Calibration of tactile pressure sensing mats for static geotechnical centrifuge applications
The use of tactile pressure sensing mats has been gaining popularity among geotechnical centrifuge modellers. Tactile sensing systems such as Tekscan allow experimenters to obtain profiles of soil-structure contact pressures and visualise the results. This report builds upon previous work on the calibration of such pressure mats and describes how they were used to measure slab-soil and wall-soil contact pressures on basements models subject to heave movements in clay, for the benefit of future researchers who want to use tactile pressure mats for static geotechnical centrifuge applications. Each Tekscan sheet should be waterproofed by lamination and then calibrated. Known loads were applied onto Tekscan sheets using the Enerpac hydraulic frame in Schofield Centre. This produced individual calibration curves for each sensel. In contrast to previous work which fit a linear calibration relationship to measure cyclic load changes, large changes in pressure were expected in the basement heave centrifuge tests, with pressures sometimes dropping to near-zero values. Therefore, a quadratic fit with a forced zero intercept was applied to each sensel to capture the non-linearity of sensitivity. The dead weight of the basement slab and heavy fluid during spin-up and in-flight reconsolidation provided an independent check of the calibration factors. This check also generates a calibration adjustment factor which may account for the influence of centrifuge gravity on the tactile sensors’ sensitivity. The data was processed using Matlab with filtering in both time (averaging over 10 frames, typically) and space (taking special averages, typically over a 3×3 grid), and then presented as graphs and heat maps.