Abstract: The compression modulus is an important concept in the soil mechanics, which is often used to evaluate the compressibility of the soil and estimate the final settlement of foundation soil. At present, there are different types of definition or formulations of the compression modulus in different versions of textbooks or design codes domestic and abroad, which is easily to induce the ambiguity in the academic and in the engineering practice. This paper firstly analyzes the various definitions of the compression modulus, and then discusses the different derivation processes of two expressive formulas, throughout a set of one-dimensional compression test data in the existing textbooks. The results show that the two formulas are consistent in general, but different strain measures are utilized. When the applied compressive pressure is not very high, there is little difference between the results from the two formulas. Only when the applied pressive pressure is very high, there is a significant difference between them. From undergraduate education point of view, it is suggested that the engineering strain should be used in the derivation of formulas for the estimating of the compression modulus in the soil mechanics.

Key words: Soil Mechanics, Compression Modulus, Compression Test, Engineering Strain, Void Ratio