Abstract– The Shahid-Kalantari highway between Urmia and Tabriz cities in Iran, has experienced more than one meter of settlement 7.8 Km east of Urmia city. The soil investigations revealed that the existence of a peaty foundation (Urmia peat) caused this settlement. This motivated a research to investigate the geotechnical characteristics of Urmia peat.
A series of consolidation and direct shear tests were conducted on samples of Urmia peat and the relationship between the key mechanical and physical properties was investigated. The results show that the amount of organic matter (degree of decomposition) and initial void ratio are two important factors which control the mechanical behaviour of this soil. It was also found that the Cα/Cc concept of compressibility is applicable for Urmia peat.