Stress & displacement measurement for geotechnical modelling using open platform

Stress and displacement measurements are key tasks for geotechnical modelling. Although broad range of techniques are available; the heterogeneity of the soil and the lack of direct observation of the foundation elements cause accurate measurements hard to obtain. Selection of whether a complicated acquisition system with expensive sensors, versus a simple but large number of sensors using open platforms, becomes a major challenge. To address this problem a range of approaches were implemented; a high-end data acquisition board connected to miniature stress transducers to measure the stress in the soil; sensitive films and a dedicated software to measure soil-structure contact stress; Arduino based IMU sensors for measuring inclination to calculate corresponding displacements and LVDTs for verification of the calculated displacements. A stress transducer, connected to a high-end data acquisition board, enclosed in a silicone pacifier that is filled with distilled water, was exposed to a set of different pressures under the soil. Although the results from experiments held on the same date were coherent, the repeatability at different dates was weak. The prescaled sensitive films and IMUs were attached on the blocks of the segmental pile, and the pile was placed in a large-scale direct shear test box which was then filled with loose sand. The pile head was fixed and was allowed to displace up to 5 cm with a rate of 1 mm per minute. It was observed that the obtained horizontal pressure by using the films was compatible with calculated value using the relation between the force and the area. Also, a series of three-point bending tests with external LVDTs were performed to verify the deflections from the inclination measured with IMUs. The calculated deflections were within the range of 10% error when compared to those measurements from LVDTs.