Wellerson Bastos, Marcos Pimenta Filho, Luiza Almeida, Marina Ferreira & Mauro Santos Junior


Vibrating wire piezometer filters can be classified into two main types based on their air entry capacity. Low Air Entry (LAE) filters have air entry values (AEV) ranging between 5 and 10kPa and are widely used in soils with varying permeability[7,15]


. Although these filters may temporarily desaturate when the soil water


level drops, they tend to resaturate quickly once the water level rises again. However, they are not suitable for suction measurements, as they cannot register significant negative pressures. On the other hand, High Air Entry (HAE) filters have AEVs exceeding 100kPa and are designed to remain saturated even in partially saturated soil conditions[7,15]


]. Nevertheless, maintaining their saturation requires meticulous care, especially


in clayey soils, where their efficiency can be compromised due to the difficulty of fully removing air bubbles. To ensure adequate saturation, various methods are recommended, as indicated in the manuals from different manufacturers. The boiling method[13]


, for instance, involves submerging the filter in deaerated


boiling water for 15 to 30 minutes, followed by slow cooling in a sealed container, allowing complete expulsion of air from the filter interior. This method is often cited as effective for HAE filters, which demand complete and uniform saturation. Another commonly used technique is the vacuum chamber method, where the dry filter is placed in a low-pressure environment before introducing deaerated water, ensuring the removal of trapped air. Alternatively, in field conditions, a manual vacuum pump can be used to extract air from the filter while it is submerged in deaerated water, enabling effective saturation in hard-to-reach locations. For LAE filters, the simple immersion method involves carefully removing the filter, filling the chamber with deaerated water and gently reinstalling the filter before performing the zero reading with the readout equipment. This procedure, as illustrated in Figure 5, is widely employed due to its simplicity in field applications and its effectiveness for most use cases of these instruments.


Figure 5. Schematic of the simple immersion saturation method for LAE filters (Source: [6,14,20]


2.3. Field zero reading procedures The initial zero reading is an essential step in the installation of vibrating wire piezometers, as it establishes the reference point for all subsequent pressure measurements. The accuracy of these measurements


110 | Dam Engineering | Vol XXXIII Issue 3


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