Three-dimensional effect of leading beam pre-retaining system on ground settlement under conditions of spatial variability of Young's modulus in NATM tunneling (case study)

Tahmasebi, Mohammad Ali; Shirinabadi, Reza; Rahimi, Esmaeil; Moosavi, Ehsan; Bangian Tabrizi, Amir Hossein

Three-dimensional effect of leading beam pre-retaining system on ground settlement under conditions of spatial variability of Young's modulus in NATM tunneling (case study)

Document Type : Technical Note

Authors

Mohammad Ali Tahmasebi

Reza Shirinabadi

Esmaeil Rahimi

Ehsan Moosavi

Amir Hossein Bangian Tabrizi

Department of Petroleum and Mining Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran.

Abstract

One of the most important issues to consider in urban tunnel excavation is excessive ground settlement. This issue becomes particularly important when the tunnel overburden height is low, so to reduce the ground settlement in these conditions, sequential excavation methods or soil reinforcement techniques, or a combination of both, are usually used. In the Zarbali Zadeh Tunnel, due to the low overburden height, both methods, namely Austrian tunneling and the use of two pre-support systems, have been used to design and construct the tunnel. To investigate the effect of the leading beam pre-support system on the maximum ground settlement, the actual soil behavior must be carefully evaluated. In this regard, the stochastic finite difference method has been used to describe the actual conditions of soil behavior. Then, the maximum surface settlement values for the presence and absence of the leading beam were obtained and compared with each other. The results of this research show that if leading beam pre-retaining systems are not used, the average percentage change and the coefficient of variation of maximum ground settlement increase by 35.5% and 61.7%, respectively.

Keywords

Oscillation scale

land subsidence

spatial variability

pre-retaining systems

random field