دانلود رایگان ترجمه مقاله تثبیت خاک های انبساطی برای استفاده در ساخت و ساز (نشریه الزویر ۲۰۱۱)

تثبیت خاک های انبساطی برای استفاده در ساخت و ساز

Stabilization of expansive soils for use in construction

Abstract

Expansive clay soils are extensively distributed worldwide, and are a source of great damage to infrastructure and buildings. These soils can cause heavy economic losses, as well as being a source of risk to the population. This article presents an experimental study in the stabilization of an expansive soil, consisting of the reduction of its swelling capacity and the improvement of its mechanical capacities by the addition of by-products and waste materials of industrial origin. This achieves the double objective of reducing the problems of this type of soil, and also of providing a use for the additives, thus eliminating the economic and environmental cost involved in managing them. From the point of view of expansivity, it was possible to reduce it to levels well below what Spanish legislation contemplates for expansive soils. As to the improved mechanical capacities of the soil, all treatments tested offered improvements of between two and four times the compressive strength of the untreated soil. Of the waste materials, the most notable is the behavior of Rice Husk Fly Ash, highly effective in stabilizing soil from the two aspects considered in this experiment.

۱ Introduction

“Expansive soils” are those which experience great changes in volume when their water content varies. These types of soil are widely distributed throughout the world (Huang and Wu, 2007; Sabtan, 2005), although they are especially abundant in arid zones, where conditions are suitable for the formation of clayey minerals of the smectite group such as montmorillonite or some types of illites (Avsar et al., 2009; Nowamooz and Masrouri, 2008; Sabtan, 2005). These clays are characterized by having a very small particle size, a large specific surface area and a high Cation Exchange Capacity (CEC) (Fityus and Buzzi, 2009; Nalbantoglu, 2004; Nalbantoglu and Gucbilmez, 2001). The swelling of this type of clay is related to three types of factors: geology, the engineering factors of the soil, and local environmental conditions. Geology primarily determines the presence in the soil of these types of expansive clay minerals. Among the engineering factors included are the soil moisture content, plasticity and dry density. The most important local environmental conditions to consider are the amount of the clay fraction in the soil, its initial moisture conditions, and confining pressure (Sabtan, 2005). Volume changes of these types of soil are a major cause of natural disasters, since they cause extensive damage to the structures and infrastructure on top of them (Assadi and Shahaboddin, 2009; Avsar et al., 2009; Chen et al., 2007; Ferber et al., 2009; Huang and Wu, 2007). This has even led some authors to refer to them as “calamitous soils” (Chen et al., 2007).

The stabilization of expansive soils by the use of additives such as lime, fly ash or cement is well documented (Du et al., 1999; Nalbantoglu, 2004; Nalbantoglu and Gucbilmez, 2001; Rao et al., 2001; Yong and Ouhadi, 2007) and has traditionally concentrated on the elimination of the expansive power of the soil. In this type of soil, additives with calcium oxide produce the flocculation of the layers of clay by the substitution of the monovalent ions by the Ca2+ ions. This balances the electrostatic charges of the layers of clay and reduces the electrochemical forces of repulsion between them. The adhesion of the particles of clay into flocs then occurs, giving rise to a soil with improved engineering properties: a more granular structure, lower plasticity, greater permeability and above all lower expansivity (Du et al., 1999; Kinuthia et al., 1999; Langroudi and Yasrobi, 2009; Lin et al., 2007; Nalbantoglu, 2004; Nalbantoglu and Gucbilmez, 2001; Rao et al., 2001; Yong and Ouhadi, 2007). In addition, the presence of the OH- ions produces an increase of the soil pH up to values of approximately 12.4. In these conditions, pozzolanic reactions take place, when the Si and the Al which form part of the sheets of the clay dissolve and combine with the available Ca2+ giving rise to cementing compounds such as Calcium Silicate Hydrates (CSH) and Calcium Aluminate Hydrates (CAH) (Chen and Lin, 2009; Guney et al., 2007; Nalbantoglu, 2004; Yong and Ouhadi, 2007). These compounds are responsible for improving the mechanical properties of the soil, as well as helping to reduce its expansivity by their cementing action. This article discusses the experimental results of the improvement of the properties of an expansive soil when it is treated with different additives. Thus, the stabilization of expansive soils has been considered from the standpoint of eliminating their capacity for swelling or shrinkage, and also from the standpoint of improving those of their mechanical properties which are of interest in civil engineering. This experiment has been based on civil engineering tests with a view to the use of these types of soil as a building material, and of the prevention of natural disasters related to their capacity for swelling or shrinkage. In the following sections of this paper we present an experimental study carried out with a highly expansive clay which was submitted to anti-expansive treatment by adding different additives. Having analyzed the reduction of the swelling capacity of the soil, a second treatment was performed in order to establish the improvement of the bearing capacity of the soil and its evolution over time due to the development of pozzolanic reactions.