The soil deformation around the pile was explored to evaluate the compatibility between the numerical calculations and laboratory testing. To study the mechanism of liquefaction-induced significant soil-pile deformation, it is found that the two forms of modeling (using Kope and Ali Algharbi earthquakes) be consistent at the same time with the experiment results. Soil-pile deformation in the laboratory experiments (Hussein and Albusoda 2021) was presented by the vertical and horizontal displacements. Soil-pile deformation from the numerical modeling was further illustrated via MIDAS GTS NX. Figure 5 shows the contour lines and the vectors of the maximum total deformation of soil layers and figure 16 shows the maximum vertical and lateral deformation of the pile, due to applying a couple of static loads (50% of the allowable vertical load and 50% of the allowable horizontal load) with two different ground acceleration (Kope and Ali Algharbi).
Dilatancy is a phenomenon related to dense soil subjected to shearing. In other word, when a dense sand layer experiences shear force, the overall volume of the intended layer increase. This phenomenon was observed by the current numerical model as shown in figure 5. The low liquefaction ratio in a dense sand layer may attribute to the dilation phenomenon which in turn considered as the liquefaction resistance (Madhira and Jaswant 2000). Thus, the phase transition was very noticeable in which the volumetric strain shifted from contraction in a loose sand layer to dilation in the dense sand layer.
From figure 5, it can be noticed from the direction of the vectors that the soil particles pushed aside during the dynamic excitation and the settlement of the soil increased as getting far from the pile body. Thus, the maximum soil settlement was observed at the far-field, similar observations were obtained by Chian and Madabhushi 2014 during the investigation of the uplift of the ground structures due to dynamic excitation.
Pile response during dynamic excitation is highly influenced by the nonlinearity of soil-pile interaction. The pile distortion during the high-intensity ground acceleration of Kope earthquake (around 0.82g) was clear in figure 6a, this deformation may be attributed to the material nonlinearity, cyclic loads during the high ground acceleration cause soil movement, which in turn affects the pile strength. As the loose soil softens due to liquefaction, the stresses around the pile start to diminish. In other words, as the soil loses its stiffness owing to liquefaction, the pile becomes an unstable column. Thus, the pile friction resistance will begin to deteriorate, and the pile may buckle as a result of existing an axial load on the pile cap. Manish et al. 2017, stated that the degree of pile deformation is controlled by pile's stiffness, depth of the saturated loose sand layer, and the intensity of the ground motion. As for the vertical settlement, it is likely that the pile will drop vertically or incline in one direction as a result of a complex effect of buckling and bending. In this manner instead of the pile is to resist both skin and end bearing resistance, the pile now is only resisting the end bearing, and this phenomenon will definitely reduce the geotechnical capacity to some extent because the contact surface area of the pile skin to resist the down drag effect has diminished (figure 16). This will not only cause buckling due to the loss of all-around stresses but will definitely cause a negative skin friction impact i.e. down drag to the pile if the end bearing is insufficient to cater for the geotechnical influence from the soil and also from the structural load.
On the other hand, the pile followed the soil motion during Ali Algharbi earthquake without a significant buckling or deformation as shown in figure 6b. That may be attributed to the low ground acceleration (around 0.1g), so the pile stiffness was enough to resist the ground shaking. In another word, the loss of skin friction of the pile is lower, due to lower vibration of the ground.
The above results were validated (by using the scaling law of Wood (2004)) by the experiment findings (Hussein and Albusoda 2021), as shown in figure 7. As predicted by numerical and experimental findings, the magnitude of the pile settlement increased with higher input acceleration (Kope earthquake). This indicates the considerable influence of shaking intensity on the soil-pile response as previously noted.
Based on these results, the pile displaced vertically and laterally relative to the surrounding soil during different load increments rather than a smooth 1-D movement as stated by Chian and Madabhushi 2012.