مهندسی عمران شریف (Aug 2017)
AN INVESTIGATION OF SEGMENTAL TUNNELS BEHAVIOR UNDER NORMAL AND REVERSE FAULTING, USING GEOTECHNICAL CENTRIFUGE MODELLING
Abstract
Full-mechanized excavation methods of tunnel have promoted segmental lining. One of the great and permanent ground deformations is called faulting. Tunnels are at the risk of faulting due to their long length. There are few studies that examine the behavior of tunnels intersecting the fault zones although it is a continuing concern for design engineers. In the present study, a physical model of a normal and reverse fault and segmental tunnel in a centrifuge has been modeled and tested, and then the results of eight centrifuge tests have been reported. The results indicate that segmental tunnels under the effects of reverse faulting have better resistance compared to the normal faulting. Tunnel failure mechanism in the reverse faulting is longitudinal deformation due to faulting compressive force. For certain amount of PGD, in the normal faulting, a small length of tunnel is affected by fault compared to the reverse faulting. It is related to the width of shear band in the model. Comparing to the free field, the tunnel in the model causes the faulting face some changes. In the normal faulting, the faulting is brought about to be inclined toward the hanging wall and in reverse faulting toward the footwall.The results show the absence of sudden failure of segmental tunnels under normal faulting and improvement of function in response to an increase in the overburden of the tunnel. Major failure and soil collapse inside the tunnel resulted from the opening of spaces between the segmental rings at the joints. This occurred in response to the dominant tensile forces caused by normal faulting. Sinkholes caused by the loss of soil into the tunnel are likely in the normal faulting. The area of the zone affected by faulting in the tunnel decreased as the overburden increased, but the severity of damage increased in response to localization of fault displacement. Sinkhole formation upon the collapse of soil into the tunnel is likely at the ground surface. In the reverse faulting longitudinal deformations on tunnel and at the ground, were observed.
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