Geotechnical Instrumentation is frequently employed for monitoring the condition of reclamation. Sometimes two piezometers are installed inside the same borehole. What is the reason behind this?

For standpipes, they normally contain one plastic tube between its intention is to measure water level only. However, for piezometers, they are used for measuring pore water pressure in a certain depth below ground. For instance, if there are two clayey layers below ground at different depths, a multiple piezometer including two separate piezometers may be sunk at the same borehole to determine the pore water pressure at these layers respectively. This arrangement has the advantage that it saves the cost of installation of separate boreholes for several piezometers. However, the installation of multiple piezometers within the same borehole is affected by occurrence of leakage along the pipes as suggested by Marius Tremblay (1989).

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.