Site investigation works undertaken as part of the Crossrail cross-London railway project over the last 10 years have involved extensive intrusive works into the ground in areas of London which were known to have been heavily bombed during the Second World War. This bombing created a legacy of unexploded ordnance risk to such works. This paper explains how a procedure was developed to enable the risk to the ground investigation works to be assessed and for appropriate and effective measures to be identified where necessary to mitigate this risk. It is shown that the developed procedure is consistent with that now recommended by the Ciria guide on unexploded ordnance, and provides a practical illustration of how an appropriate risk assessment procedure can avoid extensive and unnecessary mitigation works on site, while ensuring that when mitigation measures are undertaken, it is where and when they are truly needed to enable work to progress safely.
Napoleon Bonaparte was, in 1798, the first general to include geologists as such on a military operation. Within the UK, the following century saw geology taught, and national geological mapping initiated, as a military science. Nevertheless, military geologists were not deployed on a battlefield until World War I, first by the German and Austro-Hungarian armies and later and less intensively those of the UK and USA. Geologists were used primarily to guide abstraction of groundwater, construction of ‘mine’ tunnels and dug-outs, development of fortifications and quarrying of natural resources to enhance or repair supply routes. Only the USSR and Germany entered World War II with organized military geological expertise, but the UK and later the USA made significant use of military geologists, albeit far fewer than the c. 400 in total used by German forces. Military geologist roles in World War II included most of those of World War I, but were extended to other aspects of terrain evaluation, notably the rapid construction of temporary airfields and factors affecting cross-country vehicular movement (‘going’). After 1945, more military geologists were used in the USA than Germany or the UK, in these and wider roles, but mostly as civilians or reservists.
The Crossrail project is a new underground railway running east–west through the heart of London. It will connect with 110 km of new or upgraded sections of surface rail to Reading, Shenfield and Abbey Wood. Crossrail co-ordinated ground investigations for the central tunnelled sections began during the 1990s and continued to 2011 according to a strategy that was based on a review of other major tunnelling projects and best practice. The level of detail in the investigations varied according to local geological complexity and design requirements. However, the state of knowledge on the geological structure is hampered by London's long history, leading to assumptions on the level of complexity or simplicity. Drift-filled hollows and Lambeth Group sand channels were known features presenting risks to excavations but relationships with faulting were unknown or unproved. The emerging geological knowledge was developed through multiphase investigations and collation of third-party data to allow far-field considerations. The risk profile for tunnel boring machine tunnels is lower than that for sprayed concrete lined tunnels but the risk for both increases with increasing proximity to pre-existing infrastructure. Ground movement assessments become critical and mitigation of movements can be significantly affected by unexpected variations in ground conditions.
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