Temperature-compensated cone penetration test mini-cone using fiber optic sensors

The mechanical properties obtained by using a strain gauge are influenced by the temperature change that occurs due to the electrical resistance change of the strain gauge and cable. The temperature change, which occurs during cone penetration testing, can produce an unreliable cone tip resistance. Several types of cone penetrometers with diameters ranging from 1 to 7mmare developed by using fiber Bragg grating (FBG) sensors for the temperature compensation. The design concerns include the configuration, active and temperature sensor installation, and calibration. FBG active sensors monitor both the tip resistance and the temperature change, while the FBG temperature transducer only measures the temperature change. The experimental studies show that the tip resistance estimated by strain gauges is affected by the temperature change in both full and half Wheatstone bridges, but the tip resistance determined by the FBG sensors is independent of the temperature change. The tip resistances determined by the strain gauges and the FBG sensors are reliable after the temperature is compensated for. This study demonstrates that by using FBG sensors, cone penetrometers produce a more reliable cone tip resistance.