Too little support force at the palm surface during shield excavation can lead to destabilization of soil before the excavation face and cause ground subsidence. Construction disturbances during excavation can affect the mechanical properties of the surrounding soil, which cannot be ignored when determining the needed support force at an excavation face. Based on the Mohr - Coulomb yield criterion, the collapse of dense sandy soils before the excavation face of shallowly buried shield tunnels is simulated using PLAXIS 3D to determine the collapse mode. Furthermore, the prismatic body in the traditional 3D wedge model is modified to an inverted elliptical-truncated cone with a certain inclination so that the collapse zone is closer to real sliding soils, and the disturbance ratio r is introduced as an index to consider a construction disturbance. The expression of the active limit support force with respect to wedge inclination is derived, and the maximum support force is determined by trial and error to be the minimum support force needed. The results of the modified 3D curved model are in good agreement with the numerical simulation results, as well as the results of theoretical methods and model tests.

Offshore wind farms are located in marine environments with complex hydrological, meteorological and submarine geological conditions, which pose difficulties for wind turbine foundation design and construction. Therefore, the study of the key technologies of offshore wind turbine foundation design has important theoretical value and practical significance for the assurance of structural safety, the optimization of structural design and the extension of structural service life. In this paper, a numerical simulation model of three pile foundation is established, and a detailed FEA model of grouted area is calculated and analyzed, and influence of grout on performance under different loading conditions is calculated and analyzed. The results show that it is feasible to use the p-y curve method to describe the pile-soil interaction of the three-pile foundation of the offshore wind turbine, the stress check of the whole foundation structure under ultimate load conditions and normal load conditions meets the requirements of the DNV specification, and the result of the fatigue damage check is that the fatigue strength requirement is met in 26.7 years, which indicates that the three-pile foundation structure of the offshore wind turbine is safe and reliable and can be operated safely.