Added to this that a tunnel would have to be about 50 km long and that the removal of earth would require a fleet of trucks etc it is liable to detection.
Unless there is a bridge, tunnel, or other special structure, this roadbed is constructed of in-situ soils or on earth embankments.
只要没有桥、隧道或其他特殊建筑，路基就可以建在土堤上。
3
Based on model comparison between the semi-infinite earth and the circular tunnel with peripheral infinite earth, the conception of long and large tunnel in the electrical meaning is put forward.