Experiment informationThe 1g model

Experiment informationThe 1g model tests for twin-tunnelling were conducted by Chapman et al. (2007),and details of the tests can be found in the literature. In this paper, the tunnellingsimulation, test setup, ground conditions, and subsurface settlement monitoring arebriefly introduced. As depicted in Fig. 4, this study just investigates the observationsof Test A with lateral axial distance of 1.6D. The cover-to-diameter ratio C/D was 3.8.The minimum boundary distance was 6.25D. An auger type cutter within a shield wasused for tunnelling. The tunnelling system was mainly comprised of an auger, a shield tunnel, a guide track, and a shield restraint. The auger was withdrawn occuasionally to remove the excavated soil from inside the shield. After the augering was completed, a smaller diameter “liner” tube was connected to the tail of the shield. To generate measurable movements, a volume loss of 12% was created. T2 was constructed at 24h intervals after T1 construction completed. Digital photography was employed for measuring subsurface ground movements through Perspex windows. Subsurface settlements on five elevations above tunnel axis level (dt = 1.1D, 1.4D, 1.8D, 2.1D and 2.5D) were measured.Speswhite kaolin was used for modelling the ground material. The properties of kaolin clay can be found in the literature. The kaolin powder was mixed with water to produce a slurry having a moisture content of approximately 126% so that the slurry could be pumped and to prevent the formation of fabric features. The slurry was then pumped into the mode tank and then consolidated using hydraulic jacks. For consolidation, top and bottom drainage were allowed by using layers of sand and filter sheets. The consolidation pressure was applied step-by-step with loads of 4 kPa, 12 kPa, 25 kPa, 50 kPa and 98 kPa, respectively. After consolidation, the samples had an OCR of 2.7 and average Su values of 20 kPa.