Theoretical and experimental study of initial cracking mechanism of an expansive soil due to moisture-change

Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil, which is similar to the behavior of most materials under thermal effect. If the deformation is restricted, stress in expansive soil is caused by the swell-shrinking. The stress is defined as “moisture-change stress” and is adopted to analyze swell-shrinkage deformation based on the elasticity mechanics theory. The state when the total stress becomes equal to the soil tensile strength is considered as the cracking criterion as moisture-change increases. Then, the initial cracking mechanism due to evaporation is revealed as follows: Different rates of moisture loss at different depths result in greater shrinkage deformation on the surface while there is smaller shrinkage deformation at the underlayer in expansive soil; cracks will grow when the nonuniform shrinkage deformation increases to a certain degree. A theoretical model is established, which may be used to calculate the stress caused by moisture-change. The depth of initial cracks growing is predicted by the proposed model in expansive soil. A series of laboratory tests are carried out by exposing expansive soil samples with different moisture-changes. The process of crack propagation is investigated by resistivity method. The test results show good consistency with the predicted results by the proposed theoretical model.     

Ice Crystal Sizes and Their Impact on Microwave Assisted Freeze Drying

Freeze drying of an aqueous solution would result in the non-uniform distribution of solute concentration. Because ice is almost transparent to microwave, therefore such a non-uniform distribution may affect the microwave assisted freeze drying. The direct observation of the ice crystals formed under microscope reveals that the ice crystal sizes formed from de-ionized water depend on the cooling rate with fast cooling rate giving smaller ice crystals as expected. Once there is a sufficient amount of solute mixed with the de-ionized water, for example the reactive red, the size and its distribution are not very much dependent on either cooling rate or the final temperature provided there is sufficient time of cooling and the final temperature is not too low. The size of ice crystals formed within the solution of reactive red is usually below 100 μm with a freezing rate of 1℃·min-1 for a droplet of the size of less than 1 mm. A simplified simulation indicates that such a small ice crystal would not caus     

PLC在轴承压盖机中的应用

轴承装配是轴承生产过程中最后且极其重要的环节，而压盖机是装配线上较为复杂的部分。装配线上的轴承压盖机采用PLC进行控制后，故障率低，维修方便，运行程序更改简单容易，提高了生产效率。     

建筑装饰工程电气安装常见问题及技术措施

装饰行业已逐淅发展为建筑业的重要分支，而电气系统安装又是装饰工程的重要组成部分。它涉及面广、技术相对复杂，其质量直接关系到装饰工程的效果。电气系统的使用功能以及建筑物的整体安全。一旦出错，极易引起火灾、触电等事故，危及人身和财产安全。因此，强化装饰工程中电气安装质量十分必要。     

能量桩工程应用研究进展及PCC能量桩技术开发

能量桩是一种由地源热泵技术与桩基埋管换热器结合组成的经济高效节能减排技术。简要介绍了基于地源热泵技术的能量桩技术原理、桩型、埋管形式以及技术经济优势,总结了近年来国内外能量桩技术的研究现状及其工程应用,包括基于灌注桩的传热管埋管形式和基于预制桩的传热管埋管形式;指出了目前工程应用中存在的一些主要问题,并提出一种新型PCC能量桩技术及其施工工艺;最后简要分析了能量桩技术在国家节能减排工程中的应用前景,并提出有待进一步研究的方向。     

胶结黏土中正断层扩展的变形和孔压变化研究

基岩断层错动而引起的上覆土体变形会对地表以及地下结构物造成破坏。上覆土体的胶结特性和隐伏断层的存在,使得断层错动的变形机制更为复杂。采用滤纸技术模拟隐伏断层,通过2组离心机试验研究胶结土体中正断层裂缝的扩展机制及伴随的孔压变化规律。对土体的变形分析和孔隙水压力的监测加深了对地裂缝的认识。研究发现,正断层错动引起胶结黏土的变形机制为受弯变形。隐伏断层使得土体受弯区变小、土体破坏程度加剧。胶结黏土受弯形成的地裂缝分为张拉裂缝和剪切裂缝,这些地裂缝的发展为超孔压的消散提供了优势路径。     

论市政公用工程施工项目管理内容

论述了市政公用工程施工项目管理的内容,并对管理的重点进行了解释,为相关的管理人员提供了有益的参考和帮助。     

树枝状大分子PAMAM-DSD的合成及其在造纸中的应用

在低代端酯基PAMAM树形分子(G0.5-COOCH3)末端引入4,4′-二氨基二苯乙烯-2,2′-二磺酸,在常温常压下合成一种高分子荧光增白剂(PAMAM-DSD)。实验显示,在纸张涂布中使用PAMAM-DSD,纸张的白度以及耐光性均得到明显改善。确定了PAMAM-DSD在涂布颜料中的适宜用量。     

城市景观视觉评价标准制定的原则

论述了城市景观评价制定的四项原则,即健康原则、特色原则、客观原则和实效原则,为城市景观设计提供了有效的技术参考。     

超深开挖对单桩的竖向荷载传递及沉降的影响机理有限元分析

目前对于超深基础下的桩的设计尚未考虑超深开挖、坑底隆起对桩产生的作用。现场采用静载试验确定单桩承载力时也仍采用常规的地表加载并扣除开挖深度范围内桩侧摩阻力的方法,没有考虑深开挖效应的影响。采用经实际工程算例验证的土参数、桩身材料参数和桩土接触面参数,在均质土中建立了轴对称有限元模型,对三种不同试桩方法进行了模拟。通过开挖模拟,首先揭示了深开挖对桩的影响效应,在此基础上,对超深开挖对桩在开挖后再加载的荷载传递机理和沉降机理进行了研究。与常规试桩法和套管试桩法中的基坑底以下相同桩长的桩相比,超深开挖产生的影响效应使桩的极限承载力降低,竖向刚度减小,相同荷载下沉降加大,且其沉降中桩整体刺入所占的比例显著大于其它两者。桩侧摩阻力完全发挥时需要的桩土滑移量增大。此外,超深开挖可在桩身中产生较大的拉力,桩身中下部钢筋不能随意减少。