Two parallel trenches were dug. The minimum distance between them was about 8 feet [2.4 m], but the usual distance was 14 feet [4 m], and they were even wider on curves.
Người ta đào hai cái rãnh song song, cách nhau ít nhất khoảng 2,4 mét, nhưng thường là 4 mét, thậm chí còn rộng hơn ở những khúc quanh.