## 4 Design Examples of Cantilever RC-Retaining Walls
### Numerical Cost Analysis of Cantilever Reinforced Concrete Retaining Walls (Case 1)
#### 4.1.2 Investigation of the Influence of Soil Property Change (Case 1B)
Prototype model tests had been conducted for being experimental verification of some of the methods, but they could not produce realistic test results compared to full-scale prototypes because of scale effects. That is because the model behavior includes only a statistically small quantity of soil specimens compared with that involved with the full-scale tests. This condition cannot allow representing the whole soil medium that is going to be encountered in the field. Sandy soils can be representative examples for clarifying this situation because sand requires confinement for the generation of internal resistance [48]. Due to these reasons, in the context of this study, it is preferred to select appropriate ultimate bearing pressures at the design stage of the retaining wall to evaluate the influence on the cost and size of the system. Overall, 200, 250, 300, 350, and 400 kPa values are selected as the ultimate bearing pressure of the soil under the foundation loading condition. Different cases are fictionalized for the interpretation of the ultimate bearing capacity effect on the cost of retaining wall system. In Figure 9, two representative conditions are selected to identify the pressure effect on the cost of the wall system. In the first condition, the excavation depth is selected 9 and 12 m (Figure 9a-d). The internal friction angle and the unit weight of soil are assumed to be constant values 27\({}^{\circ}\) and 14 kN/m\({}^{3}\), respectively. In the second condition, besides the different excavation depths, surcharge load change is also evaluated (Figure 9a-d). It should be noted that the vertical axes have different numerical values in the plotted graphs. Figure 9a-b show that the increase of the excavation depth rises the costs of the whole wall system but there is no effect of the change of the ultimate bearing capacity on the costs if the surcharge load is not applied to the top of the wall. The increase of the surcharge load to 20 kPa has increased wall costs approximately 2% for the small values of ultimate bearing capacity (Figure 9c,d) but the increase of ultimate bearing capacity provides to equalize the costs. Figure 10 illustrates the influence of soil unit weight coupled with the surcharge load change on the costs. The excavation depth and the internal friction angle are selected as 9 m and 29\({}^{\circ}\), respectively. The unit weight of the soil is identified as 14 kN/m\({}^{3}\) in Figure 10a,c and 17 kN/m\({}^{3}\) in Figure 10b,d. The surcharge load that is applied on the backfill side is assumed to be 0 and 20 kPa, respectively. The increase of soil unit weight does not  
Figure 8: Change of construction costs against the shear strength angle and the unit weight of soil (**a**) \(\gamma=14\) kN/m\({}^{3}\); (**b**) \(\gamma=18\) kN/m\({}^{3}\); (**c**) \(\gamma=20\) kN/m\({}^{3}\). influence the costs if the surcharge load is not applied. The increase in the surcharge load leads to rising costs for both selected unit weights. However, the rise of ultimate bearing pressure to a limit level the costs remain constant. Depending on the selected soil parameters and specified cases, this limit level of the ultimate surcharge load can be said 300 kPa. Another case is fictionalized for designating the effect ratio and for evaluating the variance behavior of wall costs according to the increase of excavation depth. The excavation depth is assumed 12 m and internal friction of the soil is preferred to use 29\({}^{\circ}\). The unit weight of the soil is selected 14 and 17 kN/m\({}^{3}\), respectively. Surcharge load is also selected as a variant. Comparisons are conducted for Figures 10 and 11. Unlike Figure 10a, the deepening of excavation causes to raise costs, approximately 3%, for the smallest ultimate bearing pressure. The increase of soil unit weight does not affect the costs similarly for both excavation depths.