Scour leads to the loss of soil around monopile foundations for offshore wind turbines, which affects their structural safety. In this paper, the effect of scour on the lateral behaviour of monopiles was extensively investigated using finite element analysis, and calibration and comparison were undertaken using centrifuge tests. Piles with three slenderness ratios, i.e., 3, 5 and 8, were studied by keeping the diameter constant and varying the embedment length. Three scour types (local narrow, local wide and global) and four scour depths (0.5D, 1D, 1.5D and 2D; D signifies the pile diameter) were considered in this investigation. The results indicate that the lateral resistance of the pile is the greatest in the case of local narrow scour, followed by that in the cases of local wide scour and global scour. When the scour depth is larger than 1D, the influence of the scour type on the pile lateral bearing behaviour is insignificant. The influence of the scour type and scour depth on the pile lateral bearing behaviour is broadly similar for piles with slenderness ratios of 3, 5 and 8. However, the piles featured with smaller embedment lengths show a larger decrease rate in their lateral capacity, which means the effect of scour should cause more concern on small slenderness ratio monopiles.

Tunneling activity inevitably induces soil stress redistribution and ground deformation, which may affect adjacent existing pile foundations. Since many previous studies have mainly focused on circular tunnels, the effects of quasi-rectangular shield (QRS) tunneling on adjacent existing pile foundations are not well investigated and understood. In this study, a series of physical model tests were carried out to investigate the response of a single pile and pile group subjected to newly QRS tunneling beneath an existing circular tunnel in dry sand. Two distinct underpass cases were considered: an orthogonal underpass (QRS tunnel axis perpendicular to the circular tunnel axis) and an overlapping underpass (QRS tunnel axis aligned with the circular tunnel axis). The test results indicate that QRS tunneling-induced ground surface settlement and single-pile settlement in the overlapping underpass case were 3.6 and 1.2 times that in the orthogonal underpass case, respectively, with a narrower settlement trough. The axial force distribution along the single pile remained qualitatively consistent in both underpass cases, consistently exhibiting a downward load-transfer mechanism, and further leading to a monotonic growth pattern in axial force with progressive QRS tunnel excavation. The additional stress of the single pile was consistently higher in the overlapping underpass case, which had maximum axial force, negative bending moment, and maximum positive bending moment increases of 20%, 13%, and 6%, respectively, relative to the orthogonal underpass case. The front pile in the pile group exerted a pronounced shielding effect on the rear pile, while the restraining action of the pile cap also contributed measurably to the overall pile responses.

Using the foundation pit at the Jianye Road Station of Hangzhou Metro Line 6 as a case study, the deformation characteristics of a foundation pit subjected to asymmetric loads is investigated in this paper using PLAXIS 3D numerical simulation software. The influence of active pressure zone reinforcement, passive pressure zone reinforcement, and increased thickness of the diaphragm wall at the loaded side on the maximum lateral displacement of diaphragm wall retaining structure of foundation pit is also systematically analyzed. The results show that the deformation of the diaphragm walls on both sides of the foundation pit is strongly inconsistent when subjected to asymmetric loads and is affected by the asymmetric load value and its distance to the foundation pit. In order to reduce the lateral deformations of foundation pit subjected to asymmetric load, two displacement control methods are adopted in the numerical simulations. It is shown that reinforcing the active pressure zone can reduce the maximum lateral displacement of the diaphragm wall on the loaded side to a certain extent but the reinforcement should have a certain depth, resulting in poor efficiency. On the other hand, reinforcing the passive pressure zone can effectively reduce the difference in lateral deformation between the two sides of the foundation pit by increasing the depth and width of the reinforcement zones. It is also observed that the increase in the thickness of the diaphragm wall can reduce the adverse effect of asymmetric loads on the foundation pit. The research results can provide reference for using measures to reduce the influence of asymmetric loads.

Tunnels and foundation pits are two separate types of excavation that are frequently used in urban settings. Excavating tunnels and foundation pits sequentially around existing pile foundations is becoming more and more prevalent as urban underground space utilization rates increase. The deformation and load transfer mechanisms of the pile group foundation under two asymmetric excavation conditions of “first tunnel, then foundation pit” and “first foundation pit, then tunnel” are studied from the perspective of the relative positions of the tunnel–pile–foundation pit based on the constant gravity model test and 3D numerical simulation. The result shows: The pile settlement of the front pile (closer to the tunnel) caused by the excavation condition of the “first foundation pit-then tunnel” is relatively larger, while the pile settlement of the rear pile (closer to the foundation pit) caused by the excavation condition of “first tunnel-then pit” is larger. The transverse tilting of the pile group caused by the excavation of the “first foundation pit-then tunnel” is relatively larger. For the front pile, the pile tip resistance generated by “first excavation-then tunnel” is about 10% greater than it was before the initial excavation, which is greater than the result of “first tunnel-then foundation pit”. For the rear pile, the pile tip resistance generated by “first excavation-then tunnel” is about 85% greater than it was before the initial excavation, which is smaller than the result of “first tunnel-then foundation pit”. The multiple excavation sequence of “tunnel first-then foundation pit” leads to a larger induced bending moment for the front pile, whereas a larger induced bending moment for the rear pile results from the multiple excavation sequence “first foundation pit-then tunnel”.