You have to tell what kind of relation it is for multiple meta querys. Use it like this 'relation' => 'XXX', (AND, OR …), in the meta_query array.
And in your query it should look like this:
$eventi = get_posts( array(
'post_type' => 'eventi',
'posts_per_page' => - 1,
'meta_key' => 'eve_start_date', //setting the meta_key which will be used to order
'orderby' => 'meta_value', //if the meta_key (population) is numeric use meta_value_num instead
'order' => 'ASC',
'meta_query' => array(
'relation' => 'AND',
array(
'key' => 'correla_evento_a_struttura',
// name of custom field
'value' => '"' . get_the_ID() . '"',
// matches exaclty "123", not just 123. This prevents a match for "1234"
'compare' => 'LIKE'
),
array(
'key' => 'eve_start_date',
'type' => 'DATE',
// You can also try changing it to TIME or DATE if it doesn't work
'value' => date( "j F Y" ),
// deve coincidere con output usato x data -> http://www.korian.it/wp-admin/post.php?post=11522&action=edit
'compare' => '>='
),
),
) );
