ALBERT

Description: Monopiles supporting offshore wind farms are often subject to severe lateral environmental loads due to wind, waves, and currents. Previous studies reported various failure patterns for such rigid monopiles in clay; hence predicting lateral pile capacity of widely different magnitudes. In this study, both single-sided wedge failure mechanism involving passive soil failure only and two-sided wedge failure mechanism with simultaneous active and passive soil failures are proposed. The single wedge mechanism is found to be applicable if the soil behind the pile does not move together with pile resulting in a gap between the soil and the pile upon loading. On the other hand, the two-sided wedge is found appropriate for the soil behind the pile moves together with the pile upon loading. Two formulations are then derived from the two upper-bound failure mechanisms. The lateral pile capacity can be determined, and the corresponding failure mechanism identified based on the formulation which yields the lower capacity magnitude. In addition, the reliability of the formulations is verified against reported finite element methods as well as existing experimental and field test results.

Description: A variety of unconformity types are commonly developed during the rifting of a continental basin. Identifying their origin and evolution is a prerequisite to understanding the complex tectono-sedimentary evolution of the basin and to evaluate the basin’s oil and gas resources. Based on the 2D/3D seismic, geophysical logging, and subsurface lithological data, the unconformities within the rift layer of the Lishu Depression in the Songliao Basin are identified as disconformities, nonconformities, and four “types” of angular unconformities. Their evolution and origin are analyzed by associating the unconformities with the basin’s tectonic evolution. The results show that the rifting of the Lishu Depression was not a continuous process. Instead, several regional tectonic episodes influenced the basin’s evolution. Episodic compressional events and a phase of extension along the main faults determined the basin configuration and sedimentary fill characteristics of different sub-rifting stages. The tectonic history and related paleogeomorphology changes are the dominant factors in the formation of these different unconformity types. During the rifting process, the type and distribution of unconformity varied. In the initial rifting stage, the basin developed a nonconformity and four types of angular unconformities as the result of both regional uplift and fault block tilt. Rotation and tilting of the fault blocks during the intensive rifting resulted in two types of angular unconformities. Finally, in the recession rifting stage, a different form of angular unconformity and disconformity developed, mainly as a result of the regional uplift and subsequent subsidence.