压实度和含水率对冻土性质的影响

本文通过试验研究了压实度和含水率对冻土性质的影响.研究表明:相同的冻结温度下,如果保持压实度不变,随着含水率的增加土样的冻胀率也一直增加,且最佳含水率是影响土样冻胀率变化趋势的分界点;如果保持含水率不变,随着压实度的增加土样冻胀率呈减小的趋势,且变化幅度也在减小.粘性冻土的无侧限抗压强度随着含水率和压实度的增加而呈现上升的趋势,且粘性冻土的冻胀率和抗压强度与其含水率及压实度之间存在明显的函数关系.     

Soil compaction and sealing in Al‐Salmi area,western Kuwait

In the deserts of Kuwait in general and in Al‐Salmi area in particular, soil compaction and sealing are the most significant mechanisms of land degradation. In the present study, soil compaction and sealing in the Al‐Salmi area are assessed. The study is based on analysis of satellite images and aerial photographs, besides field measurements and laboratory investigations. Based on this study, a recent map is prepared for the concerned area. It shows three different soil classes. These are highly compacted (8\8 per cent), slightly compacted (1\7 per cent), and almost non‐compacted or natural (89\5 per cent). Soil compaction in Al‐Salmi area causes adverse changes in soil physical properties, e.g. infiltration rate, bulk density and soil strength. The infiltration capacity of the compacted soils has decreased by 18\46 to 91\96 per cent in comparison with non‐compacted soils. The bulk density for the compacted soil varies between 1\6 and 1\7 g cm⁻³, whereas it varies between 1\2 and 1\35 g cm⁻³ in the non‐compacted soils, that is an increased of 29\97 per cent. In some sites, the physical properties show small or no difference between compacted and natural soils due to the effect of soil sealing (crustation). Copyright © 2000 John Wiley & Sons, Ltd.     

基于均匀试验的多孔混凝土的配合比研究

根据多孔混凝土的结构特点,结合多孔混凝土应用于水利护坡工程的要求,最佳配合比设计应考虑到多孔混凝土的抗压强度和孔隙率,以强度和孔隙率为目标函数,制定了均匀试验设计方法,系统研究了水灰比、骨灰比、用水量、骨料粒径对这两项指标的影响,并采用逐步回归分析法建立强度和孔隙率与各因素的数学回归模型,从而为多孔混凝土配合比设计提供分析方法。     

排土场土体裂缝区植被根系及抗剪强度分布特征

为揭示排土场土体裂缝区植物根系和抗剪强度分布特征,采用根钻法、WinRHIZO根系分析系统和直剪仪研究了0—60 cm土层植物根系、黏聚力和内摩擦角随土层深度的变化规律。结果表明:3个样地根系特征参数不同,随土层深度增加而减小,主要分布在0—20 cm土层,根密度和根重密度为88.81～303.03个/10³cm³,0.15～2.69 mg/cm³。根系以径级d≤0.1 mm和0.1 mm相似文献   

重庆缙云山典型植被原状土抗剪强度的灰色关联度分析与评价

采用SDJ-1型三速电动直剪仪对重庆缙云山5种典型植被的原状土抗剪强度进行室内测定，得出其抗剪强度变化规律，通过运用灰色关联法对其影响因子和对5种典型植被进行分析，结果表明：所选取的影响因子对黏聚力C的影响大小依次为：干密度〉小于0．001mm黏粒含量〉不均匀系数Cu〉根密度〉天然含水率〉有机质含量；影响因子对内摩擦角ψ的影响大小依次为：不均匀系数Cu〉小于0．001mm黏粒含量〉天然含水率〉干密度〉有机质含量〉根密度；5种典型植被对土壤抗剪强度影响最大为楠竹林，平权灰色关联度为0．851，最小为灌木林，平权灰色关联度为0．711，说明楠竹林土壤在自然条件下具有较大的抗剪强度。     

Tillage and straw management for modifying physical properties of a subarctic soil

Conservation tillage practices are intended to minimize soil erosion. Yet little is known concerning changes in physical properties of subarctic soils subject to tillage practices. This study ascertained whether physical properties of a newly cleared subarctic soil are altered after 7 years of continuous barley (Hordeum vulgare L.) using different tillage and straw management strategies. Tillage and straw treatments were established in 1983 near Delta Junction, Alaska, and consisted of conventional fall and spring disk, fall chisel plow, spring disk, and no-tillage. Tillage plots were split by straw management practices, which included straw and stubble, stubble only, and no straw or stubble. Soil samples were collected from the upper 0.15 m of the profile in the spring of 1990 to assess water content, bulk density, saturated hydraulic conductivity, dry aggregate and mechanical stability, penetration resistance, water retention, and particle size distribution. Percent non-erodible aggregates, mechanical stability, and penetration resistance were greater for no-tillage compared to conventional tillage, chisel plow, and spring disk. No-tillage soils were also typically wetter, denser, and had a greater hydraulic conductivity. The spring disk treatment was least susceptible to erosion and also conserved soil water compared with chisel plow. Straw maintained on the surface conserved water and promoted soil stability.     

L型构件双圆棒榫节点抗弯强度模型及其数值模拟

为解决现有圆棒榫节点抗弯强度研究中试验偶然性的问题,采用有限元法,建立L型构件双圆棒榫节点抗弯强度模型,进行数值模拟,并通过相应的试验对模拟结果进行了验证。结果表明:1)所建立的有限元模型可用于实木榫接合家具设计中的抗弯强度预测,不同直径下有限元分析结果与试验结果平均误差均<15%,且圆棒榫变形情况与试验结果相符;2)双圆棒榫接合构件抗弯节点主要破坏形式为榫损伤,抗弯强度随直径增加而增加,但增幅减小;3)直径为10 mm的双圆棒榫可用于椅子腿部与望板接合部位,直径为8 mm的双圆棒榫可用于椅子腿与扶手连接处,性能满足GB 103547所规定的要求,直径为6 mm的双圆棒榫不适用于椅子连接。     

大麦拔节孕穗肥施用时间探讨

通过分期施肥的方法 ,从分析大麦经济产量和生物产量结果、协调穗粒重三因素的作用以及与茎杆强度的关系 ,探索拔节孕穗肥最佳施用时间 ,以达到增产增收的目的。     

硅烷处理对Henequen纤维／PHBV树脂可生物降解复合材料界面粘结性能的影响

本文通过对Henequen纤维表面进行硅烷化改性，使得纤维与树脂间存在化学键合，提高了Henequen纤维与聚羟基丁酸与戍酸酯（PHBV）树脂复合材料界面剪切强度。Henequen纤维/PHBV复合材料界面剪切强度的大小用微粘结法（Microbond)测试，结果表明纤维经硅烷处理后可使界面剪切强度从未处理情况下的5.05Mpa提高6.34Mpa。     

对国产刨花板用单张浸胶纸贴面基板的评论

用单张浸胶纸贴面基材的刨花板,其性能要求与国定标准GB4896-4905-85有所不同。最重要的是需要缩小未砂光板的厚度偏差,从国内生产装备条件分析,可达到±0.3mm。表面必须用细刨花,不宜用尺寸过细的粉尘挂面。基板密度不超出0.65—0.73g/cm~3。从现有的商品板分析,各项强度指标尚可适当降低,以节省胶料。规模为3万m~3/年及5万m~3/年的刨花板厂按以上要求生产优质基板是可行的。