34 research outputs found

    Fracture Behavior in a Rock Pillar Subjected to Coupled Thermo-Mechanical Loading

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    Using RFPA code, analyses have been carried out to investigate the stability of a rock pillar in a experiment for nuclear waste repositories, the numerically obtained stress field, temperature distribution, failure pattern of the pillar rock and associated AE events are all agree well with the in-situ data. Minor fracture initiation may take place in the vicinity of the boreholes after heating. Heating induces minor spalling at central pillar wall for 0.5 m sections below the tunnel floor, but the area of spalling is found to be limited. The core of the pillar remains intact for stress conditions corresponding to 120 days of heating which not only prove that the proposed technique provides a powerfully alternative and effective approach for the study on thermal-mechanical-damage coupling mechanism but also provide meaningful guides for the experiment design and associated applications.Godkänd;2006;20100511 (andbra);Konferensartikel i tidskrift;Bibliografisk uppgift: Volumne: 324-325</p

    The Study of Soil Fertility Spatial Variation Feature Based on GIS and Data Mining

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    International audienceStudying on the spatial distribution and variation characteristics of soil fertility by Application of geographical information systems (GIS) and data mining(DM), with the quantitative analysis of spatial variability of soil fertility in complexity, and provide the effective way for simulations which can be closer to the farmland soil fertility variability. At the same time, interpolation method based on the spatial variability of soil can provide different accuracy data for soil database, researching of space fuzzy clustering based on precise fertilization regional fertility space can provide a decision-making basis for spatial variability of soil fertility evaluation, a precise prediction and evaluation of precision agriculture are the indispensable basic information and theoretical basis of the development and implementation of precision agriculture.In this paper, the authors take the national 863 project which in the Yushu City of Jilin province as the survey region. And then get the best prediction method and discuss the different effect of the soil nutrient under spatial interpolation prediction model on the analysis of the soil nutrient space mutation characteristics of the foundation by the GIS technology and the geography statistical method. Finally, we analysis the soil fertility status by using the weighted space fuzzy clustering as well as the soil nutrient of space mutation distribution, so as to provide basis for the study on area space mutation characteristics of cultivated land soil fertility which has an important theoretical and practical effect on the precise fertilization of crop and soil fertility evaluation

    A numerical investigation of the hydraulic fracturing behaviour of conglomerate in Glutenite formation

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    Rock formations in Glutenite reservoirs typically display highly variable lithology and permeability, low and complex porosity, and significant heterogeneity. It is difficult to predict the pathway of hydraulic fractures in such rock formations. To capture the complex hydraulic fractures in rock masses, a numerical code called Rock Failure Process Analysis (RFPA2D) is introduced. Based on the characteristics of a typical Glutenite reservoir in China, a series of 2D numerical simulations on the hydraulic fractures in a small-scale model are conducted. The initiation, propagation and associated stress evolution of the hydraulic fracture during the failure process, which cannot be observed in experimental tests, are numerically simulated. Based on the numerical results, the hydraulic fracturing path and features are illustrated and discussed in detail. The influence of the confining stress ratio, gravel sizes (indicated by the diameter variation), and gravel volume content (VC) on the hydraulic fracturing pattern in a conglomerate specimen are numerically investigated, and the breakdown pressure is quantified as a function of these variables. Five hydraulic fracturing modes are identified: termination, deflection, branching (bifurcation), penetration, and attraction. The propagation trajectory of the primary hydraulic fractures is determined by the maximum and minimum stress ratios, although the fracturing path on local scales is clearly influenced by the presence of gravels in the conglomerate, particularly when the gravels are relatively large. As the stress ratio increases, the fractures typically penetrate through the gravels completely rather than propagating around the gravels, and the breakdown pressure decreases with increasing stress ratio. Furthermore, the breakdown pressure is affected by the size and volume content of the gravel in the conglomerate: as the gravel size and volume content increase, the breakdown pressure increases

    Roles of caregiver-child interaction on the association of socioeconomic status with early childhood development: a population-based study in rural China

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    Abstract Objective Socioeconomic status (SES) has been previously associated with children’s early development, health, and nutrition; however, evidence about the potential role of caregiver-child interaction in such associations was limited. This study aimed to explore the effect of caregiver-child interaction on the associations of SES with child developmental outcomes, including early neurodevelopment and social-emotional behavior. Methods A cross-sectional survey was conducted among 2078 children aged 0–6 in a rural county that just lifted out of poverty in 2020 in Central China. The Ages & Stages Questionnaires-Chinese version (ASQ-C) and the Social-Emotional (ASQ: SE) questionnaire were used to assess children's early neurodevelopment and social-emotional behavior, respectively. Caregiver-child interaction was evaluated with the Brigance Parent–Child Interactions Scale. Regression-based statistical mediation and moderation effect were conducted with the PROCESS macro of SPSS. Results Children with low SES had an increased risk of suspected neurodevelopmental delay [OR = 1.92, 95% CI: 1.50, 2.44] and social-emotional developmental delay [OR = 1.31, 95% CI: 1.04, 1.66]. The caregiver-child interaction partially mediated the associations of SES with child developmental outcomes; the proportion of the indirect effect was 14.9% for ASQ-C total score and 32.1% for ASQ: SE score. Moreover, the caregiver-child interaction had a significant moderation effect on the association of SES with ASQ-C total score (P < 0.05). A weaker association was observed in children with high-level caregiver-child interaction than in medium and low ones. Similar moderating effects were found among boys but not girls. Conclusion Caregiver-child interaction plays a vital role in the relationship between SES and child development. Children with low SES households will benefit more in terms of their early development from intervention programs strengthening caregiver-child interaction

    Numerical Simulation of Rock Uniaxial Compressive Strength and Deformation Failure Law under Different Size Conditions

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    Rock engineering occupies an important position in the 21st century. In the face of rock engineering disasters, we are only looking for the essential problems through experiments on rocks, but rock experiments cannot be realized in large numbers, so the article uses numerical simulation software RFPA (Realistic Failure Process Analysis) 2D Basic to simulate rock under different size conditions numerically. In this paper, a rock model with a diameter of 50 mm is used for simulation research. Meanwhile, five calculation models of height-to-diameter ratios of 1.0, 1.5, 2.0, 2.5, and 3 are used. Through simulation calculation, we find that the rock model failure is more than complicated when the value of the height-to-diameter ratio is exceedingly low (1), but as the height-to-diameter ratio increases, the failure mode will become simpler. The stress-concentrated failure will be in the form of axial failure. When the height-to-diameter ratio increases (1.5–2), other damage cracks appear on the basis of axial cleavage failure. As the height-to-diameter ratio continues to increase (about 2.5), only shear failure occurs. When the height-to-diameter ratio reaches a relatively high level (3), there will be both axial rip and other damage. When the height-to-diameter ratio is oversize, there will be both axial rip failure and end damage

    Pore-Scale Flow Fields of the Viscosity-Lost Partially Hydrolyzed Polyacrylamide Solution Caused by Sulfide Ion

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    The rheology of a partially hydrolyzed polyacrylamide (HPAM) solution plays an important role in its oil recovery during polymer flooding. However, multiple factors in brine, such as sulfide ions, cause a dramatic loss in the viscosity and oil recovery. To better understand the sulfide-induced viscosity loss and the consequent flow mechanisms in pore networks, the morphology of polymer solutions with and without sulfide ion was observed by scanning electron microscopy; and the variations of the pore scale flow fields were demonstrated by a microscopic visualization seepage experiment combined with Micro-PIV (Microscale Particle Image Velocimetry). The results showed that, with the presence of sulfide ion, the microstructure of the polymer changed from a uniform three-dimensional network structure to loose and uneven floccules, which resulted in viscosity loss (over 70% with 5-mg/L sulfide ion). Moreover, higher concentrations of sulfide ions (5 mg/L and 10 mg/L) resulted in earlier shear thinning characteristics than those with lower sulfide concentrations. Due to viscosity loss, the average flow velocity in the main stream of the microscopic seepage experiment increased more significantly than that without sulfide. However, the viscosity loss alone cannot independently explain the severe viscous fingering during the subsequent post-water flooding, which was about five times greater than that of the primary water flooding in terms of the velocity ratio between the mainstream and margin. A further pore-scale flow field analysis exhibited an eccentric and a bimodal velocity distribution in the throat along the radial and axial directions, respectively. The former distribution indicated that the adsorbed polymer on the pore wall was broken through by hydraulic shear due to the collapsed structure caused by sulfide ion. The latter suggested that another sulfide-induced impact was an earlier-occurring non-Newtonian characteristic with a low shear rate. Therefore, instead of viscosity loss, elastic loss is the dominant mechanism affecting the characteristics of the aggregate flow field under the action of sulfide. Microscopic flooding combined with Micro-PIV is a feasible and essential method to reveal pore scale flow mechanisms

    Achieving superior dispersion-strengthening effect in an AA5xxx Al-Mg-Mn alloy by mico-alloying

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    5xxx Al-Mg based alloys are widely applied as non-heat-treatable alloys. In this work, we designed a dispersion-strengthening Al-4Mg-1Mn-0.3Fe-0.2Si-0.2Zr-0.2Cr (wt.%) alloy. By applying ramp heating and 400 °C isothermal aging, a significant dispersion-strengthening effect through the formation of various types of dispersoids was achieved. Detailed scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed the precipitation behaviors of nanoscale Mn-rich dispersoids and Al3Zr nanoparticles during heat treatments. As a result, an increment of 48 MPa in yield strength was obtained compared with the reference 5182 alloy. Meanwhile, the modified alloy shows a good heat resistance at 400 °C with little loss of yield strength until 200 h of heating. This has been attributed to the further precipitation of Al3Zr particles which counteracts the coarsening of Mn-rich dispersoids. Moreover, the addition of peritectic element Cr was found to significantly promote the precipitation of Al6(Mn,Fe,Cr) in dendritic center regions, thus improving their global distribution across dendrite arms. The presence of dense dispersoids can also improve the recrystallization resistance of the deformed alloy during annealing, thus retaining the deformation fiber structure and significantly retarding the recrystallization behavior. This research demonstrates an effective strategy to develop high-performance 5xxx series alloys strengthened via dispersoids

    Preliminary Study on High-Energy and Low-Energy Microfracture Event Evolution Characteristics in the Development Process of Rock Failure

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    The evolution characteristics of high-energy and low-energy microfracture events play an important role in the brittle failure mechanism of rock and reasonable microseismic (MS) monitoring and acoustic emission (AE) monitoring. The bimodal distribution (BMD) model is commonly used to observe the evolution characteristics of high-energy and low-energy MS events; however, its precise mechanism remains unclear. The evolution characteristics of high-energy and low-energy microfracture events are assessed in this study based on a BMD model. MS monitoring results from the No. 22517 working face of the Dongjiahe Coal Mine are studied, and AE monitoring results of a biaxial compression experiment of a granite specimen are analyzed. High-energy MS events in the No. 22517 working face are found to be generated by an increase in the failure scale of the overlying rock mass upon exiting the insufficient mining stage and entering the sufficient mining stage. The change characteristics of the high-energy AE hits are positively correlated with crack evolution characteristics in the granite specimen and negatively correlated with changes in the Gutenberg-Richter b value. A precise high-energy and low-energy AE hit evolution mechanism is analyzed based on the microscopic structure of the granite specimen. Similarities and differences between high-energy MS events and low-energy AE hits are determined based on these results. Both are found to have bimodal characteristics; an increase in the failure scale is identified as the root cause of the high-energy component. The bimodal distribution of AE hits is far less obvious than that of MS events
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