TBM experiences, costs and time, contractual implications, risk sharing and mitigation Grandori R., Sposetti M. SELI S.p.A., Rome, Italy Online published on 26 June, 2013. Abstract The market demands new infrastructures for railway lines connecting countries worldwide. At the same time, due to the increased price of electric power, many huge hydropower projects will have to be executed all around the world. Most of these railway lines and hydro projects include extremely long tunnels to be bored by TBM under high cover and complex geologies through the Alps, the Himalayas, the Andes and other main mountain chains. Many foreseen and unforeseen difficult geological conditions will have to be faced in executing these tunnels. Part of these difficulties could be foreseen and overcome through accurate geological investigations, proper selection of the tunnels alignments and efficient support/lining designs. Despite the above the geological risk can never be completely eliminated. Special combinations of hydro-geological factors can always occur and the huge forces that nature can develop at great depth under a mountain may cause local exceptional geological conditions and behaviours that are an obstacle to the normal TBM tunnelling operations. To overcome these events special measures shall be normally implemented with consequent additional costs and delays. Top |