Show posts of subcategories inside parent-categories

I’m currently working on a website which contains a custom posttype ‘Resources’ with custom taxonomy ‘resource_category’.
The archive-page of this custom posttype should display all the parent-categories, subcategories and posts they contain.
something like this:

-Parent-category
–sub-category
—Post (title, link & excerpt)
—Post
–sub-category
—Post
-Parent-category
–sub-category
—Post
—Post
…

This is what i currently have:

<?php
$args = array(
  'orderby' => 'name',
  'order' => 'ASC',
  'taxonomy' => 'resource_category',
  );
$categories = get_categories($args);
foreach($categories as $category) { ?>
<section>
<div class="container"><div class="col1">
<h3><?php echo $category->name; ?></h3>
<?php $descendants = get_categories(array('child_of' => $category->term_id)); ?>
<?php foreach ($descendants as $child) {
$sub_args = array(
'cat'      => $child->term_id,
'order'    => 'ASC'
); query_posts( $sub_args );?>
<h4><?php echo $child->cat_name; ?></h4>
<ul>
<?php while (have_posts()): the_post(); ?>
<li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a><?php the_excerpt(); ?></li>
<?php endwhile; ?>
</ul>
<?php } ?>
</div></div>
</section>
<?php }; ?>

But it doesn’t seem to work.
Is there a way i can do this?