# Preparation, Characterization and Modeling of Unbound Granular Materials for Road Foundations
## 3 Results and Discussion
### The California Bearing Ratio (CBR)  
The CBR test is a penetration test for evaluation of the mechanical strength of road subgrades and base courses [19]. The CBR test performed on the specimens was carried out according to UNE 103-502/95 [20], with significant modifications described as follows: the specimen is first selected taking into account that 20 UNE sieve has been passed at \(>\)90% of the sample weight. The chosen samples for this studies weighted 6 kg, considering the CBR mould capacity of 5 kg. A plunger with a circular cross-section of 20 mm\({}^{2}\) is driven at a specified rate into the specimen compacted in the 152.4 mm diameter CBR steel mould. The forces required to cause a penetration of 2.54 and 5.08 mm are then expressed as percentages of the standard forces of 13.5 and 20.3 kN, respectively. In these studies, a standard piston was used to penetrate the soil at a standard rate. The pressure up to a penetration of 10 mm and its ratio to the bearing value of a standard crushed rock is termed as the CBR.  
To simulate the \"in situ\" condition of moisture content in the laboratory, the CBR-test can be performed \"unsoaked\" (at the compaction moisture content) or \"soaked\": the specimen after compaction having been immersed in water for four days before the actual CBR-testing. The \"soaked\" procedure has been carried out for this work, measuring penetration under load conditions after one, two, three and four days of immersion. The photograph of mould and penetration device are shown in Figure 4.  
Graphical analysis has been performed through the representation of the CBR versus moisture content for all samples of the lab-prepared soils. Figure 5 displays the results of the classified soil specimens after four days of immersion. The CBR exhibits clearly decreasing linear behavior, which indicates loss of stability of the soils when high moisture content exists, as expected. Concerning the stabilized soils, Figure 6 displays the graphical behavior of the CBR index for marginal soil, natural graded aggregate and tolerable soil samples stabilized with lime and micro-cement, as indicated. The values corresponding to physical properties are in agreement with PG-3 requirements, which highlights the fact that the laboratory preparation procedure of these soils have been carried out with accuracy.  
Figure 4: CBR test.  
CBR values of marginal soil stabilized with lime and micro-cement (Figure 6B) show high sensitivity of these samples upon humidity changes, but good stability otherwise. Increasing CBR with microcement filler is due to filling the voids between soil particles. The stabilized soils prepared with natural graded aggregate and tolerable soil both stabilized with 3% lime (Figure 6A) present higher sensitively to moisture content increase than stabilized soils prepared with marginal base. The sample  
Figure 5: CBR versus moisture content for (**A**) selected soils, (**B**) suitable soils, (**C**) tolerable soils and (**D**) \(Z25\) (artificial crushed graded soil).  
Figure 6: CBR versus moisture content for (**A**) NGA and tolerable soils stabilized with lime, and (**B**) marginal soil stabilized with lime and microcement.  
fabricated with natural graded aggregate stabilized with 3% lime filler features a remarkably high CBR index, which slightly decreases when the sample acquires moisture.