Analysis of Soil andTunnel Interaction in Mechanized Full-Face DrillingStages and Its Impact onGroundSettlement (Case Study: Line 7 of Tehran Metro)

Abstract

Tunnel drilling results in releasing of soil’s in-situ stress, leading to land deformation. Some level of displacement always occurs at the tunnel drilling site. This displacement sequentially affects the ground surface, causing groundsettlement. To prevent the resulting groundsettlement, measures must be taken to minimize alterations in stresses and strains within the ground. EPB drilling machines are utilized for this purpose. In this study, the movement of the full-face EPB drilling machine has been modeled in the east-to-west segment of Tehran Metro Line 7, located at kilometer 650+11, where tunnelling operation is currently undergoing. The impact and interaction between the full-face EPB drilling machine and soil leads to a reduction in volume around the tunnel, which exhibits itself as groundsettlement on the ground surface. The movement of the EPB drilling machine through a complete cycle (step-wise drilling, injection, and step-wise segmental lining) is simulated using PLAXIS 3D Tunnel software, and displacement and settlement values on the ground surface are determined using the same software. To model and determine the effects of tunneling with shield plates, specific points for shield movement in the designated section have been identified, and the impact of shield movement on the ground surface and above the tunnel has been measured as soil displacement. In total, 410 measurements resulting from the interaction between soil and the tunnel have been recorded, which are exhibited as displacement on the surface. Furthermore, to achieve greater accuracy and validate the displacement levels, groundsettlement has also been determined using FLAC3D software. Using FLAC3D software, the stress state in the environment and longitudinal groundsettlement have been determined. The amount of groundsettlement has been measured using empirical-analytical relationships, and the results obtained from modeling and empirical relationships have been compared. The highest amount of settlement resulting from modeling with PLAXIS 3D Tunnel occurred at the end of the segmenting phase, with a value of 38.38 millimeters. The highest amount of settlement in FLAC3D software is 37.84 millimeters. The results from empirical and analytical relationships closely match the modeling results, with the error percentage in various methods calculated and determined in the end.

Keywords: EPB, GroundSettlement, PLAXIS 3D Tunnel, FLAC3D, Soil and Drilling Machine Interaction.