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2. Discussion of “Foundation Performance of Tower of Pisa”
3. Miller R. D. (1974). “Geology of the Omaha Council Bluffs area.” Geological Survey Paper No. 472 U.S. Government Printing Office Washington D.C.
4. “Slurry wall collapse causes $500 000 damage.” (1974). Engrg. News Record Jan. 31 12.