In order to clarify the mechanical behavior in tunnel excavations, the authors develop and perform three-dimensional trapdoor experiments. The influence of the excavations is considered in the experiments. Based on the results, the distribution of earth pressure is found to greatly affect the process of the excavations. It can be confirmed, therefore, that a higher level of earth pressure is working on a ground where loosened conditions occur due to previously lowered trapdoors. (C) 2003 Elsevier Science Ltd. All rights reserved.