Reduced-scale model tests for cut and cover tunnels subjected to eccentric load

Abstract

Cut and cover tunnel has been considered to be an environment-friendly construction technique to reduce the anticipating destruction of ecosystem. This paper describes the results of reduced-scale model tests for cut and cover tunnels, which are especially subjected to eccentric load. Experimental tests were carried out carefully under control and according to designed procedures. The scale principle that has strong influence on model test results was characterized by flexibility theory. All the model tests were performed using sand under plane strain two-dimensional condition without water pressure and earth pressures, radial displacements, and internal and external strains of model lining were measured. Direct pressure on the top of model cell was applied by air pressure to simulate the overburden pressure induced by the construction of embankment. Two main conditions were set to observe the influences of eccentric load on cut and cover tunnels: (a) location of embankment slope; and (b) angle of embankment slope. The model cell, measuring 150 cm wide by 30 cm long, was manufactured on steel base as shown in Fig. (a). To simulate the in situ high pressure in field condition, the pressure apparatus was designed as shown in Fig. (b). Model ground was formed with dry sand by raining method and the construction sequence was simulated by pressure apparatus. Model tunnel lining was fabricated with aluminum and had a diameter of 30 cm in a half circle shape Fig. (c). Model lining thickness was determined to 8 mm based on scale principle with flexibility ratio (EI). Based on the results of experimental tests, the measurements were analyzed and interpreted: (a) The earth pressure on the side of eccentric load increases rapidly when the locations of embankment slope are within 1.0 D (D: equivalent diameter of tunnel model) from the center of model lining. (b) The earth pressure on the side of eccentric load increases in proportion to the angle of embankment slope. (c) The measurements of displacement and strain show that the lining on the side of eccentric load, deforms into the tunnel, however, contrary behavior of lining is found on opposite side. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.