# Comprehensive Evaluation of Lateral Performance of Innovative Post in Sand
## 3 Innovative Post Pile (IP)
### Load Displacement Curve  
Two groups of posts (Group 1, and Group 2) were tested. The first set was made up of a w-section pile with two welded plates at the flanges, whereas the plates in the second group were attached to the pile with clips. The paddled piles were loaded along the weak axis (i.e., axis with the lower moment of inertia). Figure 6 depicts the horizontal load-displacement responses of Group 1 posts, the ultimate capacity of S10, S12, and S16 established from the load tests were 95 KN, 82 KN, and 125 KN, respectively (considering an average value for S16 tests excluding the third test). The residual displacement after unloading for the pile was approximately 4.8 mm, 8 mm, and 4 mm for innovative posts S10, S12, and S16, respectively. In other words, the piles recovered up to 61.5%, 57.4%, and 75.0% of the displacement throughout the unloading process. It should be noted that the third test for the S16 pile deviated from the other two tests, showing a much lower lateral resistance than the other two tests. The softer behavior and lower capacity are attributed to high soil disturbance during the installation (based on observations during installation). In Group 2 tests, the 450 stringers at the end of the paddle were bent during the installation of the fourth specimen of the S20 pile. Therefore, the soil around the pile was disturbed, and the pile exhibited significant lateral displacement, as shown in Figure 7. The installation method (vibratory driving in dense sand) and installation process of the clipped piles (Group 2 piles) caused disturbance to the adjacent soil, this disturbance is mainly related to installation difficulty (i.e., which required shaking the pile, lifting and reinstalling it), and the \"C\"-shaped steel clips which  
Figure 5: Test setup and pile instrumentation: (**a**) Group 1 tests; (**b**) Group 2 tests. most likely increased soil disturbance. According to the field testing results, the ultimate lateral capacity of the S20 posts ranged from 212 kN to 196 kN, with an average of 204 kN corresponding to lateral displacements of 24.5 mm, 26 mm, and 23 mm, respectively. The recorded residual displacement has an average value of 11 mm. To evaluate the performance of the FEM 3D models compared to filed data, the error was calculated considering various failure criteria based on pile head lateral displacements: 6.25 mm by [PERSON] [25], 13 mm by [PERSON] and [PERSON] [26]. \[\text{Error }(\%)=Load(\frac{\text{Field}-\text{FEM}}{\text{Field}})\times 100 \tag{1}\]  
Table 2 compares the pile lateral capacities considering the different lateral failure criteria, derived from field test data, with those obtained from the 3D Finite element analysis. It is noted that, for S20, as the tolerance value increases, the error percentage reduces dramatically. The deviation of the FEM model from the field results at lower failure criteria can be attributed to the creation of the gap between the soil and the pile due to installation practice. Overall, the low error percentages observed demonstrate that the FEM scheme used herein is suitable for replicating the response of the PHPs and hence PLAXIS 3D can be used as a reliable tool for their design. Figure 6: Load-displacement curves obtained from pile load tests, for Group 1 tests: S10, S12, and S16. Figure 7: Load-displacement curves obtained from the pile load tests, for Group 2 tests: S20 innovative post. The anticipated load-displacement behavior of a pile under lateral load may be segmented into three phases. The first segment represents linear behaviour. This is followed by a nonlinear response segment that tends toward plasticity. The last stage is characterized by full slippage along the side of the pile's body and complete plasticity of the bearing soil manifested by another linear segment. [PERSON] and [PERSON] (2017) and [PERSON] and [PERSON] (2018) reported the same behavior for laterally loaded micropiles and PHPs in clayey, respectively. [PERSON] et al. (2018) observed sand heaving concurrently with gap opening during the second phase.