Building damage and repair due to leakage in a deep excavation

The north-south line in Amsterdam is being built underneath the historic centre of the city. Three deep stations are being constructed in deep excavations supported by diaphragm walls. During the excavation for Vijzelgracht station, leakage through the wall resulted in large settlements and damage to historic buildings, which threatened continuation of the project. The authors analysed the cause of the leakage and the damage to the buildings. With the application of robust preventative measures at two of the deep excavations it was possible to continue the project. This paper reports on the cause of the events, the damage to the buildings and the counter-measures taken. It includes lessons learned for the project and for the foundations industry.

The influence of boundary conditions on tip leakage flow

Most of the current understanding of tip leakage flows has been derived from detailed cascade experiments. However, the cascade model is inherently approximate since it is difficult to simulate the boundary conditions present in a real machine, particularly the secondary flows convecting from the upstream stator row and the relative motion of the casing and blade. This problem is further complicated when considering the high pressure turbine rotors of aero engines, where the high Mach numbers must also be matched in order to correctly model the aerodynamics and heat transfer. More realistic tests can be performed on high-speed turbines, but the experimental fidelity and resolution achievable in such set-ups is limited. In order to examine the differences between cascade models and real-engine behavior, the influence of boundary conditions on the tip leakage flow in an unshrouded high pressure turbine rotor is investigated using RANS calculations. This study examines the influence of the rotor inlet condition and relative casing motion. A baseline calculation with a simplified inlet condition and no relative endwall motion exhibits similar behavior to cascade studies. Only minor changes to the leakage flow are induced by introducing either a more realistic inlet condition or relative casing motion. However when both of these conditions are applied simultaneously the pattern of leakage flow is very different, with ingestion of flow over much of the early suction surface. The paper explores the physical processes driving this change and the impact on leakage losses and modeling requirements. Copyright © 2013 by ASME.