A NUMERICAL APPROACH TO SIMULATE STRESSES AROUND TUNNELS IN SWELLING ROCKS

Abstract

The stresses generated from rock expansion in a confined underground environment will exert additional loads to the existing support system resulting in severe damage during tunnel construction. In this study numerical investigations were carried out for Zagros tunnel in Iran, where swelling has been reported to be an inherent formation property. The presence of expandable clay was investigated using X-ray diffraction mineralogical analyses. The swelling volume strain was used to estimate the amount of stress increased due to swelling. The stress path method is used to obtain the location of swelling stresses. The stress relief zone (SRZ) was considered as the criterion to define the area around the tunnel where swelling stresses exist. In doing so, in the areas where the first stress invariant after excavation becomes lesser than its corresponding value before excavation, the swelling pressure can be built up. Then tunnel stability was investigated by numerical simulations using FLAC2D. The swelling stresses calculated from the free swelling test were applied to those elements around the tunnel within the stress relief zone. A comparison between the results of numerical investigations with field observation indicates that the proposed approach is successful in simulating swelling stress in swelling rocks.