最新刊期
卷 52 ， 期 6 ， 2020
- 摘要：The mountain flood disaster is one of the major natural disasters in the world. The global economic loss caused by flash floods in the 21st century has reached more than 46 billion US dollars per year. The area of mountain flood disaster prevention and control accounts for about 40% of the land in China, whereas the fatality caused by mountain flash floods account for approximately 70% of the death toll from flood disasters. In recent years, the construction of mountain torrent disaster prevention and control projects have been carried out in an all-round way in China. A mountain torrent disaster prevention and control system combining specialists and groups has been basically established, and the technical level of mountain torrent disaster monitoring and early warning has been significantly improved. Examples of torrential rain and flash flood disasters show that the flash flood disasters with heavy casualties and property losses often result from the combined effects of flood and sediment. In the past, scientists mostly paid attention to the flood's role while ignoring that the combined effect of flood and sediment would significantly increase the risk of mountain torrent disasters. To further improve the ability to prevent and control mountain flood disasters, it is urgent to study the critical technologies of flood and sediment disaster forecasting and early warning. The project “Research and Demonstration of Key Technologies for Forecasting and Early Warning of Flash Flood and Sediment Disasters in Mountainous Rainstorms” focuses on the joint action of flood and sediment and condenses four critical scientific and technological issues: 1) mutation mechanism of runoff and sediment yield and disaster-causing coupling mechanism of the flood-sediment process and gully-bed drastic change in mountainous area under heavy rain; 2) early identification of flood and sediment disasters and integrated intelligent monitoring technology for disaster-causing elements in mountainous rainstorms; 3) simulation and rapid prediction technology of flash flood and sediment movement process in a mountainous rainstorm; and 4) disaster risk dynamic assessment and early warning and prevention technology based on the dynamic process of mountain flood and sediment disaster. Focusing on the connotation of critical scientific and technological issues, we proposed five key research contents including 1) study on the process of runoff and sediment production in mountainous areas and the disaster mechanism of flood and sediment coupling; 2) early identification and intelligent monitoring technology for flood and sediment disasters in mountainous areas; 3) simulation and rapid prediction technology of flood and sediment movement process in a mountainous rainstorm; 4) dynamic assessment and early warning technology of flood and sediment disaster risk in mountainous areas; 5) construction and demonstration of a platform for forecasting, early warning, and prevention of flood and sediment disasters in mountainous areas. The research results will improve the real-time accuracy and intellectual level of monitoring, early warning, prevention and control of heavy rain and flash flood disasters in China.关键词：flash flood disaster;flash flood and sediment disaster;flash flood;monitoring and early warning;sediment supply;risk assessment
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发布时间：2024-01-08
FOCUS ON STATE KEY RESEARCH DEVELOPMENT PROGRAM OF CHINA
- 摘要：As a special landslide hazard, rapid and long runout landslides display high mobility, long runout travel distance and wide damage area, and bring great loss to human life and property, of which dynamic mechanisms have attracted demand attentions of the researchers all over the world. Liquefaction mechanism of landslides was proposed to explain that the formation of excess pore water pressure and the reduction of effective stress lead to the decrease of the friction coefficient of the base and the landslide long runout movement. In this paper, we reviewed the factors affecting the liquefaction intensity and the liquefaction mechanism of the landslides on the basis of previous research, and the mechanisms of the liquefied landslides were generally summarized into two types, i.e., structural liquefaction and sliding zone liquefaction. Based on remote sensing interpretation and field investigation, the preliminary research of the formation mechanisms of two typical liquefied rapid-long-runout landslides named Yushu landslide and Luanshibao landslide in Tibetan Plateau were conducted. Results showed that Yushu and Luanshibao landslides were different in triggering mechanism, movement and accumulation geomorphologic unit, and liquefaction mechanism. Yushu landslide was a collapsed deposit landslide occurring in a mountain valley with a small volume but a long runout distance triggered by heavy rainfall. The sliding zone soil was saturated loose sandy clay (fine grain) accumulated in the gully before landsliding, the particle breakage of which during shearing could be negligible. The liquefaction was mainly induced by destroying the soil structure under undrained loading. Luanshibao landslide was a granite landslide occurring in the piedmont basin triggered by oblique-thrusting during an ancient earthquake, the sliding zone soil of which was saturated loose weathered granite sand having crushability. The sliding zone liquefaction induced by grain crushing was the main reason resulting in its rapid and long runout movement.关键词：Tibetan Plateau;rapid and long runout landslide;liquefaction;movement mechanism
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发布时间：2024-01-08 - 摘要：Nixu landslide is located in the middle of the Yadong—Gulu Rift Valley in southern Tibet. The accumulation of Nixu landslide is the landform of the flat river valley. It is a typical “flat” rocky long-runout landslide developed in the back-land of the Qinghai–Tibet Plateau. The landslide accumulation area has a complete accumulation structure and typical debris flow patterns. The investigation and research on Nixu landslide will help to reveal the mechanism of movement and accumulation differentiation of this type of “flat” high-speed debris flow. A detailed ground survey of the Nixu landslide and its components in the accumulation area was carried out, combined with geophysical methods to reveal the failure characteristics of the sliding surface at the bottom of the source area as well as the mechanism of the formation of the landslide.The high resolution remote sensing interpretation and particle test were used to reveal the spatial distribution rules of various stacked structures. According to the research of the evolution of the debris flow accumulation structure and spatial morphology of Nixu landslide, it is proposed that the formation and evolution of “flat” high-speed debris flow can be divided into three sections: Structure fragmentation in the slope section of the source area, the material structure debrisification in the sliding zone, and the debris flow fluidization movement and accumulation in the leading edge. The structure of the corresponding sliding mass had the characteristics of step development of fragmentation-debrisification-fluidization. In the sliding zone and leading edge, the high-speed sliding mass movement was affected by the friction of the base, and a horizontal layered shear fracture surface could be generated inside, so that the debris flow continued to move and expand longitudinally under the “dilution effect”. The process of debris flow at the bottom transition from “dry” high-speed fluidization to solid and still was extremely rapid, and thus it maintained the accumulation morphology under the special fluid properties such as continuously distributed ridge and trunking. According to the research, it was proposed that the disintegration and destruction of Nixu landslide after earthquake were controlled by the slope of the source area, and they slided from front to back in sequence, controlled by their own potential energy conditions. The sliding body from the source area was stacked in the front edge accumulation area from left to right. It was the main reason for the deflection of the stacking plane to the downstream.关键词：flat rocky landslide;debris flow;inverse grading structure;base liquefaction
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发布时间：2024-01-08 -
Kinematic Processes and Fragmentation Characteristics of Walai Rock Avalanche Landslide in Tibet AI导读
摘要：Fragmentation is a very common phenomenon in high-speed long runout landslides, which is not only the basis of the granular flow hypothesis, but also related to energy dissipation and transmission of landslide. In order to examine the kinematic and fragmentation characteristics of long runout landslides, the Walai rock avalanche landslide was studied as an example. According to the remote sensing interpretation, field investigation and grain size tests, the geomorphologic features, sedimentary structures, kinematic processes and fragmentation characteristics of Walai rock avalanche landslide were analyzed and discussed. The geomorphic structures were quantitatively analyzed based on the high precision digital elevation model built by unmanned aerial vehicle measurement. The contour map and bedrock data were used to reconstruct the pre-topography and the volume of this rock avalanche was estimated. The results indicated that the Walai rock avalanche landslide was controlled by the rock joints, its horizontal travel distance reached 3480 m (H/L = 0.32) and the accumulated volume was about 5.1×107 m3. The geomorphic structures of the Walai rock avalanche landslide was characterized by trimlines, huge hummocks, longitudinal ridges and compressed ridges. These geomorphologic structures indicated that the Walai rock avalanche landslide moved in the northeast direction at first, and turned to the north when it encountered the eastern mountain. The carapace facies of Walai rock avalanche landslide was thin, and the blocks was approximately 30 cm, which was significantly influenced by the joints. The sedimentary featured in body facies, including the stratified layers, jigsaw structures, directional arrangements and shear failure of block, indicating that the rock avalanche moved as a laminar flow and there were collision and shear actions during the movement. The change in the size of blocks in body facies suggested that the fragmentation mainly formed due to the impact actions from the source area to the toe of the transition zone; and the fine grain distribution characteristics and absence of obvious shear zone indicated that the internal shear behavior during the radial motion stage was not stronger than that of the former.关键词：long runout landslide;geomorphologic features;sedimentary structures;grain size distribution;fragmentation characteristics- 1947
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发布时间：2024-01-08 - 摘要：The high-speed and long run-out landslide debris flow is characterized by high kinetic energy and long moving distance, which is a kind of geological disaster with a wide range of damage and great destructive power and leads to enormous loss to human beings. Numerical simulation provides an important method to study the effects. In this paper, the numerical manifold method was used to simulate the movement process of high-speed and long run-out landslide debris flow induced by strong earthquake in Niuquangou, China. The accumulation state and movement characteristics of the landslide debris flow were studied through a series of numerical tests. The effects of vegetation coverage, spatial characteristics of retaining-wall on the accumulation state of debris flow were studied, and the disaster reduction effects of retaining-wall was evaluated. The simulation results showed that the effects of increasing vegetation coverage on the landslide movement path was limited. In order to intercept landslide debris flow better, the retaining-wall should be arranged on the motion path to effectively reduce moving distance and long-distance accumulation of debris flow. When the retaining-wall was placed in different positions, it would have different effect on the landslide debris flow, and the optimal position of the retaining-wall was determined. In addition, compared with effects of increasing the height of the retaining-wall, the multiple rows of retaining-wall structure can more effectively intercept the debris flow and reduce its harm to the downstream.关键词：high-speed and long run-out landslide;retaining-structure;numerical manifold method
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发布时间：2024-01-08 - 摘要：The Batang—Mangkang section of the G4218 highway is located in the transition zone from the Jinsha River Valley to the plateau, and facing with strong neotectonic activities, broken rock masses and frequent geological disasters. Therefore, the construction and maintenance of the highway in this region are of huge difficulties. Traditional ground geological survey methods face many difficulties in highway route selection, disaster assessment and stability analysis, etc. Combining the optical remote sensing interpretation of geological hazard points with deformation observation by InSAR technology, it is expected that the geological hazard points in this region can be investigated quickly, accurately and efficiently, and reveal their development and distribution rules of geological disaster points. Under the special geological conditions of the high mountains and valleys of the Qinghai–Tibet Plateau, the common types of geological disasters in the region were summarized, and the method of integrated highway remote sensing identification was put forward based on the study of the characteristics of regional disasters and remote sensing technology. Using this method, we carried out disaster surveys on the Batang—Mangkang section, with full knowledge of optical remote sensing visual interpretation technology and InSAR technology, supplemented by field geological survey, GIS spatial analysis, engineering geological analogy, etc. The conclusions of this article are as follows:1) A total of 670 geological disasters were interpreted by optical visual remote sensing in the study area, and InSAR technology combined with four kinds of SAR data interpreted 220 active geological disasters; 2) The development rules of different types of geological disasters in the study area varied greatly with the change of topographic features, geological conditions and geological disasters and other influencing factors. There were differences in spatial distribution and formation lithology of geologic hazard using the optical remote sensing or InSAR technology; 3) According to the comparative analysis based on the field work, it was concluded that the interpretation results of optical remote sensing and InSAR had a certain relationship with the interpretation methods, imaging conditions of the images and the activity of landslide. The two methods cannot be used for mutual inspection directly; 4) The use of comprehensive remote sensing technology was universal in the highway construction of the high mountain valley of the Qinghai–Tibet Plateau. It made full use of the complementarity of optical remote sensing interpretation technology and InSAR deformation observation technology. On the basis of saving time and cost, this method can have a more comprehensive and accurate understanding of the development of regional geological disasters.关键词：Qinghai–Tibet Plateau;Jinsha River;Sichuan—Tibet Highway;optical remote sensing interpretation;InSAR;geological hazards
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发布时间：2024-01-08 - 摘要：Geological hazards occur frequently in the southwest mountainous area. In recent years, successive large-scale landslide hazards such as Maoxian landslide, Baige landslide, and Shuicheng landslide have shown that the occurrence of catastrophic landslide events is not only related to the conditions that are prone to breeding geological hazards in the area, but also connecting with the failure in accurately identifying and monitoring the development of landslide disasters. Based on active microwave remote sensing imaging, the InSAR technology was utilized to identify of active geological disasters in Meili Snow Mountain sections of the Lantsang River, where traditional ground-based geological disaster survey methods and optical remote sensing technology were limited. Multi-source remote sensing data was used, including SAR images and multi-temporal traditional optical remote sensing images. By using PALSAR–1/2 and Sentinel–1 data of ascending and descending orbits, the earth observations of multiple periods, multiple angles, multiple wavelengths and spatial resolutions were carried out. Combined with the calculation results of D-InSAR, IPTA-InSAR and Stacking, Human-computer interaction, visual interpretation, the testing data was verified comparing with the multi-temporal optical remote sensing data and three-dimensional topography collected from Google Earth. Ground verification for typical landslide disasters was conducted and its stability was analyzed by using InSAR calculation results. The results of this work are as follows: 1) A total of 92 landslide geological hazards were identified, of which 76 landslide geological hazards in the Lantsang valley section accounted for 82.6% of the total interpretation; 5 Lantsang tributaries were interpreted, and Deqin County surrounding areas interpreted 11 landslides. There were 26 landslides with a floor area greater than 200000 square meters, accounting for 28.3% of the total interpretated ones. The Permian and Triassic weak strata in the Lantsang valley area are distributed along the valley. Coupled with the influence of multiple factors such as topography, rainfall, and reservoir storage, there were many large and fast-moving landslide disasters along the valley. 2) The Meilishui landslide was a typical high-level deformation landslide in the river valley. The rapid deformation area was located at a high altitude and had a large potential energy. Many similar high-level deformation activities have been found in the river valley. 3) The Yagong landslide has always been deformed during the data observation period (2007—2019), and the scale was huge. The developed secondary landslide had a faster deformation rate, and the front edge of the landslide had serious deformation and damage, with a deformation rate of 7～11 cm/a, threatening the safety of residents and cultivated land on the platform in the middle of the landslide. 4) A total of 11 landslide deformation bodies were identified in the observation range of Deqin County, including two creep-type landslides, i.e., Dingyangding landslide and Guibading landslide, with obvious local deformation phenomena and still in the development stage. 5) Multiple disaster types can be monitored by InSAR technology. Four large debris flow ditches were developed around the county, and the source area and circulation area had different degrees of deformation; the high-altitude area had frequent activities and large deformations of moraines. In addition to the moraine landslide formed by the interaction of ice and snow, many high mountain slopes were severely weathered and broken, and there were also strong deformations. The combination of multi-orbit and multi-type SAR data in high mountain areas can effectively compensate for SAR satellite imaging defects and increase the observable area. Combining with multiple InSAR algorithms can take advantages of different SAR data and improve the identification accuracy of active landslides; in the cold, steep, and vegetation-rich mountainous area of the Lantsang, short-wavelength Sentinel–1 data can be used for stacking calculations, which significantly improved the calculation effect. The long-band PALSAR–1/2 data had better adaptability under harsh conditions, and had better performance in the IPTA-InSAR results.关键词：Lantsang;geologicial hazards;landslide;landslide identification;InSAR
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发布时间：2024-01-08 - 摘要：The barrier dams are loose accumulation bodies formed by collapse, landslide, debris flow or moraine, and most of them are composed of loosely and widely graded cohesionless soil. The barrier dams are susceptible to internal erosion during the rapid rising of upstream water level, and threaten the downstream residents’ property and life safety. CFD–DEM coupling approach is often used to model the internal erosion of barrier dam, but it often costs lots of time due to the coupling counting and corresponding data processing. Based on the encountered forces of cohesionless soils of barrier dams during the process of seepage failure, the fluid force applied to the particles was analyzed and a simplified method to modeling the internal erosion process with the discrete element method was suggested. Utilizing this method, the encountered fluid force of a particle in the flow field was applied to the DEM module in the form of an acceleration field. Then, the amount of calculation required for the dual-module interactive iteration in the traditional CFD–DEM coupling method could be reduced, and it could effectively improve the calculation efficiency based on retaining the calculation effect of the CFD–DEM coupling method. Finally, pointing at the wide-graded non-cohesive dam soil materials, the simplified ideal gap-graded sized particle model was used to compare the CFD–DEM coupling calculation results to verify the rationality and effectiveness of the fast calculation method proposed in this paper. It showed that the relative error was within 3.4%, which proved the reliability of the simplified simulation method. When a simplified simulation method was adopted to simulate specific cases, the specific magnitude of the error might change. In terms of calculation speed, the running speed of the fast simulation method in this simulation was approximately 3.5 times than that of the CFD–DEM coupled simulation method, and when the number of particles increased, the calculation speed of the simplified simulation method increased significantly.关键词：landslide dam;granular material;internal erosion;discrete element method;numerical simulation
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发布时间：2024-01-08 - 摘要：The erodibility parameters of barrier dam were an important basis for the evaluation of the outburst flood in the emergency treatment of the dammed lake. The erosion rate was typically modeled with excess shear stress model and Wilson model. However, there is no unified understanding of the range of erodibility parameters. In order to study the range of erodibility parameters of various types of soils and the relationship between the erodibility parameters of two models and soil properties, quickly determine the erodibility parameters of the dam, a database of 279 test results were collected from the literature review as well as by contacting researchers and organizations working on erosion around the world. The samples were classified into coarse-grained and fine-grained soils according to the unified soil classification system. Correlation analysis and regression analysis of the data were used to obtain the relationship between the erodibility parameters and soil properties. Four measures were used to evaluate the statistical significance of the relationship between erodibility parameters and soil parameters for coarse-grained and fine-grained soils: R2、MSE、Fvalue/Fstatistic and cross-validation. The erodibility parameters obtained from the experimental data were compared with the erodibility parameters predicted by the regression equation, the range of erodibility parameters of different soil and correlation between erosion parameters and soil parameters were obtained. According to the erodibility parameters database, the regression equation of erodibility parameters were obtained through statistical analysis of limited soil parameters and erodibility parameters to quickly predict the erosion rate of the soil. Finally, taking Baige weir plug as an example, according to the erodibility parameter database and statistical relationship established in this study, the erodibility parameters and erosion rate were analyzed rapidly. The research findings can be used to quickly determine the erosion parameters of the dam plug body, and provide help for rapid assessment of the risk of burst flood under emergency conditions.关键词：erodibility parameters;barrier dam;correlation analysis;regression analysis;emergency action
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发布时间：2024-01-08 - 摘要：Baige landslide, which located on the upper reaches of Jinsha River, happened successively on October 10 and November 3, 2018 and blocked the river twice. The dammed lakes and their breaching flood brought about severe disaster to local residents along the river. After the sliding, three cracking zones were formed at the back edge of the landslide, which may block the river again. In view of the uncertainty of the physical and mechanical parameters of the landslide, the optimization algorithm was utilized based on the maximum likelihood estimation to inverse the shear strength parameters of the landslide, and the inversion parameters were used to calculate the reliability and evaluate the stability of the cracking zones by Monte Carlo method. The results showed that: 1) Combining the response surface method with the maximum likelihood based probability back analysis method, the calculation process was simple and the calculation method had a strong adaptability. 2) According to the inversion results of Baige “11·3” landslide, the posterior distribution of shear strength cohesion and internal friction angle were N(13.05 kPa, 32) and N(0.64, 0.042), respectively. The uncertainty of prior parameters could be reduced by inversion. 3) The local failure mode of each cracking zone was obtained by searching the most dangerous sliding surface. The calculated scope of the most dangerous sliding area of each cracking zone was approximately the same as that of the instability area obtained from the field investigation and monitoring, and the failure probability under the local failure mode was significantly greater than that under the overall failure mode, indicating that the failure of the cracking zone was mainly progressive traction failure. 4) The volumes of the cracking zones C1–1, C2–1 and C3–1 at the back edge of Baige landslide were 7×105 m3, 3.2×106 m3 and 1.3×106 m3, respectively, with the corresponding instability probability of 21.70%, 33.90% and 27.30%, all of which were extremely dangerous. It is necessary to carry out risk assessment on the damming-breaching-flooding disaster chain, and put forward appropriate disposal measures and emergency plans.关键词：Baige landslide;cracking zone;shear strength parameters;back analysis;instability probability
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发布时间：2024-01-08
CATASTROPHIC MECHANISMS AND RISK CONTROL OF MAJOR LANDSLIDES IN TIBETAN PLATEAU
- 摘要：Restricted by terrain, a large number of roads and railways often appear along the reservoir line and along the river line, and water level changes are an important factor causing landslides on the banks. At present, most of the researches on slope seepage focus on the unsaturated uniform flow, and the study on the non-equilibrium flow of macropore slope is still lagging behind. In this study, the stability factor of unsaturated seepage flow and unsaturated macropore flow slope was analyzed, and the influence law of the factors including water level rise rate (v), hydraulic conductivity in macropores (Ksf), hydraulic conductivity of the matrix-fracture interface (Ksa), the equivalent diffusion distance between two domains (a), and the volumetric fraction of macropore domain (wf) on the stabilization of slope were analyzed by macropore flow model. The results showed that the water content in the matrix area of the slope was close to saturation in the unsaturated macropore flow, and the water content in the matrix domain was obviously less than that in the matrix domain of the slope under unsaturated macroporous seepage with rise of the water level. The hydraulic gradient of the shallow inward slope was obviously larger than that of the unsaturated large pore flow slope under unsaturated seepage. The moisture content in the matrix domain was much larger than that in the macropore domain (up to 18.9 times) at the same location because the permeability coefficient of matrix domain is much smaller than that of macroporous domain. The stability factor of reservoir bank slope decreased first and then increased with the increase of reservoir water level, and it reached the minimum at the same water level (close to the height of the highest storage level ) at the same time. Under the same seepage conditions, the stability of unsaturated macropore flow was weaker than that of unsaturated seepage. Reducing Ksf, a, wf or increasing Ksa made the water exchange between the two regions become slow. As the moisture rapidly migrates to the depth of the slope, it caused the groundwater level to rise and the maximal decrease of slope stability was 17.7%. The influence of v, Ksf and wf slope stability was relatively large and equivalent, while Ksa and a were relatively small and they were about half of the former.关键词：water level rise;immersed slope;non-equilibrium flow;mechanical response;slope stability
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发布时间：2024-01-08 - 摘要：The influence of the reservoirs discharge variation on riverbed armoring in mountainous rivers was investigated. The flume experiments were carried out by using clear water (no upstream sediment supply) under two conditions: alternating discharges and increasing discharges. For each case, the bed load transport rate, flow depth and bed morphology were measured. The bed load transport rate in the period of riverbed armoring was simulated using an exponential decay function. Based on the analysis of bed shear stresses and the change of bed load transport rates before and after the formation of armoring layer, the process of riverbed scouring and armoring and the critical condition of the armored layer’s breakage were studied. The variation of armored bed topography can directly reflect the degree of riverbed scouring. The experimental results showed that the exponential decay law was capable of simulating bed-load transport rate during riverbed armoring, and the simulation results were close to the extremum outsourcing line of the measurements. For alternating discharges, the maximum discharge, which occurred at the first time during each period, was the control factor for the formation and destruction of armoring layer, because the bed-load transport rate produced by the extreme discharge at the first time was always greater than that produced by a smaller discharge or the extreme discharge at the second time. In each period, the condition (armoring versus scouring) of the riverbed surface was determined by the extreme discharge and the initial armoring discharge. Compared to the initial armoring discharge, a larger extreme discharge leads to more significant armored bed. For increasing discharges, the condition of armoring layer was determined by bed shear stress τ under the current discharge and the critical bed shear stress τ0 of the armoring layer. When τ < τ0, the change of armored bed was not obvious; when τ ≥1.1τ0, the armored bed became unstable and the sediment transport rate increased significantly.关键词：armoring layer;bed-load transport rate;bed shear stress;clear-water scouring
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发布时间：2024-01-08 - 摘要：The interpretation method of GPR (ground penetrating radar) detection image by human eye is easily affected by the subjectivity and experience of interpreters. In order to avoid this shortcoming, a spectral energy interpretation method based on Counterlet contour transform and K-Means++ clustering analysis was proposed. Based on the actual highway tunnels, the original detection data of unfavorable geological bodies were obtained through on-site detection. IDSP (interactive detection-surveying prediction) detection data analysis software was used to generate the original image, and time domain and frequency domain preprocessing such as background removal and filtering were implemented to improve the signal-to-noise ratio. Based on subband distribution coefficient, Counterlet was used to decompose and reconstruct the preprocessed image and the K-Means++ algorithm was used to convert the frequency information in the reconstructed image into color features. The color features were extracted by MATLAB, and a sample library of color features of unfavorable geological bodies was established accordingly. The original detection image was matched and compared with the sample library to realize automatic interpretation. Facts and figures showed that it was feasible to decompose and reconstruct multi-directional, multi-resolution and multi-scale GPR images by using Counterlet contour transformation, the curve edge approximation effect was good and the reconstructed images had no information loss. K-Means++ algorithm can realize the conversion of energy to frequency to color in the gray-scale image of GPR, and the converted image has prominent and intuitive color. The matching and comparison of spectral energy can realize automatic interpretation more accurately and quickly and avoid individual subjectivity.关键词：highway tunnel;ground penetrating radar;prediction;frequency spectrum energy;interpretation
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发布时间：2024-01-08 -
Internal Temperature and Humidity Response of Concrete Under Atmospheric Environment in Qingdao Area AI导读
摘要：In the harsh coastal environment, the micro-environment of concrete directly affects carbonation of concrete, chloride penetration into concrete and corrosion of rebar in concrete. The temperature and humidity of the micro-environment inside concrete are affected by the temperature and humidity of the natural environment, and are different from that of the natural environment. In order to study the relationship between them, the effect of temperature and humidity at sheltered and exposed atmospheric environments in Qingdao area, and the response of temperature and humidity at different depths in concrete were monitored on the spot for one year. Results indicated that the temperature and humidity of the atmosphere showed obvious harmonic periodic fluctuation in the period of 24 hours, and the temperature peak was opposite to the relative humidity peak. The variation amplitude of daily temperature and humidity in exposed environment was greater than that in sheltered environment. The maximum temperature difference between the two environments was up to 9 ℃, and the maximum difference of relative humidity was up to 20%. The response of temperature at different depths inside concrete was consistent and the numerical difference was small. In a short period of time, the response value of relative humidity inside the concrete fluctuated slightly, and it increased gradually with the increase of depth. Based on theoretical analyses, the action spectrum of temperature and humidity at atmospheric environment and the response spectrum of internal temperature and humidity of concrete were established. The field measurement results verified that the model could represent the effect of environmental temperature and humidity and the change regulations of temperature and humidity inside concrete well, and it provided a basis for the accurate evaluation and prediction of the durability of concrete structures.关键词：concrete;atmospheric environment;temperature;relative humidity;response spectrum- 2292
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发布时间：2024-01-08 - 摘要：The experiment focused on the absorption and drainage characteristics of recycled coarse aggregate. The recycled coarse aggregate bonded with strain gauges was embedded in C30 strength grade concrete, and the shrinkage strain of recycled coarse aggregate in concrete during drying shrinkage was measured directly. Based on the relationship between the strain and drainage rate of recycled coarse aggregate under different humidity conditions, the drainage characteristics of recycled coarse aggregate in concrete were calculated, and the relationship between the drainage rate of recycled coarse aggregate and the drainage rate of recycled coarse aggregate was established. The results showed that the trend line of strain and saturation curve of regenerated coarse aggregate was relatively close to that of natural coarse aggregate in the process of draining and drainage, and the strain variation caused by dry and wet of the two kinds of aggregate had a reversible trend. There was a linear relationship between the strain and the drainage rate of recycled coarse aggregate and natural aggregate. The shrinkage strain of coarse aggregate in concrete was smaller than that of specimen, and the shrinkage strains of recycled coarse aggregate and recycled concrete were larger than that of natural aggregate and concrete. The drainage rate of recycled concrete was higher than that of internal recycled coarse aggregate.关键词：recycled aggregate concrete;recycled aggregate;drying shrinkage;shrinkage strain;drainage rate
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发布时间：2024-01-08 - 摘要：Natural soil slopes often consist in two or more soil layers due to the geological and human factors. Under heavy rainfall, rainwater infiltrates into the slope, and when the rainfall intensity is greater than the infiltration rate of the soil, the runoff occurs very shortly on the slope surface. Understanding the interaction process of slope runoff and surface infiltration under rainfall conditions is critical for flash flood and landslide risk management. However, the mechanism of the interaction between surface and underground seepage of layered soil slopes has so far remained poorly understood. The studies of rainfall infiltration into the two-layered slope with coarse-over-fine stratification usually ignore the influence of slope runoff resulting in an unrealistic infiltration analysis. A coupled model was established to analyze the rainfall runoff and the rainwater redistribution process after rainfall, and the corresponding calculation program was compiled by Python to solve this problem based on the Moore two-layer infiltration and slope runoff governing equations. The numerical analysis results showed that the rainfall infiltration process of the slope soil was related to the runoff depth on the slope surface. When rainfall intensity was smaller than hydraulic conductivity of surface soil, initial infiltration rate was equal to rainfall intensity, and gradually decreased with the rainfall duration after the runoff on the slope, and finally tended to be stable. The infiltration rate dramatically dropped and eventually equaled the permeability of the subsoil when the wetting front crossed the interface of the soil layers. It indicated that the infiltration rate of the slope with coarse-over-fine stratification was mainly controlled by the lower fine soil layer. The runoff was rapidly degraded after the rainfall stops, and the infiltrated rainwater continued to move downward under the combined action of gravity and the matrix suction of the soil under the wetting front. The runoff was rapidly degraded after the rainfall stops, and the infiltrated rainwater continued to move downward under the combined action of gravity and the matrix suction of the soil under the wetting front. The depth of wetting front tended to be gentle with rainwater redistribution. The example showed that the calculation model and calculation method were feasible, which could better reflect the rainfall infiltration process of the actual layered soil slope, and provided calculation basis for similar layered soil slope.关键词：layered soil;slope;rainfall;slope runoff;coupling;Moore model
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发布时间：2024-01-08 - 摘要：In order to study the difference of fracture process of concrete with different moisture contents, the dry specimen was soaked for different time to reach different moisture contents. The failure process of three-point bending beam was monitored by acoustic emission technique. Comparing the difference of acoustic emission signals, such as hit, count and energy, was applied reflect the different effects of different moisture contents on the mechanical behavior of concrete fracture process, and combined with the hit, count and energy to catch up the initial fracture load, further analysis influences of the initial fracture toughness and unstable fracture toughness on different moisture contents was carried out. The experimental results showed that the variation law of acoustic emission parameters could more intuitively analyze the influence of moisture content on the fracture process of concrete compared with the P–CMOD curve. As moisture content increased, before initiation fracture, the accumulative value of hit increases, however after initiation fracture, the values of acoustic emission parameters of peaks and accumulative values all decreasd. The threshold value of damage evolution decreased with the increase of moisture content, and the maximum was decreased by 64% at saturated content from the value in completely dry condition. The width of the fracture process zone of the saturated specimen increased by 20.8% compared with the dried specimen.关键词：concrete;moisture content;acoustic emission;initial fracture toughness;unstable fracture toughness
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发布时间：2024-01-08 - 摘要：In order to investigate the influence factors of the mechanical properties and the microscopic pore structure of fly ash based geopolymer mortar, the curing temperature, high temperature curing time, water phase content z, water glass modulus n, solution/cement ratio R and the cement/sand ratio J were studied by orthogonal design and single variable method, respectively. And its mathematical model was proposed. The relationship between microscopic pore characteristics and mechanical properties of mortar was analyzed by mercury intrusion porosimetry (MIP). The results showed that increasing the curing temperature can significantly increase the compressive strength of the mortar, and the optimum temperature is 70～80 °C. The maximum compressive strength and flexural strength of mortar can be obtained by continuous curing at high temperature for 4 d, while 91.9% of the maximum compressive strength and 71.3% of the maximum flexural strength can be obtained respectively by curing for 24 h. The sensitivity factors from large to small on mechanical properties of mortar as follows as water phase content, water glass modulus, the cement/sand ratio and the solution/cement ratio. The strength of mortar decreases sharply with the increase of water content z, and the two have almost linear relationship. The compressive strength and flexural strength of the mortar first increase and then decrease with the increase of the modulus n of the water glass, satisfying the quadratic curve relationship. The effect of cement/sand ratio and solution/cement ratio on the strength of mortar can be ignored. When the porosity is similar, the larger the volume ratio of the gel aperture (≤10 nm) and the transition aperture (10～100 nm), the higher the strength of the mortar. However, the effect of porosity on the strength is significantly greater than the influence of pore size distribution.关键词：fly ash;geopolymer;compressive strength;mercury intrusion porosimetry;orthogonal test
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发布时间：2024-01-08 - 摘要：In the ancient concrete building, concrete beams with plain steel reinforcement under the load will evolve from flexural failure to shear failure with the increase of service time. The existing bearing capacity analysis model of the concrete beam with plain steel reinforcement couldn’t distinguish these two failure modes. By selecting concrete beam reinforced with plain bars as research object, the calculated formula of bonding strength between plain steel bar and concrete was proposed and the effect of relatively small bond strength on the load bearing capacity of concrete beams was analyzed in detail. Based on the strut-tie model and the standard truss model, the bearing capacity of the concrete beams was calculated. The results showed that the average ratio of the test values to the analytical values of the strut-tie model and the standard truss model was 1.460 and 1.309, respectively, and the variance was 0.858 and 0.781, respectively. The variable angle truss calculation model was established which could distinguish the failure mode of the concrete beams with plain steel reinforcement. The suggested model was validated by the experimental data of 32 concrete beams. The average ratio of the test results of the bearing capacity of the concrete beams to the calculated values of the variable angle truss model was 1.034 and the variance was 0.100, which indicated that test results and prediction results were in a good agreement. The modified variable angle truss model could precisely predict the failure mode of the reinforced concrete beam with plain steel bar. Thus, the suggested model could be used to calculate the load bearing capacity and analyze the failure mode of concrete beams reinforced with plain steel bars.关键词：strut-tie model;various angle truss model;plain bar;bond;concrete beam
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发布时间：2024-01-08 - 摘要：The experimental study investigates the takeoff characteristics of lower jet trajectory from the dovetail-shaped flip bucket under different inlet conditions. The experiment analyzes the influences of velocity and water depth on lower takeoff characteristics, especially the variation of takeoff angle of lower jet trajectory. The following items are addressed: 1) relationship between takeoff angle of lower jet trajectory and inlet velocity as well as inlet water depth; 2) characteristics of the takeoff angle as a function of changes of inlet Fr0; 3) the empirical formulas for calculating takeoff angle of lower jet trajectory. The results indicate that the effects of inlet conditions are significant on lower takeoff characteristics. Additionally, with the established empirical formulas, the calculated values of horizontal distance of lower nappe profile are in good agreement with the experimental data.关键词：experimental study;dovetail-shaped flip bucket;takeoff angle of lower jet trajectory;horizontal distance of lower trajectory
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发布时间：2024-01-08
HYDRAULIC & CIVIL ENGINEERING
- 摘要：Hydraulic servo control systems mostly adopt servo valve and proportional valve as control components, which has the advantages of high power to weight ratio, high accuracy and fast response, and is widely used in industry, agriculture, light textile industry and transportation. However, the structure of servo valve and proportional valve is complex, the cost is high, and the quality of oil are required. Adopting incremental digital valve with the advantages of simple structure, low cost, strong anti-pollution ability and convenient maintenance as the control component of servo control system has a wide application prospect. Taking the incremental digital valve controlled cylinder position control system as research object, based on the structure and the operating principle of the incremental digital valve, the mathematical model of the position control system was established. And based on MATLAB/Simulink, the simulation model of the position control system was established. Then, the dynamic performance of the incremental digital valve controlled cylinder position control system with different input signals and structural parameters were compared and analyzed through simulation. Finally, the incremental digital valve-controlled cylinder position control system experiment platform was built to test the dynamic performance under different working conditions. Through combining simulation with experiment, the feasibility of incremental digital valve principle was verified, the dynamic response ability of the incremental digital valve control cylinder position control system under different conditions was analyzed, and the main factors influencing the dynamic response ability were found, which provides the theoretical and experimental basis for the structure improvement of incremental digital valve and the dynamic performance optimization.关键词：incremental digital valve;position control system;dynamic performance analysis
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发布时间：2024-01-08 -
Effects of Working Fluids on Operating Characteristics of the Cryogenic Loop Heat Pipe in 180～230 K AI导读
摘要：The cryogenic loop heat pipe is a high-efficiency two-phase heat transfer device that is commonly used in space thermal control systems. In order to investigate the suitable working fluids for LHP in 180～230 K for space exploration applications, the effects of working fluids on the operating characteristics including start-ups, responses of the operating temperatures to the heat load rise, and thermal resistances of the LHP at steady states were researched by employing ethylene, ethane and propylene as fluid candidates. The experimental results and analysis showed that by controlling the temperatures of the evaporator and the compensation chamber at least 10 K below the critical temperatures of the fluids, the LHP achieved successful start-up with heat loads of 5 W. With approximate evaporator temperatures before the start-up, the start-up temperature rise were both within 2 K for the ethane and propylene charged LHP, the start-up time of the ethane charged LHP was less than that of the propylene charged one, and the latent heat and liquid viscosity of working fluids were largely responsible for the differences in the start-up time. The effect of working fluids on the responses of the LHP operating temperatures to the heat load rise was not obvious. The evaporator temperatures decreased and then increased with the rising heat load. The lowest evaporator temperatures occurred with heat loads of 20～30 W, and the time for the LHP to reach the new steady-state decreased with the heat load rise. The pressure drops of the working fluids in the external loop accounted for the significant differences among the heat transfer thermal resistances of the LHP at steady states, and the vapor phase pressure drops took the majority part of the external pressure drops. The smaller vapor pressure drop led to the smaller thermal resistance. The vapor pressure drops of the ethylene charged LHP were less than that of the ethane and then the propylene charged LHP with the same heat loads, and the vapor pressure drops for all three fluids decreased with the increasing temperature. Correspondingly, the thermal resistances of the ethylene charged LHP were less than that of the ethane and then the propylene charged one, all thermal resistances decreased with the rising temperature. The smallest thermal resistance obtained experimentally was 0.21 K/W.关键词：loop heat pipe;ethylene;working fluid;start-up;thermal resistance;pressure drop- 1711
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发布时间：2024-01-08 - 摘要：Monocrystalline silicon is widely used in the field of photoelectric systems, and it is easy to cause its thermal damage and change of performance under the action of laser. For the urgent needs of high-precision laser weapons and laser fine processing industry, the thermal damage of monocrystalline silicon irradiated by pulse train of millisecond laser andthe relationship among the laser energy density, number of pulses and other important parameters of thermal damage were analyzed, and the damage law and mechanism were explored. Thermal damage of monocrystalline silicon by pulse train of millisecond laser was studied from both simulation and experimental aspects. Based on the heat conduction equation, a thermal damage model of monocrystalline silicon irradiated by pulse train of millisecond laserwas established, finite element and finite difference methods were used to solve temperature field of monocrystalline silicon treated by pulse train of millisecond laser. The equivalent specific heat capacity was introduced into the model to deal with the phase change after melting and vaporization, and the temperature rise of the model was corrected. The temperature measurement system of millisecond pulse laser damage monocrystalline silicon was constructed, and the high-precision spot temperature meter was used to measure the laser irradiation center point temperature in real time. Research indicated that when a pulsed laser is applied to monocrystalline silicon target, the center point of the laser irradiation and the radial and axial positions have a temperature accumulation effect, and the radial temperature rise range is much larger than the axial direction; With the increase of laser energy density, the temperature accumulation effect is significant; As the number of pulses increases, the melting time of monocrystalline silicon and the time from the melting point to the normal temperature are lengthened; when the number of laser pulses is increased to 90;The thermal damage threshold of monocrystalline silicon decreases to 73.8% of the single pulse damage threshold; When the number of pulses increases, the damage area of monocrystalline silicon increases. Comparing the experimental and simulation results, it can be seen that the laws of the two aspects are basically the same. The simulation model can reasonably describe the process of millisecond pulse laser damage to monocrystalline silicon.关键词：millisecond pulse;laser;monocrystalline silicon;pulse train;thermal damage
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发布时间：2024-01-08
MECHANICAL ENGINEERING
- 摘要：Chloride penetration is the main reason for corrosion of steel bars in reinforced concrete in marine environment, salt lake area and saline soil area. Therefore, the measurement of chloride distribution in reinforced concrete structures timely and accurately is of great significance for durability assessment, maintenance and repair of reinforced concrete structures under severe environment. In this paper, a solid-state Mn/MnO2 reference electrode with dense structure and stable performance, which can be embedded in concrete, was prepared by pressed powder method. Results showed that loading pressure is an important parameter that affects the strength and density of Mn/MnO2 electrode prepared. During the preparation of Mn/MnO2 electrode, it is necessary to control the loading pressure. The suggested pressure loading pressure is 96 MPa. And the Mn/MnO2 electrode must be activated before use. After activated, the response time of the Mn/MnO2 electrode is less than 60 second. Also, the Mn/MnO2 electrode has stable performance, good reproducibility and good resistance of polarization. The potential value of the Mn/MnO2 electrode increases linearly with the increase of temperature between 5 ℃ and 65 ℃. Besides, the pH value between 8 and 13 has nearly no effect on the potential value of the Mn/MnO2 electrode. So, if the Mn/MnO2 electrode prepared in this paper is used as reference electrode of chloride sensor, the temperature of concrete at the location of chloride sensor is also needed to record simultaneously. And the potential value of the Mn/MnO2 electrode must be corrected by temperature.关键词：reference electrode;pressed powder method;performance;influencing factors
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发布时间：2024-01-08
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Abnormal behavior detection in crowded scenes has drawn extensive interests in computer vision community due to its various applications, e.g., video surveillance, video analytics, and action recognition. However, it is still a challenging task due to the large-scale variation, perspective distortion, and labeling biases. In this paper, an abnormal crowd behavior detection method based on streak flow and convolutional neural network (SFCNN–ABD) was proposed to address this problem. The SFCNN–ABD was composed of two stream CNNs, in which the backbone network was composed of two deep residual networks including spatial network and temporal network respectively. The spatial network utilized the raw video frames to extract the appearance features of crowded scenes, whereas the temporal network used the streak flow to extract the kinematic features. The streak flow can accurately recognize the spatial and temporal changes in the scene, and thus can further boost the proposed the performance. For abnormal behavior detection, salient spatial features were learned via a convolutional neural network (CNN) and temporal features with the aid of streak flow and CNN. Finally, the outputs of these two networks were averaged to detect the abnormal crowd behavior. Experimental results on UMN and VIF benchmark datasets indicate that the proposed method outperforms several state-of-the-art methods in terms of the accuracy and thus demonstrates the effectiveness of the proposed method.关键词：abnormal crowd behavior detection;streak flow;spatial–temporal CNN;ResNet101
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发布时间：2024-01-08 - 摘要：There are many methods to extract fetal electrocardiogram (FECG) from multi-channel abdominal signals. Based on the assumptions of statistical independence and non-Gaussianity among signals, the blind source separation is widely concerned. However, due to the influence of maternal ECG (MECG) signals and a variety of complex bioelectrical noises mixed in the abdominal ECG signals, as well as the unreasonable arrangement of the abdominal electrodes, the extraction results of FECG by the traditional blind source separation algorithm are often unsatisfactory. In this paper, an EMD–QPCE method was proposed for the extraction of multi-channel FECG based on the empirical mode decomposition (EMD) and quasi-periodic component extraction (QPCE). Firstly, the abdominal mixed ECG signals of each channel were decomposed into a series of intrinsic mode functions (IMF) by EMD, and the components of MECG signals in the IMFs were eliminated to enhance the FECG information. Then, the IMFs of the same order in each channel signals were combined and the IMFs with the FECG information were extracted by QPCE. Finally, an FECG was reconstructed from the IMFs containing the FECG information. Experiments were carried out on real ECG signals in DaISy, ADFECGDB and Challenge 2013 databases. The results showed that compared with the traditional ICA, PCA and QPCE methods, the EMD–QPCE method proposed in this paper greatly improved the success rate and the quality for the FECG extraction. Sensitivity of extraction (Se) for FECG of the proposed method was 92.31%, Positive predictive value (PPV) was 98.77%, accuracy index F1 was 95.43% and average fetal heart rate error was 0.595%. It showed a very good accuracy, which verified the effectiveness and superiority of the proposed method.关键词：empirical mode decomposition;quasi-periodic component extraction;fetal electrocardiogram extraction
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发布时间：2024-01-08
INFORMATION ENGINEERING
- 摘要：In order to solve the problem that wind power is hard to predict due to its characteristics such as large fluctuation and strong randomness, a ultra-short-term wind power prediction model for wind farms was proposed based on fuzzy C-means (FCM), which selects similar daily and salp swarm algorithm to optimize the extreme learning machine (SSA–ELM). Firstly, the FCM data clustering method was used to select similar days with higher correlation with the predicted days, of which the historical wind speed, temperature, wind direction and other climatic factors that are highly correlated with wind power formed a multi-input sample set. Secondly, the network parameters were determined in the training process through the training set, and the input weight matrix and hidden layer deviation of the extremely learning machine were optimized to improve the adaptability and accuracy of the prediction model by using the salp swarm algorithm in an iterative process. Finally, according to the ultra-short-term wind power interconnection related regulations, using the actual data of a wind farm in Henan province from ultra-short-term prediction based on similar days, three aspects of the four seasons and rolling prediction error of the representative simulation experiment, and the extreme learning machine (ELM) and BP neural network model were analyzed. The results show that the proposed model has faster convergence speed and higher prediction precision. It is demonstrated that the proposed ultra-short-term wind power prediction model based on FCM and SSA–ELM has good tracking and generalization ability.关键词：wind power prediction;similar day;salp swarm algorithms;extreme learning machine
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发布时间：2024-01-08
ELECTRICAL ENGINEERING
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