„SEE Tunnel:Promoting Tunneling in SEE Region“ ITA WTC 2015 Congress and 41st General Assembly May 22-28, 2015, Lacroma Valamar Congress Center, Dubrovnik, Croatia Investigation of the influence of cracking on the stiffness and ca- pacity of segmental tunnel lining Dimitrios Litsas, National Technical University of Athens, Greece, litsas.cv@gmail.com Georgia Paterianaki, National Technical University of Athens, Greece, gpaterianaki@gmail.com Michael Kavvadas, National Technical University of Athens, Greece, kavvadas@central.ntua.gr Mechanized Tunnelling in Development and Use Keywords: Segmental lining, Cracking, Shield Tunnelling, FEM Summary The rotational stiffness of cracked segments reduces the overall stiffness of the segmental lining ring and may influence the stiffness and capacity of lining system compared to that assumed in the design. This paper firstly investigates the non-linear behavior of the longitudinal joints and cracks by comparing analytical closed form solutions with the results of numerical analyses. Then, the paper investigates the effects of segment joints and cracks on the response of the lining, by performing parametric numerical analyses of segmental lining systems with joints and cracks and by comparing with the results of analyses where lining is modelled as a continuous cylindrical shell. Numerical analyses are performed in three-dimensions with the finite element program ABAQUS, while joints and cracks of the lining are modelled with non-linear rotational springs. The ground around the tunnel is subjected to full overburden pressure (vertical and horizontal stress), a common assumption in urban transportation tunnels. The analyses investigate the frequency and distribution of the cracks, the tunnel depth, and the ratio of the horizontal to vertical overburden pressure. The results of the analyses are presented in dimensionless graphs which can be used in preliminary analyses of the effect of cracking on the segmental tunnel linings. 1. Introduction TBM tunnels are usually supported with precast reinforced concrete segmental linings. This type of lining is usually designed as a continuous cylindrical shell, i.e., without taking into consideration the rotational stiffness of the longitudinal and ring joints between adjacent segments, which plays a significant role on the developed internal forces of the segmental lining. Furthermore, segment cracking is a common problem in tunnel linings, caused either by irregular jacking forces applied by the advancing TBM or by mishandling during the assembly process of the segment erector [1], [2]. 2. Segmental lining joints 2.1 Longitudinal joints Longitudinal joints are created by the contact between the segments in order to form a segmental ring. The joints mostly work under pressure due to the compressive state where a segmental lining usually lies. Compressive normal force prevents the opening of the joint though, the opening of a joint is not an unusual case, since if the relative rotation of the one segment reached to a relatively high certain limit an opening will occur at the joint. As a result the aforementioned opening makes the joint more flexible by reducing its stiffness. The most well-known analytical applied method for estimating the non-linear rotational behavior of the longitudinal joint was firstly developed by [3] and improved by [4]. Particularly, Janssen assuming elastic concrete behavior defined a smaller contact zone (lt) than the height of the