Concrete clad tunnel foundations stressing - involves composite load bearing structure behind steel formwork, with concrete delivered by pump

摘要

A tunnel is constructed so that the support structure's stability is determined by tension. As concrete (6) is produced, the composite support structure is erected behind steel formwork, with both foundations and concrete connected under pressure to a pneumatic or hydraulic pressure assembly (5), by combined action of concreting pump (15) and pressure pads (2). Pressure level and duration are such as to generate prestressing of the same level as that derived from radial secondary tension in the tunnel ridge from vertical foundation loading, and at least as great as that at half tunnel height from horizontal loading.