Gravel-pile composite foundation has been applied widely to reinforce actual engineering; and the characteristics of its stress and strain have been studied deeply. The consolidation of the reinforced foundation has been researched to a certain extent

but the known analytic formulas are mostly complicated

so they are difficult to be used in engineering. Radial soil around pile is considered as a whole element in this paper

the effect of the coating caused by construction is not necessary to be considered. According to the theory of equivalent of seepage discharge to volume change

a simplified formula for consolidation of double-layered ground reinforced by gravel-piles is derived from the concept of average excess pore water pressure. This method can solve the average excess pore water pressure and average percent consolidation of the gravel pile and its surrounding soil

and the average percent consolidation of the entire reinforced foundation can be also obtained. This formula is laconic and has the advantage of application.