Stresses at Tunnel Intersections

The experimental program described herein was conducted to determine the stress distributions associated with three common types of cylindrical tunnel intersections (tee, cross, and right angle) when they are located in a uniform, uniaxial, stress field. The stresses were determined by using conventional three-dimensional photoelasticity methods. The results of the study indicate that the maximum tensile stresses (circumferential and axial) in the region of the intersections are equal to or slightly less than those that exist in the tunnel away from the intersection. The maximum compressive stresses at the corner of the intersection are approximately 60% greater than the compressive stresses in the tunnel away from the intersection. The high stress region is localized, however, and the maximum circumferential compression decays to the tunnel value within a distance of one diameter of the intersection. The maximum compressive stress on the wall of the tunnel opposite the corner (tee and right angle intersections) is not significantly influenced by the presence of the intersection.