The purpose of this examination was to explain the internal stability of the ground reinforcing pile composed of the different two materials with greatly different deformation characteristics. This pile was consisting of the soil cement column and the nodular thin steel pipe of which elastic modulus and yielding strain were greatly different. The mechanism of internal stability for this pile was temporarily formulated using the punching capacity of the nodular thin steel pipe and the compressive capacity of this pile and then, the compatibility of the formula was experimentally verified. As the result, compared the design value to the limit value of the punching capacity, the design value provide assurance of the short-term safety factor (1.5), indicating that this pile become unified. In addition, the yield of the thin steel pile occurs the internal yield of this pile. The yielding compressive capacity of this pile is equal to the sum of the load of each material when the thin steel pipe reaches to the yielding stress. Furthermore, after reaching the internal yield of this pile, the deformation characteristics of this pile depends on the mechanical characteristics of the soil cement column because the thin steel pipe has already yielded.
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