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Premier Symposium Méditerranéen de Géoengineering «SMGE09» Alger 20 et 21 juin 2009 1. Introduction The lime treatment of soils is one of the oldest techniques used (more than 5000 years old). Indeed, even before the Romans, 2000 years ago, other peoples were already acquainted with that procedure. For instance, Shersi pyramids in Tibet were built with clay and lime compacted mixtures. Also, throughout the years, in China and India, lime treatment was used in various ways (Ancade, 1997). Presently, the lime potential in reducing the water content and the plasticity of soils is well recognized and, therefore, its application in soil mixtures, namely within the framework of geotechnical works, is normally taken into account in technical specifications. These mixtures have also been often used to improve the mechanical characteristics (deformability and strength) of compacted soils, particularly soils that, due their significant amount of fines, are usually discarded, both in fills and in the substructure of transportation infra-structures, roads or railways. This aspect is very important, because the consequences of unbalanced earth works (embankments and excavation/cuttings) are decisive, in terms of economic and environmental costs. Nevertheless, the lack of knowledge of the long term performances of these mixtures, together with the specific equipment demands, the insufficient knowledge about the application techniques and, sometimes, the lack of an adequate cost-benefit analysis, have placed major obstacles to accepting the use of such treatment in Portugal. Therefore, its use has not been systematically adopted. In fact, apart from the works indicated in this paper, regarding highways A2 (subsection Almodôvar – São Bartolomeu de Messines) and A10 (subsection Arruda dos Vinhos – IC11), which were carried out by the Brisa, SA in 2001 and 2005, respectively, the lime treatment of soils has only been used in a very few works. Furthermore, special reference is made to the works studied by Neves (1993), regarding the construction of the “North-South Axle Road (subsection Telheiras - Sete Rios)” and the “Lisbon Inner Ring Road – CRIL” (subsection Alto do Duque – Buraca), as well as to the earthworks included in the modernization of the North Line (subsections Azambuja - Vale de Santarém and Entroncamento Norte – Albergaria tunnel), which were performed in 2003 by the railway administration. Nevertheless, this scenario has been significantly changing in construction pratice. In fact, the technical and environmental requirements placed by the new transportation infra-structures, in particular the high speed railway network and the new Lisbon airport, is most likely to promote the use of the lime treatment of soils, as an alternative to their replacement. 2. Case Studies This paper presents various studies related with the lime treatment of embankment and capping layers of pavements. Those studies concern two major roads constructed in Portugal: highways A2 and A10. The 240 km long highway A2, constructed in 2002, is the main link between Lisbon and Algarve project has taken into account the possibility of using lime treated soils on the pavement capping layer. The insufficient amount of appropriate soils to be used in capping layer within an acceptable distance was the main reason for adopting the lime treatment of soils. Highway A10 is a multi-purpose road aimed for those traveling from the Central and the West region of Lisbon towards the North of the country. It also serves those traveling from the West central part and from the north of Portugal down to Algarve, thus avoiding passing through Lisbon. The lay-out solution which was developed for the section of highway A10 led to a significant volume of excavations and embankments. Furthermore, it required the use of borrow materials with appropriate characteristics and in sufficient quantities, which were unavailable within acceptable distances. These factors have led to the solution of treating soils for the construction of embankments. Quicklime was the binder used in both works. Table 1 indicates the lime properties. In accordance with the specifications of the Portuguese Standard NP EN 459-1 (2002), this lime is classified as CL90-Q.
Premier Symposium Méditerranéen de Géoengineering «SMGE09» Alger 20 et 21 juin 2009 Table 1. Lime characteristics Properties Values CO 2 ≤ 3.5% CaO ≥ 92% SiO 2 ≤ 0.3% S ≤ 0.3% Retained on sieve #2.0 mm < 5% Bulk density ≈ 1.0 3. Study of the Mechanical Caracteristics After Treatment 3.1. General aspects The quality control during the execution of earthworks and the evaluation of the bearing capacity of platforms, within the framework of transportation infra-structures, can be based on the definition of minimum values of the deformation modulus measured at the top of the layers by means of non-destructive load tests. Despite the possibility of the imposed load and the associated response being rather different from those actually obtained during the passage of vehicles, the in situ characterization resulting from that class of tests has been proving to be very useful and reliable for assessing the different structural layers. 3.2. Numerical modeling of the load test Based on the deflections obtained from falling weight deflectometer (FWD) load tests, it was possible to determine the equivalent deformation modulus. Even more, it was possible to determine the values of the deformation modulus of the different layers, by employing a numerical model using the finite element method (FEM), by means of modeling in axysymmetric conditions. Using the commercial software Plaxis ® , it was possible to model the load test on a linear elastic stratified medium. In an iterative way, deformation modulus of the different layers were changed as to converge the calculated deflection curves with those obtained in situ with the FWD. 3.2.1 Highway A2 The upper part (25 to 30 cm) of the capping layer (40 to 45 cm) was lime treated. Thus, two structures were considered for the load test modeling (Figure 1). Figure 1. Structures considered for the load test modeling (A2). Falling weight deflectometer tests In each FWD test point, three impacts were performed on a 30 cm diameter plate load, corresponding to 20, 30 and 45 kN. The deflection transducers (geophones) were placed at the following distances (in cm) from the load plate centre: 0 (Df1); 30 (Df2); 45 (Df3); 60 (Df4); 90 (Df5); 120 (Df6); 150 (Df7); 180 (Df8) e 210 (Df9). Figure 2 presents the finite element mesh used for structure 1, taking into account the boundary conditions and the different layers of the pavement substructure. All the finite element meshes considered in the other cases presented in this paper are identical, except for the thicknesses of the different layers.
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