Certain points on tunnel section start to displace before measurements begin from within the tunnel. This paper is focused on methods to estimate the unmeasured displacements and to predict the total final displacements using measurement data obtained in early stages of excavation. Exponential and linear functions are used to assess unmeasured displacements, and final displacements are predicted from the total displacements estimated at a distance of one tunnel diameter from the working face.
In tunnel, each point on a cross section begins to displace even before the face reaches the section and continues to displace as the face advances past the section until the excavated tunnel becomes stable. Then the displacements cease. For the safe construction of NATM, the most important procedure is to measure displacement at points, such as the crown and the spring line, on the predetermined section and to predict the final safe displacements. These final displacements might be estimated by a variety of numerical methods but most of them are not reliable because of the uncertainty of input data. For the prediction of final displacement, therefore, it is more practical and safe to use the displacement measured at an early stages of excavation, preferably within the range of one tunnel diameter from the advancing face. Unfortunately, in many cases, the measurements start after the face has reached some distance past the measuring section, resulting in loss of most important displacement data at the early stage of excavation. This paper is focused on how to evaluate the displacements developed before measurements start, and then with total displacement consisting of unmeasured and measured components at the early stage of excavation, it is possible to predict displacements at all stages over the entire tunnelling operation.
