Casagrande filters

The piezometers are widely used to measure the piezometric quota of groundwater and for the measurement of pore pressure in saturated soils. The main feature that distinguishes the various types of piezometers is the volume of water required to get the measurement. The smaller the volume is, the more suitable the piezometer is to measure pressure variations very rapidly. According to the previous description, there are two main types of piezometers: those in open pipe and those of Casagrande type. The open pipe piezometer consists of one or more perforated pipes connected to the surface by means of one or more pipes with dead ends. In this case, water gets through the tube, then through the filter of sand and gravel obtained by filling the space between the pipe and the walls of the hole. Within the piezometer in open tube, water stabilizes at a specific level that represents the level of the surrounding groundwater. If the filter cell is cut off from the rest of the hole, it will serve to measure the water pressure in the layer in which it is installed. In this case, we deal with Casagrande filters, which are used for pore pressure measurements of soils on the average permeable. The measurement of the water level inside of open pipe and Casagrande piezometers is commonly done by using the electric water level meters or electric pressure transducer, possibly connected to a data acquisition unit.