## 4 Results and Discussion  
The effect of the O-cell location with respect to competent caliche layers was investigated. In Case Study I, the O-cell was installed far from the caliche layer, whereas, in the second scenario (Case Study II), the O-cell was installed close to a strong caliche layer. It can be perceived from the results that the caliche is not fully mobilized when the load cell is located very far from it. The load is dissipated through the soil layers before transferring to the caliche layer, and only a slight portion of the load was reached to mobilize the caliche. Hence, the resistance developed from the caliche was the reaction of this deposit to a small portion of the total applied load. The mobilization did not fully represent the caliche's capability. The caliche layer subjected to axial loading from the top of the pile mobilized further compared to the downward loading, due to its close distance to the loading source. In this loading condition, higher shear resistance is developed, as shown in Figure 14. This shows the existing caliche layer can carry more loads than the reported measurements based on different directions of the load application. In the analyses, most of the soils were normally consolidated and elastic compression of the drilled shaft was considered. The effect of elastic compression on the drilled shaft, in the top-loaded drilled shaft, was calculated based on the pattern of developed side shear stress using Equation (1). where \(C_{1}\) is the centroid of unit side friction values for the strain gauge zones in the upper shaft unit, \(Q\) stands for the applied downward or upward load by the O-cell hydraulic jack, \(P\) is the applied axial load, \(L\) indicates the drilled shaft length, \(E\) represents the shaft's modulus of the elasticity and \(A\) shows the cross-section of the drilled shaft in this equation. \[\delta_{\downarrow}=[(C_{1})Q^{\prime}_{\downarrow}+(1-C_{1})P]\frac{L}{EA} \tag{1}\]  
Equation (2) was applied to include the effect of the elastic compression of the upper section of the pile. \[\delta_{\uparrow}=[(C_{1})Q^{\prime}_{\uparrow}]\frac{L}{EA} \tag{2}\]  
The developed side shear resistance along the pile length subjected to the axial load (\(P\)) or equal upward/downward load by O-cell (\(Q\)) is presented in Figure 14. To estimate the top-down elastic behavior, it is possible to subtract from the total for the section, as considered in Equation (1). The elastic compression is integrated in the measured upward response, as presented in Equation (2). The effect of the elastic compression during the downward load application by the Osterberg test can be ignored, as the procedure of the load application is downward is similar to the direction of the load application by the conventional top-down test. Therefore, the results are comparable, and there is no need for further  
Figure 14: Developed Side Shear Resistance. calculation in the procedure of constructing equivalent load-displacement based on the Osterberg test's downward curve. However, the upward application by the Osterberg test should be adjusted by considering the effect of the elastic compression to simulate the most realistic load-displacement curves compared to the top-down test. During the Osterberg test, the unit side resistance was developed between 20 and 50 feet, where the mobilization of the existing calcite deposits was less than the developed side resistance during the theoretical conventional loading of the shaft. The measured side resistance during the conventional load was about 6 ksf, which was almost twice the developed side resistance during the Osterberg test. Since the caliche was located far from the O-cell, it was not sufficiently mobilized to develop full capacity. The top-down load test reported more interaction of pile and caliche, as higher side resistance values were reported. The increase in caliche side resistance also affected the calculations of elastic shortening.