Along NS trending road cut between &Ccedil / ayyolu and incek, relatively thick tuffite layer of the Han&ccedil / ili formation has been exposed. It is alternating with other lacustrine deposits such as clayey limestone, marl, siltstone and mudstone. These units unconformably overlie the Mesozoic basement limestones of Akbayir formation. The illite rich tuffite consists of glass shards tridymite, biotite, quartz and plagioclase. It has a persistent areal extend and forms the foundation of the residential buildings at several localities. In this thesis, it is aimed to assess the engineering geological properties of the tuffite layer and to investigate its suitability as a foundation material. In order to accomplish this task, field studies and laboratory tests were conducted. Field studies involve detailed site geological observation. Laboratory studies include tests to investigate mechanical, physical and mineralogical properties of the tuffite. v Analyses revealed very weak nature of tuffite with strength values ranging between 0.1 MPa and 1.00 MPa. The tuffite is characterized with very high effective porosity (43.3%) and very low dry and saturated densities (1.19 Mg/m3 and 1.62 Mg/m3, respectively). The slake-durability tests yield medium durability. The durability index of tuffite is rated as very poor. Considering index properties and the durability assessment it is concluded that tuffite serves as a poor foundation material.