From the foundation design and construction point of view, it is fundamental to have reliable information about the ground water level which lies within the zone of influence of a foundation to be settled. For this, the simplest way to gain information is to observe the nearby ground water table in open wells when they are available. We can find out the ground water table from boreholes. As we advance the borehole through drilling process, after the steady state condition has been reached, i.e. after an interval of 24 to 48 hours after completion of drilling process the ground water table has to be determined.
Casagrande Method for Ground Water Observation
As shown in the figure 1, Casagrande piezometer has an ordinary tube like structure. The piezometer unlike other tubes has a Norton porous tube inside which should be inserted into the ground at the desired level. The porous tube is connected to the ground surface through plastic tube. As the tube is lowered at certain depth, water enters the porous tube of casagrande piezometer and reaches the plastic tube. Thus, the ground water level is calculated by measuring the level of water in the plastic tube. For this purpose, the top of plastic tube is always kept above the ground surface.