Obot, Obotowo W., O. O. Ite, and J. M. Ben. “Variant Design and Fabrication of an Earth Tunneling Machine”. European Journal of Engineering and Technology Research 3, no. 3 (March 28, 2018): 63–66. Accessed July 4, 2024. https://ej-eng.org/index.php/ejeng/article/view/421.