Arthur Casagrande (August 28, 1902 – September 6, 1981) was an Austrian civil engineer.

At the age of 22 (1924) he obtained his degree in civil engineering from the Austrian National University. He then remains at the university as a full-time hydraulics laboratory assistant. After the First World War there was not much job offer for the field of civil engineering, this and the death of his father caused Casagrande to decide to emigrate to the United States.

While there he visited MIT (Massachusetts Institute of Technology) for a job interview, where he met Professor Karl von Terzaghi, who immediately hired him as his private assistant. He soon became Terzaghi's right-hand man, who was his greatest inspiration. From 1926 to 1932, Casagrande worked alongside Terzaghi on various investigations of techniques and devices for the study of soils, all of which belonged to MIT. In 1929 both (Casagrande and Terzaghi) traveled to Vienna to install what would be the largest research center for soil mechanics.

He returned on his own to the United States and, from MIT, became a pioneer making great contributions to soil mechanics, such as: the Casagrande spoon to determine the liquid limit, the hydrometer test, he was the first to conduct the triaxial shear test, among others. It is safe to assume that "line A" on the plasticity chart is for Arthur's name.

In 1932 he entered Harvard University, where he began the soil and foundation mechanics program. All programs on this subject worldwide adopt the same format as that devised by Casagrande, and that is why he is recognized, after Terzaghi, as the most relevant figure in soil mechanics. Casagrande served as an inspiration for many important geotechnical engineers in history. Although Terzaghi is also credited with the advances produced at Harvard, it was Casagrande who actually developed the programs used today.

In 1936 he organized the first conference on soil mechanics and foundation engineering, something that Terzaghi considered too much due to the short time he had in this science. However, after this conference, soil mechanics becomes an essential part of civil engineering, and this period is considered the formation of modern soil mechanics. Casagrande's work at Harvard lasted around four decades, during which he published numerous publications.

Casagrande's contributions to soil mechanics were recognized by awarding him the “Rankine Lecturer” by the Association of Civil Engineers of the United Kingdom, and he also received the first “Terzaghi Lecturer” award by the ASCE (American Society of Civil Engineers).