## 3 Effect of Different Influencing Factors  
Effects of Wheel Diameter and Pile Embedment Depth (\(D_{\rm w}\)/\(L\) and \(L\)/\(D_{p}\))  
To investigate the effects of the wheel diameter and pile embedment depth on the lateral bearing performance, a group of numerical analyses is carried out with seven different wheel diameter ratios for the composite foundation (\(D_{\rm w}/L\) = 0, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8, \(L\)/\(D_{\rm p}\) = 7, 9, 11 and 13; Group I, Table 1). Figure 4a shows the normalized lateral capacities (\(H_{\rm ult}/(2\pi R^{3}\gamma^{\prime}_{\rm s})\)) of the composite foundation with different wheel diameters. It is apparent that the lateral capacity and the wheel diameter show an almost linear relationship when \(D_{\rm w}/L\) is within the range of 0 to 0.5. The slope of the curve experiences a rapid increase at the turning point of about \(D_{\rm w}/L\) = 0.5, which shows a good agreement with the observation from the previous investigations [10, 11, 32]. The soil plastic strain distribution at the ultimate condition in terms of plastic strain within and around the composite \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Analysis** & \(D_{\rm w}\)/\(L\) & \(V/V_{\rm ult}\) & \(e\)/\(D_{\rm p}\) & \(T_{\rm s}\)/\(L\) & \(s_{\rm sum}\) & \(\varphi\) (sand) & \(T_{\rm w}\)/\(D_{p}\) & **Notes** \\ \hline Group I & 0, 0.5, wheel & 5.9, 12.7, 6.4, 13.2 & 9 & 1 & 0 & 33\({}^{\circ}\) & 0.8 & Numerical model validation [27] \\  & & (MN) & & & & & & Investigation for the effect of the wheel diameter \\ Group II & 0–0.8 & 0 & 10 & 0.5 & 30 kPa & 33\({}^{\circ}\) & 0.5 & the effect of the wheel diameter \\  & & & & & & & Investigation for the effect of the \\ Group III & 0.6 & 0–95\% & 6–16 & 0.5 & 30 kPa & 33\({}^{\circ}\) & 0.5 & the effect of the combined pre-vertical \\  & & & & & 20 kPa, 40 kPa & & & & \\ Group IV & 0.6 & 0 & 10 & 0.1–0.8 & (\(k\) = 1.75 and 2 kPa) & 20–40\({}^{\circ}\) & 0.5 & effect of thickness of sand layer \\ Group V & 0.6 & 0 & 10 & 0.5 & 30 kPa & 33\({}^{\circ}\) & 0.5–1.25 & Investigation for the effect of wheel thickness \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the numerical simulations. Figure 3: Lateral load-deflection curves obtained from FEM and centrifuge tests. foundation are also illustrated in Figure 3(a). It can be seen that through comparing the composite foundation and the monopile, the main difference of the failure pattern lay on the area at the right side of the foundation. When \(D_{\mathrm{w}}/L=0\), the plastic strain generates from the bed surface at about 3 \(D_{\mathrm{p}}\) away from the right side of the pile, which propagates inwards to the right exterior side of the pile, forming a hill-type failure zone \(\left<f_{2}\right>\). Besides, the failure zone \(f_{3}\) develops from the mudline to the interface of the sand and clay layer along the left pile body side. The failure zone \(f_{4}\) occurs on both sides of the pile in the clay layer due to the rotational movement of the pile. As for the composite foundation with \(D_{\mathrm{w}}/L=0.6\), a semi ellipse-shape failure zone \(\left<f_{1}\right>\) occurs near the right external side of the wheel edge due to the intrusion of the wheel during rotation. Failure zone \(\left<f_{2}\right>\) at the intersection area of the pile and the wheel shows a relative smaller value compared to that of the monopile. The failure zone \(\left<f_{3}\right>\) propagates along the left side of the pile, and eventually reaches the interface of the two soil layers. Similar shape of failure zone \(\left<f_{4}\right>\) can be captured on the composite foundation as that on the monopile. It is evident that the failure pattern of the composite foundation is considerably different from that of the monopile due to the integration of the wheel. As the wheel diameter \(D_{\mathrm{w}}/L\) increases from 0.6 to 0.8, the failure zone \(\left<f_{1}\right>\) enlarges along the loading direction, indicating a greater bearing capacity.