J. F. Springer, “Segmental Block Sewers,” Municipal Engineering, Volume LI, No. 6 (December 1916), pp. 214-216.
PDF version (printer-friendly).
Walter C. Parmley, The Parmley System of Arch Construction: Catalogue E, Segmental Concrete, Plain and Reinforced (New York, NY: Walter C. Parmley, 1927), pp. 3-68.
PDF version – 8.8 mb (printer-friendly).