I think you may need to stringify the data using JSON.stringify.
var data = JSON.stringify({
'StrContactDetails': Details,
'IsPrimary':true
});
$.ajax({
type: "POST",
url: @url.Action("Dhp","SaveEmergencyContact"),
data: data,
success: function(){},
contentType: 'application/json'
});
So the controller method would look like,
public ActionResult SaveEmergencyContact(string StrContactDetails, bool IsPrimary)