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ABSTRACT: Basaltic rocks display a wide range of porosity depending on size of vesicles as a result of their complex genesis. Predicting of strength of rock material have crucial importance for design of engineering structures such as dams, foundations, tunnels, and other engineering projects. The presence of vesicles within basaltic rocks has a direct impact on the uniaxial compressive strength (UCS) of the rock material. To investigate the relation between the UCS and vesicle ratio of basaltic rock, 32 core samples having a wide range of vesicle sizes were drilled from basaltic rock blocks taken from Diyarbakir-Karacadag, which is located in the Southeast Anatolian Region of Turkey. In the first step of the study, an image analysis technique is used to estimate the apparent porosity values of cores due to its vesicular structure. The upper, lower and lateral surfaces of core samples are scanned as digital images with high resolution and the images were analyzed by using ESRI GIS software. By using the threshold capability of the software, vesicle and rock material areas for every image was determined for statistical evaluations. Statistical relationships using different type of equations were investigated to estimate the porosity value for each core sample. In the second step, laboratory studies have been carried out to determine the UCS, porosity and apparent void ratio of core samples. According to comparison between UCS and porosity by using image analyses method, a rapid exponential decrease in UCS was obtained with an increase in the porosity value up to 10%. 1 INTRODUCTION Basalts have been used as construction materials in the form of crushed stone in several projects. The engineering properties of these rocks vary greatly because of variations in their weathering state and the presence of vesicles. These vesicles are non-connected so it difficult to determine some of the physical properties of the rock such as density and porosity values. If the pores are non-connected as in the case of vesicular basalt, determination of the porosity by laboratory test techniques becomes unsuitable. In these techniques, water never fills all the non-connected voids and the sample will only be partly saturated. Also, predicting of strength of rock material have crucial importance for design of engineering structures such as dams, foundations, tunnels, and in other engineering projects. The presence of vesicles within basaltic rocks has a direct impact on the uniaxial compressive strength (UCS) of the rock material.