If you got bellow error when use memcached in Laravel, please check following steps.
exception 'Symfony\Component\Debug\Exception\FatalErrorException' with message 'Class 'Memcached' not found' in /var/www/gw/vendor/laravel/framework/src/Illuminate/Cache/MemcachedConnector.php:51
Install memcached
$ sudo apt-get install php5-memcached memcached
Enabled php5-memcached
sudo php5enmod memcached
Restart apache web server
$ sudo service apache2 restart
Check memcached service status
$ sudo service memcached status
* memcached is running
Clear cache
$ php artisan cache:clear