Trąmpczyński, W, and D. Szyba. “Brief Notes: Kinematically Admissible Solutions for the Incipient Stage of Earth Moving Processes in the Cases of Various Pushing Wall Forms”. Engineering Transactions, vol. 39, no. 1, Mar. 1991, pp. 123-34, https://et3.ippt.pan.pl/index.php/et/article/view/1618.