Source: http://www.ests.um5.ac.ma/cours/Dipl%C3%B4me%20Universitaire%20de%20Technologie/G%C3%A9nie%20Civil/Semestre%2002/G%C3%A9otechnique%20I/Td_elt%20de%20correction%20g%C3%A9o1.pdf