Pdo按编号插入多行

I have little problem and i have no idea how to make it work. I want to make query that inserts rows by number. Example: If posted number is 8 then query adds 8 rows.

Any idea how to do it with pdo?

SQL

INSERT INTO
    foo(bar,baz)
VALUES
    ("val1", "val2"),
    ("val1", "val2"),
    ("val1", "val2"),
    ("val1", "val2"),
    ("val1", "val2"),
    ("val1", "val2"),
    ("val1", "val2"),
    ("val1", "val2")
;

PHP

//Insert Statement
$sql = 'INSERT INTO foo(bar,baz) VALUES ';

//Values ("val1", "val2"),("val1", "val2"),("val1", "val2"),..
for ($i = 0; $i <= 8; $i++) {
    $sql.= '("val1", "val2"),';
}

//Remove last Comma, and set ";" at the end.
$sql = rtrim($sql, ",") . ';';