Longitudinal joints in segmental linings: To spear or not to spear?

Temporary bolting in segmental lining design is usually considered ‘good practice’ in many parts of the world, but the little guidance that exists usually specifies that bolts be designed to hold the gasket closed. Those guides neither refer to other features of modern lining and TBM operation that more heavily contribute to maintaining the gasket closed nor elements of modern segment geometry that impact the effectiveness of the bolts. This lack of details results in a disconnection between design practice and the reality of modern segmental linings. The actual performance of the bolt-gasket system is rarely investigated, and they are adopted purely based on precedence regardless of whether they can maintain the gasket closed. This paper will show how the routinely ignored geometrical factors of the segments are crucial to the ability of the bolts to restrain segment movement under gasket loads. It will also show, using explicit analysis of joints, how guiding rods have the potential to prevent excessive segment movement under gasket loads better and more reliably than temporary spear bolts.