For civil engineering, calculations are of central importance; they provide a sense of security. However, in soil mechanics the reliability of calculations is reduced for several reasons: aside from incomplete constitutive equations and their calibration based on experiments burdened with errors, some other problems are the spatial scatter of soil properties, missing knowledge of the initial stress field and infinite extending of the considered bodies. Validations reveal the poor reliability of computation results. To cope with such problems increased margins of safety, cautious building (observational method) and reliance upon authorities like experts, computer codes and codes of practice are used.