change a code that work for merge but not for intersect

inner $arraytot I have more subarray that I can merge two a two with cicle:

$result = array();
foreach($arraytot as $value) {
$result = array_merge($result, $value);
}

but if I use array_intersect not work;
this because I think at first iteration it does an intersection between
$result that is a empty array and the 1st subarray, so the result is a void
array and for the next iteration it will have always an intersection with a
void array and the subarray;