The thinner pen paradox

In order to assess potential movements and the risk to the assets during and after construction, a monitoring system with suitable levels of accuracy, repeatability and frequency is required to provide construction teams with up to date information on which to base construction decisions. The optical system (Robotic Total Stations (RTS) and 3D Prisms) has been widely used on Crossrail for this purpose and this shall be the main focus of this paper.

As part of the risk assessment procedure prior to starting construction it is necessary to carry out damage assessments for all foundations and structures within the zone of influence (ZOI) of a potential construction. These assessments provide absolute deformation parameters for each asset such as the maximum tensile building strain for different building lengths in each hogging and sagging zone, the maximum bending and shearing tensile strains for short and long buildings and the bending and horizontal strain components for short and long buildings. Generally, these parameters are compared to the predicted volume losses and a risk-based approach to damage assessment is adopted with triggers determined accordingly.