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Remediation of acid generating colliery spoil using steel slag – case studies

Ghataora G. S., Ghazireh N., Hall N.

Studia Geotechnica et Mechanica

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2015

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Vol. 37, nr 2

75--84

EN

One of the legacies of the coal mining industry is the existence of numerous colliery spoil mounds. Run-off waters from some of these mounds result in oxidation of sulphur compounds causing pH to drop to perhaps as low as 2.5. At this pH, mobility for metals increases and it results in destruction of both flora and fauna. In order to reduce acidity, a number of solutions have been investigated with varying degree of success. A recent study to reduce acidity in spoil run-off water included the use of Basic Oxygen Steel slag. Its slow release of lime resulted in longer term remediation compared with other techniques. In addition to this, steel slag contains elements which are essential for plant growth and can be regarded as a weak fertiliser. This was substantiated in two field trials, which had the aim of not only remediating acidity from two different types of colliery spoils, but also to develop a composition that supports grass growth. The objectives were achieved at both sites and some of the results of over 5000 chemical tests conducted during these studies are reported in this paper.

2

Effect of fibre reinforcement on the properties of ground granulated blast furnace slag-cement-bentonite slurry

Williams M., Ghataora G. S.

Studia Geotechnica et Mechanica

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2011

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Vol. 33, nr 4

63-83

EN

Slurry walls are used as cut-off walls and are designed to meet strength and permeability criteria, with the latter often being a governing factor. An investigation was undertaken to explore the use of polypropylene fibres in cement bentonite ground granulated blastfurnace slag slurry walls in order to assess the effect of fibres on permeability in the main. Flow, bleed and both undrained and drained strength were also measured. Fibres reduced both the flow and bleed. They also marginally increased the permeability. Undrained strength together with strain to failure increased. However, under drained conditions strain to failure increased compared to mixes with any fibre.

3

Changes in properties of clay surrounding cast in-situ piles

Ghataora G. S., Ling U. K., Lee L.

Studia Geotechnica et Mechanica

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2010

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Vol. 32, nr 4

3-15

EN

For piles in clay soils, the major contribution to working load capacity is from the shaft resistance, which is influenced by the types of piles used and construction methodology adopted. In the case of preformed piles, the time-related response relates to changes in pore water pressure. However, in the case of cast-in-situ concrete piles it is anticipated that changes in soil chemistry due to migration of ions from the concrete would have an effect on soil/pile interaction. A laboratory- scale test conducted to investigate change in soil chemistry with time and its impact on load carrying capacity of cast in-situ piles in Oxford clay showed that there was a short-term increase in moisture content of soil adjacent to the piles. It also showed that there was an increase in both hydroxyl and calcium ion concentration. These also affected adhesion factor, which increased with time to a limiting value.

4

Behaviour of fibre-reinforced and stabilized clayey soils subjected to cyclic loading

Dall'Aqua G. P., Ghataora G. S., Ling U. K.

Studia Geotechnica et Mechanica

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2010

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Vol. 32, nr 3

3-16

EN

Much research has been undertaken on the use of fibres to reinforce soils for varying range of applications such as adobe bricks and walls and pavements, but little is available on the response of these materials to repeated loading the subgrade soils in road pavement may be subjected to. Thus, with a view on the application of pavement design, an investigation was undertaken to assess the effect of fibre on kaolinite and laterite stabilised with both cement and lime subjected to repeated loading. Crimped monofilament of 12 mm long polypropylene fibre with a diameter of 18 microns was used to reinforce both the soils at concentration of 0.3% stabilized with 4% and 6% of lime and cement. Results show that kaolinite soils reinforced with 0.3% of fibres together stabilized with 6% cement under repeated axial load test deform less than 1% after 3,600 load cycles and could be used in pavement construction. For laterite soils under the worst case scenario conditions of soaking, the samples of plain soil and those stabilized with cement did not have enough strength and collapse before loading. However, reinforced and stabilised, particularly were strong enough after soaking to be used in the upper parts of a pavement.