## 3 Results of the Parametric Study  
### Basic Performance of Large Pile Groups  
In this section, the soil parameter profiles determined through back-analysis as described by [PERSON] [26] will be adopted for the parametric study. For the convenience of analysis and to capture the basic behaviour of pile groups, the linear regression-analysed  
Figure 7: **(a) Geology of ground for the [PERSON] [26] case; (b) Predicted Ksi profile; (c) Predicted \(\tau_{\text{f}}\) profile. 1: Very Stiff Gray and Tan Clay (CL-CH) 2: Stiff Gray and Tan Sandy Clay with Sand Seams (CL)3: Stiff to Very Stiff Red and Light-Gray Clay (CH) 4: Stiff to Very Stiff Light-Gray and Tan Sandy Clay with Sand Pockets (CL). **  
\(\overline{K}_{si}\) and \(\overline{\tau}_{f}\) profiles (Equations (16) and (17)) are adopted to model the nonlinear soil-pile interface in this parametric study. As the first step in parametric research, the 9 \(\times\) 9 pile groups will be studied to understand the performance of the large pile groups. The pile cap is assumed to be rigid and has no contact with the ground. The pile slenderness ratio, _L/D_, is assumed to be 20 and the spacing ratio, _S/D_, is assumed to be 3. Figure 8 shows the load-settlement curves of the various individual piles at different locations in the 9 \(\times\) 9 pile groups. The results show that the load-settlement behaviour is different at the various pile locations. Under a given settlement, the individual pile located at the corner of the group (pile 1) carries the largest axial load and the lowest load occurs at the centre pile (pile 5). As the total load increases and the failure state approaches, the differences in the pile loads carried by individual piles at different locations become very small and they all fail at the same ultimate load. Figure 9a,c show the degrees of mobilisation of the shaft shear stress that develop along the pile at different pile locations under load levels of 80%, 50%, and 30% of the ultimate load. Generally, at a low-stress level, the degree of mobilisation of the shaft shear stress at a shallower pile depth is larger than that at a deeper pile depth. This indicates that shaft shear stresses are gradually mobilised from the top of the piles and transferred to deeper portions of the piles. However, as the stress level increases, the mobilisation of the shaft shear stress becomes more uniform with depth. It should be noted that the distributions of the shaft shear stresses with depth for the 9 \(\times\) 9 pile group are substantially more uniform in comparison with that of the single pile. Furthermore, it can also be observed that the mobilisation of the shaft shear stress is the highest for the corner range piles and the lowest for the core range piles. At 80% of the ultimate load, the corner pile is almost fully mobilised along the entire pile shaft and more shear stresses are transferred from the corner piles to the core piles just prior to the ultimate failure of the pile group. Figure 10b shows the load ratio (\(P_{i}\)/\(P_{avg}\)) between the vertical load induced at a given pile location (\(P_{i}\)) and the average vertical load carried by the pile groups (\(P_{avg}\)) with the applied load level. Generally, when the total load is less than approximately 30% of the ultimate load, the responses of individual piles are largely elastic. The load carried by the corner pile is approximately 1.3 times the average applied load, whereas the centre pile carries approximately 0.8 times the average applied load. The load ratio remains constant at this range of load levels, which implies that the load distribution among the pile group basically remains unchanged and that the stiffness of the pile group remains constant. [PERSON] et al. (2019) observed similar features in experiments when piles that were loaded through a stiff pile cap took a higher proportion of an applied load than the central piles.