Model Test on Mechanical Behavior of Two Shallowburied Closelyspaced Tunnels at Different Elevations Under Unsymmetrical Load

Abstract:

Reduced scale model tests of two parallel shallowburied closelyspaced tunnels at different elevations under unsymmetrical load were carried out to simulate the interaction effects of different excavation sequences (excavation of the right tunnel first and excavation of the left tunnel first),and variations of stresses and settlements in the wall rock especially in the rock pillar were obtained.The results of tests show that,for the shallowburied closelyspaced tunnels,especially when the two tunnels are at different elevations,the excavation of both the right tunnel and left tunnel has significant effects on the pillar; moreover,the final surface and subsurface settlements caused by the former excavation sequence are 3% to 48% larger than those caused by the later; and the release of stresses in the rock caused by the former excavation sequence is 3% to 46% higher than those of the later.So,it is believed that excavating the left tunnel first can improne the stability of the two tunnels.The empirical method is not suitable as it suggests the outer tunnel (the right tunnel in this paper) should be excavated first when the closelyspaced tunnels are at a same elevation under unsymmetrical load.Furthermore,the results of numerical simulation and field investigation verify the rationality of model tests.

Key words:closelyspaced tunnels; model test; tunnel excavation; release of stress; settlement