Terzaghi Theory Terzaghi theory is a fundamental concept in soil mechanics, which was developed by Karl Terzaghi in the 1920s. It describes the behavior of soil as a two-phase system consisting of solid particles and pore fluid and explains how the stresses and strains in soil are related to one another. The theory is based on the principles of effective stress and total stress and is used to analyze the stability and settlement of foundations, slopes, and other soil structures. Terzaghi's work laid the foundation for modern soil mechanics and geotechnical engineering. Terzaghi's theory also includes the concept of soil compressibility, which describes how soil changes volume in response to changes in stress. According to the theory, the soil will compress and lose volume when subjected to an increase in stress and will expand and gain volume when stress is reduced. This behavior is known as compression and rebound and is important in the design of foundations and other structu