Preparation of the standard sized cores from geological mixtures or fragmented rocks such as melanges, fault rocks, coarse pyroclastic rocks, breccias and sheared serpentinites is often extremely difficult. Therefore, determination of the mechanical parameters such as cohesion, friction angle and UCS is extraordinarily difficult for these types of rocks. This paper presents the results of studies using Ankara Agglomerate to develop an empirical approach for the determination of the UCS for a volcaniclastic mixture of strong andesite blocks within weak tuff matrix, formed from the aggregation of volcanically exploded rock debris mixed with ash fall (tuff), i.e. a bock-in-matrix rock or 'bimrock'. The uniaxial compressive strength of a volcanic bimrock can be predicted using the conceptual approach within as-yet poorly understood error limits. Therefore. the approach introduced is open to improvement depending on the number of data and cases including different type of bimrocks. (c) 2005 Elsevier Ltd. All rights reserved.