Two days back I got a 6.5 inch borewell drilled upto 35o ft. I encounterd a water of 1inch at about 80ft and the other at 220ft of 1inch. For this a 39ft MS steel pipe of 2mm guage is used as casing. The rock was found at 36ft and the drilling in rock was for 3 more feet totalling up for 39ft.
While drilling was in progress, The driller said that he met a loose soil gap in between 70 and 80ft. I just enquired asked him as how could he asses the soil that is present at 80 below. He said that while drilling, the drill bit abruptly dropped 1 foot below instead of progressing in a steady way. He said that the water that came out during that period was mud mixed brown water.
On further discussions with the driller, He said that there is a gap in the rock of 1foot height and it may colapse the borewell depth to 80ft. He also warned that the pump and other accessories may get clogged in the soil below.
The dirller gave an advise of inserting 5" plastic pipes with holes in it upto 350ft -till the bottom from top. He said this was the only way to rescue the borewell and stopping it from collapsing. Though it an expensive advise, I went for it which costed a huge money apart from drilling expenses.
The question is- does the dirller's advise really works? Did he really met a loose soil gap (bit dropping) while drilling?
As I am constucting a new house and I wont be able to fiddle with the well by getting dirlling machine to the spot after the constuction I plan to set right the things now.