Some properties of A sedimentary laterite soil as engineering construction material

A sedimentary laterite soil is examined for its suitability as a construction material by the consideration of its mineralogy and basic geotechnical properties as well as its consolidation and permeability in the compacted state. Three compaction energy levels are utilised. Mineralogically, the soil contains virtually nothing undesirable while its basic geotechnical properties are those generally ascribed to non-problematic soils. The compressibility of the soil varies from moderate to low depending on the energy of compaction. It is however impervious for all the compaction energy levels. The sedimentary laterite soil constitute a good engineering construction material as it has already been successfully used as base and sub-base material in road construction. Results obtained in this study show that this laterite soil is also suitable for use as fill materials in embankment and dam construction.     

The compressibility characteristics of a compacted laterite soil

Laterite soils occupy large parts of the tropical regions of the world. They are used, in the compacted state, as bases for roads and air-field pavements, as fills for foundations, embankments and earth dams. Although the response to load with decreasing void ratio (compressibility) is important under the conditions of use, it has not been the subject of considerable study. Engineering studies in laterite soils have been limited to classification, compaction characteristics and sometimes, shear strength. The compressibility characteristics of a compacted laterite soil from Paraiba State, North-East Brazil has been examined in the oedometer. The results indicate the presence of collapsible soil grains which comminute under load. The behaviour of soil with collapsible soil grains is described.     

The geotechnical properties of lateritic and non-lateritic soils of southeastern Nigeria and their evaluation for road construction

The soils within the entire length of the Port Harcourt—Enugu expressway consist of (1) concretionary laterite gravels (2) non-lateritic tropical sandy/clayey soils which are gravelly in some places and (3) silty to fat clays formed from shales. The particle size distribution and the plasticity of the majority of the soils indicate that by standard acceptance specifications they are unsuitable for base materials. Field compaction results revealed that the relative compaction of 95–100% can be easily achieved in the field using 10–12 ton vibratory rollers. Although the pavement materials used for the expressway are inferior under conventional standards, mostly isolated rather than widespread pavement failures have so far occurred. Such failures are presumed to be more related to poor field compaction rather than the inferior quality of the construction materials. Where the troublesome weathered shale forms the subgrade, severe pavement failure usually occurs.     

Change in the hydromechanical characteristics of embankment material due to compaction state conditions

In recent years, earthquakes and heavy rains have frequently caused soil embankments to collapse. In order to prevent the collapse of embankments, it is well known that sufficient compaction and drainage control are necessary. Although numerous research findings have described compacted soils, compaction management has been essentially based on simple parameters such as dry density, degree of saturation or air content. It is important for the construction of a stiff embankment that the effect of compaction condition on the mechanical properties and inherent anisotropy of compacted soil should be recognized in detail. In the present study, the relationships between the compaction condition and the mechanical properties obtained from laboratory tests using saturated specimens are presented. Specifically, undrained monotonic and cyclic shear strength, shear modulus, and permeability are reported. The arrangements of soil particles were also observed with a microscope. From the observation of fabric characteristics of soil particles, an inherent anisotropy of compacted soil is discussed. Furthermore, a conceptualization of the relationship between the fabric of soil particles and the mechanical characteristics for each compaction condition is suggested.     

掺砂红土的力学特性及掺砂机理研究

通过对不同掺砂比例的红土进行液塑限、击实、无侧限抗压强度、直剪和扫描电镜等试验的对比研究,明确了不同掺砂比例对红土的含水性、击实性、强度等力学特性以及微结构特征的影响.试验结果表明:红土掺砂后,可以显著降低红土的液塑限、塑性指数和最优含水率,提高最大干密度、无侧限抗压强度和抗剪强度.随着掺砂比例的增加,掺砂红土的液塑限...     

A new laboratory apparatus for studying dynamic compaction grouting into granular soils

As granular soils may be compressible or have inadequate strength, compaction is particularly useful when soils are subjected to dynamic loading or cyclic loading. A new laboratory apparatus for investigating dynamic compaction has been designed and fabricated. The basic principle of this new technique is to introduce vibrations during the expansion process in static compaction grouting. In these tests, the injection pressure, the excess pore water pressure, and the change in void ratio of the specimens are measured. The main focus is to investigate the development of the injection pressure, the void ratio, and the excess pore water pressure due to dynamic compaction and the subsequent consolidation of the soils. In addition, the relative density of the soils is used to evaluate the dynamic compaction efficiency. Scaled laboratory experiments are conducted to study the effect of this dynamic compaction frequency on compaction efficiency. The experimental results show that the change in void ratio in the dynamic compaction tests is about four times greater than that in the static compaction tests. Dynamic compaction frequency plays an important role in soil densification due to dynamic compaction.     

Microstructural investigation on laterite soils

Considerable researches have been carried out to demonstrate the importante of microstructure in the interpretation of engineering behaviour of soils. Instances where the investigations are on laterite soils are however scanty in literature. The microstructure of laterite soils obtained from Eastern Nigeria and North-East Brazil, have been examined with the aid of optical and scanning electron microscopes. Investigations reveal the development of the well-known concretionary structure in laterite as a stage by stage process involving the accumulation of sesquioxides. The sesquioxides are accumulated initially as amorphous implantations in the pore spaces, the crystallisation of which leads to bonding of soil elements and formation of concretionary structure. The nature of cementation in the concretionary structure determines the resistance to degradation of the soils grains. The resistance to degradation would in turn influence the engineering behaviour.     

江苏泗阳城区浅层粉土工程地质特性分析

根据研究区158个场地近千个浅层钻孔的试验成果,从沉积特性入手分析了研究区浅层粉土的成因类型与典型沉积组合剖面。通过室内试验成果的统计分析,研究了浅层粉土颗粒组成特征、化学矿物成份及其基本物理力学性质,同时,结合静探试验与荷载试验成果,分别建立了与主要物理力学性质指标的相关性经验方程。采用变水头试验与典型工程抽水试验、取土坑击实试验以及标准贯入试验分别对研究区浅层粉土的渗透性、击实性和振动液化性进行了分析,结果表明:研究区浅层粉土通过室内变水头试验与现场抽水试验得出的渗透性指标相差1~2个数量级,现场抽水试验更接近粉土的实际渗透性指标;研究区浅层粉土具有水稳定性差、不易压实的特点;研究区浅层粉土多为可液化土层,液化等级从轻微液化至严重液化,地域性特征明显。研究成果给泗阳城市规划建设提供了一定的借鉴作用,也为进一步深入研究本地区浅层粉土提供基础资料。     

Limestone ash waste as a substitute for lime in soil improvement for engineering construction

 A by-product of the manufacture of cement at Nkalagu, Nigeria, is the waste material comprising 70% CaO and 30% undecomposed CaCO₃, referred to as limestone ash. The potential of this waste as a substitute for lime in the improvement of the engineering properties of laterite soils for construction purposes has been assessed. The geotechnical properties of lateritic soils when untreated and when treated with varying percentages of limestone ash have been established, including particle size analyses, Atterberg limits, Proctor compaction, California bearing ratio (CBR) and shear strength. The results confirmed those obtained by other workers on the use of lime stabilisation and indicate that limestone ash may form a substitute for lime in soil improvement for engineering construction. Received: 14 November 1997 · Accepted: 16 August 1999     

木质素改良粉土热学与力学特性相关性试验研究

为揭示木质素改良粉土热学与力学特性随养护龄期的演化规律,通过击实试验、热阻系数测试、无侧限抗压强度试验、回弹模量试验、压汞试验和扫描电镜分析试验,探讨改良土热阻系数、强度和刚度与木质素掺量、含水率和养护龄期的变化规律,同时定性/定量评价改良土微观结构变化,分析改良土热学特性与力学特性间的相互关系。结果表明:改良土最大干密度较素土增加,最优含水率减小,干密度对含水率变化的敏感性增加;热阻系数随掺量和养护龄期增加而增加,60 d养护龄期后热阻系数趋于相同,热阻系数与土体密实度和组成成分的热传导特性密切相关;改良土强度随掺量和龄期增长而增加,28 d龄期12%掺量改良土强度约为素土强度6倍;回弹模量的变化特征与无侧限抗压强度类似,对于改良粉土,木质素最优掺量约为12%;改良土孔隙总体积和平均孔径显著减小,木质素包裹、连结土颗粒并填充孔隙,形成更致密土体结构。     

Effects of primary curing conditions and subsequent crumbling on properties of compacted soils treated with paper sludge ash-based stabilizers

Soil stabilization using paper sludge ash-based stabilizers (PSASs) has been developed as a technique for using the sustainable materials generated from industrial processes in construction projects. PSASs can be produced by insolubilizing the heavy metals in original paper sludge (PS) ash particles, i.e., the waste generated by the incineration of the PS discharged from paper mills. The aim of this study was to investigate the effects of the primary curing conditions and subsequent crumbling on the physical, compaction, and strength characteristics of PSAS-treated soils, using two types of PSASs with different water absorption and retention performances. For comparison, the same investigation was conducted on soils treated with blast furnace cement type B (BFCB). The experimental results revealed that, after crumbling, the PSAS-treated samples produced sand and gravel-like granules, regardless of the sealed or air primary curing conditions. In addition, the lower the water content at crumbling, the smaller the particle size. This was also true for the BFCB-treated samples. Consequently, the compaction test results demonstrated that, for one of the two types of PSASs, the dry densities of the PSAS-treated samples with sealed primary curing were almost the same as those without primary curing. The same trend was observed for the BFCB-treated samples. However, for the other type of PSAS, the dry densities of the PSAS-treated samples with sealed primary curing were lower than those without primary curing. This could be due to the difference in the degrees of disturbance caused by crumbling, depending on the type of PSAS. The rapid formation of hydrates in one type of PSAS may have significantly disturbed the treated samples owing to crumbling, resulting in a decrease in dry density. Finally, after secondary curing in a soaked environment, cone index tests were conducted on the PSAS- and BFCB-treated samples. The results indicated that the cone indices of the PSAS-treated samples with primary curing were higher or lower than those of the samples without primary curing, depending on the primary curing environment, number of curing days, and type of PSAS. The different trends, depending on the conditions, were considered to be caused by the combined effects of the “strength reduction owing to crumbling,” and “strength increase owing to water content reduction at compaction.” These mechanisms suggest that, for PSAS-treated soils with early strength development, the strength reduction caused by crumbling must be considered. However, for PSAS-treated soils with slow strength development, adjusting the water content of the treated soils through primary curing before compaction is an effective approach. Moreover, it is suggested that the curing conditions used for the laboratory mixtures be designed and set to reflect the field conditions and to minimize any discrepancies between the field and laboratory observations for the PSAS treatment.     

Effective Method for Dynamic Compaction of Slightly Cohesive Saturated Soils

Results of theoretical and experimental investigations under laboratory conditions are cited for a method of dynamic compaction of slightly cohesive saturated soils subject to aeration around the perimeter of the zone of compaction. The method described makes it possible to improve the compactive effect as a result of amplification of oscillations in the compaction zone, and attenuate them appreciably beyond the limits of the aerated wall; this considerably reduces dynamic effects on nearby structures.     

Geotechnical characterization of expansive soils and their implications in ground movements in Dakar

To better understand the role of problematic soils in the instability phenomena observed in Dakar, investigations and laboratory tests have been undertaken including the clay mineralogy, physical properties, mechanical properties, shear strength and shrink/swell characteristics of the soils—fine/coarse-grained volcanic tuffs and residual (weathered) soil. The results were related to the slope instability and foundation failures observed in Dakar and recommendations made to mitigate the effects of these problematic soils in future developments.      

黄河冲积平原区PHC管桩的挤密效应研究

依托黄河冲积平原区某电厂工程项目,对工程场地进行原位测试和室内土工试验,研究了PHC管桩对地基土的挤密效应。结果表明,随着桩径向距逐渐变小,土体受到的挤密效果逐渐增强;随着粘粒含量的增加,土体受到的挤密效果逐渐减弱,对粉土和砂土的挤密效果明显强于粘性土;PHC管桩可消除桩间地基土液化性和提高其强度,使桩区附近土体液化等级降低,但其作用随距离增大而减小。     

An updated and expanded set of thermal property data for green roof growing media

Vegetated (green) roofs alter the roof surface energy balance and hence affect both building energy consumption and the transport of heat into the environment. Quantitative evaluation of the energetics of green roof systems requires accurate knowledge of the moisture-dependent thermal properties of the growing media. To support this need for data and to supplement previously published data we conducted a laboratory study to measure thermal conductivity, volumetric heat capacity, and thermal diffusivity of 12 green roof soil samples of varying composition. The results indicate that thermal properties vary significantly as a function of growing media design. Growing media incorporating expanded slate as their aggregate had thermal conductivities that were two to three times those of media that used a porous silica-based aggregate. Media incorporating expanded clay as the aggregate had thermal conductivities roughly in the middle of these extremes. In general the thermal conductivity nearly tripled as the growing media moisture levels were increased from relatively dry to saturated. Also, it was found that compaction typical of green roof systems that have been installed for multiple seasons can increase thermal conductivity of moist soils by 30-40% over their uncompressed values.     

Stress-strain behaviour of some compacted laterite soils from north-east Brazil

Laterite soils in compacted from are widely used as fills and road construction materials in countries within the tropics. Certain unusual engineering characteristics have been established for some of them and these have been the subject of previous investigations. The present work concerns the examination of one such unusual engineering characteristic. The stress-strain behaviour of three compacted laterite soils from North-East Brazil have been examined using the shear-box machine. The investigation reveals the existence of a “collapse behaviour” previously identified only in undisturbed laterite soils. The “collapse behaviour” has been interpreted in terms of degradable soil particles which comminute under load. The comminution occurs before the ultimate failure of the soil body is reached.     

Behaviour of Granular Materials in Relation to Their Fabric Dependencies

The roles of dilatancy and fabric on the behaviour of granular materials are both numerically and experimentally explored for the study of material instability and failure. This investigation has two basic ingredients: namely a stress dilatancy model with microstructural information embedded through a fabric tensor, and an experimental rendition of force transmission and structure in an assembly of 2-D photoelastic disks. In order to highlight material instability, model simulations of sand behaviour are carried out in axi-symmetric stress conditions along proportional strain paths with varying degrees of controlled dilation (or compaction) including isochoric deformations as a special case. It is shown that sand, otherwise stable under isochoric (undrained) conditions, can actually succumb to an instability or a liquefaction behaviour under other loading paths. This suggests that flow type of failures in soils may not be necessarily restricted to the classic saturated loose sand case in undrained conditions, but could manifest itself under other conditions as well.     

石灰改良红土击实特性研究

通过击实试验,研究了石灰掺量对石灰改良红土击实特性的影响规律,结果表明石灰改良红土的最大干密度随含石灰量的增大而增大,增大的趋势先快后慢,石灰改良红土的最优含水量随含石灰量的增大而增加,且增加趋势先快后慢。     

Visualization and quantification of soil laboratory impact compaction

As important methods to guide the field soil compaction, the standard and modified Proctor tests for laboratory compaction have remained unchanged for decades, which should be improved to better understand the compaction process and the properties of soils. In this study, an accelerometer was installed on a Marshall impact compactor to capture the dynamic response of three types of soils during compaction. The experimental test results indicated that the acceleration curve for each blow gradually evolved to a stable pattern following the progress of compaction, and the impact and gyratory locking points were linearly related with coefficient of determination R² equal to 0.59. The impact compaction curve could be further constructed by filtering the structural resonance, which can be used to quantify the compactability of soil materials. Although each type of soil had a unique set of compaction curves, the slope and value of compaction curve altered accordingly as the moisture content changed for the same soil. In addition, the average acceleration value at the final compaction stage could serve as the target value of soil stiffness.     

碎石土振动压实特性试验研究

利用自行研制开发的表面振动压实仪。对6种级配碎石土进行了室内振动压实试验，取得了不同激振力、不同激振频率和不同激振时间作用下的大量试验数据，研究了级配碎石十最大干密度与激振力、激振频牢之间的关系。提出了反映碎石上粒径级配的不均匀系数、曲率系数和特征粒径的级配特征值，并建赢了碎石上级配特征值、最大干密度、振动参数间的相关关系，存在良好的相关性。系统地研究了碎石土振动压实特性，研究结果具有蕈要的理论研究意义和工程指导作用。