# Comprehensive Evaluation of Lateral Performance of Innovative Post in Sand
## 3 Innovative Post Pile (IP)
### Failure Mechanism  
The pile ultimate lateral capacity depends on the characteristics of the surrounding soil and the pile material and cross-section and length. Long innovative posts are considered flexible piles, and short innovative posts are considered rigid piles, primarily based on their rigidity slenderness and relative rigidity compared to surrounding soil. The pile slenderness ratio, L/D, indicates the pile type and its potential mode of failure. The \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Specimen**} & \multicolumn{3}{c}{**Failure Criteria**} & \multicolumn{2}{c}{**Difference (KN)**} & \multicolumn{2}{c}{**True Error (\%)**} \\ \hline S10 & PLAXIS & 61.55 & 79.54 & \(-9.064\) & - & \(-12.84\%\) & - \\  & Field & 70.614 & - & \(-9.064\) & - & \(-12.84\%\) & - \\ \hline S12 & PLAXIS & 64.53 & 87.87 & \(-0.02\) & 8 & \(-0.03\%\) & \(10.02\%\) \\  & Field & 64.55 & 79.87 & & & & \\ \hline S16 & PLAXIS & 78.72 & 111.76 & & & & \\ S16 (1 st) & Field & 75.71 & 128.24 & 3.01 & \(-16.48\) & \(-3.98\%\) & \(12.85\%\) \\ S16 (2 nd) & Field & 73.84 & 100.99 & 4.88 & \(10.77\) & \(-6.61\%\) & \(-10.66\%\) \\ \hline S20 & PLAXIS & 121.3 & 165.14 & & & & \\ S20 (1 st) & Field & 100.22 & 161.03 & 21.08 & 4.11 & \(-21.03\%\) & \(-2.55\%\) \\ S20 (2 nd) & Field & 95.4 & 153.6 & 25.9 & 11.54 & \(-27.15\%\) & \(-7.51\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of lateral load capacity different design methods. Figure 8: Load-displacement curve and envelope load-displacement curve for S10 and S20 posts (test 1). ultimate lateral capacity of long piles is dictated by its flexural stiffness. In this case, as the applied lateral load increases, the maximum bending moment that develops at the pile cross-section increases until it reaches the yield moment of the pile. The short pile lateral resistance is primarily influenced by the soil strength. This resistance corresponds to the applied lateral load that develops yield strain within the soil mass in front of the pile shaft. The failure of a short pile with fixed-head condition occurs due to lateral displacement, while failure of a short pile with free head condition is a consequence of the pile rotation which leads to passive soil resistance with high strains on the front side of the pile upper portion and behind the lower portion of the pile (below the point of rotation). Pile stiffness assessment can be conducted by considering the ratio of embedded length to diameter, denoted as L/D. A pile with an L/D ratio less than 6 typically exhibits behavior characteristic of a short pile, while one with an L/D ratio greater than 10 is more inclined to behave like a long pile, as indicated by previous studies [29] [PERSON] et al. [30] established a threshold for flexible piles, defining them with L/D values exceeding 20. Evaluation of pile rigidity may entail determining the pile flexibility factor, denoted as \(K_{r}\), as presented by [PERSON] and [PERSON] [31]. \[K_{r}=\frac{E_{p}I_{p}}{E_{s}L_{p}^{4}} \tag{2}\]  
where \(E_{p}\) and \(E_{s}\) are [PERSON]'s modulus of the pile and soil, \(I_{p}\) and \(L_{p}\) are the moment of inertia of and embedded length of the pile. It is anticipated that short piles will have \(K_{r}>0.01\), while flexible piles will have \(K_{r}\leq 10^{-5}\). The allowable design load for sound walls is usually governed by the serviceability limit state rather than the ultimate limit state. Hence, the experience-based lateral serviceability standards for piles are established. The capacity of piles to resist lateral forces is characterized by the load applied at the pile head, corresponding to a specific lateral deflection of the pile head. Consequently, this discussion incorporates various failure criteria grounded in pile head lateral displacements. Table 3 presents different lateral failure criteria and the associated pile lateral capacities derived from field test data aligned with these criteria. As expected, the lateral capacity increases as the lateral deflection tolerance increases.