Fibre optic cable and micro-anchor pullout tests in sand

The paper describes a step in the development of a new distributed fibre optic strain sensing system using BOTDA technology for direct application in soil. A family of special tight buffered either metal free or steel armoured cables, which can endure the harsh soil environment, were designed together with a cable manufacturer. In addition, a system with micro-anchors attached to the cables was developed, which ensures that the cable moves together with the surrounding soil up to the micro anchor failure. The behaviour of the different cables and micro anchors was investigated in pullout tests in dry sand under low confining pressures at the real scale. The effects of dilatancy were studied with different initial sand densities and overburden pressures. In addition to the pullout tests, a full scale shear zone simulation with this novel sensor was carried out, in order to verify the sensor behaviour under real conditions.