Risk, how it is managed, and how it is allocated as between contracting parties, is perhaps the most important subject-matter for consideration by anyone embarking upon a building or engineering project. One particular source of risk to which building and engineering projects are prone is the risk that site conditions will turn out to be less favourable than anticipated at the time of entering into the particular contract. Over and over, projects have been affected by unexpectedly bad ground conditions, and by the physical state of existing structures on which work is to be performed being worse than was foreseen. Running silt or sand, hard rock, inherent ground water2 are typical culprits in this project quagmire. There are many others.3 The effects of unexpectedly adverse site conditions may be manifold. Works may have been planned on certain assumptions: that excavation could be effected using certain plant, that ground would be suitable for certain foundations, or that the ground would permit the use of particular work methods. The discovery of bad ground may necessitate a change to those work methods, possibly a complete revision of those work methods or the design of the works themselves. In extreme cases the works may need to be abandoned altogether. Even if the required work is capable of being performed in the manner originally contemplated, it may take longer than planned, or cost more, or both, all because of unexpectedly bad site conditions.