The effects caused by changes in load and drainage conditions are usually very minor. This observation is particularly true for all tasks that deal with the effects of flowing water, as minor deviations in layering, which cannot be revealed by test drilling, can have a significant impact. For this reason, the application of theoretical soil mechanics in earth and foundation engineering differs fundamentally from the application of technical mechanics in steel, wood, and solid construction. The elastic properties of materials like steel or reinforced concrete are only slightly variable, and the laws of applied mechanics can be transferred to practical applications without restriction. In contrast, theoretical investigations in soil mechanics only represent working hypotheses.