For expansion to four lanes of the Kochi Expressway, The Hinokio Tunnel Project was drawn up to construct a new tunnel parallel to an existing tunnel. The zones of weak ground that had experienced significant displacements in Phase I construction were prone to fail under the influence of the new tunneling. For monitoring the influence exerted by Phase II excavation upon the existing tunnel, this tunnel side was instrumented in advance. By the monitor scheme, safety of work was achieved. The measurement results are helpful for grasping the tunnel load generation mechanism
