This limited depth of passive resistance has been recognized by the International Building Code
(2009), which states: “piles driven into firm ground can be considered fixed and laterally supported
at 5 ft (1.5 m) below the ground surface and in soft material at 10 ft (3 m) below the ground surface”
(Sec. 1810.2.1). The next two sections will present passive earth pressure theory for cohesionless and
cohesive soil.