Axial and circumferential behavior of rock-socketed FRP-SSC composite piles monitored by distributed optical fiber sensors

Abstract

Traditional pile foundations in harsh marine environment may experience steel corrosion or concrete deterioration. Besides, conventional measuring devices such as strain gauges and vibrating wire extensometers are sensitive to environment and only provide discrete strain data at certain points leading to inadequate information of the entire pile response. This study investigates an innovative and sustainable design of fiber-reinforced polymer (FRP) seawater sea-sand concrete (SSC) composite piles under static loading in physical model tests. Two rock-socketed model piles with different structural configurations, i.e., FRP rebars reinforced SSC and FRP tube confined SSC, were installed in the physical model tests. A fully distributed sensing method based on optical frequency domain reflectometry was used to measure the axial and circumferential strain profiles along the pile length. Besides, the displacement accumulation, end bearing pressure, and shaft friction mobilization within the rock socket under static monotonic loading were analyzed and explored in detail. The test results indicated that the distributed axial strain profiles of both model piles appeared to follow similar trends along the depth with strain concentrations in one third region near the pile head, which led to pile failure at that section. The continuous strain data enabled calculating reliable shaft friction values which showed maximum mobilization in the upper one third region of the socket. The distributed circumferential strain profiles along the pile length provided reliable information of the localized potential failures around the pile circumference, corresponding well with that from axial strain measurement. Finally, existing analytical solutions of partially embedded piles were adopted to describe the test results, showing good agreement of the test findings.