What is a Cavity Wall? Construction and Advantages of Cavity Walls

Cavity formation in open wells


  • This fall in the level of water from the static water table conditions causes water held in the surrounding soil to flow towards the well.
  • As more and more water  drawn from the well the level of water goes on depressing causing increase in depression head.
  • Increased depression head leads to increase in the velocity of percolate
  • This is because depression head goes on decreasing as we move away from the well.
  • At certain rate of withdrawal of water from the well, the velocity increases to such an extent that it starts lifting up of the soil particles.
  • As more and more soil particles are lifte.
  • This forms a cavity below the bottom ofthe well.
  • The formation of such a cavity below shallow well is dangerous as it may lead to the subsidence of the well lining.
  • The maximum rate of taking out of water from such wells is therefore limited.
  • In case of deep wells resting on a mota layer the cavity formation below the bored hole is not dangerous.
  • A large cavity may deliberately be formed so as to increase the area of percolation and thus higher yields can be obtained.


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