Lever-arm based sample deformation transducer for axial and radial measurements in triaxial apparatus

This paper presents an innovative non-contact system for measuring axial and radial strains in a triaxial apparatus specifically tailored for small diameter soil specimens. By employing miniature magnetometers positioned both inside and outside the triaxial cell, the design overcomes errors inherent in internal and external sensor mounting and interactions with the test medium. Initial signal conditioning is performed on a microcontroller while a trained neural network translates the non-linear relationship between magnetic field readings and actual displacements. The system achieves a resolution of 0.001 mm and is fully resistant to high pressures and water ingress. Calibration and comparative experiments on standard materials and natural soils demonstrate its superior accuracy in determining elastic moduli, detecting stiffness degradation at very low strains, and identifying yield limits, outperforming conventional external measurement techniques. This versatile approach provides a powerful tool for advanced soil mechanical characterization in both laboratory testing and numerical modeling.