Engineering activities in permafrost regions have a major impact on the local permafrost environment. The construction and operation of the China-Russia Crude Oil Pipeline (CRCOP) have changed the surface conditions and the soil’s thermal state. However, the response of the permafrost environment to CRCOP is less studied. This article carries out ground temperature monitoring, ground surface deformation (GSD) and pipeline deformation observations, electrical resistivity tomography (ERT) measurements, and unmanned aerial vehicle (UAV) surveys to study permafrost thawing, talik development, topographic change, and pond distribution. The results indicated that the oil temperature has increased yearly and the permafrost around the pipeline has degraded quickly. The artificial permafrost table (APT) has decreased at a rate of 0.68 m/a at a location 2 m away from the center of pipeline, and reached –11.4 m deep by 2022. The talik around CRCOP Ⅰ was larger than that around CRCOP Ⅱ and the two taliks were gradually approaching each other. Permafrost-thawing-induced pipeline subsidence and surface settlement have led to thermokarst depressions and water accumulation. The sinking rates of CRCOP Ⅰ and Ⅱ are approximately 0.2 m/a and 0.45 m/a, respectively. The ground surface settlement rate on the right-of-way of pipeline (on-ROW) is about 5.49 cm/a. Settlement rate in ponding areas is 8.18 cm/a, significantly larger than 4.81 cm/a in non-ponding areas. The ponding area on-ROW accounts for 67.4% and it on CRCOP Ⅰ is larger than that on CRCOP Ⅱ. Pipeline construction, high oil temperature, and permafrost thawing have led to the development of geohazards, which have potential to be worsen under the influence of fires, climate warming, and human activities. Multisource data provides ground verification for satellite images to extract deformation and ponding information along pipelines, and provides a scientific basis for assessing the thermal impact of pipelines and geohazard development.
Global warming has led to increasing pile foundation deterioration in permafrost regions. Theoretical analysis and indoor model tests were used to analyse variations in the shaft resistance and ultimate bearing capacity (UBC) for various permafrost active-layer thicknesses (Z a ). A relationship for atmospheric temperature, Z a and ground temperature was developed. The equivalent adfreezing force was used as an index to evaluate the degradation of pile foundation bearing behaviour and a theoretical model was established. Based on the theoretical degradation model and indoor experimental data, a model was established to reflect the deterioration of pile foundation bearing behaviour in warm permafrost regions. The model was verified using numerical simulations. The results showed that shaft resistance at the ultimate state can be divided into three stages (stable change, rapid increase and attenuation). The depth of the maximum values decreased from −0.40 m to −0.65 m with an increase in Z a . The pile head load (Q) against pile head settlement (S) curves were divided into three stages (elastic stage, elastic–plastic and plastic). A greater Z a made the plastic stage of the Q–S relationship occur earlier, resulting in a gradual decrease in UBC. The degradation variable (D) of bearing behaviour showed rapidly and then slowly increasing deterioration. This study provides experimental support for clarifying the degradation mechanism of pile foundation bearing behaviour and a degradation model to consider and quantify the impact of climate change on pile foundations in degraded permafrost.
Accurate and error-free digital elevation model (DEM) data are a basic guarantee for the safe flight of unmanned aerial vehicles (UAVs) during surveys in the wild, especially in moun-tainous areas with large topographic undulations. Existing free and open-source DEM data gen-erally cover large areas, with relatively high spatial resolutions (~90, 30, and even 12.5 m), but they do not have the advantage of timeliness and cannot accurately reflect current and up-to-date topographical information in the survey area. UAV pre-scanning missions can provide highly accurate and recent terrain data as a reference for UAV route planning and ensure security for subsequent aerial survey missions; however, they are time consuming. In addition, being limited to the electric charge of the UAV, pre-scanning increases the human, financial, and time consumption of field missions, and it is not applicable for field aerial survey missions in reality, unless otherwise specified, especially in harsh environments. In this paper, we used interferometric synthetic aper-ture radar (InSAR) technology to process Sentinel-1a data to obtain the DEMs of the survey area, which were used for route planning, and other free and open-source DEMs were also used for flightline plans. The digital surface models (DSMs) were obtained from the structure of the UAV pre-scan mission images, applying structure for motion (SfM) technology as the elevation reference. Comparing the errors between the InSAR-derived DEMs and the four open-source DEMs based on the reference DSM to analyze the practicability of flight route planning, the results showed that among the four DEMs, the SRTM DEM with a spatial resolution of 30 m performed best, which was considered as the first reference for UAV route plans when the survey area in complex mountainous regions is covered with a poor or inoperative network. The InSAR-derived DEMs from the Sentinel-1 images have great potential value for UAV flight planning, with a large perpendicular baseline and short temporal baseline. This work quantitatively analyzed the errors among the different DEMs and provided a discussion regarding UAV flightline plans based on external DEMs. This can not only effectively reduce the manpower, materials, and time consumption of field operations, improving the efficiency of UAV survey tasks, but it also broadens the use of InSAR technology. Furthermore, with the launch of high-resolution SAR satellites, InSAR-derived DEMs with high spatial and temporal resolutions provide an optimistic and credible strategy for UAV route planning with small errors.
Buildings are always affected by frost heave and thaw settlement in cold regions, even where saline soil is present. This paper describes the triaxial testing results of frozen silty clay with high salt content and examines the influence of confining pressure and temperature on its mechanical characteristics. Conventional triaxial compression tests were conducted under different confining pressures (0.5–7.0 MPa) and temperatures (−6 °C, −8 °C, −10 °C, and −12 °C). The test results show that when the confining pressure is less than 1 MPa, the frozen saline silty clay is dominated by brittle behavior with the X-shaped dilatancy failure mode. As the confining pressure increases, the sample gradually transitions from brittle to plastic behavior. The strength of frozen saline silty clay rises first and then decreases with increasing confining pressure. The improved Duncan-Chang hyperbolic model can describe the stress-strain relationship of frozen saline silty clay. And the parabolic strength criterion can be used to describe the strength evolution of frozen saline silty clay. The function relation of strength parameters with temperature is obtained by fitting, and the results of the parabolic strength criterion are in good agreement with the experimental results, especially when confining pressure is less than 5 MPa. Therefore, the study has important guiding significance for design and construction when considering high salinity soil as an engineering material in cold regions.
The detection of concealed water-conducting structures is essential for preventing water inrush disasters. Aiming to mitigate the limitations inherent in using any single technique, a comprehensive approach that combines integrated mining geophysical exploration, hydrogeological drilling, and hydrochemical exploration (GDH) is proposed for the exploration of concealed water-conducting structures. By conducting a thorough analysis of the background geological data obtained through surface exploration, potentially concealed water-conducting structures can be predicted. Then, a combination of the seismic reflection method (SRM) and mine transient electromagnetic method (MTEM) can be used to detect the location and water-bearing properties of the target structures. Afterwards, the target drilling areas are defined by the anomalies detected by the integrated mine geophysical technique, and the drilling method can directly acquire the hydrogeological information of water-conducting structures and verify the results of the geophysical methods. By means of hydrochemical analysis, inrush water sources and their runoff conditions can be identified, and the spatial relationship betweenof the source aquifers and mining space can be determined; hence, the properties, scale, and configuration of the water-conducting structures can finally be evaluated. Employing a water-conducting fault in a mine as a case study, we verified that the integrated method overcomes the limitations and possible biases of each method, providing a multiple-method solution that can accurately detect concealed water-conducting structures to help prevent water inrush disasters.
Due to the presence of ice and unfrozen water in pores of frozen rock, the rock fracture behaviors are susceptible to temperature In this study, the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness (KIC) of frozen rock at different temperatures (i.e. −20 °C, −15 °C, −12 °C, −10 °C, −8 °C, −6 °C, −4 °C, −2 °C, and 0 °C). Acoustic emission (AE) and digital image correlation (DIC) methods are utilized to analyze the microcrack propagation during fracturing. The melting of pore ice is measured using nuclear magnetic resonance (NMR) method. The results indicate that: (1) The KIC of frozen rock decreases moderately between −20 °C and −4 °C, and rapidly between −4 °C and 0 °C. (2) At −20 °C to −4 °C, the fracturing process, deduced from the DIC results at the notch tip, exhibits three stages: elastic deformation, microcrack propagation and microcrack coalescence. However, at −4 °C–0 °C, only the latter two stages are observed. (3) At −4 °C–0 °C, the AE activities during fracturing are less than that at −20 °C to −4 °C, while more small events are reported. (4) The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature, that is, a moderate decrease is followed by a sharp decrease and −4 °C is exactly the critical temperature. Next, we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow: from −20 °C to −4 °C, the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton, leading to the decrease in fracture parameters. From −4 °C to 0 °C, the cementation effect of ice almost vanishes, and the filling effect of pore ice is reduced significantly, which facilitates microcrack propagation and thus the easier fracture of frozen rocks.
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