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Jw Evans

Bio: Jw Evans is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 8 citations.

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Journal ArticleDOI
TL;DR: This article found up to 90 per cent of clay minerals, but particle-size analyses showed a much smaller proportion of clay-sized minerals, due to particle aggregation or to the occurrence of unusually large clay mineral particles.
Abstract: Summary African red clays and Keuper Marl are materials of contrasting origin and mineralogical composition. The red clays are residual soils produced by weathering of rocks at the land surface under relatively high temperature and rainfall and good drainage. Bases and silica are leached, leaving the soil rich in iron and aluminium. In Kenya the clay minerals and iron oxide occur respectively as metahalloysite and hematite under relatively dry conditions, and as hydrated halloysite and goethite under moister conditions. The plasticity of the clay minerals is modified by the iron oxide. Black montmorillonitic clays, rich in bases and silica, occur in association with the red clays but on lower ground. The Keuper Marl is the product of weathering of higher land, which accumulated to a great thickness in a wide basin. Conditions of internal drainage led to enrichment of bases and silica. Calcium and magnesium are present as calcite and dolomite, and silica is present as quartz. All the clay minerals found were rich in magnesium and silica. Illite and chlorite were universal, and much of the chlorite was of the swelling type. In addition, sepiolite and palygorskite commonly occurred. Quantitative x-ray analyses showed up to 90 per cent of clay minerals, but particle-size analyses showed a much smaller proportion of clay-sized minerals, due to particle aggregation or to the occurrence of unusually large clay mineral particles.

34 citations

Journal ArticleDOI
TL;DR: This paper described Quaternary soils according to the climatic conditions under which they were formed (glacial, periglacial, temperate, arid and tropical) and discussed the geological characteristics of the soils and the processes that have acted in forming or altering them.
Abstract: This introductory paper describes Quaternary soils according to the climatic conditions under which they were formed (glacial, periglacial, temperate, arid and tropical). The paper discusses the geological characteristics of the soils and the processes that have acted in forming or altering them, as well as their geotechnical properties.

18 citations

Journal ArticleDOI
TL;DR: In this paper, the authors outline the planning and implementation of a site investigation carried out on a limited budget for 110 miles of proposed new highway in Fiji by using geotechnical expertise in tropical soils.
Abstract: Summary The paper outlines the planning and implementation of a site investigation carried out on a limited budget for 110 miles of proposed new highway in Fiji A comparison is drawn between the cost of investigation of earthworks and general foundation conditions, rock materials, and engineering structures, estimated during the planning stage by allocating funds in the same proportion as the estimated construction cost, and the actual cost of investigation of each The programming and staffing of the investigation are considered Examples are quoted showing how economical results were obtained by the use of geotechnical expertise in tropical soils Attention is drawn to the method of classifying residual soils in grade zones developed during the investigation according to their geotephnical properties Problems of laboratory investigations of tropical materials are considered The value of large scale tests such as trial embankments as a means of assisting in the preparation of a realistic compaction specification for residual soils, and also as a means of testing construction methods in swamp areas are discussed

18 citations

Journal Article
TL;DR: In this article, samples of deltaic lateritic soils were subjected to mechanical (with or without controlled sand addition), cement and cement-sand (composite) stabilisation methods to improve strength for improved engineering applications.
Abstract: Deltaic laterite is the most suitable and most widely used soil material for road embankment in the Niger Delta. Usually, its natural characteristics fall short of the minimum requirements for such applications hence it has to be stabilised to improve its properties. In this study, samples of deltaic lateritic soils were subjected to mechanical (with or without controlled sand addition), cement and cement-sand (composite) stabilisation methods to improve strength for improved engineering applications. Mechanical stabilisation was found to satisfy subgrade requirements while the addition of sand produced sub-base material quality at best depending on compacted maximum dry density (MDD), which itself is dependent on the optimum sand content (OSC). The OSC was also shown to affect the optimum moisture content (OMC) and the soaked California bearing ratio (CBR) of stabilised specimens. Combination of the test results produced a graphical model to predict the influence of mechanical stabilisation on the soil materials using the percentage fines (that is, passing through a 75 mm sieve) obtainable from wet sieving. Cement stabilisation of the soil (by indigenous highway standard) produced base-course quality materials with cement content in excess of 12 %, which is economically unviable. However, the addition of controlled proportions of sharp sand (also abundant in the Niger Delta) to the soilcement mixtures produced base-course quality materials with 6 % cement (less than half of that obtained through only cement stabilisation) and about 40 % sand content. A model was also presented to predict the other constituents of sand-cement stabilisation using the percentage fines obtainable from wet sieving.

8 citations

Dissertation
01 Jan 2016
TL;DR: In this paper, the authors describe the important effects of climate impacts on slope stability and demonstrate that within a slope the mobilised shear strength drops quickly during a rainfall event (due to rainfall infiltration) but recovers much more slowly during drying.
Abstract: Climate change poses real threats to the sustainability of slopes, particularly in the tropical region of the world. Its effects have caused a greater occurrence of extreme climate events that are reflected in a greater occurrence of slope failure incidents for this region. The hydro-mechanical characteristics of soils linked with climate variation are factors that can explain deterioration in slope stability. Therefore, the ability to analyse the hydro-mechanical behaviour properly is worthy of investigation and this can be done by the use of experimental investigation and numerical modelling using both saturated and unsaturated soil properties. In this thesis, the description of the important effects of climate impacts on slope stability has been made for a failed tropical residual soil slope located in Precinct 9, Putrajaya, Malaysia. Part of the work involved soil sampling for the acquisition of undisturbed soil samples from the slope. Series of advanced saturated and unsaturated laboratory testing for both hydrological and mechanical properties have also been implemented and were used in transient, unsaturated numerical modelling of slope stability analysis (using Plaxis 2D). The results demonstrate that within a slope the mobilised shear strength drops quickly during a rainfall event (due to rainfall infiltration) but recovers much more slowly during drying. This shows how a series of regular rain storms with short periods of drying in between can cause a ratcheting effect, with rapid loss of strength during each period of rain that is not recovered during the intermediate drying periods. In addition, the results also show that the adoption of critical state soil parameters is more suitable to match the observed failure. The failure was due to a very extreme amount of rainwater infiltration in the two days before the incident, including the largest daily rainfall in 2007 of 140mm.

8 citations