Effect of dry-wet cycles on dynamic properties and microstructures of sandstone:Experiments and modelling

Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.This paper conducted ultrasonic detection,split Hopkinson pressure bar(SHPB)impact,mercury intrusion porosimetry(MIP),and backscatter electron observation(BSE)tests to investigate the dynamical behaviour and microstructure of sandstone with cyclical dry-wet damage.A coupling FEM-DEM model was constructed for reappearing mesoscopic structure damage.The results show that dry-wet cycles decrease the dynamic compressive strength(DCS)with a maximum reduction of 39.40%,the elastic limit strength is reduced from 41.75 to 25.62 MPa.The sieved fragments obtain the highest crack growth rate during the 23rd dry-wet cycle with a predictable life of 25 cycles for each rock particle.The pore fractal features of the macropores and micro-meso pores show great differences between the early and late cycles,which verifies the computational statistics analysis of particle deterioration.The numerical results show that the failure patterns are governed by the strain in pre-peak stage and the shear cracks are dominant.The dry-wet cycles reduce the energy transfer efficiency and lead to the discretization of force chain and crack fields.

Effect of Dry-Wet Cycles on the Transport and Mechanical Properties of Cement Mortar Subjected to Sulfate Attack

This study deals with the analysis of the detrimental effects of a“sulfate attack”on cement mortar for different dry-wet cycles.The mass loss,tensile strength,and gas permeability coefficient were determined and analyzed under different exposure conditions.At the same time,nitrogen adsorption(NAD),scanning electron microscopy(SEM),and X-ray diffraction(XRD)techniques were used to analyze the corresponding variations in the microstructure and the corrosion products.The results show that certain properties of the cement mortar evolve differently according to the durations of the dry-wet cycles and that some damage is caused to the mortars in aqueous solution.The pores fill with corrosion products,increasing the mortar specimen mass and tensile strength while reducing the permeability coefficient and pore size distribution.As corrosion proceeds,the crystallization pressure of the corrosion products increases,resulting in a 16%reduction in tensile strength from the initial value and a 2.6-factor increase in the permeability coefficient,indicating sensitivity to sulfate attack damage.Furthermore,the main corrosion products generated in the experiment are gypsum and ettringite.Application of osmotic pressure and extension of the immersion time can accelerate the erosion process.

The law of strength damage and deterioration of jointed sandstone after dry-wet cycles

Under the periodic rise and fall of the water level in the Three Gorges Reservoir in China,the rock mass in the ebb and flow zone of the slope is always in a state of a dry-wet cycle.In order to explore the influence of dry-wet cycle on mechanical properties of jointed sandstone,the triaxial and uniaxial compression tests of dry-wet cycle of jointed sandstone were carried out.For the experiment,four groups of samples with different numbers of joints were set up,and the jointed rock samples were subjected to 20 dry-wet cycles.Using both the triaxial compression test and the Mohr-Coulomb(M-C)rock fracture criterion,the strength envelope of the sandstone samples was fitted,and their strength degradation was further analyzed and studied.The results show that:(1)The peak intensity and elastic modulus of the sandstone samples decrease with increased number of dry-wet cycles.(2)The total deterioration of mechanical properties of intact rock samples is bigger than that of jointed sandstone samples as the number of dry-wet cycles increases.(3)With the increase of confining pressure,the peak intensity of intact sandstone samples increases much more than that of jointed sandstone samples,which indicates that joints and their numbers have obvious influence.(4)Joints and their numbers play an important role in guiding the damage effects of sandstone samples,which weaken the damage caused by dry-wet cycles.Therefore,the envelope of the M-C strength criterion of intact sandstone samples moves more than that of jointed sandstone samples.

Stability analysis of gravity anchor foundation of layered argillaceous sandstone under dry-wet cycles

To investigate the stability of gravity anchors of suspension bridges,in-situ tests of the vertical bearing capacity of the bedrock,shear resistance of the anchor-rock interface,shear resistance of the bedrock were conducted in a suspension bridge project.Under dry-wet cycles,the deterioration law of the mechanical properties of argillaceous sandstone was identified in laboratory tests:the elastic modulus,cohesion and friction of the argillaceous sandstone deteriorated significantly at first few dry-wet cycles and then declined slowly after 10 cycles,ultimately these three mechanical parameters were reduced to about 1/3,1/3,2/3 of the initial value respectively.Moreover,numerical simulation was used to restore in-situ shear tests and a good agreement was obtained.Base on the results of in-situ and laboratory tests,the stability of the gravity anchor foundation under natural conditions and drywet cycles was calculated and its failure modes were analyzed.The results demonstrated that the dry-wet cycles caused uneven settlement of the anchor foundation,resulting in more serious stress concentration in the substrate.The dry-wet cycles remarkably reduced the stability coefficient of the anchor foundation,whose failure mode shifted from overturning failure under natural conditions to sliding failure.When there was weak interlayer in the rock layer,the anti-sliding stability of the anchor foundation was affected drastically.

Effects of dry-wet cycles on three-dimensional pore structure and permeability characteristics of granite residual soil using X-ray micro computed tomography

Due to seasonal climate alterations,the microstructure and permeability of granite residual soil are easily affected by multiple dry-wet cycles.The X-ray micro computed tomography(micro-CT)acted as a nondestructive tool for characterizing the microstructure of soil samples exposed to a range of damage levels induced by dry-wet cycles.Subsequently,the variations of pore distribution and permeability due to drywet cycling effects were revealed based on three-dimensional(3D)pore distribution analysis and seepage simulations.According to the results,granite residual soils could be separated into four different components,namely,pores,clay,quartz,and hematite,from micro-CT images.The reconstructed 3D pore models dynamically demonstrated the expanding and connecting patterns of pore structures during drywet cycles.The values of porosity and connectivity are positively correlated with the number of dry-wet cycles,which were expressed by exponential and linear functions,respectively.The pore volume probability distribution curves of granite residual soil coincide with the χ^(2)distribution curve,which verifies the effectiveness of the assumption of χ^(2)distribution probability.The pore volume distribution curves suggest that the pores in soils were divided into four types based on their volumes,i.e.micropores,mesopores,macropores,and cracks.From a quantitative and visual perspective,considerable small pores are gradually transformed into cracks with a large volume and a high connectivity.Under the action of dry-wet cycles,the number of seepage flow streamlines which contribute to water permeation in seepage simulation increases distinctly,as well as the permeability and hydraulic conductivity.The calculated hydraulic conductivity is comparable with measured ones with an acceptable error margin in general,verifying the accuracy of seepage simulations based on micro-CT results.

Investigation of Sulfate Attack Resistance of Shotcrete under Dry-wet Cycles

In order to research the sulfate attack resistance of shotcrete, the sulfate attack of shotcrete in the presence and absence of steel fiber was experimentally studied by using dry-wet cycle method. Meanwhile, compared with ordinary concrete by the same mixture, the difference of sulfate attack resistance of shotcrete was studied. The experimental results showed that, with dry-wet cycles increasing, the changes of loss rate of relative dynamic elastic modulus and mass loss rate of specimens included three stages： initial descent stage, stable stage, and rapid descent stage, respectively. However, the changes of mechanical properties first increased and then decreased. Furthermore, the corrosion products of shotcrete after sulfate attack were observed by using the method of XRD, thermal analysis, and SEM, respectively, and the failure mode of shotcrete turned from ettringite destruction to ettringite-gypsum comprehensive failure. Meanwhile, the contents of ettringite and gypsum increased with increasing dry-wet cycle. Simultaneously, the stratified powders drilled from shotcrete under 150＇s dry-wet cycle were analyzed for the mineral phase composition and thermal analysis. With the drywet cycle increasing, the content of ettringite first increased and then decreased and tended to stable. However, the determination of gypsum decreased gradually and even to 0 when the depth was more than 12 mm.

Effects of freeze-thaw cycle and dry-wet alternation on slope stability

The typical loess on high slopes along the BaoLan High-speed Rail, China, was selected as the research object. The influence of the freeze-thaw cycle and dry-wet alternation on the shear-strength parameters of the unsaturated loess was investigated by laboratory experimental methods. Moreover, the temperature field, seepage field, and stability of slopes with different gradients were simulated under the effect of the freeze-thaw cycle and dry-wet alternation by using the geotechnical analysis software Geo-Studio. The research results showed(1) when the freeze-thaw cycle was repeated on the slope, with the frozen depth increasing, the melted depth did the same; besides, the closed loop of isotherms formed on the slope;(2) under the action of dry-wet circulation, the negative pore-water pressure and volumetric water content showed an upward tendency. However, owing to the different slope gradients, rainfall infiltration was not the same. As time went by, the differences of the negative pore-water pressure and volumetric water content between the slopes of different gradients continued to increase;(3) with the freeze-thaw cycle and dry-wet alternation increasing, the slope-safety factor decreased. Especially in the early period, the slope-safety factor changed remarkably. For slopes undergoing freeze-thaw action, the slope-safety factor was negatively correlated with the gradient. However, with regard to slopes undergoing dry-wet alternation, the result became more complex because the slope-safety factor was related to both seepage strength and slope grade. Accordingly, further research is needed to study the effect of seepage strength and slope grade on the stability of loess slopes.

The Quantification of Micro-structural Damage of Weak Muddy Intercalation in Dry-wet Cycles Combining in-situ SEM and DIP

In order to reflect truly the damage evolution mechanism of weak muddy intercalation in dry-wet cycles, two typical weak muddy intercalations were selected for dry-wet cycles. The mineral changes of specimens were analyzed via X-ray diffraction after dry-wet cycles. By combining in-situ SEM and digital image processing(DIP), the damage evolution process and damage characteristic parameters of each stage were obtained. The experimental results indicate that the hydration and dissolution of minerals can not be a determinant factor in structure damage. The micro-structural damage is due to disintegration of mineral aggregates, leading to changes in the number and size of cracks and pores. The damage degree of specimens is related to its initial structure, and the micro-structural damage intensifies and finally tends to stabilize with cycle times increased.

Cognitive Cycle in Mind Model CAM

Cognitive cycle is a basic procedure of mental activities in cognitive level. Human cognition consists of cascading cycles of recurring brain events. This paper presents a cognitive cycle for the mind model CAM (Consciousness And Memory). Each cognitive cycle perceives the current situation, through motivation phase with reference to ongoing goals, and then composes internal or external action streams to reach the goals in response. We use dynamic description logic which is an extended description logic with action to formalize descriptions and algorithms of cognitive cycle. Two important algorithms, including hierarchical goal and action composition, is proposed in the paper.

Ontology of Domains. Ontological Description Software Engineering Domain—The Standard Life Cycle

Basic concepts and notions of ontological description of domains are implemented in the conceptual model being understandable to ordinary users of this domain. Ontological approach is used for the presentation of software engineering domain—Life Cycle (LC) ISO/IEC 12207 with the aim to automate LC processes and to generate different variants of LC for development systems. And the second aim of Conceptual Model must teach the student to standard process LC, which includes general, organizational and supported processes. These processes are presented in graphical terms of DSL, which are transformed to XML for processing systems in the modern environment (IBM, VS.Net, JAVA and so on). The testing process is given in ontology terms of Protégé systems, and semantics of tasks of this process is implemented in Ruby. Domain ontology LC is displayed by the several students of MIPT Russia and Kiev National University as laboratory practicum course “Software Engineering”.

中重度牙周炎患者维护期应用PDCA循环管理模式联合脉冲式冲牙器的临床疗效

目的:观察中重度牙周炎患者维护期应用质量控制(PDCA)循环管理模式联合脉冲式冲牙器的临床效果,为PDCA循环管理模式在牙周炎患者中的应用提供理论依据。方法:通过预定的试验纳入标准、排除标准和剔除标准选取50例中重度牙周炎患者,随机分为实验组(n=25)和对照组(n=25),实验组患者通过脉冲式冲牙器联合巴氏(BASS)刷牙法维护,对照组患者单纯通过BASS刷牙法维护。2组患者均采用PDCA循环管理模式,在自我维护2、4、8和12周分别要求患者复诊,通过患者菌斑堆积量进行个性化纠正和指导,在自我维护4和12周时观察并记录2组患者牙周临床检查指标,包括菌斑指数(PLI)、探诊深度(PD)和出血指数(BI),检测龈沟液中肿瘤坏死因子α(TNF-α)和白细胞介素17(IL-17)水平。结果:经过4和12周自我维护,与对照组比较,实验组患者PLI、PD和BI明显降低(P<0.01);与基线时比较,自我维护4和12周时2组患者PLI、PD和BI均明显升高(P<0.05或P<0.01);与自我维护4周时比较,自我维护12周时2组患者PLI、PD和BI值明显升高(P<0.01)。经过4和12周自我维护,与对照组比较,实验组患者龈沟液中TNF-α和IL-17水平明显降低(P<0.01);与基线时比较,自我维护4和12周时2组患者龈沟液中TNF-α和IL-17水平均明显升高(P<0.01)。结论:在PDCA循环管理模式下应用脉冲式冲牙器可明显降低中重度牙周炎患者的PLI、PD、BI和龈沟液中炎症因子水平,有效抑制菌斑的形成并控制牙龈炎症状态,有利于中重度牙周炎患者治疗效果的维护。

构建老年认知障碍福利多元照护体系的行动研究——以北京市X医院老年健康社会工作服务为例

随着我国人口老龄化进程的加快,老年认知障碍患病人数与日俱增,这一疾病严重影响了老年人的生活质量并给家庭和社会造成巨大的负担与压力。现阶段,老年认知障碍在国家及社会层面关注度低、主动筛查和识别能力弱、治疗及照护成本高、社会服务体系碎片化等问题凸显,积极探索构建由政府、医疗机构、社区、慈善团体、市场及民间社会组织等多元福利主体构成的覆盖老年认知障碍病程全周期的照护体系势在必行。研究基于北京市X医院老年认知障碍患者及家庭全周期支援项目实践,以福利多元理论为框架,通过行动研究构建老年认知障碍福利多元照护体系的实施路径与机制。基于老年认知障碍群体现实样态的描绘,健康社会工作者打破原有医务社会工作服务存在的服务对象单一、服务场所禁锢、患者不同疾病周期需求割裂及资源链接成效欠佳等弊端,转而使用健康社会工作的视角,利用行动研究的方法尝试从认知障碍疾病管理的4个阶段进行破局:在认知障碍疾病早发现阶段,能够明确服务主体的职责,实现服务成效的最大化;在认知障碍疾病早治疗阶段,能够打通服务主体间的壁垒,实现资源的价值化流动;在认知障碍患者疾病自我管理阶段,能够调动服务主体的主观能动性,实现服务对象的积极转变;在认知障碍友好化倡导阶段,能够回应服务主体的内在需求,实现照护体系的可持续化发展。

硫酸盐侵蚀和干湿、冻融循环下混凝土单轴受压损伤对比

为研究宁夏典型服役环境下混凝土材料的损伤特点,本文在硫酸钠侵蚀和干湿、冻融循环三因素的共同作用和耦合作用下研究混凝土棱柱体试样的不同单轴受压应力-应变特点。改变硫酸钠溶液浓度和腐蚀次数,测量试样的质量损失率、相对动弹性模量以及应力-应变曲线。结果表明:随着腐蚀次数的增加,耦合作用下质量损失率和相对动弹模均先增大后减小,共同作用下则均逐渐减小;随着硫酸钠溶液浓度的增大,两种腐蚀制度下试样的应力-应变曲线上升段斜率和峰值应力均逐渐减小,且共同作用比耦合作用劣化效果更明显;随着腐蚀次数的增加,两种腐蚀制度下试样的应力-应变曲线上升段斜率均逐渐减小,耦合作用下峰值应力先增大后减小,共同作用下则逐渐减小,两种腐蚀制度下峰值应变均逐渐增大,共同作用比耦合作用劣化更大。本文提出的两种腐蚀制度下的混凝土应力-应变曲线预测模型可为宁夏服役环境下的混凝土结构寿命预测提供依据。

冻融循环作用下粉砂质硫酸盐渍土变形特性研究

【目的】为探究南疆地区粉砂质硫酸盐渍土的变形特性,【方法】在封闭系统条件下对粉砂土进行冻融循环试验,利用扫描电镜对土体结构进行表征分析。【结果】结果显示:粉砂质硫酸盐渍土硫酸钠含量为0和1.0%时变形以融沉为主,5次循环后变形量分别为-1.30 mm、-1.02 mm;硫酸钠含量为2.0%、5.0%、8.0%时变形表现为盐胀-冻胀变形,5次循环后变形量分别为2.46 mm、8.53 mm、3.43 mm。【结论】结果表明:粉砂质硫酸盐渍土在冻融循环作用下温度和硫酸钠含量是影响土体发生冻融变形的主要因素。在低温区间土体的变形随温度的降低表现为盐胀-冻胀,在升温过程中土体先后出现冰融和盐溶变形;土体的最终变形量与硫酸钠含量的变化表现为先增后减,当硫酸钠含量为5.0%时,土体的盐-冻胀率达到最大为2.5%。运用扫描电镜可发现粉砂质硫酸盐渍土经冻融循环后在自重作用下会产生沉降,内部盐分重结晶是抑制沉降甚至造成土体膨胀的主要原因。

基于行动周期理论的南京老城公共充电站规划协同

如何建设以公共充电站为代表的新型基础设施是老城更新急需解决的问题,目前对其规划协同的讨论有所不足。梳理城市政体理论和行动者网络理论的相关概念,结合生命周期视角创新性提出行动周期理论;以南京为例,通过数据量化分析和实地质性调研,发现老城公共充电站不充分、不平衡的现状空间布局和周期性演变特征;运用行动周期理论分析规划协同的行动者网络构建与转译进程,解释空间演变原因;提出优化建议,以期促进南京老城公共充电站的规划建设,为老城新型基础设施建设提供启示。

季冻区露天矿山边坡稳定性分析及加固措施研究

季节性冻土区露天矿边坡受不良地质作用影响及恶劣环境影响,不断出现变形、裂缝、滑移等病害,严重威胁矿山开采安全。基于图木尔廷—敖包锌矿东边坡失稳,开展了季冻区露天矿山边坡稳定性影响因素的研究,主要包括不良地质作用、冻融循环作用、开采爆破振动、水的直接作用等4个方面。在分析计算基础上,提出了包含削坡减载、边坡加固、疏排水工程及坡表喷涂和覆土的综合加固整治方案。经验算,按照设计方案进行加固后,能够有效提高东边坡的稳定性,解决困扰多年的东边坡稳定难题。达到从根本上消除安全隐患、保障矿山可持续开采的目的。

掺PVA纤维的水工混凝土抗冻性能研究

文章通过冻融循环试验,探究了三种体积掺量(1.0%、1.5%、2.0%)和两种长度规格(8mm、12mm) PVA纤维对水工混凝土抗冻性的影响规律。试验表明,水工混凝土相对动弹模量均随着冻融次数的增加整体呈递减趋势,并以未掺纤维组的降幅更显著;冻融75次时未掺PVA纤维试件已发生破坏,此时的相对动弹模量减小到56.5%,而冻融150次时掺PVA纤维试件依然未被破坏,相对动弹模量仍> 85%,研究成果可以为解决东北地区水工结构冻融破坏问题提供一定参考。

miR-223对银屑病细胞增殖、周期、凋亡和炎症反应的影响及机制

目的探讨微小RNA-223(miR-223)表达对银屑病细胞增殖、周期、凋亡和炎症反应的影响及机制。方法体外培养人永生化角质形成细胞HaCaT,将细胞分为对照组、模型组、模型+miR-NC组、模型+miR-223 inhibitor组,除对照组外,其余各组均采用M5法诱导HaCaT细胞建立银屑病细胞模型。采用RT-qPCR法检测各组细胞miR-223表达,CCK-8法、流式细胞术分别检测各组细胞增殖活性、细胞周期及凋亡情况,ELISA法检测上清液中IL-6、IL-1β和TGF-β1,Western blotting法检测第10号染色体同源丢失性磷酸酶张力蛋白基因(PTEN)蛋白表达。结果与对照组比较,模型组细胞miR-223表达升高(P<0.05),48、72、96 h时OD值、细胞周期S期占比增高(P均<0.05),细胞周期G0/G1占比和凋亡率降低(P均<0.05),IL-6、IL-1β和TGF-β1水平明显增高(P均<0.05),PTEN蛋白表达降低(P<0.05)。与模型+miR-NC组比较,模型+miR-223 inhibitor组miR-223表达明显下降(P<0.05),48、72、96 h时OD值、细胞周期S期占比明显降低(P均<0.05),细胞周期G0/G1占比和凋亡率明显升高(P均<0.05),IL-6、IL-1β和TGF-β1水平明显降低(P均<0.05),PTEN蛋白表达升高(P<0.05)。模型组与模型+miR-NC组比较,上述各指标差异无统计学意义(P均>0.05)。结论miR-223在银屑病细胞中表达增高,下调miR-223水平能抑制银屑病细胞增殖及炎症反应,将细胞周期阻滞于G0/G1期,促进细胞凋亡;其机制可能与其调控PTEN有关。

重楼皂苷Ⅵ通过调控SNRPD1抑制肝癌细胞增殖的机制研究

目的探讨重楼皂苷Ⅵ通过调控小核核糖核蛋白D1(SNRPD1)抑制肝癌细胞增殖的作用机制。方法①21只雄性裸鼠,采用皮下注射人肝癌Huh7细胞建立裸鼠肝癌移植瘤模型。裸鼠随机分为模型组(药物溶剂)、5 mg/kg重楼皂苷Ⅵ组、10 mg/kg重楼皂苷Ⅵ组,每组7只。连续腹腔注射给予相应干预10 d,观察各组裸鼠瘤体体积变化。②将人肝癌Huh7和JHH7细胞分为对照组和重楼皂苷Ⅵ组,采用重楼皂苷Ⅵ(0~15μmol/L)给予相应干预后,用细胞计数试剂盒(CCK-8)法和克隆形成实验检测细胞增殖情况,流式细胞术检测细胞周期情况,Western blot法和实时荧光定量逆转录聚合酶链式反应(RT-qPCR)法检测SNRPD1、细胞周期蛋白D1(Cyclin D1)、周期蛋白依赖性激酶4(CDK4)蛋白和基因的表达情况。采用分子对接技术预测重楼皂苷Ⅵ和SNRPD1蛋白的潜在靶向结合情况。结果①与模型组比较,10 mg/kg重楼皂苷Ⅵ能抑制Huh7细胞裸鼠移植瘤生长(P<0.05)。②与对照组比较,重楼皂苷Ⅵ能抑制人肝癌Huh7和JHH7细胞的增殖(P<0.05)、细胞克隆形成(P<0.05)及诱导细胞周期的阻滞(P<0.05)。分子对接结果显示,重楼皂苷Ⅵ潜在靶向SNRPD1蛋白;Western blot和RT⁃qPCR结果显示,与对照组比较,重楼皂苷Ⅵ可以下调SNRPD1的蛋白表达水平(P<0.05),但不能下调SNRPD1 mRNA表达水平(P>0.05)。与对照组比较,重楼皂苷Ⅵ能下调SNRPD1的下游细胞周期蛋白Cyclin D1和CDK4的表达水平(P<0.05)。结论重楼皂苷Ⅵ可能通过调控SNRPD1发挥抗肝癌作用。

中美核燃料循环设施核事故应急状态分级对比与探讨

本文介绍了美国核管会(NRC)及中国核燃料循环设施应急状态分级发展的历史及现状,对比了中美核燃料循环设施应急状态分级的差异,并给出分析结果,建议对后处理设施开展完整的二级PSA研究,给出相关事故谱,为进行应急状态分级及应急行动水平制定提供充分的技术支撑。