Abstract
This paper presents a framework combining Monte Carlo Simulation (MCS) and the Newmark sliding block model with representative slip surfaces (RSS) (model II) and multiple response surfaces ...method (MRSM) to conduct seismic reliability analysis and risk assessment of soil slopes. An empirical threshold is introduced to define the limit state function to identify the failure samples in MCS and the sliding area and Newmark sliding displacement are multiplied to quantify the failure consequence. The proposed methodology is illustrated through a soil slope with multiple layers. The calculation results demonstrate that traditional Newmark sliding block model (model I) tend to underestimate the variations of yield acceleration. Both the failure probability and landslide risk exhibit decreasing trends with the increase of threshold. Significant discrepancy in failure probability and landslide risk between two models is found even for a small threshold. Therefore, the proposed methodology is highly recommended in seismic reliability analysis and risk assessment. The contributions of RSSs to the failure probability and landslide risk are insensitive to the variation of displacement thresholds.
Tailings dams, as essential mining structures, are being built globally for containing the chief waste stream of the mining industry. Catastrophic tailings dam breaches have occurred frequently over ...the past decade, causing severe impacts on the environment, economy, and human health. The foreknowledge of the tailings dam breach overland flow is crucial for the risk assessment and emergency response planning in order to prevent or minimize possible losses. Using unmanned aerial vehicles (UAV) photogrammetry and smoothed particle hydrodynamics (SPH) numerical method, this study proposed a multidisciplinary procedure for modelling a hypothetical tailings dam breach run out flow over the downstream complex terrain. A case study on a 97-m-height tailings dam in Shandong Province of China was carried out. The proposed procedure was proven applicable to determine the overland tailings flow. The submerged area and flow velocities suggested that the downstream G2 highway would hardly be threatened and more concerns should be paid on the factory plants and workers deployed between the dam toe and the highway. Additionally, the application of UAV photogrammetry in the mining industry as a supplementary surveying method can be further expanded, especially for the numerous small-scale mining sites. The proposed procedure is then recommended for the safety management of the tailings’ storage facilities globally.
In this paper, a comprehensive analysis of spatiotemporal characteristics of reverse-dip slope toppling is conducted by taking the Xiaodongcao slope as an example. First, a spatial partitioning ...analysis of toppling deformation is performed based on the field reconnaissance and interpretation of engineering geological data. Then, the variations of toppling deformation in time domain are analyzed for different areas of the slope with monitored data of surface displacement. Finally, the isochrones of toppling displacement evolution are constructed by using inverse distance weighted interpolation of surface monitoring data at discrete locations. The results presented in the study have shown that: (1) the displacement at the rear of the slope is dominated by vertical deformation, whereas the horizontal deformation is predominant at the slope front which also controls the overall deformation of the bank slope; (2) the overall evolution of slope deformation is dominated by the strip area at the center of the slope. In particular, the overall deformation of the slope lags behind the central region, and the displacement in this strip area could trigger an overall displacement of the bank slope. It is thus inferred that the stripe area serves as the locked segment for the toppling deformation of the slope.
In this paper, the sensitivity factors of CO2 huff-n-puff for multifractured horizontal wells (MFHWs) in tight oil reservoirs were investigated through an experimental test and numerical simulation. ...The pressure-volume-temperature (PVT) experiment and the slim tube experiment are used to understand the interaction mechanism between CO2 and crude oil, and the minimum miscibility pressure (MMP) of the CO2-crude oil system is 17 MPa. The single-well model was firstly established to analyze the sensitivity factors on production performance of MFHWs by using CO2 huff-n-puff. The controlling factors of CO2 huff-n-puff for MFHWs in tight oil reservoirs were divided into three categories (i.e., reservoir parameters, well parameters, and injection-production parameters), and the impact of individual parameter on well performance was discussed in detail. The range of reservoir parameters suitable for CO2 huff-n-puff of MFHWs is obtained. The reservoir permeability is from 0.1 mD to 1 mD, the reservoir thickness changes from 10 m to 30 m, and the reservoir porosity is from 7% to 12%. Based on the reservoir parameters of the target reservoir, the reasonable well and fracture parameters are obtained. The sensitivity intensity was followed by the horizontal well length, fracture conductivity, fracture spacing, and fracture half-length. CO2 injection-production parameters are further optimized, and the sensitivity intensity was followed by the single-cycle cumulative CO2 injection rate, the soaking time, the injection rates, and the production rates. It provides a reference for parameter optimization of CO2 huff-n-puff for MFHWs in tight oil reservoirs.
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•A conceptual model for farmland ecosystem resilience (FER) assessment was developed.•Disturbance-response processes and self-regulation mechanism of FER were revealed.•The ...sustainability of Ethiopia's farmland ecosystems has generally improved.•The antagonism and synergy between the response factors appeared more significant.
In the context of global warming, the sustainability of farmland ecosystems is increasingly impacted by multiple disturbances from both natural and human-induced sources. This study constructed a conceptual model and indicator system of farmland ecosystem resilience (FER) based on the disturbance-response processes of farmland ecosystems. FER assessment, supported by 30 specific indicators, was tested in Ethiopia, one of the most food-insecure countries in the world and the factors impending farmland ecosystem sustainability were discussed based on the obstacle degree values (ODVs). The results showed that the FER change rate in Ethiopia was 0.3 %/year during 2003–2018, indicating positive sustainability on the whole. However, in the five years of 2004, 2007, 2008, 2011, and 2017, the FER decreased, among which the largest decline was −0.017 in 2017. Natural comprehensive disturbance (ND), human activity disturbance (HD), resilience of farmland supply (RFS), and resilience of social support (RS) were the key constraints of FER, while the ODVs of ND and RFS showed increasing trends. We also found that there were general antagonistic and synergistic effects among the response factors and the synergistic enhancement between disturbance factors was more pronounced than the antagonistic buffering effect. This study provides a fresh perspective for farmland ecosystem managers and stakeholders to examine disturbance risks and assess the sustainability of farmland ecosystems.
A probabilistic limit equilibrium framework combining empirical load transfer factor and anisotropy of soil cohesion is developed to conduct pile‐reinforced slope reliability analysis. The anisotropy ...of soil cohesion is determined conditioned on that the thrust force direction is parallel to the major principal direction and it is easily combined with load transfer factor, which are related with soil parameters, and pile parameters. The proposed method is illustrated against a homogeneous soil slope. The sensitivity studies of pile parameters on factor of safety (FS; calculated at respective means of soil parameters) and β demonstrated that the anisotropy of soil cohesion tends to pose significant effect on reliability index β than on FS. The effect of anisotropy of soil cohesion on FS is found to be slightly different under different pile locations, whereas its effect on β is observed to be least if piles are drilled at the middle part of slope and more significant effect is observed when piles are drilled at the lower and upper part of slope. The plots from the sensitivity studies provide an alternative tool for pile designs aiming at the target reliability index β. The proposed method contributes to the pile‐reinforced slope stability within limit equilibrium framework.
The effect of anisotropy of soil cohesion on the pile‐reinforced slope stability is explored and found to be more significant from the aspect of reliability index than from that of factor of safety.
A year-long field study on the seasonal characteristics of fine particulate matter (PM2.5) was conducted at the Qilian Shan Station of Glaciology and Ecologic Environment (QSS), a remote site on the ...northeast edge of the Tibetan Plateau. The PM2.5 samples were collected weekly using a low volume (16.7L/min) sampler, and then analyzed by ion chromatography for the water soluble ionic species (WSIs). The annual average mass loading of PM2.5, retrieved from co-located measurement on aerosol size distribution, was 9.5±5.4μgm−3 with WSIs accounting for 39±2%. The WSIs were dominated by SO42− (39%), CO32− (19%), Ca2+ (16%), NO3− (10%), and NH4+ (6%), suggesting important contributions from both anthropogenic aerosol and mineral dust. The mass loading of total WSIs showed a seasonal variation with higher concentrations in spring (6.3μgm−3) and summer (5.1μgm−3) and lower concentrations in winter (2.2μgm−3) and fall (1.7μgm−3). A linear regression of ammonium versus sulfate by equivalent concentration showed a slope of 0.51, suggesting an excess of acids. The excess sulfuric and nitric acids likely reacted with mineral dust, as evidenced by the tight correlation between Ca2++NH4+ and SO42−+NO3−. The oxidation ratios of nitrogen and sulfur estimated based on the datasets of SO2 and NO2 from the closest air quality station at Jiayuguan (~150km from sampling site) showed that the gas-particle partitioning of nitrogen on dust was more efficient than that of sulfur. The size distribution of SO42− showed a dominant accumulation mode, with a mode diameter (Dp) ranging from 0.18 to 0.56μm. In comparison, NO3− and Ca2+ showed a prominent coarse mode with Dp ranging from 1 to 10μm. The results of air mass trajectory cluster and potential source contribution function analysis demonstrated that the source regions of the mineral dust were located in the arid areas of northwest China while the anthropogenic aerosol was likely from urban areas in the low elevation areas to the east of QSS. The effects of meteorological parameters on the particle mass loading were also evaluated.
•A year-long field study was conducted in the mountain area of the northern Tibetan Plateau.•A clear seasonal variation of aerosol loading was observed.•The particulate matter showed a mixture of mineral dust and antropogenic aerosol.
Land Use/Cover Change (LUCC) has gradually became an important direction in the research of global changes. LUCC is a complex system, and entropy is a measure of the degree of disorder of a system. ...According to land use information entropy, this paper analyzes changes in land use from the perspective of the system. Research on the entropy of LUCC structures has a certain "guiding role" for the optimization and adjustment of regional land use structure. Based on the five periods of LUCC data from the year of 1990 to 2010, this paper focuses on analyzing three types of LUCC entropies among counties in China-namely, Shannon, Renyi, and Tsallis entropies. The findings suggest that: (1) Shannon entropy can reflect the volatility of the LUCC, that Renyi and Tsallis entropies also have this function when their parameter has a positive value, and that Renyi and Tsallis entropies can reflect the extreme case of the LUCC when their parameter has a negative value.; (2) The entropy of China's LUCC is uneven in time and space distributions, and that there is a large trend during 1990-2010, the central region generally has high entropy in space.
For deep resource exploitation and engineering construction, the mechanical properties of soft and hard interbedded rock masses are important factors impacting engineering stability. Simultaneously, ...the influence of temperature on the strength of deep rock masses poses a significant obstacle to the exploitation of deep resources and the utilization of underground space. In this paper, the particle flow code (PFC
2D
) is utilized to establish the thermal-mechanical coupling numerical model of soft and hard interbedded rock masses, and then the uniaxial compression response of soft and hard interbedded rock masses following thermal damage is studied. The displacement and contact force produced by applying temperature, as well as the failure strength, strain, and crack development of the specimen after uniaxial compression is analyzed. The findings reveal that: 1) The peak displacement caused by applied temperature increases first and subsequently decreases with the increase of soft rock thickness ratio (
Hs/H
), whereas the peak displacement increases linearly with increasing temperature. The peak contact force varies in two stages with the increase of the soft rock thickness ratio (
Hs/H
), and with the same trends. 2) As the soft rock thickness ratio increases (
Hs/H
), the number of cracks decreases steadily. When the soft rock thickness ratio
Hs/H
< 0.5, the relationship curve between vertical strain and crack changes in two stages: the stage of crack development along with the stage of vertical strain gradually increases with crack development. When the thickness ratio of soft rock
Hs/H
> 0.5, the relationship curve changes in three stages: crack development stage, vertical strain increase stage, and vertical strain increase stage with crack development. 3) When the soft rock thickness ratio
Hs/H
< 0.5, the failure strength gradually decreases as soft rock thickness increases at
T
= 100°C, 200°C. The failure strength gradually increases as the soft rock thickness increases in general at
T
= 400°C. Soft rock thickness ratio
Hs/H
> 0.5, the failure strength increases with the increase of soft rock thickness at
T
= 300°C, 400°C. At
T
= 100°C, 200°C, the tendency of the failure strength changes less.
When constructing subway tunnels in coastal cities, boulders with high strength and large volume are often encountered. A large number of engineering practices have shown that the existence of ...boulders will destroy the unity and homogeneity of the stratum. If the tunnel is not properly handled during crossing construction, it will lead to the collapse of surrounding rock; in serious cases, it may induce ground collapse, damage the surrounding buildings, and endanger the safety of people’s lives and property. Firstly, with the help of similar material simulation test, this paper reproduces the phenomenon of vault collapse and surface collapse when the tunnel passes through the boulder stratum, explores the law of stratum collapse and surface settlement caused by the boulder in the process of tunnel excavation, and puts forward the “weightlessness weak surface effect” of the boulder stratum disturbed. Then, taking the Liu-Bai inter-district tunnel project of Shenzhen Metro Line 13 as an example, Midas GTS NX numerical simulation software is used to compare and analyze the influence characteristics of surrounding rock deformation and surface settlement caused by the presence or absence of boulders in the tunnel through the stratum and verify the “weightlessness weak surface effect” of the boulder stratum disturbed. Finally, the engineering treatment measures for the Liu-Bai inter-district tunnel project of Shenzhen Metro Line 13 crossing the boulder stratum are given. The research results are of great significance to guide the prediction and treatment of collapse and surface settlement when crossing the boulder stratum in the tunnel construction project.
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