A structural pile assembly includes a driven pile and pressurized grout contained beneath the pile so as to exert an upward force on the pile. An enclosure, such as a bladder or bellows, is filled with grout from a reservoir via a conduit which preferably extends axially along the length of the pile and is left in place after the grout hardens. A pressure gauge measures the pressure of the grout within the enclosure, permitting the direct measurement of end bearing and side bearing capacities of the resulting pile assembly. The load bearing capacity of the pile is enhanced by the pressurized grout, and is preferably at least twice the end bearing capacity of an unpressurized pile.