Create grid type custom post thumbnail slider with flexslider

I am trying to this grid view gallery slider with flexslider. My html code is :

<ul class="slides">
<li>
 <div class="photo-1">
 <img src="images/photostream/one.jpg" width="101" height="102">
 <span class="flex-photoCaption"><a href=""> <i class="fa fa-search"></i></a></span>
 </div>
 <div class="photo-1">
 <a href=""><img src="images/photostream/two.jpg" width="101" height="102"></a>
  <span class="flex-photoCaption"> <a href=""><i class="fa fa-search"></i></a></span>
 </div>
 <div class="photo-1">
  <a href=""><img src="images/photostream/three.jpg" width="101" height="102"></a>
 <span class="flex-photoCaption"> <a href=""><i class="fa fa-search"></i></a></span>
  </div>
  <div class="photo-1">
   <a href=""><img src="images/photostream/four.jpg" width="101" height="102"></a>
 <span class="flex-photoCaption"> <a href=""><i class="fa fa-search"></i></a></span>
   </div>
   </li>
<li>
  <div class="photo-1">
 <img src="images/photostream/one.jpg" width="101" height="102">
  <span class="flex-photoCaption"><a href=""> <i class="fa fa-search"></i></a></span>
  </div>
   <div class="photo-1">
   <a href=""><img src="images/photostream/two.jpg" width="101" height="102"></a>
   <span class="flex-photoCaption"> <a href=""><i class="fa fa-search"></i></a></span>
   </div>
  <div class="photo-1">
    <a href=""><img src="images/photostream/three.jpg" width="101" height="102"></a>
  <span class="flex-photoCaption"> <a href=""><i class="fa fa-search"></i></a></span>
    </div>
  <div class="photo-1">
   <a href=""><img src="images/photostream/four.jpg" width="101" height="102"></a>
 <span class="flex-photoCaption"> <a href=""><i class="fa fa-search"></i></a></span>
  </div>
   </li>

 </ul>

I am writing :

<ul class="slides">
<?php 
global $post;
$photo_args = array(

 'post_type' => 'photo_gallery',
 'posts_per_page' => -1,
 'order'  => 'ASC',
);
 $photo_querys = get_posts( $photo_args );
 ?>
<?php foreach($photo_querys as $post)  : setup_postdata($post); ?>
<li>
 <?php 

$element_show = 1;
$element_show  = '<div class="photo-1">'. the_post_thumbnail('gallery_image').'
<span class="flex-photoCaption"><a href=" '. get_permalink(). '"> <i class="fa fa-search"></i></a></span></div>';

$element_to_show = 2 * $element_show  ;?>
 <?php echo $element_to_show ; ?>
</li>
<?php  endforeach; ?>
<?php wp_reset_postdata();  ?>
</ul>

Images are showing but there is showing "0" value after the "li" elements

This is from my view source

<li style="width: 120px; float: left; display: block;">
<img draggable="false" src="http://localhost/azadfoundation/final/wp-content/uploads/2014/11/selfdefense8_fs-100x102.jpg" class="attachment-gallery_image wp-post-image" alt="selfdefense8_fs" height="102" width="100">                                          
0
</li>

The below image is the output

I know I am going wrong. Can anyone please help ? Thanks in advance.