The following reference works are cited in this example problem:
Eurocode7: Geotechnical Design - Part 1: General Rules. DIN EN 1997-1:2014-3 (E).
Lazebnik, G. E. & Tsinker, G. P. (1998). Lateral earth pressure at rest. Monitoring of Soil-Structure Interaction: Instruments for Measuring Soil Pressures. 165-183. New York: Springer.
Rankine, W.J.M. (1857). On the stability of loose earth. Philosophical Transactions of the Royal Society of London. 147, 9-27.