1. Introduction
In the field of civil engineering, various methods are adopted to improve the geotechnical properties of soils in order to meet the requirements for stability and maintenance cost reduction. Clayey soil stabilization by various additives may be one of these methods, because of the substitution of inappropriate soils by adequate ones has become increasingly expensive and ecologically unsafe. Besides that, stabilization by cement is not preferable due to its growing cost and environmental concerns related to its production (Al-Swaidani et al., 2016). Luting materials such as lime have been successfully employed in the geotechnical engineering discipline for soil stabilization purpose and mechanical properties improvement, especially for clayey and silty soils. Lime is widely used in civil engineering applications such as road construction, embankments, foundation slabs and piles (Al Rawas and Goosen, 2006).
The carried out studies in the literature show that the addition of lime increased the optimum moisture content and strength, and reduce the plasticity index and maximum dry density of the soil (Guney et al., 2007; Croft, 1967; Ola, 1977; Rahman, 1986; George et al., 1992; Bell, 1996; Gay and Schad, 2000; Hossain et al., 2007). On the same matter, extensive studies have been carried out on the stabilization of clayey soils using lime (Basma and Tuncer, 1991; Kassim and Chern, 2004; Mohamed et al., 2009; Sherwood, 1993). As investigated by Sabry (1977), many significant engineering properties of soft soils also can be beneficially modified by lime treatment, as lime decreases the plasticity index, increases the workability and shrinkage limit, reduces shrinkage cracking, eliminates almost all swelling problems, and increases soil strength.
In another way, several researchers (Al-Rawas et al., 2005; Goswami and Singh, 2005; Rahman, 1986; Muntohar and Hantoro, 2000; Attoh-Okine, 1995; Nalbantoglu, 2006; Lasledj and Al-Mukhtar, 2008; Osula, 1996; Ola 1977; Bagherpour and Choobbasti, 2003; Kavak and Akyarli, 2007; Manasseh and Olufemi, 2008; Okagbue and Yakubu, 2000; Ansary et al., 2006) found that in most cases, the effect of lime is more or less instantaneous on the plasticity properties of the clayey soils.
On shear strength characteristics, hence in some studies (Lin et al., 2007; Chen and Lin, 2009) postulated that the observed shear failure mode of stabilized soil samples with lime is similar to brittle materials. Moreover, some researchers (Consoli et al., 2012; Calik et al., 2014) found that the soil strength properties were greatly improved after lime treatment. According to the study of Consoli et al. (2012 and 2014), the decrease of pores and lime volume increase are directly responsible for the increase of soil-lime mixture strength.
This paper presents the effect of hydrated lime on the Atterberg limits, compaction characteristics, and unconfined compressive strength of Sulaimnai city, Northern Iraq CL soil, which classified according to the unified soil classification system (USCS). All tests were conducted in accordance with the ASTM standards (1990 - 2000).