A Novel Test Method for Characterizing Tempo-Spatial Variations in Elastic Modulus of Underwater Concrete

Concrete structures used in underwater engineering, such as immersed tube tunnels, are subject to a range of challenging coupling circumstances including mechanical load (M), fluid flow (F), fluid pressure (P), and chemical attack (C). Concrete in different areas also experiences compressive or tensile stress under mechanical load. However, most experimental setups only consider limited coupling scenarios, such as M-C, M-F-C, or M-P-C, and the sample is typically in a single stress state, either compressive or tensile. To overcome these limitations, a novel stress-seepage-chemical coupling erosion setup (SSC-CES) was developed to perform durability tests on concrete. This setup allows for simulation of the service conditions of an immersed tube tunnel, including M-F-P-C coupling and distribution of compressive and tensile stresses. This study presents also a detailed description of the setup's components, configurations, and working principles, and discuss how sealing and alignment problems for the sample were addressed to ensure accurate fluid pressure and stress loading. The indentation technique was furthermore applied to obtain the local mechanical properties of different erosion areas, enabling analysis of tempo-spatial variations in elastic modulus. Finally, a test was conducted to examine the M-F-P-C coupling effect using the developed SSC-CES and indentation technique. Results indicated that the elastic modulus weakened from the erosion surface and gradually approached the initial value with increasing depth. Additionally, it showed a transition from slight increase to gradual decrease with erosion time. Notably, the elastic modulus in the tensile stress area was considerably lower than that in the compression stress area. These test results confirm the reliability of the developed SSC-CES and the rationality of the analysis method using micro-indentation technology. The system effectively supports the study of durability evaluation of immersed tube tunnels under M-F-P-C coupling.