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The interaction mechanism between grouted anchor cables and the surrounding rock mass or soil are complicated and difficult to investigate using conventional monitoring technologies. This study focuses on the in-situ pullout behavior of grouted anchor cables using Brillouin Optical Time-Domain Analysis technique. A series of pullout tests were conducted on anchor cables with five different anchor lengths and three grouting methods. Distributed fiber optic sensors were used to measure the strain distribution of cable bolts from tip to top. The in-situ pullout test results show that both ultimate pullout resistance and ultimate displacement at the ultimate pullout resistance increase with anchor length. The bond strength suffers a slight variation with an increase in anchor length. Both ultimate pullout resistance and the ultimate displacement for Type-B grouting (grouting with reaming) and Type-C grouting (secondary grouting) are larger than those for Type-A grouting (one-time grouting). The shear bond strength of Type-C grouting is greater than that of Type-A grouting. Results from Gaussian functions analysis show that it is feasible to use the function to characterize the axial stress of anchor cables. Furthermore, the overall mobilized percentage η was evaluated. The anchor cables with smaller anchor lengths will result in greater η. The η for the anchor cables of 6 m reaches 92% at the last load, whereas the anchor cables of 18 m were mobilized by only 29% at the last load. The grouting method has a negligible effect on the η, increasing from 22% to 29% in process of the pullout test. [ABSTRACT FROM AUTHOR]

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]

Soil pressure is an important parameter for soil tillage. This study provides an alternative method for the fabrication of novel fiber optic pressure sensors which can be used for the measurement of soil pressure in the field. Optical Frequency Domain Reflectometry (OFDR) based distributed fiber optic sensor was adopted as a sensing element and embedded inside 3D printed prototypes to fabricate pressure sensors. During the fabrication process, both internal temperature and strain distributions of the printed Polylactic Acid filament (PLA) were systematically monitored and analyzed. Monitoring data show that the inner temperature rise of all prototypes is limited (less than 45 ℃) in comparison with the printing temperature of the printer nozzle (220 ℃). Both the peak temperature and the obtained temperature at the end of printing are linearly proportional to the change in infill densities. Both the measured peak strain and final strain at the end of printing are less than 580 με, which resulted from the thermal expansion of melted PLA extruded out of the printer's nozzle. All measured strains were found to increase linearly as the increase of infill densities. Calibration tests of pressure sensors, including static and cyclic loading tests, and soil compaction tests, indicate that the measured strain of the fiber optic sensor embedded inside the pressure sensor can be used to calculate vertical pressure applied on the top surface. • Soil pressure is an important parameter for infrastructures and soil tillage. • Optical Frequency Domain Reflectometry based on distributed fiber optic sensor. • 3D printing technique is used to control measurement sensitivity of pressure sensor. • The fabricated pressure sensors were also calibrated in laboratory tests. [ABSTRACT FROM AUTHOR]

• PUS-based DFOS monitoring system is adaptable to various PUS components. • PUS-based DFOS monitoring system accurately reflects the component performance. • A hierarchical performance assessment framework is proposed for PUS. • PUS-CIMAM highlights the key process and regions for the large-span components. • PUS-CIMAM reveals the impact of adjacent ring construction disturbances. Mechanical performance of prefabricated structural components during construction is critical for ensuring long-term safety and durability of prefabricated underground stations (PUS). This study aims to address the issues of structure mechanical performance of large-scale prefabricated components during assembling process. First, a strain transfer model for five-layered armored fiber optic is proposed and validated experimentally through test. Second a PUS-based distributed fiber optic sensors (DFOS) monitoring system was established. Third, a PUS based hierarchical performance assessment framework was constructed. Finally, a PUS based theoretical Construction Intelligent Monitoring Assessment Model (CIMAM) was established to quantitively assess structure safety level. A case study of Shenzhen Metro PUS was performed, and the results showed that: (a) PUS-based DFOS monitoring system presents high accuracy and high resolution, (b) The monitoring system reflects the PUS reactions during the whole construction process with good adaptability and intelligence, (c) PUS-CIMAM results show that the assembly process of components is a significant control link, particularly the performance of large-span roof during assembling process is a key controlling component, and (d) PUS-CIMAM reveals the adjacent ring construction has a disturbing effect. [ABSTRACT FROM AUTHOR]

This study proposed an analytical model to investigate strain transfer mechanism between FBG sensor and measured geogrid. Both geometric and mechanical parameters (bonding length, bonding thickness, bonding width, and Young's modulus) of interaction interface can be taken into account in this model. Both laboratory tensile tests of geogrid and experimental data in published literatures were used to verify the developed model. Validation study shows that the maximum relative error between experimental values and theoretical values is 8.2%, indicating that this theoretical model can be used to reflect geogrid deformation. Parametric study indicates that bonding length, bonding thickness, bonding width, Young's modulus of adhesive layer, and substrate layer have significant influence on strain transfer coefficient. Grey Relational Analysis (GRA) method was used to analyze influencing sensitivity of different parameters. GRA parameter values of bonding width and length are higher than 0.72, indicating that bonding width and bonding length are relatively dominant factors affecting average strain transfer coefficient in comparison with bonding thickness, Young's moduli of substrate and adhesive layers (their related GRA values are all lower than 0.692). • An analytical model to quantitatively evaluate strain transfer between FBG sensor and measured geogrids was proposed. • Influence of different parameters on strain transfer mechanism was quantitatively investigated. • Grey Relational Analysis method was used to analyzed the sensitivity of different parameters. [ABSTRACT FROM AUTHOR]