2D Elasto-Plastic Finite Element Analysis of Tunnels in Dubai, UAE

Abstract

Major cities in UAE in general and Dubai in particular are facing significant challenges in terms of traffic flow patterns. Tunnels are being considered as viable option to alleviate the problems faced by transportation networks. The construction of tunnels at different depths requires insight into the behavior of regional soils to avoid unfavorable effects on surface settlements. This research is an attempt to evaluate the effect of geotechnical properties of regional soil, tunnel diameter, and overburden depth on the deformation around the tunnel and ground surface. The study involved finite element modeling of regional soils with commercially available software package of PLAXIS 2D. The results of this study indicate that geotechnical properties across the Dubai city vary and affect the deformation characteristics of the ground due to tunnel excavation. The deformations around the tunnel and at the ground surface are significantly affected by the depth of the tunnel and diameter of the tunnel. The largest effect was created by the combination of 8 m tunnel at a depth of 10 m from the ground surface. To control the deformations to within acceptable limits, tunnel shall be located within the Calcareous Limestone at depths exceeding 20 m. Limiting deformations to within acceptable limits; however, imposes larger support pressures which can result in excessive investment in support design. Maximum deformations with in the tunnel are noted in the crown. This happens due to the arching effect of the soil above the crown which tends to share the stresses if some deformations are allowed. The deformations at the surface diminish laterally from the tunnel axis. The effect of tunneling on surface settlements is negligible after a lateral distance of 6 times the diameter of the tunnel from the tunnel alignment. Settlement monitoring guidelines are also developed as the result of this study. It is recommended to monitor the ground surface for settlement at least 3 times the tunnel diameter in both lateral directions. The settlement monitoring line should be installed in advance leading the face of the tunnel by 30 m. Three alert levels have been proposed. Search Terms: Tunnels; Finite Elements; Deformations; TBM; UAE