Effect of Soil Particle Size on the Accuracy of Tactile Pressure Sensors

This paper investigates the effects of soil particle size on the measurement accuracy of single-point type tactile pressure sensors when used for measuring soil contact stresses. Sensors with two different diameters (${\mathrm{D}}_{\mathrm{sens}}$) are integrated into an oedometer cell. Granular materials with a wide range of particle diameters (${\mathrm{D}}_{50}$) and angularities (from rounded to irregular shaped) are evaluated, resulting in a wide range of ratios of ${\mathrm{D}}_{\mathrm{sens}}/{\mathrm{D}}_{50}$ from 2.6 to 105.8. The test results show that the soil particle size significantly affects and exponentially correlates with the measurement accuracy of the sensor. A threshold ${\mathrm{D}}_{\mathrm{sens}}/{\mathrm{D}}_{50}$ of 10.5 is identified for the sensor, beyond which the error is less than 5%. It is also shown that even for ratios of ${\mathrm{D}}_{\mathrm{sens}}/{\mathrm{D}}_{50}$ as large as 40, an error of approximately 2% can be observed, which is intrinsic to the sensor.