GMT site, enclosure, and facilities: 2020 design and construction update

The Giant Magellan Telescope (GMT), one of three next-generation extremely large telescopes (ELTs), will have a 25.4- meter diameter effective aperture, and will be located on the summit of Cerro Las Campanas in Chile. Developing a new observatory for cutting-edge science operations and a 50-year lifespan poses a variety of design challenges. This paper discusses the designs that have been adopted in the GMT site master plan, including designs for the site infrastructure, telescope enclosure, and facilities. The GMTO site has been in active construction since 2015, and in the past two years has completed important steps in site development including completion of hard rock excavations for the telescope and enclosure foundations, construction of the underground utility distribution systems, and other infrastructure upgrades to support the current and upcoming construction work.