Nonlinear mechanical analysis of polymer precast panel for temporary support of tunnels

Abstract

The increase of population in developed cities has improved the requirement for new advanced transportation method such as urban railway system. Therefore, the needs of developing advanced technology in the tunnelling construction for the use of underground railway system are necessary. Underground railways are one of the most accepted systems used for transporting a large amount of people in highly populated cities, which its development requires a set of advanced science such as in the tunnelling construction process. One of the significant failure may occur in tunnels is ceiling collapse. This failure is a major concern during construction to avoid hazardous for workers. In the past few decades, the combination of sprayed concrete and steel meshes (shotcrete) are utilised as temporary support for tunnels during the construction process. This was a time consuming procedure and for a team of workers, they face plenty of obstacles from safety concern to limited working space area when mounting some heavy panel inside the tunnels. To overcome these problems, an experimental test was carried out using Hard Density Polyethylene (HDPE) which is approximately has the same stiffness to shotcrete but 50% less of the weight of the structure. A rectangular beam sample of was manufactured as a precast panel and experimentally tested under three-point bending load as in the real conditions. Maximum deflection and total reaction force of the panels was recorded. The nonlinear mechanical behaviour of the specimen is analysed based on the bending stiffness. Considering the hyper-elastic behaviour of HDPE, the overall response of the sample had shown a good acceptable strength 14.3% higher than the desired strength which can approve the right material selection. In addition, discussion was given on total stiffness and reduced stiffness because of nonlinear behaviour of the HDPE. The value of strain is measured at the bottom surface of the HDPE beam along the length and width the sample for further discussion. This type of polymer can be assumed as large strain material and it is showing a large deformation under three-point bending condition which can help to inform workers about the safety of the whole structure.