Innovative self-sensing and recyclable composite strand anchor for pit support: Design, experimentation, and application

• An innovative self-sensing and recyclable composite anchor • Composite anchor integrated with fiber bragg grating (FBG) sensor • Static, self-sensing and field application tests were conducted on composite anchor • The embedded FBG sensor accurately captures stress and strain data within the anchor • The designed composite anchors facilitate efficient recovery post-construction Effective prestressed anchors are essential for providing critical stability and load control and ensuring the success of pit support engineering projects. Real-time monitoring of the stress state of these anchors is vital to ensuring both construction and maintenance safety. Despite various technologies being developed to track the stress state of anchors, it remains challenging to ensure monitoring accuracy, long-term reliability, and cost-effectiveness simultaneously. Traditional sensors, such as strain gauges and extensometers, often struggle to be installed within the limited space inside the anchors and face difficulties in capturing the stress and strain data of the anchors in real time over extended periods. To address those challenges, an innovative self-sensing and recyclable composite anchor integrated with fiber bragg grating (FBG) sensor that can monitor its stress-strain state in real-time is developed. The composite strand anchor consists of six external steel wires twisted around a central carbon fiber reinforced polymer (CFRP) wire, with an FBG sensor embedded in the CFRP wire during the pultrusion process. Static and self-sensing tests, as well as application tests in pit support, were conducted on this composite strand anchor. The static tensile test results show that the composite strand anchor has a tensile strength of 1703.1 MPa, slightly higher than that of a steel strand, and an elastic modulus of 194 GPa, slightly lower than that of a steel strand due to the central CFRP wire instead of a steel one. The self-sensing tests demonstrate that the FBG sensor can measure the stress and strain of the composite strand anchor with high sensitivity and accuracy, with an error of less than 1.5%. Additionally, the designed anchors facilitate efficient recovery post-construction, significantly reducing environmental impact and material costs. The recovery process, involving simple mechanical operations, ensures that anchors are easily extracted without damage, supporting their reuse in subsequent projects. This recyclable anchor technology not only offers significant economic benefits by reducing material and procurement costs through anchor recycling but also enhances construction efficiency, simplifies recovery operations, shortens project cycles, and reduces the risk of construction delays. Additionally, this technology aligns with sustainability goals by significantly reducing construction waste and environmental impact. The convenience of its operation ensures the structural integrity of the anchors during recovery, maintaining consistent performance and reliability for subsequent use.