Page "Geotechnical engineering" Paragraph 9

Several foundation-related engineering problems, such as the Leaning Tower of Pisa, prompted scientists to begin taking a more scientific-based approach to examining the subsurface.

The earliest advances occurred in the development of earth pressure theories for the construction of retaining walls.

Henri Gautier, a French Royal Engineer, recognized the " natural slope " of different soils in 1717, an idea later known as the soil's angle of repose.

A rudimentary soil classification system was also developed based on a material's unit weight, which is no longer considered a good indication of soil type.