<?php

$sum = 0;
$ar = array( 
array(
  array(10,10,10),
  array(10,10,10),
  array(10,10,10),
  array(10,10,10)
),
array(
  array(20,20,20),
  array(20,20,20),
  array(20,20,20),
  array(20,20,20)
),
array(
  array(30,30,30),
  array(30,30,30),
  array(30,30,30),
  array(30,30,30)
)
);

array_walk_recursive(
	$ar,
	function($v) use (&$sum) {
		$sum += $v;
	}
);

echo $sum;