Optical-fiber sensing technologies are being theoretically and practically researched. These technologies, possessing linear and real-time properties, realize the sectional analysis of strain and temperature and improve point monitoring methods in deep foundation pit supporting systems. In this paper, a field experimental model of the deep foundation pit supporting system was designed in the subway station in Suzhou, China, which utilizes optical-fiber sensing technology. In this field experiment, conventional monitoring methods, namely steel-bar meters, inclinometer, and water-level observation hole were firstly employed for comparative study. Distributed optical-fiber sensors (DOFS) were employed at the same time based on Brillouin optical time-domain analysis (BOTDA). The experimental results show that the DOFS can more comprehensively monitor the pit support system than the conventional methods. The fiber sensors data reflect the positive and negative strain distribution of the walls in a linear section and detect a leakage by analyzing abnormal data. The fiber sensors data response a linear increase of the axial strain with excavation depth, and a bending phenomenon is discovered by the data curves because of the excavation depth difference of the testing support. With temperature compensation, the fiber monitoring data are more accurate to the excavation result than the steel-bar does. Thus, the sensors can get a combined action function of steel-bar which used for testing axial force and temperature, inclinometer which used for testing wall horizontal displacement, and water-level observation holes with accurately monitoring data.

Distributed Acoustic Sensing (DAS) is a powerful technology for large-scale monitoring, but its applications are often limited by low sensitivity to weak acoustic signals. To overcome this limitation, we developed a thin-walled cylindrical DAS sensor and systematically investigated how its core structural parameters—elastic modulus, wall thickness, and diameter—influence sensitivity. A theoretical model linking the cylinder’s circumferential strain to the fiber’s optical phase shift was also developed to elucidate the enhancement mechanism. Results show that sensitivity increases exponentially when reducing the cylinder’s elastic modulus (from 193 to 2.3 GPa) or wall thickness (from 5 to 1 mm), reaching a maximum of 0.98 rad/Pa. Furthermore, sensitivity increases linearly with diameter, with an average gain of 0.02 rad/Pa per millimeter. These findings provide a practical and scalable structural design strategy for significantly enhancing DAS sensitivity, enabling more effective sensing for applications like microseismic monitoring, subsurface imaging, and weak vibration detection.

The stabilization of expansive and clayey soils remains a persistent challenge in geotechnical engineering. This study investigates the potential of magnetized water-a sustainable, physical treatment method-to enhance the engineering properties of such problematic soils. Through a comparative analysis using expansive and clayey soils from Nanjing, China, we evaluated changes in particle size distribution, Atterberg limits, permeability, compaction, and shear strength. The results indicate that magnetized water treatment induces the disintegration of coarse soil aggregates, shifting the particle size distribution toward finer fractions. This microstructural remodeling significantly improved mechanical performance: shear strength cohesion increased by 61.8%, the internal friction angle rose by 17.8%, and the maximum dry density improved. Hydrologically, the treatment reduced the plasticity index by up to 33.4% and decreased permeability due to the pore-filling effect of the dispersed fine particles. Scanning electron microscopy and porosity analyses support a microscale mechanism wherein the enhanced solubility and altered molecular cluster structure of magnetized water dissolve aggregate cementation, promoting a denser, more stable soil matrix. These findings suggest that magnetized water offers a viable, eco-friendly alternative to chemical binders for soil improvement applications.