Bore well partial failure at 80 feet due to side earth crust breaking into pebbles.

Need Suggestions

Prior before drilling we have consulted Geologist of Ground water department as per his advise we have to go up to 200 feet. Till 50 feet we didn't had any issues, At 80 feet the bore vendor said the side rocks are soft rocks which are breaking into pebbles which is not advisable to drill further, if you drill further the bore rod may struck and we may not able to remove it, and so he stopped. Could you please suggest how should we proceed further ? Is there any way to overcome this.