Midas GTS NX: Junction Design in Rock – A State of the Art Review

Seth Pollak, Senior Engineer, Arup

Hannes Lagger, Associate Director, Arup

"As space constraints on land drive more facilities underground, the idea of the linear tunnel has been replaced by one of complex geometries and intersections as engineers struggle to create excavations that fulfill the requirements. This is never truer than in urban areas where new projects must be threaded around existing utilities, foundations, and other tunnels. The resulting stress distributions and ground deformations can be difficult to predict, even with the aid of a full 3D model. The application of current analytical design tools to the temporary support of junctions is mainly limited to homogeneous and isotropic materials – such as soils or massive, elastic rock. Few design tools are currently available in the industry to deal with discontinuous or weak rock masses, where stress distributions result in shearing and dilation in the rock mass around the excavation. This article aims to address where the industry is in terms of a rational approach for temporary support design for junctions in discontinuous rock masses, and highlights some recent projects where junctions have been successfully designed and build, with data collected to verify the performance in various types of rock."