The major section of the city of Tehran, Iran has been developed on cemented 15 coarse-grained alluvium. This deposit consists of gravely sand to sandy gravel with some 16 cobbles and is dominantly cemented by carbonaceous materials. In order to understand the 17 mechanical behaviour of this soil, a series of undrained triaxial compression tests and 18 unconfined compression tests were performed on uncemented and artificially cemented sam19 ples. Portland cement type I was used as the cementation agent for preparing artificially 20 cemented samples. Uncemented samples and lightly cemented samples (1.5% cement) tested at 21 high confining pressure showed contractive behaviour accompanied with positive excess pore 22 water pressure and a barrelling failure mode. However, cemented samples and uncemented 23 samples tested at low confining pressure (25 and 50 kN/m2) showed dilative behaviour 24 accompanied with negative excess pore water pressure. Shear zones were formed in these 25 samples and a clear peak in excess pore water pressure and stress ratio against strain could be 26 observed. Test results showed that the limiting stress ratio surface for cemented samples is 27 curved and expands as the cementation and density increase. Unconfined compression 28 strength of cemented samples increases with increases in cementation and density as well.