally (Fig. 1). This fluctuation was shown to be consistent in phase and magnitude with that which could be predicted from the seasonal fluctuation in ground temperatures and the temperature-viscosity characteristics of the bitumen used. Full details of the work are given in Hutchinson & Jensen (1968).