[4] Hanrahan played a role in establishing geotechnical engineering research at UCD by developing the first postgraduate course in soil mechanics there in 1955.
An initial repair strategy had involved the uncontrolled use of gravel for consolidation, leading to uneven settlements and road deformations.
To rectify this, Hanrahan proposed reconstruction using bales of horticultural peat as a lightweight fill, topped with gravel, which successfully stabilised the road.
He built upon foundational studies on soft soils by Albert Sybrandus Keverling Buisman and others, conducting laboratory tests on peat to explore its physical properties such as permeability, shear, and consolidation characteristics.
[6][7] Hanrahan's work extended the theoretical framework provided by Keverling Buisman by offering practical insights and empirical data, particularly focusing on the unique behaviour of peat under various conditions.
This progression signified a development from theoretical and generalized concepts of soft soil mechanics towards more specific and detailed understanding of peat's behavior in engineering applications.
[9] Hanrahan had an interest in the Irish language, Gaelic games, and he was a lifelong member of the St Vincent de Paul Society.