Structural analysis of contact deficiencies in segmented lining

Several authors have described the main mechanism of formation of cracks in the segmented lining during the construction of tunnels with tunnel boring machines. The most frequent types of cracks are caused by a condition of uneven support generated by contact deficiencies between the segments. This paper analyzes the influence of these contact deficiencies over the structural behavior of the lining and the consequent damage produced. In the first part of the study, two types of finite elements used to simulate the contact deficiencies are compared and validated with a simplified analytical approach. Models are used in a parametric study that yields the relation between the structural damage and the contact deficiencies. It was found that the contact deficiencies affect the maximum load resisted by the segments. The curves that relate the resistant capacity and the contact deficiency present a similar shape for all models indicating the transition between two different failure mechanisms. This transition marks a severe reduction of the segment resistant capacity, which may be used as a reference value for the estimation of the limit contact imperfection. For imperfections above this limit, the resistant capacity of the structure reduces rapidly and the damages occur for very low load levels. It was also evidenced that the packing stiffness, the width and the thickness of the segment have a clear influence on the value of the critical contact deficiency. (C) 2011 Elsevier Ltd. All rights reserved.