This photo is from the Auburn Dam construction site, California, USA. According to the design, the thrust of the abutment was normal to the foliation, which is of great importance for the stability of the dam. The stiffness of the material in the perpendicular direction was much greater due to the orientation of the joints. However in the third direction, which is perpendicular to the aforementioned and to the orientation of joints (normal to the plane of of the screen) the stiffness would have been even greater.
Information collected during the field trip in the Sierra Nevada, as part of the "Engineering Geology" course curriculum, instructed by Professor N. Sitar, Department of Civil & Environmental Engineering, University of California at Berkeley.