Double-shield tunnel boring machine

Tunnel Boring Machines For projects with difficult ground that still demand the speed of a Main Beam TBM Fractured rock can be an insurmountable obstacle if you buy the wrong machine. Your crew safety and efficiency is at risk, and so is your schedule. With a Robbins Double Shield Tunnel Boring Machine (TBM), your project can have a great safety record and peak performance. Robbins is no stranger to this type of TBM design. In fact, this is another type of TBM we invented! In 1972 Robbins built the world’s first Double Shield TBM for a customer who anticipated tunneling through large sections of fractured rock. In recent years, several Robbins Double Shield TBMs have broken world records for production. WHAT IS A DOUBLE SHIELD? A Double Shield TBM consists of a rotating cutterhead mounted to the cutterhead support, followed by three shields: a telescopic shield (a smaller diameter inner shield which slides within the larger outer shield), a gripper shield and a tail shield. In normal operation (“double shield mode”), the gripper shoes are energized, pushing against the tunnel walls to react the boring forces. The main propel cylinders are then extended to push the cutterhead support and cutterhead forward. The rotating cutterhead cuts the rock. The telescopic shield extends as the machine advances keeping everything in the machine under cover and protected from the ground surrounding it.