Ensuring the continued stability of Amsterdam's historic buildings while a new underground railway system is built has been achieved by pioneering analysis of soil settlement by a geotechnical software tool.
DIANA, an advanced geosynthetic analysis package, was used to predict the effects of tunnelling under the city. Various types and layers of soil can produce different deformation effects, making the analysis of tunnel operations - including whether or not the foundations of buildings will be disturbed - highly complex.
Previous research into the geological characteristics of the city found that soft soil layers passed partly through a high water table, with layers of sand, soft clay and a mixture of peat also present. Cross sections of the Amsterdam soil were taken and fed into the DIANA program.
Design team leader for the Amsterdam project, Frank Kaarberg, says: 'It is a very advanced geometrical and physical non-linear program which can recognise pile formations, and takes into account cracks and second order deformation.'
Using the program, the effects of cutting through different subsoils are clearly visible, and the software gives recommendations as to the shape of the tunnel boring machine, cutting action and the shape of the tunnel wall. It also recommends the appropriate boring components for different soil types. The aim in Amsterdam was to find a way of making sure that any deformation caused by passing through different layers could be minimised, and the possibility of damage to buildings eradicated.
Pressure control liquids adjusted the front of the boring machine, and the inclusion of an Interactive Boring Control System kept a check on the machine's progress according to initial design plans.
The UK agent for DIANA is Wilde & Partners.