It was assumed that the shaft was excavated in 20 metre sections, each section being excavated instantaneously, along with four probe boreholes at the base of the section. Ten days later the probe boreholes were sealed, and the next 20 metre section was excavated.

The figure above is an AVIZIER image of the NAPSAC model, showing the shaft (top right), its probe boreholes, and the surrounding fracture network. The figure below shows an oblique view of the CONNECTFLOW model, with the porous medium shaft, and 10% of the background fracture network.

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The NAPSAC model represented the shaft using a number of vertical planes that extended all the way to the final depth of the shaft. The vertical planes were divided into sub-planes. The transmissivities of the sub-planes were set to be small initially, to represent the undisturbed initial state, and their transmissivities were progressively increased with time, layer by layer, to represent the excavation of the shaft.

The excavation of a deep shaft or drift is an element of many construction projects. In particular, excavation of this type will be needed in order to investigate potential sites for radioactive waste repositories. In such a case, it is important to be able to predict likely groundwater inflows into the shaft during excavation, both to assist in construction, and also to validate hydrogeological models of the site being investigated.

These results indicate that NAPSAC and CONNECTFLOW can be used to model the transient excavation of a shaft, simply by changing material properties and boundary conditions as a function of time. The technique of domain decomposition enables these types of system to be modelled very efficiently, and the software allows for a flexible modelling strategy.