寒区渠基黏土热参数最优概率分布

为分析寒区渠基黏土热参数的随机分布特征及概率分布模型,以寒区渠基黏土的导热系数为样本,结合经典分布拟合法、多项式逼近法、最大熵法和正态信息扩散法,分别对寒区渠基黏土热参数的概率分布规律进行了研究。首先通过分析热参数的离散性,并比较概率分布曲线、拟合检验值和累计概率分布值,对不同方法描述热参数随机性的优劣进行了评价;然后,基于寒区渠基黏土热学参数对温度的敏感性,提出了一个可以达到理想拟合精度的寒区渠基黏土热参数概率推断的区间取值标准。研究结果表明：寒区渠基黏土的热参数具有随机变量的特征;正态信息扩散法可以描述热参数样本的随机波动性;在4种方法中,正态信息扩散法的拟合精度最高。使用3.5σ法,将[μ-3.5σ,μ+3.5σ]（μ为随机变量的均值,σ为标准差）作为概率函数推断时的取值区间,同时考虑偏度的影响,可使得累计概率值达到1.000 0的精度,能够较准确地推断热参数的概率分布函数。     

高围压下冻土强度弱化的机理分析

围压作用下,影响冻结砂土强度弱化的主要原因是孔隙冰的压融,矿物颗粒细化的微裂隙的发育。影响冻结粉质粘土强度弱化的主要原因是孔隙冰的压融和微裂隙的发育,这些过程是不独立存在的,而是共同影响,共同作用,从而导致了冻土强度的弱化。     

Alluvial soils as subgrade material: Laboratory and statistical evaluation

In India, rural roads are constantly being constructed. To ensure proper design of rural roads, it is desirable to have an appropriate selection of design parameters. The California bearing ratio (CBR) method of pavement design is the most commonly used method employed for the foundation design of rural roads. In the CBR method, the CBR value of the subgrade soil is critical in deciding the overall thickness of the pavement. Additionally, for good drainage, a typical specification for the pavement foundation design requires the value of permeability coefficient of the subgrade material to be specified. Thus, permeability and CBR constitute two important parameters in the design and assessment of long-term performance of the pavement. In this study, laboratory investigation has been carried out on a number of soil samples procured from a roadwork project site. Preliminary tests, such as index tests and particle size distribution tests, useful for soil classification, were followed by light compaction, CBR and variable head permeability tests. Further, observations from the laboratory investigation are statistically analysed to study correlations among various parameters. Because the predominant soil type found in the study area is alluvial, this study also highlights the suitability of alluvial soils as pavement subgrade material.     

Continuous determination of drying-path SWRC of fine-grained soils

Establishing the soil water retention curve, SWRC or the soil water characteristic curve, SWCC, is very useful for determination of unsaturated properties of soils. However, it has been observed that SWRC of a soil is not unique and depends on various factors such as the initial moisture content, density of soil, method of compaction, soil fabric and the path (drying or wetting) adopted for establishing it. In this context, many techniques and instruments have been employed by earlier researchers for determination of the SWRC of soils. However, these techniques entail weighing of the samples during prolonged testing, manually, and hence yield discrete data points. In this situation, AquaSorp® Isotherm Generator (manufactured by Decagon Devices Inc., USA) has been found to be quite useful for continuous determination of the drying-path SWRC of fine-grained soils. This device has been primarily employed for food products, powders and amorphous materials. Hence, demonstration of the utility and limitations of this device for SWRC determination of fine-grained soils becomes essential. With this in mind, extensive studies were conducted on commercially available soils (Kaolinite and Bentonite) by employing this device. In order to understand the influence of specimen specific parameters on the obtained SWRCs, the molding water content and thickness of the specimens were varied and the results have been evaluated critically. Details of the methodology adopted for these investigations, and the findings of the study are presented in this technical note. Based on a critical comparison of the results obtained from this device with those obtained from the dewpoint potentiameter, WP4®, the utility of this device for continuous determination of drying-path SWRC of the soils has also been demonstrated.     

长春市城市土壤中重金属元素的积累及其微生物特性研究

由于人为活动的影响,长春市城市土壤中重金属Cu、Zn、Pb、Cd已有了显著积累。在重金属的胁迫下,土壤微生物特征发生了明显变化,微生物代谢活动明显增强,但微生物生物量却有较大的降低。微生物生理生态参数土壤微生物量碳与总有机碳的比值(Cmic/Corg)和代谢商QCO2(微生物呼吸作用强度与微生物量碳的比值)变化异常。研究表明,微生物特性可作为城市土壤环境中重金属含量变异的有效指标。     

氯化钯作基体改进剂石墨炉原子吸收光谱法测定土壤中的铍

铍是一种对人体有害的金属元素,土壤中铍的测定目前尚无国家标准方法.本文采用盐酸-硝酸-氢氟酸体系微波消解、石墨炉原子吸收光谱法测定土壤样品中的铍,实验了钯、硝酸铝、硝酸镁、钙盐的增敏效果.结果表明,以氯化钯为基体改进剂,灰化温度和原子化温度分别提高到1100℃和2650℃,原子化峰形尖锐,背景吸收很小,提高了测定灵敏度;其他三种基体改进剂虽然也能提高测定灵敏度,但背景吸收较大.采用优化的实验条件,Fe、Mg、K、Na、Ca、Ti、Cu、Ba、Mn、Zn、Pb、Sr等共存元素对测定不产生干扰.铍的浓度在0 ～4.00 μg/L范围内线性良好,方法检出限为0.01 μg/g,精密度(RSD,n=6)为3.5％ ～6.7％,实际土壤样品的加标回收率为84.0％ ～ 113.0％,土壤国家标准物质的测定值在标准值的误差范围内.本法与萃取光度法、电感耦合等离子体发射光谱/质谱法相比,操作简便,分析成本较低.     

干旱区绿洲土壤共存重金属元素形态变化及生物有效性实验分析——以Cd、Zn、Ni元素为例

采用盆栽试验,初步研究了干旱区绿洲土壤—胡萝卜系统中镉、锌、镍3种重金属的形态变化特征及其生物有效性问题。结果表明:供试绿洲土壤原状土中,Cd、Zn、Ni均以稳定的残渣态形式存在,而处理土壤中重金属被钝化的量有限,Cd的存在形式主要以碳酸盐态为主,Zn、Ni则主要以铁锰氧化态为主;3种元素的活性大小依次为Cd>Ni>Zn。根据回归分析,元素Zn对胡萝卜块茎和茎叶吸收Zn量贡献最大的分别是Zn的碳酸盐结合态和铁锰氧化态;元素Ni对胡萝卜各部位吸收贡献最大的均为Ni的铁锰氧化态。     

非饱和土弹塑性模型参数的试验确定及有限元法

简要介绍广泛应用的非饱和土Alonso模型的原理与发展,并通过3组共7个试样的非饱和土三轴试验,得到模型的11个参数。在饱和土Cam本构关系的基础上,推导出一个基于非饱和土Alonso模型的应力-应变增量方程的计算公式,该方程与饱和土的本构方程形式相同。编制了能够考虑净应力和吸力二者对土体硬化规律影响的有限元程序,从而为非饱和土弹塑性计算提供一条途径,便于进一步应用于实际工程。     

桩在饱和土中水平振动的辐射阻尼简化算法

将适用于单相土－桩系统的Novak的平面应变假设和Gazetas的分象限假设推广到饱和土－桩系统中。通过简化后的微分方程推导了饱和土－桩系统辐射阻尼系数的解析解答。最后用算例说明了饱和土中两个压缩波的特性，比较了饱和土和单相土的单位桩长辐射阻尼系数，比较了简化算法和三维有限元方法求得的桩头幅射阻尼比，结果证明简化算法在一定条件下适用于计算层饱和土－桩系统的辐射阻尼。     

土的可恢复剪胀的一种解释

从土的各向异怀角度对土的可恢复剪胀现象进行了解释。基于各向异性情况下的土体弹性本构关系理论分析，认为土的可恢复剪胀现象可部分归因于土的各向异性引起的弹性剪胀。借助有关土体弹性参数实验结果，研究了应力诱导各迥异性对土体弹性剪胀的影响，结果表明：随土体应力诱导各向异性的增大，土体的弹性剪胀也增大。从土体弹性剪胀角度研究了土的卸荷体缩条件，认为土体卸荷体缩取决于加载应力路径的应力增量比，给出了土体出现卸荷体缩的区域。