If you don't want to destroy the original array with splice then you could do

my @a = 1..30;
my @b = map{ [ @a[ $_ .. $_ +2 ] ] } map{ $_ *3 } 0 .. $#a/3;

print "@$_" for @b;;
1 2 3
4 5 6
7 8 9
10 11 12
13 14 15
16 17 18
19 20 21
22 23 24
25 26 27
28 29 30
[download]