原状黄土冻融过程抗剪强度劣化机理试验分析

通过对西安Q₃原状黄土在封闭系统冻融作用下的电镜扫描和直剪试验,研究了冻融作用对原状黄土微观结构和强度的影响。试验表明：冻融过程中原状黄土微观结构发生显著变化,大颗粒集粒数量明显减少,小粒径土颗粒所占比重增加,孔隙面积比增加。进一步基于损伤力学理论,得到微观结构冻融损伤度随冻融次数增加呈指数增加趋势,反映出冻融作用一定程度上破坏黄土体的结构强度,但多次冻融后黄土体结构强度趋于稳定的残余强度。冻融过程土样表面结构发生破坏,且含水率越高,土体表面特征破坏越严重。粘聚力随冻融次数增加呈指数衰减趋势,且含水率越高,粘聚力衰减幅值和速率越小;粘聚力随含水率增加表现出线性衰减特征,且冻融后粘聚力与含水率的变化规律近似重合;内摩擦角无明显规律性变化。粘聚强度冻融损伤系数随冻融次数增加呈指数增加趋势,随含水率升高有增大趋势。基于试验数据规律性,进一步提出了原状黄土粘聚强度劣化模型,该模型经试验验证可较好描述原状黄土粘聚强度劣化规律。     

Influences on Engineering Properties of AS Firming Agent Modified Soil by Freeze-thaw Cycles

To study the freeze-thaw durability of Aught-Set(AS) firming agent modified soil, a series of triaxial tests were conducted. The mutual relationships between stress-strain relationship, static strength, dynamic modulus and critical dynamic stress of AS firming agent modified soil and curing time, freeze-thaw cycles, cooling temperature were deeply analyzed. The results show that the unconfined compressive strength of 7 d is 75% than that of 28 d. The stress-strain curves of AS firming-agent modified soil are strain-softening and in brittle failure shape. The static strength, critical dynamic stress and resilient modulus decrease in exponential form with the increase of freeze-thaw cycles, and after 6 cycles of freezing and thawing, the trend is stable. Under the same dynamic stress, the cumulative plastic strain of samples develop from stable state to failure because of freezing and thawing. After many times of freeze-thaw cycles, the lower the negative temperature, the little influence on the mechanic properties.     

老化处理对2种披碱草属牧草种子生理生化的影响

采用高温高湿(42℃,RH 100%)人工老化法处理加拿大披碱草和老芒麦种子,并对不同老化时间种子进行发芽指标、电导率、脱氢酶活性、酸性磷酸酯酶活性和丙二醛含量的测定。结果表明:在老化处理过程中,加拿大披碱草种子发芽指标在老化初期先呈缓慢上升趋势,随老化时间延长,呈现出下降趋势,老芒麦呈现下降趋势;在两种牧草种子老化过程中,电导率升高;脱氢酶和酸性磷酸酯酶活性下降。脱氢酶和酸性磷酸酯酶都可以用来衡量加拿大披碱草种子活力;而丙二醛含量不适合用于评价本材料种子活力。     

季节性冻融期不同地下水位埋深下土壤温度变化特征

土壤温度是土壤热状况的综合表征指标,影响土壤养分分布和冬春季节作物生长发育。以山西省水文水资源勘测局太谷均衡实验站为试验基地,对冻融期4种不同地下水位埋深下的土壤温度进行了分析研究。结果表明：在地下水浅埋区,冻融期地温的变化滞后气温变化,且滞后时间随土壤深度的增加而增大。12月初-2月下旬,地下水位为1．0m埋深的土壤温度较高;消融期地下水位为1．5m埋深下的土壤温度迅速回升。而0．5m埋深下的土壤温度较低且回升较慢;同一地下水埋深下,随着土壤深度的增加。剖面温度增高。50cm深度之下的土壤温度受地下水位埋深的影响较弱。研究成果可为冬春作物播种、预防冻害提供参考依据。     

新疆石河子冻土特征及冻土融化期地温、冻土深度预报研究

为了确保春季播种安全,有必要开展播种期地温的监测和冻土融化深度预报业务。利用新疆农八师冻土气象观测资料,运用相关系数和线性回归方法,分析冻土特征及融化过程中地温变化、深度变化规律,建立春季冻土融化预报模型。结果表明,新疆农八师垦区稳定冻土期在11月中旬至翌年3月下旬,冻土最大深度呈逐年变浅趋势,倾向率为-5.4 cm/10 a;冻土结冻日期推后,倾向率为2.0 d/10 a;冻土化通日期提前,倾向率为-1.5 d/10 a。冻土融化期在3月中旬至4月上旬,冻土融化速率在3.1~4.0 cm/d之间。春季地温与平均气温、冻土融化深度与正积温具有显著的正相关,以此建立了相应的预报模型。10 cm地温预报模型历史回代准确率在96%以上,冻土融化深度预报模型历史回代准确率在94%以上。通过模型可以开展春季地温和土壤融化预报业务。     

Experimental Study on the Extended Length of Negative Reinforcement Cut-in Phases in Continuous Beams

In this paper through the static loading tests of 6 inflexion zones and 2 cantilever zones in full-size constrained R/C beams, the stress performance in rebars cut-in-phases and subjected to negative moment is studied. The stress properties of extended length of rebars with different shear-span ratiosare analysed on basis of the full measurement of strain distributions combined with the investigation on state and regularity of the diagonal cracks development and series of new knowledge are obtained. It is found that current Concrete Design Code provisions on the extended length are inadequate for the high shear-span ratio and superfluous for the low shear-span ratio. The theoretical and experimental foundations are provided for determining proper value of extended length for rebars cut-in-phases.     

低温胁迫对棉花种子萌发的影响

为了研究低温胁迫对棉花种子萌发特性的影响,以新陆中88为试验材料,采用纸培和砂培的方式进行种子萌发试验,将棉花种子的发芽温度设置为5℃、10℃和15℃不同的低温,低温持续时间分别为1d、2d、3d、4d、5d.结果表明,在同一温度下低温持续时间对种子发芽率、发芽势、幼苗高度、主根长度、叶面积、电导率均有所影响,持续时间...     

Deformation Feature of the Particle Improved Roadbed of Qinghai-Tibetan Railway

The design idea and the spot experimental scheme of the particle improved roadbed are analysed in detail and deformed law with time of the particle improved roadbed in the cycle of freezing and thawing. The results indicate that the deformation of the particle improved roadbed presents the corresponding frost - heave deformation with the cycle of freezing and thawing. As compared with the ventilated embankment, the particle improved roadbed can, to some extent, shorten the freezing period and ease the frost-heave deformation.     

Meso-scale numerical investigation on the crack process of concrete cover induced by rebar non-uniform corrosion

Concrete cover cracking induced by corrosion of steel reinforcement is a major influencing factor for durability and serviceability of reinforced concrete structures. In order to investigate the cracking process of concrete cover induced by rebar corrosion, the heterogeneity of concrete meso-structure and non-uniformity of rebar corrosion are accounted for. The undamaged concrete is assumed to be a three-phase composite material composed of aggregate, mortar matrix and the interfacial transition zone (ITZ). And a concrete random aggregate structure is established for the study on the mechanical behavior of the non-uniform radial corrosion expansion. In the present simulations, non-uniform radial displacement is adopted to simulate the non-uniform corrosion of the rebar; the plasticity damaged model is used to describe the mechanical behavior of the mortar matrix and the ITZ, and the aggregate is assumed to be elastic. The cracking of concrete cover due to the non-uniform corrosion of the middle located rebar is numerically simulated. The comparison of the analysis and the test result on failure pattern of cover concrete shows fairly good agreement. And then the failure patterns under uniform corrosion and non-uniform corrosion obtained from the macro-scale homogeneous model and the meso-scale heterogeneous model are compared. Furthermore, the influences of concrete cover thickness and rebar diameter on the failure pattern of concrete cover, the expansive pressure and the corrosion rate of the rebar when cover concrete cracks are investigated.     

增温和施氮对小兴安岭叶凋落物分解的影响

为研究小兴安岭叶凋落物对温度升高、氮沉降及其交互作用的响应。试验采用空间移位方法,进行施氮(LN)、增温(WT)、施氮增温(WLN)和对照(CK)4种处理。结果表明：（1）氮沉降对叶凋落物分解的作用表现为先抑制后逐渐促进,在第1年冻融期后抑制显著(P<0.05);（2）温度升高情况下,第1年生长季较对照相比显著减缓了凋落叶分解(13.8%),显著加快了第2年生长季凋落叶的分解(9.4%);（3）施氮增温共同驱动下凋落物分解情况与增温处理一致,均表现为先抑制后促进;（4）各处理凋落物质量损失率与元素释放率较对照相比皆表现为先抑制后促进,不同处理的叶凋落物质量损失率为LN(55.2%)>WT(54.4%)>WLN(53.4%)>CK(53.2%)。本研究表明：施氮、增温及交互作用对叶凋落物分解均表现为初期抑制、然后加速叶凋落物的分解,与长白山相比,小兴安岭叶凋落物分解对施氮处理的响应更加敏感。     

果蔬制品冻藏技术研究进展

冻藏技术是一种被国际上公认为最常用、最安全、最高效的储运技术.冻藏可以通过降低组织中的水分活性,抑制微生物的生长,减少酶的活性,从而达到延长储藏期的效果.果蔬组织普遍含水量较高,在冷冻过程中比动物组织更容易形成冰晶,使果蔬在冻融后出现褐变、汁液流失、软化等品质劣变.目前果蔬冻藏相较于保鲜技术还不是一种主要的果蔬贮藏方式,但该技术发展前景良好.本文从果蔬的冻藏技术、速冻技术、果蔬脱水冻藏技术及玻璃态贮藏四方面综述果蔬冻藏的研究进展.     

提高西门塔尔牛冷冻精液使用效果的研究

为提高西门塔尔牛冷冻精液的使用效果,从筛选稀释液配方、选择最佳解冻温度与解冻后保存温度三个方面进行了研究。实验结果表明：（1）通过比较三种冷冻精液保存稀释液对冷冻后精子活力的影响,表明稀释液Ⅲ和稀释液Ⅱ的保存效果均极显著优于稀释液Ⅰ的保存效果（P<0.01）,稀释液Ⅲ与稀释液Ⅱ间的保存效果差异不显著（P>0.05）（2）将牛细管冻精在不同温度、不同时间下进行解冻,解冻后精子活率随解冻温度升高（40℃~65℃）而升高,但高温下（80℃）解冻精子活率低于解冻温度为（40℃~65℃）（3）在两个温度范围进行精液解冻后保存试验,结果以（0℃~5℃）范围解冻后保存效果较好。     

工业木质素包膜缓释尿素释放规律的研究

为了探明工业木质素包膜缓释肥料的养分释放规律,以及温度、pH和后熟期对于包膜尿素养分释放的影响,进行了一系列的试验。实验结果表明：包膜尿素养分释放曲线呈“S”型,28天养分释放率达到73.77%,养分微分溶出率为1.83%,理论释放时间为50.25天。当温度对于养分的释放影响是十分显著的。当培养温度由25℃提高到40℃时,养分的初期溶出率由8.03%提升到16.24%,微分溶出率由1.83%变为1.88%,理论养分释放期由51.25天缩短至45.55天。H+和OH-的存在均会促进养分的释放。当室温放置时间为30天内时,肥料的缓释性能是最佳的。     

Deterioration Model and Reliability Analysis on Concrete Material at Stress States

According to the analysis of existing test data, the stress influence coefficient and water-cement ratio influence coefficient in the existing concrete carbonation depth forecasting models are modified and improved. Based on the reliability analysis, the rule of deterioration life is presented. The analysis shows that the rate of carbonation of concrete is accelerated or restricted at the status of tensile or compressive stress, respectively. Especially with the increase of the level of tensile stress, the carbonation rate of concrete will become faster and faster. According to the results of reliability analysis, the relation between probability and reliability of the concrete deterioration is one-to-one corresponsive, meanwhile, the concrete cover thicknesses and stress levels have great influences on the durability life of concrete structures. And with the same reliability, the time of deterioration of concrete decreases with a higher stress levels and a less cover thickness.     

贮藏温度对甜高粱秸秆糖分含量的影响

研究冷冻（-18℃）、冷藏（5℃）、室温（20℃）等3种不同贮藏温度下甜高粱秸秆的糖分和水分含量的变化规律,讨论贮藏温度对甜高粱秸秆贮藏效果的影响。结果表明：冷冻贮藏水分变化相对平稳,室温下秸秆水分剧烈降低;3种不同温度下秸秆总糖含量之间的差异达极显著水平,冷冻贮藏下各时期总糖含量的变化差异不显著,冷藏和室温下总糖含量的变化差异极显著;冷冻条件对贮藏前期茎秆还原糖含量的影响不显著,秸秆还原糖含量的变化曲线平稳;蔗糖含量在整个贮藏期内总的变化均呈降低的趋势,低温处理的茎秆蔗糖含量降低趋势较慢,蔗糖含量明显高于同期的室温贮藏秸秆的蔗糖含量。糖含量随着处理时间的延长,变化不显著者可认为贮藏效果较好,变化显著者可认为糖代谢活动活跃而影响糖含量的变化,所以3种方法中冷冻贮藏方法较为合适。甜高粱茎秆在生产加工过程中如果条件允许以冷冻的方式进行贮藏。     

钢筋非均匀锈蚀引起混凝土保护层内裂分析

根据自然环境下保护层锈胀开裂前的钢筋锈蚀形态,将锈蚀层简化为半椭圆状的非均匀分布,从而建立了钢筋非均匀锈蚀理论模型。经过求解得到了混凝土中锈胀应力理论解,并与有限元计算结果对比,验证了理论解的精确性。根据理论解可知最大周向应力在水平轴上,因此锈蚀层的发展会首先引起保护层内部水平裂纹的产生。增加钢筋直径可有效减低锈胀应力,提高结构抗锈裂的能力。与均匀锈蚀理论模型对比结果表明：均匀锈蚀要远小于非均匀锈蚀条件下的临界锈蚀层厚度,均匀锈蚀的计算结果偏于保守。因此,对锈胀问题进行理论分析时,应采用更接近真实锈蚀形态的非均匀锈蚀模型。     

Theoretical Contour Line of Reinforcement Bar of Non uniform Corrosion

Most of the previous studies on corrosion of the steel bar in reinforced concrete structures is based on the assumption that the bar is uniformly corroded. The actual measurement in projects proved that most of the reinforcement bar is in non uniform corrosion state. Based on electrochemical principles of metal corrosion and combined with the real corrosion course of the bar in concrete structures, a theoretical model of the contour line of reinforcement bar due to non uniform corrosion is established, through deducing the speed of corrosion and theoretical corrosion penetration and volume changes due to corrosion of reinforcement in general air at different position and different time. At the same time, the model is verified with the results from relative references and measured data.     

索承式桥梁吊索钢丝腐蚀疲劳寿命评估

根据吊索镀锌钢丝腐蚀疲劳破坏特点,把镀锌钢丝腐蚀疲劳纹形成和扩展过程分解成镀锌层腐蚀失效、蚀坑萌生、蚀坑形成、短裂纹扩展、长裂纹扩展和断裂破坏等阶段,建立各阶段时间表达式,得到镀锌钢丝疲劳寿命表达式,提出基于断裂力学的吊索钢丝腐蚀疲劳寿命评估研究结果方法。通过算例分析复杂运营条件下腐蚀环境和应力幅等因素对吊索钢丝腐蚀疲劳寿命的影响,研究结果表明：吊索钢丝腐蚀疲劳寿命主要由钢丝镀锌层腐蚀、蚀坑发展和短裂纹扩展等3个阶段组成,为了准确地评估吊索腐蚀疲劳寿命,需要掌握大桥的运营环境和交通荷载。     

枇杷花粉干冻法超低温保存研究

采用花粉干冻法对枇杷花粉超低温保存进行了研究。将枇杷盛花期的花粉干燥后直接液氮超低温保存,取出后观察其萌发率。结果表明：花粉的含水量是决定枇杷花粉超低温保存成败的关键因素。脱水至30％左右的含水量能够保证超低温保存花粉的生活力;解冻温度及方式对超低温保存后花粉的生活力没有明显的影响。     

Three-dimensional Random Damage Prediction Model of Concrete Caused by Freeze-thaw

In order to effectively assess the damage of concrete in freeze-thaw condition, prediction model for concrete frost damage is presented based on damage mechanical theory and the experimental test. The degeneration of tension strength of air-entraining concrete is tested after freezing and thawing. Provided with the fact that the degeneration of concrete is an interior damage evolving process, freezing and thawing damage accumulation of concrete is analyzed based on the discrete grid with probability of stochastic method. And Three-dimensional multi-parameters Weibull distribution model about concrete damage evolutions is presented. Parameters are estimated based on gradient method, and the mathematical model is verified according to the tested data. Corresponding algorithm is designed and programming is completed by C + + programming language to establish concrete durability prediction model under freeze-thaw conditions. It is indicated that the damage of concrete develops in nonlinear way as the freezing and thawing increases.