Search

Particle size has an effect on the mechanical properties of tailings materials. The mechanics and crushing characteristics of tailings at high pressure are a research focus for high tailings dams. Tailings with different particle sizes were tested under laboratory high-pressure triaxial compression. The effect of particle size on the compression characteristics of tailings was studied, along with the strength and deformation of tailings with different particle sizes. Based on particle size distribution, the crushing characteristics of the tailings were quantitatively analysed. A mathematical model for crushing index and tailings strength was established. Under high pressure, shearing contraction failure occurred in the tailings samples. The stress–strain relation of the tailings showed strain softening at low confining pressure and continuous hardening at high confining pressure. The confining pressure at which the stress–strain relation changed from strain softening to strain hardening increased with increased particle size. Due to the higher degree of particle crushing for coarse tailings during the shearing under high pressure, the volume deformation of the coarse samples decreases continuously further. It shows increase in the amount of particle breakage as the confining pressure, but the increase rate decreased with the confining pressure increased. The Box Lucas loading accumulation model was used to describe the change in particle breakage with confining pressure. The peak strength of tailings increased exponentially with the improved relative crushing rate.

Plant root–soil water interactions are fundamental to vegetation–water relationships. Soil water availability and distribution impact the temporal–spatial dynamics of roots and vice versa. In the Loess Plateau (LP) of China, where semi-arid and arid climates prevail and deep loess soil dominates, drying soil layers (DSLs) have been extensively reported in artificial forestland. While the underlying mechanisms that cause DSLs remain unclear, they hypothetically involve root–soil water interactions. Although available root growth models are weak with respect to simulating the rooting depth, this study addresses the hypothesis of the involvement of root–soil water interactions in DSLs using a root growth model that simulates both the dynamic rooting depth and fine-root distribution, coupled with soil water, based on cost–benefit optimization. Evaluation of field data from an artificial black locust (Robinia pseudoacacia L.) forest site in the southern LP positively proves the model's performance. Further, a long-term simulation, forced by a 50-year climatic data series with varying precipitation, was performed to examine the DSLs. The results demonstrate that incorporating the dynamic rooting depth into the current root growth models is necessary to reproduce soil drying processes. The simulations revealed that the upper boundary of the DSLs fluctuates strongly with infiltration events, whereas the lower boundary extends successively with increasing rooting depth. Most infiltration was intercepted by the top 2.0 m layer, which was the most active zone of infiltration and root water uptake. Below this, the percentages of fine roots (5.0 %) and water uptake (6.2 %) were small but caused a persistently negative water balance and consequent DSLs. Therefore, the proposed root–water interaction approach succeeded in revealing the intrinsic properties of DSLs; their persistent extension and the lack of an opportunity for recovery from the drying state may adversely affect the implementation of artificial afforestation in this region as well as in other regions with similar climates and soils.

Fine-grained tailings have poor permeability and a long consolidation time, but treatment with flocculants can improve their mechanical properties. Changes in the physical and engineering propertie...

The strength and permeability of tailing-waste rock mixtures directly affect deposits’ stability for an alternative co-disposal technique. In the mixed co-disposal method, the void of the waste rock is filled with tailings, while the waste rock forms the particle skeleton. This method does not only improve deposits stability but also potentially reduces acid pollution. In this study, the rock percentage influence on the shear strength and permeability of tailing-waste rock mixtures was investigated by carrying out large triaxial tests and permeability tests. The shear strength, enhanced strength mechanism, and mixture permeability were analyzed. The results indicate that the shear strength and internal friction angle of the tailing-waste rock mixtures gently increased until the rock percentage reached 30% and then rapidly increased with the further increase of the rock percentage. The permeability coefficient of the mixtures slowly increased until the rock percentage reached 50% and then rapidly increased with the further increase of the rock percentage. The tailings washed out of the waste rock skeleton when the permeability was large. In this paper, 50% of waste rock is recommended for building mixture deposits.

In this paper, a new micro-creep model of salt rock is proposed based on a linear parallel bonded model (LPBM) using the two-dimensional particle flow code (PFC2D). The power function weakening form is assumed to describe the variation of the parallel bonded diameter (PBD) over time. By comparing with the parallel-bonded stress corrosion (PSC) model, a smaller stress fluctuation and smoother creep strain-time curves can be obtained by this power function model at the same stress level. The validity and adaptability of the model to simulate creep deformation of salt rock are verified through comparing the laboratory creep test curves and the Burgers model fitting result. The numerical results reveal that this model can be capable of capturing the creep deformation and damage behavior from the laboratory observations.

Clay mineral content has an important influence on the mechanical behavior of tailings, and the mechanical behavior of tailings directly affects the stability of tailings dams. XRF and XRD tests were carried out on tailings from three different regions. The chemical and mineral compositions of the tailings are analyzed. The strength and failure deformation of tailings were studied by carrying out laboratory triaxial compression tests. The effect of clay content on the stress path of tailings was investigated. The microfabric of tailings samples was examined with scanning electron microscopy (SEM) and nitrogen adsorption tests. The results show that the confining pressure corresponding to the samples exhibiting strain hardening increases with increasing clay mineral content in the tailings. The cohesion of tailings increases linearly, and the specific surface area decreases as the content of clay minerals increases. Nitrogen adsorption test results reveal from a microscopic point of view that changes in pore structure are associated with the content of clay minerals. The higher the content of clay minerals is, the higher the proportion of micropores (aggregated interior). Macroscopically, the overall porosity decreases and the fineness of the pores increases with clay content, which will directly affect the mechanical properties of tailings.

Plant root–soil water interactions are fundamental to vegetation–water relationships. Soil water availability and distribution impact the temporal–spatial dynamics of roots and vice versa. In the Loess Plateau (LP) of China, where semiarid and arid climates prevail and deep loess soil is dominant, drying soil layers (DSLs) have been extensively reported in artificial forest land; however, the underlying mechanism remains unclear. This study proposes a root growth model that simulates both the dynamic rooting depth and fine root distribution, coupled with soil water, based on cost–benefit optimisation. Evaluation of field data at an artificial forest site of black locust (Robinia pseudoacacia L.) in the southern LP positively proves its performance. Further, a long-term simulation was performed to address the DSL issues, which were forced by a 50-year climatic data series, under variations in precipitation. The results demonstrate that incorporating the dynamic rooting depth into the currently available root growth models is necessary for reproducing the drying soil processes. The top 2.0 m is the most active zone of infiltration and root water uptake, and below which the fractions of fine roots and uptake are small but cause a persistently negative water balance and consequent DSLs. The upper boundary of the DSLs fluctuates strongly with infiltration events, while the lower boundary extends successively owing to the interception of most infiltration by the top 2.0 m layer. Coupling the root–water interactions helps to reveal the intrinsic properties of DSLs, with the persistent extension of its thickness and rare opportunities for recovery from the drying state. This study may have negative implications for the implementation of artificial afforestation in this semiarid region, as well as in other regions of similar climate and soils.

Soil moisture is a key element of the hydrological cycle, and it significantly impacts the surface water and energy fluxes. However, a knowledge gap exists on the spatial variability of root-zone soil moisture at the regional scale in arid and hyperarid regions. Thus, soil moisture measurements at 142 sites were taken in Xinjiang (northwest China), and the relationships between soil moisture and 19 environmental factors were analyzed. The results showed that both absolute gravitational soil water content (SWC) and relative extractable water (REW) increased with increasing soil depth in the 0–100 cm soil profile. It generally decreased in the order of cropland > forestland > grassland > shrubland > bare land. Semivariograms suggested that SWC had moderate spatial dependence over a large range of 473–558 km, and REW was more randomly distributed at the regional scale in Xinjiang. Redundancy analysis suggested that environmental factors could explain 47.5%–50.9% of the variability of soil moisture, which was more strongly driven by land surface factors (p 0.05). Soil properties and other local variables explained, respectively, 40.7% and 32.3% of the variability of soil moisture in the 0–100 cm soil profile. Soil properties independently accounted for 12.8% and 28.1% of the variability in soil moisture in the 0–50 and 50–100 cm soil layers, respectively. Soil texture, field capacity, wilting point, organic carbon, bulk density, land use, and normalized difference vegetation index were the dominant factors influencing soil moisture variations.

Due to the presence of fine-grained interlayers (frequently called lenticles), the stability of tailings dams can deteriorate. In this study, a two-dimensional numerical model with flexible boundary was constructed, and biaxial tests were carried out for samples with interlayers at different dip angles. The influence of the interlayer inclination on the mechanical properties of tailings was analyzed. The simulation results revealed that the shear strength of tailings with interlayers decreases with the increase in the interlayer dip angle. Obvious anisotropy of shear strengths was observed due to the presence of interlayers. All the deformations of the samples with interlayers were well captured in the DEM simulations. Bulging deformations were found in the samples with interlayers at dip angles of 0°, 15° and 30°. Shear slip along the fine interlayer plane was generated in the samples with interlayers with dip angles of 45° and 60°. The principal orientation of the contact unit normal and the normal contact force aligns with the loading direction for the samples with interlayer at small dip angle (i.e., 0°). However, for the sample with interlayer at large dip angle (i.e., 60°), the principal orientation trends to the direction normal to the interlayer.

Due to the presence of fine-grained interlayer structures (usually called lenticles), the stabilities of tailings dams deteriorate. In this study, the strength and deformation of tailing samples containing fine-grained interlayers were studied by undrained tests. Based on the Coulomb theory, the slip mechanism of tailing samples was investigated. The results indicate that the stress-strain relationship of the samples that contain interlayers of large dip angles (i.e., 45° or 60°) is typical strain softening. The stress-strain relationship of the samples, with the interlayers dipping with small angles (i.e., 0° or 15°), is strain hardening. The mechanical parameters, e.g., shear strength, internal friction angle and cohesion, decrease with the increase in the dip angle of the interlayer. In tests, three different deformation patterns, i.e., bulging, slip and composite deformation, were observed from the samples with interlayers of small, large and medium dip angles, respectively (the medium dip angle is 30°). The slip occurred along the interlayer plane of the samples. When the angle of the interlayer is near 60°, the strength and deformation of the samples are controlled by the fine-grained interlayer. The findings of this study can provide reference for the stability evaluation of anisotropic tailing dams and other similar structures.

International audience; The glacierized Tien Shan-Pamir-Karakoram mountain complex supplies water to about 42 million people. Yet, the knowledge about future glacial runoff in response to future climate is limited. Here, we address this issue using a hydrological model, that includes the three components of glacial runoff: ice melt, snowmelt and the runoff of rainfall over ice. The model is forced by climate projections of the CMIP5 models. We find that the three components exhibit different long-term trajectories, sometimes opposite in sign to the long-term trend in glacier impacts. For the eastern slope basins, streamflow is projected to increase by 28% (ranging from 9 to 44%, from climate model variation (CMV)) by the late 21 st century, under the representative concentration pathway, RCP8.5. Ice melt contributes 39% (25 to 65%, CMV) of the total streamflow increase. However, streamflow from the western slopes is projected to decrease by 5% (−24 to 16%, CMV), due to the smaller contribution of ice melt, less precipitation and higher evapotranspiration. Increasing water supply from the eastern slopes suggests more water availability for currently degraded downstream ecosystems in the Xinjiang province of China, while the likely decreasing streamflow in Central Asian rivers on the western slopes indicates new regulations will be needed. The Tien Shan-Pamir-Karakoram (TPK) mountain complex is the "water tower" of the Central Asian countries east of the Aral Sea (

Saline-alkaline stress is an abiotic stress that suppresses rice plant growth and reduces yield. However, few studies have investigated the mechanism by which rice plants respond to saline-alkaline stress at a global transcriptional level. Dongdao-4 and Jigeng-88, which differ in their tolerance to saline-alkaline stress, were used to explore gene expression differences under saline-alkaline stress by RNA-seq technology. In seedlings of Dongdao-4 and Jigeng-88, 3523 and 4066 genes with differential levels of expression were detected, respectively. A total of 799 genes were upregulated in the shoots of both Dongdao-4 and Jigeng-88, while 411 genes were upregulated in the roots of both genotypes. Among the downregulated genes in Dongdao-4 and Jigeng-88, a total of 453 and 372 genes were found in shoots and roots, respectively. Gene ontology (GO) analysis showed that upregulated genes were enriched in several GO terms such as response to stress, response to jasmonic acid, organic acid metabolic process, nicotianamine biosynthetic process, and iron homeostasis. The downregulated genes were enriched in several GO terms, such as photosynthesis and response to reactive oxygen species. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that Dongdao-4 seedlings were specifically enriched in the biosynthesis of secondary metabolites such as diterpenoids and phenylpropanoids. The upregulated genes that were involved in secondary metabolite biosynthesis, amino acid biosynthesis, betalain biosynthesis, organic acid metabolic process, and iron homeostasis pathways may be central to saline-alkaline tolerance in both rice genotypes. In contrast, the genes involved in the diterpenoid and phenylpropanoid biosynthesis pathways may contribute to the greater tolerance to saline-alkaline stress in Dongdao-4 seedlings than in Jigeng-88. These results suggest that Dongdao-4 was equipped with a more efficient mechanism involved in multiple biological processes to adapt to saline-alkaline stress.

Non-structural carbohydrates (NSC) play important roles in metabolic processes of plants and represent important functional traits in plant adaptation to the external environment. However, there are few reports concerning intra-annual NSC distribution in temperate deciduous forests, especially for the purpose of comparison among different stand ages on China’s Loess Plateau. Here, NSC allocation dynamics with age ring-porous black locust tree was determined for the growing (May) and dormant (November) seasons over the period from sapling to dying trees—defined as a completely defoliated tree with dried branches in the growing season. It was noted that regardless of tree age, NSC concentration was highest in coarse roots [16.4 g per 100 g of dry mass (16.4% DM)] and stems (15.1% DM). At the tree level, NSC concentration was highest (14.3% DM) in a 30-year-old stand in November and lowest (4.1% DM) in dying stands in May. The pool of NSC at tree level was highest (25.2 kg DM per tree) in 30-year-old stands in November and lowest (0.13 kg DM per tree) in sapling stands in May. The concentration of NSC was significantly lower in May than in November for all tree ages, organs, and biochemical components. The results underscored the importance of NSC in plant growth on China’s Loess Plateau. It also provided a useful insight into the dynamics of NSC from sapling to dying broadleaved tree species.

Canopy interception loss is a key component of forest hydrological cycle that determine the amount of net rainfall reaching forest floor together with drought/climate stressors affecting dryland forest plantations. A good understanding of the relationship between canopy interception loss and forest management such as thinning is important for improved watershed management and ecological services. In this study, we measured event-based rainfall partitioning for a thinned (TH, with 38% basal area removed) and a control (CT) Robinia pseudoacacia forest plantation during leafed and leafless seasons in 2015 in the semiarid Loess Plateau region in China. Interception loss from both forest plots were simulated using the Revised Gash Analytical Model (RGAM) and the WiMo model. The results showed that observed annual throughfall, stemflow and interception loss were respectively 80.8%, 1.7% and 17.5% of the gross rainfall under CT. The corresponding values under TH were 87.9%, 0.8% and 11.3%, respectively. The RGAM and WiMo models were well calibrated and validated using filed data collected in leafed and leafless seasons. The analyses suggested that models accurately predicated interception loss under both CT and TH conditions and captured seasonal variations in canopy and meteorological parameters. The RGAM model was most sensitive to the ratio of mean evaporation rate to mean rainfall intensity, and canopy storage capacity in leafed season, and to the ratio of mean evaporation rate to mean rainfall intensity in leafless season. Moreover, 37.2% and 42.1% of the interception in leafed season evaporated from the canopy respectively during rainfall event and after rainfall. The corresponding values for leafless season were respectively 49.3% and 22.4%. Overall, the performance of the optimized RGAM and WiMo models were satisfactory with respect to modeling error (−6.9 − −2.9%) and Nash-Sutcliffe model efficiency (0.80–0.94), although that of the optimized RGAM model was slightly superior to WiMo model. The models would facilitate the implementation of water-oriented management in semiarid forest plantations through a more accurate simulation of the impact of thinning on interception loss.

The mechanical behavior and particle breakage of tailings under high confining pressure are the theoretical reference to analyze the stability of high tailings dams. Consolidated drained (CD) triaxial compression tests were carried out using a high-pressure triaxial apparatus. The strength and deformation characteristics of tailings were studied. The constitutive relation of tailings was deduced under high confining pressure. The particle breakage of tailings was analyzed qualitatively and quantitatively. The tailings exhibit strain-softening under low confining pressure and strain-hardening under high confining pressure. A modified hyperbolic model was deduced to describe the stress-strain behavior under high confining pressure. Under high confining pressure the volumetric strain always decreases with an increase in axial strain. Under low confining pressure, only a few indentations are observed on the surface of marked calcite particles. By contrast, a lot of indentations are observed on the surface of marked calcite particles under the high confining pressure. The number of broken particles increases with an increase in the confining pressure, but the increasing tendency gradually decreases.

Black locust accounts for over 90% of artificial forests in China’s Loess Plateau region. However, water use of black locust is an uphill challenge for this semi-arid region. To accurately quantify tree water use and to explain the related hydrological processes, it is important to collect reliable data for application in the estimation of sap flow and its response to environmental factors. This study measured sap flow in black locust in the 2015 and 2016 growth seasons using the thermal dissipation probes technique and laboratory-calibrated Granier’s equation. The study showed that the laboratory calibrated coefficient α was much larger than the original value presented by Granier, while the coefficient β was similar to the original one. The average daily transpiration was 2.1 mm day−1 for 2015 and 1.6 mm day−1 for 2016. Net solar radiation (Rn) was the key meteorological factor controlling sap flow, followed by vapor pressure deficit (VPD) and then temperature (T). VPD had a threshold control on sap flow at threshold values of 1.9 kPa for 2015 and 1.6 kPa for 2016. The effects of diurnal hysteresis of Rn, VPD and T on sap flow were evident, indicating that black locust water use was conservative.

Interception loss can remove a significant portion of rainwater from forested ecosystems. Therefore, the quantification and modelling of interception loss are of significant importance if human and ecosystem water demands are to be balanced under a future changing climate. This is particularly true for semi-arid/arid regions, where afforestation has become an important ecological restoration measure to tackle desertification, poverty and climate change. However, quantification and modelling of interception loss of plantations in these regions have rarely been reported. In the present study, rainfall interception loss was quantified and modelled over a one-year period (January-December 2016) for a deciduous broad-leafed R. pseudoacacia plantation and an evergreen needle-leaf P. tabuliformis plantation (common afforestation tree species) situated in the semi-arid Loess Plateau of China. The stand age, density, canopy cover and leaf area index of R. pseudoacacia during the study period were 15 years, 2000 tree ha−1, 0.48 and 1.41 m2 m−2, respectively. The corresponding values for Pinus tabuliformis were 17 years, 1200 tree ha−1, 0.62 and 2.53 m2 m−2. The measured throughfall, stemflow and derived estimates of interception loss for R. pseudoacacia were 81.1%, 1.3% and 17.6%, respectively. The corresponding values for P. tabuliformis were 75.4%, 0.7% and 23.9%. Given that the weather conditions experienced by the two forest stands were similar, the observed higher interception loss for P. tabuliformis can be explained by the higher canopy storage capacity and wet canopy evaporation rate of this species. The revised Gash analytical model of rainfall interception was well calibrated and validated against field measurements and was able to simulate the cumulative interception loss at two forest stands accurately, and it also effectively captured the seasonal variation (leafed growing and leafless dormant seasons), provided that the optimized wet-canopy evaporation rates were used. The revised model was highly sensitive to the canopy storage capacity and changes in the ratio of mean wet canopy evaporation to mean rainfall intensity and less sensitive to canopy cover, but it was found to be fairly insensitive to the trunk storage capacity.

The open hole of wellbore may pass through one or several mudstone interlayers during the construction of the salt cavern gas storage in thin interbedded salt mines. Once an interlayer is formed, leakage occurs that will cause the sealing failure of the wellbore. Based on the treatment project executed to ameliorate the wellbore sealing failure in Jintan's (China) salt cavern gas storage, a feasible grouting scheme and plugging evaluation criteria are proposed for similar, leaking interlayers. Combined with geological conditions and leaking types used to establish a radial grouting model, theoretical and numerical solutions for the plugging range are implemented. According to the grouting and plugging parameters used for analyses, the engineering practice indicates that the squeeze ultra-fine grouting can successfully plug this leaking interlayer and the depleted wellbore meets the requirements of storing natural gas that can be used for secondary utilization. The sealing effect mainly depends on the plugging range, which is affected by the grouting parameters, physicochemical properties of grout, and by the fluid–solid coupling. The results show that the viscosity rheology can inhibit grout diffusion, while the grout–rock coupling can promote grout diffusion. Their effects are completely opposite. Finally, the established plugging evaluation criteria can be used to analyze the plugging effect in the short and long-terms, and will have a good theoretical and practical guiding significance for the formation of sealing and gas leakage analysis of underground gas storage (UGS) in the future.