Investigation on compressive and pullout behavior of cast-in situ piles using BOFDA technique.

The design and construction of cast-in situ piles rely heavily on the proper evaluation of the end-bearing and skin friction behavior of piles by in situ loading test. In this study, distributed fiber optic sensors based on the Brillouin optical frequency domain analysis sensing technique were employed to determine continuous force and displacement distributions along cast-in situ piles subject to a compressive load (CBP) and a pullout load (PBP). The results showed that the axial forces for both the CBP and PBP increase with increasing load level at the same depth, and the load transfer path is from the pile head to the pile bottom. The maximum compression and elongation occur in the pile head, decreasing with the embedded depth of the pile. For the CBP, the contributions of skin friction at the fill layer, silty clay layer, and sandy clay layer decrease with an increase in the applied load. The shaft resistances of all strata except the strongly weathered rock layer show strain-softening behavior. The contribution of the tip bearing resistance is dominant after the applied load of 5580 kN. However, the contributions of skin friction at all soil strata for the PBP fluctuate as the applied load increases. The shaft resistances of all strata show strain-hardening behavior, and the base axial stress is smaller than the overall skin resistance. [ABSTRACT FROM AUTHOR]