Soft subgrades’ stabilization by using various fly ashes

This publication presents the results of research involving different types of self-cementing fly ashes (without any other activators) for the stabilization of four different types of soft subgrades from various road sites in Wisconsin, USA. The strength approaches were applied to estimate the optimum mixture design and to determine the thickness of the stabilized layer. The stabilized soil samples were prepared by mixing fly ash at different contents at varying water contents. The performance of fly ash stabilized subbase depends both on the specific source of fly ash and the engineering properties of soils. It is suggested that the performance analysis of fly ash should be based upon the laboratory tests such as index properties, compaction, unconfined compressive strength and CBR tests of a specific site. This is suggested rather than using the study of the physical properties and chemical composition of fly ash and soil. As disclosed in the literature, the strength gain due to stabilization depends mainly upon three factors; ash content, molding water content and compaction delay. The samples were subjected to unconfined compression strength and California bearing ratio (CBR) tests after 7 days curing time to develop water content–strength relationship. To evaluate the impact of compaction delay that commonly occurs in the field during construction, the sets of samples were compacted 2 h later after mixing with water. The unconfined compression strength and CBR tests were performed and used to determine the thickness of the stabilized layer in pavement design. All of these factors were taken into account throughout this research.     

Nb、Ti低合金高强度冷轧薄板退火工艺对机械性能的影响

采用硬度法测得Nb、Ti低合金高强度冷轧薄板的再结晶温度为 6 0 0℃。再结晶温度以下退火时 ,钢的屈服强度随温度和时间的增加而降低 ,延伸率则增大 ;再结晶温度以上退火时 ,钢的屈服强度及延伸率变化不明显。实验提出合理选择热轧钢坯的强度 ,可避免不必要地增大冷轧机的负荷。     

简易升降类机械式停车设备安全隐患探析

随着人们生活水平的提高,单个家庭购买多部汽车的情况在逐年增加,停车位一位难求的矛盾比较突出。住宅小区家庭用户购买的单个平面停车位向立体2个停车位拓展情况成为趋势。本文从防载车板坠落装置设置、同步检测装置、载车板升降过程中视线盲区三个方面分析其安全隐患,并有针对性地提出一些建议,旨在减少简易升降类机械式停车设备的安全隐患提供有益帮助。     

海洋污损硅藻附着强度的定量测定

以海洋底栖硅藻新月菱形藻MMDL533作为模型污损物种,利用显微镜-图像分析软件、平行平板流动装置测定了其在羟基化玻璃表面及改性玻璃上的附着性质。研究表明,环境温度为20℃时,新月菱形藻MMDL533在羟基化玻璃表面的附着量最大,在1 h的接触时间后达到87±9/mm2;同时,其附着量随着接触时间延长而变大,并在3 h后达到一个较为稳定的值(110±15/mm2左右);当用水流冲刷后细胞的移除率来表征细胞在特定表面的附着强度时,新月菱形藻MMDL533的附着强度随着表面接触角逐渐增大,并在80°左右达到最大值,然后呈下降趋势。     

河道淤泥的轻质化处理及其工程性质

基于河道淤泥综合有效利用的目的,利用其高含水的特征,采用气泡混合轻质化技术对河道淤泥进行轻质化处理。通过室内试验的方法,考察和评价了以河道淤泥为原料土的气泡混合轻质土的基本工程性质,包括它的强度特性、变形特性、渗透性及耐久性能等。研究结果显示,经气泡混合轻质化处理的河道淤泥,具备一般填土的强度与刚度特性,其品质与施工性与固化材料的掺入量有密切的关系,固化后的轻质土具有良好的防渗透能力,但在循环干湿作用下易发生品质劣化现象。研究结果可以作为河道淤泥工程应用的基本依据及质量控制指标,同时也为进一步开发研究建立一定的基础。     

Effects of operational factors on soluble microbial products in a carrier anaerobic baffled reactor treating dilute wastewater

The effects of feed strength,hydraulic residence time(HRT),and operational temperatures on soluble microbial product(SMP) production were investigated,to gain insights into the production mechanism.A carrier anaerobic batfled reactor (CABR) treating dilute wastewater was operated under a wide range of operational conditions,namely,feed strengths of 300-600 mg/L,HRTs of 9-18 h,and temperatures of 10-28℃.Generally, SMP production increased with increasing feed strength and decreasing temperature.At high temperature (28℃),SMP production increased with decreasing HRT. As the temperature Was decreased to 18 and 10℃.the SMP production was at its peak for 12 h HRT Therefore,temperature could be an important determinant of SMP production along with HRT. A higher SMP to soluble chemical oxygen demand (SCOD) ratio Was found at high temperature and long HRT because of complete volatile fatty acid degradation.SMP accounted for 50%-75% of the SCOD in the last chamber of the CABR.As a secondary metabolite.some SMP could be consumed at lower feed strength.     

Breeding skylarks (Alauda arvensis) on organic and conventional arable farms in The Netherlands

The aim of this study was to analyse the effects of differences in cropping pattern between organic and conventional arable farms on the breeding activity of skylarks and to assess the effects of arable crop management on skylark nest survival. Skylark nest density was seven times higher on organic farms than on conventional farms (0.63 vs. 0.09 nest per 10 ha). Skylarks showed a strong preference for spring cereals, lucerne and grass leys, all of which were mainly or exclusively grown on organic farms. On organic farms nests were initiated during the entire breeding season, but on conventional farms no nesting activity was found during the peak of the season (early May to early June). On organic farms 27% of all nests was successful. Increasing the availability of suitable breeding habitat during the peak of the breeding season on conventional farms might provide one means of enhancing breeding skylark populations. On organic farms, crop management should focus on reducing nest loss due to farming operations.     

基于清单分析的农业面源污染源强计算方法

为了计算农业面源污染的源强,基于清单分析的思想,建立了农业面源污染清单分析表、农业面源污染源强的计算公式及其影响参数值的确定方法,最终形成了农业面源污染源强计算的清单分析方法体系。采用士述方法,对江苏省常熟市农业面源污染源强的计算进行了实例研究,表明该方法是可行的。     

湿喷混凝土支护强度影响规律探究及改进*

为探究普朗铜矿湿喷混凝土技术应用中出现的喷层强度低、易开裂等问题原因,针对水灰比、养护温度2个因素对湿喷混凝土强度发展规律展开研究,采用扫描电子显微镜（SEM）观察湿喷混凝土的微观形貌、EDS和XRD进行物相分析。结果表明:温度是影响湿喷混凝土强度增长关键因素;水灰比越大,硬化水泥石浆体内孔隙越多,混凝土强度越低;温度和水灰比通过影响水化反应造成界面过渡区不同程度微缺陷,是影响混凝土强度根本原因。通过提高养护温度、优化配比及改进施工工艺,改进后喷层28 d强度提高约30%,生产效率提高约8%。     

分区协同开采下矿柱力学响应与稳定性分析*

为解决某钒铁矿经多年开采后,由于钒铁矿矿区赋存条件变化导致开采相互制约、资源利用率低、矿柱积压矿量大以及井下采空区隐患大等问题,制定“保钒采铁、分区协同”的开采方案。通过矿柱强度理论对矿柱的强度和承受载荷进行计算,进而通过矿柱安全系数来判断矿柱的稳定性。通过FLAC3D软件对东、西区铁矿体进行数值模拟研究,通过对开挖后的位移云图、应力云图以及塑性区分布图来分析矿柱的稳定性。研究结果表明:针对某钒铁矿东、西区提出的嗣后膏体微胶结充填法及中区提出的分段空场法转分段崩落采矿法可提高矿柱的稳定性。