During the Plio-Pleistocene period, the Térraba and Limón Sur basins in Costa Rica became filled with alluvial and volcanic materials, forming a series of coarse deposits with similar properties corresponding to the Valle del General and Paso Real formations in the south area and to the Suretka formation in the Caribbean region. This geological process gave rise to what is currently described as conglomerates with a clayey silt to gravel matrix, being mainly characterized by a low uniaxial compressive strength (UCS) that is generally inferior to 20 MPa. These conglomerates have been researched at different stages of power generation and transport infrastructure projects, which have been related to the construction of some of the most significant engineering works of the country. Based on the research for design purposes, the follow-up during the excavation, and the monitoring during the operation of the works excavated in these materials, this type of rock mass was geomechanically classified by using the RMR system.

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