Calibration method and effect factors of miniature pore water pressure transducer for geotechnical centrifuge modelling
摘要
Accurate measurement of pore water pressure is one of key technologies in geotechnical centrifugal modelling. Aiming at noticeable scatter of dynamic pore pressure measuring results in the recently repeated dynamic centrifugal liquefaction tests at home and abroad, a novel device for calibrating the response of dynamic pore water pressure transducer is proposed. Moreover, three types of internationally widespread pore water pressure transducers are selected to perform a series of comparison tests over their dynamic performance evaluation and effect factors. The main conclusions are drawn: (1) The proposed calibration device has advantages of long-term high-pressure sealing, uniform load transferring and random loading generation, which can meet reliable calibration requirements of pore water pressure dynamics for dynamic centrifugal tests. (2) Due to the compressibility of air inside the inner chamber and porous stone of transducers, air is not suitable for direct usage as a pressure medium for dynamic calibration. (3) With full saturation of the porous stone, the maximum response frequencies of the three types of sensors are all about 200 Hz, basically meeting the requirements of dynamic centrifugal liquefaction tests. (4) Using the vacuum-stirring saturation method from China's code, the three types of transducers present phenomena of different amplitude attenuations and phase delays, which indicates that different transducers, saturation methods and calibration devices are likely the reasons for noticeable scatter of pore pressure time series and liquefaction thresholds in the repeated centrifuge tests. (5) With three saturating methods of vacuum-stirring, continuous-vacuum and atmospheric pressure, the periods requiring full saturation of the three-type transducers for reliable measurement are 9 h, 16 h and 4 d, respectively. The proposed calibration device, method and conclusions are of paramount importance to advance and standardize the measurement technology