Bearing capacity of soil and settlement of foundation depends significantly on the location of ground water level (GWL). We will provide three cases of location of ground water table that influence foundation bearing capacity in our upcoming Post. During exploration of soil, we can determine level of ground water conveniently but may have some error.
In every exploration program, we can simultaneously determine the water level but in some especial cases we have to make exploratory boring only for determining water level. The purposes are like determination of artesian ground water.
Generally GWL can be determined by allowing water to reach equilibrium level in to the borehole. This will produce correct and simplified general procedure for determining GWL. Now we have to known how much time is required to reach this equilibrium.
Sandy soil:
We know that permeability of this soil is very high and equilibrium level is achieved very early. This is at most few hours after boring is done.
Clay soil:
The permeability of this fine grained soil is very low and it takes time to reach equilibrium. In most cases, it may take few weeks to be stabilized.
Depth of general water level is recorded by using a tape or any other measuring means like chain lowering into borehole.
Sometimes piezometer is used to measure depth of GWL. This method is used when accurate measurement is essential in geotechnical exploration. A piezometer used for this purposes, consists essentially of plastic standpipe which is attached to perforated pipe or any type of porous tip.
This tube is kept in position with packing of
-gravel
-coarse sand
It is usually sealed with impermeable clay (like bentonite)
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