As we can't import the calculated field in salesforce to tableau directly. Is there any turnaround for this?

 Importing directly might not be possible but you can always replicate the logic in tableau. For example, if you have done some calculations at the Salesforce end, you can do a similar calculation in the tableau calculated field as well. You can further check the article by tableau which share some best strategy on it- https://www.tableau.com/about/blog/2015/9/top-metrics-every-sales-executive-cant-live-without-43746