If you have ever backed a long trailer down a narrow driveway, you know how it goes. Every small correction at the wheel becomes a big swing at the back, the mirrors stop telling the truth, and everyone watching suddenly becomes an expert. Now stretch that trailer to 1,000 feet and park it inside a mountain, in the dark, with the entrance being the only part of the route you can actually see.<\/p>\n
That is more or less what crews in Lesotho pulled off with the machine now grinding toward the middle of the Maluti mountains. In November 2025, a tunnel boring machine longer than the Titanic entered a mountain in reverse, crawled nearly a mile down an access tunnel backward, got turned around in an underground chamber, and started cutting basalt toward a second machine digging in from the other side. Somewhere under peaks that rise past 3,000 meters (nearly 10,000 feet), the two are supposed to meet.<\/p>\n
The tunnel they are building is the Polihali Transfer Tunnel, the spine of Phase II of the Lesotho Highlands Water Project. It runs 38.5 kilometers, roughly 24 miles, between two reservoirs, and when it is done, water will flow through it from the Polihali Dam to the Katse Dam by gravity alone. No pumps. The mountain does the work.<\/p>\n
Most tunnel borers of this class get assembled at the bottom of a shaft or at a portal, pointed at the rock, and sent on their way. The Polihali machine had a longer commute. It was partly built out in the open at the portal of an access tunnel, and on November 1, 2025, it began what the Lesotho Highlands Development Authority called a reverse entry<\/a>, stepping backward into the adit.<\/p>\n From there it traveled 1.484 kilometers, a shade under a mile, through that access tunnel to an underground assembly chamber. Tunnels and Tunnelling reported the machine was only about 43 meters long at that point, with the cutterhead, main drive and segment erector bolted on and the rest still to come. The stepping-in alone was expected to take three weeks.<\/p>\n In the chamber, crews finished the build and turned the machine around to face Katse. Boring started in January 2026, and by mid-February the machine had chewed through 235.8 meters of rock, according to figures the LHDA gave to Engineering News<\/a>. The official launch ceremony came later, on April 20, 2026, when ministers from Lesotho and South Africa gathered at the site in Mokhotlong to send it off properly.<\/p>\n How long is this thing? Depends on who you ask, and both answers are absurd. The LHDA put the fully assembled machine at 305 meters<\/a>, a bit over 1,000 feet. South Africa’s Department of Water and Sanitation described each machine at about 423 meters with everything attached. Either way, it is longer than the Titanic, and it drove itself into a mountain trunk-first.<\/p>\n The Polihali borer is not working alone. Its sister machine has been cutting in from the Katse side since January 15, 2025, when tunneling was launched at a ceremony in Ha Bereng, Leribe. That start mattered beyond this one project: per the Tunnelling Journal<\/a>, it was the first TBM boring in the Lesotho highlands in over 20 years, since the tunnels of Phase I.<\/p>\n Lesotho’s Prime Minister named that first machine Khoiti ea ‘Ngoaha Kholo, which the Tunnelling Journal translates as “the rat mole of 200 years.” It advances at roughly 20 meters a day, about 65 feet, installing a segmental concrete lining as it goes. By mid-January 2026 it had covered 614.5 meters, a bit over 2,000 feet.<\/p>\n The second machine got its name a different way. Lesotho ran a public naming competition, and the winning entry came from Malira Chefa, a Grade 11 student at St. Paul High School in Botha-Bothe. Her name for the borer, Leboborane la Monyokola Thita, was announced at the April launch, and she collected M12,500 for it, with another M37,500 going to her school, according to the Lesotho News Agency<\/a>. The machine got the name and zero maloti. Seems fair.<\/p>\n Each borer is responsible for about 17 kilometers of the route, per the LHDA, with drill-and-blast crews handling the trickier geological stretches. The plan has the two machines meeting midway through the tunnel. Between them sits solid basalt, and in places the rock cover above the alignment exceeds 1,000 meters. That is more than 3,000 feet of mountain sitting on the roof.<\/p>\n The hardware has a complicated passport. Both borers are 5.38-meter double-shield machines, a configuration picked for hard rock because it can keep advancing while it installs precast concrete lining segments behind itself, rather than stopping for each ring. They were designed by Robbins, the American TBM firm, and manufactured by CCCC Tianhe in Changshu, China, then shipped by sea to Durban and hauled overland into the highlands in mid-2025.<\/p>\n Robbins has been in these mountains before. During Phase I of the same water project in the 1990s, its machines cut the original transfer tunnels, and one of its 5-meter-class borers set world records<\/a> for its diameter class along the way: a best day of 86.3 meters and a best month of 1,344.3 meters before breaking through in September 1994. Thirty years later, the same design house is back for round two, working the same volcanic basalt.<\/p>\n We have covered machines that solve the getting-underground problem in stranger ways. Elsa, the borer under the Elbe<\/a>, is a 190-meter machine squeezing through a 16-foot-wide cable tunnel, and the Polihali rig has more than 100 meters on her. Paulina is eating Gotthard granite<\/a> in Switzerland, and Stella Rose earned her name<\/a> on this side of the Atlantic. None of them had to parallel park first.<\/p>\n Lesotho is a small, high country that happens to sit on the water supply of southern Africa’s economic engine. The Lesotho Highlands Water Project captures water in the mountains and sends it downhill to South Africa, and Phase II is the expansion that adds the Polihali Dam, a 165-meter rockfill wall, plus this tunnel to link its new reservoir into the existing system.<\/p>\n The numbers explain the urgency. Once the tunnel connects, annual water transfer to South Africa is set to climb from 780 million cubic meters to 1,270 million, per the South African government<\/a>, most of it bound for Gauteng, the province that contains Johannesburg and Pretoria. Hydropower generation at Lesotho’s Muela station is expected to rise by around 30% along the way.<\/p>\nTwo machines aimed at each other under the Maluti<\/h2>\n
An American design with history in these exact mountains<\/h2>\n
The water all of this is for<\/h2>\n