This paper presents results of the 1st stages of Task A of the Decovalex 2011 project, the numerical modeling of the Aspo Pillar Stability experiment performed by the Aspo Hard Rock Laboratory of the Swedish Nuclear Fuel and Waste Management Company (SKB). The objective is to perform back calculation of the Aspo pillar behavior using state of the art numerical modeling techniques for the material behavior. The work is divided into three stages and it is the first stage of the work that will be presented in this paper. Seven international teams from six different countries participated in the task and contributed to the results presented in this paper, concerning back calculation of uniaxial and triaxial compressive core testing and elastic back calculation of the stress path for excavation-induced stresses. The results are useful for understanding the occurrence of spalling in the upper part of the pillar during excavation and the stress path modeling gives the first approximation of the yielding strength of the pillar. The calculated results agree well with observations measured during experiment.