# Preparation, Characterization and Modeling of Unbound Granular Materials for Road Foundations
## 2 Materials and Methods  
### Specim Preparation  
Initially, some natural graded unbound material (NGA), frequently used as a sub-base for road pavements in Spain, was progressively mixed with different proportions of gravel, clay, silt and sand. A number of samples of seven granular soils were then prepared. Four of them--selected, suitable, tolerable and marginal soil--were produced and sampled following the Spanish Standard UNE-EN 932-1 [10]. Since the objective was to obtain a representative bulk sample, a stack sampling procedure was used. Accordingly, sample fractions of similar size were taken from different points, heights, and depths of the stack. Following the procedure described in the UNE-EN 932-2 [11], a laboratory 50 mm sample divider was used to reduce samples and obtain coarse aggregate, as well as medium and fine fractions.  
Additionally, three more samples of stabilized soils (STS) were prepared by mixing certain classified soils with a filler chosen from several fine-sized fractions of lime, micro-cement and cement.  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Requirements** & \multicolumn{4}{c}{**Soil Categories**} \\ \cline{2-5}  & **Selected** & **Suitable** & **Tolerable** & **Marginal 5 ** \\ \hline Organic matter (\%) & \textless{}0.2 & \textless{}1 & \textless{}2 & \textless{}5 \\ Water-soluble salts (\%) & \textless{}0.2 & \textless{}0.2 & - & - \\ Maximum particle size (mm) & \textless{}100 & \textless{}100 & - & - \\ Particles passing No.200 (\%) & \textless{}801 & - & - & \\ Liquid limit (LL) & \textless{}30 & \textless{}40 & \textless{}65 & - \\ Plasticity limit (PL) & \textless{}10 & \textless{}402 & \textless{}0.733  & \textgreater{}0.734  \\ Proctor density (\(\text{kg}/\text{dm}^{3}\)) & \textgreater{}1.750 & \textgreater{}1.750 & \textgreater{}1.450 & - \\ CBR index & \textgreater{}20 & \textgreater{}5 & \textgreater{}3 & - \\ Free swelling test (\%) & - & - & \textless{}3 & \textless{}5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: PG-3 technical requirements for classified soils used in the construction of road foundations.  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Filler** & **Requirements** & **S-EST1** & **S-EST2** & **S-EST3** \\ \hline \multirow{3}{*}{Lime} & Organic matter (\%) & \textless{}2 & \textless{}1 & \textless{}1 \\  & Water-soluble sulfate (\%) & \textless{}1 & \textless{}1 & \textless{}1 \\  & Plasticity index & \textgreater{}12 & between 12 and 40 & - \\  & Liquid limit & - & - & - \\ \hline \multirow{3}{*}{Cement} & Organic matter (\%) & \textless{}2 & \textless{}1 & \textless{}1 \\  & Water-soluble sulfate (\%) & \textless{}1 & \textless{}1 & \textless{}1 \\  & Plasticity index & - & \textgreater{}40 & \textgreater{}40 \\  & Liquid limit & \textgreater{}15 & \textgreater{}15 & \textgreater{}15 \\ \hline \hline \end{tabular}
\end{table}
Table 2: PG-3 technical requirements for stabilized soil used in the construction of road foundations.  
Extra samples of artificial crushed graded soil made of crushed granitic stone (designated as ZA25 in the PG-3) were also prepared as control specimens for comparison. Table 3 summarizes the sample preparation used in this work.