Pipe roofs are widely used as an effective proactive support measure in the construction of tunnel entrances, shallow-buried and underground excavated tunnels, underground stations, and large- soft and weak soil structures. However, the stress variation characteristics of pipe roofs exceeding 40 m in length are not yet clear. This paper utilizes numerical simulation methods to conduct a comprehensive analysis of the deformation characteristics of three excavation methods: center cross-diaphragm method (CRD), both-side heading method, and the three-bench excavation method with super-long pipe roofs combined with temporary inverted arches. It specifically compares the deformation control effectiveness and stress variation patterns of pipe roofs of different lengths. The results indicate that the deformation control effectiveness of 40 m and 20 m long pipe roofs is inferior to that of super-long pipe roofs. Within a range of 30 m in front of the tunnel face and 20 m behind it, significant stress variations of the pipe roof are observed. The most influential range is within 10 m in front of the tunnel face and 5 m behind it. It is evident that the overall load-bearing capacity of the super-long pipe roof is higher than that of pipe roofs below 40 m. Furthermore, in this study, a novel approach is adopted by utilizing fiber optic grating testing technology to achieve comprehensive monitoring of the axial forces in super-long large pipe roofs. The measured data strongly corroborate the accuracy of the numerical calculations.

Thermo-poro-mechanical responses along sliding zone/surface have been extensively studied. However, it has not been recognized that the potential contribution of other crucial engineering geological interfaces beyond the slip surface to progressive failure. Here, we aim to investigate the subsurface multiphysics of reservoir landslides under two extreme hydrologic conditions (i.e. wet and dry), particularly within sliding masses. Based on ultra-weak fiber Bragg grating (UWFBG) technology, we employ specialpurpose fiber optic sensing cables that can be implanted into boreholes as nerves of the Earth to collect data on soil temperature, water content, pore water pressure, and strain. The Xinpu landslide in the middle reach of the Three Gorges Reservoir Area in China was selected as a case study to establish a paradigm for in situ thermo-hydro-poro-mechanical monitoring. These UWFBG-based sensing cables were vertically buried in a 31 m-deep borehole at the foot of the landslide, with a resolution of 1 m except for the pressure sensor. We reported field measurements covering the period 2021 and 2022 and produced the spatiotemporal pro files throughout the borehole. Results show that wet years are more likely to motivate landslide motions than dry years. The annual thermally active layer of the landslide has a critical depth of roughly 9 m and might move downward in warmer years. The dynamic groundwater table is located at depths of 9-15 m, where the peaked strain undergoes a periodical response of leap and withdrawal to annual hydrometeorological cycles. These interface behaviors may support the interpretation of the contribution of reservoir regulation to slope stability, allowing us to correlate them to local damage events and potential global destabilization. This paper also offers a natural framework for interpreting thermo-hydro-poro-mechanical signatures from creeping reservoir bank slopes, which may form the basis for a landslide monitoring and early warning system. O 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

The combination of phase change materials (PCMs) with building materials is a flourishing technology owing to the low-temperature change of the materials during phase change and the potential for enhanced heat storage and release. In this study, a new type of PCM energy pile, in which 20 stainless steel tubes (22 mm in diameter and 1400 mm in length) filled with paraffin were bound to heat exchange tubes, was proposed. An experimental system monitored by a fiber Bragg grating (FBG) to study the thermo-mechanical behavior of energy piles and surrounding soil was established. Both the PCM pile and the ordinary pile, with the same dimensions, were tested under the same experimental conditions for comparison. The results indicate that the temperature sensitivity coefficient calibration results of the FBG differ from the typical values by 8%. The temperature variation is more obvious in the ordinary pile and surrounding soil. The maximum thermal stress of the ordinary energy pile is 0.5 similar to 0.6 times larger than that of the PCM pile under flow rates ranging from 0.05 m(3)/h to 0.25 m(3)/h. The magnitudes of the pore water pressure and soil pressure variations were positively correlated with the flow rates.

Industrial equipment, such as wind turbine foundations and oil and gas pipelines in cold regions, may undergo extrusion/expansion deformation during the freezing and thawing of frozen soil, which affects their power response and safe operation. Measuring the internal deformation of frozen soil can immediately reflect the strain situation of industrial equipment to reduce the risk of equipment operation. We designed a 6-dimensional strain sensor (6-S Sensor) based on fiber Bragg gratings (FBGs) to obtain the spatial principal strain distribution. The strain range, linearity, and average error of the sensor were -4000 to 8000 mu epsilon, 0.997, and 2.94%, respectively. The sensor accurately measured the frozen and thermal expansion of frozen soil at different temperatures in the laboratory. The maximum frozen expansion was 6471.38 mu epsilon, which occurred in the X-direction. The accuracy of spatial principal strain monitoring for the sensor was evaluated through uniaxial compression. The stability of the sensor was verified by the monitoring experiment under natural temperature for half a month. This study provided a pioneering method for monitoring the internal spatial principal strain of frozen soil.