Introduction to Soil Moduli

The modulus of a soil is one of the most difficult soil parameters to estimate because it depends on so many factors. Therefore when one says for example:”The modulus of this soil is 10,000 kPa”, one should immediately ask: “What are the conditions associated with this number?” The following is a background on some of the important influencing factors for soil moduli. It is not meant to be a thorough academic discourse but rather a first step in understanding the complex world of soil moduli. In a first part, the modulus is defined. In a second part, the factors influencing the modulus and related to the state of the soil are described. In a third part, the factors related to the loading process are discussed. Fourth, some applications of soil moduli are presented. In a fifth and sixth part, the soil modulus is compared to the soil stiffness and to the soil coefficient of subgrade reaction respectively.