Development of acceptance specifications for tropical gravel paving materials

The ideal standard grading specification for gravels was meant to ensure high density and stability, and specifications on maximum limits of content of fines, liquid limit and plasticity index were meant to control the magnitude of swell of materials in the pavement structure.Experience in Ghana and elsewhere in the tropics has shown that specifications based only on these index properties may be misleading. For example, the strength criterion based upon minimum soaked CBR of 80% for separating sub-base and base gravel materials has been found to be more critical and makes it possible to modify the allowable maximum fines content, liquid limit and plasticity index for the residual gravels studied.Material selection, field compaction (construction) control and long-term field performance studies on two trunk roads were analysed.Limiting values of index properties for separating these gravels into sub-base and base course materials for pavement construction in a moist sub-humid climatic environment was proposed. For example, the maximum fines content, liquid limit and plasticity index for accepting these gravels for base course construction were increased from 10, 25 and 6% to 12.5, 37.5 and 10%, respectively.The importance of using the products of fines content and plasticity parameters for selecting these gravels was also established.     

碎石桩复合地基试验及固结分析

碎石桩复合地基在处理软弱地基土中得到相当广泛的应用。为了更好地掌握其规律性,本文针对某电厂碎石桩复合地基现场试验和桩身应力测试成果,进行了分析和总结,得出了饱和粘性土地基中桩土应力比与外荷载大小有关。其形状为上凸抛物线型,大小一般在3~6之间;静载荷试验下桩身应力分布特点与天然地基应力分布近似,影响深度为载荷板宽度的2~3倍。通过用有限元法模拟该复合地基固结性状,得知碎石桩不仅大大加快粘性土复合地基固结,而且减小了工后沉降的影响。     

小截面静压预制短桩的桩底注浆试验研究

通过对桩端置于含泥圆砾卵石层超短静压预制桩桩底注浆及注浆前后静载试验,分析了桩竖向极限承载力的提高机理。试验表明,桩底注浆可较大幅度地提高以砂卵石为持力层的静压预制桩的竖向承载力。     

偏高岭土协同石灰钝化红黏土水敏性的机制

红黏土水敏性强,添加石灰等碱性材料处治后,能获得即刻的改良效果,但由于红黏土呈弱酸性,石灰改良后其长期性能会衰减。为提高石灰稳定红黏土（简称La+L）的长期性能,添加偏高岭土（4%）协同石灰（5%）稳定红黏土（简称La+L+MK）,改善其水敏性和酸?碱互损作用。制备8种初始含水率的压实试样（初始孔隙比相同）,养护到预定时间后开展无侧限抗压强度试验,同时,测定试样的钙离子浓度、电导率和pH值。结果表明：初始含水率为26%左右时,改良土的无侧限抗压强度最高,初始含水率偏高或偏低都不利于改良土的强度增长。究其原因,试样偏干时,缺少水分,石灰水化不充分,不能形成游离态钙离子,无法进行火山灰反应,颗粒之间无法形成胶结;试样偏湿时,火山灰反应形成的胶结强度不及过量水分引起的基质吸力丧失量。试样的钙离子浓度和电导率变化规律,证实了以上原因解释的猜想。当然,添加偏高岭土后,能够显著改善偏湿状态下的石灰土强度。即使浸水饱和后,相对石灰改良土,也能够保持较高的强度,充分证明偏高岭土能够有效降低石灰土水敏性,提高其耐久性。偏高岭土直接提供了大量硅、铝氧化物,且将土体pH值降到有利于硅、铝氧化物溶解的碱性范围,加速火山灰反应,缓减或抑制石灰?红黏土的互损作用。     

钻孔咬合桩施工质量控制

钻孔咬合桩既具挡土又具止水的双重作用,施工快捷,工艺简单,对环境干扰少,比较适合于城市地铁、隧道和大、中型基坑支护工程。结合南京火车站站前广场龙蟠路新建隧道工程,介绍了钻孔咬合桩的一般施工技术要求和主要控制措施。     

海岸带数字航空摄影质量控制与评价

随着机载POS系统和数字航空摄影技术应用于海岸带地形测量,水线曲折、水域面积广阔、滩涂陡缓不一、具有潮汐变化等多因素给海岸带航空摄影质量控制带来诸多问题.因此,为了得到优质的调查结果,需对获取的航空摄影资料进行质量评价.通过分析航空摄影作业过程及获取成果的类别,从中选取能够全面衡量航空摄影质量的指标元素,对这些元素加以预先控制以提高最终成果质量;基于专家经验法和数学统计法对各指标元素赋予权重,提出了全要素直接参与的加权法对航空摄影数据质量进行评价;归纳了在获取与处理过程中影响质量的各子元素间的相关性,可利用该特点在今后的作业中进行有针对性的改善或控制,达到提高成果精度的目的.对渤海海岸带航空摄影数据的评价结果显示,整体质量优秀,与实际的制图结果吻合,成果精度满足海岸带地质调查需求,质量控制和评价方法可行.     

A damage hypoplasticity constitutive model for cemented sand and gravel materials

Acta Geotechnica - A hypoplastic constitutive model is proposed to model the cementation-induced enhanced stiffness, strength and dilative behavior of cemented sand and gravel materials. The model...     

Investigations in Kenya and Malawi using as-dug laterite as bases for bituminous surfaced roads

Summary In Kenya 1974/5 and in Malawi 1984/5 trial sections of bituminous-surfaced low volume roads were constructed using as-dug laterite in place of stone or stabilized material as a base course.The laterite did not conform with any accepted specifications but performed equally well when compared with adjoining sections of road using stone or stabilized material as a base.The construction procedures employed are described. A period of 4–6 weeks between the compaction of the base and its surfacing is considered essential if the road is to perform satisfactorily. During this period it is exposed to the weather and traffic or to periodic watering and rolling. This treatment fills any cracks with dust or mud and closes them by the kneading action of rubber-tyred traffic. The bituminous surfacing is applied where the base has dried out to about half the optimum moisture content and is extended about 1.5 m beyond each edge of the carriageway.In 1984, $40000 US per km was saved in Malawi in this way, approximately 70% being in convertible currency without incurring additional maintenance or vehicle operating costs.     

现行磷矿地质勘查规范存在问题研究探讨

对现行磷矿地质勘查规范中存在的一些问题进行了研究探讨。主要讨论了勘查类型划分、工程间距的确定、资源量估算、共伴生矿产工业指标等问题。勘查类型的划分应允许有过渡类型;对差异很大的多矿体矿床应针对不同矿体分别确定勘查类型;勘查类型的确定应实行量化指标;勘查工程间距应按不同成因的矿床确定差异标准。各勘查阶段对各类资源量应确定合理的量化比例,并与现行矿业管理政策相统一;对鄂西地区有自然分层的硅酸盐型磷矿床类型中的富矿层资源量估算应调整为按自然分层圈定;对高镁磷矿石一般工业指标应做出调整;对共伴生矿产应根据当前回收利用技术水平制定共伴生矿产回收利用的量化指标。     

王宠佑对中国地质文献索引的贡献

王宠佑是中国早期学习地质学专业的留学生,近代第一批矿冶专家,他在推动中国地质矿产事业的同时,十分关注中国矿产和地质文献的整理和研究,编纂出版了《中国矿产资源与地质文献目录》、《中国矿产资源文献目录》等地质文献目录,促进了中国早期地质事业的发展。     

Robust geochemical indices for redox and weathering on a granitic laterite landscape in Central Uganda

Most geochemical studies of laterite formation have been based on detailed examinations of a small number of hopefully “representative” profiles. Due to spatial variability in bedrock composition and geomorphic processes that sort materials by size, density, and other properties, experimental designs developed for the geochemical analysis of single soil profiles are of limited use in landscape investigations. In this study of a laterite landscape on a granitic rock in Uganda, we used element concentrations from neutron activation analysis (NAA) to develop a suite of robust geochemical indices for landscape-scale analysis of weathering and oxidation-reduction (redox) processes in laterite formation. To capture K-feldspar weathering the K/Hf ratio served as a good proxy for feldspar/zircon mineral ratios while K/Na ratios indexed feldspar concentration to quartz. Using principal components analysis, we derived an index of Rare-Earth Elements (REE) leaching (relative to Th), and an index of Heavy to Light REE (HREE/LREE) fractionation. We used the Fe/Sc ratio to ascertain the absolute (redox) vs. relative (weathering) Fe accumulation in laterite formation—with absolute Fe accumulation also associated with lower Fe/As ratios. Mn-Ce-Ba nodules and concretions were identified by characteristically high Ce values—with individual Ce values as high as 5000 μg g⁻¹. The relatively large amounts of K-feldspar (K_avg is 4000 μg g⁻¹) and low degree of HREE/LREE fractionation suggest that this landscape is weathered less than generally assumed. The Fe- and Mn-derived indices highlight the important role of oxidation-reduction processes in iron accumulation. Overall, our findings suggest that the current ferricrete-mantled hilltops were formerly located on a lower, poorly drained part of the landscape.     

浅论城市建设工程测绘项目的质量管理与服务

城市的发展越来越重视工程建设的高质量,对于测绘的重视程度和精度要求也在不断的加强,城市测绘工作涉及面广,虽然测绘工程量不大,却节约成本、保证质量的重要一步。因此,本文作者结合实际工作经验,对城市小型工程测绘项目的管理和服务进行较详尽的阐述。     

关于修改完善钛砂矿地质勘探规范部分内容的建议

砂矿(金属矿产)地质勘查规范是2002年制订颁布的,在勘查工作及报告审查中发现:该规范有些地方不严不细,缺少明确统一标准,或者不具可操作性而导致混乱.所以有进一步修改完善的必要. 砂矿(金属矿产)地质勘查规范( DZ/T0208-2002 )适用于云南、广西的残坡积型钛砂矿勘查,本文结合上述地区钛砂矿的长期实践,谈谈规...     

弱胶结砂砾岩地层钻头研制及提速工具配套研究

针对弱胶结砂砾岩地层钻井过程中面临的PDC钻头崩齿、碎齿严重,钻头先期损坏使得单只进尺少,钻井成本高等技术难题,从弱胶结砂砾岩地层岩石力学特性分析、锥齿PDC钻头研制及提速工具配套等方面着手,研究形成了适合弱胶结砂砾岩地层钻井提速的锥齿微心PDC钻头;并通过选用恒扭矩工具配合该型钻头在胜利油田利567区块进行现场应用,取得了良好的效果,大大延长了钻头的使用寿命,起到了提高机械钻速和降低钻井成本的目的。     

粉喷桩加固软土地基的质量控制

结合潭邵高速公路软基处理工程实践,从施工工艺、施工控制和质量检测等方面阐述了水泥粉喷桩在软土地基处理中的质量控制要点:室内配方试验、工艺试桩、控制水泥材料的质量、施工过程控制、成桩检测.     

天水市城区砂砾石地基的变形特征和承载力分析

本文通过对天水市秦州、麦积两区砂砾石地基进行大量颗粒分析、动力触探、灌砂法试验及人工回填打入预制桩、人工挖孔灌注桩静载荷试验,并对其各项试验结果进行统计,系统地总结了天水城区砂砾石的分布特征、颗粒组成、物理力学性质;并通过粒径直方图统计分析阐明了藉河流域颗粒级配明显好于渭河流域,承载力特征值亦高于渭河流域的几个关键问题,并通过对工程实例的试验检测,对涉及的砂砾石地基的承载力特征值及变形模量,桩的极限端阻力标准值、极限侧阻力标准值应用实际问题进行了对比、讨论和分析,因此对工程质量的检测和设计应用有着重要意义,可供类似工程参考.     

路堤荷载作用下碎石桩复合地基桩土应力比计算及试验研究

深入分析了路堤等柔性荷载作用下碎石桩复合地基的工作机理,对路堤-碎石桩-桩间土系统进行合理简化,建立了桩土应力比计算模型,并给出关键参数的求解过程。基于最小势能原理,导得路堤荷载下碎石桩复合地基桩土应力比计算解析表达式,结合大型室内模型试验,通过对比试验过程中的全程监测数据,验证了理论解的正确性。探讨了各主要影响因素与桩土应力比之间的关系,结果表明：桩土模量比和置换率是应力比的主要影响因素,路堤高度与路堤材料的影响次之;当路堤高度较小时,随着高度增加,桩土应力比提高明显;但当路堤高度增大到一定值时,桩土应力比基本不变;增大填料剪切模量可略微增大应力比。     

The use of low-grade and unsound crushed rock aggregates in Ghana for construction

Summary Ghana and many developing countries have relied heavily, in the past, on hard granites and granitic gneisses for the production of rock aggregates and rock products for civil engineering works including the construction of roads and buildings. Experience in Ghana has shown however, that the quantity of crushed rock aggregates produced from hard rocks have proved insufficient for the needs of the country. This situation has called for engineering geological studies into the use of rock types and rock formations previously designated as low grade and unsound for the production of aggregates. The major objective of this study was to review the occurrences of non-conventional hard rocks and gravels such as quartzites, silicified sandstones, metagreywackes, dolomitic limestones and quartz gravels. This was followed by the application of appropriate standard specification tests to establish criteria for the selection and recommendation for the use of low grade and unsound rocks and gravels for various civil engineering projects in Ghana and other developing countries, especially those of the subregion with similar geological formations.