<?

$a = array(array(1,2,3), array(3,2,1));
$b = array(array(4,5,6), array(6,5,4));

var_dump(array_merge($a, $b));
?>

array(4) {
  [0]=>
  array(3) {
    [0]=>
    int(1)
    [1]=>
    int(2)
    [2]=>
    int(3)
  }
  [1]=>
  array(3) {
    [0]=>
    int(3)
    [1]=>
    int(2)
    [2]=>
    int(1)
  }
  [2]=>
  array(3) {
    [0]=>
    int(4)
    [1]=>
    int(5)
    [2]=>
    int(6)
  }
  [3]=>
  array(3) {
    [0]=>
    int(6)
    [1]=>
    int(5)
    [2]=>
    int(4)
  }
}