Prediction of ground surface settlement induced by twin tunnelling in urban areas

Abstract

Tunnelling in urban areas is growing in response to efficient transportation, many urban tunnels are constructed in soft ground at shallow depths. Urban tunnels are usually constructed as twin-parallel tunnels and their adjacent constructions may cause ground settlements that distort and damage the existing structures and utilities above the tunnel. In the past few decades, tunnel boring machines have been used to drill in increasingly difficult geotechnical conditions such as soft ground like soft clay. Metro Line 3 of the Hanoi metro system is designed of twin tunnels horizontally aligned in soft ground. The prediction of ground movements is an important part of the planning stage of any urban tunnelling project. This paper presents the results of numerical simulation by using ABAQUS finite element software to predict the vertical displacement at the surface caused by twin tunnelling of Hanoi pilot light metro line 03. According to numerical simulation results, the maximum vertical displacement at the surface caused by the left line tunnel and twin tunnels bore excavations is values of 12.8 and 21.3 mm, respectively. The maximum vertical displacement can be reached after the shield passes by a distance ranging from 30÷40 m. Twin tunnelling only affects the maximum vertical displacement at approximately 20÷30 m before excavation face tunnel. After the left line tunnel bore excavations, the magnitudes of the vertical displacement directly above the face tunnel (x = 0 m) is 7.9 mm coinciding with 61.7% of the maximum vertical displacement. After the twin tunnels bore excavations, The maximum vertical displacement directly above the face tunnel (x = 0 m) is 13.1 mm coinciding with 61.5% of the maximum vertical displacement.