1. S.T. Ariaratnam, Sustainable Development through Innovative Underground Infrastructure Construction Practices, Arizona State University, USA, 2009.
2. E-Calc by Vermeer. Information on www.ucononline.com.
3. Information on www.nasttghgcalculator.com.
4. Information on www.gazprommash.ru.
5. Information on www.power-technology.com.