As per the Hvorslev method, water table level can also be located in a borehole used for soil investigation. That type of bore hole should have a casing to stabilize the sides. It uses almost the same technique, the rise in water level determines the water level locations. However, there is a slight difference. Unlike Casagrande piezometer method, this method consists of hailing the water out of the casing and observing the rate of rise of the water level in the casing at different intervals of time until the rise in Water level becomes negligible.
Figure 1 shows the rise of water level in the borehole at different time intervals. The height of water above the levels 0 – 0, 2 – 2 and 3 – 3 is calculated from the following equations.
Ho = Height above level 0 – 0 =
H2 = Height above level 2 – 2 =
H3 = Height above level 3 – 3 =
The depth of Water table is taken as the average of three levels given by heights H0, H2 and H3 i.e. level of the water table is given by