Evaluation of geomechanical and dynamic behaviors of caliche, caliche-terrace units for cukurova region

Caliche is a Plio-Quaternary aged chemical sedimantery unit. It forms especially in and over the highly to completely weathered upper most zone and on the erosional surface of the underlying carbonaceous units. The unit crops out many thousands of square kilometers in the Çukurova region to the north, which are unsuitable areas of agriculture. 1998 Adana-Ceyhan Earthquake caused severe structural damage in the Çukurova region. The fact that the most damage occurred in areas underlain by fine-grained alluvial deposits, is probably due, at least in part, to amplification of the ground motion particularly for longer period motion in this type surficial material. The most widespread similar structural damage also occurred in the Çukurova region in areas underlain by caliche deposits including either soft pan with low plastic clayey, sandy, sitly soils, or hard pan soils of mostly rocks which are very low streght appearence. In areas where structure types were mostly single or two-storey, high damage was observed in caliche grounds under dynamic loading and various researches have pointed out unclear opinions about the failure mechanisms. The aim of the study is to define the geomechanical characteristics of the caliche deposits and to identify the dynamic factors affecting the damage distribution within the caliche. The major effective factor of the damage distribution is the softpan level of the caliche with high shear wave velocity (Vs). The significance of the hardpan level is relatively low. Resonance effects occurr during an earthquake for low storey structures where their fundamental vibrational frequency matched that of the softpan thickness profile and the incoming earthquake ground motion. During the 1998 Adana-Ceyhan Earthquake, damage on caliche foundations was noted to vary with its thicknesses; the localised damage, attributable to local geology and topographic conditions was particularly highlighted. Key Words: Cukurova Region, caliche, earthquake, geomechanic, site response analysis