From the article: requires <i>&quot;Possibly compact, homogeneous rock with little tendency to fracture.&quot;</i> That&#x27;s rare geology. It&#x27;s rare for a tunneling project to find nice hard homogeneous rock through which a tunnel can simply be bored without supports. Both the Gotthard Base Tunnel in Switzerland and the NYC East Side Access, although in areas where such rocks exists, ran into incompetent rock.<p>In practice, they&#x27;d probably have to line both the hole and the plug with something like tunnel lining segments.