A grab bucket for making reinforced concrete piles of high load bearing capacity. The grab bucket includes a framework with three wings, a moving assembly movable upward and downward along the length of the framework, a fixed assembly mounted beneath the moving assembly, three grab buckets mounted pivotally to the fixed assembly and having boring teeth oriented outwards, three pushing frames for closing the three grab buckets, and a transmission configured to control opening and closing of said bucket sections in unison.