## 3 Results of the Parametric Study
### Effect of the Pile S slenderness (L/D) on the Behaviour of Pile Groups  
The distributions of loads at different pile locations for pile slenderness ratios, _L/D_, of 10, 20, and 40 are shown in Figure 10a,c, respectively. It can be seen that the developments of the load ratios, \(P_{i}/P_{\text{avg}}\), at different pile locations are not constant and are dependent on the load level and the pile slenderness ratio. The load distributions for the short pile group with _L/D_ = 10 are more nonuniform and more sensitive to changes in the load level than those for the long pile group (i.e., _L/D_ = 20 or _L/D_ = 40). These results indicate that the load-transfer mechanisms of the short pile group are quite different from those of the long pile group. The long pile group deforms similar to a rigid \"block\" and, therefore, results in a more uniform load distribution along a single pile in a pile group. However, the shorter pile group introduces different degrees of loads at different pile locations in the group. Interestingly, the load ratio for the longer pile groups remains constant up to a load level of approximately 60%, which indicates that the longer pile group is more effective in transferring the pile loads into the deeper and stronger soil strata below the pile base. Figure 9: Degrees of mobilisation of shaft stress along the pile depth at different individual pile locations under different load levels in a 9 \(\times\) 9 pile group. (a) 80% ultimate load; (b) 50% ultimate load; (c) 30% ultimate load. An alternative way of understanding the load-transfer mechanisms of pile groups is through the examination of the shaft shear stress development profiles as shown in Figure 11a-c (only showing the results at 30% of the ultimate pile group's capacity). For comparison proposes, the development of the shaft shear stress profiles for single piles is also included in the figures for reference. In the short pile groups, the development of the shaft shear stress profile (especially pile 2) is very similar to that of a single short pile, whereas the development of the shear stress of the shaft of the long pile groups is very different from the development of the shaft shear stress of a single long pile. The shaft shear stress increases rather gradually with depth for the long pile group, whereas the development of the shaft shear stress for a single long pile is highly nonlinear and is mobilised to a higher degree than for the pile group. Figure 10: Load ratios developed at individual piles of the 9 \(\times\) 9 pile group with load levels. (**a**) \(L/D=10\); (**b**) \(L/D=20\); (**c**) \(L/D=40\). Figure 12a-c show the ratios of the total shaft load of an individual pile, \(p_{yi}\), and the base load of an individual pile, \(p_{bi}\), with the pile head load carried at each individual pile, \(p_{li}\), of a 9 \(\times\) 9 pile group under different load levels and slenderness ratios. The behaviour of the single pile is also included in the figure for a direct comparison. For the single pile, the shaft shear stress is mobilised more substantially and carries most of the applied load, while only a small portion of the total load is transferred to the bottom of the pile. At the same time, more loads are being transferred to the base area of the pile groups. In pile groups with slenderness ratios, \(L/D\), of 20 and 40, the shaft load increases with the load level, which is contrary to the response of the single pile whose shaft load decreases with an increase in the total load level. As pointed out by [PERSON] [30], because the axis response is more interactive than the base response, the interaction is that the load is transferred to a larger proportion of the base of the group pile than the single isolated pile. Through three-dimensional finite element analysis, [PERSON] [31] proposed that the load transmitted to the bottom of a pile is much higher for the 3 \(\times\) 3 and 3 \(\times\) 5 pile groups than for the single pile. Similar behaviour was also observed in experiments by [PERSON] et al. [32] and by [PERSON] [33].