Geotechnical investigation of some soils from S.W. Nigeria for use as mineral seals in waste disposal landfills

Three soils from S.W. Nigeria including two laterite soils are considered for use as mineral seals in the landfill disposal of wastes. The critical factor which determines the suitability of any soil for this purpose is permeability. The workability of such a soil is also important. All these in turn depend on the basic geotechnical properties of the soil. The soils investigated have very low permeabilities. These together with their geotechnical properties which conform with the general proposals make them ideal for use as mineral seals.     

An investigation of the peculiar characteristics of laterite soils from southern Nigeria

Problem laterite soils are those that do not yield reproducible results using standard laboratory testing procedures. The soils are difficult to evaluate as engineering construction materials. The peculiar problems of these soils have been identified as thermal and mechanical instabilities i.e. the susceptibility to significant changes on the addition of small levels of thermal or mechanical energy. A laboratory investigation of the instability characteristics of laterite soils from the forest and savannah-woodland zones of Southern Nigeria has been carried out. Mechanical instability was determined by multiple compaction test and thermal instability by oven-drying under varying conditions. The results indicate that the soils studied can be unstable on the application of thermal and mechanical energies. Parameters obtainable from the grain-size distribution of soils subjected to the different conditions were found suitable for assessing thermal and mechanical instabilities. The maximum dry density and optimum moisture content obtained from the compaction curve are independent of the number of compaction.     

Geotechnical characterisation of alluvial soils used to contain industrial liquid wastes

A wide range of geotechnical tests has been carried out to characterise an extensive alluvial deposit that is used as containment for a landfill in which liquid wastes are disposed. The landfill covers an area of 357 ha. Data obtained from the current and previous studies have been used to explore the variability of the properties of two alluvial layers. The upper layer is predominantly silty clay, while the lower layer contains a much wider range of particle sizes. Variations in hydraulic conductivity covering seven orders of magnitude have been measured in both layers. The selection of appropriate parameters for contamination migration studies is discussed.      

Geotechnical characteristics of the clayey soils and rocks of the North Lefkoşa,Nicosia, Cyprus

This paper outlines the engineering geological properties of the clayey soils of North Lefkoşa (Nicosia, Cyprus). On the basis of their physical properties and their engineering characteristics, the Miocene, Pliocene and Quaternary deposits were divided into six units: unconsolidated man-made fill, unconsolidated surficial recent alluvium, unconsolidated surficial young alluvium, consolidated old alluvium, highly weathered soft rock units and slightly weathered relatively resistant rock units. Laboratory tests indicated a generally high swelling potential, which would account for the damage seen in many single and two-storey buildings as well as major roads.      

Clay mineralogy,major elements geochemistry and strength characteristics of three highway subgrade soils in Southwestern Nigeria

The clay mineralogical assemblage, major elements geochemistry and strength characteristics in terms of the California Bearing Ratio (CBR) of three genetically different residual soils in Southwestern Nigeria were investigated. The study revealed a fairly strong negative correlation of-0.58 between the amount of kaolinite and the silica-sesquioxides of iron and aluminium ratio. It also showed a weak positive correlation of 0.004 between the amount of kaolinite and ferric oxide. The amount of ferric oxide and kaolinite showed positive correlation of 0.24 and 0.29 respectively with the strength (measured in term of (CBR) of the studied soils. The study has stressed the relevance of a knowledge of geological characteristics prior to a rational understanding of some geotechnical properties of residual soils.     

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.      

Effects of fungicide residues on the physico-chemical characteristics of soils of a major cocoa-producing area of Nigeria

The effects of copper-based fungicide residues on some physico-chemical properties of soils in some cocoa-producing areas of Nigeria were investigated. The results show that the fungicide residues cause significant increases in the soil pH, organic matter and copper concentrations while lowering the concentrations of inorganic nitrogen, available phosphorus, exchangeable potassium and sodium. Slight increases were also observed for the cation exchange capacity (CEC) and exchangeable Ca2+ and Mg2+ but there are no significant changes in the Zn, Fe and Mn concentrations with fungicide treatment. It is concluded that the copper-based fungicide residues predispose the soils to nitrogen, phosphorus and potassium (N, P and K) deficiencies and perhaps copper toxicity if not properly managed.     

Geotechnical analysis of two Nigerian soils for use as clay liners

The cretaceous Auchi shale and the Tertiary Imo shale in SW Nigeria were investigated for their suitability for use as a clay seal in waste disposal landfills. Geotechnical analyses indicated they are highly plastic inorganic clays. Although their geotechnical and chemical properties were within the range suggested by various authors for use as mineral seals, care would need to be taken with the Okada shales as they contain smectite and would be difficult to work and liable to cracking.      

Geotechnical characteristics of the Plaisancian marls of Algiers

The Plaisancian Marl covers an extensive area to the south west of the Port of Algiers and forms the bedrock on which much of the future urban development will take place, in the area known as the Sahel of Algiers. Previous attempts to build on this formation were inadequately planned and as a result, soil instabilities occurred with significant financial consequences. This paper discusses the geomorphological setting and the environmental context in which the marls were formed before presenting the principal geotechnical characteristics of this problematic formation and the types of instabilities which are likely to occur and affect development in this area. Geormophologically, the Sahel is a succession of hills formed of Plaisancian Marls with gradients varying from 5 to 30% and a general slope to the south towards the Mitidja plain. The topography is dominated by post-Astian tectonics, which caused the uplift of the Atlas Mountains and formed the anticline of the Sahel and the depression of the Mitidja. The geomorphological setting of the Marls is therefore a dip-slope where the dip direction is relatively consistent with the direction of the slope. Algiers is characterised by a Mediterranean climate with warm, often wet winters and long dry summers when there is a very marked water deficit. The main Marl unit is more than 200 m thick and generally forms a homogeneous massive stratum. This is overlain by weathered/fissured material. The thickness of this upper horizon varies according to the angle of slope and the topographic location. The geotechnical study has indicated the Plaisancian Marl is a fine grained soil with very high plasticity and low permeability. These properties are consistent with the mineralogy of the sediment. A significant amount of montmorillonite was recorded in the X-ray diffraction analysis with an increase in montmorillonite in the near surface horizon. Interstratified illite-montmorillonite is also present, indicating the likelihood of depotassification. These very fine sediments containing varying proportions of smectite have a low shear strength and high shrink/swell capacity. As a consequence, the instabilities are frequently associated with volumetric change due to swelling and desiccation. In addition, cracks which have developed in the ground naturally over hundreds and thousands of years may be exacerbated by engineering construction due to changes in stress in the near surface horizons. The paper draws attention to many of these problems and it is hoped will assist planners to take due cognisance of the impact of the lithology, morophology and climate on the viability of any proposed works.     

Swelling characteristics of soils subjected to acid contamination

The ever-increasing number of failures of industrial structures due to the heaving of acid-contaminated foundation soils has necessitated a better understanding of soil behavior under changing and extreme environmental conditions. Thus, this paper attempts to micro-mechanistically explain the swelling characteristics of soils contaminated with inorganic acids. Three soils with widely varying physical and chemical properties, namely, natural black cotton soil and commercially available bentonite and kaolin clay, were selected for the investigation. Special Teflon-made oedometer cells, which are entirely non-reactive to acid, were used to assess the swelling behavior. The soils were inundated with two concentrations of sulfuric acid and phosphoric acid and allowed to swell. The results indicate that, in montmorillonitic soils, the type of cation in the exchangeable complex plays a dominant role in governing the swelling behavior of clays during acid contamination. The mineralogical changes due to cation exchange reactions, along with the partial mineral dissolution, resulted in the acid-induced swelling in montmorillonitic soils. In the kaolin clay, the face-to-edge association of the particles due to the adsorption of H⁺ by broken edges led to an increase in swelling along with mineralogical changes.     

Influence of sample preparation and mode of testing on the shear strength characteristics of laterite soils from Southwestern Nigeria

The Shear Strengths of four laterite soils from Southwestern Nigeria are investigated through:

1. consolidated undrained triaxial compression tests with pore water measurements on Standard Proctor compacted soils and
2. direct shear tests on remoulded soils.

The Shear Strength parameter obtained in both cases are high with those of the first method being generally higher than those of the second method. However, in view of the relative ease of execution, the second method is preferred especially with regards to local/minor and farm constructions.     

Stabilization of maiduguri black cotton soils of Nigeria with sand

The Lake Chad Basin is an extensive Quaternary lacustrine deposit of black clay soils. Laboratory investigations show that this soil consists of abundant proportions of montmorillonite and generally poses a major problem for Civil Engineering construction due to high volume changes. Alternative soils or aggregates suitable for base construction are very difficult to obtain in these localities and hence soil stabilization is of great economic importance to the construction industry. Methods of stabilizing this soil include lime stabilization, cement stabilization, mechanical stabilization, or heat treatment. This paper is primarily concerned with sand stabilization because of the presence of large deposits of dune sands at these locations. The result indicates that sand stabilization shows promise for improving the value of black cotton clays in pavement construction and is the most economical of all the applicable methods. However the method is recommended only for improving the subgrade and as a sub-base.     

Geotechnical properties of some residual micaceous soils in the Kumasi Metropolitan area (Ghana)

Micaceous soils derived from granites, granitic gneisses and phyllites within the Kumasi Metropolitan Area have been used in road construction. The mica flakes are normally silt—and sand-sized but sizes greater than these are not uncommon. The texture, consistency limits, compaction characteristics and California Bearing Ratio of some of these soils have been examined. Based on these results appropriate recommendations have been made with a view to raising the standard of these materials to meet highway specifications when in service.     

The performance of some soils under stabilization in Ondo State,Nigeria

This study was aimed at classifying and improving soils from some parts of Ondo State, Nigeria, using cement and lime as stabilizing agents. The brownish-red clay (Ak-1) and brownish gravelly clay (Ak-2) were derived from migmatitic rocks (consisting of granite gneisses and metasediments) and charnockites in the north and central part, while the reddish clayey sand (Ok-1) was derived from the Quaternary coastal plain sands and alluvial sands in the southern flank of Ondo State. They have high “fines” ranging between 50 % and 80 % thereby requiring improvement before use as pavement material. Their maximum dry densities were achieved at an average of between 4 % and 6 % cement, although peak CBRs were obtained at between 8 % and 10 % lime. It was observed that cement is a more economical additive in pavement construction.     

Use of pore pressure to determine strength characteristics of thawing soils

A procedure for determination of strength characteristics of thawing soils subject to shear under laboratory conditions is proposed on the basis of results of investigations. __________ Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 16–19, July–August, 2007.     

Physicomechanical characteristics of heterogeneous compacted soils

The writers present results of investigations of the strength and deformation characteristics of heterogeneous soils and their relation with respect to the composition, density, water content, and degree of compaction. The effect of the composition on the maximum dry density of the soil and the optimal water content is established. Conclusions are drawn about the possibility of use of heterogeneous soils as earth pads, grading fills, backfills, etc. in place of soils of the same type or of homogeneous characteristics.TsMIPKS. Kazakhstan PromstroiNIIproekt Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 2–5, May–June, 1993.