International Journal of Rock Mechanics & Mining Sciences 130 (2020) 104338 Available online 22 April 2020 1365-1609/© 2020 Elsevier Ltd. All rights reserved. Cuttability and drillability studies towards predicting performance of mechanical miners excavating in hyperbaric conditions of deep seafoor mining Cemal Balci a , Hanif Copur a, * , Nuh Bilgin a , Levent Ozdemir b , Glen R. Jones c a Istanbul Technical University, Mining Eng Dept, Istanbul, Turkey b Ozdemir and Associates, Denver, CO, USA c Nautilus Minerals Inc, Australia A R T I C L E INFO Keywords: Deep seafoor mining Hyperbaric conditions Performance prediction Specifc energy Cuttability Drillability ABSTRACT The research program outlined in this paper starts with the assumption that if there is a signifcant relationship between drilling and cutting specifc energies in atmospheric conditions, there would also be a signifcant relationship between these variables in hyperbaric conditions. Five “model rock samples” having uniaxial compressive strength varying from 9 to 160 MPa were subjected to full-scale laboratory drilling tests with polycrystalline diamond compact (PDC) drill bits and a core drill, as well as laboratory full- and small-scale linear cutting tests with a conical and chisel cutter in atmospheric conditions. As a result, signifcant correlations be- tween drilling and cutting specifc energies were found for atmospheric conditions of laboratory. PDC drill bits and core drill bit used in laboratory tests were also used in the subsea drilling operations under hyperbaric conditions in Bismarck Sea. The conical cutter used in the laboratory tests are intended to be used on mechanical miners for subsea metal production. Core samples taken from Bismarck undersea mineral deposits were also subjected to physical and mechanical property tests in the deck and separately in the laboratories of Istanbul Technical University; and small-scale linear cutting tests were also applied in the university. Signifcant corre- lations were also found between the results of small- and full-scale cutting test. It is concluded that the capa- bilities of in-situ measurements will permit to detect some physical and mechanical properties of undersea mineral deposits. These properties interpreted with laboratory drilling and cutting tests would serve a basis to predict performance of mechanical miners to be used in hyperbaric conditions. 1. Introduction It is believed that in general mining of subsea minerals will be of great concern in the near future in developing new resources for the good of human being. Since its inception in 1982, the International Seabed Authority (ISA), charged with regulating human activities on the deep-seafoor beyond the continental shelf, has issued 27 contracts for mineral exploration, encompassing a combined area of more than 1.4 million km 2 , and continues to develop rules for commercial mining of seafoor deposits. At the same time, some seabed mining operations have already been taking place within continental shelf areas of nation states, generally at relatively shallow depths, and with others at advanced stages of planning. 1 Seafoor massive sulphide (SMS) deposits, found at water depths up to 3,600 m, are products of high-temperature hydrothermal activity associated with seafoor volcanism. SMSs are considered for future commercial exploitation because of the presence of rich metal content such as copper, zinc, gold and silver. Physical parameters (geotechnical and geophysical) of SMSs are important for mining purposes to allow estimation of both the size of deposits and the amount of ore. 2 The frst commercial enterprise, expected to target mineral-rich sulfdes in deeper waters, at depths between 1,500 and 2,000 m on the continental shelf of Papua New Guinea, is scheduled to begin in early 2020. The main commercial focus of Nautilus Minerals is the Solwara 1 project to extract high-grade copper and gold from SMS deposits located at depths around 1,500–2,000 m in the Bismarck Sea. In 2009, Papua New Guinea granted Nautilus Minerals an environmental permit for the development of Solwara 1 in the Bismarck Sea for a term of 25 years and * Corresponding author. E-mail address: copurh@itu.edu.tr (H. Copur). Contents lists available at ScienceDirect International Journal of Rock Mechanics and Mining Sciences journal homepage: http://www.elsevier.com/locate/ijrmms https://doi.org/10.1016/j.ijrmms.2020.104338 Received 3 December 2019; Received in revised form 31 March 2020; Accepted 31 March 2020