Stabilisation of Weathered Marls using Lime or Cement

Khaled Grine, Imelhain Assia

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Ground Improvement/Remediation

ABSTRACT: The article deals with an experimental study on weathered marls from the surrounding area of Algiers, in order to investigate their stabilisation using additives in small proportion consisting principally of lime or cement. The results show that the physical parameters such as plasticity and volume changes are greatly reduced after addition of a small proportion of lime or cement. The compressibility tests show that lime and cement affect the soil in the way that they increase its stiffness. However, the strength parameters such as (CBR) and (UCS) values are greatly enhanced after addition of an amount of lime or cement. Comparison between the stabilising effect of lime and cement treatment on the weathered marls used for this investigation show that lime has better effects than cement on the stabilisation of such soils.

RÉSUMÉ: alentours principalement de la chaux ou du ciment. Les résultats montrde ciment. Les testes de compressibilité montrent que la chaux ainsi que le ciment affectent le sol dans le sens ou résistance à la compression non confiné (UCS) des marnes augmentent de façon considérable. La comparaison es dans cette étude montre, . 1 INTRODUCTION Marls are fine coherent marine sedimentary deposits, consisting mainly from a mixture of clay and calcium carbonate (CaCo3), in a proportion varying from 30% to 70%. They cover an extensive area of the east, south east and west of Algiers on which much of the urban development is taking place. The main marls unit can be more than 200 m thick forming generally a homogeneous massive substratum. Their behaviour depends on the amount of carbonate and the type of the clay minerals content. Functions of the intensity of weathering, the marls are classified in three categories. From the bottom to the tope: Intact marls Intermediate marls weathered marls Weathering affects generally the top part of Marley formations to a maximal depth of 5 to 6 m. The geotechnical studies of such soils have shown that the marls are fine grained soils with low permeability, low strength (when weathered), containing a significant amount of montmorillonite increasing in the weathered horizons, illite and varying proportion of smectite. The mineralogical content make the weathered marls very sensitive to water, which in most cases result in a high volume changes (swelling, shrinkage) and loss in strength which makes these formations very instable. This instability does affect structures constructed on such formations where wide tension crakes can be observed upon them as a result. It also leads to slop instability when the gradient of the slope is greater than 10%, Figure 1, Imelhaine (2009). Indeed, many attempts to build on Marley soils around Algiers have indicated many soil instabilities occurrence with significant financial consequences. Figure1. Cracks on structure and walking path degradation duo to soil movement within Marley soils (West of Algiers) Previous studies on soil treatments have shown that additives such as lime mainly for clayey soils and cement for coarser ones have been used successfully to enhance strength, reduce volume changes and consequently stabilise the soil. This is known as soil stabilisation. Lime stabilisation is achieved with calcium oxide (quick lime) or calcium hydroxide (hydrated lime). Cement stabilisation is often achieved by using ordinary Portland cement (OPC). In the case of lime stabilisation, the stabilisation effect depends on the reaction between lime and the clay minerals. The main effects of these reaction are, an increase in the shear strength and bearing capacity of the soil, a reduction in the susceptibility to swelling and shrinkage, a reduction in the moisture content and improvement of workability and compaction

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