A. Firoozfar, A. Rostami, H. Ghaderi, H. Zamani, and A. Rostamkhani, “Assessing the Effects of Length, Slope and Distance between Piles on the Bearing Capacity of a Pile Group under Axial Loading in Granular Soil”, Eng. Technol. Appl. Sci. Res., vol. 7, no. 5, pp. 1894–1899, Oct. 2017.