Jelly, 14 bytes
“_|__”ṁ700s70Y
###How?
How?
“_|__”ṁ700s70Y - Main link: no arguments
“_|__” - literal ['_','|','_','_']
ṁ700 - mould like something 700 long
s70 - split into chunks of length 70
Y - join with line feeds