降雨对土坡稳定的影响

为了模拟降雨过程中边坡土体强度的变化,以室内常规不固结不排水三轴试验为基础,探讨了含水量的变化对土体抗剪强度参数及应力-应变关系的影响,并从孔隙水压力的角度探讨了降雨过程中含水量的变化对土体变形的影响.试验结果表明:抗剪强度参数与含水率变量总体上呈非线性关系,但对于粘聚力(c)和内摩擦角(φ),在含水质量分数为18.64%处均达最大值,并且随着含水量的增加,c、φ值均单调递减;重塑黏性土的应力-应变关系呈近似双曲线,并且随着含水量的增减应力-应变关系曲线越来越接近两边的坐标轴.最后,从土体强度和变形的两个角度分析可知,降雨过程中所造成的含水量的提高最终导致了边坡的破坏.     

混凝土盐类结晶破坏的理论与实践

水泥混凝土孔中盐类结晶压力很大,所产生的破坏属于物理原因,但比化学侵蚀的破坏更严重、速度更快.盐类结晶所产生的压力随孔液过饱和度的增大、结晶产物密度的增大和环境温度的提高而增大.同一类化学成分的物质,随结晶水增多,密度下降,结晶压力降低.盐类结晶产生的必要条件是混凝土孔液达到饱和及过饱和,除了环境的介质外,温度变化和干湿循环是混凝土孔液达到饱和及过饱和的重要外部条件.盐类结晶破坏的条件是盐类在毛细孔中不断结晶和积聚.我国北方地区冬季撒除冰盐引起的立交桥和混凝土路面的盐剥破坏,主要是混凝土孔液中NaC1结晶所致.水泥化学中的硫酸盐腐蚀其实质是钙矾石和石膏结晶压力的破坏,属于盐类结晶破坏范畴.     

人工冻结法施工中的温度场研究

为了解人工冻结法施工中的温度场发展变化规律,本文采用数值模拟方法,对影响人工冻结温度场的因素进行了分析计算。结果表明:随着导热系数的增加,土体降温速度加快,土体冻结所需时间大幅度缩短;随着初始地温的增加,土体冻结速度变慢,冻结所需时间有较大幅度增大;盐水温度对温度场影响较大,随着盐水温度的降低,水泥土降温速度加快,土体冻结所需时间缩短,盐水温度变化既影响水泥土降温过程中的相变阶段,也影响土体相变前的降温阶段;隧道顶部覆土厚度对冻结温度场的影响非常小,可以忽略不计;冻结法施工过程中,大气温度变化对冻结温度场的影响非常小,但如果施工期很长,气温变化引起地温变化,就会对冻结温度场产生较大影响。     

二维喷嘴内稠密气固射流稳定性实验

利用高速摄像仪对二维喷嘴内稠密气固射流稳定性进行了实验研究,考察了颗粒粒径、料仓压力以及喷嘴收缩角等因素对射流流动模式及稳定性的影响。结果表明：对于颗粒粒径为78μm的气固射流,随着料仓压力的增大,射流出口速度增大,射流固含率降低,在料仓压力≥0.03MPa、射流速度≥4.82m/s、射流固含率≤0.168时,喷嘴内稠密气固射流出现气泡型的不稳定流动模式;随着颗粒粒径的增大,气固射流固含率降低,喷嘴内稠密气固射流从气泡模式转变为颗粒团不稳定流动模式;改变喷嘴收缩角对射流不稳定模式影响不大。利用微型压力传感器对喷嘴直管不同位置压力进行测量,结果表明压力脉动主要是由于气固射流中气泡及颗粒团的产生及演变导致的。研究表明,随着料仓压力增大,颗粒在喷嘴内向下运动过程中压降增加,渗透进颗粒流的气体分率增加,将导致喷嘴内气固相互作用增强,进而引起气固射流不稳定。     

压力对银杏内酯气体抗溶剂结晶的晶形影响

研究了银杏内酯的气体抗溶剂结晶(GAS)过程。探讨了压力对晶体形貌的影响,结果发现,随着压力的增大,所得银杏内酯晶体颗粒变小。     

回填土作用下的竖向分层土主动土压力分析

分层土主动土压力以水平向研究较多,竖向分层土土压力计算还少见。基于极限平衡分析方法,推导回填土作用下的竖向分层土主动土压力计算公式,并分析墙土摩擦角δ、墙背倾角β、回填土深度h、回填土范围a、回填土抗剪强度指标C和φ对主动土压力及破裂角的影响。研究结果表明：本文土压力计算方法适用更广,规范法给出公式是本文方法的特殊情况;主动土压力随着δ、β、C、φ的增大逐渐降低,随着h和a的增大逐渐增加,其中a、C、φ对土压力影响较大;破裂角随着δ、β、h、C的增大逐渐降低,随着回填土范围a的增大先上升后逐渐趋缓,随着φ的增大先降低后增加。     

黄泛区粉土物理特性区域差异性试验研究

河南东部地区为典型黄泛区,随着该地区基础建设的迅速发展,迫切需要对该地区粉土的物理力学性质进一步研究。本文通过筛分试验、液塑限试验和击实试验,基于土体的颗粒组成、液塑限、最大干密度和最优含水率指标,研究河南东部区域黄泛区粉土的物理特性差异。结果表明:河南东部不同区域黄泛区粉土颗粒级配、液塑限存在明显差异,细粒含量差别显著,细粒含量越多液塑限越大;该地区不同区域最大干密度基本相同,最优含水率有差异,说明粉土的最终压实度相近,最优含水率与细粒含量有关。     

三轴应力条件下泡沫轻质土压缩特性

为探究在复杂应力条件下泡沫轻质土的压缩特性,通过不固结不排水三轴压缩试验研究了三种不同湿密度的泡沫轻质土在多种围压状态下的应力-应变分布规律、抗剪强度特性和破坏形态.结果 表明,泡沫轻质土的三轴压缩变形过程可划分为弹性变形-应变硬化-压密破坏三个阶段.同一湿密度泡沫轻质土的偏应力和峰值应变随加载围压增大均呈现先增大后减小规律.提高泡沫轻质土湿密度,降低孔隙率,能够增大其粘聚力及内摩擦角,粘聚力约为同龄期无侧限抗压强度0.34倍,实测轻质土侧向压力系数与理论计算值一致.轻质土试件破坏形态与其力学强度有关,可根据最终破坏形态分为剪切破坏和压密破坏两类.     

微米颗粒污垢特性的数值模拟

通过分析微米级颗粒污垢的特性研究了其在圆管内的沉积过程。首次将雷诺应力方程、拉格朗日方程与相关经验公式相结合建立颗粒污垢沉积和剥蚀的数值模型,用来计算颗粒污垢热阻。以20μm氧化镁颗粒为例,计算结果与实验污垢热阻值吻合良好。结果表明:随着流速的增加,污垢热阻渐近值有所降低;随着颗粒浓度的增加,结垢速率加快,污垢热阻渐近值明显增大;污垢热阻渐近值随管段入口温度的升高而降低。     

PP-g-VAc非等温结晶动力学的研究

用DSC对两种不同接枝率的聚丙烯接枝醋酸乙烯酯共聚物(PP g VAc)进行了非等温结晶动力学的研究,采用Reziorny修正的Avrami方程和莫志深提出的R t法对非等温结晶动力学进行了分析。研究结果表明:这两种方法能够很好地对PP g VAc的非等温结晶过程进行描述,VAc接枝链由于破坏了分子链的规整性并产生部分交联,导致结晶速率和结晶能力降低:结晶时间(t1/2)增大、结晶速率常数(Zc)降低,接枝共聚物的结晶焓降低,聚丙烯结晶成核和生长的方式没有改变,高接枝率下PP(GP=14 8%)的结晶温度上升,结晶参数F(T)随接枝率而增大。     

马路坪矿深部红页岩底鼓形成机理研究

针对马路坪矿深部红页岩巷道底板出现的底鼓问题,对深部软岩巷道的底鼓成因和机理进行了分析,从而得出随着巷道掘进深度的增加,巷道底板弹性区的应力增长梯度及其静水压力增长梯度呈线性关系,与巷道底板的塑性区呈现近似线性相关关系,研究结果为马路坪矿探部红页岩软岩巷道底鼓的防治提供了理论依据.     

不同含水率下赤泥改良土的动弹模及阻尼比研究

为研究不同初始含水状态下赤泥改良土的动力学参数,利用GDS动三轴仪对不同含水率下改良土进行了不同频率下的循环加载试验,研究分析了振次、含水率、加载频率对改良土动弹性模量和阻尼比的影响.试验结果表明:动应力幅值一定时,动弹模随振次增加基本无变化,阻尼比随振次增加呈波动变化,且提出并证明了可用第10振次下的动弹模阻尼比值代表各级荷载下的动弹模阻尼比值;动弹模随动应变幅值的增加先增大后减小,并用二次函数对其进行了拟合,阻尼比随动应变的增加先减小后增大;改良土动弹模在其最优含水率处达到最大,较高的含水率使改良土动弹模明显下降;较小应变幅下动弹模随频率增加而减小,较大应变幅时动弹模随频率增加而增大,阻尼比在加载频率较高时较大.     

不同含水率褐煤粉的输送流动特性及稳定性

在高压浓相输送实验台上利用氮气进行了褐煤粉输送实验,考察了褐煤粉含水率对输送压损特性、质量流量及稳定性的影响,采用小波分析理论对输送压损信号进行了分析,根据差压波动不同频率段的能量、波幅和方差等特征参数,并结合褐煤粉不同含水率下的输送特性及煤粉的表观形貌分析,进行系统输送稳定性判别. 结果表明,随煤含水率增大,其输送压损和质量流量减小,输送稳定性明显下降,压损呈周期脉冲. 含水率低于5.36%时,系统输送特性良好,含水率为5.36%~8.56%时,系统不稳定,含水率超过8.56%时,系统稳定性急剧下降,并经常堵塞. 差压信息的小波分析结果显示,在不同含水率褐煤粉的输送过程中,当差压信号的能量、波幅和方差主要分布在低频段时,输送过程较稳定,当这些特征参数向高频段转移时,输送稳定性随之下降.     

氯丁橡胶/有机黏土纳米复合材料应变诱导结晶行为

通过熔体插层法制备氯丁橡胶/有机黏土纳米复合材料(CRCNs),利用偏光显微镜观察CRCNs在不同应变条件下微观结构的变化。主要研究有机黏土对CRCNs应变诱导结晶行为的影响,并通过XRD和SEM表征了CRCNs的微观结构。结果表明: 当有机黏土含量为5 phr时,CRCNs的综合力学性能最优。随着应变的增加,CRCNs的应力也在增加;当应变达到一定值时, CRCNs的应力迅速增加,应变诱导结晶集中产生。随着有机黏土含量的增加, CRCNs拉伸诱导结晶行为在高应变条件下产生。分析原因是氯丁橡胶基体中有机黏土与橡胶分子的插层结构逐渐减少,诱导结晶能力变弱。     

Drying Characteristics of Coriander Seed Particles in a Reduced Pressure Superheated Steam Fluidized Bed

Drying characteristics of coriander seed particles were experimentally analyzed in a reduced pressure superheated steam fluidized bed. The typical moisture gain, reported in some other studies during the warm-up period of the process, was reduced in most of the cases by supplying additional heat into the column. The experimental results demonstrated that the drying rate increases and the equilibrium moisture content decreases by increasing the operating temperature. However, variation of the operating pressure (40–67 kPa) and the superficial steam velocity (2.3–4.0 m/s) did not present significant effects on the moisture contents. The degree of superheating was found to be the most important parameter for the process. The experiments also showed that the equilibrium moisture content decreases upon increasing the degree of superheating. Finally, employing a reduced pressure superheated steam fluidized bed appears as an option to carry out drying processes at relatively lower temperatures.     

Self‐reinforcing isotactic polypropylene prepared using crystallizable solvents

A new approach to reinforce and toughen isotactic polypropylene (iPP) with improved processability is evaluated. The concept involves using a crystallizable solvent that, at process temperatures melts, is miscible with the polymer thereby reducing its process viscosity. As the polymer cools, the solvent undergoes thermally induced phase separation (TIPS) to produce crystallites that increase the modulus of the solid through reinforcement and promote an increase in impact resistance by mechanisms similar to rubber‐toughened materials. Tetrabromobisphenol‐A (TBBPA) is introduced to iPP that forms a homogeneous mixture at elevated temperature and acts as a processing aid, but undergoes phase separation and subsequent crystallization upon cooling to form rigid particles which, in turn, acts as a toughening agent at room temperature. A phase diagram constructed with Flory‐Huggins solution thermodynamics shows good agreement with the experimental results. The steady state shear viscosity decreases as TBBPA content increases for the mixtures in melt state, indicating improved processability. The decrease in viscosity enhances crystallization rate of iPP significantly, most likely due to increased diffusivity, while the structure of iPP crystals remain unchanged. Tensile tests show that as TBBPA content increases (up to 15 wt %), the yield stress decreases while elongation at break increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Observations of ice lens formation and frost heave in young Portland cement paste

As part of a research program to image frozen cement past specimens, abnormal microstructural formations are seen in specimens frozen after 10-h hydration. The formations are areas of loose microstructure with aspect ratios of 6-10, which appear perpendicular to the direction of cooling in the specimen. After sublimation of the water in the specimens during the imaging process, these formations collapse, indicating that ice is instrumental to their structure. These formations coincide with longitudinal cracks in the specimen, which do not appear to be due to specimen preparation and are consistent with an internal tensile strain. The authors have hypothesized that ice lens formation and frost heave, or a similar freezing mechanism, is responsible for these microstructural features, which are seen in 10-h specimens and are absent in all other cement paste specimens. Triaxial permeability tests have also shown that the cement paste mix used in this study has a permeability at 10-h age of ∼10⁻⁶ cm/s. This permeability is similar to that of silty soil, some of the most susceptible to frost heave.     

铁尾矿粉改良水泥土的强度与动力特性试验研究

为提高水泥改良土强度,验证尾矿粉能够起到对水泥土的增强效果,对已用水泥改良过的路基土,在尾矿粉掺入量不同的条件下,经改良后水泥土的强度特性,以及对被最佳掺量的尾矿粉改良后的水泥土,在围压和频率不同的条件下进行动力特性的试验研究,制备了不同尾矿粉掺量(0%、2%、4%、6%、8%、10%)的试验土样进行无侧限抗压强度试验和动三轴试验;试验结果表明:随着尾矿粉掺入量的增加,无侧限抗压强度先增大后减小,土的应力应变曲线先急剧增加达到峰值后逐渐趋于平缓.当尾矿粉掺量达到最佳时,分析不同围压和不同频率的条件下G/Gmax~γ、λ~γ变化规律.对于同一动剪应变幅,动剪模量比随围压的增加而增大.阻尼比随动剪应变幅的增大而增大,随围压的增大而减小.G/Gmax~γ、λ~γ关系受频率影响不太敏感,都集中于一狭小范围.该试验能够提高水泥土强度的尾矿粉最佳掺量为6%.     

颗粒负荷对小型旋风器性能影响的模拟分析

为探究颗粒负荷对小型旋风器内气固两相流动的影响,基于雷诺应力模型（RSM）和欧拉-欧拉方法的混合流模型（Mixture）进行气体-颗粒、颗粒-颗粒的相间耦合计算。采用粒径为0.5～5μm的颗粒组在40L/min、60L/min和80L/min的入口流量下模拟0~3kg/m³的5种不同颗粒浓度工况,通过对比旋风器内纯气相流场和颗粒负荷流场的不同,研究了颗粒的存在对流场的影响;探究了入口流量和浓度变化对旋风器内分离效率和压降特性的影响。基于模型有效性验证的数值模拟结果表明：较高颗粒浓度负荷使旋风器内的气相流场发生显著变化。随着入口流量的增大,旋风器的分离效率先增大后减小,压降呈非线性增大。随着颗粒浓度的增大,旋风器的分离效率逐渐增大,压降先减小后增大。     

Acrylic latices stabilized by polymerizable non-ionic surfactant

The final latex particle size is controlled by the concentration of polymerizable non-ionic surfactant NE-40 in the emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The particle size decreases with increasing NE-40 concentration and increases with increasing persulphate initiator concentration. The dependence of particle size on the initiator concentration does not follow conventional Smith–Ewart theory, which is attributed to the bridging flocculation process during the particle nucleation period. The differences in the particle nucleation and growth stages and colloidal stability observed in the NE-40 and nonyl phenol-40 mol ethylene oxide adduct (NP-40) stabilized systems can be attributed to the different distribution patterns of surfactant molecules in the particles. Experimental data also indicate that the particle size decreases with increasing electrolyte concentration, or agitation speed. The total scrap, presumably caused by the bridging flocculation process, increases rapidly with increase in the NaCl concentration The amount of large flocs formed during polymerization is generally greater for the run operated at higher agitation speed. As expected, the latex products stabilized by non-ionic surfactants show excellent stability toward added sodium salt.