A triaxial in-situ stress measurement system for investigating radial variability of the vertical-to-lateral pressure ratio in grain silos

Accurately measuring the three-dimensional stress state within bulk granular materials remains a significant challenge in instrumentation, limiting the validation and improvement of predictive models for bulk solid structures, such as grain silos. In this study, we introduce a novel triaxial pressure sensor for in-situ measurements in grain silos. This work aims to measure vertical and radial pressure distributions in bulk solids. The sensor was developed to allow for potential refinement and validation of mathematical models, focusing on the coefficient of vertical-to-lateral pressure ratio (k). We cover the design, calibration, and initial application of the sensor in a large-scale grain silo experimental setup. The sensor consisted of three orthogonal piston-style pressure cells housed in a 3D-printed spherical shell, with an estimated accuracy of ±0.35 kPa. Initial experimental measurements were obtained using the sensors placed in soft red winter wheat (13.5% moisture content) within a silo measuring 1.8 m in diameter and 6 m in height. Our preliminary data indicated differences in pressure readings at different radial positions, with calculated k-values of 0.23 near the wall, 0.17 at mid-radius, and 0.37 at the centre. While these observations suggest potential variations in k across the silo radius, additional experimental runs would be necessary to establish statistical reliability. The data were fit to Janssen's model by exploring the parameter space of the material properties (μ,ϕ,R). This sensor technology represents an advancement in measurement capability that could potentially contribute to more accurate mathematical models for bulk solid storage management in the future.