## 4 Conclusions  
A laterally loaded single pile is a soil-structure interaction problem that represents an interdisciplinary subject characterized by material non-linearities affecting both the soil and the pile. The possibility to capture the variation of the pile-soil relative stiffness during the application of a lateral load is a key aspect for the assessment of the overall lateral response. Even today, in fact, most of the computational platforms are specialized either for structural or for geotechnical applications.  
Moreover, it is well known that the response of a single pile subjected to lateral load is mainly affected by the shallower soil layers. It is, therefore, an important aspect a proper evaluation of suction in case of partially saturated conditions. Such, in fact, can be responsible for a higher initial stiffness of a single pile under lateral load and for a higher lateral resistance that should be considered.  
For these reasons, a hybrid BEM-py curve method has been developed to study single piles under horizontal loading. This approach allows analyzing single piles with free or fixed head restraint conditions. The proposed method is innovative because it considers the highly non-linear response of circular reinforced concrete pile sections, taking also into account the influence of tension stiffening, and considers suction for partially saturated soils by means of the Modified-Kovacs Model.  
The proposed method has two main advantages compared to more sophisticated codes: the time saved for computation (typically less than one minute for a complete analysis) and the simplicity  
Figure 13: Computed bending moments of B7 single pile at various load levels (results obtained considering suction).  
in input data determination, since these can be obtained by means of a standard site investigation. The reliability of this method was verified here by comparing results from data from full scale and centrifuge tests on single piles (with a total of 22 case histories studied).  
The results obtained have highlighted the possibility to provide a good forecast of the most representative aspects of the single pile lateral response.  
The prediction errors are for most of the cases lower than 20%. The errors are higher for the case histories in which the piles were steel-pipes filled with grout, so the initial pile flexural rigidity could be affected by the steel/grout interaction. The proposed model reproduces in a very accurate way the measured data for reinforced concrete piles in sand. A detailed comparison is also presented between measured and computed data on a large-diameter reinforced concrete bored single pile laterally loaded in a full-scale test program realized by [PERSON] et al. [43]. The computed results are in good agreement with the experimental data. Finally, it is important to underline that all the analyses have been carried out not as back-analyses but as class A predictions, using as input the actual pile properties and the soil strength and stiffness parameters according to the interpretation of the in situ and laboratory tests data.  
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.  
[PERSON] and [PERSON] developed the proposed model for the laterally loaded single pile, [PERSON] analyzed the data and performed the comparison with experimental tests; [PERSON], [PERSON] and [PERSON] wrote the paper.  
The authors declare no conflict of interest.