## 3 Material Properties and Test Program  
### Subgrade and Fill Material Properties  
In the experimental study, the silt-clay mixture soil used to create a problematic subgrade on the road section was obtained from a natural land (about 1.5-2.0 m deep) on which there was no construction in the Duzici district of Osmaniye province. In addition, the filling material to be used as the base or subbase and rockfill layers in the road section were obtained from the Stone Quarry located in the Kadirli district of Osmaniye province.  
A group of conventional laboratory tests (sieve analysis, compaction, consistency limits, pycnometer, and CBR) were performed to determine the physical and engineering properties of the silty clay soil that would form the subgrade of the road and the filler material that would form the base/subbase course layer in the laboratory. The subgrade soil's clay content varied from 60 to 70%. Also, it was classified as high-plasticity clay (CI) according to the Unified Soil Classification System (USCS). Rock fill and granular fill materials have the same geological origin and consist of limestone. The granular fill material for this project consisted of crushed aggregates and was classified as GW (well-graded gravel with sand), according to the USCS classification system [29]. It contained 2-3 percent fines and more than 35 percent gravel (Figure 1a). In addition, large-sized rocks (average 30 cm in diameter) from the same quarry were used to create the rock-filling layer in the road section (Figure 1b).  
The granular fill layer was prepared at an optimum moisture content of 4.80% and a maximum dry unit weight of 21.30 kN/m\({}^{3}\) obtained from the standard proctor test. The granulometer curves of the soils used in field tests are presented in Figure 2, and their physical properties are presented in Table 1.  
Figure 1: Filling materials: (**a**) the granular fill, (**b**) the rockfill.  
Figure 2: Particle size distribution of subgrade and subbase soil.  
The CBR tests were carried out for the bearing capacity of the subgrade and subbase/base course material. The CBR values of the subbase/base course layer (fill material) were 32.74% and 56.71% for 2.5 and 5.0 mm displacement, respectively.  
The CBR tests in the laboratory run on the base course material [30] resulted in a California Bearing Ratio (CBR) value of about 56; however, in-field CBR tests indicated that the average in-place CBR strength of the base layer was approximately 80-90 with dynamic cone penetrometer (DCP) tests [31]. This difference is due primarily to the conditions under which the base course was tested in the lab compared to how these values were obtained in the field. When performing laboratory CBR tests, limiting the material's grain size is necessary since standard cylindrical models are used. Therefore, this limitation is thought to significantly affect the material's strength [32]. Moreover, the bearing capacity at higher penetration (5 mm) was greater than at 2.5 mm penetration, so the higher values are recommended to be reported by the standard. Considering that the aggregates are better interlocked with each other during compaction in the field, it can give higher CBR values. It is known that water content is a very important parameter in the subgrade layer to ensure weak soil conditions. For this reason, CBR experiments were carried out in the laboratory on subgrades prepared with different water contents. The results obtained are shown in Figure 3. As a result, it was concluded that the subsoil should be prepared with an average water content of 26% in order to ensure weak ground conditions (CBR 3-5). This water content was also checked by DCP experiments in the field and by water content tests in the laboratory.