array_merge
does not work the way you expect/need it to, but honestly I am not sure why you are making this so complicated. All you need is:
$args = array(
's' => 'keyword1 keyword2',
'orders' => 'DESC',
'showposts' => 60
);
// var_dump($args); // debug
$query = new WP_Query($args);
var_dump($query->request); // debug
The built is search parser will break the s
string on the spaces and construct a functional query for the terms.