CGWL Observation Digital Water Level Recorder DWLR types Contac Us functions behaviours conditions appurtenant sub-surface foundations Piezometers water level construction applications simplest form pore pressure extension pipe Casagrande tip allegianceindia earth/rock fills accurate results economical design Proper evaluation piezometric level higher reliability working principles design improvement concrete structures geotechnical domain pore water pressure pressure transducers geotechnical sensors piezometer definition vibrating wire piezometer The  Casagrande piezometer Allegiance Water Management important geotechnical monitoring instruments