 
 <prompt> ```Summarize dis article:

Tunnel boring machines, wey dem dey call TBMs or "moles," get circular plates for di front wey dem dey call shields. Disc-shaped cutters for di shield dey tear through rock and dirt, wey dey pass through openings for di shield onto a conveyor belt inside di TBM wey go deposit am for back of di machine. Di types of TBM shields dey vary according to whether di mole dey dig into soft, wet ground or hard rock. Shield diameters fit range from Aker Wirth’s 26.3-foot (8.03 m) shield on top its TBM wey dem use for Switzerland’s Linth-Limmern power stations to Hitachi Zosen’s “Big Bertha,” wey get diameter of 57.5 feet (17.5 m). Moles wey dem design to dig tunnels below di water table also get chambers for di front to pressurize di ground wey dem dey dig through. For big jobs, dem fit need multiple TBMs. The Channel Tunnel need 11. For surface level tunnel, dis one no dey hard. If di tunnel dey bored deep underground, an access shaft, wey usually dey circular, dey drilled and lined with concrete. Di TBM dey lowered into am, and di tunnel dey excavated from dat point. For long tunnels, dem fit drill multiple access shafts. When di tunnel don finish, di access shafts fit become ventilation shafts and/or emergency exits. If dem no use am like dat, dem go leave am for di life of di tunnel. Segments of pre-cast concrete dey erected behind di TBM to form a ring at pre-determined intervals. Di sprayed concrete, or shotcrete, dey coat and stabilize di tunnel walls. The shotcrete fit include steel or polypropylene fibers to strengthen am, much the way steel rebar dey used to strengthen cast concrete. The shotcrete also dey contain an accelerant to help am stick to di tunnel walls and dry quick.

Summary:``` <response>: "Choose di correct tunneling machine for di work. Carry di machine enta position. Set up tunnel supports as di machine dey bore through. Spray concrete for di excavated walls between di support rings." 