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The bored precast piling method is used to obtain bearing loads via construction of an enlarged base and a pile fixture part by injecting and agitating cement milk into mud in an excavated hole, whereby the pile tip reaches the bearing stratum. Achieving the requisite strength of the soil-cement mix, from which the enlarged base is constructed, is critical for ensuring that the bearing load is withstood. In this study, several aspects of this piling method were investigated to assess its applicability to a wide range of soil types and to construct a rapid and highly accurate quality control method. First, the material composition of the soil-cement mix used in the enlarged base of a bored precast pile was investigated. Next, the parameters affecting the evaluation of the strength of the soil-cement mix were identified via laboratory mixing tests, and an equation for strength estimation was established. Finally, a method was proposed for analyzing the material composition of the soil-cement mix at the site, and technology was developed to enable early estimation of the 28-day(s) compressive strength based on the material composition. Ultimately, the estimation accuracy of this methodology was verified at 80 sites. Keywords bored precast piling method, cement-water ratio, compressive strength, early estimation, soil cement This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.