Somebody had posted on this site about a waterjet TBM as a Chinese innovation.

Well, a friend of mine has e-mailed me the link to a paper of researches from Brazil's 'Universidade Federal de Santa Catarina'. Paper is not that old. From 2018. It is published in an academic periodical called REM: International Engineering Journal. I understand it is published by a Escola de Minas  ('School of Mines" I guess, and No, it is not Colorado.).

They have designed a rectangular  water jet tunnel boring machine and did some mathematical modelling comparing it with conventional tunnel boring machine. I think their conclusion was it would work in soft rock but not so in hard rock tunneling.

Quite interesting paper. I am including here the abstract, but I am sure you will want to read the whole article by following the link below.

Water jet tunneling: a theoretical advanced rate evaluation

Rafael Pacheco dos Santos

José Marcos Faccin Guimarães

Patrícia de Oliveira Faria

Marcos Aurélio Marques Noronha

Universidade Federal de Santa Catarina - UFSC, Departamento de Engenharia Civil, Florianópolis - Santa Catarina - Brasil.

Keywords: tunnel boring machine; hydrodemotion; prediction model

https://www.scielo.br/scielo.php?script=sci_arttext&pid=S2448-167X2018000200159