<?php


$input ="[['name' => 'test'], ['type' => 'VARCHAR(15)'], ['null' => false], ['prim' => true]],
[['name' => 'test'], ['type' => 'VARCHAR(15)'], ['null' => false], ['prim' => true]]";

$raw = '['.str_replace(array("[[","]]","=>","'","[","]"),array("{","}",":",'"',"",""),$input).']';

$output = json_decode($raw,true);

print_r($output);