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https://www.robbinstbm.com/wp-content/uploads/2017/05/IMG_5256-1024x768.jpg1024768Robbins Double Shield TBMs are the long-haul specialists of the tunnel boring world. Since their development in 1972, Double Shield machines have excavated some of the world’s longest tunnels and achieved world records in the process. The secret lies in their ability to simultaneously bore and line the tunnel with segments, making for faster excavation even in difficult ground.