$arr1=array(
  array(12,3,5,8,18,11,9)
);
$new=array();                           //新数组
foreach ($arr1 as $key=>$value){
    
            //循环第一层数组
    foreach ($value as $k=>$v){
    
             //循环第二层数组
        if ($v>10){
    
                         //判断
            $a=$v." ";                  //将第二层的值赋值给#a
            $new[]=$a;                  //将$a赋值给新数组
        }
    }
}   
print_r($new);                      //输出新数组