Buried water pipelines, as crucial urban infrastructure, play an essential role. However, the damage to the pipeline structure has emerged as a severe public safety hazard. Monitoring the state of the pipeline structure holds great significance for the normal operation of water pipelines. In this paper, a damage monitoring method for buried pipelines based on distributed acoustic sensing technology is proposed. Through a series of field experiments conducted on a pipeline, the feasibility of utilizing the attached fiber-optic cable to acquire vibration information has been demonstrated. The recorded vibration signals can indicate various damage statuses during the pipeline damage process, including rock/soil fall, pipeline seepage, and pipe wall failure. The results suggest that the fiber-optic cable accompanying the pipelines can be exploited as sensing resources to monitor damage risks to the pipelines, which presents advantages in the damage identification and location of buried pipelines. This research provides a valuable reference for the application of distributed acoustic sensing technology in the damage monitoring of urban buried water pipelines.

The solidification and molding of lunar regolith are essential for constructing lunar habitats. This study introduces an innovative lunar regolith molding technique that synergistically combines solar concentration, flexible optical fiber bundle energy transfer, and powder bed fusion. A functional prototype is developed to validate the proposed scheme. Systematic experiments including fixed beam spot melting, line melting, surface melting, and body melting are conducted using simulated basalt lunar regolith. Through in-situ observation of the melt pool's formation, evolution, and expansion dynamics, we identify a sequential transformation mechanism on the powder bed's surface: initial curling evolves into detachment from the bed, subsequent incorporation into a molten droplet, and ultimate solidification. A comprehensive evaluation of density and mechanical properties across multiple parameter combinations reveals that energy flux density of 3.33 MW/m2 with a scan speed of 30 mm/min, inter-track spacing of 3 mm, and layer thickness of 2 mm enables the production of structurally integral samples with continuous morphology. The resulting specimens demonstrate a maximum compressive strength of 4.25 MPa and a density of 2.31 g/cm3. This solar-powered additive manufacturing approach establishes a viable reference framework for large-scale on-site construction of lunar research stations.

Occurrence of loess landslide has been more frequent due to the drastic global climate change, rapid expansion of human disturbances and continuous intensification of engineering activities. The activation and evolution mechanisms of the loess landslides under the rainfall are yet to be studied. In this paper, with reference to the Yangpoyao slope with seepage fissures under rainfall, an adjustable-angle landslide model test system is developed, integrating the rainfall simulation system, the measurement system and the data acquisition system, and the deformation development of the model, the rainfall infiltration, the change of water content and the destructive process of the model are monitored by the monitoring technology of multi-means and multi-methods throughout the course of the disaster. A distributed fibre-optic sensor system with the characteristics of continuity and high precision is used to monitor the temperature and strain within the slope model. The deformation evolution mechanism of fissured loess slopes under rainfall was elucidated through the observation of experimental phenomena and the analysis of the internal strain values of the soil, as measured by fibre optic sensors. The experimental results show that the collapse process of loess slopes can be categorised into three types, i.e. sinkhole collapse, block collapse and gully collapse, and that the deformation and damage patterns of the loess landslide model are mainly caused by shallow soil movement induced by erosion. Through the comparative analysis of the model test and the photographs of the field investigation, it is further demonstrated that the damage pattern shown in the physical model test is basically consistent with the slope condition of the real Yangpoyao slope, which provides a new theoretical reference for natural disaster prediction and management of loess slopes and landslides.

Deep cement mixing (DCM) piles are widely utilized for reinforcing soft clay foundations, particularly in coastal regions where soil stability is critical. Monitoring the quality and early-stage behavior of cemented soil is essential to ensure the effectiveness of DCM pile projects in meeting design requirements. Innovative methods for on-site monitoring are necessary to enhance the reliability and efficiency of these reinforcement techniques. In this study, a novel approach is proposed utilizing polymer optical fiber (POF) sensors based on physical optical sensing principles to monitor the initial hydration degree and overall quality of cemented soil during the early curing stage. The proposed method relies on the principle of physical optical sensing, where POF sensors are employed to measure changes in reflected light intensity (LI) and temperature in cemented soil. Two crucial variables, namely the initial water content and the amount of cement, are considered in analyzing their impact on the LI and temperature changes over time. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis are conducted on cemented soil samples with varying water-cement ratios to investigate their mechanical properties and microstructure evolution. The results of the UCS tests indicate that higher initial water content prolongs the initial hydration reaction time required for cemented soil with different cement contents. Analysis of LI curves reveals a rapidly rising trend as the hydration reaction progresses, particularly evident in samples with higher initial water content. SEM analysis further demonstrates that a stable POF LI corresponds to the completion of the hydration process, with hydrated gel formation resulting in a more compact microstructure and smaller voids. The findings highlight the significant influence of cement quantity and initial water content on the mechanical strength and microstructure of cemented soil. By analyzing changes in reflected LI and temperature, the proposed monitoring method provides valuable insights into the early-stage behavior and quality of cemented soil during the curing process. This innovative use of POF sensors for on-site monitoring offers a novel approach to evaluating cemented soil in DCM pile projects.

Disaster monitoring and prediction play significant roles in the fields of geology and geotechnical engineering. Distributed fiber optic sensing technology plays a significant role in long-distance, long-cycle, highly hidden, strong sudden disaster monitoring by virtue of its continuous, real-time, anti-interference, good stability and other advantages. However, effectively evaluating and addressing the coordination deformation issue between the sensing fiber optic cable and the measured rock and soil mass is crucial for different engineering problems. This coordination is essential for accurately analyzing deformation distribution and understanding the evolutionary patterns of rock and soil masses. In this paper, the development of a three-dimensional active deformation controllable confining pressure fiber-sand coupling test device is presented. The device aims to investigate the coordination between the metal base cable sensing fiber and the compression deformation of coarse sand medium under a confining pressure range of 0 to 4.0 MPa. Experimental results show that the metal base cable exhibits inadequate coordination with sand compression deformation at low confining pressures, displaying nonlinear deformation characteristics. However, as the confining pressure increases, the coupling effect between the sensor cable and the sand intensifies, resulting in linear deformation changes. Notably, when the confining pressure reaches 1.6 MPa, there is a significant enhancement in coordinated deformation, transitioning the deformation from nonlinear to linear behavior. Based on the aforementioned deformation characteristics, we propose a numerical model of confining surface projection. To predict the actual displacement of non-test data, we employ the spline interpolation algorithm with non-kink boundary conditions. The results demonstrate the reliability of the model. Furthermore, the experimental study highlights the higher accuracy of the metal base cable for sand deformation testing under high confining pressure conditions. The findings of this study serve as a scientific reference for the application of distributed optical fiber sensing technology in deep stratum deformation monitoring.

Geogrid is widely used in slope, retaining wall, embankment, and other projects as the new geosynthetic material. In order to master the deformation behavior of geogrid, this study employs advanced optical frequency domain reflectometry (OFDR) technology to capture the deformation of geogrid; the optical fiber sensor installation method is considered; the influence of colloidal layer on strain transmission is explored; the medium type around the geogrid is changed; and the deformation characteristics of geogrid during the pulling process are analyzed. The results reveal that the strain of slotted layout is larger compared with tie layout, and the deformation trends of the two layouts are the same. The colloidal layer demonstrates an excellent strain transfer efficiency, with a coefficient of 97%. The geogrid pulling test successfully measures the deformation of geogrid in both sand and air medium using OFDR technology. The strain of the geogrid in sand medium is small; it indicates that the surrounding medium effectively restrains the deformation of geogrid.