Drilling borewell through pebbles and boulders in Hyderabad, AP : Advice required


I am from Hyderabad, Moosapet. We planned to drill 800 ft for a new borewell as per geologist's suggestions, as our old borewell with 350 ft dried up. We started 6.5 inch drilling and there was no yield till 335ft, and at 335 to 340 feet we were able to get water and suddenly the driller came to us saying he cannot go further as he was getting boulders and pebbles. He was concerned about the drill bit getting stuck inside. Finally up on our request he tried again & gave up. The drilling was stopped at 345 feet and a very low yield is observed. 80ft of PVC casing was installed.

Is there any method that will help us drill through the "pebbles & boulders" layer? Kindly advice on further action.

Harry Morwin