Abstract：Abstract：In order to ensure the security of the construction of Longshan two-arcade twin tunnel which has large span，shallow depth and bad wall rock condition，the extensive measurement and reasonable prediction of the displacements of the wall rock are necessary. After the multi-step finite element model，which can simulate the real construction process is established，the measured displacements caused by the first construction step are used in back analysis to achieve the needed parameters；and prediction of the displacements resulted from the second construction step is made based on these parameters. When the second construction step is accomplished，newly measured displacements are compared with the calculated ones. Then newly measured displacements are fed back to the established finite element model and another back analysis is taken to get the parameters which can represent the influence of these reasons of considerable differences. The prediction of displacements caused by the third step is then made based on the computed parameters. The same process is repeated until the construction is completed. It is shown from the results that if the construction state is ignored，considerable difference will occur between predicted displacements and measured ones. On the contrary，if the computation model can simulate the real construction process and the construction state，the results are encouraging. The construction state can be represented by some special parameters；and these parameters can be gotten from back analysis. Therefore，the dynamic method applied to the presentation is an effective way to predict reasonable displacements caused by construction.
