R, 62 bytes

Don't have the rep to comment, so posting as an answer: @user3297046's answeranswer can be golfed-down to 62 bytes:

cat(gsub('(.{70})','\\1
',paste(rep('_|__',175),collapse='')))

which results in

_|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|
___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|__
_|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|
___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|__
_|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|
___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|__
_|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|
___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|__
_|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|
___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|___|__