As part of stability assessment of an underground room and pillar quarry in Oya, a geotechnical mapping was conducted and a single dominant joint set was observed in the quarry. The joints are large and persistent, and seen cross cutting the pillars. In an attempt to investigate the effects of joints on the pillar strength, a series of laboratory experiments were conducted on pillar samples of Oya tuff. The experiment comprises of intact, and discontinuum samples with through going joints at various dip angles. For long term safety after mining and countermeasure for joints effects backfilling experiments were conducted as well as the degree of backfilling. The results indicate the joint geometry (dip angle) has adverse effects on the pillars strength. It was further realized that the effects of joint inherent properties are less pronounced on the joint dip angles perpendicular and parallel to the uniaxial loadings.