Technical Note Water content, porosity and cement content as parameters controlling strength of artificially cemented silty soil Nilo Cesar Consoli a, ⁎, Daniela Aliati Rosa b , Rodrigo Caberlon Cruz b , Amanda Dalla Rosa b a Dept. of Civil Engineering, Federal University of Rio Grande do Sul, Brazil b Federal University of Rio Grande do Sul, Brazil abstract article info Article history: Received 28 November 2010 Received in revised form 13 April 2011 Accepted 6 May 2011 Available online 31 July 2011 Keywords: Fine grained soils Water content Cement Porosity Compressive strength Compacted soils Present study aims to assess the strength controlling parameters of a fine grained soil molded at three distinct water contents considering four distinctive cement amounts and three distinguishing dry unit weights to show that the effect of diverse soil structures formed during compaction of fine grained soils at distinct water contents, the porosity of the specimens and the amount of cement inserted on them play a fundamental role in target strength assessment of such materials. The controlling parameters evaluated were water content (ω), cement content (C), porosity (η) and porosity/volumetric cement content ratio (η/C iv ). A number of unconfined compression tests were carried out in the present work. The results show that, for each specific water content studied, a linear function fits the unconfined compressive strength (q u )–cement content (C) relationship, the strength (q u ) increases exponentially with the reduction in porosity (η) and a power function fits relation strength (q u )–porosity/volumetric cement content ratio (η/C iv ) for the studied silt– cement mixtures. Finally, a unique relationship can be achieved linking the unconfined compressive strength (q u ) of the studied fine grained soil with molding water content (ω), porosity (η) and volumetric cement content (C iv ). © 2011 Elsevier B.V. All rights reserved. 1. Introduction Soil–cement is a mixture of soil with Portland cement and water, usually compacted to specific density. As the cement hydrates, the soil–cement–water mixture gains strength and improves the engi- neering properties of the raw soil. The major variables that control the properties and characteristics of soil–cement mixtures are the type of soil, the proportion of cement in the mix, the moisture conditions, and the degree of compaction (Moore et al., 1970). The soil–cement technique has been used successfully in pavement base layers, channel linings, slope protection for earth dams, as a base layer to shallow foundations and to prevent sand liquefaction (e.g. Porbaha et al., 1998; Consoli et al., 2009). The unconfined compression tests have been used as the most convenient means to investigate the effect of different variables on the soil–cement strength and to carry out dosage methodologies. Previous studies by Horpibulsuk et al. (2003) have shown that the water/ cement ratio (defined as the water mass divided by the cement mass) was a useful parameter in the analysis of the strength development of cemented soils in which pores of the samples were predominantly water-filled, so that the water content would reflect the amount of voids. In the present study, the voids are only partially filled by water, and there is not a unique relationship between the voids and the amount of water. The roles played by the porosity and by the moisture content are different. While water affects the strength by possibly changing the soil structure, porosity affects the strength by modifying the number of contact points among the soil particles. Therefore for the soil cement in the unsaturated state, as is usual in geotechnical engineering practice, a relationship between water content, porosity and cement content should be more appropriate in the analysis and control of its mechanical strength. This study aims at quantifying the influence of the molding water content (and consequently the influence of soil structure acquired during compaction of fine grained soils treated with cementitious agents, as shown by Consoli et al., 2001), the porosity and the amount of cement on the unconfined compressive strength of a silt–cement mixture, as well as searching for a unique relationship linking the unconfined compressive strength (q u ) with molding water content (ω) and porosity/cement ratio (η/ C iv ) for such material. The main contribution of present work is demonstrating for the first time ever the existence of a unique relationship linking q u with ω (and consequently each distinct soil structure acquired during compaction) and η/C iv for artificially cemented fine grained soils. So, in the case of having a fine grained soil to be treated with cement, the compaction water content shows to be as important as cement content and porosity in reaching a giving strength in such materials. Engineering Geology 122 (2011) 328–333 ⁎ Corresponding author. Tel.: + 55 51 81239266; fax: + 55 51 33083999. E-mail addresses: consoli@ufrgs.br (N.C. Consoli), danialiatirosa@yahoo.com.br (D.A. Rosa), rccaberlon@hotmail.com (R.C. Cruz), amandadallarosa@yahoo.com.br (A.D. Rosa). 0013-7952/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2011.05.017 Contents lists available at ScienceDirect Engineering Geology journal homepage: www.elsevier.com/locate/enggeo