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I am building a bio methanisation plant here in kerala. The digester is of Dheenabandhu model...i.e almost a sphere shape. The half of the same (hemisphere) is under ground and the rest is above ground.

The underground part is built by 100mm RCC over 100mm PCC. But unfortunately since the water table is high (almost ground level) during construction itself water percolated into the underground hemisphere structure.We tried to close every entry but the water kept penetrating inside.If one entry is closed it will make another opening.

Now, the concrete is set and still ground water is percolating inside the RCC structure.

Please suggest a good method to arrest the leakages of the porous underground RCC structure, where the watertable around is quite high(almost upto ground level)

Best regards,
Geoffrey.
Kerala, India.

Answer
Hello Geoffrey, You didn't mention any ground preparation, French drains, dewatering methods used during construction..a ground water dewatering system to keep the water at bay while building your base would have helped, a clay bentonite subsurface with a heavy vapor barrier laid down under the pcc followed by the rolled concrete should have prevented any infiltration.  At this point it may be too late, especially if the water is coming up through the base.  The nice thing about bentonite is that it swells when wet forcing the substrate to compress even further.  One option I can think of is to install a perimeter drain with a sump to draw the ground water down and away from the sphere.  If there is any kind of elevation you can possibly gravity drain it away from the system thus avoiding the energy required to pump the water away.  You didn't mention how large of a tank it is bit it may be possible to lay down bentonite mats inside the shell and then add another layer of concrete on top of that.  If total volume is a priority this may decease your capacity however. A fiberglass lining or gunite pebblecrete may be a possibility.   Waterproofing should always take place at the outermost point, if you can unearth the sides and apply a heavy mastic coating that may help keep some of the intrusion at bay..if I had a better picture of your installation methods I might have other ideas as well..sincerely Bruce E. Johnson, bejohnsonconsulting.com

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Bruce E. Johnson

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I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.

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Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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