Abstract: Gravel-pile composite foundation has been widely applied to the practical engineering projects, 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 that they are difficult to be used in practical application. Radial soil around piles 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 is derived from the concept of average excess pore water pressure. This method can solve the average excess pore water pressure and average degree of consolidation of the gravel piles and its surrounding soil, and the average degree of consolidation of the entire reinforced foundation can be also obtained. This formula is laconic and has the advantage of being easy to find application.