Understanding, and hence predicting, the ground displacements associated with multiple tunnel constructions in soft ground (soil rather than rock) is particularly important in urban areas. It has been shown by a number of previous authors that the effect of previously strained soil above the first tunnel has an effect on the ground displacements observed above subsequent tunnels constructed in close proximity to the first. This paper describes the design, development and preliminary test results for a purpose built test tank for modelling, at approximately 1/50 scale, multiple tunnels constructed in soft clay. The tank is 1.80m long, 0.60m wide and 0.45m high (this height is doubled when the consolidation section of the tank is added). The soil is consolidated from slurry to a prescribed strength by specifying the moisture content. A water bag arrangement is used to maintain a surcharge at the soil surface after consolidation in order to produce a realistic over-consolidation ratio. The tunnels (0.08m diameter) are constructed using an augering technique, with a shield and lining arrangement that allows a consistent 'volume loss' to be produced during construction. The tank has side faces made of clear Perspex, which enables the movement of the soil close to these faces to be observed. The soil displacements are recorded using digital cameras and analysed by computer. The paper describes some of the promising initial test data and the trends observed.
ASJC Scopus subject areas
- Building and Construction
- Geotechnical Engineering and Engineering Geology