Unable to get value from checkbox bootstrap toggle in PHP

Html and PHP :

<input type="checkbox"  name="get_ckvalue" data-toggle="toggle"  data-on="Available" data-off="Day Off" value="true" />

<?php
echo $_POST['get_ckvalue']; // Give null as a output 
?>

I am using checkbox button with bootstrap toggle and i want to get the value (true/false) , but i am getting null as a result . i don't know what is wrong . How can i get the value from checkbox . i am new to html and bootstrap . Thank in advanced . its just the fragment of code . i have successfully submitted the POST .