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In this study, aeolian sand was used as fine aggregate to partially replace natural river sand in the range of 25 to 100% to prepare aeolian sand concrete (ASC). The ASC under freeze–thaw conditions in chloride environment was studied. Based on the compressive strength loss rate and the relative dynamic modulus of elasticity (the relative DME) obtained from the study as damage variables and combined with the Weibull distribution model, the freeze–thaw damage model of ASC was established to predict the service life of ASC in China's northwestern cold regions. The microstructure of ASC under freeze–thaw conditions was also observed and studied. The results showed that 100% ASC had the best frost resistance, and the compressive strength loss rate and relative dynamic elastic modulus after 200 freeze–thaw cycles were 18.2 and 90.8%, respectively. These evaluation indexes show that the concrete has not reached the freeze–thaw damage state. The linear damage evolution model can accurately predict the durability of ASC in a cold environment, and predict that the service life of 100% ASC in 3.5% chloride solution is more than 25 years, which meets the requirements of concrete in water conservancy projects in Northwest China. [ABSTRACT FROM AUTHOR]

Background: Acute lung injury (ALI) is a serious illness that has few treatment options available. Tribuloside, a natural flavonoid extracted from the Tribulus Terrestris plant in China, is potent in addressing many health issues such as headaches, dizziness, itching, and vitiligo. Objective: This study intends to explore the mechanisms of action of Tribuloside in treating ALI through a combination of network pharmacology and experimental validation. Methods: We obtained the 2D structure and SMILES number of Tribuloside from the PubChem database. We used the SwissTargetPrediction database to identify pharmacological targets. We found 1215 targets linked to ALI by examining the GeneCards database. We used the String database and Cytoscape software to create the "drug or disease-target" network as well as the protein-protein interactions (PPI). Key targets were identified by evaluating associated biological processes and pathway enrichment. A Venny Diagram showed 49 intersection points between Tribuloside and ALI. Molecular docking with AutoDockTools found that Tribuloside had a high affinity for IL6, BCL2, TNF, STAT3, IL1B, and MAPK3, the top 6 targets in the PPI network by Degree values. To test Tribuloside's therapeutic efficacy in ALI, an acute lung damage model in mice was constructed using lipopolysaccharide. Tribuloside treatment reduced inflammatory cell infiltration, decreased fibrotic area, repaired damaged alveoli, and suppressed inflammatory factors IL-6, TNF-α, and IL-1β in the lungs through many pathways and targets. Conclusion: This study reveals that Tribuloside has the potential to treat ALI by targeting various pathways and targets, according to network pharmacology predictions and experimental confirmation. [ABSTRACT FROM AUTHOR]

Drilling and blasting method used for excavation causes damage to surrounding rock mass, and frequent blasting often leads to cumulative damage effects. Thus, understanding the distribution of Blast-Induced Damage (BID) zone is critical to assess the slope stability of open-pit mines. Herein, this study aims to investigate the cumulative damage effects and safety control criteria on the final wall of the open-pit slope under blasting. The cumulative damage zone was defined using a continuous damage model coupled with tensile damage and Drucker–Prager yield criteria embedded in the finite difference method. The simulation results were validated against field data collected from the Wushan open-pit mine in Inner Mongolia, China. The results demonstrate that the cumulative damage of the final wall exhibited a non-linear decreasing trend from the bench face to the interior of the slope, successfully reproducing the spatial distribution of the BID obtained from the in situ test, and revealing that the maximum cumulative damage depth occurred at the slope crest. Additionally, a safety control criterion for the critical damage zone of open-pit final slope was proposed based on the investigation of the effects of dynamic loading rate and stemming length on excessive overbreak. The results highlight how important it is to account for cumulative damage effects when assessing the final slope stability of an open pit and optimizing the mining design. Highlights: The cumulative damage effects on the final wall of the open-pit under blasting are investigated. A model coupled with tensile damage and Drucker-Prager yield criteria is established and incorporated into finite difference method to simulate the blast-induced damage zone. The subsurface damage depth is obtained using the digital drilling images technology. The dynamic loading rate and stemming length could significantly affect the excessive overbreak along the crest. [ABSTRACT FROM AUTHOR]

An increasing number of field investigations have revealed that the transverse cracks in semirigid asphalt pavement are more likely to initiate in the top of the asphalt layer rather than in the bottom of the asphalt layer, which conflicts with the widely accepted view that bottom-initiated reflective cracking is the dominant distress. To analyze the initiation cause of this kind of surface crack, a numerical simulation model coupled with multiphysics fields was built. It was based on the viscoelastic-plastic damage model, using the finite-element software Abaqus to calculate the damage distribution coupled with the temperature field as well as the loading field. The simulation results show that asphalt layers have two main damage regions in the semirigid base crack section, located in the top asphalt layer and the bottom asphalt layer. The increase of asphalt layer thickness and the decrease of heavy loads are the most possible causes of surface-initiated cracks replacing reflective cracks in semirigid pavements in recent years in China. [ABSTRACT FROM AUTHOR]

The world is facing the problem of depletion of natural sand and gravel resources, and a large amount of coal gangue solid waste is produced in Inner Mongolia, China, which has low utilization rate and causes ecological pollution. In order to improve the gangue in the mining infrastructure construction of a wide range of application prospects, the use of coal gangue as the coarse aggregate of pumice concrete is of great significance. Inner Mongolia is a cold region, and gangue mixed aggregate concrete (MFC) will certainly face the damage caused by freeze–thaw cycles. Therefore, design gangue by different volume replacement rate (0%, 20%, 40%, 60%, 80%, 100%) to replace pumice coarse aggregate. The results show that with the increase of gangue substitution rate, the mass loss rate, relative dynamic elastic modulus, and peak stress of MFC decrease, but the trend of peak strain increases. It is mainly attributed to the less Al2O3 and SiO2 content of gangue, which makes the MFC hydration products decrease with the increase of substitution rate and more original microcracks and pores in the specimens. In addition, the damage model of MFC was established by using Weibull statistical distribution theory and the principle of LEMAITRE equivalent effect variation assumption, and the damage evolution characteristics were explored by combining the experimental results. It can provide the theoretical basis for the application of MFC in cold regions. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Unsaturated expansive soil is widely distributed in China and has complex engineering properties. This paper proposes the unified hydraulic effect shear strength theory of unsaturated expansive soil based on the effective stress principle, swelling force principle, and soil–water characteristics. Considering the viscoelasticity and structural damage of unsaturated expansive soil during loading, a fractional hardening–damage model of unsaturated expansive soil was established. The model parameters were established on the basis of the proposed calculation method of shear strength and the triaxial shear experiment on unsaturated expansive soil. The proposed model was verified by the experimental data and a traditional damage model. The proposed model can satisfactorily describe the entire process of the strain-hardening law of unsaturated expansive soil. Finally, by investigating the damage variables of the proposed model, it was found that: (a) when the values of confining pressure and matric suction are close, the coupling of confining pressure and matric suction contributes more to the shear strength; (b) there is a damage threshold for unsaturated expansive soil, and is mainly reflected by strength criterion of infinitesimal body; (c) the strain hardening law of unsaturated expansive soil is mainly reflected by fractional derivative operator. [ABSTRACT FROM AUTHOR]

CU test and CD test were performed to capture the stress-strain characteristics of the clay in Dongting Lake area, China. Since the classical constitutive model cannot ideally describe the strain hardening behavior of the clay, an improved constitutive model that involved three damage factors was proposed. The damage first factor D 1 , which represents elemental volume strength F , was fitted by the Weibull function. The second and third damage factors D 2 and D 3 , which represent the porosity ratio e and the drainage rate P ε respectively, were fitted by Harris function. The CD test damage model is constructed by D 1 , D 2 , and D 3 . In the CU test, the porosity ratio e is a constant value, and the drainage volume is 0, so that D 2 is constant value and D 3 is 0. Therefore, the CU test damage model of the clay was constructed using the damage first factor D 1 . In the end, the accuracy of the proposed CU/CD damage constitutive models of the clay was validated with the experimental results. It is found that the results fitted by the proposed methodology are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The aim of the study is the deep understanding of the essential reactivity of the environmentally friendly mortar by which its applicability can be justified. Created in the study was the environmentally friendly mortar, which helped relieve the increasing requirements on conventional building materials that are produced from exhausted freshwater and river sand nowadays. Seawater (SW) and sea sand (SS) collected from the Eastern Seas of China were used to produce the mortar at various ages, including 10-day, 33-day, and 91-day. Both the curing and working conditions of the mortar were natural marine ones. The physicochemical-mechanical behaviors were investigated using uniaxial compression tests (UCTs), Energy Dispersive Spectrometer (EDS), X-ray Diffraction (XRD), and thermal-field emission scanning electron microscopy (SEM) analysis to understand the essential reactivity of the mortar with age accumulation. The results indicated that hydration products and favorable components were generated promisingly in the mortar: the C-S-H (xCaO·SiO2·zH2O) development was certainly achieved in the critical environment during the curing and working period; the extensive generation of C-A-S-H (CaO·Al2O3·2SiO2·4H2O) helped densify the C-S-H grid, which caused the promising development of the uniaxial compression strength (UCS); the framework porosity of the mortar was restrained effectively due to the development of Friedel's salt that re-bonded the interfacial cracks between SS and the hydration products with the age accumulation in the critical environment. Consequently, UCS and the resistance against damage of the mortar showed increasing behavior even in the critical environment. The study established Friedel's salt working models and strength and damage models to interpret the physicochemical reactivity of the mortar as: the source of the strength and toughness was the proper polymerization between the native saline components and the hydration product mixture generated throughout the production, curing, and application without the leaching phenomenon. The novel models and interpretation of the physicochemical reactivity ensured the applicability of the mortar produced with SW and SS in the critical environment. [ABSTRACT FROM AUTHOR]

Accurate information about the distribution of natural fractures is a key factor for the success of the exploration and development of oil and gas in carbonate rock formations. Forward modeling of natural fractures generated by tectonic movement within carbonate rock formations was investigated by jointly using the continuum damage model and finite element numerical technology. Geological analysis of natural fractures was used as the basis of the geomechanical finite element calculation. A workflow of numerical calculations for natural fractures was proposed. These achievements were applied to investigate natural fractures' distribution within Ordovician carbonate rock formations of the Fuman Oilfield, Xinjiang, in the west of China. Finite element sub-modeling technology was used to further investigate natural fractures within key target reservoir formations with a finer mesh. The contour of natural fractures represented by the localization band of continuum damage variables was obtained. A comparison of the numerical results of the natural fractures' distribution represented by continuum damage variables with those of natural fractures interpreted from seismic data shows that: (1) the numerical solution of natural fractures matches the measured data, and their orientations are in good accordance; (2) their distribution and locations are basically the same, with some small differences in local details; (3) the numerical results indicate that the maximum value of the damage variable SDEG within the zones of natural fractures is 0.2686, and the widths of the bands of natural fractures/faults are in the range of 500 m to 1000 m. Validation of the results of the distribution of natural fractures was performed indirectly via the distribution of the minimum horizontal stress gradient ShG. [ABSTRACT FROM AUTHOR]

To explore the shear creep characteristics of weak inter layers under repeated rain action, the Permian carbonaceous shale soft interlayers in southwestern China were taken as the research object, and the real-time infiltration water/air pressure cyclic shear test system was used to carry out the infiltration water/air pressure test system. In the cyclic shear creep test, the shear creep characteristics and long-term strength deterioration mechanism of the weak interlayer were analyzed, and a creep damage constitutive model considering Weibull distribution was established. The results showed that; l) The weak interlayer has obvious creep characteristics. With the increase of the number of permeating water/air pressure cycles, the shear deformation before failure gradually increases, showing two different failure modes, toughness, and brittleness during failure; 2) With the increase of water penetration/The increase in the number of air pressure cycles, the deterioration degree of the weak interlayer shows an increasing trend, but eventually tends to a certain value, the degree of deterioration can be expressed by the function Di = 0.7717 X [1-exp(-0.1n)]; 3) Based on the experimental data, a damage viscoplastic element based on the Weibull distribution theory is proposed, and a water/air pressure cycle creep damage model is constructed, which can well describe the three stages of creep of a weak interlayer. The research results have important guiding significance for the long-term stability analysis of high and steep slopes with weak interlayers. [ABSTRACT FROM AUTHOR]

To deeply explore the seismic vulnerability characteristics of typical structures and obtain the differences in the seismic capacity of multiple structural categories in actual earthquakes, combined with mathematical statistics and probabilistic damage model analysis methods, the bulk of collection and statistics were made on the structural seismic damage observation data (98,051.8122 × 104 m2 and 995,269 buildings) of 213 destructive earthquakes in China from 1975 to 2013. Seismic damage sample databases of wooden roof truss structures, adobe and timber structures, brick wood structures, masonry structures, RC structures, and bottom frame seismic wall masonry structure were established. A seismic damage investigation and analysis were conducted. All samples' vulnerability grades were evaluated using the latest version of the Chinese seismic intensity scale (CSIS-20). The actual damage vulnerability probability matrix and surface model of structures in multiple intensity regions based on the investigated area and quantity parameters were established. A nonlinear regression prediction model analysis method was proposed. A typical structural vulnerability prediction model considering the failure ratio and exceedance probability in the multi-intensity region was established and verified by the earthquake damage database. In addition, a vulnerability matrix prediction model considering updating the mean vulnerability index parameter was proposed, and a comparison model of the vulnerability prediction matrix of typical regional structures was developed. [ABSTRACT FROM AUTHOR]

Coal-fired power plants are one of the major sources of coal consumption in China; they discharge various air pollutants and cause serious human health damage. There is an urgent need to focus on the associated health effects. Thus, this study aims to advance an integrated life cycle assessment (LCA)–based health damage model to quantify the health burden of air pollutant emissions from coal-fired power generation (CFPG) and to achieve an economic interpretation of health damage. A case study of the Zaozhuang coal-fired power project was conducted to better visualize and mitigate the impacts. The results reveal that willingness to pay (WTP) for health damage caused by the CFPG project in 1 year amounted to USD 15.71 million, and the total amount of life lost was 155.81 years. During the CFPG process, coal combustion caused the most health damage, respiratory disease was the type of damage with the greatest influence on health, and SO2 was the air pollutant that causes the most serious health damage. The model developed in this study can be broadly applied to assess the potential life loss due to air pollutant emissions from CFPG systems. The identified key points for health damage prevention can also be used as practical solutions for decision-making regarding the prioritization of control sources for environmental management. [ABSTRACT FROM AUTHOR]

Three types of rocks are selected to conduct uniaxial compression and microscope experimental to study the influences of freeze-thaw cycles on crushed-rocks from Gonghe-Yushu high-graded highway, which is the first high-grade highway built in permafrost regions in China. Using the hypothesis of Lemaitre's strain equivalence principle and a theoretical model of crushed-rock deterioration after freeze-thaw cycles was established and verified by the experimental data. The experimental results showed that with an increase of the number of freeze-thaw cycles, the microcracks of saturated red sandstone increased, and this phenomenon is not obvious on other rocks. Moreover, different degrees of spalling and cracks appeared, with common physical parameters gradually decreasing. The uniaxial compressive strength of rock decreases exponentially with the increase of the number of freeze-thaw cycles. The mechanism of the influence of freeze-thaw cycles on the fine structure of the three different crushed-rocks were then analyzed using SEM scanning. Freeze-thaw cycles weaken the connection between rock mineral particles and increase the surface micropores. The damage model of freeze-thaw and load can well describe the damage law of crushed-rocks. [ABSTRACT FROM AUTHOR]

Debris slopes are widely distributed across the Three Gorges Reservoir area in China, and seasonal fluctuations of the water level in the area tend to cause high-frequency microseisms that subsequently induce landslides on such debris slopes. In this study, a cumulative damage model of debris slope with varying slope characteristics under the effects of frequent microseisms was established, based on the accurate definition of slope damage variables. The cumulative damage behaviour and the mechanisms of slope instability and sliding under frequent microseisms were thus systematically investigated through a series of shaking table tests and discrete element numerical simulations, and the influences of related parameters such as bedrock, dry density and stone content were discussed. The results showed that the instability mode of a debris slope can be divided into a vibration-compaction stage, a crack generation stage, a crack development stage, and an instability stage. Under the action of frequent microseisms, debris slope undergoes the last three stages cyclically, which causes the accumulation to slide out in layers under the synergistic action of tension and shear, causing the slope to become destabilised. There are two sliding surfaces as well as the parallel tensile surfaces in the final instability of the debris slope. In the process of instability, the development trend of the damage accumulation curve remains similar for debris slopes with different parameters. However, the initial vibration compaction effect in the bedrock-free model is stronger than that in the bedrock model, with the overall cumulative damage degree in the former being lower than that of the latter. The damage degree of the debris slope with high dry density also develops more slowly than that of the debris slope with low dry density. The damage development rate of the debris slope does not always decrease with the increase of stone content. The damage degree growth rate of the debris slope with the optimal stone content is the lowest, and the increase or decrease of the stone content makes the debris slope instability happen earlier. The numerical simulation study also further reveals that the damage in the debris slope mainly develops in the form of crack formation and penetration, in which, shear failure occurs more frequently in the debris slope. [ABSTRACT FROM AUTHOR]

The mechanical behavior of basalt is critical to the stability and safety of large structures erected on basalt. In this paper, a series of tests (hydrostatic compression test, triaxial compression tests, and triaxial cyclic loading test) are conducted on basalt specimens from the Baihetan hydropower station in southwest China. The test results show that the crack closure (σcc), crack initiation (σci), and crack damage (σcd) stresses are approximately 39%–43%, 54%–68%, and 74%–96% of the peak strength (σp), respectively. Based on the experimental results, a coupled elastoplastic damage model is proposed for basalt within a thermodynamic framework. In this model, elastic stiffness is affected by induced damage. Linear yield function and nonassociated flow rule are used to control inelastic dilatancy. Model parameters are determined from the triaxial compression tests and triaxial loading tests performed in this study. Comparison between numerical results and test results shows that the proposed model can accurately simulate the mechanical behavior of basalt under triaxial compression conditions. [ABSTRACT FROM AUTHOR]

Rock mass containing central locked segments is susceptible to freeze–thaw weathering and could result in rock instability and even serious geological hazards. This work conducts uniaxial compression and acoustic emission synchronization tests to experimentally investigate the rock bridge deformation and failure characteristics of central locked samples drilled from plateaus in China. The influences of freeze–thaw cycles and rock bridge angle on the fracturing and acoustic emission pattern were characterized. Results show that the physical and mechanical parameters deteriorate in varying degrees with the increase of freeze–thaw cycles. The compression stress curves display as fluctuation trend and multiple stress drops, indicating that the rock bridge improves the plastic properties of samples. The points of stress drops are in good agreement with sudden increment of acoustic emission count curve. The acoustic emission count and released acoustic emission energy decrease with the increase of freeze–thaw cycles. The damage model established based on acoustic emission parameters reflects the process of crack propagation and coalescence of central locked sample subjected to freeze–thaw cycles during uniaxial compression. Damage variable evolution rate decreases with increasing of freeze–thaw cycles. The damage evolution rate and the associated crack growth rate is the smallest for a rock with bridge angle of 30 °. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A sound understanding of the influence of cyclic loading on mechanical properties of rock is of great importance for the management and optimization of engineering rock mass structures such as nuclear waste repositories and geothermal resources. In the present manuscript, we first performed a series of conventional uniaxial compressive tests and fatigue failure tests (i.e. cyclic loading tests) on sandstone samples from Sichuan Province, China. The experimental results show that the fatigue failure of sandstone is achieved once the cumulative axial deformation under cyclic loading reaches the axial strain that corresponds to the post-peak phase of the stress–strain curve from a conventional uniaxial test. Based on our laboratory data, and considering that the fatigue process is characterized by local material degradation as well as irreversible deformation that accumulates during each loading cycle, we propose here a two-dimensional meso-scale elasto-plastic damage model to simulate the fatigue behavior of rock during cyclic loading. We then performed a suite of numerical simulations using this model to better understand the fatigue process in sandstone. The results of our numerical modeling show that the ratios of maximum stress and stress amplitude to the uniaxial compressive strength are the most important factors affecting the fatigue life of sandstone. A larger maximum stress and/or stress amplitude results in a shorter fatigue life for the numerical sandstone specimen. However, we find no significant correlation between sample homogeneity and fatigue life. Importantly, our modeled results show that specimen failure occurs once the cumulative axial deformation under cyclic loading reaches the axial strain that corresponds to the post-peak phase of the stress–strain curve from a conventional uniaxial test simulation, in accordance with our laboratory testing. Therefore, the model presented herein provides a new platform to investigate the fatigue failure of rocks. [ABSTRACT FROM AUTHOR]

Pore defects in rocks represent a significant factor contributing to creep hazards in rock engineering. To investigate the sensitivity of rock creep characteristics to porosity, prefabricated pore tests and creep tests were conducted on red sandstone obtained from the Yuezhi Mountain Tunnel in Sichuan Province, China. The energy theory and the developed Clumps with random geometry (CRG) model were used to characterize the rock damage during creep loading. The results show that the percolation erosion test effectively alters the porosity of the rock and make the pores uniformly distributed in the rock. There is a significant disparity in the creep characteristics of sandstones with varying porosities, particularly noticeable in the stable creep rate and accelerated creep initiation time. Moreover, the increase in porosity leads to a higher proportion of shear cracks and an accelerated energy dissipation rate during the rock creep process. Drawing upon the findings from the tests and simulations, a porosified Nishihara creep damage constitutive model is put forward. Analysis reveals that the deformation parameters of the creep constitutive model decrease progressively with rising porosity, whereas the damage parameters exhibit a contrasting trend. • The effect of porosity on the creep properties of sandstone is analyzed. • Rock creep damage parameters are determined using energy methods. • Higher porosity results in more shear cracks and elevated creep energy dissipation. • Rock creep and damage parameters are closely related to porosity. [ABSTRACT FROM AUTHOR]

The red sandstone in the Luohe Formation in Shaanxi Province, China, contains a rich aquifer system. The excavation of coal mines and tunnels through the Luohe Formation affects the mechanical properties of the rocks in the surrounding environment, creating the need to determine the effect of the porewater pressure and unloading rate on the mechanical properties of the red sandstone. Using the constant axial pressure unloading method, triaxial unloading tests were performed under different unloading rates (0.1, 0.3 and 0.6 MPa s−1 and porewater pressure conditions (0, 1.0, 1.5 and 2.0 MPa). Based on the results, an unloading statistical damage model of red sandstone was established under the impacts of unloading rate and porewater pressure. During the loading stage, as the porewater pressure increased, the slope of the stress–strain curve and elastic modulus gradually decreased. During the unloading stage, lateral deformation larger than the axial deformation was observed owing to the influence of porewater pressure. The porewater pressure effect became significant as the unloading rate decreased. An increase in porewater pressure or a decrease in the unloading rate increased the confining strain flexibility. Unloading failure of rock samples was dominated by tensile shear failure, thus indicating that a faster unloading rate or larger porewater pressure causes more tensile cracks and severe fracture in the rock samples. [ABSTRACT FROM AUTHOR]

To study the evolution of mechanical properties of steel rebars in the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system under repeated train loads, a 1/4 scale three-span ballastless slab track simple-supported bridge structural system specimen was manufactured and subjected to a multistage fatigue test with 18 million cycles. The experimental results show that the strain amplitude of the steel bar changes proportionally to the fatigue stress amplitude, and there is an obvious strain increase in the loading stage 4, where the fatigue stress amplitude is the largest. During the test, the cumulative strain–amplitude ratio first decreases then increases. At the end of the test, the cumulative strain–amplitude ratio increases by 5.46% and 5.32%, respectively, at L/2 and L/4 sections. The load–strain curve of the steel rebar keeps the shape of an oblique straight line. The slope increases first and then decreases with a degradation at the end of the test of 5.15% and 4.81%, respectively, at L/2 and L/4 sections. The mechanical properties of the rebar are enhanced under the first three million fatigue loading cycles: this is the fatigue strengthening stage. The mechanical properties of reinforcement gradually degrade from the three millionth cycle to the end of the test: this is the fatigue damage stage. Finally, based on the material fatigue damage model and the multistage cumulative damage criterion, the change rule of the load–strain curve slope of steel rebars in the fatigue damage stage is obtained by finite element simulation. The simulation results agree well with the experimental data, proving the validity of the calculation method proposed in this paper. [ABSTRACT FROM AUTHOR]

Large squeezing deformation of layered soft rock tunnel under high geo-stress has a significant time-dependent deformation behavior. In this paper, we studied the deformation mechanism during the construction period of deep-buried soft-rock tunnel by means of a combination of field observations and a numerical method. First, a new classification criterion for large deformations based on the power exponent variation law between the deformation and the strength-stress ratio is proposed. Then, the initial damage tensor reflecting the bedding plane (joint) distribution and an equivalent damage evolution equation derived from the viscoplastic strain are introduced based on the geometric research method, i.e., a new rheological damage model (RDL model) of layered soft rock is established consisting of elastic, viscous, viscoelastic, viscoplastic and plastic elements. A field test was conducted on the Maoxian tunnel in Sichuan province, southwestern China, which is in broken phyllite (layered soft rock) under high geo-stress. The tunnel has experienced large deformation due to serious squeezing pressure, thus we adopted double primary support method to overcome the supporting structure failure problems. The rheological parameters of phyllite in the Maoxian tunnel were recognized by using SA-PSO optimization, and the RDL model does a good job in describing the time-dependent deformation behavior of a layered soft-rock tunnel under high geo-stress. Thus, the RDL model was used to investigate the supporting effect and bearing mechanism of the double primary support method. Compared with the single primary support method, the surrounding rock pressure, secondary lining force, surrounding rock deformation, and the depth of the damage to the rock mass was reduced by 40%–60% after the double primary support method was used. [ABSTRACT FROM AUTHOR]

Cracks will be introduced into mortar specimens and embedded copper sheets to simulate fractured concrete according to the designed 20 mm crack lengths and angles. By taking into consideration the actual environment of a hydro-fluctuation belt for a typical bank slope in the Three Gorges Reservoir Region of the Yangtze River, China, a dry–wet cycle testing program will be designed to study the mechanical properties of the fracture mortar specimens immersed in different sulfate solutions. The failure characteristics and modes of the fracture mortar specimens will be measured and analyzed. The tests results show that the strength initially decreased and then increased with an increasing crack angle from 0° to 90°, and this was the smallest for the specimens with a 45° angle. Deterioration occurred in the specimens subjected to dry–wet cycles in different sulfate solutions. The damage extent is expressed as the change in elasticity. A formula for damage evolution of the fracture specimens will be proposed and the relationship between the deformation properties and damage properties of the specimens will be developed for the combined action of dry–wet cycles and sulfate attack. Based on the proposed damage model, the damage evolution equation and elastic damage constitutive model will be derived under the combined action of dry–wet cycles and sulfate attack, and this damage constitutive relation could be used to the study damage evolution for the fracture mortar specimens under the combined effects of dry–wet cycles and sulfate attack. [ABSTRACT FROM AUTHOR]

Multicomponent thermal fluid huff and puff is an innovative heavy oil development technology for heavy oil reservoirs, which has been widely used in offshore oilfields in China and has proved to be a promising method for enhancing oil recovery. Components of multicomponent thermal fluids contain many components, including carbon dioxide, nitrogen, and steam. Under high temperature and high pressure conditions, the complex physical and chemical reactions between multicomponent thermal fluids and reservoir rocks occur, which damage the pore structure and permeability of core. In this paper, the authors set up a reservoir damage experimental device, tested the formation permeability before and after the injection of multiple-component thermal fluids, and obtained the formation damage model. The multicomponent thermal fluid formation damage model is embedded in the component control equation, the finite difference method is used to discretize the control equation, and a new multielement thermal fluid numerical simulator is established. The physical simulation experiment of multicomponent thermal fluid huff and puff is carried out by using the actual sand-packed model. By comparing the experimental results with the numerical simulation results, it is proved that the new numerical simulation model considering formation damage proposed in this paper is accurate and reliable. [ABSTRACT FROM AUTHOR]

A particle-based discrete element model combined with digital image processing to take into account the grain geometry and size distribution is used to investigate the mechanical and microcracking behavior of Beishan granite (BG), a typical crystalline rock potential for nuclear waste disposal in China. First, the procedure to construct a digital image-based grain-based model is introduced. The unsupervised K-means clustering algorithm is used to determine mineral boundaries, and four micro-parameters are assigned according to the Weibull distribution to reflect micro-heterogeneity of rock. Then, the model is calibrated to the macro-properties of BG obtained from laboratory tests, and consistency between model simulation and laboratory test results of both microcracking processes and failure modes is found. It is shown that intragrain cracks are initiated successively in quartz, feldspar, and mica; and their numbers in quartz and feldspar are much more than that in mica. Crack cluster, forking cracks and cataclastic microcracking are typical in quartz, while the "voids" is found in mica. Grain property heterogeneity has a significant impact on micro-cracking behavior and macro-properties of the model, with greater heterogeneity resulting in a lower uniaxial compression strength and elastic modulus, and a more scattered distribution of microcrack inclination. The modeling procedures presented here provide an effective method for investigating mechanical and damage behavior of granites, with specific consideration of heterogeneity involving the distribution of mineral grains and their mechanical properties. [ABSTRACT FROM AUTHOR]

China's western mining area is an arid and semiarid area with a fragile ecological environment, and the high-intensity mining activities aggravate ecological damage. Reasonable choice of the mining parameters (i.e., mining height, panel width, and advancing speed) can not only improve the mining efficiency but also weaken the mining-induced deformation and failures of the overburden and surface. The statistical analysis of the relationship between the mining parameters and periodic weighting interval (PWI) proves that mining parameters have significant influence on overburden failure. In this study, the damage constitutive equation was derived, and the overburden damage degree was defined to quantitatively characterize mining-induced stratum damage in a three-dimensional space. FLAC3D numerical models embedded with a damage constitutive equation were built to compare the panel width effect and advancing speed effect between the overburden damage degree and the water-conducted fracture zone (WCFZ). The reasonable range for mining parameters of the panel 12401 was provided based on the fitting function of the overburden damage degree versus mining parameters. The field measurements were carried out on panel 12401 of the Shangwan coal mine, including the advancing speed, PWI, and ground crack development. The results show that, under constant engineering and geological conditions, the damage degree of overburden will be weakened by increasing the advancing speed, reducing the mining height, or shortening the panel width. The overburden damage degree is more accurate than the height of the water-conducted fractured zone. The reasonable mining parameters of the panel 12401 are 8.8 m in mining height, 300 m in panel width, and 13.47 to 20.58 m/d in advancing speed, respectively. The field measurement results of the PWI and ground cracks have verified the validity using the overburden damage degree to determine high-intensity mining parameters. [ABSTRACT FROM AUTHOR]

BACKGROUND: Protein degradation is the main reason of exercise induced muscle damage (ElMO). High-intensity exercise may lead to the misfolding of proteins and fonn aggregates, which is harmful to the ultrastructure of skeleton muscle. OBJECTIVE: To determine the formation and role of protein aggregate (especially the desmin aggregate) in ElMO. METHODS: Sixty-four adult male Sprague-Dawtey rats (purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd., China) were randomly divided into eight groups (control, post-exercise 0, 3, 6, 12, 24, 48, and 72 hours, eight rats in each). A damage model was established by downhill running (-160, 16m/min, 90 minutes). All rats were then killed at corresponding time points to take the soleus as specimen. Severity of damage was observed histologically under a transmission electron microscope. Expression of ubiquitin in the insoluble protein of soleus muscle was detected using western blot, and expression of desmin aggregates was observed by immunofluorescence double labeling. All experimental procedures were approved by the Beijing Sport University Institutional Review Board. RESULTS AND CONCLUSION: (1) After a large-load eccentric exercise, the sarcomere of the soleus muscle was widened, the Z-line was broken, and the myofibril was broken and distorted, all of which was most serious at 12 hours after exercise, and recovered completely at 72 hours after exercise. (2) Western blot results indicated that the expression of ubiquitin in the skeletal muscle increased first and then decreased after a large-load eccentric exercise. The expression peaked at 12 hours after exercise and returned to normal at 72 hours after exercise. (3)0verall expression of desmin aggregates significantly raised (P < 0.01) instantly when the ElMO occurred. It reached the peak at 12 hours after exercise, then reduced somewhat (P < 0.01) at 24 and 48 hours, and finally recovered at 72 hours. (4)These findings indicate that desmin aggregation may be one of the causes of ElMO. [ABSTRACT FROM AUTHOR]

Asphalt pavement experiences various wet-dry histories in the service stage. However, the influence of wet-dry history on asphalt mixture is unknown. Therefore, to clarify the performance degradation mechanism and predict the performance of asphalt mixture under the action of wet-dry history, the creep-recovery test, indirect tensile stiffness modulus test and indirect tensile strength test were conducted at different temperatures. The finite element method was adopted to analyze the moisture diffusing profile inside the specimen after wet-dry cycles. A moisture damage model considering the soaking time and repeated characteristics was developed to predict the damaged properties. Results show that wet-dry cycles cause a slight mass loss of asphalt mixture. Wet-dry cycling action leads to the increment in high-temperature deformation, and reductions in stiffness modulus and tensile strength. The increase of high-temperature deformation is primarily caused by viscoplastic component. Even if the soaking time is short, high moisture damage occurs while the wet-dry cycle is sufficient. Numerical simulations show that the moisture concentration profiles inside asphalt mixture vary under different wet-dry histories, leading to variations in the damage zone. The degree of damage is also closely related to the acting time of moisture. The critical immersion time of the dense asphalt mixture (about 43 hours) was determined in this study. When the immersion period is shorter than the critical immersion time, the strength loss is greater than the modulus. On the contrary, the degree of modulus damage is higher than that of strength. Considering the actual rainfall climate in China, the strength damage of the on-site asphalt mixture in the field predominates. The proposed model could reflect the weakening trends of modulus and strength. It has good universal applicability in predicting the damaged Marshall stability, modulus, and strength at different temperatures. • A wet-dry cycling experiment for asphalt mixture was designed. • Effect of wet-dry history on the high, medium and low temperature properties of dense asphalt mixture was investigated. • An accumulative moisture damage model was developed and validated. [ABSTRACT FROM AUTHOR]

Brick cavity wall structures are widely distributed in southeastern China; however, their integrity and seismic behavior are extremely poor. To solve this problem, a new technique is proposed to enhance the seismic behavior of brick cavity walls using steel fiber reactive powder concrete (SFRPC) overlays. Two unreinforced cavity walls and four cavity walls strengthened with SFRPC overlays (applied over the entire wall surface) were tested under cyclic loading. In this study, the damage and failure modes of the specimens were analyzed in terms of the load displacement curves; furthermore, a comparative investigation was performed considering the load capacity, ductility, stiffness degradation, and energy dissipation capacity to demonstrate the merits of brick cavity walls strengthened with SFRPC overlays. The effect of strengthening using different thicknesses of reinforcement was investigated. In addition, damage analyses of the walls were performed based on the modified Park–Ang damage assessment model. [ABSTRACT FROM AUTHOR]

Due to complex geological structures and strong crustal activity, geological disasters occur frequently in the upper reaches of the Yalong River, Southwest China. Toppling failure on anti-dip rock slopes is a common phenomenon; in particular, after the Wenchuan earthquake in 2008, numerous landslides caused by toppling deformation occurred in reservoir areas, seriously threatening the construction and operation of large-scale water conservancy projects and hydropower projects. Taking three typical toppling slopes in the basin as research objects, the dynamic behaviour, failure evolution, and failure plane location of toppling failure under seismic waves were investigated by shaking table tests and UDEC simulations. The test results indicated that slope angle and stratum dip angle were both inversely proportional to the stability of the slope in the tested ranges. The failure evolution of toppling on anti-dip rock slopes could be divided into four stages: (1) the development stage of tensile cracks in the strata; (2) the formative stage of tensile cracks at the crest of the slope; (3) the formative stage of toppling zones; and (4) the failure stage. Two equations were proposed to reveal the relationships between the surface peak ground acceleration and the horizontal depth of the failure plane and displacement of the slope surface. The propagation and coalescence of discontinuous cross joint in the slope and the entire failure evolution simulated by the UDEC damage model agreed well with the shaking table test results. [ABSTRACT FROM AUTHOR]

To probe into the time-dependent behaviour of the ballastless track–bridge structural system under train load, based on the import of the static and fatigue damage constitutive model of materials to simulate damage deterioration of the structural system and interface cohesive zone model to the interface layer, a three-dimensional nonlinear finite element model of the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system was established using the equivalent static method. Then, using this model, we developed the numerical simulation analysis of the influence law of material damage deterioration on structural system performance under train load and revealed the fatigue evolution of the structural system. The results show that the beam remains in compressed status for the whole process, the track is in compression in the midspan and in tension at the beam end, and the tensile stress is larger near the shear groove under the double-track static load. Under the fatigue load, stiffness degradation of the structural system is not obvious, and integral rigidity of the structural system is dependent on the rigidity of the beam. Strength reduction of the materials caused stress redistribution of the structural system and had a larger effect on the stress of each layer of track structure than on the stress on the beam. The fatigue degradation of the cement-emulsified asphalt (CA) mortar layer material has a significant impact on the structural system, which directly affects structural layer stress variation with the fatigue loading cycle. [ABSTRACT FROM AUTHOR]

To research the macroscopic deformation of rock microseismic damage, a high-precision microseismic monitoring system was established on the left bank slope of the Baihetan hydropower station in Southwestern China. Based on the microseismic monitoring and field deformation data, the seismic source radius was applied to characterize the rock fracture scale. Numerical simulations introduced the rock micro-fracture information into the three-dimensional numerical model of the left bank slope and established the damage constitutive model. The unloading deformation process of the left bank abutment rock mass is described by numerical calculations. The feedback analysis method considering the effect of microseismic damage is preliminary exploratory research, which provides a new idea for the stability analysis of similar high rock slopes. [ABSTRACT FROM AUTHOR]

• An integrated vulnerability assessment approach is proposed. • Improved MSW method is developed to address the local spatial dependence. • The uncertainties of damage curve shapes and risky assets are considered. • The proposed approach can provide more reliable for vulnerability results. Vulnerability assessment is an essential step for urban flood risk management. Due to the objective existence of statistical errors in the variables and spatial heterogeneity, as well as the similarity of flood experience, precautionary status and environments for neighbouring areas, an urban flood vulnerability assessment essentially entails a multi-factor decision-making process that accounts for uncertainties and the local spatial dependence of neighbourhoods. To address these issues, an uncertainty-based vulnerability assessment approach embedded with an improved moving split-window (IMSW) analysis and probabilistic method is proposed. To develop an integrated urban flood vulnerability assessment model, three technical issues need to be resolved: (1) the development of damage curves of land-use types, (2) an uncertainty model and spatial dependence model of damages based on an IMSW analysis, and (3) an uncertainty-based framework to quantify vulnerability considering the uncertainties and local spatial dependence of the damage curves as well as the spatial heterogeneity of risky assets simultaneously. The proposed method is applied to an urban area in China and provides an integrated vulnerability assessment for different land-use types. Moreover, uncertainty and sensitivity analyses were performed to analyse the spatial differentiation and the dominant parameters of vulnerability. Compared with two other commonly used methods, the proposed local-correlated method (LCM) is more in line with reality, and provides more reasonable information for making a better-informed decision. [ABSTRACT FROM AUTHOR]

Life cycle assessment (LCA) has become a vital tool for selecting and developing green products to support decision-making. While there are various regional evaluation models for conducting life cycle impact assessment (LCIA), which is one of the key steps in LCA, a systematic LCIA model is still lacking in China. In this study, we propose an endpoint damage model for LCIA. We focus on three endpoint damage categories and eleven environmental impact categories based on local characteristics in China. By using the emission factor method, extrapolation method and other methods, the total emission of each pollutant is quantified. Localized per capita normalization values were calculated. Then, the potential value for environmental impact (PVEI) is acquired, which could be used to represent the impact of pollutant emissions and resource and energy consumption on the environment. With a base year of 2017, the regional per capita normalization values of human health, ecosystem quality and resources in China are 1.94 × 10−2 DALY, 6.08 × 10−5 species, and 2.47 × 103 MJ, respectively. The developed methodology is validated by applying it to the LCIA of vehicles, and the PVEI of three vehicles is ranked as follows: methanol vehicle (MV) > battery electric vehicle (BEV) > compressed natural gas vehicle (CNGV). The findings support the development of an LCIA method for China. The localization parameters supplement and improve the method of life cycle assessment in China, improve the scientificity of life cycle assessment results, and make the evaluation results more in line with China's actual conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• Assessing disaster losses at the watershed scale is a challenging task. • Quantitative assessment of flood damage can help managers grasp the basin conditions. • The flood risk curve helps watershed develop flood protection standards. • This article presents a combined riverine flood risk model to assess flood damage. Climate change and rapid urbanization have exacerbated the occurrence and impact of floods. It is essential to carry out a quantitative flood risk assessment and manage the flood risk before a disaster occurs. This article presents a combined riverine flood risk model to obtain the exceedance probability loss (EPL) curve and expected annual damage (EAD) under the current climate. This model includes a rapid flood model and a flood damage model. It aims to simulate the flood risk and evaluate the flood damage at 10-, 30-, 50-, 100-, and 200-year return period events. The results show that: (1) The total inundation areas will sharply increase when the flood return periods are over 30 years. (2) The EAD is 1,476 million dollars in the Jiulong River Basin (JRB). When the flood return period is over 30 years, the total damage increases sharply. (3) The flood risk in the lower reaches of the JRB is higher than in the upper reaches when the flood event is beyond a 20-year return period. (4) Industrial sector damage is the largest, followed by tertiary industry, transportation, construction, agriculture, and infrastructure. The combined model chain can quickly assess the flood risk in the river basin and judge the flood risk in a watershed compared to the national level. In addition, it can be applied to other river basins, and it will provide actionable information for future flood risk management. [ABSTRACT FROM AUTHOR]

The excavation damage zone in rock slopes after drill-and-blast operations is of great significance for assessing the slope stability and design of open pit mines. The traditional method simplifies, the spatial distribution of the damage zone in a slope following blasting is as a single radius distributed, which leads to an inaccurate evaluation of slope stability. Herein, a model coupling the tensile damage and the Drucker-Prager yield criteria is established to investigate the spatial distribution characteristics of blast-induced damage zone in the final wall of an open-pit. Explosive explosion is converted to an equivalent pressure time history acting on the blasthole wall and the extension of the damage observed in the field test is reproduced successfully by numerical simulation. The proposed model is verified on the basis of the site-monitored data from the Wushan Copper mine, a large-scale open-pit mine in Inner Mongolia, China. The results show that the damage decreases with increasing depth, exhibiting a nonlinear distribution behind the slope face. The maximum depth and scopes of horizontal and vertical damage occur at the slope crest. The proposed model is compared with five widely used damage models and proves to be more capable of representing the spatial distribution of the damage zone observed in the site test. Finally, the formation mechanism of the maximum damage depth along the crest is also revealed. [ABSTRACT FROM AUTHOR]

Rock engineering especially deep rock engineering undergoing long-term effects of external loading and gravity all or most may gradually damage deformation or creep deformation accumulation, leading rock structures to damage, crack, such as severe plastic deformation or even progressive failure. In this paper, based on the nonlinear damage creep characteristics of rock and damage variable, a new nonlinear damage creep constitutive model of high-stress soft rock is defined in series with the improved Burgers model, Hooke model and St. Venant model. This new nonlinear damage creep constitutive model can work out fairly reasonably explanations for the soft rock creep deformation. A series of uniaxial compression creep tests were performed to study the creep damage characteristics of typical soft rock in Jinchuan No.2 Mine in the northwest of China. Using the increment step loading and single-step loading, the results of creep experiments and nonlinear damage creep constitutive model results are very consistent in this study. The new model not only can reflect the whole course of creep deformation, but also can reasonably describe the soft rock under different initial creep stage, steady-state creep stage and accelerated creep stage. Therefore, the new nonlinear creep damage model is a reasonable reference model for the research of soft rock creep. [ABSTRACT FROM AUTHOR]

• Six nonlinear FEMs were studied to identify thermal behaviors of CAM and joint under various temperature conditions. • The CZM and CDPM could effectively simulate the interlaminar debonding and damage behavior development in CRTS II track. • Both the displacement and stress of the structure increase with an increase in overall temperature or temperature gradient. • The damage factor of the interface between the CAM layer and track slab are vulnerable to the overall temperature. Under temperature loading, the contact interface of cement asphalt mortar (CAM) layer and T-shaped joint are two vulnerable components of China Railway Track System type II (CRTS II) slab ballastless track. The purpose of this study is to develop six types of three-dimensional (3D) nonlinear finite element (FE) models for investigating the thermal behaviors of CAM and T-shaped joint under various temperature conditions. This was achieved by modelling CAM and T-shaped joint using cohesive zone model (CZM) and concrete damaged plasticity model (CDPM), respectively. Using five CRTS II slab tracks on a simple-supported box girder as a case study, the displacement and stress responses of the track structure were investigated and compared under six cases of overall temperatures and temperature gradients, respectively. Results show that CZM and CDPM have the capabilities of simulating the interlaminar debonding and damage behavior development in CRTS II track under various temperatures conditions. The combination of CZM and CDPM could provide the worst damage scenarios, and the CDPM of the joint could significantly reduce the structure responses. In addition, the increase of overall temperature together with temperature gradient could significantly increase the deformation and stress in CAM layer, and the influence of the magnitude of overall temperature is more obvious than that of temperature gradient. [ABSTRACT FROM AUTHOR]

• The damage caused by axial CS, FT cycle, and SA was studied. • The influence threshold of the axial CS level differed for different salt solutions. • The delamination damage model described the durability degradation of the concrete. This study experimentally investigates the damage mechanism of pier concrete under the combined action of axial compressive stress (CS), freeze–thaw (FT) cycles, and salt attacks (SA). An indoor accelerated corrosion test of pier concrete under the combined action of CS, FT, and SA was conducted based on field investigations of concrete corrosion of piers in the saline soil of Xinjiang province in China. The experimental results of macro and micro analyses showed that the durability degradation of the pier concrete could be attributed to the damage to the cement slurry, aggregates, interface areas, and pore structure. A new delamination damage model was established to describe the mechanism of the combined damage, including the deterioration of the mortar layer, the generation of microcracks in the interface zone, the deposition of corrosion products, and crack development. The quantitative assessment of the durability degradation of the pier concrete was more accurate when the mass loss (ML) and relative dynamic elastic modulus (RDEM) were considered. These unique findings provide an important reference for the design and durability evaluation of pier concrete in saline soils. [ABSTRACT FROM AUTHOR]

A blast-induced damage model integrating the tensile damage model with the Drucker-Prager yield condition is established. Based on the excavation of a large cross-section tunnel in China, the damage process of surrounding rock under multiple full-face blasting is simulated by the established rock damage model embedded into the LS-DYNA computer code through its user subroutines and a cumulative damage formulation in the LS-DYNA. The simulation results are well verified against field test data. The results show that the maximum damage depth of surrounding rock is determined by the blasting of the excavated cross-sections closest to the surrounding rock. Both the maximum damage depth and the maximum peak particle velocity (PPV) occur in the middle of the tunnel invert. Based on the defined damage threshold D cr and the modeled maximum damage depth of surrounding rock, the influence of initiation sequence on the critical PPV for rock damage is studied, and a critical PPV associated with rock damage is proposed for tunnel blasting excavation. [ABSTRACT FROM AUTHOR]

Freeze-thaw (FT) cycles in cold regions have a huge effect on the stability of surrounding rock. Sandstone in the Tongchuan area of northwestern China was used as the research object to study the changes in physical and mechanical properties of rocks after FT cycles. After analyzing the force of the internal pore boundary of the rock, it is found that the internal large pores are more likely to make the rock unstable after being stressed. A FT damage model considering the weight of different pore sizes is established. Through static and dynamic tests, the mechanical properties of FT sandstone are studied. The study found that the static and dynamic peak stresses of sandstone decrease with the increase of FT times, and the dynamic increase factors (DIF) shows an increasing trend with the increase of FT times and impact speed. The mechanical test further proves that the compressive strength of sandstone decreases with the decrease of damage factor. The static and dynamic compressive strength showed a good exponential relationship with the damage factor. The relationship between dynamic compressive strength and initial static compressive strength considering the damage factor and impact speed is established. • The pores of rocks after freeze-thaw cycles are discussed. • A freeze-thaw damage model considering the weight of pore size to damage is established. • The results of the static and dynamic tests are analyzed, and a new empirical equation is established. [ABSTRACT FROM AUTHOR]

GJ series steel is a new type of high-performance structural steel, which has emerged in China steel construction, and it has been widely utilized in steel-framed building structures. To investigate the low cycle fatigue performance and cumulative damage behaviors and find a suitable constitutive relationship of GJ series steel under cyclic loading, a total of eighteen Q345GJ steel low cycle fatigue experiments have been carried out. The mechanical behavior of Q345GJ steel were discussed, including monotonic loading behavior, hysteresis loading behaviors and energy dissipation capacity. Based on the cyclic behavior of GJ series steel, a modified cumulative damage model was recommended. Then, with comparison of the Q345GJ tests data (including the data in public papers) under various loading systems, the model proposed in this paper is proved correct and can be used to simulate the cyclic behavior of Q345GJ members. [Display omitted] • The hysteretic curves, skeleton curves and other parameters of Q345GJ steel obtained from the cyclic test. • The effect of cyclic loading protocol on the energy dissipation curves of Q345GJ steel has been discussed. • A modified cumulated damage constitutive model of steel subjected to uniaxial cyclic loading was proposed. [ABSTRACT FROM AUTHOR]

Coalbed methane, as a gas in coal seam, is a kind of potential clean energy with high reserves. At present, there are two main types of coalbed methane extraction in China, one is extracting coalbed methane by ground drilling, the other is coal and gas (coalbed methane) simultaneous extraction in coal mine underground. In the process of coal and gas simultaneous extraction, the migration of gas may not only cause coal and gas outburst, gas gushing and other disasters, but also cause the greenhouse effect. Therefore, in order to achieve the goal of safe simultaneous extraction of coal and gas and reducing greenhouse gas emissions, it is particularly important to understand the flow properties of gas and the damage characteristics of raw coal in the process of coal seam mining. In this paper, the mechanical properties and seepage characteristics of raw coal samples under loading and unloading conditions are studied experimentally by using the laboratory-fabricated 'thermal-hydro-mechanical coupled with triaxial servo controlled seepage apparatus for gas-containing coal'. At the same time, X-ray tomography is carried out on the raw coal samples before and after the experiment. The deformation, damage and seepage characteristics of raw coal samples in the experimental process are recorded and analyzed. On the basis of the above, based on the information entropy theory, the change rate of information entropy is proposed as a damage characterization parameter, and its feasibility is verified by the comparison and analysis with the change rate of porosity. Finally, according to the basic definition of porosity, combined with statistical damage model, considering the gas adsorption expansion and Klinkenberg effect, the evolution model of permeability under loading and unloading conditions is developed. The model can better reflect the permeability evolution law of raw coal under loading and unloading conditions. [ABSTRACT FROM AUTHOR]

Fatigue damage caused by cyclic dynamic loading may deteriorate strength parameters of mudded intercalations. This research work aimed at defining a new fatigue damage variable expression and revealing the fatigue damage evolution laws of mudded intercalations by conducting dynamic triaxial tests. The specimens were collected in China and remodeled. The test results indicated that the dynamic stress-strain curves of mudded intercalations represented obvious strain-hardening characteristics. The new fatigue damage variable expression was formulated according to Ramberg-Osgood strain-hardening law applied to a three-direction stress state. The fatigue damage evolution laws of mudded intercalations could be described by a low-cycle damage evolution model and could be aligned with dynamic strength failure laws. The fatigue damage deepened with an increase in the cyclic ratio. The fatigue damage evolution rate was correlated with the clay mineral composition and percent of clay size particles (strongly), water content (moderately positive), confining pressure (weakly positive), and the cyclic ratio (initially, negative and then, positive). • The first study to systematically investigate the fatigue damage of mudded intercalations. • Formulating a new fatigue damage variable expression applicable to strain-hardening soil. • Experimentally revealing the impact factors of the fatigue damage of mudded intercalations along with their impacts. • A low-cycle fatigue damage model could be used to describe the dynamic damage evolution laws of mudded intercalations. [ABSTRACT FROM AUTHOR]

• Base rock cavity has multiple adverse effects on the fatigue performance of the tunnel base. • Specimen's fatigue life decreases as the stress level and cavity size increasing. • Numerical simulation results provide reference for the testing load. • A non-linear model is proposed to quantify the fatigue damage of the tunnel base with cavity. The smoothness of tunnel base directly affects the safety of train operation, and tunnel base diseases are usually difficult to detect and deal with due to the distinguishing features of heavy haul railway, the base diseases become one of the most harmful tunnel diseases. Therefore, with the increasing axle load and the basal deterioration of the existing heavy haul railway in China, studying the fatigue performance of the tunnel bottom structure is essential. A 3D train-tunnel-surrounding rock numerical model is established to obtain the dynamic response of the tunnel bottom structure under 30 t axle load trains. Then refer to the stress state and fatigue vulnerable position which are originated from the numerical simulation, a series bending fatigue tests are carried out to study the cavity influence on fatigue performance of heavy haul railway tunnel's bottom structure in this paper. A non-linear cumulative damage model is proposed to quantify fatigue damage evolution characteristics of tunnel bottom structure with base cavity through the tests. The results suggest that, the base rock cavity remarkably reduces the fatigue life of the specimen and increases the development rate of damage; the existence of cavity not only deteriorates the bearing capacity of the structure, but also greatly improves the dynamic response and stress level of the bottom structure and base rock, which has multiple adverse effects on the fatigue performance of the tunnel bottom structure, and also accelerates the expansion of the cavity itself. [ABSTRACT FROM AUTHOR]

• A new model for urban resilience considering adaptability, resistance and recovery was proposed. • Valid factual information during the Morakot was adopted to validate this model. • Critical parameters of the model such as damage intensity, experience coefficient etc. were studied. • Some optimal suggestions were provided to efficiently improve urban resilience. Due to the greater emphasis on cities' preparatory and recover ability for disaster, urban resilience is widely concerned, which is different from the traditional management mode of natural disaster and provides a new theoretical framework for urban security governance. In this paper, considering adaptability, resistance and recovery as the main characteristic factor of urban resilience, an urban resilience model was developed. This model could be used to simulate the resilience of a city under different disaster scenarios. Valid information was collected from Taiwan of China during the Morakot, and the urban resilience model was tested by the practical data, and then the resilience in Taiwan was analyzed by the constructed model. The results show that the model could reflect the resilience change of cities during disasters to some extent. Further, according to the disaster characteristics, five disaster scenarios were set to analyze various resilience characteristics. In addition, the critical parameters of the model were studied. We found that the greater intensity of disaster damage, the more serious damage of urban system function, and the earlier peak time of disaster damage intensity appears, the faster damage rate of urban system function will be. Furthermore, the larger coefficient of external disaster relief capability, the lower loss of urban system function and the better recovery capability. The higher coefficient of disaster experience, the richer the disaster response experience, the more perfect urban infrastructure of disaster response, and the smaller loss of urban system function. Based on our results, we analyze the characteristics of urban resilience and provide some optimal suggestions to efficiently improve urban resilience. [ABSTRACT FROM AUTHOR]

In order to investigate hydro-mechanical properties of fine-grained sandstone in Xiangjiaba hydropower station in China, a series of triaxial compression tests of saturated fine-grained sandstone were conducted. Two groups of hydro-mechanical triaxial compression tests of saturated sandstone are conducted: firstly, confining pressure is constant at 10 MPa while pore pressure is varied from 4, 6, and 8 MPa; secondly, pore pressure is constant at 6 MPa while confining pressure is varied from 10, 15, and 20 MPa. The effects of the confining and pore pressures on strength and deformation behaviors of saturated fine-grained sandstone are discussed. Based on the test results, a novel coupled elastoplastic damage model is proposed to considering hydro-mechanical coupling properties of saturated fine-grained sandstone using the effective stress concept. Furthermore, the numerical formulations of a return mapping algorithm for the coupled model implementation are introduced in detail. Finally, the validity and efficiency of the model are compared between numerical simulation and test results. Therefore, the coupled model is effectively applied in the stability analysis of practical engineering. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O 3) is known to damage plant cells and suppress leaf photosynthesis, which can further reduce terrestrial carbon uptake and leave more carbon dioxide (CO 2) in the atmosphere. While recent studies have assessed the effects of O 3 on terrestrial carbon fluxes, the potential impacts on atmospheric CO 2 concentrations have not been quantified. Here, we use a regional climate model (RegCM-CHEM4) coupled with the Yale Interactive terrestrial Biosphere model YIBs to estimate the effects of O 3 exposure on atmospheric CO 2 over China. Compared to simulations without O 3 effects, sensitivity experiments with O 3 damage show a significant reduction (12.1 ± 4.4%) in the gross primary productivity (GPP), up to 35% in summer. Meanwhile, terrestrial carbon sink is suppressed by 112.2 ± 22.5 Tg C for 2013 at the national level. Strong inhibitions of O 3 on carbon fluxes are found in North, Northeast and South Central China, where O 3 levels are high. Consequently, we find a significant increase in atmospheric CO 2 concentrations due to O 3 -induced terrestrial carbon sink reduction. The increases of CO 2 are more evident in the growing season. The maximum CO 2 enhancement reaches as high as 6 ppm in Yunnan and Guizhou provinces. Our assessments indicate that tropospheric O 3 has a detrimental impact on plant carbon uptake and leads to more CO 2 accumulating in the atmosphere. Such impacts of O 3 should be taken into account in global carbon cycle and future climate change. • Climate-chemistry and vegetation models are coupled to investigate interactions between O 3 and CO 2. • Effects of O 3 exposure on terrestrial carbon fluxes are estimated over China. • O 3 -induced terrestrial carbon sink reduction increases atmospheric CO 2 concentrations. [ABSTRACT FROM AUTHOR]