A low-cost miniature immersible pore water pressure transducer

Abstract

The ability to measure pore water pressure accurately in geotechnical models is vital for allowing researchers to quantify effective stress and, frequently, its temporal variation. The earliest use of electrical devices to measure pore water pressure in specific locations within a model employed a standard laboratory pressure transducer located outside the boundaries of the model connected to tubing inserted into the model. However, this technique was superseded by the development (some 40 years ago) of submersible miniature pore water pressure measuring devices that could be located within a model to measure pore pressure directly at specified locations. In particular, miniaturisation allowed these transducers to be used in small scale centrifuge models. This facilitated, across the full spectrum of geotechnical engineering modelling, both enhanced understanding of mechanisms, by permitting quantitative analysis, and validation of numerical techniques. The earliest miniature transducers, the PDCR81 device manufactured by Druck, rapidly became universally adopted by the geotechnical modelling community. The production of this device was halted about 10 years ago, but other manufacturers have developed similar miniature pore water pressure transducers. Whilst the newer devices have been demonstrated to be effective their unit cost is relatively expensive; owing to the low volume of manufacture. This can result in forced limitations in the number that may be in a model, or a reluctance to use them in zones of models where they might be damaged. The requirement for a cheaper but equally reliable device prompted the work described in this paper. This is now achievable because of the development for the consumer market of a mass produced robust, immersible pressure device that has a very low unit cost. The paper will describe the development of a miniature transducer, employing this device, that can be located within models in a similar way to the PDCR81