A novel non-contacting laser displacement transducer technique for volume change measurements of unsaturated soils

A novel non-contact total volume change measurement system was designed using an ultra high accuracy laser displacement sensor to measure the water level changes resulting from the volume change of the soil specimen. The suggested system consists of an open inner cell located inside a Bishop and Wesley cell, an external measurement cell connected to the open inner cell (a necessary arrangement due to the limited space in the Bishop and Wesley cell), and a Linearised Charge-Coupled Device (Li-CCD) laser displacement sensor fixed above the measurement cell. A number of calibrations were performed to account for the effects of various factors including water compressibility, temperature, cell pressure and system creep. Comparative measurements of volume changes of saturated samples during triaxial testing using the suggested technique and conventional techniques were then performed. These showed overall very good agreement between the methodologies and gave confidence in the suggested technique. This preliminary study therefore proved the feasibility of the technique and showed promise for the development of a fairly simple tool enabling accurate volume measurements during triaxial testing. Further studies and refinement of the tool are necessary for the adoption of the technique with confidence and its potential commercial exploitation.