Active Soils of the Niger Delta in Road Pavement Design and Construction

Active soils existing to irreplaceable extents (both laterally and vertically) within the freshwater zone of the Niger delta are known and have been shown to be highly undesirable in their natural forms for road construction. This is because they swell extensively in the rainy season and shrink proportionately in the dry months together with any structure including road pavement constructed with or placed on them. In this paper, four samples of these soils collected from across the Niger delta were subjected to chemical stabilization with slaked-lime and calcium chloride (CaCl₂) to reduce swelling potential while resulting mixtures (corresponding to tolerable swelling limits) were stabilized with Portland cement to improve strength. First, swell indicator (i.e. 24-h free swell index) was found to diminish with increasing stabilizer content while for combined plot (independent of location/percentage fines), about 10.7% and 6% slaked-lime and CaCl₂ were found to be required to achieve the minimum (2.5% free swell) tolerable, normal or non-swell soil condition. Under this condition and for individual soil materials, addition of cement was found to enhance continual increase in MDD, soaked-CBR and durability index such that the soil becomes better compactible, stronger and more durable with increasing cement content. About 2.6% and 14.6% cement contents were found needed to respectively produce sub-base and base-course materials in roadworks with the latter much more durable than the former. The graphs so obtain could also constitute a complete graphical model for preparing deltaic active soils for use as road pavement materials.     

Engineering properties of unfired clay masonry bricks

The shortage of low cost and affordable housing in the UK has led to many investigations into new building masonry materials. Fired clay masonry bricks are conventionally used for mainstream masonry wall construction but suffer from the rising price of energy plus other related environmental problems such as high energy usage and carbon dioxide emission. The use of stabilised unfired clay bricks for masonry construction may solve these problems.This paper reports on the engineering properties of unfired clay bricks produced during the first industrial trial of unfired clay material development carried out at Hanson Brick Company, in Stewartby, Bedfordshire, under the Knowledge Exploitation Fund (KEF) Collaborative Industrial Research Project (CIRP) programme. The mixes were formulated using a locally available industrial by-product (Ground Granulated Blastfurnace Slag — GGBS) which is activated with an alkaline (lime or Portland cement) combined with clay soil. Portland cement was not used in the formulation of the unfired stabilised masonry bricks, except as a control, which is a significant scientific breakthrough for the building industry. Another breakthrough is the fact that only about 1.5% lime was used for GGBS activation. This level of lime is not sufficient for most road construction applications where less strength values are needed and where 3–8% lime is required for effective soil stabilisation. Hence, the final pricing of the unfired clay bricks is expected to be relatively low.The laboratory results demonstrate that the compressive strength, moisture content, rate of water absorption, percentage of void, density and durability assessment (repeated 24-hour freezing/thawing cycles) were all within the acceptable engineering standards for clay masonry units. The paper also discusses on the environmental performance of the unfired clay in comparison to the bricks, used in mainstream construction of today. The bricks produced using this technology can be used for low-medium cost housing and energy efficient masonry wall construction.     

Spent oil shale use in earthwork construction

Spent oil shale (or blaes) is a potentially valuable engineering material and is present in large quantities in the West Lothian area of Scotland. It can be used successfully as general fill or capping layer. However, due to its high quality it may be more suited to use as selected granular fill or sub-base. In particular, cement stabilisation will reduce frost susceptibility and may be a particularly appropriate outlet for spent oil shale for use as sub-base. However, an increase in control and testing may be required, having an effect on the cost of using such materials. Conditions under which spent oil shale should not be used are also identified.     

Effect of sodium sulphate on the shear strength of clayey soils stabilised with additives

The effect of sulphates on the soil stabilisation using mineral additives such as lime, cement and fly ash has been reported by several researchers. The effect of sodium sulphate (Na₂SO₄) (0–6% by dry weight of soil) on the behaviour of the grey clayey soil (GS) and red clayey soil (RS) stabilised with lime (L) (0–8%), natural pozzolana (NP) (0–20%) and with a combination of lime-natural pozzolana (L–NP) was investigated. The soil specimens were subjected to testing of direct shear strength after 7, 30, 60 and 120 days of curing period. In the absence of Na₂SO₄, the results show that both clayey soils can be successfully stabilised with L or with a combination of L–NP, which substantially increases their shear strength and produces high values of shear parameters. However, at short curing period and for any content of Na₂SO₄, a further increase in shear strength and shear parameters is observed. Moreover, after 30 days of curing, the RS specimens stabilised with L or with NP alone are altered when the Na₂SO₄ is greater than 2%, whereas the GS specimens are not altered. However, the alteration of RS specimens is little when the L and NP are combined on curing with a high content of Na₂SO₄. Generally, the effect of Na₂SO₄ on both stabilised clayey soils depends on the curing time, percentage of additives used and their type, mineralogical composition of stabilised soils and Na₂SO₄ content.     

水泥加固红土的受力特性及其微结构特征

水泥加固红土的击实、剪切、压缩和渗透等受力特性及其微结构特征受到水泥加入比例和试样养护时间的影响。研究结果表明,水泥加固红土存在最佳击实制样时间,水泥加入越多,最大干密度越大、最优含水率越小。其抗剪强度和抗剪强度指标随水泥加入比例的增加和试样养护时间的延长逐渐增大,但增大的程度逐渐减慢,对粘聚力的影响大于对内摩擦角的影响;其压缩性和渗透性随水泥加入比例的增加和试样养护时间的延长显著减小,但减小的程度逐渐变缓;水泥加入比例的影响大于试样养护时间的影响。实质上,水泥的加入和试样的养护导致水泥加固红土呈现出包裹、填充和胶结的微结构特征,引起水泥加固红土的击实、剪切、压缩和渗透等力学特性的宏观变化。     

Swell-compressibility characteristics of lime-blended and cement-blended expansive clays – A comparative study

Chemical stabilisation of expansive soils has been quite efficacious in reducing swelling characteristics, namely, swell potential (S%) and swelling pressure (p_s). When chemicals such as lime and cement are added to an expansive clay, flocculation and cementation take place. Flocculation, which is an immediate reaction, is instrumental in reducing plasticity and swell potential significantly. It also reduces the time required for equilibrium heave. This paper presents experimental data on lime-blended and cement-blended expansive clay specimens. Free swell index (FSI), heave, rate of heave and swelling pressure were studied. FSI, heave and rate of heave decreased with increasing lime content and cement content in the blends. But, during a 3-day inundation (a period, generally allowed for the sample to attain to equilibrium heave), cementitious products developed and resisted the applied compressive loads stiffly, resulting in high swelling pressures in the case of lime-blended specimens. Swelling pressure could not be determined in the case of cement-blended specimens. Hence, short inundation tests (inundating the specimens only for 15 minutes) were performed. But, even from these tests, swelling pressure could not be determined for cement-blended specimens. This indicated the development of strong cementitious products in them. It was interesting to find that, in both long and short duration, the lime- and cement-blended specimens attained to equilibrium heave in the same time period. FSI decreased from 185% to 63.63% when lime content was increased from 0% to 4%, and from 185% to 110% when cement content was increased from 0% to 20%. Swell potential reduced by 42.5% at 4% lime and by 46.4% at 20% cement. Swelling pressure increased from 210 kPa to 320 kPa when lime content was increased from 0% to 4%. Linear shrinkage of the specimens also decreased with increasing additive content.     

Experimental Investigation of Cement Treated Sand Behavior Under Triaxial Test

In this paper, an experimental investigation of cement treated sand is performed under triaxial tests in order to quantify the effects of cementation on the stress–strain behavior, stiffness and shear strength. Samples were cured up to 180 days. The results show that the stress–strain behavior of cemented sands is nonlinear with contractive–dilative stages. The stress–strain response is strongly influenced by effective confining pressure and cement content. Stiffness and strength are greatly improved by an increase in binder content. An increase of the angle of shearing resistance and cohesion intercept with increasing cement content is observed consistently. Brittle behavior is observed at low confining pressure and high cement content. After yielding, the increase in the dilatancy accelerates. Two competing related processes determine the peak strength: Bond breakages cause a strength reduction but the associated dilatancy leads to a strength increase. This finding and the experimental observation that the dilatancy at the peak state increases with increasing cement content explain why the measured peak-state strength parameters, c′ and φ_p′, are relevant to the binder content.     

Sustainable Improvement of Tropical Residual Soil Using an Environmentally Friendly Additive

Many tropical residual laterites have relatively poor engineering properties due to the significant percentage of fine-grained soil particles that they contain, which are formed by the soil weathering process. The widespread presence of laterite soils in tropical regions often requires that some form of soil improvement be performed to allow for their use in various civil engineering applications, such as for road base or subbase construction. One of the most commonly utilized stabilization techniques for laterite soils is the application of additives that chemically react with the minerals that are present in soil to enhance its overall strength; effective soil stabilization can allow for the use of site-specific soils, and can consequently result in significant cost savings for a given project. With an increasing focus on the use of more environmentally friendly and sustainable materials in the built and natural environments, there is an emerging interest in eco-friendly additives that are an alternative to traditional chemical stabilizers. The current study examines the viability of xanthan gum as an environmentally friendly stabilizer that can improve the engineering properties of tropical residual laterite soil. Unconfined compressive strength (UCS) tests, standard direct shear tests, Brunauer, Emmett, and Teller (N₂-BET) surface area analysis tests and field emission scanning electron microscopy (FESEM) tests were used to investigate the effectiveness of xanthan gum for stabilization of a tropical laterite soil. The UCS test results showed that addition of 1.5% xanthan gum by weight yielded optimum stabilization, increasing the unconfined compressive strength of the laterite soil noticeably. Similarly, direct shear testing of 1.5% xanthan gum stabilized laterite specimens showed increasing Mohr–Coulomb shear strength parameters with increases in curing time. From the FESEM results, it was observed that the stabilization process modified the pore-network morphology of the laterite soil, while also forming new white layers on the surface of the clay particles. Analysis of the test results indicated that xanthan gum stabilization was effective for use on a tropical residual laterite soil, providing an eco-friendly and sustainable alternative to traditional soil stabilization additives such as cement or lime.     

广西红土击实特性的影响因素及机理分析

红土是由原岩在湿热气候条件下经过红土化作用形成的具有高含水率、大孔隙比、较高强度和较低压缩性的一种特殊土。由于其特殊的工程地质性质形成了红土具有较大工后沉降的特性。目前,工程中普遍采用强夯的地基处理方法对其进行处理,对于夯后红土地基变形则通过现场监测结合室内试验的方法进行研究。笔者通过室内击实试验和击实后红土的高压固结试验,深入探讨影响红土击实效果和击实后压实性的主要因素,并对各影响因素进行影响机理分析。试验结果表明：红土的击实效果与击实功成正比,与黏粒质量分数、塑性指数、游离氧化铁质量分数成反比;击实后红土的压缩模量受含水率、干密度及饱和度等因素的综合影响,并且各因素的影响程度不尽相同;当含水率大于18%时,土体处于近饱和状态,含水率与干密度已经不能反映饱和红土的压实性了,即在实际的强夯工程上这种土的含水率不宜大于18%,否则会产生较大的工后沉降。     

Arsenic remediation by Australian laterites

The efficiency of Australian laterites in arsenic adsorption has been examined using three laterite samples collected from different locations in South Australia. The characteristics such as electrical conductivity, pH, mineral compositions, and isoelectric point of laterite samples have been measured. The laterite samples are mainly composed of iron and aluminum oxides, and rutile (TiO₂). Two batch experiments have been performed to compare the efficiencies of different laterites to remove AS (III) from water at two different doses, and to examine whether pH influences arsenic adsorption. For 50 mg/l arsenic solution, at doses 1,000 g (laterite)/l (arsenic solution) and 200 g/l, the laterites removed more than 97% and 87–97%, respectively. At the dose of 200 g/l, adsorption capacity has been found to be 200–243 mg/kg. Out of the laterite samples from three localities, the Kangaroo Island laterite performed the best. This is probably related to its high content of gibbsite. It has been found that arsenic adsorption by laterite is not significantly affected at the examined pH ranges of 4.7–10.0.     

Interoperable processing of digital elevation models in grid infrastructures

Based on the service specifications of the Open Geospatial Consortium (OGC), Spatial Data Infrastructures (SDI) support the visualization, access to vector and raster data or managing and search for spatial data. A standard for distributed spatial data processing was missing for a long time. This issue was addressed by the development of the OpenGIS Web Processing Service (WPS) specification. However, to process and analyze massive Digital Elevation Models (DEM) computing power and disk memory are scarce commodities. Here we show that Grid Computing in combination with OGC Web Services (OWS) is well suited to accomplish high processing performance and storage capacity for large-scale processing tasks of the geo community. To process these massive amounts of geo-data we develop terrain processing services which are made available as grid services. Our results will be demonstrating how to bridge the gap between the grid world and the OGC world for more sophisticated terrain processing.     

Utilization of bituminous limestone ash from EL-LAJJUN area for engineering applications

The following work aims at minimizing the environmental impact of the solid wastes (ash) that is produced after the utilization of the bituminous limestone in thermal power stations and /or retort processes. Limy ash has been prepared from the El-Lajjun bituminous limestone by direct combustion at 1,200, 950, and 525°C respectively. The laboratory tests have been selected with respect to construction needs and possible post construction conditions. Utilization of the various types of ash in the stabilization problematic soils from Jordan as brown soils and the clayey marl has revealed optimum results. The unconfined compressive strength of the parent brown soil and the clayey marl has been raised from 5 kg/cm² to 50 and 25 kg/cm², respectively. The CBR value has been raised from 4.5 to 150% for both problematic soil types. Various mortars and construction elements can be produced at normal room curing temperature without the use of ordinary Portland cement (OPC). Low quality sub-base and base course can be mixed with ash to produce cement treated base (CTB) and roller compacted concrete (RCC) without OPC. Durable pavements, embankments can be constructed with very long life and low cost. CTB and RCC utilizing ash can be used in dam construction instead of normal soil in earth fill dams. The high alkalinity of El-Lajjun ash is considered as a disadvantage to be utilized in normal concrete mixes for structural purposes. Ash only can be mixed with aggregates to produce lean concrete like for blinding purposes to be prepared for foundation activities.     

Investigation of solid waste soil as road construction material

The geotechnical properties of solid waste soils for use as sub-base materials in road construction were investigated. A series of field tests and laboratory tests were performed to assess the physical and mechanical properties of the solid waste soils sampled from a landfill site, near to a riverside, which had been reclaimed over the last two decades. The tests showed that geotechnical properties are clearly affected by the magnitude of organic matter content. As the organic matter content increases, the maximum dry unit weight, the shear strength and bearing capacity of ground decrease, while the void ratio and compressibility increase. If the organic matter content is more than about 8% in solid waste soils, it is not suitable for use as a sub-base material in road construction due to the significant decrease of shear strength and bearing capacity.     

红黏土承载比的土团尺寸效应研究

高液限红黏土用于路基填筑时,因其不良的水理特性,需要掺石灰或水泥改良。但红黏土成团现象十分突出,进行灰土拌和时不易达到均匀状态,影响预期改良效果。通过对不同直径的红黏土土团及石灰改良土土团进行承载比试验,结果表明：干密度随着土团直径尺寸的增大呈现先增大后减小的特征,红黏土和石灰土的最大干密度对应的土团直径处在0.2～ 5 mm范围内;而最大承载比CBR值对应的土团直径分别处在5～10 mm和2～5 mm的范围内。石灰土和红黏土的吸水率、膨胀率均随着土团尺寸的增大,呈现先减小后增大的整体变化趋势。在2～10 mm的范围内,两种土的膨胀量最小。石灰改良只对直径小于5 mm的土团的膨胀特性起到明显的抑制作用。可见,现场施工中严格控制土团的大小对保证土体的强度和水稳定性具有十分重要的意义。     

Construction techniques for the Taklamakan Desert Highway: research on the construction materials and the results of field tests

After conducting many laboratory and field experiments, several key technical issues related to the construction of China’s Taklamakan Desert Highway have been satisfactorily resolved. In particular, considerable progress has been made on the dry compaction of a sand sub-base, road design parameters, the creation of a structure that combines a sub-grade and asphalt pavement, analysis of the stability of a sand sub-base strengthened with geotextiles, and on the development of a complete set of construction techniques. The achievements of this research were successfully applied for the first time in the Taklamakan Desert, where the environmental conditions are extremely harsh. The results suggest that the construction of this highway was economical and that the simple construction methods produced a reliable highway. The resulting highway is believed to be the world’s first long-distance graded highway running through a huge desert with migrating dunes.     

Experimental Evaluation of Construction Waste and Ground Granulated Blast Furnace Slag as Alternative Soil Stabilisers

In this study, the effect of ground granulated blast furnace slag (GGBFS) and recycled construction waste (CW) on bentonite clay stabilisation were investigated. The unconfined compressive strength (UCS) of specimens was evaluated with different combinations of GGBFS and CW over various curing periods. A series of micro analysis tests consisting of scanning electron microscope, energy dispersive spectrometer and X-ray diffraction were also conducted to determine the microstructural arrangement and mineralogical effect of the stabilisation treatment. The UCS results showed an increment in strength after introduction of GGBFS and CW and the longer curing period produced more pronounced results. The optimum additive ratio was calculated as 5 % of slag and 20 % of construction waste under all curing conditions. The micro analytical results also indicated formation of structural bonds between admixtures and bentonite in stabilised specimens, as slag crystals and bentonite particles were observed to occupy the cavities and vesicles on the construction waste grains. However, the experimental data shows that the strength improvement is not significant with the addition of only construction waste.     

Shear strength studies on soil-quarry dust mixtures

Due to the high demand for rubble and aggregates for construction purposes, rubble quarries and aggregate crushers are very common. Out of the different quarry wastes, quarry dust is one, which is produced in abundance. About 20–25% of the total production in each crusher unit is left out as the waste material-quarry dust. Bulk utilization of this waste material is possible through geotechnical applications like embankments, back-fill material, sub-base material and the like. It becomes a useful additive to the natural soil to improve its strength characteristics. For the above applications one of the important engineering properties is the shear strength. The purpose of the present investigation is to understand the shear strength behavior of quarry dust and soil-quarry dust mixes.     

昆明长水国际机场砂页岩残积红土动力特性研究

昆明长水国际机场残积红土既是区域内重要的土地资源,更是各类工程建设的建筑地基,由于裂化特性,在现代气候条件下,红土出现了严重的开裂变形,其工程性质不断恶化。文章针对昆明长水国际机场砂页岩残积红土开展了一系列固结不排水动三轴试验分析研究。变形试验结果表明:砂页岩残积红土在某一次循环动应力中存在屈服应变;在相同的应变水平下,动弹性模量随着固结围压的增大而增大;同时砂页岩残积红土的阻尼比在动应变小幅度的增加时会发生骤降,并随着动应变的增加逐渐趋平。同时通过动强度试验得出砂页岩残积红土破坏动强度随着固结围压的增大而增大,并得到砂页岩残积红土在固结比K_c=1时的动抗剪强度指标,即c_d=25.182 kPa,φ_d=12.985°,将其与固结不排水的静三轴试验下得出的抗剪强度指标进行了对比与分析。红土在动力作用下的剪切破坏实质是其土体中的弱结合水大量丧失,导致其颗粒之间的粘结力降低,从而内部单元体产生了相对位移。该研究成果对红土系统深入研究及工程实践应用具有重大的指导意义。      

非饱和红土基质吸力与含水率及密度关系试验研究

非饱和土中存在的基质吸力对其性质有着十分重要的影响,而基质吸力又与土的含水率之间存在着密切的关系。为了探讨基质吸力与非饱和红土含水率和密度之间的关系,采用滤纸法在试验室进行了基质吸力的量测,得到了不同干密度下非饱和红土的土-水特征曲线,拟合出了该类非饱和红土土-水特征曲线公式。试验结果分析表明：在相同的干密度下,随着含水率的增加,基质吸力呈现出急剧减小的趋势。当含水率 <24 %时,这一变化规律特别明显。对参数 分析发现,在非饱和状态下基质吸力对红土强度的提高是有限的。通过分析不同干密度对基质吸力的影响规律得出,基质吸力在含水率较高时对密度状态的变化不敏感,而在含水率较低时对密度状态的变化比较敏感。     

Geotechnical properties of stabilised Indian red earth

Locally available soils amended with sufficient bentonite are generally used for construction of liners for water and waste retention facilities. The amount of bentonite required to keep the hydraulic conductivity low varies with the nature of the local soil. Many studies have shown that bentonite content higher than 20% by weight is not usually required. This is also the case with Indian red earth containing predominantly quartz and kaolinite minerals. Incorporating bentonite, though keeps the hydraulic conductivity of soil low, increases the swelling and shrinkage potential; increases the loss of strength due to reduction in cohesion. This paper aims to improve the geotechnical properties of red earth and bentonite mixture with lime or cement. The studies reveal that the geotechnical properties of red earth with 20% by weight bentonite stabilised with 1% by weight of lime or cement are greatly enhanced, particularly after curing for 28 days. it has been shown that the early gain in strength is better with cement whereas its long-term strength gain is better with lime.