## 3 Seismic Behavior of Micropiles
### Factors of Influence
#### 3.2.1 MP-Related Factors
The reason for that, according to the paper's author [15], is the use of the rubber packer that has a nozzle that drains the slime inside the borehole, which usually develops when using geotextile packers; draining the slime results in a better grouting and thus better performance [15]. [PERSON] et al. [11] performed a comprehensive analysis of seismic performance of a soil-micropile-superstructure system in interaction, starting with a parametric analysis to measure the influence of selected parameters, and then followed by sensitivity analysis to determine the most influential parameters on the performance. The analyzed parameters were inclination angle, MP spacing ratio, MP diameter, etc. Authors concluded that in termsof maximum shear and bending stresses in the MPs studied, the number of MPs used and the slenderness ratio (L/d = 20-60, where L is the length and d the diameter) are among the most influential parameters (the difference in the values of the shear and bending stresses is more than 35% between the cases studied), while MP diameter (d = 0.25-0.45 m) was not so important, which is similar to the behavior of other types of piles [11]. Based on these literature results, it can be affirmed that the behavior of MPs is a combination between the behavior of a \"normal\" pile (more precisely a bored pile), but modified primarily due to the technological differences of the MP installation process, and for this, when a gap in the literature exists regarding a certain aspect of MP behavior, it is common to rely on other sources of literature. This is reflected in the design and analysis process, as many practices are adopted from the ones used with other types of piles. However, occasionally this is done without real or sufficient calibrated data. This practice was accepted in the past in some cases when a sufficient experience existed and MPs were not used to carry an important structure, but at present, it can no longer be accepted, as MPs are involved increasingly more in very complex and important projects. Furthermore, considering the advancement in MP technology, experience alone may no longer be sufficient [1; 2; 3; 10]. [PERSON] et al. [13] studied the effect of MP inclination on the structure dynamic amplification factor, and again a strong relation was found between MP angle of inclination and the amplification factor, which might be due to the stiffness differences between vertical and inclined MPs or to the kinematic interaction. Inclination effects can also be found in [16], which considers the load sharing between the MPs and MPR (micropiled raft). When the inclination angle increases, the part of the load carried by the MPs from the total load imposed on the MPR also increases [13; 16]. In the following figures, some results are presented for comparison. Figure 5 (modified after [13]) shows how the response (the acceleration in this case) is influenced by the MP's inclination angle, once for the pile cap (Cap) and then for the attached mass (Mass) for two excitation types: harmonic and time history record (called \"seismic\" on the graph in Figure 5). Figure 6 (modified after [12]) shows how the dynamic amplification factor is influenced by both the fixity condition (fixed or pinned) and the MP's inclination angle (\(0^{\circ}\), \(20^{\circ}\)) for two values of the frequency, both for the pile cap (Cap) and for the attached superstructure (structure). Figure 5: Soil–MPs–structure response with different inclination angles (compilation after [13]). Figure 6: Dynamic amplification factor with different fixity/inclination of MPs (compilation after [12]). It can be seen from the first chart (Figure 5) that increasing the MP's inclination led to increments in the acceleration of both the cap and the attached mass (dynamic amplification factor increases) in the case of the harmonic excitation.